Australia’s National Science Agency Water resource assessment for the Victoria catchment A report from the CSIRO Victoria River Water Resource Assessment for the National Water Grid Editors: Cuan Petheram, Seonaid Philip, Ian Watson, Caroline Bruce and Chris Chilcott ISBN 978-1-4863-2105-6 (print) ISBN 978-1-4863-2106-3 (online) Citation Petheram C, Philip S, Watson I, Bruce C and Chilcott C (eds) (2024) Water resource assessment for the Victoria catchment. A report from the CSIRO Victoria River Water Resource Assessment for the National Water Grid. CSIRO, Australia. Chapters should be cited in the format of the following example: Bruce C, Petheram C, Philip S and Watson I (2024) Chapter 1: Preamble. In: Petheram C, Philip S, Watson I, Bruce C and Chilcott C (eds) (2024) Water resource assessment for the Victoria catchment. A report from the CSIRO Victoria River Water Resource Assessment for the National Water Grid. CSIRO, Australia. Copyright © Commonwealth Scientific and Industrial Research Organisation 2024. To the extent permitted by law, all rights are reserved and no part of this publication covered by copyright may be reproduced or copied in any form or by any means except with the written permission of CSIRO. Important disclaimer CSIRO advises that the information contained in this publication comprises general statements based on scientific research. The reader is advised and needs to be aware that such information may be incomplete or unable to be used in any specific situation. No reliance or actions must therefore be made on that information without seeking prior expert professional, scientific and technical advice. To the extent permitted by law, CSIRO (including its employees and consultants) excludes all liability to any person for any consequences, including but not limited to all losses, damages, costs, expenses and any other compensation, arising directly or indirectly from using this publication (in part or in whole) and any information or material contained in it. CSIRO is committed to providing web accessible content wherever possible. If you are having difficulties with accessing this document, please contact Email CSIRO Enquiries . CSIRO Victoria River Water Resource Assessment acknowledgements This report was funded through the National Water Grid’s Science Program, which sits within the Australian Government’s Department of Climate Change, Energy, the Environment and Water. Aspects of the Assessment have been undertaken in conjunction with the Northern Territory (NT) Government. The Assessment was guided by two committees: i. The Assessment’s Governance Committee: CRC for Northern Australia/James Cook University; CSIRO; National Water Grid (Department of Climate Change, Energy, the Environment and Water); Northern Land Council; NT Department of Environment, Parks and Water Security; NT Department of Industry, Tourism and Trade; Office of Northern Australia; Queensland Department of Agriculture and Fisheries; Queensland Department of Regional Development, Manufacturing and Water ii. The Assessment’s joint Roper and Victoria River catchments Steering Committee: Amateur Fishermen’s Association of the NT; Austrade; Centrefarm; CSIRO; National Water Grid (Department of Climate Change, Energy, the Environment and Water); Northern Land Council; NT Cattlemen’s Association; NT Department of Environment, Parks and Water Security; NT Department of Industry, Tourism and Trade; NT Farmers; NT Seafood Council; Office of Northern Australia; Parks Australia; Regional Development Australia; Roper Gulf Regional Council Shire; Watertrust Responsibility for the Assessment’s content lies with CSIRO. The Assessment’s committees did not have an opportunity to review the Assessment results or outputs prior to their release. This report was reviewed by Dr Brian Keating (Independent consultant). Individual chapters were reviewed by Dr Rebecca Doble, CSIRO (Chapter 2); Dr Chris Pavey, CSIRO (Chapter 3); Dr Heather Pasley, CSIRO (Chapter 4); Mr Chris Turnadge, CSIRO (Chapter 5); Dr Nikki Dumbrell, CSIRO (Chapter 6); Dr Adam Liedloff, CSIRO (Chapter 7). The material in this report draws largely from the companion technical reports, which were themselves internally and externally reviewed. For further acknowledgements, see page xxv. Acknowledgement of Country CSIRO acknowledges the Traditional Owners of the lands, seas and waters of the area that we live and work on across Australia. We acknowledge their continuing connection to their culture and pay our respects to their Elders past and present. Photo The Victoria River is the longest singularly named river in the NT with permanent water. Photo: CSIRO – Nathan Dyer Director’s foreword Sustainable development and regional economic prosperity are priorities for the Australian and Northern Territory (NT) governments. However, more comprehensive information on land and water resources across northern Australia is required to complement local information held by Indigenous Peoples and other landholders. Knowledge of the scale, nature, location and distribution of likely environmental, social, cultural and economic opportunities and the risks of any proposed developments is critical to sustainable development. Especially where resource use is contested, this knowledge informs the consultation and planning that underpin the resource security required to unlock investment, while at the same time protecting the environment and cultural values. In 2021, the Australian Government commissioned CSIRO to complete the Victoria River Water Resource Assessment. In response, CSIRO accessed expertise and collaborations from across Australia to generate data and provide insight to support consideration of the use of land and water resources in the Victoria catchment. The Assessment focuses mainly on the potential for agricultural development, and the opportunities and constraints that development could experience. It also considers climate change impacts and a range of future development pathways without being prescriptive of what they might be. The detailed information provided on land and water resources, their potential uses and the consequences of those uses are carefully designed to be relevant to a wide range of regional-scale planning considerations by Indigenous Peoples, landholders, citizens, investors, local government, and the Australian and NT governments. By fostering shared understanding of the opportunities and the risks among this wide array of stakeholders and decision makers, better informed conversations about future options will be possible. Importantly, the Assessment does not recommend one development over another, nor assume any particular development pathway, nor even assume that water resource development will occur. It provides a range of possibilities and the information required to interpret them (including risks that may attend any opportunities), consistent with regional values and aspirations. All data and reports produced by the Assessment will be publicly available. C:\Users\bru119\AppData\Local\Microsoft\Windows\Temporary Internet Files\Content.Word\C_Chilcott_high.jpg Chris Chilcott Project Director Key findings for the Victoria catchment The Victoria catchment has an area of approximately 82,400 km2. It flows into the Joseph Bonaparte Gulf in the Timor Sea which is an important part of northern Australia’s marine environment with high ecological and economic values. Within the catchment, 31% of the land is Aboriginal freehold tenure, which includes the 16% of the catchment which is national park. The Bradshaw Field Training Area occupies 7%, to which access is restricted. The dominant land use across the Victoria catchment is grazing of beef cattle on native rangelands (62% of the catchment area). There is less than 100 ha of irrigated agriculture, which is about 0.001% of the catchment. There are no active mines in the study area, although known mineral occurrences include barite, copper, lead and prehnite. Mining and petroleum exploration licences cover 61% of the study area. The catchment has a population of approximately 1600 people, of whom about 75% are Indigenous Australians. In contrast, Indigenous Australians make up 25% of the population of the NT and 3% of Australia as a whole. There are no large urban centres. The population density of the Victoria catchment (1 person per 50 km2) is one of the lowest in Australia, and communities in the catchment are ranked as being among the most disadvantaged in Australia. Business and tourist visitation to the Victoria catchment is highly seasonal and modest in number (~27,000/year) and valued at less than $20 million/year. Tourists to the Victoria catchment area are mostly classified as self-drive tourists. Indigenous Peoples have continuously occupied and managed the Victoria catchment for tens of thousands of years. They retain significant and growing rights and interests in land and water resources, including crucial roles in water and development planning and as co-investors in future development. Key language groups include the Gurindji, Ngarinyman, Ngaliwurru, Nungali, Miriuwung and Gajerrong. A number of related groups and subgroups occur within the traditional lands of these regional language groups. The Victoria River, at approximately 560 km in length, is the second longest river with permanent water in the NT. However, unlike the NT’s better known Daly and Roper rivers, late dry-season flows in the Victoria River are small, and most permanent waterholes are likely to be a result of residual flow from the previous wet season. The Victoria River has the second‑largest median annual streamflow (5370 GL) of any river in the NT, and the fourth largest in northern Australia west of the Great Dividing Range. Approximately 93% of the streamflow in the Victoria catchment occurs between January and March. The Victoria catchment is unregulated (i.e. it has no dams or weirs) and existing annual licensed surface water extractions are approximately 2 GL (0.04% of median annual discharge). However, the study area includes a large earth embankment gully dam (35 GL capacity) in the catchment of Forsyth Creek, which flows into Joseph Bonaparte Gulf adjacent to the Victoria River. Current annual licensed surface water extractions from the catchment of Forsyth Creek are 150 GL. With irrigation, the Victoria catchment has a climate that is suitable for a range of annual and perennial horticulture, and broadacre crops and forages. The regions in the Victoria catchment with the most potential for irrigated agriculture are areas adjacent to the upper West Baines River and the Victoria and Wickham rivers downstream of Yarralin, the sandy and loamy soils and clay soils north‑east of Top Springs, and the extensive sandy and loamy soils along the south-eastern margin of the catchment. The opportunities and risks of development in each of these regions are starkly different. Opportunities for irrigated agriculture along the Wickham and Victoria rivers are generally limited by the availability of suitable soil and topography adjacent to the rivers, whereas along the West Baines River and near Top Springs and along the eastern margins of the catchment, irrigated agriculture is limited by available water. The cracking clay soils on the broad alluvial plains of the West Baines River upstream of the Victoria Highway (54,000 ha) offer the greatest potential for broadacre irrigation in the Victoria catchment. Note that this estimate of soil area, and the ones below, includes land considered suitable but with limitations and would require careful soil management. Along the West Baines River upstream of the highway, it is physically possible to extract up to 100 GL of surface water in 75% of years, which is sufficient water to irrigate up to 7000 ha of dry-season broadacre crops. Further downstream there is an additional 50,000 ha of cracking clay soils; however, the suitability of soil for irrigated agriculture during the wet-season becomes increasingly marginal due to increasing seasonal wetness (leading to waterlogging and trafficability issues) and flooding, so enterprises would become increasingly less commercially viable. Nonetheless, it would be physically possible to extract an additional 300 GL of surface water in 75% of years from the West Baines River below the highway crossing. The proximity of West Baines to the Victoria Highway, and to the service town and cotton gin in Kununurra in WA, may offer an advantage to new irrigation developments relative to many other parts of northern Australia. Less expansive opportunities for water harvesting exist adjacent (within 5 km) to the Wickham and Victoria rivers (22,000 ha), limited by where ringtanks for storing water can be constructed on heavier alluvial clay soils. The commercial viability of water harvesting enterprises along these river reaches would be highly variable due to increasing elevation away from the river and/or the width of sandy and loamy levee soils, both of which increase piping and pumping costs. Notwithstanding this, and including the Baines River, it is physically possible, although not necessarily commercially viable, to extract up to 690 GL of surface water in 75% of years from the major rivers in the Victoria catchment. That amount is sufficient water to irrigate up to 50,000 ha of alluvial clay and sandy and loamy soils where they exist as contiguous areas. This volume of water extraction would result in a reduction in mean and median annual discharges from the Victoria River into the Joseph Bonaparte Gulf of 9% and 12%, respectively. Based on historical trends in irrigation development and existing surface water plans across northern Australia, more- modest scales of surface water development, for example, 10 to 150 GL (i.e. ~0.2% to ~3% of median annual discharge from the Victoria River), would be more likely. North-east of Top Springs and along the eastern and southern margins of the Victoria catchment are approximately 62,000 and 695,000 ha, respectively, of well-drained sandy and loamy soils that are potentially suitable, with considerable limitations, for irrigated annual and perennial horticultural crops under dry-season trickle irrigation. However, there is only sufficient surface water to irrigate less than 0.3% of this area. Due to the absence of reliable surface water in this part of the study area, water would need to be sourced from the regional‑scale Cambrian Limestone Aquifer (CLA), which underlies the eastern margin of the Victoria catchment. It is physically possible to extract 10 GL of groundwater each year from this part of the CLA, which is sufficient water to irrigate 1000 to 2000 ha of mixed broadacre cropping and horticulture. However, this part of the catchment is particularly remote, and transport costs pose a major constraint to irrigation enterprises in this region. Commercially viable opportunities would most likely be limited to annual horticulture targeting winter supply gaps in southern markets, such as from a wet-season planting (December to early March), which is possible on these well-drained soils. Irrigated agriculture and aquaculture in the Victoria catchment are only likely to be financially viable where there is an alignment of good prices for high-value produce and market advantages. This makes achieving scale challenging. Other factors include availability of suitable markets for the products, investment in fundamental infrastructure such as all-weather roads and bridges, and land tenure arrangements that support development. New agricultural developments in the study area are most likely to start irrigating broadacre crops on heavier clay soils before progressing to higher-value and higher-input enterprises, such as horticulture on sandy and loamy soils, as farmers build confidence in their skills and expertise in this largely greenfield region. Along the very remote coastal margins of the study area, about 93,000 ha of land is suitable for prawn and barramundi aquaculture, using earthen ponds. Growing irrigated forages or hay to feed cattle to be turned off at a younger age is unlikely to be financially viable. Feeding forages or hay increases beef production and total income, but increased costs mean that gross margins would be less than baseline cattle operations, and the high capital outlay would in most cases be prohibitive. Rainfed cropping in the catchment is likely to be opportunistic (i.e. only possible when suitable conditions allow) and depend upon farmers’ appetite for risk and future local demand. The total annual economic activity (direct and indirect) generated from 10,000 ha of irrigated mixed broadacre (65%) and horticulture (35%) agriculture in the Victoria catchment could potentially contribute up to $280 million, supporting up to 200 full-time-equivalent jobs. Economic data from the NT indicate benefits arising from agriculture developments have been heavily skewed to non‑Indigenous households relative to Indigenous households. The potential area of land actually developed for irrigated agriculture based on surface water and/or groundwater will depend heavily upon community and government values, acceptance of potential impacts to water‑dependent ecosystems and existing groundwater users, the profitability of irrigated agricultural enterprises in the Victoria catchment, and those who would economically benefit. Changes to streamflow under projected drier future climates are likely to be considerably greater than changes that would result from plausible groundwater and surface water developments. Of the global climate models examined, 28% projected a drier future climate over the Victoria catchment and 47% projected ‘little change’. The adopted future dry climate was based upon a global climate model that, in terms of mean precipitation, was 7% drier than the historical climate. Using this as an input, it was found that modelled reduction in median annual streamflow projected to 2060 at the Victoria River mouth was 25%. This value exceeded the modelled reduction in median annual streamflow under the largest potential water harvesting development scenarios (12%), assuming a historical climate. The Victoria River, although not pristine, has many unique characteristics and valuable ecological assets, which support existing industries such as commercial and recreational fishing. Whether based on groundwater or offstream storage, irrigated agricultural development has a wide range of potential benefits and risks that differentially intersect diverse stakeholder views on ecology, economy and culture. The detailed reports upon which this summary is based provide information that can be used to help consider the trade-offs from potential developments. Overview of the Victoria catchment The Victoria catchment sits inside the Australian savanna biome, the world’s largest intact tropical savanna, and like much of Australia’s north has free‑flowing rivers. The Victoria catchment has a highly variable climate Northern Australia’s tropical climate is notable for the extremely high variability of rainfall between seasons and especially between years. This has major implications for evaluating and managing risks to development, infrastructure and industry. The climate of the Victoria catchment is hot and semi-arid. Generally, the Victoria catchment is a water-limited environment, so effective methods for capturing, storing and using water are critical. • The mean and median annual rainfall amounts – averaged across the Victoria catchment – are 681 mm and 690 mm, respectively. A strong rainfall gradient runs from the northernmost tip (1050 mm annual median) to the southernmost part (410 mm annual median) of the catchment. • Averaged across the catchment, 5% of the rainfall occurs in the dry season (May to October). Median annual dry‑season rainfall ranges from 18 mm in the west to 34 mm in the north. • Annual rainfall totals in the Victoria catchment are highly variable. Annual totals are approximately 1.3 times more variable than in comparable parts of the world. Using Kalkarindji as an example, between 1890 and 2022, the highest annual rainfall (1204 mm in the 2000–2001 water year (1 September to 31 August)) was nearly eight times the lowest annual rainfall (159 mm in 1953–1954). The seasonality of rainfall presents opportunities and challenges for both wet- and dry‑season cropping. • Information about water availability (i.e. soil water and water in storages) helps minimise risk when it is known ahead of important agricultural decisions – before planting time for most dry- season crops. Such information allows farmers to manage risk by choosing crops that optimise use of the available water or by deciding to forego cropping for a season. Rainfall is difficult to store. • Mean annual potential evaporation is higher than rainfall, exceeding 1900 mm over the entire catchment. Unlike rainfall, potential evaporation does not exhibit a strong gradient across the catchment. • Large farm-scale ringtanks lose about 30% to 50% of their water to evaporation and seepage between April and October. Deeper farm-scale gully dams lose about 20% to 40% of their water over the same period. Using stored water early in the season is the most effective way to reduce these losses. The Victoria catchment is less exposed to cyclonic winds than are most other northerly draining catchments in Australia’s north. • Of the 53 consecutive cyclone seasons prior to 2021–22, the Victoria catchment had no tropical cyclones in 72% of those seasons, had one cyclone in 22% of seasons and two cyclones in 6% of seasons. An almost equal number of global climate models project a drier future climate and a wetter future climate for the Victoria catchment. Consequently it is prudent to plan for water scarcity. • For the Victoria catchment, 28% of climate models project a drier future, 25% project a wetter future and 47% project a future within ±5% of the historical mean, indicating ‘little change’. Recent research indicates tropical cyclones will be fewer but more intense in the future, although uncertainties remain. • Palaeoclimate records indicate past climates have been both wetter and drier over the past several thousand years. • Climate and hydrology data that support short- to medium-term water resource planning should capture the full range of likely or plausible conditions and variability at different timescales, and particularly for periods when water is scarce. These are the periods that most affect businesses and the environment. • Detailed scenario modelling and planning should be broader than just comparing results under the baseline climate to a single alternative future climate scenario. • Future changes in temperature, vapour pressure deficit, solar radiation, wind speed and carbon dioxide concentrations will separately act to increase or decrease crop water demand and crop yield under irrigation in northern Australia. However, changes under future climates to the amount of irrigation water required and crop yield are likely to be modest compared to improvements arising from new crop varieties and technology over the next 40 years. Historically, these types of improvements have been difficult to predict, but they are potentially large. The Victoria River is one of northern Australia’s largest free‑flowing rivers At approximately 560 km in length, the Victoria River is the longest singularly named river in the NT with permanent water and it has the second‑largest median annual streamflow of any NT river. • The mean and median annual river discharges from the Victoria catchment into the Joseph Bonaparte Gulf are 6990 and 5370 GL, respectively. A small proportion of very wet years bias the mean, which is 30% higher than the median annual discharge. • Modelled annual streamflow ranges from 800 to 23,000 GL. The annual variability relative to the mean annual streamflow is comparable with other rivers in northern Australia of similar mean annual runoff (streamflow divided by catchment area), but the annual variability in runoff is two to three times greater than rivers from other parts of the world with similar climates. • A unique characteristic of the Victoria River is that it has a 25 km wide mouth at Queens Channel, part of the Joseph Bonaparte Gulf. • The Joseph Bonaparte Gulf region experiences some of the largest tides in the country. Tidal variation at the mouth of the Victoria River is up to 8 m, and tides propagate to just downstream of Timber Creek, about 140 km upstream of Queens Channel. • Approximately 54% of streamflow into the Victoria River comes from the large tributary rivers of the Baines (22%), Angalarri (8%), Gregory (4%), Wickham (9%), Armstrong (7%) and Camfield (4%) rivers. The Victoria River and its major tributaries are largely ephemeral. Most of the water in the main river channel during the late dry season is the result of residual flow from the previous wet season, rather than groundwater. • On average, approximately 93% of the streamflow in the Victoria catchment occurs between January and March. This is higher than the better known Daly (80%) and Roper (84%) rivers, both of which are groundwater fed, but is typical of many rivers across northern Australia. • Mid-to-late dry-season streamflow in the Victoria River and most of its major tributaries is low, less than 200 ML/day. • Current licensed surface water extractions in the study area are approximately 152 GL/year; however, 150 GL is licensed in the catchment of Forsyth Creek, which flows into the Joseph Bonaparte Gulf adjacent to the Victoria River. Licensed surface water extractions from the catchment of the Victoria River are only about 2 GL/year (0.04% of median annual discharge). Although the area of land frequently flooded in the Victoria catchment is proportionally less than that of many other catchments in northern Australia, the proximity of some Indigenous communities to the Victoria River makes them susceptible to large flood events. • The incised nature of the Victoria River in its lower reaches means the most frequently flooded areas are the junctions of the Baines and Angalarri rivers with the Victoria River and a choke point on the Victoria River 55 km upstream of Victoria River Roadhouse. • The Victoria Highway, a critical transport artery with about 33,000 freight trailer movements each year, can become impassable due to flooding at times during the wet season. • Flood peaks typically take about 2 to 3 days to travel from Dashwood Crossing to Timber Creek at a mean speed of 3.4 km/h. • Between 1953 and 2023 (70 years), there were 80 ‘observed’ streamflow events that broke the banks of the Victoria River at Coolibah Homestead (25 km downstream of Victoria River Roadhouse). All occurred between September and May (inclusive), and about 91% of the events occurred between December and March (inclusive). • Of the ten events with the largest flood peak discharge at Coolibah Homestead, six occurred in March, three in February and one in December. • In 2023, a large flood displaced the residents of the townships of Kalkarindji and Nitjpurru (Pigeon Hole) on the Victoria River for several months. Based on the observed record (1953 to 2023), this event had an annual exceedance probability (AEP) of 2.6% at Coolibah Homestead. • Flooding is ecologically critical because it connects offstream wetlands to the main river channel, allowing the exchange of fauna, flora and nutrients to support the important ecological functions of wetlands. Under a potential dry future climate (7% reduction in rainfall), median annual river discharge from the Victoria River into the Joseph Bonaparte Gulf is projected to decrease by 25%. The Victoria catchment has many unique ecological characteristics and contains important species and habitats The Victoria catchment contains a significant diversity of species and habitats, including freshwater, terrestrial and marine assets of great cultural, conservation and commercial importance. • Much of the natural environment of the Victoria catchment consists of rolling plains, mesas, escarpments and plateaux with savanna, spinifex, grasslands and woodlands. The catchment and surrounding marine environment contain a rich diversity of important ecological assets. The region is considered the transitional zone and boundary between the Kimberley and Top End ecological communities. The Victoria catchment is largely intact, but it is not pristine. • Previous studies have rated the riverine habitat in the Victoria catchment as being of high or very high overall quality and largely intact. They identified the catchment as having high wilderness value and being predominantly unaffected by clearing or development, although ecological threatening processes operate. • Existing threatening processes include cattle grazing, roads, river crossings, and impacts from introduced species, including feral animals and weeds. • Fishing in northern Australia is highly valuable, and the waters of the Victoria catchment and nearby marine zone contribute to important recreational, commercial and Indigenous catches, including barramundi, redleg banana prawn and a variety of other species. • One of the most significant environmental threats to remote regions across northern Australia is that of introduced plants and animals. In the Victoria catchment, pig, water buffalo, cane toad and cat are among the invasive animals. • Weed species of interest in and around the Victoria catchment include 20 species of national significance. Invasive plants of concern include gamba grass (Andropogon gayanus), para grass (Brachiaria mutica), giant sensitive plant (Mimosa pigra) and prickly acacia (Vachellia nilotica). The Victoria catchment includes wetlands of national importance and other important habitats for biodiversity conservation. • Protected areas in the Victoria catchment include one gazetted national park (Judbarra), a proposed extension to an existing national park (Keep River), two marine national parks (Joseph Bonaparte Gulf Marine Park and North Kimberley Marine Park (Western Australia), which is adjacent to the Joseph Bonaparte Gulf Marine Park and follows the Western Australian coastline to the NT border), two Indigenous Protected Areas and two Directory of Important Wetlands in Australia (DIWA) sites (Bradshaw Field Training Area and the Legune coastal floodplain). • The Legune coastal floodplain is a wetland identified as an Important Bird and Biodiversity Area by Birdlife International. Surveys have recorded more than 15,000 individuals from over 45 species, including magpie goose (Anseranas semipalmata), brolga (Antigone rubicunda) and red- capped plover (Charadrius ruficapillus). • The freshwater sections of the Victoria catchment include diverse habitats such as persistent and ephemeral rivers, anabranches, wetlands, floodplains and groundwater-dependent ecosystems. • Riparian habitats that fringe the rivers and streams of the Victoria catchment have been rated as having moderate to high tree cover and structural diversity compared to riparian vegetation elsewhere. Further away from the creeks and rivers, the overstorey vegetation in the Victoria catchment becomes sparser. • Groundwater-dependent ecosystems occur across many parts of the Victoria catchment and have different forms, including aquatic, terrestrial and subterranean habitats. Aquatic groundwater-dependent ecosystems contain springs and river sections that hold water throughout most dry seasons. • Groundwater discharge may be critical for maintaining some vegetation condition, such as the habitats of monsoon vine forest located within the Bradshaw Field Training Area DIWA site. Subterranean aquatic ecosystems in the Victoria catchment include known sinkholes associated with the Montejinni Limestone, which are mapped along the south-eastern edge of the Victoria catchment. The connection of these sinkholes to underlying groundwater systems is unknown. • The mouth and estuary of the Victoria River, Queens Channel, is up to 25 km wide and includes extensive mudflats and mangrove stands. The mangrove communities along the estuary are recognised as being of high structural value, but low in species richness with about ten species recorded. The dominant mangrove species in the catchment is Avicennia marina, which is largely confined to the estuary. The Victoria catchment supports listed and threatened species and many lesser-known plants and animals that are also of great importance. • The Commonwealth’s Protected Matters Search Tool includes 45 plant and animal species listed as Threatened for the Victoria catchment, four of which are listed as Critically Endangered under the Commonwealth Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act): the nabarlek rock wallaby (Petrogale concinna concinna), Rosewood keeled snail (Ordtrachia septentrionalis), curlew sandpiper (Calidris ferruginea) and eastern curlew (Numenius madagascariensis). Also listed are 49 migratory bird species. • The aquatic habitats of the Victoria catchment support some of northern Australia’s most archetypical and important wildlife species. Sawfish, marine turtles, the Australian snubfin dolphin and river sharks inhabit the estuaries of the Victoria River and the coastal waters of the Joseph Bonaparte Gulf. • Recent surveys demonstrate the river is a globally significant stronghold for three endangered species: freshwater sawfish (Pristis pristis; listed as Vulnerable under the EPBC Act and Critically Endangered on the International Union for Conservation of Nature (IUCN) Red List of Threatened Species); speartooth shark (Glyphis glyphis; Critically Endangered, EPBC Act and IUCN Red List); and northern river shark (Glyphis garricki; Endangered, EPBC Act and IUCN Red List). • Healthy floodplain ecosystems and free-flowing rivers mean that very few freshwater fishes in the study area are threatened with extinction. • Bird species including the red knot (Calidris canutus; Endangered, EPBC Act) and the critically endangered eastern curlew and curlew sandpiper use habitats such as the Legune coastal floodplain as an important stopover habitat. Indigenous values, rights and development goals Indigenous Peoples constitute almost 75% of the Victoria catchment population. • Traditional Owners have Aboriginal freehold land ownership and hold native title and cultural heritage rights. They control, or are the custodians of, significant natural and cultural resources, including land, water, coastline and sea. • Aboriginal freehold title, held under the Commonwealth Aboriginal Land Rights (Northern Territory) Act 1976 (ALRA) makes up 31% of the Victoria catchment. Over half of this holding is the jointly managed Judbarra National Park, for which a 99-year lease is held by the NT Government. ALRA land cannot be sold and is granted to Aboriginal Land Trusts, which have the power to grant an interest over the land. • Native title exists in parts of the native title determination areas that cover an additional 34% of the catchment. • Water-dependent fishing and hunting have key health and economic roles for Indigenous Peoples in the Victoria catchment. The river supports food security, good nutrition, gathering and knowledge-sharing and is crucial to the songlines that connect geographical and cultural relationships. • The history of pre-colonial and colonial patterns of land and natural resource use in the Victoria catchment is important to understanding present circumstances. This history has shaped residential patterns, and it also informs responses by the Indigenous Peoples to future development possibilities. From an Indigenous perspective, ancestral powers are still present in the landscape and intimately connect Peoples, Country and culture. • Ancestral powers must be considered in any action that takes place on Country. • Riverine and aquatic areas are known to be strongly correlated with cultural heritage sites. • Some current cultural heritage considerations restrict Indigenous capacity to respond to development proposals because some knowledge is culturally sensitive and cannot be shared with those who do not have the cultural right and authority to know. Catchment-wide deliberative processes will be vital to ensuring that Indigenous water rights and interests are included in future water‑dependent development and planning. • Effective Traditional Owner corporate and wider regional governance processes underpin successful catchment‑scale processes and support Traditional Owner management of external pressure for development. Indigenous participants in the Assessment identified the Assessment itself as a manifestation of that pressure. • Indigenous Peoples in the Victoria catchment have not had substantial exposure to water planning or catchment management processes. There is a clear need to build this capability before asking people to make decisions about water-dependent development. • If water resources were to be developed, participants in the Assessment would generally prefer flood harvesting, which would fill offstream storages. There was widespread resistance to large instream dams in major rivers. • Groundwater is currently used for a number of communities, but water quality concerns exist. • Indigenous Peoples have business and water development objectives designed to create opportunities for existing residential populations and to improve nutrition and safe remote- community water supply. • Indigenous Peoples want to be owners, partners, investors and stakeholders in any future development. This reflects their status as the longest-term residents with deep inter- generational ties to the catchment. Opportunities for agriculture and aquaculture There is very little rainfed or irrigated cropping underway in the Victoria catchment, although several pastoral stations have grown a limited amount of forage to provide higher‑quality feed to their cattle. Although an abundance of soil is suitable for irrigated agriculture in the Victoria catchment, the lack of coincidence of suitable soil, water and favourable topography considerably constrains the area that could potentially be irrigated. • Up to approximately 3 million ha of soils in the Victoria catchment are classified as moderately suitable with considerable limitations (Class 3) or better (Class 1 or Class 2) for irrigated agriculture, depending on the crop and irrigation method chosen. • Class 3 soils have considerable limitations that lower production potential or require more careful management than more suitable soils, such as Class 2 soils. • Just over 3 million ha of soils in the Victoria catchment are rated as Class 3 or better for trickle- irrigated intensive crops, such as melons, in the dry season. Most of this area is Class 2 land. • About 2.9 million ha of the Victoria catchment are rated as Class 3 or better for annual hay, forage or silage crops such as forage sorghum using spray irrigation in the dry season; over 2 million ha of that area is Class 2. However, under furrow irrigation, only 625,000 ha are Class 3 or better in the dry season and only 425,000 ha in the wet season, highlighting the poor drainage (and thus waterlogging) of the heavier soils. The soils in different parts of the study area are starkly different. • For the purposes of evaluating the opportunities and risks of irrigation development, the Victoria catchment can be conceptualised as two river systems: the smaller Baines River subcatchment which includes the West and East Baines rivers (15,100 km2), and joins the Victoria River towards its estuary, and the larger Victoria River (55,300 km2) upstream of this junction. • Within the entire Baines catchment there are approximately 103,000 ha of contiguous clay soils suitable for broadacre irrigation, with considerable limitations, under surface irrigation. The cracking clay soils on the broad alluvial plains of the West Baines River upstream of the Victoria Highway offer the greatest potential for broadacre irrigation in the Victoria catchment. Further downstream, the suitability of soil for irrigated agriculture becomes increasingly marginal due to increasing seasonal wetness (leading to waterlogging and trafficability issues) and flooding, so enterprises would become increasingly less commercially viable and/or would operate with higher risk. • Taking into consideration the need to site offstream storages on heavier clay soils, approximately 22,000 ha of contiguous alluvial clay and well-drained sandy and loamy soils within 5 km of the Wickham and Victoria rivers (allowing a 100 m riparian buffer) could potentially be developed for dry-season irrigation. However, the complexity of the landscape along these rivers, which includes sandy levee soils and increasing elevation away from the Wickham and Victoria rivers, means the location and configuration of water harvesting operations would need to be carefully planned to be commercially viable. Once the better opportunities were developed, additional developments would become increasingly less viable. • North-east of Top Springs there are approximately 52,000 ha of clay soils potentially suitable, with considerable limitations, for broadacre irrigated agriculture under dry-season surface irrigation. There are also 62,000 ha of well-drained sandy and loamy soils potentially suitable, with considerable limitations, for irrigated annual and perennial horticultural crops under dry- season trickle irrigation. • Along the very remote eastern and southern margins of the Victoria catchment are 695,000 ha of well-drained sandy and loamy soils that are potentially suitable, with considerable limitations, for irrigated annual and perennial horticultural crops under dry-season trickle irrigation. • When of sufficient depth and water-holding capacity, the loamy soils of the Sturt Plateau on the eastern margins, as well as the sandy and loamy soils in the south-east and south-west of the Victoria catchment, are suitable for a broad range of spray- and trickle-irrigated crops planted in both wet and dry seasons. Irrigation enables higher yields and more flexible and reliable production than rainfed crops • Many annual crops can be grown at most times of the year with irrigation in the Victoria catchment. Irrigation provides increased yields and flexibility in sowing date. • Sowing dates must be selected to balance the need for the best growing environment (optimising solar radiation and temperature) with water availability, pest avoidance, trafficability, crop sequences, supply chain requirements, infrastructure requirements, market demand, seasonal commodity prices and, in the case of genetically modified cotton, planting windows specified within the cotton industry. • Irrigated crops likely to be commercially viable with a dry-season planting (late March to August) include annual horticulture and cotton. Irrigated crops likely to be commercially viable with a wet-season planting (December to early March) include cotton, forages and peanuts. • Seasonal irrigation water applied to crops can vary enormously with crop type (e.g. due to variations in duration of growth, rooting depth), season of growth, soil type and rainfall received. For example, wet-season and dry-season cotton on a clay soil in a climate similar to Top Springs requires about 4.6 ML/ha and 5.7 ML/ha, respectively, of irrigation water in at least 50% of years. A high-yielding perennial forage such as Rhodes grass on a clay soil requires about 24.0 ML/ha each year, averaged across a full production cycle. • Rainfed cropping is theoretically possible in some years, but agronomic and market-related constraints mean it is most likely to be opportunistic in the Victoria catchment based on rainfall received and stored soil water, or it may serve as an adjunct to irrigated farming. How cleared land is managed in the years when rainfall is insufficient for rainfed cropping will be crucial for sustainable farming operations and the industry’s social licence to operate. Excess rainfall can also constrain crop production on some soils. • The cracking clay soils on the alluvial plains of some of the major rivers in the Victoria catchment have high to very high water-holding capacity, but much of the area is subject to frequent flooding and inadequate soil drainage. In some places, small and/or narrow areas have a level of landscape complexity that will constrain farming practices. • High rainfall and possible inundation mean that wet‑season cropping on the alluvial clay soils carries considerable risk due to potential difficulties with access to paddocks, trafficability and waterlogging of immature crops.• Accumulation of soil salinity due to irrigation in these clay soils is currently unknown but must be monitored, especially in the imperfectly drained cracking clay soils on the lower Baines, Angalarri and Victoria rivers. Establishing irrigated cropping in a new region (i.e. greenfield development) is challenging. It has high input costs and high capital requirements and requires an experienced skills set. • For broadacre crops, gross margins of the order of $4,000 per hectare per year are required to provide a sufficient return on investment where on-farm development capital costs are about $20,000/ha. Crops likely to achieve such a return include Rhodes grass hay and wet‑season cotton, noting that the gross margins of hay are highly sensitive to local demand, price and the cost of transport. • Horticultural gross margins would have to be higher than broadacre crops, in the order of $7,000 to $11,000 per hectare per year, to provide an adequate return on the higher capital costs of developing this more intensive type of farming (relative to broadacre). Profitability of horticulture is extremely sensitive to prices received, so the locational advantage of supplying out-of-season (winter) produce to southern markets is critical to viability. Horticulture will struggle to meet these gross margins in the Victoria catchment; perennial fruit trees may be more successful, although it will be difficult to achieve the higher gross margins required. Bushfoods are an emerging niche industry across northern Australia. However, most bushfoods continue to be wild‑harvested with very little grown commercially. Limited information on commercial bushfood operations is publicly available. Growing more than one crop per year may enhance the viability of greenfield irrigation development. • There are proven benefits to sequentially cropping more than one crop per year in the same field in northern Australia, particularly where additional net revenue can be generated from the same initial investment in farm development. • Numerous options for crop sequences could be considered, but these would need to be tested and adapted to the particular opportunities and constraints of the Victoria catchment’s soils and climate. While somewhat opportunistic, the most likely sequential farming systems on the heavier clays could be those combining short-duration crops such as annual horticulture (e.g. melons), legumes such as mungbean and chickpea, and grass forages. • Trafficability constraints on the alluvial clay soils will limit the options for sequential cropping systems because of the tight time frames to grow and harvest the first crop before preparing the land and planting the next crop. The well-drained loamy soils pose fewer constraints for scheduling sowing times and the farm operations required for sequencing two crops in the same field each year. Even so, sequential cropping systems that include cotton may not be possible in all years due to trafficability constraints; that is, it may not be possible to plant cotton early enough in the season for another crop to follow. • Tight scheduling requirements mean that even viable crop sequences may be opportunistic. The challenges in developing locally appropriate sequential cropping systems, and the management practices and skills to support them, should not be under estimated. Irrigated cropping has the potential to produce off-site environmental impacts, although these can be mitigated by good management and new technology. • The pesticide and fertiliser application rates required to sustain crop growth in these climates vary widely among crop types. Selecting crops and production systems that minimise the requirement for pesticides and fertilisers can simultaneously reduce costs and negative environmental impacts. • Refining application rates of fertiliser to better match crop requirements, using controlled- release fertilisers and improving irrigation management are effective ways to minimise nutrient additions to waterways and, hence, the risk of harmful microalgae blooms. • Adherence to well-established best management practices can significantly reduce erosion where intense rainfall and slope would otherwise promote risk. This would also serve to decrease the risk of herbicides, pesticides and excess nitrogen entering the natural environment. • More than 99% of the cotton grown in Australia is genetically modified. The genetic modifications have allowed the cotton industry to substantially reduce insecticide (by greater than 85%) and herbicide application to much lower levels than previously used. In addition to reducing the likelihood and severity of off-site impacts, genetically modified crops offer health benefits to farm workers who handle fewer chemicals. This technology has considerable relevance to northern Australia. Irrigated forages can increase the number of cattle sold and the income of cattle enterprises. However, the increased income is usually offset by the high initial capital costs and ongoing costs of irrigating a forage crop. • The dominant beef production system in the Victoria catchment is breeding cattle, rather than fattening them for slaughter, with the major market being the sale of young animals for live export. • While native pastures are generally well adapted to harsh environments, they impose constraints on beef production through their low productivity and digestibility and their declining quality through the dry season. Growing irrigated forages and hay would allow higher- quality feed to be fed to specific classes of livestock to achieve higher production and/or different markets. These species could include perennial grasses, forage crops and legumes. • Grazing of irrigated forages by young cattle, or feeding them hay, decreases the time they take to reach sale weight and, in particular, increases their daily weight gain through the dry season. • While ostensibly simple, there are many unknowns regarding the best way to implement a system whereby irrigated forages and hay are grown on-farm to augment an existing cattle production system. • Growing forages or hay to feed young cattle for the export market was not financially viable in the modelled scenarios tested. While beef production and total income increased, gross margins were less than for baseline cattle operations. Pond-based black tiger prawns or barramundi (in saltwater) or redclaw crayfish (in fresh water) offer potentially high returns Along the very remote coastal margins of the study area, about 93,000 ha of land is suitable for prawn and barramundi aquaculture, using earthen ponds. • Prawn and barramundi aquaculture elsewhere in northern Australia have proven land-based production practices and well‑established markets for harvested products. These are not fully established for other aquaculture species being trialled in northern Australia. • Prawns could potentially be farmed in either extensive (low-density, low-input) or intensive (higher-density, higher-input) pond-based systems. Land-based farming of barramundi would likely be intensive. • The most suitable areas of land for pond-based marine aquaculture systems are restricted to the areas of the catchment under tidal influence and the river margins where cracking clay and seasonally or permanently wet soils dominate. • Annual operating costs for intensive aquaculture are so high that they can exceed the initial cost of developing the enterprise. Operational efficiency is, therefore, the most important consideration for new enterprises, particularly the production efficiency in converting feed to saleable product. Surface water storage potential Indigenous customary, residential and economic sites are usually concentrated along major watercourses and drainage lines. Consequently, potential instream dams are more likely to have an impact on areas of high cultural significance than are most other infrastructure developments of comparable size. • Complex changes in habitat resulting from inundation could create new habitat to benefit some species, while other species could experience a negative impact through loss of habitat. In the Victoria catchment, the potential for irrigated agriculture based on large instream dams is low relative to some other large catchments in northern Australia. This is due to the lack of coincidence between locations that are potentially suitable for large instream dams and the larger contiguous areas of soil suitable for irrigated agriculture. • Due to the limited areas of contiguous soil suitable for irrigated agriculture and favourable topography for reticulation infrastructure, the more feasible potential dam sites are on smaller headwater catchments. • Considering proximity to the Victoria Highway (~85 km) and the service centre of Kununurra (~220 km), a hypothetical large instream dam on the upper West Baines catchment could yield 64 GL in 85% of years and cost $396 million (−20% to +50%) to construct, assuming favourable geological conditions. This equates to a unit capital cost of $6188/ML. Due to the favourable topography at this location, a reticulation scheme with a nominal 3780 ha under irrigation is estimated to cost an additional $12.67 million or $3350/ha of irrigated area (excluding farm development and infrastructure). This is broadly representative of the cost of the better opportunities for large-scale water storage and irrigated agriculture in the Victoria catchment. • The Victoria River Roadhouse is about 200 km from Katherine, the nearest point on the Darwin– Katherine Interconnected System (DKIS) regulated power network. This distance limits opportunities for hydro-electric power generation in the Victoria catchment. Even if transmission lines were to connect the Victoria catchment to the DKIS, the DKIS is electrically isolated from other grids in Australia, so any large-scale electrical generation infrastructure in the Victoria catchment would still be disconnected from the National Electricity Market. • An instream dam upstream of Kalkarindji, designed and managed specifically for flood mitigation, could potentially reduce flood peak magnitude downstream. For the ten largest modelled rainfall events, the dam reduced peak flow by around 50% at Kalkarindji and less than 20% at Nitjpurru (Pigeon Hole). • Suitably sited large farm-scale gully dams are a relatively cost-effective method of supplying water. The topography of the Victoria catchment is highly suitable for large farm-scale gully dams throughout much of the catchment. The major limitation is that the soil is rocky and shallow, so access would be required to a nearby clay borrow pit to provide material for the cut- off trench and dam wall core zone. Potential gully dams requiring material from elsewhere will be less economically viable. The alluvial clay soils on the West Baines River upstream of the Victoria Highway and the narrow river frontages along the Victoria and Wickham rivers offer some opportunities for water harvesting. • Although the upper West Baines River has more soil suitable for irrigated agriculture than water, some of the suitable soils would be needed for water storage. Along the Victoria River and its other major tributaries, the scale of potential surface water development is constrained by soil suitable for irrigated agriculture rather than by water. • Along the Victoria River, loamy levees mean that soils suitable for ringtanks can be up to 1 km away. This distance and the increasing elevation away from the river considerably increase the capital and operational costs of water harvesting enterprises by increasing the cost of piping and pumping water. • It is physically possible (based on coincidence of suitable soil, water and topography) to extract 690 GL and irrigate 50,000 ha of broadacre crops on the clay alluvial soil and sandy and loamy soils during the dry season in 75% of years. This would be achieved by pumping or diverting water from the Baines River (~28,000 ha with area limited by water) and the Victoria River and its other major tributaries (~22,000 ha with area limited by soil) and storing it in offstream storages such as ringtanks. This extraction results in a modelled reduction in the mean and median annual discharges from the Victoria catchment of about 9% and 12%, respectively. • Using the Northern Territory Government’s recently released surface water take policy, the annual consumptive pool available for the entire Victoria River catchment, including the Baines River, is approximately 130 GL (2% of median annual discharge), when using the 1890–2022 modelled period. If this period is reduced to 1970–2022, the annual consumptive pool increases to approximately 200 GL. Groundwater in the Victoria catchment offers year‑round niche opportunities that are locationally distinct from surface water development opportunities • Groundwater is already widely used in parts of the Victoria catchment for providing drinking water for livestock but also for community water supplies and domestic use. The most productive groundwater systems in the Victoria catchment are the regional-scale Cambrian Limestone Aquifer (CLA) along the very remote eastern margins of the catchment and the local- to intermediate-scale Proterozoic dolostone aquifers (PDAs) in the centre and south of the catchment. • The CLA is a large regional-scale groundwater system that extends over 1500 km from north- west Queensland to north-west NT. It occurs across three sedimentary basins: the Georgina, Wiso and Daly geological basins. • Currently no licensed groundwater entitlements from the CLA exist in the Victoria catchment. The nearest licensed entitlements from the CLA are about 150 km to the north-east of the Victoria catchment and occur in the proposed Flora Tindall Water Allocation Plan area in the Daly catchment. • These three licensed entitlements are assigned for agricultural use and total 7.4 GL/year. However, actual groundwater use is currently less. • There is currently very little development of groundwater from the PDAs other than for stock and domestic bores and the community water supply at Timber Creek. No water allocation plan currently exists for the Victoria catchment. • Water in both the CLA and PDAs is mostly fresh (total dissolved solids <1000 mg/L) with chemistry reflective of the carbonate rocks within which they are hosted. This results in the water having a high hardness, which may result in scaling on water infrastructure. • Water discharging from the CLA and PDAs supports numerous ecologically and culturally important springs. Spring flows depend on short-term rainfall patterns and are known to gradually decrease in discharge as the dry season progresses with some springs not being able to maintain permanent flows. • Any extraction of groundwater for consumptive purposes will result in a corresponding reduction in discharge to rivers, springs and vegetation. • The time lag between groundwater extraction and the corresponding change in the expression of groundwater where it naturally discharges may be many decades in intermediate-scale groundwater systems and longer in regional systems. This presents management challenges but also adaptive management opportunities. With appropriately sited groundwater borefields along the eastern and southern margins of the Victoria catchment, an estimated 10 GL/year could potentially be extracted from the CLA to the south of Top Springs. This depends on community and government acceptance of impacts to groundwater-dependent ecosystems and existing stock and domestic groundwater users. • This volume of groundwater could potentially enable up to an additional 1350 ha (0.015% of the catchment) of irrigated agriculture depending upon the percentage mix of broadacre crops, horticulture and hay production. • The CLA discharges naturally via a combination of intermittent lateral outflow to streams where they are incised into the aquifer outcrop (Armstrong River and Bullock, Cattle and Montejinni creeks) and perennial localised spring discharge (Old Top, Lonely, Palm and Horse springs). Where groundwater in the CLA approaches the ground surface, it is also evaporated from the soil and riparian and spring-fed vegetation. • Due to the relatively short groundwater flow paths (~20 km) between hypothetical groundwater extractions and groundwater discharge zones, a hypothetical groundwater extraction of 9 to 12 GL/year from the CLA would result in a 13% to 16% modelled reduction in groundwater discharge to spring complexes near Top Springs at about 2060. • Modelled reduction in groundwater levels ranges from about 15 m at the centre of the hypothetical developments to 1 m up to 20 km away by about 2060. Due to the long distances and long timescales over which groundwater lateral flow occurs, modelled impacts to licensed entitlements in the proposed Flora Tindall Water Allocation Plan or the proposed Mataranka Water Allocation Plan would be negligible. • Under a projected dry future climate that assumes a 10% reduction in rainfall across the entire CLA (rather than just within the Victoria catchment) and no future hypothetical groundwater development, the modelled reduction in groundwater recharge to the CLA near Top Springs is 32%, and the modelled reduction in groundwater discharge to the nearby spring complexes is 33%. • The modelled changes in the water balance under a projected drier future climate are larger than for the modelled future hypothetical groundwater development. This highlights the sensitivity of groundwater storage in and discharge from the CLA near Top Springs to natural variations in climate. There may be potential to extract up to 20 GL/year from the PDAs in the centre and south of the Victoria catchment. • Very little data are available for these aquifers and opportunities will be localised. • Outcropping and subcropping units of dolostone aquifers are scattered across the centre and southern parts of the Victoria catchment where they are actively recharged. They tend to steeply dip below the subsurface, but in many cases nearby units are likely to be hydraulically connected. Elsewhere, the aquifers are confined by overlying basalt, sandstone and shale. • The PDAs discharge naturally via a combination of intermittent lateral outflow to streams where they are incised into the aquifer outcrops (East Baines River and Crawford, Giles and Middle creeks) and perennial localised discharge at discrete springs in contact with low-permeability basalt, sandstone and shale on the margin of the outcropping areas (Bulls Head, Kidman, Crawford, Depot, Farquharson and Wickham springs). • Despite outcropping and subcropping dolostone aquifers covering approximately 7000 km2 of the Victoria catchment, they only coincide with contiguous areas of soils suitable for irrigated agriculture at two locations. • The largest area is along the south-west margin of the catchment, where 85,000 ha of loamy and sandy soils suitable for irrigated horticulture overlay a PDA and is traversed by the unsealed Buntine Highway. Elsewhere 15,000 ha of clay soils suitable for broadacre irrigated cropping along Battle Creek, a minor tributary of the Victoria River, overlay part of a PDA. There are limited opportunities for managed aquifer recharge in the Victoria catchment. • Areas of the Victoria catchment with permeable soils and favourable slope and storage capacity for managed aquifer recharge (e.g. Sturt Plateau along the eastern margin of the Victoria catchment) have rivers that are highly intermittent, so there is no reliable and cost‑effective source of water for managed aquifer recharge. Changes in volumes and timing of river flows have ecological impacts • Although irrigated agriculture may occupy only a small percentage of the landscape, relatively small areas of irrigation can use large quantities of water, and the resulting changes in the flow regime can have profound effects on flow-dependent flora and fauna and their habitats. • Changes in river flow may extend considerable distances downstream and onto the floodplain, including into the marine environment and their impacts can be exacerbated by other changes, including changes to connectivity, water quality and invasive species. The magnitude and spatial extent of ecological impacts arising from water resource development are highly dependent on the type of development, location, extraction volume and mitigation measures implemented. •Ecological impacts, inferred here by calculating change in ecological flow dependency for a range of fresh water‑dependent ecological assets, increase non-linearly with increasing scale of surface water development (i.e. large instream dams and water harvesting). •At equivalent levels of water resource development (i.e. in terms of volume of water extracted), and without significant mitigation measures, instream dams have a larger mean impact to surface-flow-dependent ecology than water harvesting, averaged across the Victoria catchment. •Impacts from water harvesting tend to accumulate downstream, so ecological assets found near the bottom of the catchment experienced the greatest average catchment impact. Cryptic waders, threadfin, prawns and floodplain wetlands are among the ecological assets most affected by flow changes for water harvesting. Catfish, grunter and inchannel waterholes, found throughout the study area, are the ecological assets least affected. •Water harvesting developments extracting 80 to 690 GL/year of water without any mitigation strategies resulted in negligible changes to ecology flow dependencies of freshwater assets when averaged across the Victoria catchment. Local impacts below points of extraction, however, were moderate to major for some freshwater assets at the higher extraction volumes and moderate for near-shore marine assets at higher extraction volumes. Mitigation strategies that protect low flows and first flows of a wet season are successful in reducing impacts to ecological assets. These can be particularly effective if implemented for water harvesting developments. •At equivalent volumes of water extraction, imposing an end-of-system (EOS) annual flowrequirement, where water harvesting can only commence after a specified volume of water hasflowed past the EOS and into the Joseph Bonaparte Gulf, is an effective mitigation measure forwater harvesting. However, because the early wet-season streamflow in the Baines River is onlymoderately correlated with the early wet-season streamflow in the Victoria River, assigning anEOS annual flow requirement for each river may result in more targeted ecological outcomesthan a single EOS annual flow requirement for the entire catchment. •For EOS annual flow requirements greater than 200 GL, additional mitigation measures (e.g. increasing pump‑start capacity or decreasing pump rate) have little additional modelledecological benefit for water harvesting. •Relative to catchments with large dry-season flows maintained by groundwater discharge from aregional‑scale groundwater system (e.g. the Roper catchment), increasing pump-start thresholdsin the Victoria catchment to above 400 ML/day only results in marginal improvements toecological flow dependencies. •A dry future climate has the potential to have a larger mean impact on ecological flowdependencies across the Victoria catchment than the largest physically plausible water resourcedevelopment scenario. However, the perturbations to flow arising from a combined drier futureclimate and water resource development result in greater impacts on ecology flow dependencythan either factor on their own. For instream dams, location matters, and there is potential for risks of large local impacts. Improved outcomes are associated with maintaining attributes of the natural flow regime. •Potential dams located in small headwater catchments may result in a extreme change in theecological flow dependency immediately downstream of the dam. However, impacts reduce downstream with the accumulation of additional tributary flows, so when averaged over the entire catchment or measured at the EOS, the change in ecological flow dependency is minor. • Providing transparent flows (flows allowed to ‘pass through’ the dam for ecological purposes) improves flow regimes for ecology by reducing the mean yield of potential dams. Mean outcomes for fish assets can be improved from minor to negligible, and for waterbirds from moderate to minor, at catchment scales. But it’s not just flow, other impacts and considerations are also important. • At catchment scales, the direct impacts of irrigated agriculture on the terrestrial environment are typically small. However, indirect impacts such as weeds, pests and landscape fragmentation may be considerable, particularly to riparian zones. • Loss of connectivity associated with new instream structures and changes in low flows may limit movement patterns of many species within the catchment. This may include some road causeways and low structures within a river to divert water or create pumping pools to enable water harvesting. Inefficient farm practices, poorly managed irrigation outflows and uncontrolled runoff from irrigation areas close to drainage lines could have a larger impact on ecological condition than likely changes in river flow patterns and volume in the Victoria catchment. • Nitrogen, phosphorus, and potassium are the three nutrients used primarily in agricultural fertilisers. Irrigation outflows and tailwater run-off from irrigation events can be high in these nutrients as well as pesticides, herbicides and total dissolved solids. • If best-practice is not followed, the concentrations of these contaminants can be elevated in receiving surface and groundwater bodies. However, the extent to which irrigated agriculture impacts the quality of receiving waters is highly variable and depends on a wide range of factors including crop type, farm management and mitigation measures, type and scale of development, water application method, proximity to drainage lines and environmental factors such as climate, soil type, topography, hydrogeochemistry and susceptibility of irrigated land to flooding. • Studies in parts of Queensland with a seasonal hydrology have found that first flow events following irrigation or rainfall play a critical role in determining water quality. Studies have shown that pesticide concentrations in furrow irrigation runoff are highest following initial irrigation events but decrease in subsequent events. • When pesticide application rates are managed well and irrigation schedules are aligned with crop growth stages, the concentration of pesticides in receiving waters are typically low, studies in the Ord River Irrigation Area have found. • Vegetated areas can intercept agricultural run-off, reducing pesticide concentrations in surface waters approximately three times more than in areas of bare soil. This highlights the importance of maintaining a wide riparian buffer zone. • Water quality issues will be most significant closest to the source, because of dilution and naturally occurring processes by which aquatic systems can partially process contaminants and regulate water quality, such as denitrification in the case of nitrogen and microbial degradation and ultraviolet photolysis in the case of pesticides. There are no equivalent natural processes for reducing phosphorus. Commercial viability and other considerations The economic value of irrigated agriculture in the Victoria catchment has the potential to increase substantially from a very low base. • The total annual gross value of agricultural production in the Victoria catchment in 2020–21 was $110 million, all of which came from beef cattle production. • About 29% of all jobs in the Victoria catchment are associated with the grazing industry. Large public dams would be marginal in the Victoria catchment, but suitably sited on-farm water sources could provide good prospects for viable new irrigated enterprises. • Large dams could be marginally viable if public investors accepted a 3% discount rate or partial contributions to water infrastructure costs similar to established irrigation schemes in other parts of Australia. • On-farm water sources provide better prospects and, where sufficiently cheap water development opportunities can be found, could likely support viable broadacre farms and horticulture where development costs were low. • Proponents of large infrastructure projects have a systematic tendency to substantially under estimate development costs and risks and to over estimate the scale and rate at which benefits will be achieved. This Assessment provides information on realistic unit costs and demand trajectories to allow potential irrigation developments to be benchmarked and assessed on a like-for-like basis. • The viability of irrigated developments would be determined by: (i) markets and supply chains that can provide a sufficient price, scale and reliability of demand, (ii) farmers’ skills in managing the operational and financial complexity of adapting crop mixes and production systems suited to Victoria catchment environments, (iii) the nature of water resources in terms of the volume and reliability of supply relative to optimal planting windows, (iv) the nature of the soil resources and their proximity to supply chains, and (v) the costs needed to develop those resources and grow crops compared with alternative locations. It is prudent to stage developments to limit negative economic impact and to allow small‑scale trialling on new farms. • Farm productivity is subject to a range of risks, and setbacks that occur early have the greatest effect on a development’s viability. A period of initial underperformance must be anticipated for establishing greenfield farming in a new location, and this must be planned for. • There is a strong incentive to start any new irrigation development with well-established and understood crops, farming systems and technologies, and to incorporate lessons from past experiences of agricultural development in northern Australia. • The Victoria catchment, unlike most northern Australian catchments, has the benefit of being close to the Ord River Irrigation Area (the Ord). Many of the more productive clay soils in the Victoria catchment are similar to those of the Ord, so experiences from the Ord will have some level of transferability to parts of the Victoria catchment. The recently announced 67,500 ha Keep Plains Agricultural Development adjacent to the Ord River Irrigation Area would also provide experiential learning for any new development in the Victoria catchment. • Staging allows ‘learning by doing’ at a small scale, where risks can be contained while testing initial assumptions of costs and benefits and while farming systems adapt to unforeseen challenges in local conditions. Irrigated agriculture has a greater potential than rainfed production to generate economic and community activity. • Studies in the southern Murray–Darling Basin have shown that irrigation generates a level of economic and community activity that is three to five times higher than would be generated by rainfed production. Irrigated developments can unlock the economies of scale for supply chains and support services that allow rainfed farming to establish more easily around the irrigated core. • A large proportion of increased economic activity during the construction phase of potential irrigation developments in the Victoria catchment would be expected to leak outside the study area. Assuming $250 million in capital costs, which could potentially enable 10,000 ha of irrigated agriculture (~20 new farm-scale developments with on-farm water sources), the total regional economic activity within the Victoria catchment associated with the construction phase would be approximately $180 million (assuming 65% leakage out of the study area). Additional benefits would flow to other regions, including Kununurra, Katherine, Darwin and potentially some areas outside the NT. • The total annual increased economic activity (direct and indirect) from 10,000 ha of irrigated mixed broadacre (65%) and horticulture (35%) agriculture in the Victoria catchment could potentially amount to $280 million, supporting up to 185 full-time-equivalent jobs. • Based on economic data for the entire NT, the additional income that flows to Indigenous households from beef cattle developments would be one-ninth of that which flows to non- Indigenous households. The additional income that flows to Indigenous households from other agricultural developments (excluding beef) would be one-seventeenth of that which flows to non-Indigenous households. This indicates that, if agricultural developments in the Victoria catchment are to equally benefit Indigenous and non‑Indigenous households, concerted action will need to be taken by all stakeholders, including government, industry groups and proponents. Sustainable irrigated development requires resolution of diverse stakeholder values and interests. • Establishing and maintaining a social licence to operate is a precondition for substantial irrigation development. • The geographic, institutional, social and economic diversity of stakeholders increases the resources required to develop a social licence and reduces the size of the ‘sweet spot’ in which a social licence can be established. • Key interests and values that stakeholders seek to address include the purpose and beneficiaries of development, the environmental conditions and environmental services that development may alter, and the degree to which stakeholders are engaged. The Victoria River Water Resource Assessment Team Project Director Chris Chilcott Project Leaders Cuan Petheram, Ian Watson Project Support Caroline Bruce, Seonaid Philip Communications Emily Brown, Chanel Koeleman, Jo Ashley, Nathan Dyer Activities Agriculture and socio- economics Tony Webster, Caroline Bruce, Kaylene Camuti1, Matt Curnock, Jenny Hayward, Simon Irvin, Shokhrukh Jalilov, Diane Jarvis1, Adam Liedloff, Stephen McFallan, Yvette Oliver, Di Prestwidge2, Tiemen Rhebergen, Robert Speed3, Chris Stokes, Thomas Vanderbyl3, John Virtue4 Climate David McJannet, Lynn Seo Ecology Danial Stratford, Rik Buckworth, Pascal Castellazzi, Bayley Costin, Roy Aijun Deng, Ruan Gannon, Steve Gao, Sophie Gilbey, Rob Kenyon, Shelly Lachish, Simon Linke, Heather McGinness, Linda Merrin, Katie Motson5, Rocio Ponce Reyes, Nathan Waltham5 Groundwater hydrology Andrew R. Taylor, Karen Barry, Russell Crosbie, Geoff Hodgson, Anthony Knapton6, Shane Mule, Jodie Pritchard, Axel Suckow, Steven Tickell7 Indigenous water values, rights, interests and development goals Marcus Barber/Kirsty Wissing, Peta Braedon, Kristina Fisher, Petina Pert Land suitability Ian Watson, Jenet Austin, Bart Edmeades7, Linda Gregory, Jason Hill7, Seonaid Philip, Ross Searle, Uta Stockmann, Mark Thomas, Francis Wait7, Peter L. Wilson, Peter R. Wilson, Peter Zund Surface water hydrology Justin Hughes, Matt Gibbs, Fazlul Karim, Steve Marvanek, Catherine Ticehurst, Biao Wang Surface water storage Cuan Petheram, Giulio Altamura8, Fred Baynes9, Kev Devlin4, Nick Hombsch8, Peter Hyde8, Lee Rogers, Ang Yang Note: Assessment team as at September, 2024. All contributors are affiliated with CSIRO unless indicated otherwise. Activity Leaders are underlined. For the Indigenous water values, rights, interests and development goals activity, Marcus Barber was Activity Leader for the project duration except August 2022 – July 2023 when Kirsty Wissing (a CSIRO employee at the time) undertook this role. 1James Cook University; 2DBP Consulting; 3Badu Advisory Pty Ltd; 4Independent contractor; 5 Centre for Tropical Water and Aquatic Ecosystem Research. James Cook University; 6CloudGMS; 7NT Department of Environment, Parks and Water Security; 8Rider Levett Bucknall; 9Baynes Geologic Acknowledgements A large number of people provided a great deal of help, support and encouragement to the Victoria River Water Resource Assessment (the Assessment) team over the past three years. Their contribution was generous and enthusiastic and we could not have completed the work without them. Each of the accompanying technical reports (see Appendix A) contains its own set of acknowledgements. Here we acknowledge those people who went ‘above and beyond’ and/or who contributed across the Assessment activities. The people and organisations listed below are in no particular order. The Assessment team received tremendous support from people in the NT Government and associated agencies. They are too numerous to all be mentioned here but they not only provided access to files and reports, spatial and other data, information on legislation and regulations, groundwater bores and answered innumerable questions but they also provided the team with their professional expertise and encouragement. For the NT – Simon Cruickshank, Sally Heaton, Lauren Cooper, Brad Sauer, Nathaneal Mills, Brett Herbert, Rob Williams, Peter Waugh, Sean Lawrie, Nerida Horner as well as the manager and staff of Kidman Springs. Colleagues in other jurisdictions also provided support, including Simone McCallum (Western Australia). The Assessment gratefully acknowledges the members of the Indigenous Traditional Owner groups, and corporations from the Victoria catchment, as well as individuals who participated in the Assessment and who shared their deep perspectives about water, Country, culture, and development. The Northern Land Council and Central Land Council provided important opportunities to communicate with Traditional Owners about the work, and essential guidance about whom to prioritise as participants. Our sincere thanks to the Victoria Daly Regional Council, who on multiple occasions provided local advice that was crucial to the success of the project. Others who provided support include Barry Croke and the managers and/or staff of Killarney, Montejinni, Auvergne, Camfield, Pigeon Hole, Moolooloo and Victoria River Downs stations. Our documentation, and its consistency across multiple reports, were much improved by a set of copy-editors and Word-wranglers who provided great service, fast turnaround times and patient application (often multiple times) of the Assessment’s style and convention standards. They include Joely Taylor, Margie Beilharz, Jeanette Birtles, Sonja Chandler, Karen Mobbs and Sally Woollett. Greg Rinder provided graphics assistance. Colleagues in CSIRO, both past and present, provided freely of their time and expertise to help with the Assessment. This was often at short notice and of sufficient scale that managing their commitment to other projects became challenging. The list is long, but we’d particularly like to thank (in no particular order) Tony Zhen, Ali Wood, Nikki Dumbrell, Daniel Grainger, Veronica Hannan, Mahdi Montazeri, Jorge Pena-Arancibia, Jan McMahon, Kellie Muffatti, Chris Pavey, Carmel Pollino, Sonja Serbov, Jai Vaze, Francis Chiew, Dilini Wijeweera, Rachel Harm, Jodie Hayward, Heather Stewart, June Chin, Christian Lawrence, Gillian Foley, Anne Freer, Sharon Hall, Sonja Heyenga, Amy Edwards, Sally Tetreault Campbell, Larissa Sherman, Phil Davies, Anna Rorke and Chris Turnadge. This project was funded through the National Water Grid’s Science Program, which sits within the Department of Climate Change, Energy, the Environment and Water. Staff in the Science Program supported the smooth administration of the Assessment despite the many challenges that arose during the project years. A long list of expert reviewers provided advice that improved the quality of our methods report, the various technical reports, the catchment report and the case study report. The Governance Committee and Steering Committee (listed on the verso pages) provided important input and feedback into the Assessment as it progressed. Finally, the complexity and scale of this Assessment meant that we spent more time away from our families than we might otherwise have chosen. The whole team recognises this can only happen with the love and support of our families, so thank you. The Victoria catchment is the eastern most extent of the Boab tree in Australia Photo: CSIRO – Nathan Dyer Contents Director’s foreword .......................................................................................................................... i Key findings for the Victoria catchment ......................................................................................... ii Overview of the Victoria catchment ................................................................................... v Indigenous values, rights and development goals .............................................................. x Opportunities for agriculture and aquaculture .................................................................. xi Groundwater in the Victoria catchment offers year‑round niche opportunities that are locationally distinct from surface water development opportunities ............................ xvii Changes in volumes and timing of river flows have ecological impacts .......................... xix Commercial viability and other considerations ............................................................... xxii The Victoria River Water Resource Assessment Team ............................................................... xxiv Acknowledgements ...................................................................................................................... xxv Part I Introduction and overview 1 1 Preamble ............................................................................................................................. 2 1.1 Context .................................................................................................................. 2 1.2 The Victoria River Water Resource Assessment ................................................... 4 1.3 Report objectives and structure ............................................................................ 9 1.4 Key background ................................................................................................... 12 1.5 References ........................................................................................................... 16 Part II Resource information for assessing potential development opportunities 18 2 Physical environment of the Victoria catchment ............................................................. 19 2.1 Summary .............................................................................................................. 20 2.2 Geology and physical geography of the Victoria catchment .............................. 23 2.3 Soils of the Victoria catchment ........................................................................... 30 2.4 Climate of the Victoria catchment ...................................................................... 46 2.5 Hydrology of the Victoria catchment .................................................................. 59 2.6 References ........................................................................................................... 98 3 Living and built environment of the Victoria catchment ............................................... 103 3.1 Summary ............................................................................................................ 104 3.2 Victoria catchment and its environmental values ............................................. 107 3.3 Demographic and economic profile .................................................................. 127 3.4 Indigenous values, rights, interests and development goals ............................ 158 3.5 Legal and policy environment ........................................................................... 170 3.6 References ......................................................................................................... 174 Part III Opportunities for water resource development 191 4 Opportunities for agriculture in the Victoria catchment................................................ 192 4.1 Summary ............................................................................................................ 193 4.2 Land suitability assessment ............................................................................... 197 4.3 Crop and forage opportunities in the Victoria catchment ................................ 203 4.4 Crop synopses .................................................................................................... 231 4.5 Aquaculture ....................................................................................................... 265 4.6 References ......................................................................................................... 278 5 Opportunities for water resource development in the Victoria catchment .................. 281 5.1 Summary ............................................................................................................ 282 5.2 Introduction ....................................................................................................... 286 5.3 Groundwater and subsurface water storage opportunities ............................. 287 5.4 Surface water storage opportunities ................................................................ 312 5.5 Water distribution systems – conveyance of water from storage to crop ....... 354 5.6 References ......................................................................................................... 361 Part IV Economics of development and accompanying risks 366 6 Overview of economic opportunities and constraints in the Victoria catchment ......... 367 6.1 Summary ............................................................................................................ 368 6.2 Introduction ....................................................................................................... 369 6.3 Balancing scheme-scale costs and benefits ...................................................... 371 6.4 Cost–benefit considerations for water infrastructure viability ......................... 388 6.5 Regional-scale economic impact of irrigated development ............................. 397 6.6 References ......................................................................................................... 404 7 Ecological, biosecurity, off-site, downstream and irrigation-induced salinity risks ....... 407 7.1 Summary ............................................................................................................ 408 7.2 Introduction ....................................................................................................... 412 7.3 Ecological implications of altered flow regimes ................................................ 414 7.4 Biosecurity considerations ................................................................................ 443 7.5 Off-site and downstream impacts ..................................................................... 458 7.6 Irrigation-induced salinity.................................................................................. 465 7.7 References ......................................................................................................... 466 Appendices 482 ........................................................................................................................... 483 Assessment products ...................................................................................................... 483 ........................................................................................................................... 486 Shortened forms ............................................................................................................. 486 Units ........................................................................................................................... 489 ........................................................................................................................... 490 List of figures ................................................................................................................... 490 List of tables .................................................................................................................... 499 Part I Introduction and overview Chapter 1 provides background and context for the Victoria River Water Resource Assessment (referred to as the Assessment). This chapter provides the context for and critical foundational information about the Assessment, with key concepts introduced and explained. Jasper Gorge in Judbarra National Park is a key tourist attraction in the Victoria catchment. Photo: CSIRO – Nathan Dyer 1 Preamble Authors: Caroline Bruce, Cuan Petheram, Seonaid Philip, Ian Watson 1.1 Context Sustainable development is a priority for the Northern Territory (NT) and Australian governments, and a number of strategies have been developed to progress this. The NT Government Agribusiness Strategy 2030 (undated) is a good example of what sustainable development represents, describing itself as ‘a partnership to grow the size of the Agribusiness sector to $2 Billion by 2030 fostering vibrant, healthy and prosperous communities throughout the NT.’ This and other strategies see the need for continued research; for example, the NT Government (2023) announced a priority action with respect to the Territory Water Plan that sought to accelerate the existing water science program ‘to support best practice water resource management and sustainable development.’ For very remote areas like the catchment of the Victoria River (Figure 1-1) the land, water and other environmental resources or assets will be key in determining how sustainable development might occur. Primary questions for any consideration of sustainable development relate to the nature and the scale of opportunities (e.g. how water might be sourced to grow crops and how much water could be extracted), and their risks. The Assessment recognises that sustainable development is not a finite concept; it depends on the different interests and perceptions brought by individuals and communities. Understanding how people perceive risks is critical, especially in the context of areas such as the Victoria catchment, where almost three-quarters of the population is Indigenous (compared with 3.2% for Australia as a whole) and where many Indigenous Peoples still live on the same lands they have inhabited for thousands of years. Approximately 31% of the Victoria catchment is owned by Indigenous peoples as inalienable freehold. Irrespective of their perspective on development, most people would agree that having access to reliable information about land and water resources enables informed discussion and good decision making. Such information includes the amount and type of a resource or asset; where it occurs in relation to complementary resources; what commercial uses it might have; how the resource changes within a year and across years; the underlying socio-economic context; and the potential impacts of development on people, land and water. Most of northern Australia’s land and water resources have not been mapped sufficiently to reliably inform resource allocation, mitigation of investment or environmental risks, or the construction of policy settings that can support good decision making. The Victoria River Water Resource Assessment findings summarised in this report aim to partly address this gap, to enable better decision making on private investment and government expenditure, taking into account intersections between existing and potential resource users, and enabling net development benefits to be maximised. Figure 1-1 Map of Australia showing Assessment area (Victoria catchment) and other recent or ongoing CSIRO Assessments The Murray–Darling Basin and major irrigation areas and major dams (>500 GL capacity) in Australia are shown for context. The Assessment differs somewhat from many resource assessments in that it considers a wide range of resources or assets, rather than being a single mapping exercise of, say, soils. It also provides a lot of contextual information about the socio-economic profile of the catchment, and the economic possibilities and environmental impacts of development. Further, it considers many of the different resource and asset types in an integrated way, rather than separately. The Assessment does not take an advocacy position on development, or on particular opportunities or risks. Rather, the Assessment provides resource information in a way that can inform future decision making and policy development. The outcome of no change in land use or water resource development is also valid. CSIRO has been leading similar assessments since 2012 (Figure 1-1). At that time, the Australian Government commissioned CSIRO to undertake the Flinders and Gilbert Agricultural Resource Assessment in northern Queensland as part of the North Queensland Irrigated Agriculture Strategy, a joint Australian Government and Queensland Government initiative. This assessment had a strong agricultural focus and developed fundamental soil and water datasets, providing a comprehensive and integrated evaluation of the feasibility, economic viability and sustainability of agricultural development in two catchments in northern Queensland (Petheram et al., 2013a, 2013b). Through this work and in response to two Australian Government white papers from 2015 (the White Paper on Developing Northern Australia (PMC, 2015) and the Agricultural Competitiveness White Paper (Commonwealth of Australia, 2015)) the Australian Government commissioned CSIRO in 2016 to undertake additional, more water-focused assessments, in the Australia and WRAs overview map \\FS1-CBR.nexus.csiro.au\{lw-rowra}\work\10_Reporting\1_All\1_GIS\1_Map_docs\Re-A-503_Map_Australia_and_river_basins_SG_Vic_Preamble_V1_ArcGIS10_8.mxd For more information on this figure please contact CSIRO on enquiries@csiro.au 1 Only those islands greater than 1000 ha are mapped. Fitzroy catchment in WA (Petheram et al., 2018a) four catchments around Darwin in the NT (Petheram et al., 2018b) and the Mitchell catchment in Queensland (Petheram et al., 2018c). Collectively these three assessments are known as the Northern Australia Water Resource Assessment (NAWRA). More recently, an assessment was released for the catchment of the Roper River in the NT (Watson et al., 2023) and simultaneous assessments have been undertaken for the Victoria catchment in the NT (summarised in this catchment report) and the catchments of the Southern Gulf rivers (hereafter ‘Southern Gulf catchments’), that is, Settlement Creek, Gregory— Nicholson River and Leichhardt River, Morning Inlet and the Wellesley Island groups1 of the NT and Queensland (Watson et al., 2024). These last three assessments have again been commissioned by the Australian Government through the National Water Grid’s Science Program, which sits within the Department of Climate Change, Energy, the Environment and Water. While land, water and other environmental resources and/or assets can be put to a variety of uses (including the option of ‘no change in use’), this assessment was primarily concerned with how the land and water might be used for irrigated agriculture, since that is the most likely pathway to intensified use of these resources in the coming years. 1.2 The Victoria River Water Resource Assessment The Victoria River Water Resource Assessment has undertaken fundamental baseline data collection on water, soil and other environmental assets in order to support regional and Country planning, resource management and sustainable development. The Victoria catchment was identified by the Australian and NT governments as being a suitable candidate for a large-scale assessment of the water and soil resources. This was due to both interest in, and concerns about, the development of irrigated agriculture in the catchment. With the proximity of the Victoria River catchment to Kununurra and the Ord River Irrigation Area (ORIA) one of the major agriculture centres in northern Australia, the area is seen as having the potential for overcoming some of the challenges that typify agriculture in northern Australia. The Assessment aimed to: •improve baseline datasets of water, soil and other environmental resources and/or assets •understand the nature and scale of potential water resource development options •understand the water values, rights, interests and development goals of Indigenouscommunities •assess the potential environmental, social and economic impacts and risks of water resource andirrigation development. It is important to note that, although these four aims are listed sequentially above, activities in one part of the Assessment often informed (and hence influenced) activities in an another part. For example, understanding ecosystem water requirements (described in Part IV of this report) was particularly important in establishing rules around water extraction and diversion (i.e. how much water can be taken and when it should be taken; described in Part III of this report). Thus, the procedure of assessing a study area inevitably involved iterative steps, rather than a simple linear process. The techniques and approaches used in the Assessment were specifically tailored to the study area. In covering the aims listed above, the Assessment was designed to: • explicitly address the needs of and aspirations for local development by providing objective assessment of resource availability, with consideration of environmental and cultural issues • meet the information needs of governments as they assess sustainable and equitable management of public resources, with due consideration of environmental and cultural issues • address the due diligence requirements of private investors, by exploring questions of profitability and income reliability of agricultural and other developments. Drawing on the resources of all three tiers of government, the Assessment built on previous studies, drew on existing stores of local knowledge and employed an experienced science team, with quality assured through peer-review processes. The Assessment, which incurred delays in 2021 due to the COVID-19 pandemic, took just over 3 years to complete, between 1 July 2021 and 30 September 2024. 1.2.1 Scope of work The Assessment comprised activities that together were designed to explore the scale of the opportunity for water resource development in the Victoria catchment. A set of technical reports was produced as part of the Assessment (listed in Appendix A) from which the material in this catchment report was largely drawn. Functionally, the Assessment adopted an activities-based approach to the work (which is reflected in the content and structure of the outputs and products, as per Section 1.2.3) with the following activity groups: land suitability; surface water hydrology and climate; groundwater hydrology; agriculture and socio-economics; surface water storage; Indigenous water values, rights, interests and development goals; and ecology. In stating what the Assessment did, it is equally instructive to state what it did not do. The Assessment did not seek to advocate irrigation development or assess or enable any particular development; rather, it identified the resources that could be deployed in support of potential irrigation enterprises, evaluated the feasibility of development (at a catchment scale) and considered the scale of the opportunities that might exist. In doing so, the Assessment examined the monetary and non-monetary values associated with existing use of those resources, to enable a wide range of stakeholders to assess for themselves the costs and benefits of given courses of action. The Assessment is fundamentally a resource evaluation, the results of which can be used to inform planning decisions by citizens, investors, a range of organisations and the various tiers of government: local council, and the NT and Australian governments. The Assessment does not replace, or seek to replace, any planning processes; it does not recommend changes to existing plans or planning processes. The Assessment sought to lower the barriers to investment in the Assessment area by addressing many of the questions that potential investors would have about production systems and methods, crop yield expectations and benchmarks, and potential profitability and reliability. This information base was established for the Assessment area as a whole, not for individual paddocks, projects or businesses. The Assessment identified those areas that are most suited for new agricultural or aquaculture developments and industries, and, by inference, those that are not well suited. It did not assume that particular sections of the study area were in or out of scope. For example, the Assessment was ‘blind’ to issues such as land-clearing regulations that may exclude land from development now, but which might change in the future. The Assessment identified the types and scales of water storage and access arrangements that might be possible, and the likely consequences (both costs and benefits) of pursuing these possibilities. It did not assume that particular types or scales of water storage or water access were preferable to others, nor did it recommend preferred development possibilities. The Assessment examined resource use unconstrained by legislation or regulations, to allow the results to be applied to the widest range of uses, for the longest time frame possible. In doing so, it did not assume a particular future regulatory environment, but did consider a range of existing legislation, regulation and policy, and the impact of these on development. It was not the intention – and nor was it possible – for the Assessment to address all aspects of water, irrigation and agriculture development in northern Australia. Important aspects not addressed by the Assessment include the impacts of irrigation development on terrestrial ecology. 1.2.2 Plausibility of development pathways To understand how the hydrology, ecology and economic factors in the Victoria catchment interact with and respond to various types and scales of development, a wide range of potential development scenarios were examined. These ranged from small incremental increases in surface and groundwater extraction to water volumes defined only by the physical limits of the catchment. These scenarios disregarded regulatory considerations (related to, for example, water, land tenure or land clearing) that may exclude land from development now but might change over time to permit new prospects in the future. The likelihood of various scenarios will be strongly influenced by the regulatory framework at any point in time and by community acceptance of irrigated agriculture, and its benefits and risks. One way of understanding the nature and likely scale and rate of change in irrigated agricultural development, and to have meaningful discussions about future prospects in the Victoria catchment, is to examine the scale and historical rate of change in irrigated agriculture across northern Australia. Preliminary data from a recent analysis by the Assessment team shows that in 2023 there were about 62,000 ha of irrigated agriculture across the 310 million ha of northern Australia, as defined below. This is equivalent to about 0.02% of the land area. There are many definitions of northern Australia. The one used for these area estimations is defined as that part of northern Australia west of the Great Dividing Range and north of the Tropic of Capricorn ( There was a net increase of approximately 1300 ha per year of irrigated land across northern Australia (as defined above) during the 24 years between 1999 and 2023. About 26% of this increase was in the ORIA (WA), and about 18% in the Daly River catchment (NT), with the remainder of the increase across 18 other catchments. There are few reasons to suggest that the average rate of increase in irrigated land over the next few years will be very different to that seen between 1999 and 2023, notwithstanding that the NT Land Corporation announced a preferred developer in early 2022 of 67,500 ha of land in the NT (considered as Ord Stage 3), which is likely to be a mix of irrigated and mostly rainfed cropping land, but dependent on existing water capture and storage as part of the ORIA. There are also signs that the northern jurisdictions are taking a more conservative approach to release of water than they have in the past. For example, the NT Government’s (2024) policy for taking surface water in the wet season allows for a default maximum take of 5% ‘of the 25th percentile of total flows for the three highest flow months of the year based on the previous 50 years flow or modelled rainfall data of the river basin.’ This is a reduction from its previous policy of 20% of river flows at any time in any part of a river. Similarly, the Western Australian Government has taken a conservative approach to water planning in the Fitzroy catchment in the Kimberley, and the Queensland Water Strategy (Queensland Government, 2023) now has a priority to ‘Increase First Nations’ access to and ownership of water, and greater inclusion of cultural values and traditional knowledge in water decisions.’ Figure 1-2 shows the number of large dams (defined here as having a storage capacity of 10 GL or greater and are listed in the Australian National Committee on Large Dams database) constructed across Australia and northern Australia (west and east of the Great Dividing Range) over time. Over the past 40 years only nine large dams have been constructed across all of northern Australia (including the east coast), and only three of these nine dams were constructed for supplying water for irrigation, rather than for supplying water for mining or urban use. One of the three dams was also listed as having the purposes of flood mitigation, recreation and water supply for urban use. All three of the dams constructed to supply water for irrigation are east of the Great Dividing Range. No large dam has been constructed anywhere in northern Australia for the supply of water for irrigation for more than 25 years. Figure 1-2 Number of large dams constructed in Australia and northern Australia over time Large dams are defined as dams with a storage capacity of 10 GL or greater and are listed in the Australian National Committee on Large Dams database. Irrespective of the physical resources that may support water and irrigated agricultural development in the Victoria catchment, if the future trajectory of irrigation development is similar to historical trends, the scale of future irrigation development in the Victoria catchment is likely to be modest and unlikely to encompass large dam development. 1.2.3 Assessment products The Assessment produced written and internet-based products. These are summarised below, and the written products are listed in full in Appendix A. Downloadable reports and other outputs can be found at: https://www.csiro.au/victoriariver Written products For more information on this figure please contact CSIRO on enquiries@csiro.au 06012018024018301850187018901910193019501970199020102030Number of damsYear completedNorthern AustraliaAustralia The Assessment produced the following documents: • technical reports, which present scientific work in sufficient detail for technical and scientific experts to independently verify the work • a catchment report, which combines key material from the technical reports, providing well- informed but non-scientific readers with the information required for informed judgments about the general opportunities and risks for, and costs and benefits associated with, water resource development, including irrigated agriculture or aquaculture • a summary report, which is provided for a general public audience • a factsheet, which provides a summary of the key findings for the Victoria catchment for a general public audience. Audiovisual product The following audiovisual product was produced by the Assessment: • a video, providing an overview of the work. Internet-based platforms The following internet-based platforms were used to deliver information generated by the Assessment: • CSIRO Data Access Portal – a portal that enables the user to download key research datasets generated by the Assessment • NAWRA Explorer – a web-based tool that enables the user to visualise and interrogate key spatial datasets generated by the Assessment • internet-based applications that enable the user to run selected models generated by the Assessment. 1.3 Report objectives and structure This is the catchment report for the Victoria catchment. It summarises information from the technical reports for each activity and provides tools and information to enable stakeholders to see the opportunities for development and the risks associated with them. Using the establishment of a ‘greenfield’ (not having had any previous development for irrigation) irrigation development as an example, Figure 1-3 illustrates many of the complex considerations required for such development; key report sections that inform these considerations are also indicated. Figure 1-3 Schematic of key components and concepts in the establishment of a greenfield irrigation development Numbers shown in blue refer to sections of this report. For more information on this figure please contact CSIRO on enquiries@csiro.au The structure of the Victoria catchment report is as follows: • Part I (Chapter 1) provides background, context and a general overview of the Assessment. • Part II (Chapter 2 and Chapter 3) looks at current resources and conditions within the catchment. • Part III (Chapter 4 and Chapter 5) considers the opportunities for water and agricultural and aquaculture development based on the available resources. • Part IV (Chapter 6 and Chapter 7) provides information on the economics of development and a range of risks of development, as well as on those risks that might accompany development. 1.3.1 Part I – Introduction This part of the report provides a general overview of the Assessment. Chapter 1 (this chapter) covers the background and context of the Assessment. Key findings can be found in the front materials of this report. 1.3.2 Part II – Resource information for assessing potential development opportunities Chapter 2 is concerned with the physical environment, seeking to describe the soil and water resources present in the Victoria catchment, including: • geology and physical geography: focusing on those aspects that are important for understanding the distribution of soils, groundwater flow systems, suitable water storage locations and geology of economic significance • soils: covering the soil types within the catchment, the distribution of key soil attributes and their general suitability for irrigated agriculture • climate: outlining the general climatic circulatory systems affecting the catchment and providing information on key climate parameters of relevance to irrigation under current and future climates • hydrology: describing and quantifying the surface water and groundwater hydrology of the catchment. Chapter 3 is concerned with the living and built environment, providing information about the people and the ecology of the Victoria catchment and the institutional context of the catchment, describing: • ecology: ecological systems and assets of the Victoria catchment, including the key habitats, key biota and their important interactions and connections • socio-economic profile: current demographics, and existing industries and infrastructure of relevance to water resource development in the Victoria catchment • Indigenous values, rights, interests and development objectives, generated through the direct participation of Victoria catchment Traditional Owners. 1.3.3 Part III – Opportunities for water resource development Chapter 4 presents information about the opportunities for irrigated agriculture and aquaculture in the Victoria catchment, describing: •land suitability for a range of crop × season × irrigation type combinations, and for aquaculture, including key soil-related management considerations •cropping and other agricultural opportunities, including crop yields and water use •gross margins at the farm scale •prospects for integration of forages and crops into existing beef enterprises •aquaculture opportunities. Chapter 5 presents information about opportunities for extracting and/or storing water for use in the Victoria catchment, describing: •groundwater and subsurface storage opportunities •surface water storage opportunities in the Victoria catchment, including major dams, large farm- scale dams and natural water bodies •estimates of the quantity of water that could be pumped or diverted from the Victoria River andits major tributaries •water distribution systems (i.e. for conveyance of water from a dam and application to the crop) •costs of potential broad-scale irrigation development. 1.3.4 Part IV – Economics of development and accompanying risks Chapter 6 covers economic opportunities and constraints for water resource development, describing: •balance of scheme-scale costs and benefits •cost–benefit considerations for water infrastructure viability •regional-scale economic impacts of irrigated development. Chapter 7 discusses a range of risks of development, including those that might accompany development, describing: •ecological impacts of altered flow regimes on aquatic, riparian and near-shore marine ecology •biosecurity risks to agricultural or aquaculture enterprises •potential off-site impacts (due to sediment, nutrients and agri-pollutants) to receiving waters inthe catchment •irrigation-induced salinity due to rising watertables. 1.3.5 Appendices This report contains three appendices: Appendix A – list of information products Appendix B – shortened forms and units Appendix C – lists of figures and tables. 1.4 Key background 1.4.1 The Victoria catchment The Victoria catchment has an area of 82,400 km2 and lies within the NT, extending from the Joseph Bonaparte Gulf in the north, along and to the east of the NT–WA border, to the Tanami Desert in the south (Figure 1-4). The climate is hot and semi-arid. The catchment has a complex geological history comprising outcropping rocks and sediments that were deposited, and in some cases modified, over five major geological eras. In the central parts of the catchment, harder more-resistive sandstones form ranges and gorges, while to the east the topography varies from steep hills to undulating plains. The Victoria catchment is sparsely populated with a total population of approximately 2000 (ABS, 2021), with small population centres at Kalkarindji, Timber Creek, Yarralin, Daguragu, Amanbidji and Nitjpurru (Pigeon Hole). The largest of these settlements is Kalkarindji, with a population of 383 at the 2021 Census. There are also some smaller Indigenous communities, outstations and roadhouses. Indigenous Peoples in the Victoria catchment have retained strong ties to one another and to local cultural landscapes, but either chose or were obliged to move into the aforementioned larger settlements. Contemporary Indigenous residential populations include those with recognised traditional ownership rights and connections to the Victoria catchment, as well as people whose primary cultural connections lie elsewhere. Kununurra (population 4515 in 2021) is the closest urban service centre and is approximately 85 km by road from the western boundary of the catchment. The nearest major city and population centre is the NT capital, Darwin (the population of the Greater Darwin area was 139,902 in 2021), approximately 600 km by road from Timber Creek. The Victoria River is approximately 560 km in length, from south of Kalkarindji to Entrance Island at the river mouth. The main agricultural land use in the Assessment area is for grazing native vegetation (62% of the area). Aboriginal freehold tenure makes up 31% of the area, which includes the 16% of the catchment which is national park. The Bradshaw Field Training Area occupies 7%, to which access is restricted. The protected areas in the Victoria catchment and the marine region include one gazetted national park (Judbarra), a proposed extension to an existing national park (Keep River), two marine national parks, two Indigenous Protected Areas and two Directory of Important Wetlands in Australia sites. In the north of the Assessment area lies the Bradshaw Field Training Area, an Australian Government facility, with its southern boundary following the Victoria River. Cropping (both rainfed and irrigated) are very sparsely practised (<0.02% of the catchment area). Figure 1-4 The Victoria catchment Land without colour overlay is pastoral leasehold land. ALRA = Aboriginal Land Rights (Northern Territory) Act 1976; IPA = Indigenous Protected Area; NP = national park. Vic overview map \\FS1-CBR.nexus.csiro.au\{lw-rowra}\work\10_Reporting\2_Victoria\1_GIS\1_Map_Docs\CR-V-Ch1_515_Victoria_overview_v01.mxd For more information on this figure please contact CSIRO on enquiries@csiro.au 1.4.2 Wet–dry seasonal cycle: the water year Northern Australia has a highly seasonal climate, with most rain falling during the 4-month period from December to March. Unless specified otherwise, this Assessment defines the wet season as being the 6-month period from 1 November to 30 April, and the dry season as the 6-month period from 1 May to 31 October. However, it should be noted that the transition from the dry to the wet season typically occurs in October or November, and the definition of the northern wet season commonly used by meteorologists is 1 October to 30 April. All results in the Assessment are reported over the water year, defined as the period 1 September to 31 August, unless specified otherwise. This allows each individual wet season to be counted in a single 12-month period, rather than being split over two calendar years (i.e. counted as two separate seasons). This is more realistic for reporting climate statistics from hydrological and agricultural assessment viewpoints. 1.4.3 Scenario definitions The Assessment considered four scenarios, reflecting combinations of different levels of development, and historical and future climates, much like those used in the Northern Australia Sustainable Yields project (CSIRO, 2009a, 2009b, 2009c), the Flinders and Gilbert Agricultural Resource Assessment (Petheram et al., 2013a, 2013b), the Northern Australia Water Resource Assessments (Petheram et al., 2018a, 2018b, 2018c) and the Roper River Water Resource Assessment (Watson et al., 2023): • Scenario A – historical climate and current development • Scenario B – historical climate and future development • Scenario C – future climate and current development • Scenario D – future climate and future development. Scenario A Scenario A assumes a historical climate and current levels of development. The historical climate series is defined as the observed climate (rainfall, temperature and potential evaporation for water years from 1 September 1890 to 31 August 2022). All results presented in this report are calculated over this period, unless otherwise specified. Current surface water licence entitlements in the study area are about 152 GL. However, 150 GL of entitlements are located in the catchment of Forsyth Creek, which discharges into the Joseph Bonaparte Gulf adjacent to the Victoria River and was not included in the river modelling scenarios. Current surface water licence entitlements in the Victoria catchment are small (<2 GL/year), which is the equivalent of 0.04% of the median annual flow of the Victoria River. Consequently, Scenario A assumes no existing surface water extractions. Scenario A was used as the baseline against which assessments of relative change were made. Historical tidal data were used to specify downstream boundary conditions for the flood modelling. Scenario B Scenario B is historical climate and future hypothetical development assessed at approximately 2060. Scenario B uses the same historical climate series as Scenario A. River inflow, groundwater recharge and flow, and agricultural productivity were modified to reflect potential future development. Potential development options are entirely hypothetical and were devised to assess the response of hydrological, ecological and economic systems to future development ranging from small incremental increases in surface water and groundwater extraction through to extraction volumes representative of the likely physical limits of the Victoria catchment (i.e. considering the co-location of suitable soil and water). Price and cost information was indexed to December 2023 unless otherwise specified. The impacts of changes in flow due to this future development were assessed, including impacts on: • instream, riparian and near-shore ecosystems • Indigenous water values • economic costs and benefits • opportunity costs of expanding irrigation • institutional, economic and social considerations that may impede or enable adoption of irrigated agriculture. Scenario C Scenario C is future climate and current levels of surface water and groundwater development assessed at approximately 2060. Future climate impacts on water resources were explored within a sensitivity analysis framework by applying percentage changes in rainfall and potential evaporation to modify the 132-year historical climate series (as in Scenario A). The percentage change values adopted were informed by projected changes in rainfall and potential evaporation under Shared Socio-economic Pathways (SSP) 2-4.5 and 5-8.5 as defined in the IPCC Sixth Assessment Report on Climate change (IPCC, 2022). SSP 2-4.5 is broadly considered representative of a likely projection given current global commitments to reducing emissions, and SSP 5-8.5 is representative of an (unlikely) upper bound. Scenario D Scenario D is future climate and future hypothetical development. It uses the same future climate series as Scenario C. River inflow, groundwater recharge and flow and agricultural productivity were modified to reflect potential future development, as in Scenario B. Therefore, in this report, the climate data for scenarios A and B are the same (historical observations from 1 September 1890 to 31 August 2022), and the climate data for scenarios C and D are the same (the above historical data scaled to reflect a plausible range of future climates). 1.5 References Australian Bureau of Statistics (ABS) (2021) Census of population and housing time series profile. Catalogue number 2003.0 for various SA regions falling partly within Victoria catchment. Viewed 23 September 2023, https://www.abs.gov.au/census. Anon (2024) Budget 2024-25. A future made in Australia. Viewed 11 September 2024, https://budget.gov.au/content/factsheets/download/factsheet-fmia.pdf. Commonwealth of Australia (2015) Agricultural Competitiveness White Paper, Canberra. Viewed 24 September 2024, https://www.agriculture.gov.au/sites/default/files/documents/ag- competitiveness-white-paper_0.pdf CSIRO (2009a) Water in the Gulf of Carpentaria Drainage Division. A report to the Australian Government from the CSIRO Northern Australia Sustainable Yields Project. CSIRO Water for a Healthy Country Flagship, Australia. https://doi.org/10.4225/08/5859749d4c71e. CSIRO (2009b) Water in the Timor Sea Drainage Division. A report to the Australian Government from the CSIRO Northern Australia Sustainable Yields Project. CSIRO Water for a Healthy Country Flagship, Australia. https://doi.org/10.4225/08/585ac5bf09d7c. CSIRO (2009c) Water in the Northern North-East Coast Drainage Division. A report to the Australian Government from the CSIRO Northern Australia Sustainable Yields Project. CSIRO Water for a Healthy Country Flagship, Australia. https://doi.org/10.4225/08/585972c545457. Intergovernmental Panel on Climate Change (IPCC) (2022) Climate Change 2022: Impacts, adaptation, and vulnerability. Contribution of Working Group II to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, Cambridge, UK and New York, NY. NT Government (undated) Agribusiness 2030. Viewed 6 September 2024, https://industry.nt.gov.au/__data/assets/pdf_file/0005/1232771/agribusiness-strategy- 2030.pdf. NT Government (2023) Territory Water Plan. A plan to deliver water security for all Territorians, now and into the future. Viewed 6 September 2024, https://watersecurity.nt.gov.au/__data/assets/pdf_file/0003/1247520/territory-water- plan.pdf. NT Government (2024) Surface water take – wet season flow policy. Viewed 25 July 2024, https://nt.gov.au/__data/assets/pdf_file/0008/1348190/surface-water-take-wet-season- flow-policy.pdf. Petheram C and Bristow K (2008) Towards an understanding of the hydrological factors, constraints and opportunities for irrigation in northern Australia: a review. Science Report No. 13/08. CRC for Irrigation Futures Technical Report No. 06/08. CSIRO Land and Water, Australia. Petheram C, Watson I and Stone P (eds) (2013a) Agricultural resource assessment for the Flinders catchment. A report to the Australian Government from the CSIRO Flinders and Gilbert Agricultural Resource Assessment, part of the North Queensland Irrigated Agriculture Strategy. CSIRO Water for Healthy Country and Sustainable Agriculture flagships, Australia. Petheram C, Watson I and Stone P (eds) (2013b) Agricultural resource assessment for the Gilbert catchment. A report to the Australian Government from the CSIRO Flinders and Gilbert Agricultural Resource Assessment, part of the North Queensland Irrigated Agriculture Strategy. CSIRO Water for Healthy Country and Sustainable Agriculture flagships, Australia. Petheram C, Bruce C, Chilcott C and Watson I (eds) (2018a) Water resource assessment for the Fitzroy catchment. A report to the Australian Government from the CSIRO Northern Australia Water Resource Assessment, part of the National Water Infrastructure Development Fund: Water Resource Assessments. CSIRO, Australia. Petheram C, Chilcott C, Watson I, Bruce CI (eds) (2018b) Water resource assessment for the Darwin catchments. A report to the Australian Government from the CSIRO Northern Australia Water Resource Assessment, part of the National Water Infrastructure Development Fund: Water Resource Assessments. CSIRO, Australia. Petheram C, Watson I, Bruce C and Chilcott C (eds) (2018c) Water resource assessment for the Mitchell catchment. A report to the Australian Government from the CSIRO Northern Australia Water Resource Assessment, part of the National Water Infrastructure Development Fund: Water Resource Assessments. CSIRO, Australia. Prime Minister and Cabinet (PMC) (2015) Our North, Our Future: White Paper on Developing Northern Australia, Prime Minister and Cabinet, Commonwealth Government of Australia, 2015. Viewed 24 September, https://www.infrastructure.gov.au/sites/default/files/documents/nawp-fullreport.pdf Watson I, Bruce C, Philip S, Petheram C and Chilcott C (eds) (2024) Water resource assessment for the Southern Gulf catchments. A report from the CSIRO Southern Gulf Water Resource Assessment for the National Water Grid. CSIRO, Australia. Watson I, Petheram C, Bruce C and Chilcott C (eds) (2023) Water resource assessment for the Roper catchment. A report from the CSIRO Roper River Water Resource Assessment for the National Water Grid. CSIRO, Australia. Part II Resource information for assessing potential development opportunities Chapters 2 and 3 provide baseline information that readers can use to understand what soils and water resources are present in the Victoria catchment and the current living and built environment of the Victoria catchment. This information covers: • the physical environment (Chapter 2) • the people, ecology and institutional context (Chapter 3). The Wickham River downstream of Yarralin. Adjacent to the river are red loamy and sandy levee soils potentially suitable for irrigated horticulture. On the break of slope, these soils are susceptible to erosion, as can be seen on the margins of the river banks. Also pictured are contiguous areas of treeless alluvial clay soils that are potentially suitable for irrigated broadacre crops. Photo: CSIRO – Nathan Dyer 2 Physical environment of the Victoria catchment Authors: Andrew R Taylor, Justin Hughes, Seonaid Philip, Jodie Pritchard, Steve Marvanek, Peter R Wilson, David McJannet, Fazlul Karim, Bill Wang, Cuan Petheram, Russell Crosbie Chapter 2 examines the physical environment of the catchment of the Victoria River and seeks to identify the available soil and water resources. It provides fundamental information about the geology, soil, climate, and the river and groundwater systems of the catchment. These resources underpin the natural environment and existing industries, providing physical bounds to the potential scale of irrigation development. Key components and concepts are shown in Figure 2-1. Figure 2-1 Schematic diagram of key natural components and concepts in the establishment of a greenfield irrigation development "\\fs1-cbr.nexus.csiro.au\{lw-rowra}\work\10_Reporting\1_All\9_Graphics_artist\3_Vic and SoG\C Bruce Vic CR Chp2_8_2024.jpg" For more information on this figure please contact CSIRO on enquiries@csiro.au Numbers in blue refer to sections in this report. 2.1 Summary This chapter provides a resource assessment of the geology, soil, climate, and groundwater and surface water resources of the Victoria catchment. No attempt is made in this chapter to calculate physically plausible areas of land or volumes of water that could potentially be used for agriculture or aquaculture developments. Those analyses are reported in chapters 4 and 5. 2.1.1 Key findings Soils Soils with potential for agriculture in the Victoria catchment are mostly red loamy soils (17.5% of the catchment), cracking clay soils (11.7%) and other smaller areas of soils such as friable non-cracking clays or clay loams (6.5%). The cracking clay soils with potential are found on the alluvial plains and relict alluvial plains of the Victoria River and tributaries with broad areas along the West Baines River. They are moderately deep to very deep, slowly permeable and have high to very high water-holding capacity, but they may have restricted rooting depth in some areas due to very high salt levels in the subsoil. The alluvial plains on the lower Victoria and Baines rivers are poorly drained and subject to flooding. Cracking clay soils are also common in the south of the catchment on the Basalt gentle plains and the Basalt hills physiographic units but can be too rocky and/or shallow for agricultural development. The red loamy soils are typically found on the deeply weathered sediments in the south-west and south and the edge of the Sturt Plateau in the south-east; they are usually nutrient deficient and have low to high soil water storage. Some of the friable non-cracking clays or clay loams are subject to severe sheet and gully erosion. Some areas of soils highly suited to irrigated agriculture are found in narrow, ribbon-like distributions (e.g. loamy soils along the Wickam River around Yarralin), which may limit infrastructure layout and consequently agricultural opportunities. Over half the catchment (57.4%) is made up of shallow and/or rocky soils. Climate The Victoria catchment has a hot and arid climate that is highly seasonal and has an extended dry season. It receives a mean rainfall of 681 mm/year, 95% of which falls during the wet season. Mean daily temperatures and potential evaporation are high relative to other parts of Australia. On average, potential evaporation is approximately 1900 mm/year. Overall, the climate of the Victoria catchment is generally suitable for growing a wide range of crops, though in most years rainfall would need to be supplemented with irrigation. Variation in rainfall from one year to the next is moderate compared to elsewhere in northern Australia but is high compared to other parts of the world with similar mean annual rainfall. The length of consecutive dry years in the Victoria catchment is not unusual when compared to other catchments in northern Australia, and the magnitude of dry spells is similar to many regions in the Murray–Darling Basin and east coast of Australia. Since the 1969–70 water year (1 September to 31 August), the Victoria catchment has experienced one tropical cyclone in 21% of cyclone seasons and two tropical cyclones in 6% of seasons. Approximately 13% of the global climate models (GCMs) project an increase in mean annual rainfall by more than 5%, about half project a decrease in mean annual rainfall by more than 5% and about a third indicate ‘little change’. Surface water and groundwater The timing and event-driven nature of rainfall events and high potential evaporation rates across the Victoria catchment have important consequences for the catchment’s hydrology. Approximately 98% of runoff occurs during the wet season (November to April, inclusive), and 93% of all runoff occurs during the 4-month period from December to March, which is a high concentration of runoff compared to southern Australia. This means that, in the absence of groundwater, water storages are essential for dry-season irrigation. The major aquifers in the Victoria catchment occur within the fractured and karstic (i.e. having features formed by dissolution) Cambrian limestone along the eastern margin and the Proterozoic dolostone in the centre and south of the catchment. The Montejinni Limestone along the eastern margin hosts the Cambrian Limestone Aquifer (CLA). The CLA is a complex, interconnected and highly productive regional-scale groundwater system (about 460,000 km2 in area). It extends for about 1000 km to the south-east and a couple of hundred kilometres both north and south of the eastern boundary of the Victoria catchment. In the Victoria catchment, the CLA occurs in the subsurface across an area of approximately 12,000 km2. Mean annual volumetric recharge over the entire CLA and over the part of the CLA that falls within the Victoria catchment are calculated to be 995 and 80 GL/year, respectively. Yields from bores are highly variable due to the complex nature of the karstic aquifer and can range up to 10 L/second. However, bore yields for the CLA in the Victoria catchment are currently poorly characterised. East of the catchment boundary where proper testing has been carried out, bore yields are commonly found to range from 10 to 50 L/second. The CLA in the Victoria catchment hosts fresh (<500 mg/L total dissolved solids (TDS)) to slightly brackish (<2500 mg/L TDS) groundwater suitable for a variety of different uses. Proterozoic dolostone aquifers (PDAs) hosted mostly in the Skull Creek and Timber Creek formations in the centre of the catchment, and the Campbell Springs and Pear Tree dolostones in the south of the catchment, host productive intermediate-scale groundwater systems. Like the CLA, the PDAs are complex due to the variability and interconnectivity between fractures, fissures and karsts. The PDAs outcrop and subcrop across an area of about 7000 km2 in the centre (between Timber Creek and Yarralin) and south (near and west of Kalkarindji) of the catchment. Bore yields are highly variable due to the complex nature of the karstic aquifers and commonly range from 5 to 15 L/second. Where appropriately constructed production bores have been installed and pumping tests conducted, bores can yield up to 40 L/second. Water quality in the dolostone aquifers is generally fresh (<500 mg/L TDS) but can be slightly brackish (<2000 mg/L TDS) in places, which is suitable for a variety of uses. Currently, there are no licensed groundwater entitlements in the Victoria catchment. There are three licensed entitlements totalling 7.4 GL/year from the CLA for use in agriculture about 150 km to the north-east and outside the Victoria catchment. Groundwater is the most common water source for stock and domestic use as well as community water supplies. The median and mean annual discharges from the Victoria catchment into the Joseph Bonaparte Gulf are 5730 and 6990 GL, respectively. Annual variation is high, and the annual flow is modelled to range from 800 to 23,000 GL. Flow is highly seasonal: 93% of all flow occurs in the months of December to March, inclusive. Current surface water licensed entitlements in the study area total about 152 GL, across four licenses. However, apart from one license for 0.7 GL which occurs in the Victoria catchment, the three larger licenced entitlements are far downstream and close to the coast (see Section 3.3.4). Many rivers in the catchment, particularly those in the southern parts of the catchment, are ephemeral and reduced to a few scarce and vulnerable waterholes during the dry season. The northern-most reaches of the Victoria River are tidal and can experience high tidal ranges (>8 m). Tidal influence is detectable as far south as near Timber Creek. 2.1.2 Introduction This chapter seeks to address the question: What soil and water resources are available for irrigated agriculture in the Victoria catchment? The chapter is structured as follows: • Section 2.2 examines the geology of the Victoria catchment, which is important in understanding the distribution of groundwater, soil and areas of low and high relief, which in turn influence flooding and the deposition of soil. • Section 2.3 examines the distribution and attributes of soils in the Victoria catchment and discusses management considerations. • Section 2.4 examines the climate of the Victoria catchment, including historical data and future projections of patterns in rainfall. • Section 2.5 examines the groundwater and surface water hydrology of the Victoria catchment, including groundwater recharge, streamflow and flooding. Figure 2-2 Soil sampling in the West Baines catchment A car in a field of trees Description automatically generated Photo: CSIRO – Nathan Dyer 2.2 Geology and physical geography of the Victoria catchment 2.2.1 Geological history The geological history of an area describes the major periods of deposition and tectonics (i.e. major structural changes) as well as weathering and erosion. These processes are closely linked to the physical environment that influences the evolution and formation of resources such as valuable minerals, coal, groundwater and soil. Geology also determines topography, which in turn is a key factor in the location of potential dam sites, flooding and deposition of soil. These resources are all important considerations when identifying suitable locations for large water storages and when understanding past and present ecological systems and patterns of human settlement. The oldest rocks in the area are Proterozoic (2500 to 540 million years old) and consist of repeated thick sequences of sediments, including some units containing significant amounts of dolostone (dolomite-rich rocks that are prone to solution over a geological timescale) (Figure 2-3). These sediments were deposited in a series of basins extending across the area and then gently folded, faulted and uplifted to form highlands. By the end of the Proterozoic, the highlands had been eroded down to a level not far above that of the current topography. During the Cambrian, 540 to 485 Ma (million years ago), there was widespread extrusion of basalt lava onto the eroded surface of the Proterozoic sediments. This event was followed by deposition of a sequence of limestones and dolostones (Figure 2-3). Further gentle folding, faulting and uplift then occurred followed by another cycle of erosion, which started after the Cambrian and continued to the mid-Cretaceous (about 100 Ma), again resulting in erosion down to a level not far above that of the current topography. During the remainder of the Cretaceous (to about 66 Ma), subsidence and high global sea levels resulted in deposition of a thin succession of Cretaceous shallow marine sandstone, conglomerate and mudstone. These layers were probably deposited across the whole area but are now only preserved in the south-east of the catchment. The present landscape has been produced by warping and dissection of a series of erosion surfaces formed during several cycles of erosion that started in the late Cretaceous about 70 Ma and ended in the mid-Cenozoic about 25 Ma. During this time, stable crustal conditions, subaerial exposure and prolonged subaerial weathering of the remaining Proterozoic, Cambrian and Cretaceous rocks resulted in the formation of deep weathering profiles and associated iron-cemented cappings on those rocks. Between the mid-Cenozoic and the present day, there has been gentle uplift and warping of the various surfaces and their weathered cappings. Continued erosion led to the emergence of the present-day landscape, which involved the development of incised valley systems that have been superimposed on the underlying Proterozoic rocks. Erosion has produced broader valleys where the dolomite-rich sediments were exposed and weathering and solution could occur. Extensive floodplains and coastal deposits were built up on the margins of modern drainage systems and the coastline, respectively. Figure 2-3 Surface geology of the Victoria catchment Surface geology map \\FS1-CBR.nexus.csiro.au\{lw-rowra}\work\11_Groundwater\2_Victoria\1_GIS\1_Map_docs\1_Export\Gr-V-500_surface_geology_v02CR.png For more information on this figure please contact CSIRO on enquiries@csiro.au Source: adapted from Raymond (2012) 2.2.2 Physiography of the Victoria catchment The geological controls outlined in Section 2.2.1 have resulted in multiple physiographic units within the Victoria catchment as shown in Figure 2-4 and described in Table 2-1. The eight physiographic units, with shortened names in parentheses, are: • coastal marine plains (Marine plains) • alluvial plains of rivers and creeks (Alluvial plains) • level lateritic plains, plateaux and escarpments (Tertiary sedimentary plains) • gently undulating plains and rises on basalt (Basalt gentle plains) • gently undulating plains and pediments on dolomite and limestone, minor shales/mudstones/siltstones (Limestone gentle plains) • undulating rises to steep hills on basalt (Basalt hills) • hills and ridges on limestone (Limestone hills) • dissected plateaux, escarpments, steep hills and ridges on sandstones, siltstones and shales (Sandstone hills). The physiographic units serve as a useful framework to understand the potential agricultural lands and soils in terms of qualities and limitations, as each unit is derived from a distinct group of lithologies and landforms that give rise to a particular set of soil types and geomorphic patterns. In addition, they are useful for characterising sites that may offer potential to store water in the landscape. Potentially feasible dam sites occur where resistant ridges of rock that have been incised by the river systems outcrop on both sides of river valleys. The rocks are generally weathered to varying degrees, and the depth of weathering, the amount of outcrop on the valley slopes, the occurrence of dolomitic rocks that may contain solution features, and the width and depth of alluvium in the base of the valley are fundamental controls on the suitability of the potential dam sites. Where the rocks are relatively unweathered and outcrop on the abutments of the potential dam site, less stripping will be required to achieve a satisfactory founding level for the dam. In general, where stripping removes the more weathered rock, it is anticipated that the Proterozoic sandstones, siltstones, mudstones and conglomerates will form a reasonably watertight dam foundation requiring conventional grout curtains and foundation preparation. However, because dolostones are soluble over a geological timescale, it is possible that, where they occur within the Proterozoic sequences, potentially leaky dam abutments and reservoir rims may be present, which would require specialised and costly foundation treatment such as extensive grouting. Where this condition is possible, based on review of the 250,000 geological map sheets, it has been noted. The extent and depth of the Cenozoic or Quaternary alluvial sands and gravels in the floor of the valley are also important geological controls on dam feasibility, as these materials will have to be removed to achieve a satisfactory founding level for the dam. Table 2-1 provides more information on each physiographic unit shown in Figure 2-4: the area in hectares and as a percentage of the study area. Figure 2-4 Physiographic units of the Victoria catchment Physiographic map \\FS1-CBR.nexus.csiro.au\{lw-rowra}\work\10_Reporting\2_Victoria\1_GIS\1_Map_Docs\CR-V-514_LL501_location_v5-10_Physiographic_v1.mxd For more information on this figure please contact CSIRO on enquiries@csiro.au Physiographic units based on Sweet (1977). Significant settlements and roads are overlaid on hillshaded terrain relief. Table 2-1 Victoria catchment physiographic unit descriptions, shortened names, areas and percentage areas PHYSIOGRAPHIC UNIT DESCRIPTION SHORTENED NAME AREA (HA) % OF STUDY AREA Coastal marine plains Marine plains 143,000 1.8 Alluvial plains of rivers and creeks Alluvial plains 643,000 7.8 Level lateritic plains, plateaux and escarpments Tertiary sedimentary plains 1,320,000 16.0 Gently undulating plains and rises on basalt Basalt gentle plains 1,031,000 12.5 Gently undulating plains and pediments on dolomite and limestone, minor shales/mudstones/siltstones Limestone gentle plains 741,000 9.0 Undulating rises to steep hills on basalt Basalt hills 1,100,000 13.3 Hills and ridges on limestone Limestone hills 540,000 6.6 Dissected plateaux, escarpments, steep hills and ridges on sandstones, siltstones and shales Sandstone hills 2,722,000 33.0 2.2.3 Major hydrogeological basins and provinces of the Victoria catchment Six major hydrogeological provinces with a generally north-east to south-west trending orientation occur across the Victoria catchment (Figure 2-5). From oldest to youngest these are the: (i) Birrindudu Basin, underlying a large portion of the central part of the catchment and outcropping in the centre and south-west, (ii) Fitzmaurice Basin, which outcrops across a small part of the north-west of the catchment and is bound to the south-east by the Victoria River Fault Zone, (iii) Victoria Basin, which overlies the Birrindudu Basin and underlies the central and northern parts of the catchment, outcropping mostly across the north, (iv) Kalkarindji Igneous Province (KIP), which overlies the Wiso, Victoria and Birrindudu basins and occurs most prominently across the east and south of the catchment, (v) Wiso Basin, which underlies and outcrops along the eastern margin of the catchment, and (vi) Bonaparte Basin, which outcrops in the most north-west peninsula. The Palaeo-Mesoproterozoic Birrindudu Basin is a sedimentary basin mostly comprising sedimentary sequences of sandstone, dolostone and siltstone (Dunster and Ahmad, 2013a). The basin overlies metamorphic basement rocks of the Halls Creek and Pine Creek orogens in the Victoria catchment and has a subsurface extent of approximately 37,000 km2 (Dunster and Ahmad, 2013a). The basin extends in the subsurface south and west of the catchment over an area of about 82,000 km2 across the NT, extending beyond the catchment boundary beneath the cover of overlying basins and provinces (Dunster and Ahmad, 2013). Sedimentary sequences of the Birrindudu Basin can be more than 10 km thick, and major outcrops for the basin occur in the centre of the Victoria catchment (Figure 2-5). Where the dolostone rocks have been weathered, they host productive karstic aquifers. Where more resistive sandstone rocks outcrop, they often form mountain ranges. Topographic features associated with the Birrindudu Basin include the Fitzgerald Range in the centre of the catchment, which in places is dissected by the Victoria, Wickham and East Baines rivers (Cutovinos et al., 2013). Figure 2-5 Major geological basins and provinces of the Victoria catchment Australian Geological Provinces data source: Raymond (2018); Regional geological faults data source: Department of Industry, Tourism and Trade (2010) The Palaeo-Mesoproterozoic Fitzmaurice Basin has an outcropping and subcropping area of approximately 2000 km2 in the Victoria catchment and extends north and west of the catchment boundary. It also overlies metamorphic rocks of the Pine Creek and Hall Creek orogens (Dunster, 2013). The Fitzmaurice Basin is mostly comprised of a series of stacked sandstone sequences of interlayered siltstone and shale with a conglomerate base and has a collective thickness of more than 3.5 km (Dunster, 2013). It is bounded to the south-east by the Victoria and Birrindudu basins along the Victoria Fault Zone and in the north-west by the younger Bonaparte Basin (Figure 2-5). Rocks of Geological basins and provinces map \\FS1-CBR.nexus.csiro.au\{lw-rowra}\work\11_Groundwater\2_Victoria\1_GIS\1_Map_docs\Gr-V-501_GW_provinces_v07CR.mxd For more information on this figure please contact CSIRO on enquiries@csiro.au Fitzmaurice Basin are heavily faulted and gently folded in places and host partial aquifers with only minor groundwater resources. The sandstone rocks form mountain ranges such as the Pinkerton, Spencer and Yambarran ranges, which are dissected by the lower reaches of the Victoria River (Dunster, 2013). The Neoproterozoic Victoria Basin is a sedimentary basin hosting the Auvergne Group, which is mostly composed of interlayered sandstone and siltstone rocks (Dunster and Ahmad, 2013b). In the Victoria catchment, the Victoria Basin overlies the Pine Creek Orogen in the north-west and the Birrindudu Basin in the south-east. The Victoria Basin outcrops and subcrops mostly across the north of the catchment and has a subsurface extent beneath the catchment of approximately 26,000 km2. Its entire subsurface extent in the NT is approximately 36,000 km2 under the cover of the overlying KIP (Dunster and Ahmad, 2013b). The Victoria Basin is bordered by the Victoria River Fault Zone to the north-west and the Wiso Basin to the south-east (Figure 2-5). Outcropping rocks of the Victoria Basin are faulted in places and host localised fractured and weathered rock aquifers. The resistive sandstones form the Newcastle and Stokes ranges in the north of the catchment, which are in places dissected by the East Baines and Victoria rivers and Timber Creek (Cutovinos et al., 2014). The Neoproterozoic Wolfe Basin is composed of glacial and fluvioglacial sediments. It overlies the Birrindudu Basin and only occurs as a minor outcrop in the west of the Victoria catchment with the remainder obscured by the overlying KIP (Glass et al., 2013) (Figure 2-5). As the Wolfe Basin only intersects a minor part of the Victoria catchment, it is not described in detail here. The Kalkarindji Igneous Province was produced by widespread basaltic lava flows deposited over about 2,000,000 km2 during the early Cambrian (Glass et al., 2013). In the Victoria catchment, the KIP has a subsurface extent of approximately 40,000 km2 and is mostly composed of basalt and basalt breccia with minor sandstone and chert interbeds that can collectively be more than 300 m thick. The KIP overlies the Birrindudu and Victoria basins in the east and south of the catchment and underlies the Wiso Basin along the eastern margin (Figure 2-5). Outcropping rocks of the KIP form gentle basalt hills such as the Tent Hills in the east of the catchment, which are dissected in places by the Armstrong River and its tributaries (Glass et al., 2013). Where the basalt is fractured and faulted or occurs in conjunction with chert and/or sandstone, it hosts localised fractured rock aquifers. The middle Cambrian Wiso Basin is a sedimentary basin occupying approximately 140,000 km2 of the NT and is mostly composed of sandstone, siltstone, limestone and dolostone. The Wiso Basin is interconnected laterally with the Daly and Georgina basins to the north-east and south-east of the Victoria catchment, respectively (Kruse and Munson, 2013a, 2013b). Collectively these basins have a combined total area of about 460,000 km2, of which only a small portion (~12,000 km2) in the north- west coincides with the Victoria catchment. In the Victoria catchment, the Wiso Basin overlies and is bounded to the north-east by the KIP (Glass et al., 2013) (Figure 2-5). The sandstone, siltstone, limestone and dolostone sequences of the Wiso Basin are typically less than 300 m thick and are overlain by Cretaceous siltstone and claystone of the Mesozoic geological Carpentaria Basin (Kruse and Munson, 2013b; Munson et al., 2013). Outcropping limestone rocks of the Wiso Basin sometimes form gentle undulating plains to the east of Top Springs that are incised by tributaries of the Armstrong River (Cutovinos et al., 2013). Where the limestone and dolostone rocks have been weathered, they host productive karstic aquifers. The onshore and offshore parts of the late Palaeozoic to Cenozoic Bonaparte Basin have a total subsurface extent of approximately 270,000 km2, of which the onshore component only occupies an area of approximately 20,000 km2 (Ahmad and Munson, 2013). The basin is mostly composed of siliciclastic rocks and carbonate sedimentary rocks deposited in marine and fluvial environments that have a maximum onshore thickness of about 5 km (Ahmad and Munson, 2013). The onshore part of the basin in the Victoria catchment is small with a subsurface extent of approximately 1000 km2. In the Victoria catchment, the basin overlies the Halls Creek Orogen and is bound to the east by the Pine Creek Orogen and to the south by the Fitzmaurice Basin (Figure 2-5). It is mostly obscured by overlying Cenozoic sediments such as estuarine and delta deposits, black soil plains, sand plains and alluvium. Sandstone rocks of the basin host localised aquifers in places. 2.3 Soils of the Victoria catchment 2.3.1 Introduction Soils in a landscape occur as complex patterns resulting from the interplay of five key factors: parent material, climate, organisms, topography and time (Fitzpatrick, 1986; Jenny, 1941). Consequently, soils can be highly variable across a landscape. Different soils have different attributes that determine their suitability for growing different crops and guide how they need to be managed. The distribution of the different soils and their attributes closely reflects the geology and landform of the catchments. Hence, data and maps of soil and soil attributes that provide a spatial representation of how soils vary across a landscape are fundamental to regional-scale land use planning. This section briefly describes the spatial distribution of soil groups (Section 2.3.2) and soil attributes (Section 2.3.3) in the Victoria catchment. Management considerations for irrigated agriculture are summarised in Table 2-2. Maps showing the suitability of different areas for different crops under different irrigation types in different seasons are presented in Chapter 4. Unless otherwise stated, the material in Section 2.3 is based on findings described in the companion technical report on digital soil mapping and land suitability (Thomas et al., 2024). Soils and their attributes were collected and described according to Australian soil survey standards (National Committee on Soil and Terrain, 2009). 2.3.2 Soil characteristics The soils of the Victoria catchment are presented in a soil generic group (SGG) classification (Figure 2-6; Table 2-2; Table 2-3). These groupings provide a means of aggregating soils with broadly similar properties and management considerations. The distinctive groupings have different potential for agriculture: some have almost no potential (e.g. the shallow and/or rocky soils – SGG 7), and some have moderate to high potential (e.g. the cracking clay soils – SGG 9), assuming other factors such as flooding and the amount of salt in the profile are not limiting. The SGGs were designed to simultaneously cover a number of purposes: (i) to be descriptive so as to assist non-expert communication regarding soil and resources, (ii) to be relatable to agricultural potential, and (iii) to align, where practical, to the Australian Soil Classification (ASC) (Isbell and CSIRO, 2016). Soil generic groups were first used in Queensland to facilitate extension in the sugar industry, and they have been modified to suit the range of soils encountered in the Assessment area. Figure 2-6 The soil generic groups (SGGs) of the Victoria catchment produced by digital soil mapping The inset map shows the data reliability, which for SGG mapping is based on the confusion index as described in the companion technical report on digital soil mapping and land suitability (Thomas et al., 2024). Labels on the map relate to the locational description of soils later in this Section (2.3.2). Soil generic group map and identified locations \\FS1-CBR.nexus.csiro.au\{lw-rowra}\work\10_Reporting\2_Victoria\1_GIS\1_Map_Docs\CR-V-513_SGGandLocats_v1-10_10-8.mxd For more information on this figure please contact CSIRO on enquiries@csiro.au Table 2-2 Soil generic groups (SGGs), descriptions, management considerations and correlations to Australian Soil Classification (ASC) for the Victoria catchment SGG SGG OVERVIEW GENERAL DESCRIPTION LANDFORM MAJOR MANAGEMENT CONSIDERATIONS ASC† CORRELATION 1.1 Sand or loam over relatively friable red clay subsoils Strong texture contrast between the A and B horizons: A horizons generally not bleached; B horizon not sodic and may be acid or alkaline. Moderately deep to deep well-drained red soils Undulating plains to hilly areas on a wide variety of parent materials The non-acid soils are widely used for agriculture; the strongly acid soils are generally used for native and improved pastures Red Chromosols and Kurosols except those with strongly bleached A horizons (the AT, AV, AY, AZ, BA or BB subgroups) 1.2 Sand or loam over relatively friable brown, yellow and grey clay subsoils As above but moderately well-drained to imperfectly drained brown, yellow and grey soils As above As above but may be restricted by drainage- related issues Brown, yellow and grey Chromosols and Kurosols except those with strongly bleached A horizons (the AT, AV, AY, AZ, BA or BB subgroups) 2 Friable non- cracking clay or clay loam soils Moderate to strongly structured, neutral to strongly acid soils with little or only gradual increase in clay content with depth. Grey to red, moderately deep to very deep soils Plains, plateaux and undulating plains to hilly areas on a wide variety of parent materials Generally high agricultural potential because of their good structure, moderate to high chemical fertility and water-holding capacity. Ferrosols on young basalt and other basic landscapes may be shallow and rocky Ferrosols and Dermosols without sodic B horizons (EO, HA, HC, HO, BA or HB subgroups) 3 Seasonally or permanently wet soils A wide variety of soils grouped together because of their seasonal or permanent inundation. No discrimination between saline and fresh water Coastal areas to inland wetlands, swamps and drainage depressions. Mostly unconsolidated sediments, usually alluvium Require drainage works before development can proceed. Acid sulfate soils and salinity are associated problems in some areas Hydrosols and Aquic Vertosols and Podosols with long-term saturation 4.1 Red loamy soils Well-drained, neutral to acid red soils with little, or only gradual, increase in clay content at depth. Moderately deep to very deep red soils Level to gently undulating plains and plateaux, and some unconsolidated sediments, usually alluvium Moderate to high agricultural potential with spray or trickle irrigation due to their good drainage. Low to moderate water- holding capacity; often hardsetting surfaces Red Kandosols 4.2 Brown, yellow and grey loamy soils As above but moderately well-drained to imperfectly drained brown, yellow and grey soils As above As above but may be restricted by drainage- related issues Brown, yellow and grey Kandosols 5 Peaty soils Soils high in organic matter Predominantly swamps Low agricultural potential due to very poor drainage Organosols SGG SGG OVERVIEW GENERAL DESCRIPTION LANDFORM MAJOR MANAGEMENT CONSIDERATIONS ASC† CORRELATION 6.1 Red sandy soils Moderately deep to very deep red sands. May be gravelly Sandplains and dunes. Aeolian, fluvial and siliceous parent material Low agricultural potential due to excessive drainage and poor water-holding capacity. Potential for irrigated agriculture Red Tenosols and Red Rudosols 6.2 Brown, yellow and grey sandy soils Moderately deep to very deep brown, yellow and grey sands. May be gravelly As above Low agricultural potential due to poor water-holding capacity combined with seasonal drainage restrictions. May have potential for irrigated agriculture Brown, yellow and grey Tenosols. Rudosols and Podosols without long-term saturation 7 Shallow and/or rocky soils Very shallow to shallow (<0.5 m). Usually sandy or loamy but may be clayey. Generally weakly developed soils that may contain gravel Crests and slopes of hilly and dissected plateaux in a wide variety of landscapes Negligible agricultural potential due to lack of soil depth, poor water- holding capacity and presence of rock Most soils <0.5 m, mainly very shallow to shallow Rudosols, Tenosols, Calcarosols and Kandosols 8 Sand or loam over sodic clay subsoils Strong texture contrast between the A and B horizons; A horizons usually bleached. Usually alkaline but occasionally neutral to acid subsoils. Moderately deep to deep Lower slopes and plains in a wide variety of landscapes Generally low to moderate agricultural potential due to restricted drainage, poor root penetration and susceptibility to gully and tunnel erosion. Those with thick to very thick A horizons are favoured Sodosols, bleached Chromosols and Kurosols (those with AT, AV, AY, AZ, BA or BB subgroups) and Dermosols with sodic B horizons (EO, HA, HC, HO, BA or HB subgroups) 9 Cracking clay soils Clay soils with shrink–swell properties that cause cracking when dry. Usually alkaline and moderately deep to very deep Floodplains and other alluvial plains. Level to gently undulating plains and rises (formed on labile sedimentary rock). Minor occurrences in basalt landscapes Generally moderate to high agricultural potential. The flooding limitation will need to be assessed locally. Many soils are high in salt (particularly those associated with the treeless plains). Gilgai and coarse structured surfaces may occur Vertosols 10 Highly calcareous soils Moderately deep to deep soils that are calcareous throughout the profile Plains to hilly areas Generally moderate to low agricultural potential depending on soil depth and presence of rock Calcarosols † Isbell and CSIRO (2016). The soil groups and soil characteristics presented below are evaluated in the context of their relationship to physiographic units within the catchment (Figure 2-4). These physiographic units serve as a useful framework to understand the distribution of SGGs and soil characteristics. The Victoria catchment contains soils from nine of the ten SGGs (Figure 2-6) − peaty soils (SGG 5) are not found. Of the nine SGGs found in the catchment, only three occupy more than 10% of the area (Table 2-3). Together these three soils occupy 87% of the catchment: the cracking clay soils (SGG 9, 11.7%) principally associated with the alluvial plains and relict alluvial plains of the West Baines and Victoria rivers and major tributaries – these are likely to be the first soils developed; red loamy soils (SGG 4.1, 17.5%) principally found on the deeply weathered sediments in the south-west, south and south-east – these soils make up the largest area with potential for development; and shallow and/or rocky soils (SGG 7, 57.4%), which make up over half the catchment and are derived from a wide range of geologies and geomorphic processes – these soils have very little or no potential for development. The red sandy soils (SGG 6.1, 1.6%), although a minor unit, are a large contiguous area in the far south-east of the catchment. Red soils are generally well drained, whereas yellow, grey and even bluey-green soils indicate increasingly persistent wetness and, ultimately, permanent waterlogging. Mottles indicate cycling between wetting and drying soil conditions, a sign of imperfect drainage and seasonal inundation. Table 2-3 Area and proportions covered by each soil generic group (SGG) in the Victoria catchment SGG DESCRIPTION AREA (HA) % OF STUDY AREA 1.1 Sand or loam over relatively friable red clay subsoils 780 0.01 1.2 Sand or loam over relatively friable brown, yellow and grey clay subsoils 2,010 0.02 2 Friable non-cracking clay or clay loam soils 536,580 6.5 3 Seasonally or permanently wet soils 295,660 3.6 4.1 Red loamy soils 1,439,840 17.5 4.2 Brown, yellow and grey loamy soils 80,440 0.9 5 Peaty soils 0 0 6.1 Red sandy soils 127,470 1.6 6.2 Brown, yellow and grey sandy soils 46,060 0.56 7 Shallow and/or rocky soils 4,730,850 57.4 8 Sand or loam over sodic clay subsoils 990 0.01 9 Cracking clay soils 962,440 11.7 10 Highly calcareous soils 16,880 0.2 SGG 9 soils are slowly permeable cracking clays (Vertosols) comprising 962,440 ha of the catchment. These occur on the alluvial plains associated with the West Baines (CA1 in Figure 2-6) and Victoria rivers and major tributaries (CA2), as relict alluvial plains throughout the catchment where they are associated with the Alluvial plains physiographic unit (Figure 2-4) (CR1 on the West Baines River and CR2 on tributaries of the Victoria River), and as level to gently undulating plains where they have an association with the Basalt gentle plains (CB1) and the Basalt hills physiographic units (CB2). Collectively these moderately deep to very deep (0.5 to >1.5 m), imperfectly to well-drained, slowly permeable, brown, red or grey, and occasionally black, cracking clay soils are non-sodic to strongly sodic at depth and have soft self-mulching or hardsetting surfaces. Sodicity is inherited from the parent material. The soils have high to very high water-holding capacity (>140 mm) but may have a restricted rooting depth due to very high salt levels in the subsoil. The brown, red, grey and black cracking clay soils are suited to a variety of dry-season grain, forage and pulse crops, sugarcane and cotton. The very deep (>1.5 m) clay plains of the West Baines River (CA1) and Victoria River (CA2) alluvial plains are predominantly imperfectly drained to moderately well-drained grey and brown hardsetting cracking clay soils, frequently with small (<0.3 m) normal gilgai depressions (Figure 2-7). These soils on the lower West Baines River alluvial plains grade to seasonally wet soils (SGG 3), including Aquic Vertosols (W1). Figure 2-7 Brown Vertosol SGG 9 soils on alluvial plains along the West Baines River. Gilgai microrelief is evident Photo: CSIRO The relict alluvial plains shown in Figure 2-8 are dominated by imperfectly drained self-mulching grey cracking clay soils grading to moderately well-drained grey-brown clay soils in the lower-rainfall southern parts of the catchment (CR3). These plains were deposited over a diverse range of geologies and frequently have shallow (0.1 to 0.2 m) normal to linear gilgai and surface gravels or stones of various lithology. These very deep (>1.5 m) grey to grey-brown clay soils are distinctly different to the SGG 9 Vertosols developed from basalt, which tend to be well structured and self-mulching, stonier and often shallower. Soil or landscape photo \\FS1-CBR.nexus.csiro.au\{lw-rowra}\work\3_Land_suitability\2_Victoria\2_Reporting\Photos\SGG_PWB For more information on this figure please contact CSIRO on enquiries@csiro.au Figure 2-8 A plain with grey Vertosol SGG 9 soils on relict alluvial plains near Top Springs. Linear gilgai surface microrelief is evident in the mid-left distance Photo: CSIRO – Nathan Dyer SGGs 4.1 and 4.2 (Kandosols) are the moderately deep to very deep (0.5 to >1.5 m) loamy soils separated by colour that reflects their landscape position. The well-drained red loamy variant SGG 4.1 covering 1,439,840 ha represents a significant area (17.5%) of the catchment, while the yellow loamy (SGG 4.2) variant covers less than 1%. Combined, these soils dominate the deeply weathered sediments of the Sturt Plateau (K1 in Figure 2-6) in the east to south-east and other deeply weathered landscapes to the south and west of Kalkarindji (K2). The deeply weathered character of these soils means that their distribution strongly correlates with the Tertiary sedimentary plains physiographic unit (Figure 2-4). Generally, the intact deeply weathered surface has moderately deep to deep (0.5 to <1.5 m) red soils (SGG 4.1) with moderate amounts of iron nodules (Figure 2-9). The depth to iron pans and the amount of iron nodules in the profile relate to position in the landscape. For example, shallow pans are associated with residual plateaux and residual concentrations of iron nodules on and/or in the soil profile in these positions. Alternatively, iron nodules could have been transported to places lower in the landscape. Soil or landscape photo \\FS1-CBR.nexus.csiro.au\{lw-rowra}\work\3_Land_suitability\2_Victoria\2_Reporting\Photos\SGG_PWB For more information on this figure please contact CSIRO on enquiries@csiro.au Figure 2-9 Well-drained red loamy soils (SGG 4.1) with iron nodules on the Sturt Plateau Photo: CSIRO SGG 4 soils on the deeply weathered landscapes are usually nutrient deficient with low to high soil profile water storage (70 to 140 mm). Irrigation potential is limited to spray and trickle irrigated crops on the moderately deep to deep soils with low to high soil water storage. Water storage is reduced as iron nodule content in these soils increases. SGG 4 Kandosols on the alluvial plains (K3) and minor locations elsewhere in the Victoria catchment are uncommon and often fragmented with narrow flat areas dissected by stream channels and deep gullies. The soils are highly suited to irrigated agriculture, but the characteristically narrow, ribbon- like distribution of these soils in the landscape may limit infrastructure layout and consequently agricultural opportunities. These moderately permeable soils have a moderate to high (100 to 140 mm) soil water storage capacity. Shallow and/or rocky soils (SGG 7; 4,730,850 ha) make up over half the catchment (Table 2-3). This grouping covers a wide range of different shallow (<0.5 m) and/or rocky soil types. They have a range of parent geologies, which means that they correspond to multiple physiographic units, especially upland units like Sandstone hills, Basalt hills, and Limestone hills (Figure 2-4). Soils like these tend to have very low to low soil water storage (<70 mm) and are sometimes found on eroded slopes and where intense gully patterns have fragmented the land surface to make the land agriculturally unviable. Examples of SGG 7 soils include shallow (<0.5 m) Kandosols with abundant iron nodules, iron pans and exposed laterite on the rises and scarp areas of deeply weathered landscapes (Figure 2-10). Soil or landscape photo \\FS1-CBR.nexus.csiro.au\{lw-rowra}\work\3_Land_suitability\2_Victoria\2_Reporting\Photos\SGG_PWB For more information on this figure please contact CSIRO on enquiries@csiro.au Figure 2-10 Shallow and rocky soils (SGG 7) on laterite outcrops and scarps of deeply weathered landscapes Photo: CSIRO SGG 2 soils, the friable clays and clay loams, occur extensively throughout the catchment but represent only 6.5% of the area (Table 2-3; 536,580 ha). The well-drained, moderately permeable, very deep (>1.5 m) red and brown soils associated with the levees of the rivers and major tributaries are subject to severe sheet and gully erosion and moderate wind erosion in the lower-rainfall areas of the southern catchment (F1 in Figure 2-6). These non-sodic soils have very strong slaking properties (breakdown of dry soil aggregates to micro-particles when wet) in the subsoils, making them less resistant to erosion. McCloskey (2010) describes the erosion processes and erosion extent on the riparian zone of the Victoria River. The strong soil slaking, deeply incised river channel with steep slopes in the riparian zone, intensive rainfall events and past land management have all contributed to the severe erosion and very large sediment loads entering the waterways. Extensive areas of these soils (F2) also feature in the Alluvial plains physiographic unit (Figure 2-4). The well-drained, moderately deep (0.5 to 1 m) red friable loams developed on the dolomite and limestone plains and pediments (F3) are subject to severe sheet erosion due to erosion of the thin (predominantly <0.1 m) sandy surface and exposure of the strongly slaking subsoil. The high silt and fine sand in the clay subsoil develop a strongly hardsetting scalded surface when eroded, which results in extensive runoff and rill erosion. In the lower-rainfall southern parts of the catchment (F1), these soils are also subject to wind erosion, leaving exposed scalded subsoils. These sheet-eroded soils are difficult to rehabilitate and have limited development potential. As they occur in association with extensive areas of shallow soils and rock outcrops, the areas suitable for agricultural development are usually small and fragmented. Soil or landscape photo \\FS1-CBR.nexus.csiro.au\{lw-rowra}\work\3_Land_suitability\2_Victoria\2_Reporting\Photos\SGG_PWB For more information on this figure please contact CSIRO on enquiries@csiro.au SGG 3 soils include seasonally wet or permanently wet soils (Hydrosols and Aquic Vertosols). These soils comprise 295,660 ha (3.6%) of the catchment (Table 2-3) and occur extensively on the lower Baines (W1 in Figure 2-6), lower Victoria (W2) and Angalarri rivers (W3), and the low-lying alluvial coastal and marine plains (W4). The soils typically have a mottled grey clay subsoil, often with debil-debil microrelief. The low-lying seasonally wet non-saline alluvial plains of the lower Victoria River (W5) are suited to a limited number of dry-season irrigated crops. All other seasonally wet to permanently wet soils have limited potential for agricultural development. The coastal alluvial plains and very poorly drained saline marine plains subject to tidal inundation (W4) have very deep strongly mottled grey non-cracking and cracking clay soils subject to storm surge from cyclones. These near- coastal areas have potential for acid sulfate soils and are best represented in the Marine plains physiographic unit (Figure 2-4). SGG 6.1 soils are the deep red sandy, highly permeable soils (Tenosols; 127,470 ha of the catchment) on the sandplains and sand dunes of the northern extent of the Tanami Desert (S1 in Figure 2-6) coinciding with the Tertiary sedimentary plain physiographic unit in the far south of the catchment. Soils have a very low soil water storage (<70 mm) with potential for irrigated horticulture using trickle or drip systems. In the absence of irrigation, agricultural potential of these soils is low. 2.3.3 Soil attribute mapping Using a combination of new field sampling, pre-existing field data and digital soil mapping techniques, the Assessment mapped 18 attributes affecting the agricultural and aquaculture suitability of soil in the Victoria catchment, as described in the companion technical report on digital soil mapping and land suitability (Thomas et al., 2024). Descriptions and maps are presented below for six key attributes: •surface soil pH •soil thickness •soil surface texture •permeability •available water capacity (AWC) in the upper 100 cm of the soil profile (referred to as AWC 100) •rockiness. An important feature of each predicted attributes map (e.g. Figure 2-11a) is the companion reliability map showing the relative confidence in the accuracy of the attribute predictions (e.g. Figure 2-11b). Reliability statistical methods are described in the companion technical report on digital soil mapping and land suitability (Thomas et al., 2024). Note that mapping is only provided here for regional-scale assessment. Areas of high reliability allow users to be more confident in the quality of mapping, whereas areas of low reliability show where users should be cautious. Attributes are evaluated in terms of their relationship with the physiographic units (Figure 2-4). Surface soil pH The pH value of a soil reflects the degree to which the soil is alkaline or acidic, which affects the extent to which nutrients are available to plants for growth. Surface soil pH is the pH in the top 10 cm of the soil. For the majority of plant species, most soil nutrients are available when the pH range is 5.5 to 6.5. Nutrient imbalances are common for soils with pH greater than 8.5 or less than 5.5 and can lead to toxicity problems. The surface of most soils in the Victoria catchment are in the pH range 5.5 to 8.5 (Figure 2-11a) and thus would not limit crop growth in most instances. In terms of physiographic units (Figure 2-4), Marine plains, Limestone hills and Basalt gentle plains (i.e. clayier soils like SGGs 2, 3, 7 and 9) typically show values in the pH range 7.0 to 8.5, that is, neutral to alkaline. The remaining SGGs and physiographic units coincide with soils in the acid to neutral range (pH 5.5 to 7.0). The highly calcareous soils (SGG 10) developed on dolomite and limestone have consistently high surface pH (>8.0). Mapping reliability is highest in areas of the Tertiary sedimentary plains and some areas of Limestone gentle plains, which are the more homogeneous landscapes, and consistently lowest for the Marine plains physiographic unit where lack of data produces less reliable results (Figure 2-11b). Figure 2-11 (a) Surface soil pH (top 10 cm) of the Victoria catchment as predicted by digital soil mapping and (b) reliability of the prediction Map of soil surface pH DSM attribute \\FS1-CBR.nexus.csiro.au\{lw-rowra}\work\3_Land_suitability\2_Victoria\1_GIS\1_Map_docs\LL-V-513_DSM_1x2_v2_Surf_pH.mxd For more information on this figure please contact CSIRO on enquiries@csiro.au Soil thickness Soil thickness is a measure of the potential root space and the depth of soil from which plants obtain their water and nutrients. Deeper soils (e.g. SGGs 2, 3, 4.1, 4.2, 6.1 and 9) are strongly associated with the Marine plains, Alluvial plains and Tertiary sedimentary plains physiographic units (Figure 2-12a). Shallower soils (which coincide with SGG 7 in particular) dominate the physiographic units with high relief, including Sandstone hills, Limestone hills and Basalt hills units. Moderately deep soils (especially SGGs 2 and 9) dominate the physiographic units with moderate relief, including the Basalt gentle plains and Limestone gentle plains. Shallower soils (e.g. SGG 7) are consistent with erosional landscapes where the rate of removal of weathering material exceeds the rate of accumulation. Mapping reliability is moderate to high overall and strongest where soils are moderately deep to deep, reflecting a data collection bias towards deeper soils. The less reliable areas are the higher-relief physiographic units having less data (Figure 2-12b). Figure 2-12 (a) Soil thickness of the Victoria catchment as predicted by digital soil mapping and (b) reliability of the prediction Map of soil thickness DSM attribute \\FS1-CBR.nexus.csiro.au\{lw-rowra}\work\3_Land_suitability\2_Victoria\1_GIS\1_Map_docs\LL-V-516_DSM_1x2_v2_Soil_Thickness.mxd For more information on this figure please contact CSIRO on enquiries@csiro.au Soil surface texture Soil texture refers to the proportion of sand, silt and clay particles that make up the mineral fraction of a soil. Surface texture influences soil water-holding capacity, soil permeability, soil drainage, water and wind erosion, workability and soil nutrient levels. Light soils are generally those high in sand, and heavy soils are dominated by clay. Surface textures in the Victoria catchment are dominated by sandy soils, which coincide with Tertiary sedimentary plains, Sandstone hills, Limestone hills and Limestone gentle plains physiographic units (Figure 2-13a). These areas are dominated by SGGs 2, 4.1, 4.2, 6.1 and 7. The presence of these light-textured soils in the low-relief plains of the Tertiary sedimentary plains unit is explained by sandstone geology and in some places the influence of the Tanami dunefields and sands blown in, mantling the Tertiary landscapes. There are also extensive areas of clayey surface soils on basalt parent material (i.e. physiographic units Basalt hills and Basalt gentle plains; SGGs 2, 7 and 9) and on alluvial areas including the Marine plains and Alluvial plains physiographic units, which are generally composed of SGGs 3 and 9. Areas of loamy soils are less common in the catchment; they are generally associated with some Tertiary sedimentary plains (SGG 4.1) and zones within the Alluvial plains, Limestone gentle plains, Basalt hills and Basalt gentle plains (SGG 2) physiographic units. Areas of highest prediction reliability (Figure 2-13b) are found around the physiographic units of the Tertiary sedimentary plains, areas of Basalt gentle plains and much of the Sandstone hills, reflecting consistent textures within the units. Reliability tends to be lower around physiographic units of Marine plains, Basalt hills and Limestone gentle plains, reflecting a lack of data. Figure 2-13 (a) Soil surface texture of the Victoria catchment as predicted by digital soil mapping and (b) reliability of the prediction Map of surface texture DSM attribute \\FS1-CBR.nexus.csiro.au\{lw-rowra}\work\3_Land_suitability\2_Victoria\1_GIS\1_Map_docs\LL-V-515_DSM_1x2_v2_Texture.mxd For more information on this figure please contact CSIRO on enquiries@csiro.au Permeability The permeability of the profile is a measure of how easily water moves through a soil. Flood and furrow irrigation is most successful on soils with low and very low permeability, which reduces root zone drainage (i.e. water passing below the root zone of a plant), rising watertables and nutrient leaching. Spray or trickle irrigation is more efficient than flood and furrow irrigation on soils with moderate to high permeability. The lowest soil permeabilities are found in the clay-rich soils, especially those coinciding with Marine plains, Alluvial plains and Basalt gentle plains physiographic units, hence dominated by SGGs 3 and 9 (Figure 2-14a). Most of the Assessment area is covered by moderate- to high-permeability soils. The highest permeabilities are experienced in the sandier soils that dominate physiographic units including Sandstone hills and Tertiary sedimentary plains, where SGGs 6.1 and 7 predominate. Mapping reliability (Figure 2-14b) is generally low to moderate throughout with little correlation to physiographic units or SGGs due to the complexity in landscape positions and their related permeability within each unit. Figure 2-14 (a) Soil permeability of the Victoria catchment as predicted by digital soil mapping and (b) reliability of the prediction Map of soil permeability DSM attribute \\FS1-CBR.nexus.csiro.au\{lw-rowra}\work\3_Land_suitability\2_Victoria\1_GIS\1_Map_docs\LL-V-511_DSM_1x2_v2_Perm.mxd For more information on this figure please contact CSIRO on enquiries@csiro.au Availability water capacity to 100 cm AWC 100 is the maximum volume of water that the top 100 cm of soil can hold for plant use. The higher the AWC 100 value, the greater the capacity of the soil to supply plants with water. For irrigated agriculture, it is one factor that determines irrigation frequency and the volume of water required to wet up the soil profile. Soils with low AWC 100 require more frequent watering and lower volumes of water per irrigation. For rainfed agriculture, AWC 100 determines the capacity of crops to grow and prosper during dry spells. The largest AWC values are found where soils are deep and are clay-rich (Figure 2-15a), especially the physiographic units (Figure 2-4) of Marine plains, Alluvial plains and Basalt gentle plains (SGGs 3 and 9). Moderate AWCs are found in Tertiary sedimentary plains and Limestone gentle plains physiographic units. These moderate AWC soils tend to coincide with SGGs 2 and 4.1. The other physiographic units have low AWCs, reflecting the combination of shallowness and coarser textures. Mapping reliability (Figure 2-15b) is generally moderate to high, reflecting confidence in the data collected. It is notably lower for the Basalt gentle plains and Marine plains physiographic units and some areas of the Alluvial plains where there is more variation in the limited data. Figure 2-15 (a) Available water capacity in the upper 100 cm of the soil profile (AWC 100) as predicted by digital soil mapping in the Victoria catchment and (b) reliability of the prediction Map of AWC to 100 cm DSM attribute \\FS1-CBR.nexus.csiro.au\{lw-rowra}\work\3_Land_suitability\2_Victoria\1_GIS\1_Map_docs\LL-V-512_DSM_1x2_v2_AWC.mxd For more information on this figure please contact CSIRO on enquiries@csiro.au Rockiness The rockiness of the soil affects agricultural management and the growth of some crops, particularly root crops. Coarse fragments (e.g. pebbles, gravel, cobbles, stones and boulders), hard segregations and rock outcrops in the plough zone can damage and/or interfere with the efficient use of agricultural machinery. Surface gravel, stone and rock are particularly important and can interfere significantly with planting, cultivation and harvesting machinery used for root crops, small crops, annual forage crops and sugarcane. The alluvial physiographic units (Marine plains and Alluvial plains) and the Tertiary sedimentary plains physiographic unit are generally free of surface rocks (Figure 2-4; Figure 2-16a). These non-rocky soils are dominated by SGGs 2, 3 and 9 on the alluvial plains and 4.1 and 6.1 on Tertiary sedimentary plains. All other units tend to be rocky at the surface, consistent with their shallow status (e.g. SGG 7) or with high-relief conditions associated with hilly physiographic units. The moderately deep to deep cracking clay soils on the Basalt gentle plains have surface rock due to the shrink−swell properties of the soil pushing rocks to the surface. The reliability of mapping is variable throughout, although generally most reliable in the Alluvial plain physiographic unit and in areas of the Tertiary sedimentary plains where soils are consistently rock free, and in the Sandstone hills and Limestone hills physiographic units (Figure 2-16b), where soils are consistently rocky. The less reliable areas have variable levels of rock and thus poor correlation. Figure 2-16 (a) Surface rockiness in soils of the Victoria catchment represented by presence or absence as predicted by digital soil mapping and (b) reliability of the prediction Map of soil rockiness DSM attribute \\FS1-CBR.nexus.csiro.au\{lw-rowra}\work\3_Land_suitability\2_Victoria\1_GIS\1_Map_docs\LL-V-514_DSM_1x2_v2_Rockiness.mxd For more information on this figure please contact CSIRO on enquiries@csiro.au 2.4 Climate of the Victoria catchment 2.4.1 Introduction Weather, which is defined as short-term atmospheric conditions, is the key source of uncertainty affecting hydrology and crop yield. It influences the rate and vigour of crop growth, and catastrophic weather events can cause extensive crop losses. Climate is defined as weather of a specific region averaged over a long period of time. Key climate parameters controlling plant growth and crop productivity include rainfall, temperature, radiation, humidity, and wind speed and direction. Of all the climate parameters affecting hydrology and agriculture in water-limited environments, rainfall is usually the most important. Rainfall is the main determinant of runoff and recharge and is a fundamental requirement for plant growth. For this reason, reporting of climate parameters is heavily biased towards rainfall data. Other climate variables affecting crop yield are discussed in the companion technical report on climate (McJannet et al., 2023). Climate data presented in this report were calculated using SILO (Scientific Information for Land Owners) climate data surfaces (Jeffrey et al., 2001) unless stated otherwise. Very few climate observations are available in the region before 1890, therefore the 132-year period from 1 September 1890 to 31 August 2022 is used in the analysis presented below. Unless otherwise stated, the material in Section 2.4 is based on findings described in the companion technical report on climate (McJannet et al., 2023). 2.4.2 Weather patterns over the Victoria catchment The Victoria catchment is characterised by distinctive wet and dry seasons (Figure 2-17) due to its location in the Australian summer monsoon belt. Rainfall is highest in the northern parts of the catchment which are more frequently affected by monsoon westerly winds. The monsoon trough, a primary trigger for diurnal thunderstorm activity over the catchment, separates moist maritime winds to its north and much drier continental air to its south. The mean annual rainfall, averaged over the Victoria catchment for the 132-year historical period, is 681 mm. All climate results in the Assessment will be reported over the water year, defined as the period 1 September to 31 August, unless specified otherwise. Annual rainfall is highest in the northern part of the catchment and lowest in the most southerly part the catchment (Figure 2-17). This is because the more northerly regions of the catchment receive more wet-season rainfall as a result of active monsoon episodes. The Victoria catchment is relatively flat, so there is no noticeable topographic influence on climate parameters such as rainfall or temperature. Approximately 95% of the annual rainfall total in the Victoria catchment falls during the wet-season months (1 November to 30 April). The spatial distribution of rainfall during the wet and dry seasons is shown in Figure 2-17. Median wet-season rainfall exhibits a very similar spatial pattern to median annual rainfall, while median dry-season rainfall exhibits no strong spatial patterns. The highest monthly rainfall totals typically occur during January, February and March (Figure 2-18). Figure 2-17 Historical rainfall, potential evaporation and rainfall deficit Median (a) annual, (b) wet-season and (c) dry-season rainfall; median (d) annual, (e) wet-season and (f) dry-season potential evaporation; and median (g) annual, (h) wet-season and (i) dry-season rainfall deficit in the Victoria catchment. Rainfall deficit is rainfall minus potential evaporation. The lack of rainfall during the dry season is largely due to the predominance of dry continental south- easterlies and the significant dry air aloft that inhibits shower and thunderstorm formation. During the months in which the climate is transitioning to the wet season (i.e. typically mid-September to mid-December), strong sea breezes pump moist air inland, fuelling the steady growth of shower and thunderstorm activity over a period of weeks to months. This can result in highly variable rainfall during these months. Tropical cyclones and tropical lows contribute a considerable proportion of total annual rainfall, but the actual amount is highly variable from one year to the next (see the companion technical report For more information on this figure please contact CSIRO on enquiries@csiro.au on climate (McJannet et al., 2023)) since tropical cyclones do not affect the Victoria catchment in nearly three out of four years. For the 53 tropical cyclone seasons from 1969–70 to 2021–22, 72% of seasons registered no tropical cyclones tracking over the Victoria catchment, 21% experienced one tropical cyclone and 6% experienced two (BOM, 2023). 2.4.3 Potential evaporation and potential evapotranspiration Evaporation is the process by which water is lost from open water, plants and soils to the atmosphere; it is a ‘drying’ process. It has become common usage to also refer to this as evapotranspiration. Evaporation primarily affects the potential for irrigation by influencing: • runoff and deep drainage and, hence, the ability to fill water storages (Section 2.5) • crop water requirements (Section 4.3) • losses from water storages (Section 5.3). Potential evaporation (PE), or potential evapotranspiration (PET), is defined as the amount of evaporation that would occur if an unlimited source of water was available. The Victoria catchment has a mean annual PE of 1900 mm (over the period 1890 to 2022), but unlike rainfall, has no strong north–south gradient across the catchment (Figure 2-17d). Preliminary estimates of mean annual (or seasonal) irrigation demand and net evaporation from water storages are sometimes calculated by subtracting the mean annual (or seasonal) PE from the mean annual (or seasonal) rainfall. This is commonly referred to as the mean annual (or seasonal) rainfall deficit (Figure 2-17g-i). The mean annual rainfall deficit, or mean annual net evaporative water loss, in the Victoria catchment is about 1250 mm, and the deficit increases with distance from the coast. Two common methods for characterising climates are the United Nations Environment Program aridity index and the Köppen–Geiger classification (Köppen, 1936; Peel et al., 2007). The aridity index classifies the Victoria catchment as mainly ‘Semi-arid’, and the Köppen–Geiger classification classifies it as ‘Arid hot steppe’ (see the companion technical report on climate (McJannet et al., 2023)). 2.4.4 Variability and long-term trends in rainfall and potential evaporation Climate variability is a natural phenomenon that can be observed in many ways, for example, warmer-than-average dry seasons or low- and high-rainfall wet seasons. Climate variability can also operate over long-term cycles of decades or more. Climate trends represent long-term, consistent directional changes such as warming or increasingly higher mean rainfall. Separating climate variability from climate change is difficult, especially when comparing climate on a year-to-year basis. In the Victoria catchment, 95% of the rain falls during the wet season (November to April). The highest monthly rainfall in the Victoria catchment typically falls in January or February (Figure 2-18). The months with the lowest rainfall are June to September. In Figure 2-18, the blue shading (labelled ‘A range’) represents the range under Scenario A (i.e. the historical climate from 1 September 1890 to 31 August 2022). The upper limit of the A range is the value at which monthly rainfall (or PE in Figure 2-19) is exceeded during only 10% of years (10% exceedance). The lower limit of the A range is the value at which monthly rainfall (or PE) is exceeded during 90% of years (90% exceedance). The difference between the upper and lower limits of the A range provides a measure of the potential variation in monthly values from one year to the next. PE also exhibits a seasonal pattern: mean PE is at its highest during October (~205 mm) and its lowest during June (~110 mm) (Figure 2-19). Months where PE is high correspond to those months in which the demand for water by plants is also high. Mean wet-season and dry-season PEs in the Victoria catchment are shown in Figure 2-17. Compared to rainfall, the variation in monthly PE from one year to the next is small (Figure 2-19). The variation in rainfall from one year to the next is moderate compared to elsewhere in northern Australia but is high compared to other parts of the world with similar mean annual rainfall. Under Scenario A, rainfall for the Victoria catchment still exhibits considerable variation from one year to the next (Figure 2-18). Using Kalkarindji as an example, the highest annual rainfall (1204 mm, which occurred in the 2000–01 wet season) is nearly eight times the lowest annual rainfall (159 mm in 1953–54) and more than twice the median annual rainfall value (507 mm). The 10-year running mean provides an indication of the sequences of wet or dry years (i.e. variability at decadal timescales). For an annual time series, the 10-year running mean is the mean of the past 10 years of data including the current year. At Kalkarindji, for example, the 10-year running mean varied from 369 to 741 mm. This figure illustrates that the period between 2000 and 2010 was particularly wet relative to the historical record. Under Scenario A, PE exhibits much less inter-annual variability than rainfall (not shown, see the companion technical report on climate (McJannet et al., 2023)). The coefficient of variation (CV) provides a measure of the variability of rainfall from one year to the next. CV is calculated as the standard deviation of mean annual rainfall divided by the mean annual rainfall, and the larger the CV value, the larger the variation in annual rainfall relative to a location’s mean annual rainfall. Figure 2-20a shows the CV of annual rainfall for rainfall stations with a long- term record around Australia. Figure 2-20b shows that the inter-annual variation in rainfall in the Victoria catchment is about average for northern Australia catchments but is larger than stations in southern Australia with similar mean annual rainfall. Furthermore, Petheram et al. (2008) observed that the inter-annual variability of rainfall in northern Australia is about 30% higher than that observed at rainfall stations from the rest of the world for the same type of climate as northern Australia. Hence, caution should be exercised before drawing comparisons between the agricultural potential of the Victoria catchment and other parts of the world with a similar climate. Several factors are driving this high inter-annual variation in Australia’s climate, including the El Niño– Southern Oscillation (ENSO), the Indian Ocean Dipole, the Southern Annular Mode, the Madden– Julian Oscillation and the Interdecadal Pacific Oscillation. Figure 2-18 Historical monthly rainfall (left) and time series of annual rainfall (right) in the Victoria catchment at Auvergne, Yarralin, Kalkarindji and Top Springs ‘A range’ is the 10th to 90th exceedance values for monthly rainfall. Note: the ‘A mean’ line is directly under the ‘A median’ line in some months in these figures. The solid blue line in the right column is the 10-year running mean. For more information on this figure please contact CSIRO on enquiries@csiro.au Figure 2-19 Historical monthly potential evaporation (PE) (left) and time series of annual PE (right) in the Victoria catchment at Auvergne, Yarralin, Kalkarindji and Top Springs ‘A range’ is the 10th to 90th exceedance values for monthly PE. Note: the ‘A mean’ line is directly under the ‘A median’ line in some months in these figures. The solid blue line in the right column is the 10-year running mean. For more information on this figure please contact CSIRO on enquiries@csiro.au (a) (b) \\FS1-CBR.nexus.csiro.au\{lw-rowra}\work\1_Climate\2_Victoria\1_GIS\1_Map_Docs\1_Exports\Cl-V-516_Cv_map_of_selected_stations_v1_1031.png Figure 2-20 (a) Coefficient of variation (CV) of annual rainfall and (b) the CV of annual rainfall plotted against mean annual rainfall for 99 rainfall stations around Australia (a) The grey polygon indicates the extent of the Victoria catchment. (b) The rainfall station in the Victoria catchment is indicated by a red symbol. The light blue diamonds are rainfall stations from the rest of northern Australia (RoNA), and hollow squares are rainfall stations from southern Australia (SA). Of these influences, the ENSO phenomenon is considered to be the primary source of global climate variability over the 2- to 6-year timescale (Rasmusson and Arkin, 1993), and it is reported to be a significant cause of climate variability for much of eastern and northern Australia. One of the modes of ENSO, El Niño, has come to be a term synonymous with drought in the western Pacific and eastern and northern Australia (though El Niño does not necessarily mean a ‘drought’ will occur). Rainfall stations along eastern and northern Australia have been observed to have a strong correlation (0.5 to 0.6) with the Southern Oscillation Index (SOI), a measure of the strength of ENSO, during spring, suggesting that ENSO plays a key role in between-year rainfall variability (McBride and Nicholls, 1983). Another known impact of ENSO in northern Australia is the tendency for the onset of useful rains after the dry season to be earlier than normal in La Niña years and later than normal in El Niño years. For all years between 1890 and 2022, the mean rainfall onset date (defined as being the date on which 50 mm of rain has accumulated after the dry season) for the Victoria catchment is the last 10 days of December (see the companion technical report on climate (McJannet et al., 2023)). The mean SOI for the September to December period in each year was used to determine whether given years were in negative (SOI < −8, El Niño), positive (SOI > 8, La Niña) or neutral SOI (−8 < SOI < 8). Using this method, in El Niño, neutral and La Niña years, respectively, the median rainfall onset dates for the Victoria catchment are late December, mid-December and early December. Trends Previously, CSIRO (2009) found that rainfall in northern Australia between 1997 and 2007 was statistically different to that between 1930 and 1997. In other work, Evans et al. (2014) found a strong relationship between monsoon active periods and the Madden–Julian Oscillation, and that the increasing rainfall trend observed at Darwin Airport was related to increased frequency of active monsoon days rather than increased intensity during active periods. CLA-001 \\fs1-cbr.nexus.csiro.au\{lw-rowra}\work\1_Climate\1_All\2_Reporting\NAWRA2-TR-Cl-A-WB1-v11.xlsm Runs of wet and dry years The rainfall-generating systems in northern Australia and their modes of variability combine to produce irregular runs of wet and dry years. In particular, length and magnitude (intensity) of dry spells strongly influence the scale, profitability and risk of water-resource-related investments. The Victoria catchment is likely to experience dry periods of similar severity to many areas in the Murray– Darling Basin and on the east coast of Australia. Victoria catchment is characterised by irregular periods of consistently low rainfall when successive wet seasons fail, in addition to the typical annual dry season. Runs of wet years and dry years occur when consecutive years of rainfall occur that are above or below the median, respectively. These are shown in Figure 2-21 at Auvergne, Yarralin, Kalkarindji and Top Springs stations as annual differences from the median rainfall. A run of consistently dry years may be associated with drought (though an agreed definition of drought continues to be elusive). Analysis of annual rainfall at stations in the Victoria catchment indicates equally long runs of wet and dry years and nothing unusual about the length of the runs of dry years. Palaeoclimate records for northern Australia The instrumental record of climate data is very short in a geological sense, particularly in northern Australia, so a brief review of palaeoclimate data is provided. The literature indicates that atmospheric patterns approximating the present climate conditions in northern Australia (e.g. the Pacific circulation responsible for ENSO) have been in place since about 3 to 2.5 Ma (Bowman et al., 2010). This suggests many ecosystems in northern Australia have experienced monsoonal conditions for many millions of years. However, past climates have been both wetter and drier than the instrumental record for northern Australia, and the influence of ENSO has varied considerably over recent geological time. Several authors have found that present levels of tropical cyclone activity (i.e. over the instrumental record) in northern Australia are low (Denniston et al., 2015; Forsyth et al., 2010; Nott and Jagger, 2013) and possibly unprecedented over the past 550 to 1500 years (Haig et al., 2014). Furthermore, the recurrence frequencies of high-intensity tropical cyclones (Category 4 to Category 5 events) may have been an order of magnitude higher than that inferred from the current short instrumental records. Figure 2-21 Runs of wet and dry years at Auvergne, Yarralin, Kalkarindji and Top Springs (1890 to 2022) Wet years are shown by the blue columns and dry years by the red columns. For more information on this figure please contact CSIRO on enquiries@csiro.au 2.4.5 Changes in rainfall and evaporation under a future climate The effects of projected climate change on rainfall and PE are presented in Figure 2-22, Figure 2-23 and Figure 2-24. This analysis used 32 global climate models (GCMs) to represent a world where the global mean surface air temperatures are 1.6 °C higher than approximate 1990 global temperatures. This emission scenario is referred to as SSP2-4.5 (IPCC, 2022) and in this report as Scenario C. SSP2- 4.5 is the most likely future climate scenario according to Hausfather and Peters (2020). Because the scale of GCM outputs is too coarse for use in catchment- and point-scale hydrological and agricultural computer models, they were transformed to catchment-scale variables using a simple scaling technique (PS, pattern scaled) and are referred to as GCM-PSs. See the companion technical report on climate (McJannet et al., 2023) for further details. In Figure 2-22 the rainfall and PE projections of the 32 GCM-PSs are spatially averaged across the Victoria catchment, and the GCM-PSs are ranked in order of increasing mean annual rainfall. This figure shows that four (13%) of the projections for GCM-PSs indicate an increase in mean annual rainfall by more than 5%, two (6%) of the projections indicate a decrease in mean annual rainfall by more than 5%, and about 81% of the projections indicate a change in future mean annual rainfall of less than 5% under a 1.6 °C warming scenario. Hence, it can be argued that, based on the selected 32 GCM-PSs, the consensus result is that mean annual rainfall in the Victoria catchment is not likely to change under Scenario C. The spatial distribution of mean annual rainfall under Scenario C is shown in Figure 2-23. In this figure, only the third-wettest GCM-PS (i.e. 10% exceedance or Scenario Cwet), the middle (or 11th- wettest) GCM-PS (i.e. 50% exceedance or Scenario Cmid), and the third-driest GCM-PS (i.e. 90% exceedance or Scenario Cdry) are shown. Figure 2-24a shows mean monthly rainfall under scenarios A and C. The data suggest that mean monthly rainfall under Scenario Cmid will be similar to mean monthly rainfall under Scenario A. Under scenarios Cwet, Cmid and Cdry, the seasonality of rainfall in northern Australia is similar to that under Scenario A. Figure 2-22 Percentage change in rainfall and potential evaporation per degree of global warming for the 32 Scenario C simulations relative to Scenario A values for the Victoria catchment GCM-PSs are ranked by increasing rainfall for SSP2-4.5. "\\fs1-cbr\{lw-rowra}\work\1_Climate\2_Victoria\2_Reporting\plots\future_climate\mean.annual.percentage.change.per.degree.SSP245.png" For more information on this figure, table or equation please contact CSIRO on enquiries@csiro.au Figure 2-23 Spatial distribution of mean annual rainfall across the Victoria catchment under scenarios (a) Cwet, (b) Cmid and (c) Cdry Figure 2-24 (a) Monthly rainfall and (b) potential evaporation for the Victoria catchment under scenarios A and C ‘C range’ is based on the computation of the 10% and 90% monthly exceedance values, so the lower and upper limits in ‘C range’ are not the same as scenarios Cdry and Cwet. Note: the ‘A mean’ line is directly under the ‘Cmid’ line in (a). Potential evaporation The mean annual change in GCM-PS PE shows projected PE increases of about 2% to 10% (Figure 2-22). Under scenarios Cwet, Cmid and Cdry, PE exhibits a similar seasonality to that under Scenario A (Figure 2-24b). However, different methods of calculating PE give different results. Consequently, there is considerable uncertainty as to how PE may change under a warmer climate. See Petheram et al. (2012) and Petheram and Yang (2013) for more detailed discussions. Sea-level rise and sea-surface temperature projections Global mean sea levels have risen at a rate of 1.7 ± 0.2 mm/year between 1900 and 2010, a rate in the order of ten times faster than the preceding century. Australian tide gauge trends are similar to the global trends (CSIRO and Bureau of Meteorology, 2015). Sea-level projections for the Victoria catchment are summarised in Table 2-4. This information may be considered in coastal aquaculture developments and flood inundation of coastal areas. Mean annual rainfall scenarios \\FS1-CBR.nexus.csiro.au\{lw-rowra}\work\1_Climate\2_Victoria\1_GIS\1_Map_Docs\Cl-V-514-annuralRainfal-Cwet-Cmid-Cdry-v2.mxd For more information on this figure please contact CSIRO on enquiries@csiro.au "\\fs1-cbr\{lw-rowra}\work\1_Climate\2_Victoria\3_future_climate\summary\ssp245\mean_month_rain_pet.png" Table 2-4 Projected sea-level rise for the coast of the Victoria catchment Values are the median of Coupled Model Intercomparison Project (CMIP) Phase 5 global climate models (GCMs). Numbers in parentheses are the 5% to 95% range of the same. Projected sea-level rise values are relative to a mean calculated between 1986 and 2005. For more information on this figure, table or equation please contact CSIRO on enquiries@csiro.au RCP = Representative Concentration Pathway Source: CoastAdapt (2017) Sea-surface temperature increases around Australia are projected with very high confidence for all emissions scenarios, which show warming of around 0.4 to 1.0 °C in 2030 under Representative Concentration Pathway (RCP) 4.5, and 2 to 4 °C in 2090 under RCP 8.5, relative to a 1986 to 2005 baseline (CSIRO and Bureau of Meteorology, 2015). There will be regional differences in sea-surface temperature warming due to local hydrodynamic responses; however, there is only medium confidence in coastal projections as climate models do not resolve local processes (CSIRO and Bureau of Meteorology, 2015). For the Victoria catchment, the corresponding projected sea-surface temperature increases are 0.8 °C (range across climate models is 0.6 to 1.1 °C) in 2030 under RCP 4.5 and 3.0 °C (2.5 to 3.9 °C) in 2090 under RCP 8.5. These changes are relative to a 1986 to 2005 baseline (CSIRO and Bureau of Meteorology, 2015). Note that the data in Table 2-4 use the CMIP5 dataset to provide estimates of sea-level rise. An updated product that uses CMIP6 was not available at the time of writing. 2.4.6 Establishment of an appropriate hydroclimate baseline The allocation of water and the design and planning of water resources infrastructure and systems require great care and consideration and need to be based on scientific evidence and take a genuine long-term view. A hydroclimate baseline from 1890 to 2022 (i.e. current) was deemed the most suitable baseline for the Assessment. A poorly considered design can result in an unsustainable system or preclude the development of a more suitable and possibly larger system, thus adversely affecting existing and future users, industries and the environment. Once water is overallocated, it is economically, financially, socially and politically difficult to reduce allocations in the future, unless water allocations are only assigned over short time frames (e.g. <15 years) and then reassessed. However, many water resource investments, particularly agricultural investments, require time frames longer than 30 years as there are often large initial infrastructure costs and a long learning period before full production potential is realised. Consequently, investors require certainty that, over their investment time frame (and potentially beyond), their access to water will remain at the level of reliability initially allocated. A key consideration in developing a water resource plan, or in assessing the water resources of a catchment, is the time period over which the water resources will be analysed, also referred to as the hydroclimate ‘baseline’ (e.g. Chiew et al., 2009). If the hydroclimate baseline is too short, it can introduce biases in a water resource assessment for various reasons. First, the transformation of rainfall to runoff and rainfall to groundwater recharge is non-linear. For example, averaged across the catchment of the Flinders River in northern Australia (Figure 1-1), the mean annual rainfall is only 8% higher than the median annual rainfall, yet the mean annual runoff is 59% higher than the median annual runoff (Lerat et al., 2013). Similarly, the median annual rainfall between 1895 and 1945 was the same as the median annual rainfall between 1948 and 1987 (less than 0.5% difference), yet there was a 21% difference in the median annual runoff between these two time periods (and a 40% difference in the mean annual runoff) (Lerat et al., 2013). Consequently, great care is required if using rainfall data alone to justify the use of short periods over which to analyse the water resources of a catchment. In developing a water resource plan, the volume of water allocated for consumptive purposes is usually constrained by the drier years (referred to as dry spells when consecutive dry years occur) in the historical record (see Section 2.4.4). This is because it is usually during dry spells that water extraction most adversely affects existing industries and the environment. All other factors (e.g. market demand, interest rates) being equal, consecutive dry years are usually also the most limiting time periods for new water resource developments and/or investments, such as irrigated agricultural enterprises, particularly if the dry spells coincide with the start of an investment cycle. Consequently, it is important to ensure a representative range of dry spells (i.e. of different durations, magnitudes and sequencing) are captured over the Assessment time period. For example, two time periods may have very similar median annual runoffs, but the duration, magnitude and sequencing of the dry spells may be sufficiently different that they pose different risks to investors and result in different modelled ecological outcomes. In those instances where there is the potential for a long memory, such as in intermediate- and regional-scale groundwater systems or in river systems with large reservoirs, long periods of record are preferable to minimise the influence of initial starting conditions (e.g. assumptions regarding initial reservoir storage volume), to properly assess the reliability of water supply from large storages and to encapsulate the range of likely conditions (McMahon and Adeloye, 2005). All these arguments favour using as long a time period as practically possible. However, in some circumstances a shorter period may be preferable on the basis that it is a more conservative option. For example, in south-western Australia, water resource assessments to support water resource planning are typically assessed from 1975 onwards (Chiew et al., 2012; McFarlane et al., 2012). This is because there has been a marked reduction in runoff in south-western Australia since the mid-1970s, and this declining trend in rainfall is consistent with the majority of GCM projections, which project reductions of rainfall into the future (McJannet et al., 2023). Although there were few rainfall stations in the study area at the turn of the 20th century relative to 2019 (McJannet et al., 2023), an exploratory analysis of rainfall statistics of the early period of the instrumental record does not appear to be anomalous when compared to the longer-term instrumental record. In deciding upon an appropriate time period over which to analyse the water resources of the Victoria catchment, consideration was given to the above arguments, as well as to palaeoclimate records, observed trends in the historical instrumental rainfall data and future climate projections. For the Victoria catchment, although there is evidence of an increasing trend in rainfall in the recent instrumental record, 81% of the GCM-PSs project no change in mean annual rainfall for a 1.6 °C warming scenario. Furthermore, palaeoclimate records indicate that multiple wetter and drier periods have occurred in the recent geological past (Northern Australia Water Resource Assessment technical report on climate (Charles et al., 2017)). Very few climate data are available in the Victoria catchment before 1890, so the baseline adopted for this Assessment was 1890 to 2022. Note, however, that as climate is changing on a variety of timescales, detailed scenario modelling and planning (e.g. the design of major water infrastructure) should be broader than just comparing a single hydroclimate baseline to an alternative future. 2.5 Hydrology of the Victoria catchment 2.5.1 Introduction The timing and event-driven nature of rainfall events and high PE rates across the Victoria catchment have important consequences for the catchment’s hydrology. The spatial and temporal patterns of rainfall and PE across the Victoria catchment are discussed in Section 2.4. Rainfall can be broadly broken into evaporated and non-evaporated components (the latter is also referred to as ‘excess water’). The non-evaporated component can be broadly broken into overland flow and recharge (Figure 2-25). Recharge replenishes groundwater systems, which in turn discharge into rivers and the ocean. Overland flow and groundwater discharged into rivers combine to become streamflow. Streamflow in the Assessment is defined as a volume per unit of time. Runoff is defined as the millimetre depth equivalent of streamflow. Flooding is a phenomenon that occurs when the flow in a river exceeds the river channel’s capacity to carry the water, resulting in water spilling onto the land adjacent to the river. Figure 2-25 Simplified schematic diagram of terrestrial water balance in the Victoria catchment Runoff is the millimetre depth equivalent of streamflow. Overland flow includes shallow subsurface flow. Numbers indicate mean annual values spatially averaged across the catchment under Scenario A. Numbers will vary locally. For more information on this figure please contact CSIRO on enquiries@csiro.au Section 2.5 covers the remaining terms of the terrestrial water balance (accounting for water inputs and outputs) of the Victoria catchment, with particular reference to the processes and terms relevant to irrigation at the catchment scale. Information is provided on groundwater, groundwater recharge and surface water – groundwater connectivity. Runoff, streamflow, flooding and persistent waterholes in the Victoria catchment are then discussed. Figure 2-25 is a schematic diagram of the water balance of the Victoria catchment, along with estimates of the mean annual value spatially averaged across the catchment and an estimate of the uncertainty for each term. The ‘water balance’ comprises all the water inflows and outflows to and from a particular catchment over a given time period. Unless stated otherwise, the material in sections 2.5.2 to 2.5.4 is based on findings described in the companion technical report on groundwater characterisation (Taylor et al., 2024). Similarly, the material in Section 2.5.5 draws on the findings of the companion technical report on river modelling (Hughes et al., 2024), unless stated otherwise. 2.5.2 Groundwater Within the Victoria catchment, the distribution, availability and quality of groundwater resources are heavily influenced by the physical characteristics of the sediments and rocks of the major hydrogeological basins and provinces (see Section 2.2). Aquifers are the rocks and sediments in the subsurface that store and transmit groundwater. Figure 2-26 summarises the spatial distribution of the rocks of the major geological groups and units hosted in each hydrogeological basin and province. The physical properties of the different rocks and sediments that comprise each geological unit influence the nature of the different aquifer types and the groundwater systems they host. Essentially, the catchment has three main types of aquifers: • fractured and/or karstic dolostones and limestones and fractured and weathered or porous sandstones hosting productive aquifers • fractured and weathered basalt or sandstones hosting variably productive aquifers • fractured and weathered shale, siltstone and mudstone rocks hosting only partial aquifers. In addition, minor aquifers occur across parts of the catchment hosted in: (i) surficial sediments that predominantly include undifferentiated sandstone, siltstone and claystone, and (ii) in alluvium (clay, silt, sand and gravel) associated with the major rivers and their tributaries. These minor aquifers are limited in extent and host variably productive aquifers. The limestone and dolostone rocks of the Montejinni Limestone in the Wiso Basin are generally flat lying to gently dipping and occur along the eastern margin of the Victoria catchment. The Montejinni Limestone hosts one of the most productive groundwater systems beneath the catchment – the Cambrian Limestone Aquifer (CLA). The CLA is a key water resource in the NT and extends for about 1000 kilometres to the south-east and a couple of hundred kilometres to the north and south of the catchment, occupying an area of approximately 460,000 km2 across parts of the NT (see Figure 2-30). In the Victoria catchment, the CLA underlies approximately 12,000 km2 of its eastern margin. These carbonate rocks are fractured and fissured and weathered by dissolution in places, forming a complex, interconnected and highly productive regional-scale groundwater system. That is, the distance between the recharge areas (where there is inflow of water through the soil, past the root zone and into an aquifer) and discharge areas (where there is outflow of water from an aquifer into a water body or as evaporation from the soil or vegetation) across parts of the aquifer can be hundreds of kilometres, and the time taken for groundwater to discharge following recharge can potentially be in the order of hundreds to thousands of years or even longer. Hence, the surface water catchment boundary is not the groundwater flow boundary (or groundwater divide). Groundwater in the CLA flows from areas inside the catchment with higher groundwater levels to areas outside the catchment with lower groundwater levels. Dolostone and sandstone rocks of the Bullita and Limbunya groups of the Birrindudu Basin occur in the centre and south of the Victoria catchment and exhibit structural complexity in places where they can dip steeply in the subsurface (Figure 2-26). The combined groups have a subsurface extent within the catchment of approximately 37,000 km2, of which about 7000 km2 either outcrops or subcrops beneath overlying Cenozoic sediments. These carbonate rocks are fractured and fissured and weathered by dissolution in places, and the sandstones are fractured and/or porous, creating productive aquifers that host intermediate-scale groundwater systems. That is, the distance between the recharge and discharge areas can be a few kilometres to tens of kilometres, and the time taken for groundwater to discharge following recharge can potentially be in the order of tens to hundreds of years and possibly up to a few thousand years. As the Limbunya Group extends for about 100 km to the south of the Victoria catchment, the surface water catchment boundary is not the groundwater flow boundary for aquifers hosted in this geological group (Figure 2-26). Groundwater in the dolostones and sandstones flows from areas outside the Victoria catchment with higher groundwater levels to areas inside the catchment with lower groundwater levels. Basaltic rocks of the Antrim Plateau Volcanics in the KIP, have a subsurface extent of approximately 40,000 km2 beneath the eastern, southern and western parts of the Victoria catchment (Figure 2-26). These basalt rocks either outcrop or subcrop beneath surficial Cenozoic cover across an area of approximately 28,000 km2 in the catchment. They are almost entirely flat lying but are faulted, fractured and weathered. In addition, the basalt rocks can co-occur with sandstone and chert interbeds or basal agglomerate in places, and they host localised and isolated groundwater systems of varying productivity. Sandstone and siltstone rocks of the Auvergne and Wattie groups of the Victoria and Birrindudu basins, respectively, are flat lying to gently dipping and faulted in places, and they host localised and isolated groundwater systems of varying productivity. These weathered and fractured rocks occur across large areas of the north, centre and west of the Victoria catchment and host local-scale groundwater systems (Figure 2-26). The sandstone, siltstone and shale rocks of the Duerdin, Tijunna and Weaber groups occur in places across the north of the Victoria catchment with the siltstone and shale rocks only hosting partial aquifers containing little groundwater (Figure 2-26) (Dunster et al., 2000). Where sandstone rocks occur and they are fractured and/or porous, they host localised groundwater systems of variable productivity. Figure 2-26 Simplified regional geology of the Victoria catchment This map does not represent outcropping areas of all geological units: the blanket of surficial Cretaceous to Cenozoic rocks and sediments has been removed to highlight the spatial extent of various regional geological units in the subsurface. Geology data sources adapted from: Department of Industry, Tourism and Trade (2014) and Department of Environment, Parks and Water Security (2008); Geological faults data source: Department of Industry, Tourism and Trade (2010) Simplified regional geology \\fs1-cbr.nexus.csiro.au\{lw-rowra}\work\11_Groundwater\2_Victoria\1_GIS\1_Map_docs\Gr-V-504_simplified_regional_geology_v4_CR.mxd For more information on this figure please contact CSIRO on enquiries@csiro.au Hydrogeological units The major hydrogeological units of the Victoria catchment are shown in Figure 2-27. The rocks and sediments of these hydrogeological units host a diverse range of aquifers that vary in extent, storage and productivity. Figure 2-27 Simplified regional hydrogeology of the Victoria catchment This map does not represent outcropping areas of all hydrogeological units; the blanket of surficial Cretaceous to Cenozoic rocks and sediments has been removed to highlight the spatial extent of various regional hydrogeological units in the subsurface. Geology data sources adapted from: Department of Industry, Tourism and Trade (2014) and Department of Environment, Parks and Water Security (2008); Springs data source: Department of Environment, Parks and Water Security (2013); Sinkholes data source: Department of Environment, Parks and Water Security (2014) Simplified regional hydrogeology map \\FS1-CBR.nexus.csiro.au\{lw-rowra}\work\11_Groundwater\2_Victoria\1_GIS\1_Map_docs\Gr-V-503_simplified_regional_hydrogeology_v05_CR.mxd For more information on this figure please contact CSIRO on enquiries@csiro.au Major aquifers in the Victoria catchment contain intermediate- to regional-scale groundwater systems and are found in the fractured and karstic Cambrian limestone and Proterozoic dolostone, respectively (Figure 2-27 and Figure 2-29). For this Assessment, major aquifer systems are considered to be aquifers that occur across large areas and contain regional- and intermediate-scale groundwater systems with adequate storage volumes (i.e. gigalitres to teralitres) that could potentially yield water at a sufficient rate (>10 L/second) and be of a sufficient water quality (<1000 mg/L TDS) for a range of irrigated cropping. These larger groundwater systems provide greater opportunities for groundwater development because they often: (i) store and transmit larger amounts of water, (ii) provide opportunities for development away from existing groundwater users and groundwater-dependent ecosystems, and (iii) have greater potential to coincide with larger areas of soils that may have potential for agricultural intensification. Minor aquifers in the Victoria catchment are found in the Proterozoic sandstone and shale, and Cambrian basalt, which contain local-scale groundwater systems across smaller areas with lower storage (i.e. megalitres to a few gigalitres) (Figure 2-27 and Figure 2-29). The yields from minor aquifers can vary significantly but are often low (<5 L/second), and minor aquifers have highly variable water quality ranging from fresh (~500 mg/L TDS) to saline (~20,000 mg/L TDS). The distribution and characteristics of these rocks is covered in Section 2.2. Unless otherwise stated, the material in Section 2.5.2 is based on findings described in the companion technical report on hydrogeological assessment (Taylor et al., 2024). Only the major aquifers relevant to potential opportunities for future groundwater resource development are discussed in detail. Figure 2-28 Groundwater dependent ecosystems at Kidman Springs Photo: CSIRO – Nathan Dyer Figure 2-29 Major types of aquifers occurring beneath the Victoria catchment Localised surficial aquifers hosted in Quaternary alluvium, and consolidated Cretaceous rocks and sediments, are not shown. Aquifer type data source: Department of Environment Parks and Water Security (2008) Major aquifer types map \\FS1-CBR.nexus.csiro.au\{lw-rowra}\work\11_Groundwater\2_Victoria\1_GIS\1_Map_docs\Gr-V-502_aquifer_type_v02_CR.mxd For more information on this figure please contact CSIRO on enquiries@csiro.au Limestone aquifers Limestone aquifers are hosted in the Cambrian limestone along the eastern margin of the Victoria catchment (Figure 2-27). The Cambrian limestone comprised almost entirely of limestone and dolostone rocks of the Montejinni Limestone (Figure 2-26), hosts the fractured and karstic regional- scale CLA. The CLA consists of three equivalent hydrogeological units (Montejinni Limestone, Tindall Limestone and Gum Ridge Formation) occupying an area of about 460,000 km2 across the adjoining Wiso, Daly and Georgina basins of the NT, extending to the far north-east and south-east of the catchment (Figure 2-30). However, only a small portion of the Montejinni Limestone part of the CLA in the Wiso Basin occurs beneath the Victoria catchment; about 12,000 km2 of it along the eastern margin of the catchment, equivalent to about 15% of the total catchment area (Figure 2-27 and Figure 2-30). The CLA is complex regional-scale fractured and karstic (containing sinkholes, caves, caverns and springs) aquifer exhibiting a high degree of variability. It can be highly productive in places and is one of the largest and most productive groundwater resources in and beyond the Victoria catchment. The complexity of the system arises from the variability and interconnectivity between fractures, fissures and karsts across the spatial extent of the aquifer. Groundwater resources from the CLA in the catchment have mostly been developed for stock and domestic use and for the community water supply at Top Springs. Elsewhere to the north-east and south-east of the catchment, groundwater resources from highly productive parts of the CLA have been developed for groundwater-based irrigation. For more information on current groundwater use, see Section 3.3.4. Recharge to the CLA occurs either directly in the aquifer outcrop or where it is unconfined (connected with the atmosphere via open pore spaces of the overlying soil or rocks) beneath overlying Cretaceous sandstone, siltstone and claystone and/or Cenozoic sediments. In the Victoria catchment, the CLA outcrops around and to the north and south of Top Springs (see Figure 2-3) but remains unconfined beneath the veneer of overlying Cretaceous and Cenozoic rocks and sediments along the eastern margin of the catchment. Recharge to the CLA in the Victoria catchment occurs via a combination of: (i) localised preferential infiltration of rainfall and streamflow via sinkholes directly in the aquifer outcrop, and (ii) broad diffuse infiltration of rainfall through the overlying Cretaceous and Cenozoic rocks and sediments which then vertically leak to the underlying CLA. Low recharge rates to the CLA (see Section 2.5.3), high permeabilities of the karstic features and structural highs of the underlying Antrim Plateau Volcanics, influence the thickness of the CLA in the Victoria catchment. In some places, the CLA can be either unsaturated or have a thin saturated thickness (<20 m) (see Section 5). The aquifer discharges via a combination of: (i) intermittent lateral outflow to streams (Armstrong River and Bullock, Cattle and Montejinni creeks) where they are incised into the aquifer outcrop, (ii) perennial localised spring discharge (Old Top, Lonely, Palm and Illawarra springs) (see Figure 2-27 and Figure 2-31), (iii) vertical outflow to underlying basalt aquifers, (iv) evapotranspiration via riparian and spring-fed vegetation, and (v) groundwater extraction for stock and domestic use, including community water supply. The sources of intermittent groundwater discharge to ephemeral streams and perennial groundwater discharge to springs is from localised discharge from the aquifer outcrop around Top Springs. Figure 2-30 Simplified regional hydrogeology of the Victoria catchment relative to the entire spatial extent of the Cambrian limestone across large parts of the Northern Territory Cambrian Limestone Aquifer full extent map \\FS1-CBR.nexus.csiro.au\{lw-rowra}\work\11_Groundwater\2_Victoria\1_GIS\1_Map_docs\Gr-V-503_simplified_regional_hydrogeology_ExtRegion_v05_CR.mxd For more information on this figure please contact CSIRO on enquiries@csiro.au Figure 2-31 Lonely Spring surrounded by dense spring-fed vegetation Photo: CSIRO Groundwater flow in the aquifer is complex due to the variability in the frequency, distribution and connectivity of karstic features across the aquifer and the spatial variability in seasonal recharge and discharge across large areas. At a local scale, groundwater flow can occur via preferential flow in connected holes and caverns, but across the aquifer extent, regional flow occurs via the interconnected nature of the karstic features acting as a porous medium (i.e. one with sufficient spaces between rocks for groundwater flow to occur across large areas). Along the eastern margin of the Victoria catchment, subtle topographic gradients on the edge of the Sturt Plateau create a groundwater flow divide inside the catchment margin. Regional groundwater flow and discharge occurs to the north-east outside the catchment further into the Wiso and Daly basins. Whereas, local to intermediate scale flow occurs to the west within the aquifer outcrop discharging along the western aquifer margin at localised spring complexes around Top Springs (see Section 5). Bore yields are variable due to the complex nature of the karstic aquifer. In the Victoria catchment, few properly constructed production bores have been installed and only limited pumping tests have been conducted. However, bore yields from stock and domestic bores in the CLA often range between 2 and 10 L/second, indicating that higher yields may be achievable from larger appropriately constructed production bores (Figure 2-32). Elsewhere in the CLA, east of the catchment, it has been found that where appropriately constructed production bores have been installed, bore yields can commonly be more than 10 L/second. In some cases where the aquifer is highly karstic across large areas to the east, bore yields can be as high as 100 L/second. Groundwater quality in terms of salinity ranges from fresh (<500 mg/L TDS) to slightly brackish (<2500 mg/L TDS) (Figure 2-33). For more information on this figure please contact CSIRO on enquiries@csiro.au Figure 2-32 Groundwater bore yields for the major aquifers across the Victoria catchment Symbol shapes indicate the aquifer within which the bore is sited; colours indicate bore yield class. Cambrian basalt data shown despite hosting minor aquifers due to their large spatial extent. Bore yield data source: Department of Environment, Parks and Water Security (2019) Yield major aquifer map \\FS1-CBR.nexus.csiro.au\{lw-rowra}\work\11_Groundwater\2_Victoria\1_GIS\1_Map_docs\Gr-V-535_Yield_Major_Aquifers_v04_CR.mxd For more information on this figure please contact CSIRO on enquiries@csiro.au Dolostone aquifers Dolostones aquifers are hosted in the Proterozoic dolostone rocks of the Bullita and Limbunya groups of the Birrindudu Basin across the centre and south of the Victoria catchment (Figure 2-26 and Figure 2-27). The dolostones host productive karstic intermediate- to local-scale aquifers (Figure 2-29). However, information for them is sparse. Proterozoic dolostone aquifers (PDAs) of the Bullita Group mostly outcrop in the centre of the catchment around Timber Creek and Yarralin. PDAs of the Limbunya Group mostly outcrop in the south of the catchment, west of Daguragu and Kalkarindji, and near Limbunya, which sits just outside and to the south of the catchment boundary (Figure 2-26 and Figure 2-27). Outcropping and subcropping (which occurs immediately beneath the overlying Cenozoic cover) parts of the Bullita and Limbunya groups occur across a combined total area of about 7000 km2. The most significant PDAs are hosted in the Skull Creek and Timber Creek formations of the Buillta Group between Timber Creek and Yarralin. For the Limbunya Group, it is the Campbell Springs and Pear Tree dolostones around Daguragu and Limbunya. Similar to the CLA, the PDAs are complex due to the variability and interconnectivity between fractures, fissures and karsts across their spatial extent. Groundwater resources in the aquifers have to date only been developed for stock and domestic water supplies and for the community water supply at Timber Creek. For more information on current groundwater use, see Section 3.3.4. The nature of and interconnectivity between karstic features influence the physical properties of the PDAs and groundwater flow processes across their spatial extent. Where the PDAs are unconfined in either outcropping or subcropping areas beneath overlying Cenozoic sediments, recharge is spatially variable and is inferred to occur via a combination of: (i) localised preferential infiltration of rainfall or streamflow where streams traverse the outcrop via sinkholes, fractures and faults, and (ii) broad diffuse infiltration of rainfall through the overlying Cenozoic sediments which vertically leaks to the underlying aquifers. Elsewhere, dolostone aquifers are confined (sealed off from the atmosphere by overlying rock and the groundwater is pressurised) by overlying Proterozoic sandstones and shales of the Auvergne and Tijunna groups, respectively, or the Antrim Plateau Volcanics (Figure 2-26). These overlying units influence the spatial variability in recharge to, and discharge from, the aquifers. The PDAs discharge via a combination of: (i) intermittent lateral outflow to streams (East Baines River and Crawford, Giles and Middle creeks) where they are incised into the aquifer outcrop (Figure 2-26 and Figure 2-27), (ii) perennial localised spring discharge at Bulls Head, Kidman and Crawford springs across the Buillta Group, and Depot, Farquharson and Wickham springs across the Limbunya Group (Figure 2-27 and Figure 2-34), (iii) evapotranspiration via riparian and spring-fed vegetation, and (iv) groundwater extraction for stock and domestic use, including community water supply at Timber Creek (see Section 3.3.4). Information on the directions and scale of groundwater flow in the aquifers are sparse, and groundwater flow is anticipated to be complex due to the variability in the amount and connectivity of karstic features across the aquifer and the spatial and temporal variability in annual recharge and discharge. Groundwater flow is inferred to generally occur from the elevated parts of the outcropping areas radially towards the outcrop margins where spring complexes occur. Bore yields are variable due to the complex nature of the karstic aquifer but yields often range from 5 to 15 L/second (Figure 2-32). However, where appropriately constructed production bores have been installed and pumping tests carried out for community water supply, yields have been as high as about 40 L/second. Groundwater quality expressed as salinity is generally fresh (<500 mg/L TDS) but can be subtly brackish in places (<2000 mg/L TDS) (Figure 2-33). Figure 2-33 Groundwater salinity for the major aquifers in the Victoria catchment Symbol shapes indicate the aquifer within which the bore is sited; colours indicate the level of total dissolved solids (TDS). Cambrian basalt data shown despite hosting minor aquifers due to their large spatial extent. Groundwater salinity data source: Department of Environment, Parks and Water Security (2019) TDS 10% Major Aquifers map \\FS1-CBR.nexus.csiro.au\{lw-rowra}\work\11_Groundwater\2_Victoria\1_GIS\1_Map_docs\Gr-V-537_TDS_10%_Major_Aquifers_v04_CR.mxd For more information on this figure please contact CSIRO on enquiries@csiro.au Figure 2-34 Bulls Head Spring surrounded by dense spring-fed vegetation Photo: CSIRO Basalt aquifers Basalt aquifers are hosted in the Cambrian basalt, particularly the Antrim Plateau Volcanics of the Kalkarindji Igneous Province, and occur across large parts of the east, south and to a lesser extent the west of the Victoria catchment (Figure 2-26 and Figure 2-27). These basalt rocks are highly heterogenous and occur in association with sandstone and chert interbeds or basal agglomerate. They host fractured rock aquifer systems that supply small quantities of groundwater mainly used for stock and domestic purposes. These aquifers are highly variable in composition and contain local- scale flow systems (Figure 2-29). Most groundwater storage and flow results from the size and connectivity of secondary porosity features such as joints, fractures or faults, except where porous sandstone, chert or agglomerate occur. Recharge occurs as localised infiltration of rainfall and some streamflow (where streams traverse these geological units) through the weathered, fractured and jointed basalt. Recharge also occurs as broad diffuse infiltration of rainfall through the overlying Cenozoic strata in the south of the catchment which then vertically leaks to the underlying basalt aquifers, which are unconfined in these areas. Where basalt underlies limestone in the east of the catchment, the basalt aquifers are recharged in places from vertical leakage from the overlying limestone aquifers. The main discharge mechanisms are: (i) bores extracting groundwater for stock and domestic use, (ii) evaporation from shallow watertables, (iii) lateral discharge to streams, and (iv) localised discharge at discrete springs. Individual bore yields are variable but often low (<2 L/second, Figure 2-32), and water quality is variable, ranging from fresh (~500 mg/L TDS) to brackish (~3000 mg/L TDS, Figure 2-33). These aquifers offer little potential for future groundwater resource development beyond stock and For more information on this figure please contact CSIRO on enquiries@csiro.au domestic purposes. The exception to this may be where they occur in conjunction with, and are connected to, limestone aquifers hosted in the overlying Montejinni Limestone. Sandstone aquifers Sandstone aquifers are hosted in the Proterozoic sandstone of the Auvergne Group in the Victoria Basin, particularly the Jasper Gorge Sandstone. The Jasper Gorge Sandstone outcrops extensively across the north and west of the Victoria catchment and occupies most of the 16,000 km2 of outcropping and subcropping rocks of the Victoria Basin (Figure 2-26 and Figure 2-27). The sandstone is flat lying to gently dipping and faulted in places, and it hosts aquifers with variable productivity containing local-scale groundwater flow systems. These sandstones localised aquifers provide an important source of groundwater for stock and domestic use (Figure 2-29). Little information exists for these aquifers other than sparse information from stock and domestic bores. The most productive parts of the sandstone aquifers occur where the sandstone outcrop has undergone prolonged weathering and has been heavily fractured in and around fault zones. Groundwater storage and flow occurs via the secondary porosity features such as fractures, faults and jointing. Recharge occurs as: (i)localised infiltration of rainfall and some streamflow (where streams traverse the sandstone) intovertical fractures and joints, or (ii) broad diffuse infiltration of rainfall through the overlying Cenozoicstrata which then vertically leaks to the underlying sandstone aquifers, which are unconfined in theseareas. The main discharge mechanisms are bores extracting groundwater for stock and domestic use, evaporation (through the soil or plants) from shallow watertables (the start of the saturated zone ofan aquifer) and discharge to streams. Bore yields are variable depending on the degree and interconnectivity of fractures and joints around the bore casing. Bore yields can often be low (<2 L/second) where secondary porosity features are infrequent. However, where fracturing and jointing are common, yields of between 10 and 20 L/second can be achieved (Figure 2-35). Water quality for these aquifers is variable, ranging between fresh (~500 mg/L TDS) to brackish (~9000 mg/L TDS, Figure 2-37). These aquifers offer little potential for future groundwater resource development beyond stock and domestic purposes. Even though individual bore yields can be reasonable where fracturing is prominent, groundwater storage is still limited to these secondary porosity features, which means the aquifer can be vulnerable to depletion with prolonged (hours to days) groundwater extraction. Figure 2-35 Groundwater bore yields for minor aquifers across the Victoria catchment Symbol shapes indicate the aquifer within which the bore is sited; colours indicate bore yield class. Unknown sites could not be attributed to an aquifer or classified as a major or minor aquifer. Bore yield data source: Department of Environment, Parks and Water Security (2019) Yield minor aquifer map \\FS1-CBR.nexus.csiro.au\{lw-rowra}\work\11_Groundwater\2_Victoria\1_GIS\1_Map_docs\Gr-V-534_Yield_Minor_Aquifers_v06_CR.mxd For more information on this figure please contact CSIRO on enquiries@csiro.au Siltstone and shale aquifers Proterozoic siltstones and shales occur in the Auvergne Group of the Victoria Basin and the Tijunna Group of the Birrindudu Basin (Figure 2-5 and Figure 2-26). The most prominent siltstone and shale hydrogeological units across the Victoria catchment include the Angalarri Siltstone and Saddle Creek Formation of the Auvergne Group and the Stubb Formation of the Tijunna Group. These units host only partial aquifers that are highly localised and contain minor and very low yielding local-scale groundwater flow systems. These units outcrop over large areas in the centre and north of the catchment (Figure 2-26 and Figure 2-27). Very little information is available for these units other than from sparse stock and domestic bores. Recharge is inferred to occur via broad diffuse infiltration of rainfall and streamflow where streams traverse the outcropping areas of these units into the upper highly weathered parts of the siltstones and shales. Where these units subcrop beneath overlying Cenozoic strata, recharge occurs via diffuse vertical leakage from Cenozoic strata to the underlying aquifers, which are unconfined in these areas. The main discharge mechanisms are: (i) bores extracting groundwater for stock and domestic use, (ii) evaporation from shallow watertables, (iii) lateral discharge to streams, and (iv) localised discharge at discrete springs. These aquifers are highly variable in composition and are very low yielding (often <2 L/second, Figure 2-35). They contain highly variable water quality, and salinity ranges from fresh (<500 mg/L TDS) to brackish (i.e. ~9000 mg/L TDS, Figure 2-37). These partial aquifers host only minor groundwater resources and offer little to no potential for future groundwater resource development beyond stock and domestic purposes. Even developing them for stock and domestic purposes can be challenging due to poor bore yields and highly variable water quality. Figure 2-36 Jasper Gorge a spectacular sandstone gorge dissecting extensive plateau of low open woodlands and spinifex on shallow and rocky soils Photo: CSIRO – Nathan Dyer Figure 2-37 Groundwater salinity for the minor aquifers in the Victoria catchment Symbol shapes indicate the aquifer within which the bore is sited; colours indicate the level of total dissolved solids (TDS). Unknown sites could not be attributed to an aquifer or classified as a major or minor aquifer. Groundwater salinity data source: Department of Environment, Parks and Water Security (2019) TDS 10% Minor Aquifers map \\FS1-CBR.nexus.csiro.au\{lw-rowra}\work\11_Groundwater\2_Victoria\1_GIS\1_Map_docs\Gr-V-536_TDS_10%_Minor_Aquifers_v04_CR.mxd For more information on this figure please contact CSIRO on enquiries@csiro.au Surficial aquifers Surficial sediments and rocks include Cretaceous sandstone, siltstone and claystone of the geological Carpentaria Basin and unconsolidated Cenozoic alluvial and colluvial deposits of clay, silt, sand and gravel. Cretaceous rocks and sediments host basal sandstone aquifers, and Cenozoic alluvium hosts surficial aquifers that occasionally occur in association with minor parts of the rivers, creeks and their floodplains and channels throughout the catchment. However, these aquifers have limited extent and are poorly characterised, so there is very little information. Aquifers hosted in the Cretaceous rocks are mostly of sandstone. Recharge to these aquifers occurs via diffuse rainfall infiltration through overlying regolith. The main discharge mechanisms are: (i) bores extracting groundwater for stock and domestic use, (ii) evaporation from shallow watertables, and (iii) discharge to rivers, creeks and underlying hydrogeological units. Individual bore yields are highly variable, ranging from less than 1 L/second to approximately 10 L/second (Figure 2-35), and water quality as salinity is also highly variable, ranging from fresh (~500 mg/L TDS) to brackish (~13,000 mg/L, Figure 2-37). These aquifers offer little potential for future groundwater resource development beyond stock and domestic purposes. 2.5.3 Groundwater recharge Groundwater recharge is an important component of the water balance of an aquifer. It can inform how much an aquifer is replenished on an annual basis and therefore how sustainable a groundwater resource may be in the long term. This is particularly important for aquifers with low storage or aquifers that discharge to rivers, streams, lakes and the ocean or via transpiration from groundwater- dependent vegetation. Recharge is influenced to varying degrees by many factors, including spatial changes in soil type (and their physical properties), the amount of rainfall and evaporation, vegetation type (and transpiration), topography and depth to the watertable. Recharge can also be influenced by changes in land use, such as land clearing and irrigation. Directly measuring recharge can be very difficult as it usually represents only a small component of the water balance, can be highly variable spatially and temporally, and can vary depending on the type of measurement or estimate technique used (Petheram et al., 2002). In the Assessment, several independent approaches were used to estimate annual recharge for all aquifers in the Victoria catchment. Figure 2-38 provides an example of recharge estimates using the upscaled chloride mass balance (CMB) method. For more detail on how these estimates were derived, see the companion technical report on groundwater characterisation (Taylor et al., 2024). Figure 2-38 Annual recharge estimates for the Victoria catchment Estimates based on upscaled chloride mass balance (CMB) method for the (a) 50th, (b) 5th and (c) 95th percent exceedance. Figure 2-39 provides a summary of the range in recharge estimates for the outcropping area of seven key hydrogeological units across the Victoria catchment. Recharge estimates are based on the mean of the 5th and 95th percent exceedance and range from approximately: •8 to 28 mm/year for the Quaternary alluvium •3 to 13 mm/year for the Cambrian limestone •6 to 24 mm/year for the Cambrian basalt •8 to 63 mm/year for the Devonian–Carboniferous sandstone •10 to 38 mm/year for the Proterozoic sandstone •14 to 48 mm/year for the Proterozoic shale •15 to 49 mm/year for the Proterozoic dolostone. The estimates of groundwater recharge in the Assessment represent the spatial variability in recharge across the land surface and are a good starting point for estimating a water balance arithmetically or using a groundwater model. However, none of the methods accounts for aquifer storage (available space in the aquifer), so it is unclear whether the aquifers can accept these rates of Recharge percent exceedance map \\FS1-CBR.nexus.csiro.au\{lw-rowra}\work\11_Groundwater\2_Victoria\1_GIS\1_Map_docs\Gr-V-515_CMB_R_percentiles_Vic_v1_cr.mxd For more information on this figure please contact CSIRO on enquiries@csiro.au recharge on an annual basis. The methods also do not account for potential preferential recharge from streamflow or overbank flooding, or through karst features such as dolines and sinkholes that occur across parts of the Victoria catchment. Therefore, the key features of an aquifer must be carefully conceptualised before simply deriving a recharge volume based on the surface area of an aquifer outcrop and an estimated recharge rate. Figure 2-39 Summary of recharge statistics to outcropping areas of key hydrogeological units across the Victoria catchment Recharge rates are based on upscaled chloride mass balance (CMB) method and calculated as the 5th, 50th and 95th percent exceedance. Error bars represent the standard deviation from the mean. 2.5.4 Surface water – groundwater connectivity As discussed in Section 2.5.2, groundwater discharge to surface water features occurs from a variety of aquifers across the Victoria catchment. Areas of groundwater discharge are important for sustaining both aquatic and terrestrial groundwater-dependent ecosystems. These groundwater discharge areas have been mapped in Figure 2-40 as three categories: perennial, seasonally varying and coastal. Perennial groundwater discharge areas often exhibit springs that occur in a variety of hydrogeological settings; these can involve groundwater flow systems at a variety of scales ranging from hundreds of metres to a few tens of kilometres. Areas with seasonally varying groundwater discharge are generally associated with localised alluvial, fractured and weathered rock aquifer systems that are adjacent to streams and are recharged during the wet season. These stores of water may sustain the riparian vegetation through the dry season. Although surface water is thought to be the major source for these systems, groundwater discharge from adjacent aquifers can also occur when river levels fall during the dry season. Coastal discharge occurs within the estuary of the Victoria River. These areas may have a component of coastal submarine groundwater discharge but also have mangroves that use fresh to saline water within the freshwater–saltwater interface. For more information on this figure please contact CSIRO on enquiries@csiro.au 020406080100120Mean annual recharge (mm/y) Hydrogeological unit95th percent exceedance50th percent exceedance5th percent exceedance Figure 2-40 Spatial distribution of groundwater discharge classes including surface water – groundwater connectivity across the Victoria catchment Groundwater discharge classes are inferred from remotely sensed estimates of evapotranspiration and open water persistence. Note: the size of polygons has been greatly exaggerated to allow them to be seen at this scale. Spring data source: Department of Environment, Parks and Water Security (2013) Groundwater discharge map \\FS1-CBR.nexus.csiro.au\{lw-rowra}\work\11_Groundwater\2_Victoria\1_GIS\1_Map_docs\Gr-V-516_GW_discharge_v4_hydro_CR.mxd For more information on this figure please contact CSIRO on enquiries@csiro.au The largest area of groundwater discharge in the Victoria catchment is in the seasonally varying class associated with the alluvium along the major rivers, including the Victoria, Wickham and West Baines rivers (Figure 2-40). This groundwater discharge helps to maintain perennial waterholes in the rivers and dry-season flows. Discharge from the CLA in the Victoria catchment occurs at small springs that do not support perennial streams. The CLA in the Victoria catchment only has a small contributing area, and some of the groundwater recharged to the CLA within the Victoria catchment flows out of the catchment to the north-east. The springs sourced from the CLA in the Victoria catchment are mostly located to the south of Top Springs and occur near the boundary of the CLA and Antrim Plateau Volcanics; these include Old Top Springs, Lonely Spring, Palm Spring and Horse Spring. There are also groundwater discharges associated with the springs of the Proterozoic dolostones. These springs generally have small discharges but provide a permanent water supply through the dry season in an otherwise arid area. These include Kidman, Crawford and Dead springs sourced from the Bullita Group and Wickham and Depot springs sourced from the Limbunya Group. The local flow systems of the Cambrian basalt, Proterozoic sandstone and Proterozoic shale also support localised discharge via small discrete springs. 2.5.5 Surface water Streamflow Approximately 60% of Australia’s runoff is generated in northern Australia (Petheram et al., 2010, 2014). Unlike the large internally draining Murray–Darling Basin, however, northern Australia’s runoff is distributed across many hundreds of smaller externally draining catchments (Figure 2-41). To place the Victoria catchment in a broader context, it is useful to compare its size and the magnitude of its median annual streamflow to other river systems across Australia. Figure 2-41 shows the magnitude of median annual streamflow of major rivers across Australia prior to water resource development. The Victoria River and its tributaries, the most substantial of which are the Baines, Wickham, Armstrong, Camfield and Angalarri rivers, define a catchment area of 82,400 km2 (Figure 2-42). The Victoria River itself spans approximately 500 km from Entrance Island at its mouth to Kalkarindji in the far south of the catchment. Tidal variation at the mouth of the Victoria River is up to 8 m, and these tides propagate upstream to just downstream of Timber Creek (Power and Water Authority, 1987). As discussed in Section 2.4, the catchment has a north−south rainfall gradient which influences the local hydrological response. The Camfield River in the drier far south of the catchment has an estimated mean runoff coefficient of 5%, while the Angalarri River in the north-east of the catchment has an estimated mean runoff coefficient of 17%. Mean annual flow at the catchment outlet of the Victoria River is estimated at 6990 GL, while median annual flow is 5730 GL. Annual variation is high, and annual flow is estimated to range between 800 and 23,000 GL. Flow is highly seasonal, and 93% of all flow occurs in the months December to March, inclusive. Flow statistics for a selection of streamflow gauging stations are shown in Table 2-5. "\\fs1-cbr.nexus.csiro.au\{lw-rowra}\work\2_Hydrology\101_Victoria\1_GIS\1_Map_docs\1_Export\Hy-V-501_Aust_accumulated_AnnualMedian_flow_AWRA_Victoria_rescaled.png" Figure 2-41 Modelled streamflow under natural conditions Streamflow under natural conditions is indicative of median annual streamflow prior to European settlement (i.e. without any large-scale water resource development or extractions) assuming the historical climate (i.e. 1890 to 2015). Source: Petheram et al. (2017) Streamflow gauge observation data locations map \\FS1-CBR.nexus.csiro.au\{lw-rowra}\work\2_Hydrology\101_Victoria\1_GIS\1_Map_docs\Hy-V-502_Victoria_stream_gauges_v3_CR.mxd For more information on this figure please contact CSIRO on enquiries@csiro.au Figure 2-42 Streamflow observation data availability in the Victoria catchment Points labelled with letters refer to Figure 2-54. Table 2-5 Streamflow metrics at gauging stations in the Victoria catchment under Scenario A The 20th, 50th and 80th refer to 20%, 50% and 80% exceedance, respectively. These data are shown schematically in Figure 2-43 and Figure 2-44. For more information on this figure, table or equation please contact CSIRO on enquiries@csiro.au Figure 2-43 shows that median annual streamflow increases towards the coast in the Victoria catchment. As an indication of variability, Figure 2-44 shows the 20% and 80% exceedance of annual streamflow in the Victoria catchment. Median annual streamflow map \\FS1-CBR.nexus.csiro.au\{lw-rowra}\work\2_Hydrology\101_Victoria\1_GIS\1_Map_docs\Hy-V-000_Victoria_accumulated_AnnualMedian_flow_(E50)_v05_CR.mxd For more information on this figure please contact CSIRO on enquiries@csiro.au Figure 2-43 Median annual streamflow (50% exceedance) in the Victoria catchment under Scenario A Exceedance of annual streamflow map \\FS1-CBR.nexus.csiro.au\{lw-rowra}\work\2_Hydrology\101_Victoria\1_GIS\1_Map_docs\Hy-V-003_2x1Victoria_accumulated_E20_E80_flow_v04.mxd For more information on this figure please contact CSIRO on enquiries@csiro.au Figure 2-44 (a) 20% and (b) 80% exceedance of annual streamflow in the Victoria catchment under Scenario A Figure 2-45 illustrates the increase in catchment area and decrease in elevation along the Victoria River from a headwater catchment upstream of Kalkarindji to its mouth. The large ‘step’ changes in catchment area are where major tributaries join the river. "\\fs1-cbr.nexus.csiro.au\{lw-rowra}\work\2_Hydrology\101_Victoria\0_Working\2_Justin\6_catch_report\river_area_elevation_Victoria_v2.png" Figure 2-45 Catchment area and elevation profile along the Victoria River from upstream of Kalkarindji to its mouth Catchment runoff The simulated mean annual runoff averaged over the Victoria catchment under Scenario A is 87 mm. Figure 2-46 shows the spatial distribution of mean annual rainfall and runoff under Scenario A (1890 to 2022) across the Victoria catchment. Mean annual runoff broadly follows the same spatial patterns as mean annual rainfall: highest in the north of the study area and lowest in the south. Monthly and annual runoff data in the Victoria catchment exhibit less variation from one year to the next than other parts of northern Australia. The annual runoff volumes at 20%, 50% (median) and 80% exceedance averaged across the Victoria catchment are 125, 71 and 38 mm, respectively. That is, runoff spatially averaged across the Victoria catchment will exceed 125 mm 1 year in 5, 71 mm half the time and 38 mm 4 years in 5. Figure 2-47 shows the spatial distribution of annual runoff at 20%, 50% and 80% exceedance under Scenario A. "\\fs1-cbr.nexus.csiro.au\{lw-rowra}\work\2_Hydrology\101_Victoria\1_GIS\1_Map_docs\1_Export\Hy-V-506_Rain_Runoff_1x2.png" Figure 2-46 Mean annual (a) rainfall and (b) runoff across the Victoria catchment under Scenario A Pixel scale variation in mean annual runoff is due to modelled variation in soil type. "\\fs1-cbr.nexus.csiro.au\{lw-rowra}\work\2_Hydrology\101_Victoria\1_GIS\1_Map_docs\1_Export\Hy-V-507_20_50_80_runoff_1x3.png" Figure 2-47 Annual runoff at (a) 20%, (b) 50% and (c) 80% exceedance across the Victoria catchment under Scenario A Pixel scale variation in mean annual runoff is due to modelled variation in soil type. Intra- and inter-annual variability in runoff Rainfall, runoff and streamflow in the Victoria catchment are variable between and within years. Approximately 82% of all runoff in the Victoria catchment occurs in the 3 months from January to March, which is a very high concentration of runoff relative to rivers in southern Australia (Petheram et al., 2008). A feature of streamflow data in the Victoria catchment is the almost total absence of dry-season data, which is due to the emphasis on flood information in this area. In some locations, such as gauge 8110007 (Coolibah Homestead) and 8110013 (Dashwood Crossing), there is some evidence of near-perennial flow. Perennial flow is also likely at gauge 8110074 on Montejinni Creek (where monitoring has been discontinued). In most other cases, flow is ephemeral. Figure 2-48b illustrates that during the wet season there is a high variation in monthly runoff from one year to the next. For example, during February, the spatial mean runoff exceeded 49 mm in 20% of years and was less than 5 mm in 20% of years. The largest catchment mean annual runoff under Scenario A was 287 mm in 1973–74, and the smallest was 10 mm in 1951–52 (Figure 2-48a). The CV of annual runoff in the Victoria catchment varies from 1.4 in the drier south to 0.7 in the north. Based on data from Petheram et al. (2008), the variability in annual runoff in the Victoria catchment is low compared to the annual variability in runoff of other rivers in northern and southern Australia with a comparable mean annual runoff. A close-up of a graph "\\fs1-cbr.nexus.csiro.au\{lw-rowra}\work\2_Hydrology\101_Victoria\0_Working\6_Ang\plots_for_catchment_report\hist\catch_month_annual_runoff.png" Figure 2-48 Runoff in the Victoria catchment under Scenario A showing (a) time series of annual runoff and (b) monthly runoff averaged across the catchment The solid blue line in (a) is the 10-year running mean. In (b) ‘A range’ represents the 80% to 20% exceedance totals for that month. Flooding Intense seasonal rains from monsoonal bursts and tropical cyclones from December to March create flooding in parts of Victoria catchment and inundate large areas of floodplains on both sides of Victoria River and its two major tributaries, the Baines and Angalarri rivers (Figure 2-49). This is an unregulated catchment, and its overbank flow is generally governed by the topography of the floodplain. Flooding is widespread at the junction of Victoria and Baines rivers, downstream of Timber Creek. Since 1980, there have been 37 floods greater than an annual exceedance probability (AEP) of 1 in 1 in the catchment. While floods can occur in any month from November to April, about 92% of historical floods have occurred between January and March, inclusive. Characterising these flood events is important for a range of reasons. Flooding can be catastrophic to agricultural production in terms of loss of stock, pasture and topsoil, and damage to crops and infrastructure. It can also isolate properties and disrupt vehicle traffic providing goods and services to people in the catchment. However, flood events also provide opportunities for offstream wetlands to connect to the main river channel. The high biodiversity found in many unregulated floodplain systems in northern Australia is thought to largely depend on seasonal flood pulses, which allow biophysical exchanges to occur between rivers and offstream wetlands. Flood inundation map \\FS1-CBR.nexus.csiro.au\{lw-rowra}\work\2_Hydrology\101_Victoria\1_GIS\1_Map_docs\Hy-V-503_MODIS_flood_v02_CR.mxd For more information on this figure please contact CSIRO on enquiries@csiro.au Figure 2-49 Flood inundation map of the Victoria catchment Data captured using Moderate Resolution Imaging Spectroradiometer (MODIS) satellite imagery. This figure illustrates the maximum percentage of each MODIS pixel inundated between 2000 and 2023. Further observations of flood characteristics in the Victoria catchment are as follows: •Flood peaks typically take about 2 to 3 days to travel from Dashwood Crossing to Timber Creek at amean speed of 3.4 km/hour. •For flood events of AEP 1 in 2, 1 in 5 and 1 in 10, the peak discharges at the Coolibah Homestead onthe Victoria River are 2760, 4050 and 5800 m3/second, respectively. •Between 1953 and 2023 (70 years), events with a discharge greater than or equal to AEP 1 in 1occurred in all months from December to April, and about 91% of these events occurred betweenJanuary and March. Of the ten largest flood peak discharges at Coolibah Homestead, six occurred inMarch, three in February and one in December. •The maximum area inundated by a flood event of AEP 1 in 18 that occurred in March 2023 was1355 km2 (Figure 2-50). "\\fs1-cbr.nexus.csiro.au\{lw-rowra}\work\2_Hydrology\101_Victoria\1_GIS\1_Map_docs\1_Export\HFV-203_Inundation_HD_model.png" Figure 2-50 Flood inundation across the Victoria catchment for a flood event of 1 in 18 annual exceedance probability (AEP) in March 2023 Flood frequency in the Victoria floodplain Flood frequency analysis was performed in the Victoria catchment to establish streamflow thresholds above which a flood event would occur. Flood frequencies were estimated for the two major rivers in this catchment (Victoria and West Baines). For the Victoria River, flood frequencies were estimated using streamflow observations from gauging station 8110007 (Victoria River at Coolibah Homestead) as this gauge has a long historical record (>50 years) and has reasonable-quality data. Similarly, flood frequencies were estimated for the West Baines River using streamflow observations from gauging station 8110006 (West Baines River at Victoria Highway). Traditionally, flood frequencies are estimated based on maximum discharge for an individual event. However, in the Assessment, to help determine the magnitude of the events, the flood frequency analysis accounted for total flow volume as well as peak discharge for each event. This is motivated by the knowledge that the duration of an event, and not only its maximum discharge, can have a great impact on the inundated area. Figure 2-51 displays the relationship between peak flow and AEP for the two gauges: one on West BainesRiver (81100070) and the other on Victoria River (8110007). While flow volume is higher for largerfloods, duration of flood is a key factor for volume of flood flow. "\\fs1-cbr.nexus.csiro.au\{lw-rowra}\work\2_Hydrology\101_Victoria\0_Working\2_Justin\6_catch_report\AEP_2panelPlot.png" Figure 2-51 Peak flood discharge and annual exceedance probability (AEP) at (a) gauge 8110006 (West Baines River at Victoria Highway) and (b) gauge 8110007 (Victoria River at Coolibah Homestead) Colours indicate the total event volume of flood water in gigalitres (GL) for different events. Instream waterholes during the dry season The rivers in the Victoria catchment are largely ephemeral in the majority of reaches. Once streamflow has ceased, the rivers break up into a series of waterholes during the dry season. Waterholes that persist from one year to the next are considered to be key aquatic refugia and are likely to be sustaining ecosystems in the Victoria catchment (Section 3.2). In some reaches, waterholes may be partly or wholly sustained by groundwater discharge (Section 2.5.2). However, in other reaches there is little evidence that persistent waterholes receive water from groundwater discharge and are likely to be replenished following wet-season flows. Stream gauge data indicate that there is very little to no late dry-season flow for where gauge data are available (Figure 2-53). However, note that some late dry-season flow was recorded at gauge 8110113 (Dashwood Crossing) in response to relatively high rainfall in the 2000 to 2010 period. This was likely to be baseflow given the concurrent low dry-season rainfall. Minimum monthly flows increase for most locations from October to December; however, these increases are likely in response to early wet season storms. These data confirm that baseflow is very low and generally absent in the late dry season across most of the Victoria catchment. Minimum simulated October flows across many locations for the 132-year time series are shown in Figure 2-54. The ecological importance and functioning of key aquatic refugia are discussed in more detail in the companion technical report on ecological modelling (Stratford et al., 2024). The formation of waterholes following a cease-to-flow event can be captured using satellite imagery. Figure 2-55 shows an example of this for a reach of the Flinders River in northern Queensland. Figure 2-57 maps 1 km river reaches (or segments) in the Victoria catchment in which water is recorded in greater than 90% of dry-season satellite imagery. This is denoted the water index threshold and provides an indication of the river reaches that contain permanent water. Figure 2-52 Riparian vegetation along the West Baines River in the Victoria catchment. These areas are subject to regular flooding and the riparian vegetation plays an important role in regulating stream water quality. Photo: CSIRO – Nathan Dyer "\\fs1-cbr.nexus.csiro.au\{lw-rowra}\work\2_Hydrology\101_Victoria\0_Working\2_Justin\14_minimum_flows\minimum_drySeason_flow_observed_v3.png" Figure 2-53 Minimum dry-season flow observed at gauging stations 8110006, 8110007 and 8110113 Dry-season rainfall (July–September) and annual catchment rainfall are included below for context. "\\fs1-cbr.nexus.csiro.au\{lw-rowra}\work\2_Hydrology\101_Victoria\0_Working\2_Justin\6_catch_report\minFlowOctNovDec_v3.png" Figure 2-54 Minimum monthly flow over 132 years of simulation for October, November and December Assessed at either stream gauge locations or river model node locations indicated by labels ‘A’ and ‘B’ in Figure 2-42. Locations are listed in order from upstream (on the left) to downstream (on the right). The dashed blue horizontal lines equate to 200 ML/day, and the red horizontal dotted lines equate to 400 ML/day. Maps of instream waterhole evolution. For more information on this figure please contact CSIRO on enquiries@csiro.au Figure 2-55 Instream waterhole evolution in a reach of the Flinders River This figure shows the area of waterholes in the reach of the river a given time after flow ceased and the ability of the water index threshold to track the change in waterhole area and distribution. A dirt road with trees and a tower Description automatically generated Figure 2-56 Streamflow gauging station in the Victoria catchment Photo: CSIRO – Nathan Dyer Permanent waterholes map \\FS1-CBR.nexus.csiro.au\{lw-rowra}\work\2_Hydrology\101_Victoria\1_GIS\1_Map_docs\Hy-V-504_Victoria_permanent_waterholes_v1_CR.mxd For more information on this figure please contact CSIRO on enquiries@csiro.au Figure 2-57 Location of river reaches containing permanent water in the Victoria catchment Persistent river reaches are defined as 1 km river reaches where water was identified in greater than 90% of the dry- season Landsat (Landsat 5, 7 and 8) imagery between 1989 and 2018. Mapping of persistent river reaches is confounded by riparian vegetation in the Victoria catchment. Surface water quality A literature search on water quality in the Victoria catchment revealed only one significant investigation into water quality, which was conducted by the Power and Water Authority in 1982 and 1984 (Power and Water Authority, 1987). The investigation was conducted during baseflow conditions and measured major cations, anions, electrical conductivity, turbidity, dissolved oxygen and pH. Summaries of the spatial distribution of selected parameters are shown in Figure 2-58. "\\fs1-cbr.nexus.csiro.au\{lw-rowra}\work\2_Hydrology\101_Victoria\0_Working\2_Justin\6_catch_report\geochem_maps_v2.png" Figure 2-58 Baseflow water quality in the Victoria catchment for parameters (a) electrical conductivity (EC), (b) chloride concentration, (c) total alkalinity, (d) calcium to sodium ratio, (e) silica concentration and (f) turbidity Data source: Power and Water Authority (1987) The most obvious features of Figure 2-58 are the elevated EC, chloride and turbidity values from the mouth of the river upstream to approximately Timber Creek. These high values are associated with the tidal movement of sea water. In the case of turbidity, river velocities remain relatively high in the tidal zone even in periods of low freshwater flow, such as those experienced when these samples were taken. No analysis of heavy metal concentration in stream water has been conducted in the catchment. Presumably, this is partly because no mining has taken place within the catchment. 2.6 References Ahmad M and Munson TJ (2013) Chapter 36: Bonaparte Basin. In: Ahmad M and Munson TJ (compilers) Geology and mineral resources of the Northern Territory. Northern Territory Geological Survey, Special Publication 5. Viewed September 2023: https://geoscience.nt.gov.au/gemis/ntgsjspui/bitstream/1/81516/1/GNT_Ch36_Bon.pdf. BOM (2023) Tropical cyclone databases. Bureau of Meteorology, Canberra. Viewed 6 February 2023, Hyperlink to: Tropical cyclone databases . Bowman DMJS, Brown GK, Braby MF, Brown JR, Cook LG, Crisp MD, Ford F, Haberle S, Hughes J, Isagi Y, Joseph L, McBride J, Nelson G and Ladiges PY (2010) Biogeography of the Australian monsoon tropics. Journal of Biogeography 37(2), 201–216. Hyperlink to: Biogeography of the Australian monsoon tropics . Charles S, Petheram C, Berthet A, Browning G, Hodgson G, Wheeler M, Yang A, Gallant S, Vaze J, Wang B, Marshall A, Hendon H, Kuleshov Y, Dowdy A, Reid P, Read A, Feikema P, Hapuarachchi P, Smith T, Gregory P and Shi L (2017) Climate data and their characterisation for hydrological and agricultural scenario modelling across the Fitzroy, Darwin and Mitchell catchments. A technical report to the Australian Government from the CSIRO Northern Australia Water Resource Assessment, part of the National Water Infrastructure Development Fund: Water Resource Assessments. CSIRO, Australia. Chiew F, Post D and Moran R (2012) Hydroclimate baseline and future water availability projections for water resources planning. 34th Hydrology and Water Resources Symposium 2012, Sydney, NSW, 19–22 November 2012. Engineers Australia, Barton, 461–468. Chiew FHS, Cai W and Smith IN (2009) Advice on defining climate scenarios for use in Murray–Darling Basin Authority Basin Plan modelling. CSIRO report for the Murray–Darling Basin Authority. CoastAdapt (2017) Sea-level rise and future climate information for coastal councils: Kowanyama, QLD. National Climate Change Adaptation Research Facility and Australian Government Department of Environment and Energy. Viewed 03 May 2018, Hyperlink to: Coast Adapt website . CSIRO (2009) Water in the Van Diemen region. In: Water in the Timor Sea Drainage Division. A report to the Australian Government from the CSIRO Northern Australia Sustainable Yields Project. CSIRO Water for a Healthy Country Flagship, Australia, 363–452. CSIRO and Bureau of Meteorology (2015) Climate change in Australia. Information for Australia’s natural resource management regions: technical report. CSIRO and Bureau of Meteorology, Australia. Cutovinos A, Beier PR and Dunster JN (2013) Victoria River Downs, Northern Territory, revised 2nd edn, 1:250,000 scale geological map, SE 52-04. Northern Territory Geological Survey, Darwin. 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Department of National Resources, Bureau of Mineral Resources, Geology and Geophysics, Bulletin 168. Australian Government Publishing Service, Canberra. Taylor AR, Pritchard JL, Crosbie RS, Barry KE, Knapton A, Hodgson G, Mule S, Tickell S and Suckow A (2024) Characterising groundwater resources of the Montejinni Limestone and Skull Creek Formation in the Victoria catchment, Northern Territory. A technical report from the CSIRO Victoria River Water Resource Assessment for the National Water Grid. CSIRO, Australia. Thomas M, Philip S, Stockmann U, Wilson PR, Searle R, Hill J, Gregory L, Watson I and Wilson PL (2024) Soils and land suitability for the Victoria catchment, Northern Territory. A technical report from the CSIRO Victoria River Water Resource Assessment for the National Water Grid. CSIRO, Australia. 3 Living and built environment of the Victoria catchment Authors: Marcus Barber, Danial Stratford, Seonaid Philip, Linda Merrin, Diane Jarvis, Thomas Vanderbyl, Rob Kenyon, Nathan Waltham, Simon Linke, Kristina Fisher, Heather McGinness, Caroline Bruce, Andrew R Taylor Chapter 3 discusses a wide range of considerations relating to the living components of the catchment of the Victoria River. This includes the environments that support these components, the people who live in the catchment or have strong ties to it, and the existing transport, power and water infrastructure. The key components and concepts of Chapter 3 are shown in Figure 3-1. Block diagram of chapter sections \\FS1-CBR.nexus.csiro.au\{lw-rowra}\work\10_Reporting\1_All\9_Graphics_artist\3_Vic and SoG\C Bruce Vic CR Chp3_8_2024.jpg For more information on this figure please contact CSIRO on enquiries@csiro.au Figure 3-1 Schematic diagram of key components of the living and built environment to be considered in establishing a greenfield irrigation development Numbers refer to sections in this chapter. 3.1 Summary This chapter provides information on the living and built environment, including information about the people, the ecology, the infrastructure and the institutional context of the Victoria catchment. It also examines the values, rights, interests and development objectives of Indigenous Peoples. 3.1.1 Key findings Ecology The comparatively intact landscapes and associated water resources of the Victoria catchment support ecosystem health and biodiversity, providing crucial ecosystem services for human residence. Key human activities in the catchment that require intact landscapes include recreation, tourism, Indigenous cultural practices, fisheries (Indigenous, recreational and commercial), agricultural production (notably, cattle grazing on native pastures) and military training focused on tropical savanna environments. Within the freshwater sections of the Victoria catchment are extensive areas with high habitat values, including ephemeral and persistent rivers, wetlands, floodplains and groundwater-dependent ecosystems (GDEs), including two sites listed in the Directory of Important Wetlands in Australia (DIWA): Bradshaw Field Training Area and Legune Wetlands. For the marine and estuarine environments, the Victoria River provides some of the largest flows into the Joseph Bonaparte Gulf, supporting extensive intertidal, estuarine and marine communities. The habitats of the Victoria catchment contain plants and animals that are of great conservation significance, such as the freshwater sawfish (Pristis pristis) and dugong (Dugong dugon). They also contain iconic wildlife species such as the saltwater (Crocodylus porosus) and freshwater (Crocodylus johnstoni) crocodiles and barramundi (Lates calcarifer). Changes in land and water resources can have serious consequences for the ecology of rivers. Water resource development that changes the magnitude, timing or duration of either low or high flows can affect species, habitats and ecological processes such as connectivity. Water resource development can also facilitate or exacerbate other impacts, including the spread or establishment of invasive species, increases in other anthropogenic pressures, and changes to water quality, including the availability and distribution of nutrients. Demographics, industries and infrastructure The Victoria catchment has a population of about 1600, with a population density one 165th of Australia as a whole. The catchment contains no large urban centres, but there are several small towns and communities within the catchment, including Timber Creek (the regional centre), Yarralin, Nitjpurru (Pigeon Hole), Amanbidji, Bulla, Kalkarindji and Daguragu. The largest of these settlements is Kalkarindji (population 383 as at the 2021 Census). The typical resident of the catchment is younger, has a lower weekly household income and is more likely to identify as Indigenous than the typical resident of the NT and of Australia as a whole. The dominant land use, by area, in the catchment is grazing (62%) with conservation and protected land being 35% of the catchment. Note that, in terms of tenure, 31% of the catchment is held as Aboriginal freehold. The gross value of agricultural production (GVAP) in the Victoria catchment is approximately $110.2 million, beef cattle contributing the entire amount. The Victoria catchment is serviced by two significant roads: the Victoria and Buntine highways. The only other road that permits Type 2 road trains (vehicles up to 53 m in length) is the unsealed Buchanan Highway. A sparse network of minor roads links to these three highways. A large percentage of the catchment’s pastoral enterprises have access to the main highways and, via northern routes, to Darwin Port in the north via Katherine. The Buntine Highway carries more commercial traffic than the Victoria Highway, and all roads are subject to wet-season closures. The only access to a good-quality standard-gauge rail line is outside the catchment at Katherine in the north-east. The Victoria catchment is too remote to be covered by the main NT power networks. Off-grid electricity is provided to communities by hybrid electricity generation systems powered by diesel generators and in some cases supplemented with solar. There are no major dams or water transmission pipelines in the Victoria catchment. Urban water for domestic consumption, therefore, depends mainly on treated groundwater (from bores), which is the preferred source for larger settlements. Indigenous values, rights, interests and development goals The Assessment activity focused on Indigenous values, rights, interests and development goals provides a regionally specific account designed to help non-Indigenous decision makers understand general Indigenous valuations of water and wider connections to Country, and the rights and interests attached to those. The report also helps Indigenous decision makers (local, regional and national) understand the specific residential, ownership, natural and cultural resource management, and development issues relevant to Traditional Owners from the Victoria catchment. These are likely to be raised by Traditional Owners in future discussions about development proposals, community planning and Indigenous business objectives. The investigation focused on gathering data and consulting individuals. It did not attempt to conduct community-based planning or to identify formal Traditional Owner group positions on any of the matters raised. The data comes from face-to-face interviews with 19 locally resident and predominantly senior Traditional Owners from major language groups in the Victoria catchment. These groups include the Gurindji and Ngarinyman language groups in the southern and central parts of the catchment, the Ngaliwurru and Nungali language groups in the Timber Creek area, and Gajerrong language groups in the far west. Indigenous Peoples and the groups they belong to have significant land holdings and rights in Country through the Commonwealth Aboriginal Land Rights (Northern Territory) Act 1976 (ALRA) and the Commonwealth Native Title Act 1993. Thirty-one per cent of the Victoria catchment is freehold Aboriginal land under the ALRA. These holdings are an important focus for discussions about water and about sustainable development in the Victoria catchment. Indigenous objectives combine economic viability and sustainability with a range of wider social, cultural and environmental goals. Participants in the activity provided crucial framing information about Indigenous culture, Country and people. Traditional Owners have particular obligations to past and future generations to maintain customary practices and knowledge and care for Country properly. These obligations entail responsibilities to near neighbours and downstream groups. Key water issues for Traditional Owners in the Victoria catchment include: •ensuring water of sufficient quality to maintain healthy landscapes (environmental flows) andsustain cultural resources and practices •monitoring and reporting water availability and use, and any development impacts on waterquality for informed decision making about future development •maintaining good-quality water supplies for human consumption and recreation in communities, and outstations •securing sufficient water reserves for current and future economic activity. Through the Strategic Aboriginal Water Reserve (SAWR) process, some significant progress has been made on establishing water reserves in the NT. However, SAWR processes are only possible through the creation of a water plan, and there remain relatively limited means for Indigenous knowledge of water to be expressed in public policy and planning. The very small footprint of existing water control district declaration and associated water planning in the catchment means that Traditional Owners’ knowledge of formal government-led water planning in the area was also found to be very low. Knowledge of catchment management institutions and processes was also found to be low. Knowledge of water resource development options was more limited among participants in this Assessment than in previous assessments elsewhere in northern Australia. There is strong resistance across the catchment to the idea of instream dams. If water development were to occur, the general trend from most favourable to least favourable forms of development is: flood harvesting into smaller, offstream storages; sustainable bore and groundwater extraction; smaller instream dams inside tributaries or ancillary branches; and large instream dams in the main river channels. With respect to Traditional Owners’ development objectives and development planning, the Assessment identified five primary interrelated development goals: •securing greater recognition of Traditional Ownership of water and/or management control overwater •ensuring water supply for human consumption and recreation in communities and outstations •improving information flow and empowerment for Indigenous decision makers •protecting and strengthening regional and catchment governance in line with customaryconnections •developing new Country-based businesses and industries Group or community-based planning can help communities prioritise options for wider development. These can include establishing stand-alone Indigenous businesses or joint ventures and participating in local and regional resource development monitoring and reporting programs. Traditional Owners in the Victoria catchment possess valuable natural and cultural assets and represent a significant potential labour force. However, many people lack employment experience and skills in business development and operation. Indigenous development objectives and Indigenous development partnerships are best progressed through locally specific group- and community-based planning and prioritisation processes that are nested in a system of regional coordination. Indigenous Peoples can also act as substantial enablers of appropriate development. They seek to be engaged early and continuously in defining development pathways and options. Legal and policy environment Proponents must be aware of the complex legal, policy and regulatory landscape when contemplating and planning land and water developments within the Victoria catchment. As part of their due diligence process, proponents must secure appropriate land tenure, obtain the necessary authorisations to take water, and obtain a range of government approvals before commencing construction and operation of a development. The Victoria catchment is wholly located within the NT. Government powers and responsibilities for managing land and water resources in the Victoria catchment are shared between the Australian Government and the NT Government. Although the NT Government is responsible for land, water and environmental policy and laws and administers the planning system, the Australian Parliament retains a right of veto over all laws in the territory. The Australian Government has powers under the Commonwealth Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act) relating to matters of national environmental significance (including those arising from the World Heritage Convention, the Ramsar Convention on Wetlands of International Importance and the Convention on Biological Diversity) and the native title rights of Indigenous Peoples. 3.1.2 Introduction This chapter seeks to address the following questions. In the Victoria catchment, what are the existing: • ecological systems • demographic and economic profiles, land use, industries and infrastructure • values, rights, interests and development objectives of Indigenous Peoples? The chapter is structured as follows: • Section 3.2 examines the ecological systems and assets of the Victoria catchment, including key habitats and biota and their important interactions and connections. • Section 3.3 examines the socio-economic profile of the Victoria catchment, including current demographics, existing industries and infrastructure of relevance to water resource development. • Section 3.4 examines the Indigenous values, rights, interests and development objectives of Traditional Owners from the Victoria catchment. 3.2 Victoria catchment and its environmental values This section provides an overview of the environmental values and the freshwater, marine and terrestrial ecological assets found in the Victoria catchment. Unless otherwise stated, the material in this section is based on work described in the companion technical report on ecological assets (Stratford et al., 2024). The comparatively intact landscapes and associated water resources of the Victoria catchment support ecosystem health and biodiversity, providing crucial ecosystem services for human residence. Key human activities in the catchment that require intact landscapes include recreation, tourism, Indigenous cultural practices, fisheries (Indigenous, recreational and commercial), agricultural production (notably cattle grazing on native pastures) and military training focused on tropical savanna environments. The Victoria River is a large perennial river (i.e. it maintains flow all year) that originates near Judbarra National Park. At over 500 km in length, it is one of the longest perennial rivers in the NT. The catchment area of 82,400 km2 makes it one of the largest ocean-flowing catchments in the NT, and flows enter the south-eastern edge of the Joseph Bonaparte Gulf. The catchment and the surrounding marine environment contain a rich diversity of important ecological assets, including species, communities, habitats, processes and functions (see the conceptualised summary in Figure 3-2). The ecology of the Victoria catchment is maintained by the river’s flow regime, shaped by the region’s wet-dry climate and the catchment’s complex geomorphology and topography and driven by patterns of seasonal rainfall, evapotranspiration and groundwater discharge. For more information on this figure please contact CSIRO on enquiries@csiro.au Figure 3-2 Conceptual diagram of selected ecological values and assets of the Victoria catchment Ecological assets include species of significance, species groups, important habitats and ecological processes. See Table 3-2 for a complete list of the fresh water–dependent, marine and terrestrial ecological assets considered in the Victoria catchment. Biota icons adapted from Integration and Application Network (2023). Much of the natural environment of the Victoria catchment consists of rolling plans, mesas, escarpments and plateaux with savanna woodlands and various grasslands, including spinifex (Kirby and Faulks, 2004). The wet-dry tropical climate results in highly seasonal river flow with 90% of rainfall occurring between November and March (Kirby and Faulks, 2004). As typical for much of northern Australia, the dynamic occurring between wet and dry seasons provides both challenges and opportunities for biota (Warfe et al., 2011). During the dry season, river flows are reduced with many of the streams in the catchment receding to isolated pools. However, some of the larger tributaries in the catchment are perennial, including sections of Wickham River (upstream of Humbert River junction) and the Angalarri River (Midgley, 1981). In parts of the Victoria catchment, the persistence of water during the dry season is supported by discharge from groundwater-fed springs that persist during most dry seasons (Bureau of Meteorology, 2017); these habitats support aquatic life and fringing vegetation. In the dry season, the streams and waterholes that persist provide critical refuge habitat for many species, both aquatic and terrestrial. Many low-lying parts of the catchment flood during the wet season, inundating floodplains, connecting wetlands to the river channel and driving booms in productivity. While the extent of floodplain wetlands is comparatively moderate compared to many other tropical catchments, catchment topography means that flooding can be particularly evident in the floodplains, wetlands and intertidal flats of the estuary and around the junction of the Victoria River with both the West Baines and Angalarri rivers. Annual flooding delivers extensive sediment-rich discharges into the southern Joseph Bonaparte Gulf with sediment plumes that can extend large distances into the marine waters. Protected, listed and significant areas of the Victoria catchment The protected areas located in the Victoria catchment include one gazetted national park (Judbarra), a proposed extension to an existing national park (Keep River), two marine national parks, two Indigenous Protected Areas and two Directory of Important Wetlands in Australia (DIWA) sites (Figure 3-3). Judbarra National Park is the second-largest national park in the NT, covering approximately 1,300,000 ha (Department of Climate Change, Energy, the Environment and Water, 2022b). It is popular for tourism, showcasing gorges, escarpment country and sandstone formations, boab trees and fishing. Once fully gazetted, the Keep River National Park will cover a total area of approximately 272,000 ha. This area includes the proposed extension of an additional 215,000 ha (from the neighbouring catchment of the Keep River into the Victoria catchment), which is intended to be gazetted by 2026 (Department of Climate Change, Energy, the Environment and Water, 2022b; Department of Environment Parks and Water Security, 2023). The Wardaman Indigenous Protected Area extends across the northern Victoria catchment and beyond and covers a total area of approximately 225,000 ha (Department of Climate Change, Energy, the Environment and Water, 2022b), while the Northern Tanami Indigenous Protected Area abuts the southern boundary of the Victoria catchment with only a minimal portion within the Victoria catchment. The Joseph Bonaparte Gulf Marine Park is a Commonwealth marine park of approximately 860,000 ha and depths of 15 to 100 m (Department of Climate Change, Energy, the Environment and Water, 2022a). This marine park straddles the offshore portion of the Victoria catchment marine region and has tides up to 7 m. It is home to the Australian snubfin dolphin (Orcaella heinsohni) (Department of Agriculture, Water and the Environment, 2021a; Parks Australia, 2023). The eastern edge of the North Kimberley Marine Park (WA) is adjacent to the Joseph Boneparte Gulf Marine Park and follows the WA coastline to the WA–NT border. For more information on this figure please contact CSIRO on enquiries@csiro.au Figure 3-3 Location of protected areas and important wetlands within the Victoria catchment Assessment area Protected areas include areas managed mainly for conservation through management intervention as defined by the International Union for Conservation of Nature (IUCN). Data sources: Department of Agriculture‚ Water and the Environment (2020a); Department of Agriculture‚ Water and the Environment (2020b); Department of Agriculture‚ Water and the Environment (2021b); Department of Climate Change, Energy, the Environment and Water (2024) The two DIWA sites are the Bradshaw Field Training Area and the Legune Wetlands (Figure 3-3). The Bradshaw Field Training Area is a military training area between the Victoria River and the Angalarri River in the northern part of the catchment. The Legune Wetlands span the border of the Victoria and Keep catchments adjacent to the upper estuary and salt flats of the Keep River. These two DIWA wetlands highlight the diversity of aquatic habitats that can be found within the Victoria catchment. The Victoria catchment contains no Ramsar sites, but the neighbouring catchment of the Ord River contains two: the Lakes Argyle and Kununurra Wetlands and the Ord River Floodplain. The Bradshaw Field Training Area DIWA site lies north of the Victoria River near Timber Creek. It is bound by the Fitzmaurice River to the north and the Victoria River to the south. The site covers approximately 871,000 ha and includes two wetland complexes within the Victoria Bonaparte biogeographic region (Department of Agriculture, Water and the Environment, 2023a). Large areas of the wetlands are inundated each wet season by floods from both the Fitzmaurice and Victoria rivers, with flooding enhanced during coincidence with high tides. Some areas of the site retain permanent water during the dry season (Department of Agriculture, Water and the Environment, 2023a). The Bradshaw field training wetland site has very high species richness and wilderness value and includes areas of monsoon vine forest; it forms an important component of the conservation network within the Victoria catchment (Department of Agriculture, Water and the Environment, 2023a; Department of Climate Change, Energy, the Environment and Water, undated; NT Department of Lands, Planning and Environment, 1998). The Bradshaw Defence Area is also listed on the Australian Heritage Database for its rich vertebrate fauna. It has nationally significant species richness of mammals, reptiles and frogs, and it is considered a stronghold for species that have recorded declines in other locations, including the Gouldian finch (Erythrura gouldiae), the northern quoll (Dasyurus hallucatus) and the pale field rat (Rattus tunneyi). Over 850 flora species and 375 fauna species (comprising 22 frog, 77 reptile, 212 bird, 50 mammal and 26 fish species) are known to occur in the Bradshaw Defence Area (Department of Climate Change, Energy, the Environment and Water, undated). The Legune Wetlands straddles the Keep and Victoria catchments, receiving inflows from surface water from local creeks and some additional inflows in wet years from major floods in the Keep River (Department of Agriculture, Water and the Environment, 2023b). The wetlands include areas identified as an Important Bird and Biodiversity Area (IBA) by BirdLife International, with surveys recording more than 15,000 individuals from over 45 species, including magpie goose (Anseranas semipalmata), brolga (Antigone rubicunda) and red-capped plover (Charadrius ruficapillus) (BirdLife International, 2023; Department of Agriculture, Water and the Environment, 2023b). Habitats of importance include seasonal marshes and swamps, freshwater mangroves, mudflats and salt flats, and the site provides important dry-season habitat for waterbirds (BirdLife International, 2023; Department of Agriculture, Water and the Environment, 2023b). Important habitat types and values of the Victoria catchment The freshwater sections of the Victoria catchment include diverse habitats such as perennial and intermittent rivers, anabranches, wetlands, floodplains and groundwater-dependent ecosystems (GDEs). The diversity and complexity of habitats, and the connections between habitats within a catchment, are vital for providing the range of habitats needed to support both aquatic and terrestrial biota (Schofield et al., 2018). In the wet season, flooding connects rivers to floodplains. This water exchange means that floodplain habitats support higher levels of primary and secondary productivity than surrounding areas that are less frequently inundated (Pettit et al., 2011). Infiltration of water into the soil during the wet season and along persistent streams often enables riparian habitats to form an important interface between the aquatic and terrestrial environments. While riparian habitats often occupy a relatively small proportion of the catchment, they frequently have a higher species richness and abundance of individuals than surrounding habitats (Pettit et al., 2011; Xiang et al., 2016). Riparian habitats that fringe the rivers and streams of the Victoria catchment have been rated as having moderate to high cover and structural diversity for riparian vegetation (Kirby and Faulks, 2004). These riparian habitats include widespread Eucalyptus camaldulensis overstorey with Lophostemon grandiflorus, Terminalia platyphylla, Pandanus aquaticus and Ficus spp. Acacia holosericea and Eriachne festucacea occur as dominant understorey species across many parts of the catchment (Kirby and Faulks, 2004). Further away from the creeks and rivers, vegetation in the Victoria catchment becomes sparser. In the dry season, biodiversity is supported within perennial rivers, wetlands and the inchannel waterholes that persist in the landscape. In ephemeral rivers, the waterholes that remain become increasingly important as the dry season progresses; they provide important refuge habitat for species and enable recolonisation into surrounding habitats upon the return of larger flows (Hermoso et al., 2013). Persistent waterholes provide habitat for water-dependent species, including fish, sawfishes and reptiles such as freshwater turtles and crocodiles, as well as providing a source of water for other species more broadly within the landscape (McJannet et al., 2014; Waltham et al., 2013). GDEs occur across many parts of the Victoria catchment and come in different forms, including aquatic, terrestrial and subterranean habitats. Aquatic GDEs contain springs and river sections that hold water throughout most dry seasons due to groundwater discharge. Aquatic GDEs are important for supporting aquatic life and fringing vegetation, and in the wet-dry tropics they can provide critical refuge during periods of the late dry season (James et al., 2013). Vegetation occurring adjacent to the waterways in the Victoria catchment relies on water from a range of sources (surface water, soil water, groundwater) which are seasonally dynamic and highly spatially variable across riparian and floodplain habitats. Perennial floodplain vegetation often uses groundwater when it is within reach of the root network, particularly during the dry season or drought, but the origin of the groundwater used has only been infrequently investigated (e.g. Canham et al. (2021)). In some locations, vegetation may be sustained by water available in soils and so never use groundwater. In other locations, vegetation may use groundwater sourced from local alluvial recharge processes; alternatively, regional groundwater may be critical for maintaining vegetation condition. The latter situation applies to habitats of monsoon vine forest located within the Bradshaw Field Training Area DIWA site (NT Department of Lands, Planning and Environment, 1998). Subterranean aquatic ecosystems in the Victoria catchment include known sinkholes associated with the Montejinni Limestone that are mapped along the south-eastern edge of the Victoria catchment. These sinkholes may contain groundwater and support aquatic ecosystems throughout the dry season, but their connection to groundwater is currently unknown. Some subterranean species are distributed across a broad spatial range, while others have highly restricted ranges, which makes them more vulnerable to local changes where they occur (Oberprieler et al., 2021). Marine and estuarine habitats in northern Australia are highly productive and have high environmental and cultural value. They include some of the most important, extensive and intact habitats of their type in Australia, many of which are recognised as being of national significance. The mouth and estuary of the Victoria River is up to 25 km wide and includes extensive mudflats and mangrove stands (Kirby and Faulks, 2004). Although mangroves and mudflats are prominent along coastal margins (Department of Climate Change, Energy, the Environment and Water, undated), the mangrove communities along the estuary are recognised as being low in species richness with about ten species recorded. Of these, the dominant mangrove species in the catchment is Avicennia marina, which is largely confined to the estuary (Kirby and Faulks, 2004). The Legune IBA extends along the south-west shores of the inner Joseph Bonaparte Gulf, from the mouth of the Keep River in the west to the mouth of the Victoria River in the east and then north beyond the Victoria catchment. The Legune IBA can support over 15,000 waterbirds across mudflats, salt flats and seasonally inundated wetlands (BirdLife International, 2023). Marine habitats in northern Australia are vital for supporting important fisheries, including banana prawn, mud crabs and barramundi, as well as for biodiversity more generally, including waterbirds, marine mammals and turtles. In addition, the natural waterways of the sparsely populated catchments support globally significant stronghold populations of endangered and endemic species (e.g. sharks and rays) that often use a combination of marine and freshwater habitats. Significant species and ecological communities of the Victoria catchment The aquatic habitats of the Victoria catchment support some of northern Australia’s most archetypical and important wildlife species, including sawfishes, marine turtles, Australian snubfin dolphins and river sharks (Department of Agriculture, Water and the Environment, 2021a) that occur in the estuaries of the Victoria River and the coastal waters of the Joseph Boneparte Gulf. Recent surveys show the river to be a globally significant stronghold for three endangered species: freshwater sawfish (Pristis pristis; listed as Vulnerable under the Commonwealth Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act) and Critically endangered on the International Union for Conservation of Nature (IUCN) Red List of Threatened Species); speartooth shark (Glyphis glyphis; Critically endangered, EPBC Act and IUCN); and northern river shark (Glyphis garricki; Endangered, EPBC Act and IUCN). The speartooth shark is not among the species listed as Critically endangered in the catchment in Commonwealth’s Protected Matters Search Tool (PMST), but recent surveys have identified the species in the estuarine habitats of the Victoria River (Dr Richard Pillans (CSIRO Environment, Brisbane), 2022, pers. comm.). Saltwater crocodiles (Crocodylus porosus) frequent the Victoria River and have been recorded considerable distances into freshwater reaches (Atlas of Living Australia, 2023). Across the catchment are many lesser-known plants and animals that are also of great importance. Owing to healthy floodplain ecosystems and free-flowing rivers (Grill et al., 2019; Pettit et al., 2017), very few freshwater fish in the study area are threatened with extinction. Many of these fish species do not enter the marine environment, remaining within the riverine and wetland habitats of the catchment. Although habitats of the Victoria catchment have low levels of endemism (possibly due to the catchment forming a gradient between the biota of the Kimberley and the Top End) (Department of Climate Change, Energy, the Environment and Water, undated), Neil’s grunter (Scortum neili) is endemic to the Victoria catchment and is listed as Endangered by the IUCN. Neil’s grunter is restricted to sections of the East Baines and Angalarri rivers where it inhabits narrow, deep sections of the river that have slow-flowing fresh water shaded by overhanging trees (Gomon and Bray, 2017). Species 3.2.1 Current condition and potential threats in the Victoria catchment Land use practices and ecology A range of economic enterprises, infrastructure and other human impacts occur in the Victoria catchment. The nature and extent to which human activities have modified the habitats and affected species of the Victoria catchment varies, but most sites have some level of impact (Kirby and Faulks, 2004). Previous assessments have rated the riverine habitat in the Victoria catchment as being of high or very high overall quality and largely intact with high wilderness value and predominantly unaffected by clearing or development at the time of assessment, although threatening processes operate. These include grazing, roads, river crossings and impacts from pest species, including both feral animals and weeds (Department of Agriculture, Water and the Environment, 2023a; Kirby and Faulks, 2004). The study area includes the localities and towns of Timber Creek, Yarralin, Nitjpurru (Pigeon Hole), Top Springs, Kalkarindji and Daguragu, which provide Indigenous homelands, support a vital tourism industry and act as regional hubs for many of the stations across the catchment. While a moderate proportion of the catchment is under conservation reserves, the catchment does face environmental threats. Fishing in northern Australia is highly valuable, and the waters of the Victoria catchment and the nearby marine zone contribute to important recreational, commercial and Indigenous catches, including barramundi, redleg banana prawns (Penaeus indicus) and a variety of other species. Northern Australia more broadly encompasses some of the last relatively undisturbed tropical riverine landscapes in the world with low levels of flow regulation and low development intensity (Pettit et al., 2017; Vörösmarty et al., 2010). Riparian vegetation characteristics of the Victoria catchment are considered not to be affected by extensive clearing or development, although impact that occurs is often associated with stock and pest species accessing watering points (Kirby and Faulks, 2004). One of the most significant environmental threats to remote regions across northern Australia is that of introduced plants and animals. In the Victoria catchment, pig (Sus scrofa), water buffalo (Bubalus bubalis), camel (Camelus dromedarius), donkey (Equus asinus), cat (Felis catus) and cane toad (Rhinella marina) are among the invasive animals (Atlas of Living Australia, 2023; (Department of Agriculture, Water and the Environment, 2021a). Weed species of interest in and around the Victoria catchment include 20 species of national significance. Invasive plants of concern include gamba grass (Andropogon gayanus), para grass (Brachiaria mutica), giant sensitive plant (Mimosa pigra) and prickly acacia (Vachellia nilotica) (Department of Agriculture, Water and the Environment, 2021a). Some of these, including sensitive tree and para grass, have significantly affected undeveloped rivers more broadly in northern Australia (Davies et al., 2008). Surveys within the Bradshaw Field Training Area indicated the presence of six feral species, namely, cats, horses, donkeys, pigs, wild cattle and buffalo (NT Department of Lands, Planning and Environment, 1998). eDNA analysis of water samples taken in this study detected cane toads, wild pig, cattle and dingo (Canis familiaris) at several sites (Stratford et al., 2024). Further details on biosecurity are provided in Section 7. Water resource development and ecological changes The importance of the natural flow regime for supporting environmental function has become increasingly well understood, as has the importance of rivers operating as systems, including the connection of floodplains via inundation, the distribution of refuges, and discharges into coastal regions. Globally, water resource development has a range of known impacts on ecological systems. The influence of each of these impacts depends upon a range of factors, including catchment properties (e.g. physical, geographic and climate characteristics), the kind of development (e.g. dams, water harvesting, groundwater development), the source location or distribution of the developments within the catchment, the magnitude and pattern of change, how any changes may be managed or mitigated, and the habitats and species that will be affected and their distribution. Impacts associated with water resource development include the following, which are described below: •flow regime change •altered longitudinal and lateral connectivity •habitat modification and loss •increased invasive and non-native species •synergistic and co-occurring processes both local and global. Flow regime change Water resource development including water harvesting and creating instream structures for water retention can influence the timing, quality and quantity of water that is provided by catchment runoff into the river system. The natural flow regime (including the magnitude, duration, timing, frequency and pattern of flow events) is important in supporting a broad range of environmental processes upon which species and habitat condition depend (Lear et al., 2019; Poff et al., 1997). Flow conditions provide the physical habitat in streams and rivers which determines biotic use and composition and to which life-history strategies are adapted. Flow enables movement and migration between habitats and exchange of nutrients and materials (Bunn and Arthington, 2002; Jardine et al., 2015). In a river system, the natural periods of both low and high flow (including no-flow events) are important to support the natural function of habitats, their ecological processes and the shaping of biotic communities (King et al., 2015). Through the attenuation of flows, water resource development can lead to impacts significant distances downstream of the development, including into coastal and near-shore marine habitats (Broadley et al., 2020; Pollino et al., 2018). Altered longitudinal and lateral connectivity River flow facilitates the exchange of biota, materials, nutrients and carbon along the river and into the coastal areas (longitudinal connectivity), as well as between the river and the floodplain (lateral connectivity) (Pettit et al., 2017; Warfe et al., 2011). Physical barriers such as weirs, dams and causeways and road crossings, or a reduction in the magnitude of flows (and the duration or frequency), can affect longitudinal and lateral connectivity, changing the rate or timing of exchanges (Crook et al., 2015). These impacts can include changes in species’ migration and movement patterns as well as altered erosion processes and discharges of nutrients into rivers and coastal waters (Brodie and Mitchell, 2005). Seasonal patterns and rates of connection and disconnection caused by flood pulses are important for providing seasonal habitat and enabling movement of biota into new habitats and their return to refuge habitats after larger river flows (Crook et al., 2020). Habitat modification and loss Water resource development can cause direct loss of habitat. For example, artificially creating a lake (inundated) habitat behind an impoundment results in loss of terrestrial and stream habitat. Agricultural development converts existing habitat to more-intensive agriculture. Infrastructure, including roads, can fragment terrestrial habitat, while streams and canals can artificially connect aquatic habitats that had been historically separated. Increased invasive and non-native species Water resource development often homogenises flow and flow-related habitats, for example, through changed patterns of capture and release of flows or creation of impoundments for storage and regulation. Invasive species are often at an advantage in such modified habitats (Bunn and Arthington, 2002). Modified landscapes, such as lakes or homogenised perennial streams that were previously ephemeral, can be a pathway for the introduction of, and support the incidental, accidental or deliberate establishment of, non-native species, including pest plants and fish (Bunn and Arthington, 2002; Close et al., 2012; Ebner et al., 2020). Increased human activity can increase the risk of invasive species being introduced. Synergistic and co-occurring processes both local and global Along with water resource development comes a range of other pressures and threats, including increases in fishing; vehicles; habitat fragmentation; pesticides, fertilisers and other chemicals; erosion; degradation due to increased stock pressure; and changed fire regimes, climate change and other human disturbances, both direct and indirect. Some of these pressures are the direct result of changes in land use associated with or accompanying water resource development. Other pressures may occur locally, regionally or globally and act synergistically with water resource development and agricultural development to increase the risk to species and their habitats (Craig et al., 2017; Pettit et al., 2012). To describe the ecology of the Victoria catchment and discuss the likely impacts of future water resource development on this system, a suite of ecological assets has been selected (Table 3-1). Assets are classified as species, species groups or habitats. They can be considered either partially or fully dependent on fresh water, or terrestrial or marine dependent upon freshwater flows (or services provided by freshwater flows). This chapter considers a key subset of assets, as listed in Table 3-1 Freshwater, marine and terrestrial ecological assets with freshwater flow dependences An asterisk (*) denotes an asset outlined in this report. All listed species, species groups and habitat assets are detailed in the companion technical report on ecological assets (Stratford et al., 2024). For more information on this figure, table or equation please contact CSIRO on enquiries@csiro.au. 3.2.2 Ecological assets from the Victoria catchment Northern Australia’s rivers, floodplains and coastal regions contain high diversity, including at least 170 fish species, 150 waterbird species, 30 aquatic and semi-aquatic reptiles, 60 amphibian species and 100 macroinvertebrate families (van Dam et al., 2008). The ecologies of the freshwater and fresh water–dependent terrestrial and marine systems are supported by, and adapted to, the highly seasonal flow regimes of the wet-dry tropics. Water resource development and climate change threaten to affect these habitats and species. This section provides a synthesis of the prioritised assets relevant to the Victoria catchment for the purpose of understanding the ecological outcomes of flow regime change. Table 3-2 lists the ecological assets used. Barramundi (Lates calcarifer) Barramundi are a large (>1 m standard length) opportunistic-predatory fish (order Perciformes) that occurs throughout northern Australia. The species is catadromous (i.e. it migrates down rivers to spawn in the sea) and occurs in ‘catchment to coast’ habitats throughout the west Indo-Pacific region, including estuaries, rivers, lagoons and wetlands across northern Australia (Crook et al., 2016; Pender and Griffin, 1996; Roberts et al., 2024; Russell and Garrett, 1983, 1985). The fish is long lived (living up to about 32 years) and fast growing. Individuals begin life as a male but change to female as they age (protandrous hermaphrodite). They occupy freshwater habitats as males in the first years of life and saltwater habitats as older females. The species is of ecological importance, capable of modifying the estuarine and riverine fish and crustacean communities (Blaber et al., 1989; Brewer et al., 1995; Milton et al., 2005; Russell and Garrett, 1985). Barramundi is arguably the most important fish species for commercial, recreational and Indigenous subsistence fisheries throughout Australia’s wet-dry tropics. It makes up a substantial component of the total commercial fish catch in northern Australia (Savage and Hobsbawn, 2015). In 2013–14, barramundi comprised 28% of the $31 million wild-caught fishery production in the NT. Commercial and recreational catches make up the largest proportions of all catches in the NT, though the Indigenous catch is not well documented and may be significant in some locations. Barramundi is a fish of cultural significance for Indigenous communities as well as being an important food source (Jackson S et al., 2012). The movements of barramundi between habitats are indicators of the change in season for Indigenous communities across tropical Australia (Green et al., 2010). The movements relate to the barramundi’s habitat requirements during its life cycle, which rely on seasonal variation in river flows to access habitats. Barramundi life history renders the species critically dependent on river flows (Plagányi et al., 2023; Tanimoto et al., 2012). Large females (older fish) and smaller males (younger fish) reside in estuarine and littoral coastal habitats. Mating and spawning occur in the lower estuary during the late dry season to early wet season, and new recruits move into supra-littoral and freshwater habitats. Coastal salt flat, floodplain and palustrine (i.e. non-tidal wetland) habitats depend on overbank flows for maintenance and connectivity (Crook et al., 2016; Russell and Garrett, 1983, 1985). Barramundi are abundant in the relatively pristine habitats of the estuarine and freshwater reaches of the Victoria River. However, there are few data on recreational or commercial catch or the presence or absence of barramundi in the Victoria catchment. The Victoria River currently experiences low levels of commercial fishing for barramundi, but barramundi are common in the river estuary, and commercial interest in fishing the river is increasing (Thor Saunders (NT Fisheries Research), 2022, pers. comm.). A large tidal range and strong currents within the estuary are deterrents to successful commercial fishing (Thor Saunders (NT Fisheries Research), 2022, pers. comm). The modelled distribution of barramundi showing the probability of occurrence is shown in Figure 3-4. For more information on this figure please contact CSIRO on enquiries@csiro.au Figure 3-4 Observed locations of barramundi (Lates calcarifer) and its modelled probability of occurrence in the Victoria catchment Probability of occurrence is based upon a general linear model with model predictors. For the species distribution models, only records later than 1960 that intersected with polygons that contain waterways and that had a stated coordinate uncertainty less than 5 km were used. Red points show locations from Atlas of Living Australia. Data source: Atlas of Living Australia (2023) Grunters Northern Australia has 37 species of grunter from 11 genera, with the most species-rich genera being Hephaestus, Scortum, Syncomistes and Terapon. Grunters inhabit riverine, estuarine and marine waters. Many grunter species spend their entire lives in fresh water, while other species inhabit marine or estuarine waters, only sometimes venturing into fresh water (Pusey et al., 2004). One of the most widespread species across northern Australia is the sooty grunter (Hephaestus fuliginosus). Sooty grunters are omnivorous and eat a diverse diet, including terrestrial insects and vegetation, fish, aquatic insect larvae, macrocrustacea (shrimps and prawns) and aquatic vegetation. Sooty grunters switch diet from being insectivorous while juvenile to being top-level predators as adults, often feeding on smaller fish as well as juvenile grunters. Juvenile grunters are often associated with flowing water, suggesting that water resource development that reduces or ceases flow could pose a threat. Tree root masses and undercut banks are also important microhabitat, especially for adult fish (Pusey et al., 2004). Grunters prefer medium to high oxygen levels as well as medium to low salinity (Hogan and Nicholson, 1987). Grunters will move out of the dry-season refugial habitats and into ephemeral wet-season habitats for spawning (Bishop et al., 1990). The sooty grunter is an important recreational species, and in some of their range environmental flow is managed to maintain suitable habitat conditions (Chan et al., 2012). Because grunters are omnivorous and able to integrate many sources of food, as well as having a high total biomass, they are an important link in the overall food chain. They link lower trophic levels with top-level predators, such as long tom (Strongylura krefftii) and crocodiles. Grunters are also important species for Indigenous Peoples in northern Australia, both culturally (Finn and Jackson, 2011; Jackson et al., 2011) and as a food source (Naughton et al., 1986). The composition of grunters in the Victoria catchment is slightly different to that in catchments that drain into the Gulf of Carpentaria. In addition to the widespread spangled grunter (Leiopotherapon unicolor) and barred grunter (Amniataba percoides), in the Victoria catchment, the western sooty grunter (Hephaestus jenkinsi) replaces the eastern species H. fuliginosus. Less- abundant species include the sharpnose grunter (Syncomistes butleri), Drysdale grunter (Syncomistes rastellus) and Neil’s grunter (Scortum neili). Of these grunters, the western sooty grunter is the key species for recreational and cultural purposes (Chan et al., 2012). Grunters are likely widespread in the Victoria River, whose headwaters are spawning and nursery grounds for larger species as well as habitat for adults of the smaller species (e.g. spangled grunter). Waterholes on the main stem provide habitat for adult grunters. Neil’s grunter is of particular interest in the catchment as it is endemic to the Victoria catchment and is listed as Endangered on the IUCN Red List of Threatened Species. Adults occur in small, well- shaded, slow-flowing streams with mixed sand, silt and rock bottoms, and also in deeper rocky pools in gorges. Preferred water conditions are typically fresh and clear, between 21 and 28 °C, with a neutral or slightly basic pH. Occurrences of grunter species in the Victoria catchment are shown in Figure 3-5. The modelled probability of occurrence of spangled grunter (Leiopotherapon unicolor) is shown in Stratford et al. (2024). For more information on this figure please contact CSIRO on enquiries@csiro.au Figure 3-5 Observed locations of grunters in the Victoria catchment Data source: Atlas of Living Australia (2023) River sharks River sharks is the generic term given to species of the genus Glyphis, found in the Indo-West Pacific, each of which is endangered or critically endangered (Last and Stevens, 2008; Morgan, 2011; Stevens et al., 2009). Two Glyphis species are found in Australian waters: the speartooth shark (Glyphis glyphis; Critically endangered, EPBC Act and IUCN) and the northern river shark (Glyphis garricki; Endangered, EPBC Act and IUCN). The speartooth shark occurs across Cape York, the north-west coast of the Top End, inshore Joseph Bonaparte Gulf and the southern coast of Papua New Guinea (Pillans et al., 2009; White et al., 2015). The northern river shark occurs across the Kimberley and the Top End coast, as well as the Fly River, Papua New Guinea (Pillans et al., 2009; West et al., 2021; White et al., 2015). Tropical Australia and Papua New Guinea probably represent the last viable populations of the speartooth shark and the northern river shark across their global ranges (Pillans, 2014; Pillans et al., 2022). River sharks are poorly studied, though studies of their population structure, niche partitioning, and estuarine habitat and prey have been undertaken in the past 5 years (Dwyer et al., 2019; Every et al., 2019; Feutry et al., 2020). Within large tropical river systems, the speartooth shark uses the mangrove-fringed upstream portions of the estuary and the riverine habitats where the estuary blends to become the river as its primary habitat (indicative habitat salinity is 1 to 28 parts per thousand (ppt) in the NT and 3 to 26 ppt in western Cape York, Queensland) (Dwyer et al., 2019; Pillans, 2014; Pillans et al., 2009). It has an ontogenetic shift in habitat preference: juveniles use the upper‐estuarine and lower‐freshwater reaches of rivers (up to 100 km upstream) and adults use estuarine environments (Pillans et al., 2009). The northern river shark has been found in Cambridge Gulf and the Daly River, respectively west and east of the Victoria River. The species uses estuarine and freshwater habitats, but is more marine in habit than the speartooth shark. The northern river shark uses rivers (salinity 2 ppt), large tropical estuarine systems (salinity 7 to 21 ppt), macrotidal embayments and inshore and offshore marine habitats (salinity 32 to 36 ppt) (Pillans et al., 2009). It is thought adults use only marine environments and may be found outside estuaries. The northern river shark likely pups prior to the annual wet season with a litter size around nine. Neonates and juveniles are found in freshwater, estuarine and marine habitats, though capture locations indicate a preference for highly turbid, tidally influenced waters over muddy substrate (Stevens et al., 2005). No Glyphis species have been found in isolated freshwater habitats such as billabongs or refuge waterholes in river channels (Stevens et al., 2005). Published data on the distribution of river sharks in the Victoria River are scant. Records for northern river shark exist for Cambridge Gulf and Daly River. No published records of speartooth shark exist for regions in the Joseph Bonaparte Gulf littoral or estuarine habitats. However, Dr Richard Pillans conducted surveys of freshwater elasmobranchs in the Victoria River in 2018 and 2019 and recorded both speartooth and northern river sharks in brackish-water reaches of the river (Dr Richard Pillans (CSIRO Environment, Brisbane), 2022, pers. comm.). These surveys were conducted as part of the Ord River Offset program, which inventories natural resources in the vicinity of expanded Ord River irrigation agriculture. Dr Pillans caught three speartooth sharks and eight northern river sharks in the Victoria River upper estuary, from about 80 to 120 km upstream from Entrance Island. These new records of the presence of the two species in the Victoria River exemplify the paucity of biological data from remote tropical Australia. Shorebirds The shorebirds group consists of waterbirds with a high level of dependence on large inland flood events and end-of-system flows that provide broad areas of shallow water and mudflat environments. Flood events trigger production of significant food resources for these species – resources that are critical for fuelling long-distance migrations. Shorebirds generally eat fish or invertebrates. Most species walk and wade when foraging, probing sediment, rocks or vegetation for prey (Garnett et al., 2015; Marchant and Higgins, 1990). Shorebirds are largely migratory, mostly breeding in the northern hemisphere. They are in significant decline and are of international concern. Shorebirds depend on specific shallow-water habitats in distinct geographic areas, including northern hemisphere breeding grounds, southern hemisphere non-breeding grounds and stopover sites along migration routes such as the East Asian-Australasian Flyway (Bamford, 1992; Hansen et al., 2016). As the group is of international concern, various management and conservation strategies have been implemented (Department of Agriculture‚ Water and the Environment, 2021c), including bilateral migratory bird agreements with China (CAMBA), Japan (JAMBA), and Korea (ROKAMBA), the Bonn Convention on the Conservation of Migratory Species of Wild Animals (Bonn), and the Ramsar Convention on Wetlands of International Importance. In northern Australia, this group comprises approximately 55 species from four families, including sandpipers, godwits, curlew, stints, plovers, dotterel, lapwings and pratincoles. Details are provided in the companion technical report on ecological assets (Stratford et al., 2024). Approximately 35 species are common, regular visitors or residents. Several species in this group are endangered globally and nationally, including the bar-tailed godwit (Limosa lapponica), curlew sandpiper, eastern curlew, great knot (Calidris tenuirostris), lesser sand plover (Charadrius mongolus) and red knot. The eastern curlew is listed as Critically endangered under the EPBC Act and recognised through multiple international agreements as requiring habitat protection in Australia. Eastern curlews rely on food sources along shorelines, mudflats and rocky inlets, as well as roosting vegetation. Developments and disturbances, such as recreational, residential and industrial use of these habitats, have restricted habitat and food availability for the eastern curlew, contributing to population declines. The red-capped plover (Figure 3-6) is a shorebird that breeds in Australia rather than in the northern hemisphere. It is a small species that is widespread and common both inland and along the coast. It prefers open flat sediment areas such as mudflats and beaches for foraging and eats a range of small invertebrates, including crustaceans. It breeds in response to flooding or rain inland, and seasonally on the coast. Photo red-caped plover. For more information on this figure, table or equation please contact CSIRO on enquiries@csiro.au. Figure 3-6 Red-capped plover walking along a shore Photo: CSIRO Mangroves Mangroves are a group of woody plant species, ranging from shrub to large tree to forest, that are highly specialised to deal with daily variation in their niche within the intertidal and near-supra- littoral zones along tidal creeks, estuaries and coastlines (Duke et al., 2019; Friess et al., 2020; Layman, 2007). Their occurrence is a result of changes across temporal scales – from twice-daily tides to seasonal and annual cycles; mangroves have acclimatised to variable inundation, changing salinity, anoxic sediments, drought and floods, and sea-level change. Mangrove forests provide a complex habitat that offers a home to many marine species, including molluscs (McClenachan et al., 2021), crustaceans (Guest et al., 2006; Thimdee et al., 2001), birds (Mohd-Azlan et al., 2012), reptiles (Fukuda and Cuff, 2013) and numerous fish species. During periods of inundation at high tide, fish and crustaceans access mangrove forests for shelter against predation. Fish and crustaceans use mangroves as refugia during larval phases and settle there as benthic juveniles (Meynecke et al., 2010) or access them for food (Layman, 2007; Skilleter et al., 2005). Mangrove forests support many of the species and groups reported as biota assets in this Assessment (see Stratford et al. (2024)), particularly fishery species such as banana prawns, barramundi, mud crabs (Scylla serrata), threadfin (Polydactylus macrochir) and mullet (Blaber et al., 1995; Brewer et al., 1995). In addition to providing habitat, mangrove forests provide a diverse array of ecosystem services, including stabilising shoreline areas from erosion and severe weather events (Zhang et al., 2012), and they play an important role in greenhouse gas emission and carbon sequestration (Lovelock and Reef, 2020; Owers et al., 2022; Rogers et al., 2019). Mangroves continually shed leaves, branches and roots, contributing approximately 44 to 1022 g carbon per m2 per year from leaves and 912 to 6870 g carbon per m2 per year from roots, though these rates continue to be explored (Robertson, 1986; Robertson and Alongi, 2016). Intertidal crabs living in mangrove forests play an important role in processing and storing mangrove carbon, either through burial in their burrows or uptake directly into production. The decomposition and processing of mangrove material is important also in the cycling of nutrients. If consumed and released, these nutrients support a local food web (Abrantes et al., 2015; Guest et al., 2004), and some of the organic carbon can be transported offshore where it supports fisheries production more broadly (Connolly and Waltham, 2015; Dittmar and Lara, 2001; Lee, 1995). 3.2.3 Environmental protection A number of aquatic and terrestrial species in the Victoria catchment are currently listed as Critically endangered, Endangered or Vulnerable under the EPBC Act and by the wildlife classification system of the NT Government, which is based on the IUCN Red List of Threatened Species. Figure 3-7 shows the locations of these significant species. For more information on this figure please contact CSIRO on enquiries@csiro.au Figure 3-7 Distribution of species listed under the Environment Protection and Biodiversity Conservation Act and by the NT Government in the Victoria catchment Datasets: Department of Environment Parks and Water Security (2019); Atlas of Living Australia (2023) If a proposed development is predicted to have a significant impact on a matter of national environmental significance (e.g. populations of a nationally listed species, ecological communities, migratory species or wetland of importance), it requires approval to proceed under the EPBC Act (Table 3-2). This approval is required irrespective of local government policies. The Commonwealth’s Protected Matters Search Tool lists 45 Threatened species for the Victoria catchment, four of which are listed as Critically endangered: Nabarlek (Petrogale concinna concinna), Rosewood keeled snail (Ordtrachia septentrionalis), curlew sandpiper (Calidris ferruginea) and eastern curlew (Numenius madagascariensis). Also listed are 49 migratory species. Table 3-2 Definition of threatened categories under the Commonwealth Environment Protection and Biodiversity Conservation Act 1999 and the NT wildlife classification system For more information on this figure, table or equation please contact CSIRO on enquiries@csiro.au For more information on this figure, table or equation please contact CSIRO on enquiries@csiro.au †The NT wildlife classification categories are based on the IUCN Red List categories and criteria. An extract of each category is presented here. For the full definition see https://nt.gov.au/__data/assets/pdf_file/0010/192538/red-list-guidelines.pdf. 3.3 Demographic and economic profile 3.3.1 Introduction This chapter describes the current social and economic characteristics of the Victoria catchment in terms of the demographics of local communities (Section 3.3.2), current industries and land use (Section 3.3.3), and existing infrastructure of transport networks, supply chains, utilities and community infrastructure (Section 3.3.4). Together these characteristics describe the built and human resources that would serve as the foundation upon which any new development in the Victoria catchment would be built. Unless otherwise stated, the material in this section is based on findings described in the companion technical report on agricultural viability and socio-economics (Webster et al., 2024). 3.3.2 Demographics The Victoria catchment lies within the NT and comprises around half of the Victoria Daly Regional Council local government area. The northern part of the catchment includes part of the NT electoral division of Daly, and the southern part of the catchment includes part of the NT electoral division of Gwoja. At the federal level, the catchment forms a part of the Division of Lingiari (which encompasses most of the NT, excluding the Division of Solomon that covers an area around Darwin). Population density of the Victoria catchment is extremely low at one person per 51.4 km2. This is about one-eighth of the population density of the NT and one 165th of Australia as a whole. The catchment contains no significant urban areas (population >10,000), but there are several small towns and communities including Timber Creek (the furthest north in the catchment), Yarralin, Nitjpurru (Pigeon Hole), Amanbidji, Bulla, Daguragu and Kalkarindji (the furthest south). The largest of these settlements is Kalkarindji (population of 383 as at the 2021 Census). Katherine (population 5980 in 2021) is the closest urban service centre in the NT and is located north-east of the catchment approximately 290 km from Timber Creek. The nearest major city and population centre is the NT capital of Darwin (population of the Greater Darwin area was 139,902 in 2021) approximately 600 km from Timber Creek. The demographic profile of the catchment, based on data from the 2021, 2016, 2011 and 2006 censuses, is shown in ABS statistical area regions used in the analysis, map \\FS1-CBR.nexus.csiro.au\{lw-rowra}\work\5_Agriculture_economics\2_Victoria\1_GIS\1_Map_docs\Se-V-505_Map_Australia_Vic_tourism_SA2_v4.mxd For more information on this figure please contact CSIRO on enquiries@csiro.au Figure 3-8 Boundaries of the Australian Bureau of Statistics Statistical Area Level 2 (SA2) regions used for demographic data in this analysis and the Katherine Daly tourism region The typical resident of the catchment is younger, poorer and more likely to identify as Indigenous than the typical resident of the NT and of Australia as a whole. The catchment population is predominantly younger (median age 25 years in 2021) than is typical in the NT (33 years) and the country as a whole (38 years). However, the trend from 2011 to 2016 and to 2021 suggests that the median age is increasing a little. The population in the catchment contains a much larger proportion of Indigenous Peoples (close to 75%) than the NT (26.3%) and the country overall (3.2%). Median household incomes in the catchment were considerably below the average for the NT and the country as a whole in 2021. Furthermore, the proportion of households on low incomes (less than $650/week) was far higher, and the proportion on high incomes (more than $3000/week) far lower, than the proportion for the NT and the country as a whole (Table 3-3). Table 3-3 Major demographic indicators for the Victoria catchment For more information on this figure or table please contact CSIRO on enquiries@csiro.au †Weighted averages of scores for SA2 regions falling wholly or partially within the catchment boundary. Sources: ABS (2021), ABS (2016), ABS (2011) and ABS (2006) Census data The Victoria catchment falls within the first decile for each of the Socio-Economic Indexes for Areas (SEIFA) metrics (Table 3-4), indicating that the catchment scores below 90% of the rest of the country on each measure. All three SA2 regions that fall within the catchment boundary (Victoria River, Tanami and Barkly) individually rank within the first decile for all four measures. Table 3-4 Socio-Economic Indexes for Areas (SEIFA) scores of relative socio-economic advantage for the Victoria catchment Scores are relativised to a national mean of 1000, with higher scores indicating greater advantage. For more information on this figure or table please contact CSIRO on enquiries@csiro.au †Weighted averages of scores for SA2 regions falling wholly or partially within the catchment boundary. §Based on both the incidence of advantage and disadvantage. *Based purely on indicators of disadvantage. Source: ABS (2023) 3.3.3 Current industries and land use Employment The economic structure of the Victoria catchment differs substantially from that of the NT and Australia as a whole. The proportion of the adult population (aged 15 and older) within the labour force in the catchment is far smaller than in the NT (see participation rates in Table 3-5), indicating that a large proportion of the potential workforce is unable or unwilling to find work. Furthermore, unemployment rates are far higher than the NT and national averages (see unemployment rates in Table 3-5), indicating that a larger proportion of those who are willing and able to seek work have been unable to find work. Trends in the data appear unfavourable, with unemployment rates within the Victoria catchment higher and participation rates lower in the 2016 and 2021 censuses than in earlier periods. In contrast, rates remained broadly steady for the NT and Australia as a whole across the same time frame. There are noticeable differences in the industries providing the most jobs within the catchment compared with the nation as a whole (Table 3-5). ‘Education and training’, ‘Health care and social assistance’ and ‘Construction’ are important employers in the catchment and nationally; however, ‘Retail trade’ and ‘Professional, scientific and technical services’ feature within the top five industries by employment nationally but are far less significant in the Victoria catchment. As is also the case in the NT as a whole, ‘Public administration and safety’ is relatively more important to the employment prospects of workers in the catchment than the average across the country. Of particular relevance to this Assessment, ‘Agriculture, forestry and fishing’ is the most significant industry within the Victoria catchment. Furthermore, the sector has been growing relatively more important in the catchment over time. Over the past three censuses (2021, 2016 and 2011), the percentage of employment in the agricultural sector nationally has been reported as 2.3%, 2.5% and 2.5%, respectively, and for the NT, 2.3%, 2.0% and 1.9%, respectively. That is, the proportion of employment in the agricultural industry has been small and fairly steady. In contrast, agricultural employment within the Victoria catchment is large and growing, having provided 26.3% of employment in 2011, 24.0% in 2016 and 29.2% in 2021. The structural differences between this catchment and elsewhere can have a significant impact on the regional economic benefits that can result from development projects initiated within the catchment compared to development projects that may be initiated elsewhere. Table 3-5 Key employment data for the Victoria catchment For more information on this figure or table please contact CSIRO on enquiries@csiro.au †Weighted averages of scores for SA2 regions falling wholly or partially within the catchment boundary. Source: ABS (2021), ABS (2016), ABS (2011) and ABS (2006) Census data Land use The Victoria catchment covers an area of about 82,400 km2, much of which is conservation and natural environments (38%) (Figure 3-9). In the north of these protected lands lies the Bradshaw Field Training Area (7% of the conservation and natural environments), a facility owned by the Australian Government with a southern boundary following the Victoria River and a boundary that also extends outside the Victoria catchment in the north-east. A further 2.05% of the catchment is classified as water and wetlands, most of which is coastal and tidal waters, including reaches in the Angalarri River. Nearly all of the remaining catchment area (62%) is used for grazing natural vegetation. Intensive agriculture and cropping make up a very small portion of the catchment: dryland and irrigated agriculture and intensive animal production together comprise just 0.02% of the land area. The other intensive localised land uses are transport, communications, services, utilities and urban infrastructure (0.22%). While not considered a land use under the land use mapping (because it is a tenure), it is worth noting that Aboriginal freehold title, held under the Commonwealth Aboriginal Land Rights (Northern Territory) Act 1976 (ALRA), makes up 31% of the Victoria catchment. The title is inalienable freehold, which cannot be sold and is granted to Aboriginal Land Trusts which have the power to grant an interest over the land. Just over half of this overall 31% holding comprises the Judbarra National Park, which is overlaid by a 99-year lease with the NT Government. Native title exists in parts of the native title determination areas that occur in an additional 34% of the catchment. \\FS1-CBR.nexus.csiro.au\{lw-rowra}\work\5_Agriculture_economics\2_Victoria\1_GIS\1_Map_docs\1_Exports\Se-V-514_landuse_v3.png Figure 3-9 Land use classification for the Victoria catchment Areas of some land uses (e.g. irrigated/intensive agriculture) are too small to be shown on the map. Note: land use data shown on this map is current to 2017. Source: NT Department of Environment, Parks and Water Security (2013) Value of agriculture The estimated values of agricultural production for the Victoria catchment and the NT as a whole are given in Table 3-6. The catchment provides a substantial proportion of the revenue for livestock from the NT but has no cropping. The most recent annual survey data from the ABS describing the value of agriculture by different types of industries (2021–22 survey) are only available at a much larger scale than the Victoria catchment (state and territory level), preventing estimation of the value of agricultural products within the catchment. Hence estimates have been presented for the previous year (Table 3-6) for which data were available at a finer spatial scale (SA2 level, as used for socio-economic and demographic catchment estimates). Table 3-6 Value of agricultural production for the Victoria catchment (estimated) and the NT for 2020−21 For more information on this figure or table please contact CSIRO on enquiries@csiro.au ⴕWeighted averages of scores for SA2 regions falling wholly or partially within the catchment boundary. Source: ABS (2022) Agriculture is the major source of employment in the Victoria catchment, providing 29% of the work (Table 3-5). This is much higher than the proportion of employment in agriculture at a national level. Livestock production Extensive grazing of beef cattle, valued at $110.2 million in 2020–21 (Table 3-6), dominates agricultural production in the Victoria catchment, and about 62% of the catchment by area is used for extensive cattle grazing (pastoralism). The Big Run: the story of Victoria River Downs (Makin, 1970) documents the early history of the district, development of the cattle industry and life of pastoral settlers at Victoria River Downs Station, once the world’s largest cattle property. The first pastoral lease assigned in the NT was in 1876 on the Katherine River. Beef cattle were first introduced to the Victoria catchment in about 1878, and by 1882, the pastoral lease Victoria River Downs had been established with an area of 41,154 km2. The first cattle arrived there in 1883 (Makin 1970). The first export shipment of live cattle, from Port Darwin to Hong Kong in 1885, included cattle from the Victoria catchment. The shipment turned into an expensive failure. Later attempts to export live cattle (to Singapore and to the Philippines) were also loss-making ventures, and the general lack of markets in the early years became a serious impediment to profitability. Local markets were insufficient to underwrite the profitability. The stations were remote, and the high cost of stocking them with supplies and equipment and finding suitable staff to work on them provided substantial constraints. Furthermore, the main market was in Darwin, and the cattle lost considerable weight in the overland journey, compounding the cost of droving them there (Makin, 1970). A proposal to build the NT’s first meatworks in the Victoria catchment in 1901 did not come to fruition. Subsequently, meatworks were built in both Darwin and in Wyndham in WA (Makin, 1970). Both of these are now closed. The prospect of running sheep was also considered, with the aim of producing wool, which, once shorn, is less perishable than meat. One estimate was that the NT had the potential to run 30 million sheep. Indeed, sheep were brought on to Victoria River Downs in 1891 (Makin 1970). However, within a few years, the sheep were sold on, and shortly after there were no sheep in the Victoria catchment. Many of the constraints to profitability of the early years remain today in the Victoria catchment. It is remote from the large domestic markets in southern Australia, and it is better suited to breeding cattle than to fattening or finishing them for local slaughter. This limits the number of markets which can be targeted. The long distance to services leads to high input costs. Finding skilled staff is difficult. Therefore, the industry continues to seek ways in which to overcome some of these constraints through economies of scale, technical advances in sensor networks and potentially the introduction of on-farm forage and hay supply. Present-day cattle grazing occurs on dryland native and naturalised pastures. The within-year variation produced by the wet-dry climate is the main determinant for cattle production. Native pasture growth depends on rainfall, so pasture growth is highest from December to March. The total standing biomass and the nutritive value of the vegetation declines during the dry season. Changes in cattle liveweight closely follow this pattern with higher growth rates over the wet season than the dry season. Indeed, cattle often lose liveweight and body condition throughout the dry season until the next pulse of growth initiated by wet-season rains. A whole-of-industry survey (Cowley, 2014) provides a snapshot of the industry as it was in 2010. While some of the survey results described below have inevitably changed since then, the general enterprise type has not changed significantly in the past decade, and the following can be considered still current. Cowley (2014) presents data for the whole of the Katherine region, broken into five districts: Roper, Sturt Plateau, Katherine/Daly, Victoria River and Gulf. The information below comes from the Victoria River district (VRD) except where noted to be from the Katherine region as a whole (i.e. across all five districts). The VRD is an NT pastoral district aligned to property boundaries, not identical to but comparable with the Victoria catchment boundary. Although it does not follow the Victoria catchment boundary, it can be considered representative of those properties within the catchment. Further detail can be found in the companion technical report on agricultural viability and socio-economics (Webster et al., 2024). The VRD is characterised by large property sizes: most of those surveyed were between 2000 and 4000 km2, and the median paddock size was 120 km2 (Cowley, 2014). A large percentage of properties (56%) are company owned (Cowley, 2014) as distinct from ‘owner-manager’. Often, these company-owned, or ‘corporate’, properties are run within a system of other properties which allow transfer of cattle between properties and sharing of staff and resources (Cowley, 2014). Corporate properties are typically the larger properties in the VRD and contain the most cattle; therefore, the overall proportion of land area and production from the corporate properties is much larger than 56%. Owner-manager properties were more likely to consist of only one property and be run as a stand-alone enterprise. A large area of land is needed to maintain one unit of cattle (typically termed an AE, or adult equivalent). This carrying capacity of land is determined primarily by the soil (and landscape) type, the mean annual rainfall and its seasonality, and the consequent native vegetation type. NT Government estimates of carrying capacity in the Victoria River district range from a maximum of 12.5 to 23.0 AE/km2 (i.e. 8.0 to 4.3 ha/AE) on the basalt-derived cracking clays of the Wave Hill land system in ‘A’ condition (from a four point condition scale where ‘A’ is highest and ‘D’ is lowest) to a low of 0.5 AE/km2 (i.e. 200 ha/AE) on ‘C’ condition pastures of land systems within the Spinifex plains land type. Note that ‘D’ condition lands across the region have a recommended carrying capacity of zero AE/km2 (Pettit, undated). The typical beef production system is a cow-calf operation with sale animals turned off at weights to suit the live export market. About 78% of all cattle across the Katherine region were Brahman, with about another 17% being Brahman derived. The majority of surveyed properties in the VRD ran between 15,000 and 20,000 head of cattle. Most cattle in the VRD (68%) were bred for live export with 22% bred to be transferred and grown-out elsewhere. Across the broader Katherine region, 83% of cattle turned off made their way to live export, either directly or indirectly through floodplain agistment closer to Darwin, inter-company transfers or backgrounding. The most common live export destination was South-East Asia. Across the Katherine region, most of the cattle are sold off-property early in the dry season, at the time of the first round of mustering. The most common sales months were May to July, with a secondary peak in September and October (Cowley 2014). These peaks correspond to the common practice of two rounds of mustering, with the first early in the dry season and the second late in the dry season. While the cattle typically graze on native pastures, many properties supplementary feed hay to the weaner cohort, partly to train them to be comfortable around humans for management purposes and partly to add to their growth rates during the dry season when the nutritive value and total standing biomass of native pastures is falling. Urea-based supplements and supplements containing phosphorus are fed to a range of age and sex classes of the cattle. The urea-based supplements provide a source of nitrogen for cattle grazing dry-season vegetation. The phosphorus supplements, mostly provided over the wet season, are used because phosphorus is deficient in many areas yet is required for many of the body’s functions, such as building bones, metabolising food and producing milk (Jackson D et al., 2012). Supplements were fed in 89% of the properties surveyed in the VRD. Cropping Despite more than a century of trying to establish crop industries in the NT, there is still very little irrigated or dryland cropping in the Victoria catchment (0.02% of the catchment area), and it is only for property requirements. Agricultural experiments were conducted around the time of the First World War. The Second World War prompted another wave of interest in facilitating northern agricultural development, which included creating a set of agricultural experimental stations. In 1942, approval was given to establish army experimental farms at Katherine and Mataranka (east of the Victoria catchment) with the aim of more efficiently supplying the fruit and vegetables needed to maintain the nutrition of troops. The army experimental farm at Katherine was initially established to test what fruit and vegetables were suitable for the area. After the war this became the Katherine Experimental Station, where a wider range of crops was explored. This research station was run by the Australian Government until it was handed over to the NT Government in the 1980s. Several crops, such as peanuts in the 1950s, initially proved to be agronomically suitable for the local environment, but they could not be established as competitive local industries, partly because of difficulties with market access and high transport costs. The Victoria River Research Station, also known as Kidman Springs Research Station, commenced operations in 1960 and is the NT’s principal pastoral research station, carrying out research on cattle productivity and sustainability of the pastoral landscape. Aquaculture and fisheries There is currently no active aquaculture in the Victoria catchment. An application for prawn aquaculture farming by Project Sea Dragon Pty Ltd was lodged with the NT Government in 2015. Significant milestones were completed in 2020 progressing the approval process, and initial construction contracts awarded. The project is currently awaiting secure funding. A comprehensive situational analysis of the aquaculture industry in northern Australia (Cobcroft et al., 2020) identified key challenges, opportunities and emerging sectors. Offshore, the Victoria River drains into one of the most valuable fisheries in the country. The Northern Prawn Fishery (NPF) spans the northern Australian coast between Cape Londonderry in WA to Cape York in Queensland (Figure 3-10). Most of the catch is landed at the ports of Darwin, Karumba and Cairns. Over the 10-year period from 2010–11 to 2019–20, the annual value of the catch from the NPF has varied from $65 million to $124 million with a mean of $100 million (Steven et al., 2021). The Victoria catchment flows into the Joseph Bonaparte Gulf NPF region (Figure 3-10), one of the smallest regions by annual prawn catch. Australian Northern Prawn Fishery map \\FS1-CBR.nexus.csiro.au\{lw-rowra}\work\5_Agriculture_economics\2_Victoria\1_GIS\1_Map_docs\Se-V-501_Portrait_map_Australia_NPF_regions_v1.mxd For more information on this figure please contact CSIRO on enquiries@csiro.au Figure 3-10 Regions in the Northern Prawn Fishery The regions in alphabetical order are Arnhem-Wessels (AW), Coburg-Melville (CM), Fog Bay (FB), Joseph Bonaparte Gulf (JB), Karumba (KA), Mitchell (ML), North Groote (NG), South Groote (SG), Vanderlins (VL), Weipa (WA) and West Mornington (WM). Source: Dambacher et al. (2015) Like many tropical fisheries, the target species exhibit an inshore–offshore larval life cycle and are dependent on inshore habitats, including estuaries, during the postlarval and juvenile phases (Vance et al., 1998). Monsoon-driven freshwater flood flows cue juvenile prawns to emigrate from estuaries to the fishing grounds, and flood magnitude explains 30% to 70% of annual catch variation, depending on the prawn fishery region (Buckworth et al., 2014; Vance et al., 2003). Fishing activity for banana prawns and tiger prawns (Penaeus spp.), which combined constitute 80% of the catch, is limited to two seasons: a shorter banana prawn season from April to June and a longer tiger prawn season from August to November. The specific dates of each season are adjusted depending on catch rates. Banana prawns generally form the majority of the annual prawn catch by volume. Key target and by-product species are detailed by Woodhams et al. (2011). The catch is often frozen on-board and sold in domestic and export markets. The NPF is managed by the Australian Government (via the Australian Fisheries Management Authority) through input controls, such as gear restrictions (number of boats and nets, length of nets) and restricted entry. Initially comprising over 200 vessels in the late 1960s, the number of vessels in the NPF has reduced to 52 trawlers and 19 licensed operators after management initiatives including effort reductions and vessel buy-back programs (Dichmont et al., 2008). Given recent efforts to alleviate fishing pressure in the NPF, there is little opportunity for further expansion of the industry. However, it is generally recognised that development of water resources in the Victoria catchment would need to consider the downstream impacts on prawn breeding grounds and the NPF. Mining Mining includes extraction of minerals (including coal), petroleum and gas, and quarrying. Despite mining (minerals) and petroleum production contributing $4.4 billion and $228 million, respectively, to the NT economic output (NT Department of Treasury and Finance, 2023), no mine or petroleum projects are currently operating in the Victoria catchment. Nonetheless, approximately 61% of the Victoria catchment is covered by either mineral or petroleum exploration licence with areas without exploration licences predominantly being inside Judbarra National Park and the Bradshaw Field Training Area (Figure 3-11). Commodities, including critical and strategic minerals identified as occurring within the Victoria catchment, are mainly lead and copper in the centre of the catchment, manganese in the east and zinc in the far north-west. Several occurrences of barite have been identified in the catchment. The NT Government has programs to attract investment in critical mineral exploration and infrastructure. Water is central to the minerals and petroleum industries. Mining uses water in a variety of ways, including for transporting materials, chemical or physical processing, cooling, disposing of and storing waste materials, washing, and suppressing dust. Potable water is used in areas that house mining staff (Prosser et al., 2011). Water is also extracted or ‘used’ during de-watering at mines that extend below the water level. Petroleum companies, which use relatively small volumes of water, produce water as a by-product of extraction. Water extracted during de-watering or as a by-product of petroleum extraction must be safely discharged and may need treatment. Water consumption at mining operations is highly variable (Table 3-7). The variations are due to a range of factors, including different mining methods, ore types, ore grades, processing treatments and definitions of water usage. The overall water balance on a site depends on climate conditions, which affect water availability at the site, and the ability to reuse and recycle water within processing facilities (Northey and Haque, 2013). While not mined in the Victoria catchment, coal is by far the largest user of water in the mining sector. The water used by mining enterprises does not need to be of potable quality. Table 3-7 Global water consumption in the mining and refining of selected metals PROCESSING STAGE MEAN WATER CONSUMPTION* (M3/TONNE OF METAL) RANGE OF WATER CONSUMPTION§ (M3/TONNE OF METAL) Copper concentrate† 43.235 9.673–99.550 Lead concentrate† 6.597 0.528–11.754 Zinc concentrate† 11.93 11.07–24.65 Manganese concentrate† 1.404 1.390–1.410 Uranium concentrate (U3O8)† 2,746 46.2–8207 Gold metal‡ 265,861 79,949–477,000 Platinum metal‡ 313,496 169,968–487,876 Palladium metal‡ 210,713 56,779–327,874 †Metal concentrates are typically produced at the site where the ore is mined. ‡Includes mining, smelting and refining of pure metals, assuming mining and processing are all located within a single region or separate regions but with similar water characteristics,. *Mean water consumption value per tonne of metal equivalent in the concentrates or refined metals. §Minimum and maximum water consumption value per tonne of metal equivalent in the concentrates or refined metals. Source: Meissner (2021) Because water is typically a very small fraction of total input cost, and mining produces high-value products, mining enterprises usually develop their own water supplies, which are often regulated separately to the water entitlement system (Prosser et al., 2011). Based on the mineral occurrences in the Victoria catchment (Figure 3-11), potential water demands by mining are likely to be modest. \\FS1-CBR.nexus.csiro.au\{lw-rowra}\work\10_Reporting\2_Victoria\1_GIS\1_Map_Docs\1_Export\CR-V-512_Vic_Mineral_Occurences_and_exploration_v2.png Figure 3-11 Main commodity mineral occurrences and exploration tenements in the Victoria catchment Source: NT Geological Survey (2024) Tourism The Victoria catchment has a relatively low volume of tourist visitation, due largely to its remoteness, sparse population and little tourism development (Tourism NT, 2023). Most of these tourism visits are from self-drive tourists along the Victoria Highway (part of National Highway 1), which traverses the northern part of the catchment. Timber Creek is the gateway to Judbarra National Park (Figure 3-9) and Jasper Gorge (Figure 3-12) and is an important half-way stopping point between Katherine (289 km east) and Kununurra (226 km west). For more information on this figure please contact CSIRO on enquiries@csiro.au Figure 3-12 Jasper Gorge is seasonally accessible on the Buchanan Highway Source: CSIRO Access to much of the Victoria catchment north and south of the Victoria Highway is via unsealed roads that usually require four-wheel-drive (4WD) vehicle access. The nearest domestic airports to the Victoria catchment are located in Darwin and Katherine in the NT and Kununurra in WA. Airstrips for public use are at Timber Creek, Victoria River Downs Station and Kalkarindji. Major attractions in the Victoria catchment include the scenic Judbarra National Park, the second- largest national park in the NT (Tourism NT, 2024a), and fishing in the Victoria River and major tributaries. Fossicking is promoted as a popular activity near Kalkarindji, a locality known for an abundance of geodes on the ground (NT Government, 2016). As well as economic and employment opportunities, tourism can cause impacts such as native habitat loss, and foot traffic, bikes or vehicles may cause environmental damage such as erosion and a loss of amenity to local residents (Larson and Herr 2008). Other risks include the spread of weeds (Section 7) and root rot fungus (Phytopthora cinnamomi) carried on vehicles and people (Pickering and Hill, 2007). The Victoria River SA2 region (Figure 3-8), which closely corresponds to the Victoria catchment, received 27,000 visitors in the year ending December 2022 (Tourism NT, 2023), about 9% of the 287,000 visitors to the Katherine Daly tourism region (Figure 3-8). Visitor expenditure in the Victoria catchment was estimated at no more than $20 million/year. Across the broader Katherine Daly region (Figure 3-8), which encompasses the Victoria catchment, only 1% of visitors were of international origin, while 62% were from within the NT and 37% were from interstate. Of the intra-territory and interstate visitors, 43% and 21%, respectively, were travelling for business. Like in much of northern Australia, high summer temperatures and humidity, and wet-season rains, mean that most tourists visit during the drier, cooler months between May and October (Tourism NT, 2024b). Tourist visits across the Katherine Daly region pre-COVID-19 show peak visitation (between 33% and 45% depending on origin – interstate, intrastate or international) during the September quarter (dry season), and least visitation (between 5% and 13% depending on origin) during the March quarter (wet season) (Tourism NT, 2019). However, the lack of all- weather sealed roads in the Victoria River SA2 means tourism in the Victoria catchment is likely to be considerably more seasonal than in the broader region. In the broader region, the data are highly skewed to Katherine, which accounted for approximately half the visitors to the Katherine Daly region pre-COVID-19. For the 3-year reporting period to the end of 2022, approximately 34% of overnight visitors to the Katherine Daly tourism region visited national parks, while 12% participated in fishing, 10% took part in charter boat or river cruise tours, and 9% participated in Indigenous cultural experiences (of these last two activities, there are currently no businesses in the Victoria catchment). Fishing is one of the Victoria catchment’s biggest drawcards. A pre-COVID-19 profile of the Victoria Daly region local government area indicates that 20 tourism businesses were operating in this region at the time of their 2019 survey. Of these 20 businesses, 12 were ‘non-employing’, four had fewer than five employees and three had more than 20 employees (Tourism Research Australia, 2019). Tourism development opportunities and considerations The state of northern Australia’s tourism economy is closely tied to the state of its ecosystems (Prideaux, 2013). With a large proportion of the Victoria catchment in a relatively ‘natural’ state, there is potential for growth in nature-based tourism. However, like other remote areas of northern Australia, the region’s remoteness and distance from urban centres (Bugno and Polonsky, 2024), lack of supporting infrastructure, limited human capital and financial resources, and low awareness of tourism system characteristics (Summers et al., 2019) considerably constrain its potential. The seasonality of visitation also limits enterprise profitability (Bugno and Polonsky, 2024) and permanent employment opportunities. Also important to consider is that much of the catchment’s appeal to self-drive visitors is likely to be the absence of human presence and commercial infrastructure, which present opportunities for exploration and solitude (Lane and Waitt, 2007; Ooi and Laing, 2010). Hence, development that alters the region’s current characteristics could be alienating to some current visitor markets. While water resource development for agriculture has the potential to negatively affect tourism and future opportunities in the Victoria catchment, for example, through declining biodiversity and perceived reduced attractiveness (Pickering and Hill, 2007; Prideaux, 2013), such development may present opportunities to foster tourism growth. For example, Lake Argyle in the East Kimberley region (WA), developed as an irrigation dam to supply the Ord River Irrigation Area, is now advertised as being one of northern WA’s major attractions. It offers a wide range of tourism activities and hosts a diversity of wildlife (https://www.australiasnorthwest.com/explore/kimberley/lake-argyle/). While visitors to the Kimberley region reportedly perceived Lake Argyle in the same way they perceived some ‘natural’ local attractions such as billabongs, irrigated agriculture of the Ord River Irrigation Area is perceived differently, as being ‘domesticated’ (Waitt et al., 2003). Elsewhere in northern Australia, water resource infrastructure, including Fogg Dam (NT), Tinaroo Dam (Queensland) and Lake Moondarra (Queensland), has resulted in increased visitation by tourists for the enhanced wildlife or recreation opportunities they provide. However, the ongoing contributions of dam to their local economies vary. For example, the value of recreational fishing varies between dams depending upon whether there are other dams nearby and their proximity to tourism traffic (Rolfe and Prayaga, 2007). The relatively low visitation to the Victoria catchment suggests that the recreational fishing value of a new dam in the Victoria catchment would be limited, particularly in those parts of the Victoria catchment near Lake Argyle. Agritourism opportunities, for example, through accommodation on pastoral properties and other travel support (fuel), offer an opportunity for revenue diversification, although impediments such as highly variable seasonal demand limit profitability (Bugno and Polonsky, 2024). Tourism has the potential to enable economic development within Indigenous communities because Indigenous tourism enterprises, usually microbusinesses, often have some competitive advantages (Fuller et al., 2005). Successful tourism developments in regional and very remote areas such as the Victoria catchment are highly likely to depend on establishing private and public sector partnerships, ensuring effective engagement and careful planning with Traditional Owners and regional stakeholders, and building interregional network connectivity and support (Greiner, 2010; Lundberg and Fredman, 2012). Given the importance of climate on tourism seasonality, demand and travel patterns in northern Australia (Hadwen et al., 2011; Kulendran and Dwyer, 2010), the increased temperatures and occurrence of extreme weather-related events (e.g. drought, flood, severe fires and cyclones) associated with climate change are likely to be significant threats to the industry in the future. These will likely negatively affect tourist numbers, the length and quality of the tourist season, tourism infrastructure including roads, and the appeal of the landscape and its changing biodiversity (Amelung and Nicholls, 2014; Prideaux, 2013). 3.3.4 Current infrastructure Transport The Victoria catchment is serviced by two significant roads: the Victoria and Buntine highways (Figure 3-13). The Victoria Highway is one of many highways that make up Australia’s National Highway 1. It runs east−west for a distance of 557 km, linking the Stuart Highway (the major north−south highway through the centre of Australia) at the town of Katherine to the Great Northern Highway west of Kununurra in WA. Although sealed and well trafficked by both tourist and commercial vehicles (Figure 3-13), few services exist on this route within the catchment. Groceries and fuel can be purchased from smaller stores at locations such as Timber Creek, Kalkarindji and Yarralin. Roadhouses at Victoria River Roadhouse and Top Springs also supply fuel. Flooding causes road closures during the wet season. The Buntine Highway leaves the Victoria Highway just outside the north-east of the catchment and travels through Top Springs and Kalkarindji (sealed) before crossing into WA (unsealed west of Kalkarindji), where it intersects Duncan Road, which continues to Halls Creek. The Buntine Highway carries more commercial traffic than the Victoria Highway (Figure 3-18), largely to service the cattle industry. It provides access to Victoria River Downs Station and other stations in the central and east of the catchment and is also a popular tourist route through the scenic Jasper Gorge. Apart from these highways, the Victoria catchment is serviced by a sparse network of mainly unsealed roads, all subject to flooding and wet-season closures. Figure 3-13 shows the network of roads within the Victoria catchment categorised by rank and type of road surface. All road network information in this section is from spatial data layers in the Transport Network Strategic Investment Tool (TraNSIT; Higgins et al., 2015). Figure 3-14 shows the heavy vehicle access for roads within the Victoria catchment, as determined by the National Heavy Vehicle Regulator. Type 2 road trains are vehicles up to 53 m in length, typically a prime mover pulling three 40-foot (approximately 12 m) trailers (Figure 3-15). The Victoria, Buntine and Buchanan highways are the only roads in the catchment classified to carry Type 2 road trains (Figure 3-14). However, Type 2 road trains can also access all unclassified non- residential roads in the study area. Despite the poorer road conditions of many of the local unsealed roads, large (Type 2) road trains are permitted due to minimal safety issues from low traffic volumes and minimal road infrastructure restrictions (e.g. bridge limits, intersection turning safety). Drivers would regularly use smaller vehicle configurations on the minor roads due to the difficult terrain and single lane access, particularly during wet conditions. Figure 3-17 shows the mean speed achieved for freight vehicles for the road network. The road speed limits are usually higher than the mean speed achieved for freight vehicles, particularly on unsealed roads. Heavy vehicles using unsealed roads would usually achieve mean speeds of no more than 60 km/hour, and often lower when transporting livestock. The nearest access to a good-quality standard-gauge rail is outside the catchment at Katherine in the east. This provides freight access to Darwin Port (East Arm Wharf) to the north and to major southern markets via Alice Springs. The rail line is primarily used for bulk commodity transport (mostly minerals) to Darwin Port. There are no branch lines in the Victoria catchment, so goods must be transported to and from loading points by road. Road rankings map \\FS1-CBR.nexus.csiro.au\{lw-rowra}\work\5_Agriculture_economics\2_Victoria\1_GIS\1_Map_docs\Se-V-508_TraNSIT_road rankings_v1.mxd For more information on this figure please contact CSIRO on enquiries@csiro.au Figure 3-13 Road rankings and conditions for the Victoria catchment Rank 1 = well-maintained highways or other major roads, usually sealed; Rank 2 = secondary ‘state’ roads; Rank 3 = minor routes, usually unsealed local roads. The ‘Rank 1’ road is the Victoria Highway, which runs from Katherine (in the east) to Kununurra (in WA). Truck class map \\FS1-CBR.nexus.csiro.au\{lw-rowra}\work\5_Agriculture_economics\2_Victoria\1_GIS\1_Map_docs\Se-V-509_TraNSIT_truck type_v1.mxd For more information on this figure please contact CSIRO on enquiries@csiro.au Figure 3-14 Roads accessible to Type 2 vehicles across the Victoria catchment: minor roads are not classified Type 2 vehicles are illustrated in Figure 3-15. For more information on this figure, please contact CSIRO on enquiries@csiro.au Figure 3-15 Common configurations of heavy freight vehicles used for transporting agricultural goods in Australia Figure 3-16 Road condition and distance to market impact the economics of development in the Victoria catchment Photo: CSIRO – Nathan Dyer Road speed map \\FS1-CBR.nexus.csiro.au\{lw-rowra}\work\5_Agriculture_economics\2_Victoria\1_GIS\1_Map_docs\Se-V-510_TraNSIT_road speed_v2.mxd For more information on this figure please contact CSIRO on enquiries@csiro.au Figure 3-17 Mean speed achieved for freight vehicles on the Victoria catchment roads Source: Spatial dataset of the location and attributes of roads and ferries sourced from HERE Technologies (2021) Supply chains and processing Table 3-8 provides the volumes of commodities annually transported into and out of the Victoria catchment, and Figure 3-18 shows the locations of existing pastoral enterprises in the catchment and trucking movements on regional roads. As previously noted, agricultural production is currently dominated by beef cattle. This is reflected in the annual volumes of commodities transported across the road network with large volumes of freight transporting cattle, mainly via the Buntine Highway. Live export of cattle via Darwin Port accounts for most cattle movements, but there are also substantial transfers of cattle between properties and smaller volumes directed to domestic markets via abattoirs and feedlots. Table 3-8 Overview of commodities (excluding livestock) annually transported into and out of the Victoria catchment Indicative transport costs are means for each commodity and include differences in distances between source and destinations. For more information on this figure or table please contact CSIRO on enquiries@csiro.au Source: 2021 data from TraNSIT (Higgins et al., 2015) There are currently no processing facilities for agricultural produce within the Victoria catchment. The Katherine cotton gin, the nearest processing facility, will see its first season of operation in 2024 and could support producers in the catchment. Dryland and irrigated agriculture (0.02% of the catchment) is currently solely for property requirements. The closest meatworks was run by Australian Agricultural Company at Livingstone, about 40 km south of Darwin, but has not operated since 2018. When operating, the meatworks had all-weather road access by large (Type 2)road trains from the Victoria catchment boundary. The closest port for bulk export of agricultural produce from the Victoria catchment is in Darwin. Darwin Port, operated by Landbridge Group, handles about 20,000 to 30,000 20-foot equivalent units each year, split roughly evenly between imports and exports. The main exports are dry bulk commodities (mainly manganese) and livestock, but there are also exports of agricultural produce in refrigerated containers. Exports of new bulk agricultural produce would require construction of a new storage facility. As export opportunities arise, the Port of Wyndham, 334 km west of Timber Creek in WA, may develop and provide these services. Truck volume map \\FS1-CBR.nexus.csiro.au\{lw-rowra}\work\5_Agriculture_economics\2_Victoria\1_GIS\1_Map_docs\Se-V-511_TraNSIT_ag enterprises_v3.mxd For more information on this figure please contact CSIRO on enquiries@csiro.au Figure 3-18 Annual amounts of trucking in the Victoria catchment and the locations of pastoral properties The thickness of purple lines indicates the volume of traffic (as number of trailers per year) on regional roads connecting local properties. Energy The Victoria catchment is in a very remote part of the NT that does not have access to major electricity networks, and the small communities rely on diesel generators or hybrid diesel – solar photovoltaic systems provided by Power and Water Corporation. The two largest off-grid remote communities in the Victoria catchment rely on hybrid systems powered by diesel generators supplemented with solar: Kalkarindji (408 kW solar system) and Timber Creek. Distribution lines link nearby smaller settlements to these off-grid sources of electricity, in the Victoria catchment Daguragu is connected to Kalkarindji. The largest electricity network in the NT is the Darwin–Katherine Interconnected System (DKIS), which connects the capital of Darwin to Katherine further south by a 132 kV transmission line (Figure 3-19). Katherine is about 200 km from the Victoria River Roadhouse in the north-east of the catchment. Even if transmission lines were to connect the Victoria catchment to the DKIS, the DKIS is electrically isolated from other grids in Australia (see inset in Figure 3-19 for NT electricity and natural gas transmission system interconnections), so hence any large-scale electrical generation infrastructure in the Victoria catchment would still be disconnected from the National Electricity Market. Historically, gas pipelines have been a cheaper way of transporting energy than electrical transmission lines (DeSantis et al., 2021; GPA Engineering, 2021). Consequently, a network of natural gas pipelines has been a cost-effective way of linking energy supplies across the NT by connecting sources of gas to electricity generators and other demand centres. However, gas power generation is not available in the Victoria catchment. The Amadeus Gas Pipeline is a bi- directional pipeline running from the gas fields of the Amadeus Basin near Alice Springs in the south northwards to Darwin (Figure 3-19). The McArthur River Pipeline connects to the Amadeus Gas Pipeline at Daly Waters and runs east to the generator at the McArthur River Mine (zinc and lead). The Northern Gas Pipeline, which runs 622 km between Tennant Creek in the NT and Mount Isa in Queensland (south of the Victoria catchment), provides a connection between the energy systems of the NT and the eastern states. Power generation and transmission map \\FS1-CBR.nexus.csiro.au\{lw-rowra}\work\5_Agriculture_economics\2_Victoria\1_GIS\1_Map_docs\Se-V-507_energy generation distribution_v2.mxd For more information on this figure please contact CSIRO on enquiries@csiro.au Figure 3-19 Electricity generation and transmission network in the Victoria catchment Distribution networks are not shown, but communities marked with red lightning symbols are connected to nearby generation or transmission sources of electricity. The inset shows the pipeline and transmission network across the Northern Territory with the Amadeus Gas Pipeline running north–south (bi-directional) through Katherine. Renewable energy potential in the Victoria catchment The Victoria catchment has some of the best solar resources in Australia and a low to modest wind resource relative to other locations in Australia. A convenient metric for comparing renewable energy technologies is using the capacity factor of an energy plant, which is the ratio of electricity generated over one year to the nameplate capacity of the solar or wind farm. For example, for a capacity factor of 0.25, each 1 MW of a solar or wind farm will generate about 2190 MWh of electricity per year. In the Victoria catchment, solar photovoltaic capacity factors are uniformly high, ranging between 0.24 and 0.25. In contrast, in southern Australia and along the east coast the capacity factor can be as low as 0.12 (Figure 3-20). Wind resources for the Victoria catchment are shown in Figure 3-21 as a capacity factor at a turbine hub height of 150 m, which is a typical height for a commercial wind turbine. Although wind capacity factors in the Victoria catchment are comparable to solar capacity factors, wind farms have a higher capital cost, which can result in a higher cost of electricity production. This is particularly the case for smaller wind turbines than those whose results are shown in Figure 3-21. The generation capacity of these smaller turbines is more likely to be commensurate with the energy requirements of a farm-scale irrigation enterprise. Furthermore, solar is modular and scalable and is easier to maintain in remote locations than wind turbines. Wind energy is a relatively mature technology, and projections of the levelised cost of wind in 2040 suggest that its cost is plateauing. In contrast, solar photovoltaic is projected to steadily decrease such that by 2040 the levelised cost of solar photovoltaic would be 26% to 34% lower than the cost of wind on average (Graham et al., 2023). At Timber Creek in the Victoria catchment it was found that, based on current capital costs and diesel cost of $1.50/litre (including any rebate), diesel generators were the most cost-effective technology for supplying power to farm infrastructure requiring electricity 24 hours/day or requiring electricity for 30% or fewer days per year. For farm infrastructure operating more than 50% days of the year, and for 12 hours/day or less, a hybrid diesel – solar photovoltaic farm with the renewable fraction between 50% and 75% is the most cost-effective technology. The exception is for farm infrastructure requiring electricity for 4 hours/day and 365 days/year, for which a 100% solar photovoltaic farm (with batteries) was most the cost-effective way to provide power. Under a higher cost of diesel ($2.50/litre including rebates), the results were similar except a 100% renewable system with batteries was most cost-effective when electricity had to be supplied for 80% of days or more. By 2040, it was projected that hybrid diesel – solar photovoltaic systems (with batteries) were most cost-effective when farm infrastructure was operated for 30% of days/year or higher for 12 to 24 hours/day, or 10% of days/year when only operated for a maximum of 4 hours/day. See the companion technical report on techno-economic analysis of electricity supply (Graham, 2024) for more detail. Solar photovoltaic capacity map \\FS1-CBR.nexus.csiro.au\{lw-rowra}\work\5_Agriculture_economics\2_Victoria\1_GIS\1_Map_docs\Se-V-515_Solar_V3.mxd For more information on this figure please contact CSIRO on enquiries@csiro.au Figure 3-20 Solar photovoltaic capacity factors in the Victoria River catchment Inset shows solar photovoltaic capacity factors across Australia. Note: the inset map uses a different colour ramp. Wind capacity map \\FS1-CBR.nexus.csiro.au\{lw-rowra}\work\5_Agriculture_economics\2_Victoria\1_GIS\1_Map_docs\Se-V-516_Wind_V3.mxd For more information on this figure please contact CSIRO on enquiries@csiro.au Figure 3-21 Wind capacity factors in the Victoria River catchment Inset shows wind capacity factors across Australia. Note: the inset map uses a different colour ramp. Water Most communities in the Victoria catchment source their stock, domestic and community water supplies from groundwater. Surface water is also pumped from streams for stock and domestic use, and also from a few dams for use in agriculture and aquaculture. There are no major water transmission pipelines in the catchment and only a few small dams, except for Forsyth Creek Dam which holds up to 35 GL (CO2 Australia Pty Ltd, 2016). Almost all water use in the catchment occurs outside water control districts or water allocation plan areas. The Victoria catchment mostly lies to the west of the Daly Roper Beetaloo Water Control District, though a small portion of the district occupies the eastern margin of the catchment to the north and south of Top Springs (Figure 3-22). The only water allocation plan currently applicable to the Victoria catchment is the Georgina Wiso Water Allocation Plan, which coincides with a small portion of the eastern margin of the catchment to the east of Top Springs (Figure 3-22). Surface water entitlements Licensed surface water entitlements are sparse across the Victoria catchment. Four surface water licences have been granted for a combination of use for agriculture and aquaculture, all occurring in the northern parts of the catchment (Figure 3-22). The largest entitlement (of 100 GL/year) is for use in aquaculture with the water sourced from Forsyth Creek near the mouth of the Victoria River (Figure 3-22). The second-largest entitlement is 50 GL/year for use in agriculture with the water sourced from Forsyth Creek Dam in the upper reaches of Forsyth Creek in the north-western part of the catchment (NT Department of Environment, Parks and Water Security, 2018). Two smaller surface water entitlements exist for agricultural use: one sourced from Weaner Dam (1.2 GL/year) in the north-western Victoria catchment and the other from the Victoria River (0.7 GL/year) in the northern Victoria catchment (Figure 3-22). Groundwater entitlements There are currently no licensed groundwater entitlements in the Victoria catchment. However, there are three licensed entitlements totalling 7.4 GL/year for use in agriculture to the north-east of the Victoria catchment, occurring in the proposed Flora Tindall Water Allocation Plan area (NT Department of Environment, Parks and Water Security, 2018). The groundwater is sourced from the Tindall Limestone Aquifer, which is connected to the limestone aquifer hosted in the Montejinni Limestone along the eastern margin of the Victoria catchment. However, the closest of the three licensed bores occur far outside of the Victoria catchment, approximately 110 km to the north-east of the Victoria River Roadhouse, and approximately 150 km to the north-east of Top Springs. The Montejinni Limestone hosts the largest and most productive regional-scale groundwater system in the catchment. Groundwater resources from a variety of local- to intermediate-scale groundwater systems hosted mostly in fractured and weathered rock aquifers provide important sources of community water supplies. The annual volume of groundwater extracted for community water supplies is only small (i.e. <0.2 GL/year), so a groundwater licence is not required (Figure 3-22). Groundwater is also widely used across the catchment in small quantities for stock and domestic water supplies for which a groundwater licence is also not needed. For more information on groundwater resources of the Victoria catchment, see the companion technical report on hydrogeological assessment by Taylor et al. (2024). \\FS1-CBR.nexus.csiro.au\{lw-rowra}\work\11_Groundwater\2_Victoria\1_GIS\1_Map_docs\1_Export\Gr-V-522_water_allocation_v8.png For more information on this figure please contact CSIRO on enquiries@csiro.au Figure 3-22 Location, type and volume of annual licensed surface water and groundwater entitlements Data source: Water allocation plan areas and the Daly Roper Beetaloo Water Control District sourced from the NT Department of Environment, Parks and Water Security (2024a, 2024b) Community infrastructure The availability of community services and facilities in remote areas can play an important role in attracting people to or deterring people from living in those areas. Development of remote areas, therefore, needs to consider whether housing, education and health care are sufficient to support the anticipated growth in population and demand, or to what extent these would need to be expanded. There are no hospitals in the Victoria catchment, but like most remote parts of Australia, the area is serviced by a primary health network (PHN). Australia is divided into 31 PHNs, and one of these covers the whole of the NT. General practitioners and allied health professionals provide most primary health care in Darwin and the regional centres within the NT PHN, while smaller communities are supported by remote health clinics (NT Primary Health Network, 2020). The Victoria catchment falls within the Katherine Health Service District (HSD) (also known as the Big Rivers Region) of the NT PHN where the Sunrise Health Service Aboriginal Corporation and Katherine West Health Board provide remote health services. PHNs work closely with local hospital networks, and for the Katherine/Big Rivers Region the associated hospital is Katherine Hospital, which is located approximately 150 km by road outside the eastern border of the Victoria catchment. This hospital has 60 beds and provides emergency services, surgical and medical care, paediatrics and obstetrics (NT Primary Health Network, 2020). There are three health centres in the Victoria catchment (Kalkarindji, Timber Creek and Yarralin) staffed daily, and health clinics in four communities (Amanbidji, Bulla, Lingara and Nitjpurru (Pigeon Hole)). A network of six government schools covers the small communities throughout the Victoria catchment. A total of 321 full-time equivalent (FTE) students are enrolled in these schools with 40.3 teachers (FTE) in 2022 (Table 3-9). The largest school in the catchment is at Kalkarindji. There are a further six schools in Katherine, outside the Victoria catchment and about 290 km north-east of Timber Creek, and there is also a school of the air in Katherine that serves 183.1 students (FTE) across the region. Table 3-9 Schools servicing the Victoria catchment For more information on this figure or table please contact CSIRO on enquiries@csiro.au For more information on this figure or table please contact CSIRO on enquiries@csiro.au †FTE = full-time equivalent. Source: ACARA (2023) (data presented with permission) At the time of the 2021 Census, about 22% of private dwellings were unoccupied, which is higher than the national and NT means, although the absolute number of unoccupied dwellings is small (Table 3-10). This suggests that the current pool of housing may have some capacity to absorb small future increases in population, notwithstanding natural disasters such as fire and flooding as experienced in 2023 and 2024. Table 3-10 Number and percentage of unoccupied dwellings and population for the Victoria catchment For more information on this figure or table please contact CSIRO on enquiries@csiro.au †Weighted averages of scores for SA2 regions falling wholly or partially within the catchment boundary. Source: ABS (2021) Census data 3.4 Indigenous values, rights, interests and development goals 3.4.1 Introduction and research scope This section gives an overview of the information needed on Indigenous water issues in the Assessment area to provide foundations for further community and government planning and decision making. It provides some key background information about the Indigenous Peoples of the Victoria catchment and their specific values, rights, interests and goals in relation to water and irrigated agricultural development. Unless otherwise stated, the material in this section is based on findings described in the companion technical report on Indigenous values, rights, interests and development goals (Barber et al., 2024). Indigenous Peoples represent a substantial and growing proportion of the population across northern Australia, and they have secured rights and interests in over 70% of the land. They control significant natural and cultural resource assets, including land, water and coastlines. Indigenous Peoples are crucial owners and will increasingly become critical partners, co-investors and stakeholders in future development. Understanding the past is essential to understanding present circumstances and forms of organisation to engage with development options and future possibilities. The material provided here begins with historical information and a description of the contemporary ownership of the Assessment area. Section 3.4.2 describes the past habitation by Indigenous Peoples, the significance of water in habitation patterns, and the impact of exploration and colonisation processes. Section 3.4.3 reviews the contemporary situation with respect to Indigenous Peoples’ residence, land ownership and access. Section 3.4.4 outlines Indigenous water values and responses to development, and Section 3.4.5 describes Indigenous-generated development objectives. There has been some previous publicly available information about Indigenous connections to land and waters in the Victoria catchment, but there is far less consideration of Indigenous perspectives on general water development and associated irrigated agricultural development in the catchment. The Assessment technical report directly addresses these data needs (Barber et al., 2024). Engagement with Indigenous Peoples is a strong aspiration across governments and key industries. Nevertheless, models of engagement vary considerably, and competing understandings of what ‘engagement’ means (e.g. consultation, involvement, partnership) can substantially affect successful outcomes. Standard stakeholder models can also marginalise Indigenous Peoples’ interests, reducing what Indigenous Peoples understand as prior and inalienable ownership rights to a single ‘stake’ equivalent to all others at the table. Guided by advice from the Northern Land Council (NLC) and the Central Land Council (CLC), the Assessment undertook one-on-one and small group interviews with 19 predominantly senior Traditional Owners from within the Victoria catchment to establish a range of views regarding water and agricultural development. Comments from these interviews were analysed and major themes and issues identified. The Assessment does not try to facilitate or provide Traditional Owner group positions about any of the issues raised and is not a substitute for formal processes required by cultural heritage, environmental impact assessment, water planning or other government legislation. Nevertheless, the Assessment identifies key principles, important issues and potential pathways to guide future planning and formal negotiations with Traditional Owners. 3.4.2 Pre-colonial and colonial history Pre-colonial Indigenous societies Northern Australia contains archaeological evidence of Indigenous habitation stretching back many thousands of years (Clarkson et al., 2017). Resource-rich riverine habitats were central to Indigenous economies based on seasonally organised hunting, gathering and fishing. Rivers were also major corridors for social interaction, containing many sites of cultural importance (Barber and Jackson, 2014; McIntyre-Tamwoy et al., 2013). Pre-colonial Indigenous societies are characterised by long residence times; a detailed knowledge of ecology and food gathering techniques; complex systems of kinship and territorial organisation; and a sophisticated set of religious beliefs, referred to by Traditional Owners in the Victoria catchment as the Dreaming. These Indigenous religious cosmologies provide a source of spiritual and emotional connection as well as guidance on identity, language, law, territorial boundaries and economic relationships (Rose, 2011; Strang, 1997; Williams, 1986). From an Indigenous perspective, ancestral powers are present in the landscape in an ongoing way, intimately connected to people, Country and culture. Mythological creators have imbued significance to places through creation, leaving evidence of their actions and presence through features in the landscape (Rose, 2011). Totemic figures can be animals or plants, take human-like or inanimate object form, or be sentient beings that have agency to act (Rose 2011; Peterson, 2013). Those powers must be considered in any action that takes place on Country. Colonisation European colonisation resulted in significant levels of violence towards Indigenous Peoples with consequent negative effects on the structure and function of existing Indigenous societies across the continent. Overt violence, armed defensiveness and avoidance were all evident in colonial relationships as hostilities occurred as a result of competition for land and water resources, colonial attitudes and cultural misunderstandings. Following a number of visits by explorers earlier in the 1800s, pastoralism commenced seriously in the Victoria catchment in the 1880s, and the large and high-profile Victoria River Downs Station and the nearby Wave Hill Station were both established in 1883 (Lewis, 2012). Pastoral homesteads and outstations were sited close to permanent water and on the fertile plains and river valleys used by Indigenous Peoples for food and other resources (Lewis, 2012; McGrath, 1987). Indigenous attacks on colonial pastoral operations were made both in retaliation for past attacks by colonists and as a response to shortages of food and other resources. Major killings are recorded in both historical documentation and oral histories, and massacres and violent encounters in the early colonial period in the Victoria catchment have received some attention (Lewis, 2012; Rose, 2011; Ryan et al., 2018). The police station at Timber Creek was established in 1898 as one response to the serious situation. However, some police employees were involved in the violence, and there were further massacres in the twentieth century (Lewis, 2012). Figure 3-23 shows the locations of some key colonial massacre sites in the Victoria catchment. To ensure their safety, Indigenous Peoples were obliged to move to cattle stations and mission settlements. The stations became places for enforced dependence and colonial influence in order to both control people and protect cattle (Hokari, 2011; Rose, 2011). Poor conditions on pastoral stations were ubiquitous, and at Wave Hill Station, the combination of pastoral exploitation and a desire to control their own lands led to the local Gurindji stockmen going on strike and walking off the property in 1966 (Hardy, 1968; Ward, 2016). The Wave Hill Walk-off and associated strike lasted 7 years and was a crucial part of the wider momentum for Indigenous rights and recognitions in the 1960s and early 1970s that led to the recognition of Aboriginal land rights through the ALRA. The formation or major expansion of the townships of Kalkarindji, Daguragu and Yarralin all date from this significant period of social change (Rose, 2011; Ward, 2016). \\FS1-CBR.nexus.csiro.au\{lw-rowra}\work\6_Indigenous\2_Victoria\1_GIS\1_Map_docs\1_Exports\Ind-V-501_Massacres_v1_CR.png Figure 3-23 Colonial frontier massacres in the Victoria catchment Source: Ryan et al. (2018, 2022). 3.4.3 Contemporary Indigenous ownership, management, residence and representation Despite the pressures entailed by colonisation, Country remained crucial to Indigenous Peoples’ lives, sustaining distinct individual and group identities as well as connections to past ancestors and future descendants. People are connected to places through a combination of genealogical, traditional and residential ties. Only some of these connections are formally recognised by the Australian state. Traditional Ownership Traditional Ownership of the Victoria catchment is complex and diverse, encompassing large language groups divisible into related groups and subgroups. Ownership patterns tend to follow natural landscape features, such as rivers and hills, as well as formal boundaries between ownership groups where these have been negotiated. In other places, the edges of group territories are less distinct, and there may be shared territory or overlapping claims. Information regarding the identification of potential owners and interest holders is provided by registered organisations such as the NLC, CLC and the Aboriginal Areas Protection Authority (AAPA). Key language group names used publicly include the Gurindji and Ngarinyman in the southern and central parts of the catchment, Ngaliwurru and Nungali in the Timber Creek area, and Miriuwung and Gajerrong groups in the west. The ALRA provides a standardised form of inalienable collective freehold ownership across significant parts of the NT. The Act grants strong rights that are held and managed by Aboriginal Land Trusts that represent the Traditional Owners. Thirty-one per cent of the land tenure underlying the Victoria catchment is held under the land rights regime (Figure 3-24). However, over half of this overall holding comprises the Judbarra National Park, which is overlaid by a 99- year lease with the NT Government. The lease provides for joint management by Traditional Owners and the government and creates a very different public access regime than the stringent access permit system that operates on conventional land rights land. Consequently, Traditional Owners do not have the same direct control, unimpeded access, ability to exclude others, or amenity and privacy on national park ALRA land as they do on standard ALRA land. Across the whole of Australia, the primary form of recognition for Indigenous Peoples’ rights and interests is the Commonwealth Native Title Act 1993. In the NT, the native title system has primarily been used to secure rights for Traditional Owners in circumstances where the ALRA is not applicable. This is because native title does not provide a strong standard set of rights – rather, each native title determination outlines specific rights that were able to be determined (proven in court) in that particular case. A determination may only recognise very limited rights, such as access for specific cultural purposes under certain conditions, or it may encompass strong rights such as exclusive possession. This variability means that considerable caution should be used in interpreting a map showing substantial areas of determined native title, such as Figure 3-25. The areas may indicate constrained and specific rights to access and consultation, which is very different to the inalienable freehold granted under the ALRA. \\FS1-CBR.nexus.csiro.au\{lw-rowra}\work\6_Indigenous\2_Victoria\1_GIS\1_Map_docs\1_Exports\Ind-V-502_ALRA_v1_CR.png Figure 3-24 Aboriginal freehold land in the Victoria catchment as at November 2023 ILUA = Indigenous Land Use Agreement; ALRA = Aboriginal Land Rights (Northern Territory) Act 1976 (Cth) Data source: NT Government \\FS1-CBR.nexus.csiro.au\{lw-rowra}\work\6_Indigenous\2_Victoria\1_GIS\1_Map_docs\1_Exports\Ind-V-503_NativeTitle_v1_CR.png Figure 3-25 Native title claims and determinations in the Victoria catchment as at November 2023 Data source: National Native Title Tribunal Native title in the Victoria catchment demonstrates this pattern. Approximately 34% of the catchment is covered by determinations that native title exists in all or part (generally the large majority) of the determination area, and a further 1.6% is under current claim. But the determination areas are aligned with and named after existing pastoral lease boundaries, and the determinations themselves provide limited access rights onto leases held and operated by generally large-scale pastoral and agricultural companies. In addition, native title holders in the NLC jurisdiction are not represented by locally based Registered Native Title Bodies Corporate (RNTBCs), often known as Prescribed Bodies Corporate (PBCs). Rather, they are all represented by a small and operationally limited shell entity based at the NLC in Darwin known as the Top End (Default PBC/CLA) Aboriginal Corporation RNTBC (Figure 3-25). As a result, native title holders in much of the Victoria catchment do not have locally distinctive representative or operational capacity comparable to land trusts under the ALRA. The native title system also allows for voluntary registered agreements between native title claimants or holders and other interested parties for the use and management of land and resources. These are known as Indigenous Land Use Agreements (ILUA). Further information on these in the Victoria catchment is provided in Barber et al. (2024). The specific implementation of the ALRA and native title regimes in the Victoria catchment means that Traditional Owners in the area experience five primary states of tenure over large areas of the wider landscape beyond towns and communities. In order from the greatest amount of legal recognition, ownership, and control to the least, they are: 1.Collective freehold, primarily through the ALRA or other freehold mechanisms 2.Collective freehold through the ALRA overlaid by a 99-year lease to the NT Government for anational park 3.Limited, native title−based access rights for specific purposes to pastoral leases held by non- Indigenous people and corporations (often large pastoral and agricultural companies) 4.Crown lease for defence training purposes with an Indigenous Land Use Agreement over thelease 5.Pastoral leases and other holdings held by non-Indigenous people without current native titledeterminations or other forms of Indigenous recognition (notably Victoria River Downs, Humbert River, Delamere, Riveren and Waterloo stations). This variety of possible tenures means that the location of any proposed development is highly consequential in determining how Traditional Owners are positioned with respect to that development. They may have substantial control through the ALRA, have only limited rights to consultation under native title, or have no recognised substantial Indigenous-specific tenure and property rights. Indigenous population and residence Indigenous Peoples comprise 74.68% of the total estimated Victoria catchment population of approximately 1600 people (Table 3-3). This includes people who are Traditional Owners as well as residents who identify as Indigenous but have their origins elsewhere. Many Traditional Owners may primarily reside outside the traditional lands to which they have formal ties. These patterns of residence and dispersal reflect a combination of historical involuntary relocation, voluntary movement to seek jobs and other opportunities, and kinship and family links. Indigenous communities in the Victoria catchment include Daguragu, Nitjpurru (Pigeon Hole), Yarralin, Bulla and Amanbidji. Substantial numbers of people also live at the towns of Kalkarindji and Timber Creek. Indigenous communities face a range of social and demographic challenges, including significant unemployment, poor health and housing, water insecurity and structural impediments to economic participation, including remoteness and social and family units under high levels of stress. As two responses to these circumstances, participants in the Assessment sought economic and social conditions that would enable more of their people, particularly young people, to be employed and for the capacity to engage in formal planning processes on their own traditional lands. Indigenous governance and representation Indigenous organisational and political structure within the Victoria catchment is diverse. The NLC and the CLC are the major regional Indigenous representative organisations for the Victoria catchment. They represent and act for Traditional Owners with respect to access, participation, partnership and ownership. Local groups in the area are represented through a range of Indigenous corporations and entities, including Aboriginal Land Trusts and Aboriginal corporations. However, as noted above, native title representation is limited. Traditional Owners and their corporations varied significantly in their existing capacity, resourcing, partnerships and ability to participate in natural resource management decision making. 3.4.4 Culture, people and Country Traditional Owners in the Victoria catchment are strongly connected to their Country and to one another. Cultural responsibilities to protect and sustain Country and kinship connections with others are key drivers of belief and action. Participants in the Assessment highlighted important underlying assumptions and roles that include: • the assumption of Traditional Ownership of land and water resources • the need for formal external recognition of, and engagement with, that ownership and its associated responsibilities • the role of local histories in establishing Traditional Owners’ connections and authority • the ongoing role of religious and spiritual beliefs • the knowledge and practices that sustain group and language boundaries and identities • the importance of hunting, foraging and fishing activity to Indigenous Peoples’ cultures • inter-generational obligations to both ancestors and descendants to care for Country • regional responsibilities to near neighbours and downstream groups to maintain the integrity of the Country and related Indigenous Knowledge and practices • the significance of environmental and cultural heritage and its protection. Alongside native title and land rights, a key mechanism for protecting Country is the Northern Territory Aboriginal Sacred Sites Act 1989 (NT). The AAPA is established under this Act as an independent statutory authority that assists with recording, registering and protecting sacred sites. With respect to environmental protection and management, Indigenous cultural and natural resource management programs, often known as Indigenous rangers, can play a very significant role. Culture, people, and Country, and the connections between those concepts, are fundamental to Indigenous Peoples’ responses to development. 3.4.5 Contemporary Indigenous water values In general terms, Indigenous water values emphasise securing sufficient water of good quality to maintain healthy landscapes, remote community health and livelihoods, and to support Indigenous needs. Those needs can be defined in multiple ways. From an economic perspective, they encompass such activities as art and cultural production, hunting and gathering, tourism and recreation, and ownership and participation in larger-scale economic enterprises such as pastoralism and agriculture. All of these needs depend on natural resources, which highlights the importance of securing and maintaining good-quality water supplies. Data from the Assessment clearly demonstrate the fundamental significance of water for Traditional Owners in the Victoria catchment. Water is essential for community life, health and practical hygiene, sustaining a healthy Country, religious symbolism and ancestral connection. Statements about the importance of water from participants in the Assessment are consistent with broader statements that outline significant Indigenous water rights, values and interests, both in Australia (NAILSMA, 2008, 2009) and internationally (United Nations, 2023; World Water Council, 2003). Traditional Owners experience very high variability in the presence and absence of water in the landscape. The country can be extremely dry at the end of the dry season, while flooding incidents in 2022, 2023 and 2024 across the Victoria catchment had a significant impact on a number of major towns and communities. Daguragu, Kalkarindji, Nitjpurru (Pigeon Hole) and Timber Creek were all seriously affected by major floods that required residents to emergency evacuate and/or residentially relocate for significant periods. These experiences have heightened awareness of water, climate change, community infrastructure and regional development issues. Water is extremely important to Traditional Owners in the Victoria catchment for cultural, ecological, and practical reasons. Key issues and ongoing goals for water include: •ensuring there is enough water of sufficient quality to maintain healthy landscapes(environmental flows) and sustain cultural resources and practices •having access to all water sites •maintaining adequate and good-quality supplies of water for human consumption andrecreation in communities •monitoring and reporting of water uses •development impacts on water quality •deriving benefits from water development and water use •securing sufficient water reserves for current and future economic activity. 3.4.6 Responses to water and irrigation development In the Victoria catchment, Traditional Owner responses to water and irrigation development are interpreted through perceptions of past and current development within and beyond the catchment, and through observations of ongoing environmental and seasonal changes. Participants’ responses to water development and extraction included considerations of impacts on water quality, streamflow, water-dependent ecosystems, community water access, and human cultural practices and recreation. Large instream dams were strongly resisted. In general, larger- scale water and agricultural development were seen as incompatible with Traditional Owner values and ways of living. Concerns about water development encompassed concerns about the cumulative impacts from other industries, particularly mining. Traditional Owners’ assessments of the relative risks and benefits associated with development proposals were significantly affected by their awareness of their position as long-term custodians, marginalised socio-economic status, limited understanding of non-Indigenous water governance and development approval regimes, and knowledge of negative ongoing impacts of development projects elsewhere. Some data on preferences for particular kinds of water development were gathered. The general order of preference, from most to least favourable, was: 1. flood harvesting to supply smaller, offstream storages 2. bore and groundwater extraction 3. smaller instream dams constructed inside tributaries or branches 4. large instream dams in major river channels. Proposals for specific sites may or may not align with the order of preference above, and new information may alter the above order at both local and regional scales. How water infrastructure affects flood risk might also be a factor in the Victoria catchment. Traditional Owners wish to own and control their own developments. With respect to major water and irrigation development undertaken by others, key criteria for evaluation include: • early and further formal consultations with Traditional Owners and affected groups about options, environmental assessments and potential impacts and preferences • development that specifically addresses Indigenous needs (e.g. education, amenity, access to sites, community and outstation water supply, and recreational opportunities) • appropriate cultural heritage surveys of likely areas of impact • agreements that support Traditional Owner employment and other benefits, and continuous consultation and assessment during development, construction and operation • support for Traditional Owner roles in development that enable influence over water planning, wider catchment management and enterprise development. 3.4.7 Indigenous interests in water planning Water planning is understood to be one way of managing water development risk, but water planning also has particular challenges. In the NT, significant progress in one element has been achieved through the Strategic Aboriginal Water Reserves (SAWRs) (NT Government, 2017). This policy provides scope for further Indigenous recognition by creating reserved water allocations for Indigenous development purposes in water allocation plans. However, only a small area in the far east of the Victoria catchment is currently included in a water control district with an associated water plan. Elsewhere there are no districts or water plans through which such a reserve could be created. The Assessment highlights that formalisation and specification of Indigenous water values and water planning issues in the context of both water planning and catchment management regimes is needed. This requires: •creating the planning and regulatory structures that enable water planning and management •formal scoping discussions at local and catchment scales about how best to support TraditionalOwner involvement •refining Traditional Owner governance rights, roles and responsibilities in water planning •resourcing Traditional Owner involvement in water planning, including formal training and waterliteracy programs •allocating Indigenous-specific water for development purposes, which may include options forleasing water rights, and remote community and outstation water access and supply •further specifying the impacts of water planning on current and potential future native titlerights and on cultural heritage •coordinating water planning processes with land, catchment and development planning •addressing continuing Indigenous water research needs and information priorities. These suggested steps rely on Traditional Owners having relevant information for their decision making and having sufficient time to undertake their consultations at local and catchment scales. 3.4.8 Indigenous development objectives Indigenous Peoples have a strong desire to be understood as development partners and investors in their own right, and they have their own independent development objectives. This stance informs their responses to development proposals outlined by others. As a group, Indigenous Peoples are socially and economically disadvantaged while also being custodians of ancient landscapes. They therefore seek to balance short- to medium-term social and economic needs with long-term cultural, historical and religious responsibilities to ancestral lands. Past forums have outlined Indigenous development agendas (NAILSMA, 2012, 2013) that are consistent with the perspectives from Traditional Owners in the Assessment. These agendas are informed by two primary goals: •greater ownership of, and/or management control over, traditional land and waters •sustainable retention and/or resettlement of Indigenous Peoples on their Country. These goals are interrelated because retention and/or resettlement relies on employment and income generation, and most business opportunities identified by Traditional Owners depend on land and natural resources: pastoralism, conservation services, ecotourism, agriculture, aquaculture and marine harvesting. Each group in the Victoria catchment has multiple responsibilities and management roles, but differences in geography, accessibility, residence, assets, governance and/or skills mean that some Traditional Owners are more easily able to sustain multiple business activities; others will achieve greater success by focusing on a single activity. With respect to Indigenous objectives and development planning, five primary interrelated development goals are identified: •greater recognition of Traditional Ownership of water and/or management control overwater •ensuring water supply for human consumption and recreation in communities andoutstations •improved information flow and empowerment for Indigenous decision makers •protection and strengthening of regional and catchment governance in line with customaryconnections •development of new Country-based businesses and industries. Three Country-based industries were the most commonly raised by participants in the interviews as a focus for their own future business aspirations: agriculture, Indigenous cultural and natural resource management, and tourism. Traditional Owners in the Victoria catchment possess valuable natural, historical and cultural assets and represent a significant potential labour force, but they collectively lack skills in business development and implementation. Partnerships can address this gap, but opportunities for business to understand and invest in Traditional Owners and their lands in the Victoria catchment are currently limited. Indigenous development objectives and Indigenous development partnerships are best progressed through locally specific group- and community-based planning and prioritisation processes that are nested in a system of regional coordination. Such planning and coordination can greatly increase the success of business development and of the opportunities for Indigenous employment, retention and resettlement that arise from them. Beyond business conditions, health and community services and infrastructure will be vital to attracting and retaining a skilled labour force. The work undertaken here shows that Traditional Owners in the Victoria catchment strongly wish to participate in sustainable economic activity. They can also act as a substantial enabler of appropriate development but need to be engaged early and continuously in defining development pathways and options. 3.5 Legal and policy environment Proponents must be aware of a range of legal, policy and regulatory requirements and approvals when contemplating land and water developments within the Victoria catchment. As part of their due diligence process, proponents must be prepared to secure appropriate land tenure and authorisations to take water and to obtain the necessary approvals well in advance of commencing construction and operation of a development. This section describes the overarching Australian legal context and summarises the key issues and related legal, regulatory and approval considerations that apply to water-related developments in the Victoria catchment. Detailed information is available in the companion technical reports on water planning arrangements (Vanderbyl, 2024) and regulatory requirements for land and water development (Speed and Vanderbyl, 2024). 3.5.1 Australian legal and policy context Australia is a federal constitutional monarchy consisting of six states and two territories. The Victoria catchment is wholly located within the NT, as shown in Figure 3-26. There are three levels of government: the Australian Government, state and territory governments, and local governments. The Australian Government has powers under the EPBC Act relating to matters of national environmental significance (including those arising from the World Heritage Convention, the Ramsar Convention on Wetlands of International Importance, and the Convention on Biological Diversity) and powers relating to the native title rights of Indigenous Peoples. Generally, the NT Government is responsible for land, water and environmental policy and laws. However, the NT is an administrative territory established by the Australian Government and as such the Australian Parliament retains a right of veto over all NT laws. Land use planning is also the responsibility of the NT Government, which administers the NT Planning Scheme. 3.5.2 Key legal and regulatory requirements Land tenure and native title Proponents will need to secure appropriate tenure over the land of the proposed development site. Consideration should be given as to whether land tenure can be granted or transferred to the developer (or converted to a more suitable form of tenure) and whether any approvals will be required beyond those held by the current owner or lessee of the land. If the land is not freehold, which is the case for most of the Victoria catchment, native title requirements are likely to apply. In that case, the proponent will need to check if a native title determination has been made (or is underway) for the land, who the relevant parties are and whether the proposed development is consistent with the rights of native title holders. The proponent will then need to negotiate with the relevant Indigenous Peoples for the area prior to undertaking development activities. Most of the land in the Victoria catchment is held as either Aboriginal freehold land or pastoral leases. If the proposed development is on Aboriginal freehold land, the proponent will need to obtain the consent of the Traditional Owners and approval from the relevant Aboriginal Land Council. If the proposed development is on pastoral lease land, the proponent will require approval for non-pastoral uses from the Pastoral Land Board. Water regulatory map \\FS1-CBR.nexus.csiro.au\{lw-rowra}\work\10_Reporting\6_Vic_S_Gulf_combined\1_GIS\1_Map_docs\Badu_NT_WaterRegulatory_ArcGIS10_8_v7.mxd For more information on this figure please contact CSIRO on enquiries@csiro.au Figure 3-26 The Victoria catchment and neighbouring water plans and water control districts Authority to take water Proponents will generally need to obtain a water licence under the Northern Territory Water Act 1992 to take any surface water or groundwater that may be required to construct and operate the development. A water licence may be purchased and transferred from an existing licence holder subject to requirements or constraints relating to water trading and the purpose of the water use. Alternatively, it may be possible to seek the grant of a new water licence from unallocated water reserves. Such provisions are contained in the Georgina Wiso Water Allocation Plan, which partly intersects the Victoria catchment (Figure 3-26). Where a water allocation plan applies to a water source, then licences must only be granted consistent with the sustainable yield for the relevant water resource and in accordance with the volumes allocated to different beneficial uses. In the absence of a water allocation plan, which is the case for most of the Victoria catchment, the NT Water Allocation Planning Framework provides general rules for allocation of the available water. This framework establishes ‘contingent allocation rules’ that require a minimum amount of flow be set aside for environmental and other public purposes. The NT legally requires that the allocation of water for Aboriginal use is part of water planning. The Strategic Aboriginal Water Reserve (SAWR) became statute in the NT in 2019. The SAWR is ‘water allocated in a WAP [water allocation plan] for Aboriginal economic development in respect of eligible land’ (Section 4(1), Water Act 1992). At its maximum, the SAWR can be no more than 30% in an area with more than 30% of eligible Aboriginal land (Godden et al., 2020). An Aboriginal Water Reserve can only exist where there is eligible land at the time of the WAP. Planning requirements Proponents will need to ensure that their development will be consistent with local and territory planning requirements. This usually involves a formal application and assessment process. A single planning scheme applies across the NT, under which a proposed development may be categorised as: (i) permitted, (ii) merit assessable, (iii) impact assessable, or (iv) prohibited. NT Government websites provide detailed checklists and criteria for helping a proponent determine the category applicable to their particular development proposal. A development permit will be required for developments categorised as merit assessable and impact assessable. In addition, the NT Planning Commission may prepare a significant development report to be considered in the assessment of the development permit where a proponent’s development is over a certain investment threshold. Environmental approvals Proponents will need to obtain approvals for certain activities that have a potential environmental impact, including any building or construction activities. A proponent may require federal environmental approval under the EPBC Act if their development has the potential to affect matters of national environmental significance. Federal environmental impact assessment requirements can be met through the NT Government’s assessment process, allowing for a more streamlined assessment process. However, the ultimate decision under the EPBC Act remains with the Australian Minister for the Environment and Water. Under NT law, a proponent will require environmental approval for any actions that will have a significant impact on the environment or that are captured under a ‘referral trigger’. Where required, the NT Environment Protection Authority will conduct an environmental impact assessment. Such processes can take significant time to complete. Cultural heritage Proponents will need to identify potential cultural heritage sites and/or objects (including Indigenous cultural heritage sites and/or objects) if a proposed development will affect cultural heritage. The proponent will need to undertake searches of the NT Heritage Register and the NT Aboriginal Areas Protection Authority register of sacred sites. National heritage values will also need to be considered through any environmental impact assessment process under the EPBC Act. A cultural heritage management plan is advisable (and may be required) for significant developments. Works in a watercourse Proponents will need approval to undertake any developments that involve activities within a watercourse. In the NT, a proponent will require a permit under the Water Act 1992 to interfere with a watercourse (e.g. extraction of materials, construction within a waterway, or diversion of a watercourse). Clearing vegetation In the NT, clearing of native vegetation is a controlled activity and generally requires a permit. This applies to both freehold land (including Aboriginal freehold land) and pastoral leases. For clearing on pastoral land, permit applications are determined by the Pastoral Land Board. For freehold land, applications are assessed under the Northern Territory Planning Act 1999 and must be lodged with the Department of Infrastructure, Planning and Logistics. Exemptions apply for routine maintenance and day-to-day management activities. 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This information covers: • opportunities for irrigated agriculture and aquaculture (Chapter 4) • opportunities to extract and/or store water for use (Chapter 5). The cracking clay soils on the broad treeless alluvial plains of the West Baines River upstream of the Victoria Highway offer the greatest potential for broadacre irrigation in the Victoria catchment. Photo: CSIRO – Nathan Dyer 4 Opportunities for agriculture in the Victoria catchment Authors: Seonaid Philip, Yvette Oliver, Tiemen Rhebergen, Ian Watson, Tony Webster, Peter R Wilson, Simon Irvin Chapter 4 presents information about the opportunities for irrigated agriculture and aquaculture in the catchment of the Victoria River, describing: • land suitability for a range of crop group × season × irrigation type combinations and for aquaculture, including key soil-related management considerations • cropping and other agricultural opportunities, including crop yields and water use • gross margins at the farm scale • prospects for integration of forages and crops into existing beef enterprises • aquaculture opportunities. The key components and concepts of Chapter 4 are shown in Figure 4-1. Figure 4-1 Schematic of agriculture and aquaculture enterprises as well as crop and/or forage integration with existing beef enterprises to be considered in the establishment of a greenfield irrigation development For more information on this figure please contact CSIRO on enquiries@csiro.au 4.1 Summary This chapter provides information on land suitability and the potential for agriculture and aquaculture in the Victoria catchment. A mixture of field surveys and desktop analysis were used to generate the results presented in this chapter. For example, the land suitability results draw on extensive field visits (to describe, collect and analyse soils) and are integrated with state-of-the-art digital soil mapping. Many of the results are expressed in terms of potential. The area of land suitable for cropping or aquaculture, for example, is estimated by considering the set of relevant soil and landscape biophysical attributes at each location and determining the most limiting attribute among them. It does not include water availability; cyclone or flood risk; legislative, regulatory or tenure considerations; or ecological, social or economic drivers that will inevitably constrain the actual area of land that is developed. Crops, forages and cropping systems results are based on data analysis and simulation models, and assume good agronomic practices producing optimum yields given the soil and climate attributes in the catchment. Likewise, aquaculture is assessed in terms of potential, using a combination of land suitability and the productive capacity of a range of aquaculture species. Information is presented in a manner to enable the comparison of a variety of agricultural and aquaculture options. The results from individual components (land suitability, agriculture, aquaculture) are integrated to provide a sense of what is potentially viable in the catchment. This includes providing specific information on a wide range of crop types for agronomy, water use and land suitability for different irrigation types; analyses of economic performance, such as crop gross margins (GMs); how more-intensive mixed cropping systems might be feasible with irrigation; and analyses of what is required for different aquaculture development options to be financially viable. 4.1.1 Key findings Any agricultural resource assessment must consider two major factors: how much soil is suitable for a particular land use and where that soil is located. Based on a sample of 14 individual combinations of crop group × season of use × irrigation type, the amount of land classified as moderately suitable with considerable limitations or better ranges from 433,000 ha (Crop Group 19, wet-season furrow) to 3.1 million ha (Crop Group 3, dry-season, trickle) before constraints such as water availability, environmental and other legislation and regulations, and a range of biophysical risks are considered (crop groups are defined in Section 4.2.3). In contrast with other catchments assessed in northern Australia, the Victoria catchment has a relatively large percentage of soils classed as suitable, with minor limitations, principally the red loamy soils found on the deeply weathered low-relief Tertiary sediments in the south-western, southern and south- eastern (Sturt Plateau) parts of the catchment. Local- and intermediate-scale groundwater resources occur beneath parts of these loamy soils in the central and southern parts of the catchment (Section 2.5.2, Figure 2-27). Regional-scale groundwater resources occur beneath parts of these loamy soils in the eastern part of the catchment. Almost all licensed water use in the catchment occurs outside current water control districts or water allocation planning areas. Rainfed cropping Despite the theoretical possibility that rainfed crops could be produced using the considerable rainfall that arrives during the wet season, in practice significant agronomic and market-related challenges to rainfed crop production have prevented its expansion. Loamy Kandosols have low water-holding capacity and are hardsetting, which makes consistently achieving viable rainfed yields difficult. Areas of heavier clay soils along the West Baines River, the Victoria River and its major tributaries store more plant available water (PAW) that could support higher potential crop yields, particularly if cropped opportunistically in wetter years. However, frequent inundation and waterlogging of clay soils means that access for farming operations could be disrupted, increasing the risk to maximum yields through compromised timing of operations. Despite these challenges, higher-value crops such as pulses or cotton show potential, especially when grown in conjunction with irrigated farming. Irrigated cropping Irrigation reduces crop water stress and provides greater control over scheduling of crop operations to optimise production, including the option of growing through the cooler months of the dry season. Analyses of the performance of 19 potential irrigated cropping options in the Victoria catchment indicate that achievable annual GMs could be up to about $5000/ha for broadacre crops, $4000/ha for annual row crop horticulture, $6000/ha for perennial fruit tree horticulture and $3000/ha for silviculture (plantation trees). While GMs are a key partial metric of farm performance, they should not be treated as fixed constants determined by the cropping system alone. They are a product of the farming and business management decisions, input costs and market opportunities. As such there are often niche opportunities to improve farm GMs and profitability, but these usually come at the expense of scalability. Farm financial metrics like GMs greatly amplify any fluctuations in commodity prices and input costs, so the mean GM does not accurately reflect the often substantial cashflow challenges in managing years of losses between those of windfall profits (particularly for horticulture). Crop yields and GMs presented in this chapter indicate what might be attained for each cropping option once it has achieved its sustainable agronomic potential. It is unrealistic to assume that these levels of performance would be achieved in the early years of newly established farms, and allowance should be made for an initial period of learning (Chapter 6). Potential crop species that could be grown as a single crop per year were rated and ranked for their performance in the Victoria catchment. Wet-season crops (planted December to early May) that are rated the most likely to be viable are cotton (Gossypium spp.), forages and peanuts (Arachis hypogaea). Dry-season crops (planted late March to August) that are rated the most likely to be viable are annual horticulture, cotton and mungbean (Vigna radiata). Financial viability is determined both by crop options with the highest GMs and by associated capital and fixed costs, which are higher in more-intensive farming like horticulture. The farm-scale measures of crop performance presented in this chapter are intended to be used in conjunction with the scheme- scale analyses of financial viability in Chapter 6 (as part of an integrated multi-scale approach). Sequential cropping systems involve planting more than one crop in the same year in the same field. These systems have the potential to significantly increase farm GMs. Annual broadacre and horticultural crops have been grown sequentially for many decades in tropical northern Australia. A wide range of sequential cropping options are potentially viable in the Victoria catchment. Most suitable crop sequences include wet-season mungbean, grain sorghum or peanut with dry-season annual horticulture, wet-season mungbean, peanut, soybean or sorghum with dry-season cotton, maize, chickpea or forage, and wet-season cotton with dry-season mungbean, sorghum or forage. Scheduling back-to-back crops could be operationally tight in the Victoria catchment, particularly on clay-rich soils with poor drainage. Crop selection is market driven in northern Australian regions like the Victoria catchment. Therefore, rotations and crop sequences are dynamic as growers develop an understanding of the benefits, trade-offs and management needs of different crop mixes, and adapt to changing opportunities. Integrating forages and hay into existing beef enterprises There are many theoretical benefits to growing irrigated forages and hay on-farm to enhance existing grazing enterprises. The use of on-farm irrigated forage and hay production would allow graziers greater options for marketing cattle: meeting market liveweight specifications for cattle at a younger age, meeting the specifications required for different markets than those typically targeted by cattle enterprises in the Victoria catchment and providing cattle that meet market specification at a different time of the year. Forages and hay may also allow graziers to implement management strategies, such as early weaning or weaner feeding, which should lead to flow-on benefits throughout the herd, including increased reproductive rates. Some of these strategies are already practised within the Victoria catchment but in almost all incidences are reliant on hay or other supplements purchased on the open market. By growing hay on-farm, the scale of these management interventions might be increased, at reduced net cost. Furthermore, the addition of irrigated feeds may allow graziers to increase the total number of cattle that can be sustainably carried on a property. Analysis of two irrigated hay or two irrigated forage stand-and-graze options compared to two base enterprises (with or without purchased hay, for weaners) suggested that irrigated forages or hay increased the total income and the amount of cattle liveweight sold. GMs were highest for the two base enterprises. The two stand-and-graze options returned the lowest GMs. A net present value (NPV) analysis suggested that none of the options had a positive NPV when considered at three different beef prices and two different estimates of capital costs per ha. Irrigation enterprises of the scale required involve high capital investment and additional or novel management skills. Aquaculture There are considerable opportunities for aquaculture development in northern Australia given the region’s natural advantages of a climate suited to farming valuable tropical species, the large areas identified as suitable for aquaculture, and political stability and proximity to large global markets. The main challenges to developing and operating modern and sustainable aquaculture enterprises are regulatory barriers, global cost competitiveness, and the remoteness of much of the suitable land area. The three species with the most aquaculture potential in the Victoria catchment are black tiger prawns (Penaeus monodon), barramundi (Lates calcarifer) and red claw (Cherax quadricarinatus). Suitable land for lined ponds for freshwater species is widespread throughout the catchment due to the extensive distribution of favourable soil and land characteristics (flat land, non-rocky, deep soil). In contrast, options for freshwater species in earthen ponds are restricted to the impermeable alluvial clays to allow retention of water. The range for marine aquaculture is restricted to the tidal zones of the catchment and on the coastal plain within 2000 m of access to marine water. High annual operating costs (which can exceed the initial capital costs of development) mean that managing cashflow in the establishment years is challenging, especially for products that require multi-year grow-out periods. Input costs scale with increasing productivity, so improving production efficiency (such as feed conversion rate or labour-efficient operations) is much more important than increasing yields for aquaculture to be viable in the Victoria catchment. It would be essential for any new aquaculture development to refine the production system and achieve the required levels of operational efficiency (input costs per kilogram of produce) using just a few ponds before scaling the enterprise to a larger number of ponds. 4.1.2 Introduction Aspirations to expand agricultural development in the Victoria catchment are not new and across northern Australia there have been a number of initiatives to put in place large-scale agricultural developments since World War II (Ash, 2014; Ash and Watson, 2018). Ash and Watson (2018) assessed 11 such agricultural developments, four of which continue to operate at a regionally relevant scale, namely the Ord River Irrigation Area, the lower Burdekin, the Mareeba–Dimbulah Water Supply Scheme and the Katherine mango industry. The Lakeland Downs development also continues, although it could not be categorised as regionally significant. Ash and Watson’s assessment included both irrigated and rainfed developments and considered natural, human, physical, financial and social capitals. Key points to emerge from these analyses include the following: • The natural environment (climate, soils, pests and diseases) makes agriculture in northern Australia challenging, but these inherent environmental factors are not generally the primary reason for a lack of success. • The speed with which many of the developments were undertaken did not allow for a ‘learning by doing’ approach, leading at times to costly mistakes. • Physical capital, in the form of on-farm infrastructure, supply chain infrastructure and crop varieties, was a significant and ongoing impediment to success. For broadacre commodities that require processing facilities, these facilities need to be within a reasonable distance of production sites and at a scale to make them viable in the long term. • Financial plans tended to over estimate early production and returns on capital, and assumed overly optimistic expectations of the ability to scale up rapidly. This led to financial pressure on investors and a premature end to some developments. Furthermore, the need to have well- connected and well-paying markets was often not fully appreciated. In more remote regions, higher-value products such as fruit, vegetables and niche crops proved more successful, although high supply chain costs to both domestic and export markets remain as impediments to expansion. • Most of the developments began in areas with no history of agricultural development and there was no significant community of practitioners who could share experiences. • Management, planning and finances were the most important factors in determining the ongoing viability of agricultural developments. For developments to be successful, all factors relating to climate, soils, agronomy, pests, farm operations, management, planning, supply chains and markets need to be thought through in a comprehensive systems design. Particular attention needs to be paid to scaling up at a considered pace and being prepared for reasonable lags before achieving positive returns on investment. This chapter seeks to address the following questions for the Victoria catchment: • How much land is suitable for cropping and in which suitability class? • Is irrigated cropping economically viable? • Which crop options perform best and how can they be implemented in viable mixed farming systems? • Can crops and forages be economically integrated with beef enterprises? • What aquaculture production systems might be possible? The chapter is structured as follows: • Section 4.2 describes how the land suitability classes are derived from the attributes provided in Chapter 2, with results given for a set of 14 combinations of individual crop group × season × irrigation type. Versatile agricultural land is described, and a qualitative evaluation of cropping is provided for a set of specific locations within the catchment. • Section 4.3 provides detailed information on crop and forage opportunities, including irrigated crop yields, water use and GMs. Agronomic principles, such as selection of sowing time, are provided, including a cropping calendar for scheduling farm operations. The information is synthesised in an analysis of the cropping systems that could best take advantage of opportunities in the Victoria catchment environments while dealing with farming challenges. • Section 4.4 provides synopses for 11 crop and forage groups, including a focused discussion on specific example species. • Section 4.5 discusses the candidate species and likely production systems for aquaculture enterprises, including the prospects for integrating aquaculture with agriculture. 4.2 Land suitability assessment 4.2.1 Introduction The term ‘suitability’ in the Assessment refers to the potential of the land for a specific land use, such as furrow-irrigated cotton. The term ‘capability’ (not used in the Assessment) refers to the potential of the land for broadly defined land uses, such as cropping or pastoral (DSITI and DNRM, 2015). The overall suitability for a particular land use is determined by a number of environmental and soil attributes. These include, but are not limited to, climate at a given location, slope, drainage, permeability, available water capacity of the soil, pH, soil depth, surface condition and texture. Examples of some of these attributes are provided in Section 2.3. From these attributes, a set of limitations to suitability are derived, which are then considered against each potential land use. 4.2.2 Land suitability classes The overall suitability for a particular land use is calculated by considering the set of relevant attributes at each location and determining the most limiting attribute among them. This most limiting attribute then determines the overall land suitability classification. The classification is on a scale of 1 to 5 from ‘Suitable with negligible limitations’ (Class 1) to ‘Unsuitable with extreme limitations’ (Class 5), as shown in Table 4-1 (FAO, 1976, 1985). The companion technical report on digital soil mapping and land suitability (Thomas et al., 2024) provides a complete description of the land suitability assessment method, and the material presented in this section is taken from that report. Note that the land suitability maps and figures presented in this section do not consider flooding, risk of secondary salinisation or availability of water as discussed by Thomas et al. (2024). Consideration of these risks and others, along with further detailed soil physical, chemical and nutrient analyses, would be required to plan development at scheme, enterprise or property scale. Caution should therefore be employed when using these data and maps at fine scales. Table 4-1 Land suitability classes based on FAO (1976, 1985) as used in the Assessment For more information on this figure, table or equation please contact CSIRO on enquiries@csiro.au 4.2.3 Land suitability for crops, versatile agricultural land and evaluation of specific areas of interest The suitability framework used in this Assessment aggregates individual crops into a set of 21 crop groups (Table 4-2). The groups are based on the framework used by the NT Government (Andrews and Burgess, 2021), with some additions considered prospective based on previous CSIRO work in northern Australia (e.g. Thomas et al., 2018). From this set of crop groups, land suitability has been determined for 58 land use combinations of crop group × season × irrigation type (including rainfed) (Thomas et al., 2024). Table 4-2 Crop groups and individual land uses evaluated for irrigation (and rainfed) potential Crop groups and land uses are based on those used by Andrews and Burgess (2021), amended for the Victoria catchment with the addition of crop groups 18 to 21 based on CSIRO’s previous work in northern Australia. Those used in the Northern Australia Water Resource Assessment (Thomas et al., 2018) are in boldface. MAJOR CROP GROUP CROP GROUP INDIVIDUAL CROPS ASSESSED Tree crops/horticulture (fruit) 1 Monsoonal tropical tree crops (0.5 m root zone) – mango, coconut, dragon fruit, Kakadu plum, bamboo, lychee 2 Tropical citrus – lime, lemon, mandarin, pomelo, lemonade, grapefruit Intensive horticulture (vegetables, row crops) 3 Cucurbits – watermelon, honeydew melon, rockmelon, pumpkin, cucumber, Asian melons, zucchini, squash 4 Fruiting vegetable crops – Solanaceae (capsicum, chilli, eggplant, tomato), okra, snake bean, drumstick tree 5 Leafy vegetables and herbs – kangkong, amaranth, Chinese cabbage, bok choy, pak choy, choy sum, basil, coriander, dill, mint, spearmint, chives, oregano, lemon grass, asparagus Root crops 6 Carrot, onion, sweet potato, shallots, ginger, turmeric, galangal, yam bean, taro, peanut, cassava Grain and fibre crops 7 Cotton, grains – sorghum (grain), maize, millet (forage) 8 Rice (lowland and upland) Small-seeded crops 9 Hemp, chia, quinoa, medicinal poppy Pulse crops (food legumes) 10 Mungbean, soybean, chickpea, navy bean, lentil, guar Industrial 11 Sugarcane Hay and forage (annual) 12 Annual grass hay/forages – sorghum (forage), maize (silage) 13 Legume hay/forages – blue pea, burgundy bean, cowpea, lablab, Cavalcade, forage soybean Hay and forage (perennial) 14 Perennial grass hay/forage – Rhodes grass, panics Silviculture/forestry (plantation) 15 Indian sandalwood 16 African mahogany, Eucalyptus spp., Acacia spp. 17 Teak Intensive horticulture (vegetables, row crops) 18 Sweet corn Oilseeds 19 Sunflower, sesame Tree crops/horticulture 20 Banana, coffee 21 Cashew, macadamia, papaya A sample of 14 of these individual land use combinations – that covers a mixture of crops, irrigation types and seasons, grown or trialled in northern Australia – is shown in Figure 4-2. Depending on land use, the amount of land classified as Class 3 or better for these sample land uses ranges from just over 433,000 ha (Crop Group 19 under wet-season furrow irrigation) to just over 3 million ha (Crop Group 3 under dry-season trickle). Much of this land is rated as Class 3, and so has considerable limitations, although just over 2 million ha of Class 2 land is available for Crop Group 3 crops under trickle irrigation in the dry season and between about 860,000 ha and about 2 million ha of Class 2 land for the other crop groups under spray or trickle irrigation. Ranges of suitability geographic distributions are shown on maps in the crop synopses in Section 4.4. Figure 4-2 Area (ha) of the Victoria catchment mapped in each of the land suitability classes for 14 selected land use combinations (crop group × season × irrigation type) The five land suitability classes are described in Table 4-1 and more detail on the crop groups is given in Table 4-2. In order to provide an aggregated summary of the land suitability products, an index of agricultural versatility was derived for the Victoria catchment (Figure 4-3). Versatile agricultural land was calculated by identifying where the highest number of the 14 selected land use options presented in Figure 4-2 were mapped as being suitable (i.e. suitability classes 1 to 3). Qualitative observations on each of the areas mapped as ‘A’ to ‘E’ in Figure 4-3 are provided in Table 4-3. Figure 4-3 Agricultural versatility index map for the Victoria catchment High index values denote land that is likely to be suitable for more of the 14 selected land use options. The map shows specific areas of interest (A to E) from a land suitability perspective, which are discussed in Table 4-3. Note that the versality index mapped here does not consider flooding, risk of secondary salinisation or availability of water. Versatile agricultural land \\FS1-CBR.nexus.csiro.au\{lw-rowra}\work\10_Reporting\2_Victoria\1_GIS\1_Map_Docs\CR-V-Ch4-511_AgVers14_PotDev_v1_10-8.mxd For more information on this figure please contact CSIRO on enquiries@csiro.au Table 4-3 Qualitative land evaluation observations for Victoria catchment areas A to E shown in Figure 4-3 Further information on each soil generic group (SGG) and a map showing spatial distribution can be found in Section 2.3. AREA SOIL AND LOCATION SOIL DESCRIPTION, POTENTIAL LAND USES AND LIMITATIONS A Loamy soils of the Sturt Plateau, the plateau west of Kalkarindji and the southern part of the catchment Moderately permeable red loamy soils (SGG 4.1) with varying amounts of iron nodules. Moderately deep to deep loamy soils are suitable for a diverse range of irrigated horticulture and spray-irrigated grain and pulse crops, forage crops, timber crops, sugarcane and cotton. Soils with hard iron nodules may be suitable for small crops, but abundant nodules will restrict the amount of available soil water for crop growth and cultivation operations. Very shallow soils are generally unsuitable for cropping due to very low available soil water and restricted rooting depth. B Cracking clay soils on broad alluvial plains of the major rivers, particularly the Victoria and West Baines rivers Comprises rarely flooded plains on the Victoria and West Baines rivers and regularly flooded plains on the Baines, East Baines and lower West Baines rivers. Soils are mainly moderately well-drained to imperfectly drained brown or grey cracking clay soils (SGG 9) with self-mulching to hard-setting structured surfaces. The imperfectly drained clay soils of the alluvium grade to poorly drained grey clays (SGG 3) lower in the catchment. The cracking clay soils are suitable for furrow or spray-irrigated sugarcane, dry-season cotton, grain and pulse crops, and forage crops. The main limitations are flooding on the floodplains during the wet season, workability and landscape complexity due to the small and/or narrow areas limiting paddock size and irrigation infrastructure layout due to land dissection. Management of wet- season cropping needs to consider crop tolerance to seasonal wetness and flood duration, depth and frequency. C Brown, black and red cracking clay soils derived from basalt, mainly in the eastern and southern parts of the catchment Moderately deep to deep, moderately well-drained to well-drained, self-mulching cracking clay soils (SGG 9) on basalt plains, scattered throughout the eastern part of the catchment but mainly in the south. Surface gravels, cobble and stone are present. Soils are suitable for a range of spray-irrigated grain and pulse crops, mainly dry-season cropping. Wet-season cropping may be restricted by seasonal wetness and flooding. Extents are generally minor, resulting in small and/or narrow areas limiting paddock size and irrigation infrastructure layout. D Red friable loamy soils on levees of the Victoria and Wickham rivers Predominantly very deep, well-drained red and brown friable loams (SGG 2) on narrow levees. Soils are subject to severe sheet and gully erosion throughout the catchment, and wind erosion in the lower rainfall areas in the south. The narrow levees are suitable for a range of spray-irrigated grain and forage crops and trickle- irrigated horticultural crops, but the generally long, thin units of land restrict irrigation layout and machinery use in most areas. E Grey cracking clay soils of the Cenozoic alluvium scattered through the eastern, southern and western parts of the catchment Very deep, gilgaied, self-mulching, grey and occasionally grey-brown cracking clay soils (SGG 9) subject to seasonal wetness occur in the lower landscape positions of the deeply weathered plateaux and as level plains overlying a diverse range of other geologies. Suitable for dry-season furrow or spray-irrigated grain and pulse crops, forage crops and cotton. Deep gilgai microrelief may restrict land-levelling operations in some areas. Land suitability and its implications for crop management are discussed in more detail for a selection of crops in Section 4.4, where land use suitability of a given crop and irrigation combination are mapped, along with information critical to the consideration of the crop in an irrigated farm enterprise. Land suitability maps for all 58 land use combinations are presented in the companion technical report on digital soil mapping and land suitability (Thomas et al., 2024). 4.3 Crop and forage opportunities in the Victoria catchment 4.3.1 Introduction This section presents results on the farm ‘performance’ of individual crop options, where performance is quantified specifically as crop yields, the amount of applied irrigation water (including on-farm water losses) and GMs. Performance is presented with information on agronomic principles and farming practices to help interpret the viability of new (greenfield) farming opportunities in the Victoria catchment. The individual crop options are grouped into rainfed broadacre, irrigated broadacre, irrigated horticulture and plantation tree crops (sections 4.3.3 to 4.3.7), and viability is discussed in a section on cropping systems (Section 4.3.8). That section considers the mix of farming opportunities and practices, for both single and sequential cropping systems, with the greatest potential to be profitably and sustainably integrated within Victoria catchment environments. Finally, Section 4.3.9 evaluates the viability of integrating irrigated forages into existing beef production. These farm-scale analyses are intended to be used in conjunction with the scheme-scale analyses of viability in Chapter 6 (as part of an integrated multi-scale analysis). Nineteen irrigated crop options were selected to evaluate their potential performance in the Victoria catchment (Table 4-4). The crops were selected to be compatible with the land suitability crop groups (Table 4-2), provided that: (i) they had the potential to be viable in the Victoria catchment (based on knowledge of how well these crops grow in other parts of Australia), (ii) they were of commercial interest for possible development in the region and (iii) there was sufficient information on their agronomy, and farming costs and prices, for quantitative analysis. The analyses used a combination of Agricultural Production Systems sIMulator (APSIM) crop modelling and climate-informed extrapolation to estimate potential yield and water use for each crop. Those values were then used in a farm GM tool specifically designed for greenfield farming developments (like those in the Victoria catchment, where there are very few existing commercial farms or farm financial models). In particular, extrapolations used close similarities in climate and soils between possible cropping locations in the Victoria catchment and established irrigated cropping regions at similar latitudes near Katherine (NT) and the Ord River Irrigation Area (WA) (Figure 4-4). Full details of the approach are described in the companion technical report on agricultural viability and socio-economics (Webster et al., 2024). Section 4.4 provides further details on opportunities and constraints in the Victoria catchment, for example, crops in each of the agronomic crop types listed in Table 4-4. Table 4-4 Crop options for which performance was evaluated in terms of water use, yields and gross margins The methods used for estimating crop yield and irrigation water requirements are coded as: A = APSIM; E = climate- informed extrapolation. ‘A, E’ indicates that A is the primary method and E is used for sensibility testing. ‘Mango (KP)’ is Kensington Pride and ‘Mango (PVR)’ is an indicative new high-yielding variety likely to have plant variety rights (e.g. Calypso). Note that crops that are agronomically similar in terms of the commodities they produce (as categorised in the table) may differ in how they respond to soil constraints. The crop type categories in the table are therefore necessarily different to the crop groups used in the land suitability section (which are grouped according to shared soil requirements and constraints; Table 4-2). CROP TYPE CROP IRRIGATION WATER ESTIMATE METHOD YIELD ESTIMATE METHOD Broadacre Cereal Sorghum (grain) A, E A, E Maize A, E A, E Pulse Mungbean A, E A, E Chickpea A, E A, E Soybean A, E A, E Oilseed Sesame E E Peanut A, E A, E Industrial Cotton (dry season) A, E A, E Cotton (wet season) A, E A, E Hemp E E Forage Rhodes grass A, E A, E Horticulture (row) Rockmelon E E Watermelon E E Onion E E Capsicum E E Horticulture (tree) Mango (PVR) E E Mango (KP) E E Lime E E Plantation tree African mahogany E E Sandalwood E E (a) Mean monthly rainfall (b) Mean daily maximum temperature (c) Mean daily solar radiation (d) Mean daily minimum temperature Figure 4-4 Climate comparisons of Victoria catchment sites with established irrigation areas at Katherine (NT) and Kununurra (WA) Victoria catchment sites are Timber Creek, Kidman Springs, Montejinni and Wave Hill. Four locations were selected for the APSIM simulations to represent some of the best potential farming conditions across the varied environments in the Victoria catchment: • A Vertosol in the northern region, using Timber Creek (15.66°S, 130.48°E) climate. This soil represents some of the better farming conditions among the cracking clays on the alluvial plains of the major rivers (SGG 2 and 9, marked ‘B’ in Figure 4-3). The plant available water capacity (PAWC) of this soil for grain sorghum was 212 mm. Only small, dissected patches of this soil are suitable for cropping because of limitations from floodplain inundation, workability and the complex distribution of flood channels (which both break up patches that would be large enough to crop and cut off wet-season access to some larger pockets of otherwise suitable soil). • A Dermosol in the Yarralin area using the Kidman Springs (16.12°S, 130.96°E) climate. This soil represents some of the better farming conditions among the brown non-cracking clay soils and the red friable loamy clay soils (SGG 2, marked ‘C’ and ‘D’ in Figure 4-3). The PAWC of this soil for grain sorghum was 156 mm. • A Vertosol in the Top Springs area, using Montejinni (16.67°S, 131.76°E) climate. This soil is the same as the Vertosol described above (SGG 2 and 9, marked ‘E’ in Figure 4-3), with a different climate. • A Kandosol in the Kalkarindji area using the Wave Hill (17.39°S and 131.12°E) climate. This soil represents some of the better farming conditions among the loamy soils (SGG 4.1 and 4.2, Mean monthly rainfall graph \\fs1-cbr.nexus.csiro.au\{lw-rowra}\work\5_Agriculture_economics\2_Victoria\4_Data\1_Climate\ViWRA_Climate analysis_YO.xlsx For more information on this figure please contact CSIRO on enquiries@csiro.au Mean daily maximum temperature graph \\fs1-cbr.nexus.csiro.au\{lw-rowra}\work\5_Agriculture_economics\2_Victoria\4_Data\1_Climate\ViWRA_Climate analysis_YO.xlsx For more information on this figure please contact CSIRO on enquiries@csiro.au Mean daily solar radiation graph \\fs1-cbr.nexus.csiro.au\{lw-rowra}\work\5_Agriculture_economics\2_Victoria\4_Data\1_Climate\ViWRA_Climate analysis_YO.xlsx For more information on this figure please contact CSIRO on enquiries@csiro.au Mean daily minimum temperature graph \\fs1-cbr.nexus.csiro.au\{lw-rowra}\work\5_Agriculture_economics\2_Victoria\4_Data\1_Climate\ViWRA_Climate analysis_YO.xlsx For more information on this figure please contact CSIRO on enquiries@csiro.au For more information on this figure please contact CSIRO on enquiries@csiro.au marked ‘A’ in To assist with interpreting the later results, some information is first provided on agronomic principles related to the scheduling of critical farm operations such as sowing and irrigation in relation to Victoria catchment environments. 4.3.2 Cropping calendar and time of sowing Time of sowing can have a significant effect on achieving economical crop and forage yields, and on the availability and amount of water for irrigation required to meet crop demand. Cropping calendars identify optimum sowing times of different crops and are essential tools for scheduling farm operations (Figure 4-5) so that crops can be reliably and profitably grown. No cropping calendar existed for the Victoria catchment before the Assessment. Sowing windows vary in both timing and length among crops and regions, and they consider the likely suitability and constraints of weather conditions (e.g. heat and cold stress, radiation, and conditions for flowering, pollination and fruit development) during each subsequent growth stage of the crop. Limited field experience currently exists in the Victoria catchment for the majority of crops and forages evaluated. This cropping calendar (Figure 4-5) is therefore extrapolated from knowledge of crops derived from past and current agricultural experience in the Ord River Irrigation Area (WA), Katherine and Douglas–Daly regions (NT). Some annual crops have both wet-season and dry-season cropping options. Perennial crops are grown throughout the year, so growing seasons and planting windows are less well defined. Generally, perennial tree crops are transplanted as small plants, and in northern Australia this is usually timed towards the beginning of the wet season to take advantage of wet-season rainfall. The cropping calendar presented here considers the optimal climate conditions for crop growth and considers operational constraints specific to the local area. Such constraints include wet- season difficulties in access and trafficability, and limitations on the number of hectares that available farm equipment can sow or plant per trafficable day. For example, clay-rich alluvial Vertosols, such as those found along the Victoria, West Baines and East Baines rivers, are likely to present severe trafficability constraints through much of the wet season in the Victoria catchment, while sandier Kandosols would present far fewer trafficability restrictions in scheduling farming operations (Figure 4-6). Many suitable annual crops can be grown at any time of the year with irrigation in the Victoria catchment. Optimising crop yield alone is not the only consideration. Ultimately, sowing date selection must balance the need for the best growing environment (optimising solar radiation and temperature) with water availability, pest avoidance, trafficability during the growing season and at harvest, crop rotation, supply chain requirements, infrastructure development costs, market access considerations and potential commodity price. Many summer crops from temperate regions are suited to the tropical dry season (winter) because temperatures are closer to their optima and/or there is more consistent solar radiation (e.g. maize (Zea mays), chickpea (Cicer arietinum) and rice (Oryza sativa)). For sequential cropping systems (which grow more than a single crop in a year in the same field), growing at least one crop partially outside its optimal growing season can be justified if it increases total farm profit per year and there are no adverse biophysical consequences (e.g. pest build-up). Figure 4-5 Annual cropping calendar for irrigated agricultural options in the Victoria catchment WS = wet season; DS = dry season. Crop planting times \\FS1-CBR.nexus.csiro.au\{lw-rowra}\work\5_Agriculture_economics\4_S_Gulf\4_Data\2_Crops\Cropping_Windows.xlsx For more information on this figure please contact CSIRO on enquiries@csiro.au CROP TYPECROPDECJANFEBMARAPRMAYJUNJULAUGSEPOCTNOVCROP DURATION(days) Cereal cropsSorghum (WS)ssssssgggg110—140Sorghum (DS)gssssssssssggg110—140Maize (WS)ssssssggg110—140Maize (DS)gssssssssssggg110—140Rice (WS)ssssgggg120—160+ Rice (DS)ssssgggg90—135 Pulse crops (food legumes)Mungbean (WS)ssssggg70—85Mungbean (DS)ssssggg70—85Chickpeassssgggg100—120OilseedsSoybean (WS)ssssssgggg110—130Sesamessssssggg110—130Root cropsPeanut (WS)ssssssggggg100—140Peanut (DS)gssssggg100—140Cassavassssssssssssssggggg180—210Industrial cropsCotton (WS)ssssssgggg100—120Cotton (DS)ssssssggggg100—120Hemp (fibre)ssssssssgggg110—150Forage, hay, silageRhodes grassggspspspgggspspspspPerennial (regrows) Forage sorghumssssssssgggssssssgg60—80 (regrows) Forage milletssssssssgggssssssgg60—80 (regrows) Forage maizegssssssgggssssssgg75—90Forage legumesCavalcadessggggggssss150—180Lablabssssssssssggggg130—160Horticulture (row crops)Melonsssssssgggg70—110Oniongssssssssssgggg130—160Capsicum, chilli, tomatossssggggg70—90 from transplantPineapplespspspgggggggPerennialHorticulture (vine)Table grapesspspspgggggggggPerenialHorticulture (tree crops)MangospspspgggggggggPerennialAvocadospspspgggggggggPerennialBananaspspspspggggggggPerennialLimespspspgggggggggPerennialLemonspspspgggggggggPerennialOrangespspspgggggggggPerennialCashewspspspgggggggggPerennialMacadamiaspspspgggggggggPerennialPlantation trees (silviculture)Africian mahoganyspspspgggggggggPerennialIndian sandalwoodspspspgggggggggPerennial (a) 70% of PAWC threshold (b) 80% of PAWC threshold Figure 4-6 Soil wetness indices that indicate when seasonal trafficability constraints are likely to occur on Vertosols (high clay), Kandosols (sandy loam) and sand at Kidman Springs for (a) a threshold of 70% of plant available water capacity (PAWC) and (b) 80% of PAWC The indices show the proportion of years (for dates at weekly intervals) when plant available water (PAW) in the top 30 cm of the soil is below two threshold proportions (70% and 80%) of the maximum PAW value. Lower values indicate there would be fewer days at that time of year when fields would be accessible and trafficable. Estimates are from 100-year Agricultural Production Systems Simulator simulations without a crop. In actual farming situations, once a crop canopy is established later in the season, crop water extraction from the soil would assist in alleviating these constraints. Growers also manage time of sowing to optimally use stored soil water and in-season rainfall, and to avoid rain damage at maturity. In the Victoria catchment mean monthly rainfall is highly variable between the wet and dry seasons (Figure 4-4) and irrigation allows growers the flexibility in sowing date and in the choice and timing of crop or forage systems in response to seasonal climate conditions. Depending on the rooting depth of a particular species and the length of growing season, crops established at the end of the wet season may access a full profile of soil water (e.g. ≥200 mm PAWC for some Vertosols). While timing sowing to the end of the wet season to take advantage of soil water may reduce the overall irrigation requirement, it may expose crops to periods of unfavourable solar radiation or temperatures during plant development and flowering. It may also prevent the implementation of a sequential cropping system. 4.3.3 Rainfed cropping Rainfed cropping (crops grown without irrigation, relying only on rain) has been attempted by farmers in the NT for almost 100 years, yet only small areas of rainfed crop production currently occur each year. This indicates that despite the theoretical possibility of producing rainfed crops using the significant wet-season rainfall in the Victoria catchment, in practice major agronomic and market-related challenges to rainfed crop production have prevented its expansion to date. Without the certainty provided by irrigation, rainfed cropping is opportunistic in nature, relying on favourable conditions in which to establish, grow and harvest a crop. The annual cropping calendar in Figure 4-5 shows that, for many crops, the sowing window includes the month of February. For relatively short-season crops, such as grain sorghum and mungbean, this coincides with both the sowing time that provides close to maximum crop yield and the time at which the Trafficability of soil based on how often the soil is above a 70% PAWC threshold graph \\fs1-cbr.nexus.csiro.au\{lw-rowra}\work\5_Agriculture_economics\2_Victoria\4_Data\2_APSIMmodelling\ViWRA-Charts_APSIM_v0_YO.xlsx For more information on this figure please contact CSIRO on enquiries@csiro.au Trafficability of soil based on how often the soil is above a 80% PAWC threshold graph \\fs1-cbr.nexus.csiro.au\{lw-rowra}\work\5_Agriculture_economics\2_Victoria\4_Data\2_APSIMmodelling\ViWRA-Charts_APSIM_v0_YO.xlsx For more information on this figure please contact CSIRO on enquiries@csiro.au season’s water supply can be accessed with a high degree of confidence. Table 4-5 shows how plant available soil water content at sowing and subsequent rainfall in the 90 days after each sowing date varies over three different sowing dates for a Vertosol in the Victoria catchment at Kidman Springs. As sowing is delayed from February to April, the amount of stored soil water increases. However, there is a significant decrease in rainfall in the 3 months after sowing. Combining the median PAW in the soil profile at sowing, and the median rainfall received in the 90 days following sowing provides totals of 460, 262 and 166 mm for the February, March and April sowing dates, respectively. Table 4-5 Soil water content at sowing, and rainfall for the 90-day period following sowing for three sowing dates, based on a Kidman Springs climate on a Vertosol PAW = plant available water stored in soil profile. The 80%, 50% (median) and 20% probabilities of exceedance values are reported for the 100 years between 1920 and 2020. The lower-bound values (80% exceedance) occur in most years, while the upper-bound values only occur in the most exceptional upper 20% of years. SOWING DATE PAW AT SOWING DATE (mm) RAINFALL IN 90 DAYS FOLLOWING SOWING DATE (mm) TOTAL STORED SOIL WATER + RAINFALL IN SUBSEQUENT 90 DAYS (mm) 80% 50% 20% 80% 50% 20% 80% 50% 20% 1 February 129 149 194 175 310 425 330 460 606 1 March 134 154 189 50 104 231 200 262 393 1 April 128 142 185 1 13 50 138 166 213 For drier-than-average years (80% probability of exceedance), the soil water stored at sowing and the expected rainfall in the ensuing 90 days (<330 mm) would result in water stress and comparatively reduced crop yields. In wetter-than-average years (20% probability of exceedance), the amount of soil water at the end of February combined with the rainfall in the following 90 days (606 mm) is sufficient to grow a good short-season crop (noting that the timing of rainfall is also important because some rain is ‘lost’ to runoff, evaporation and deep drainage between rainfall events). Opportunistic rainfed cropping would target those wetter years where PAW at the time of sowing indicated a higher chance of harvesting a profitable crop. The success of rainfed cropping is clearly dependent on wet-season rainfall, but also the ability of the soil to store water for the crop to use as it finishes growing into the dry season. Figure 4-7 highlights the effects of diminishing water availability and increasing evapotranspiration likely to be encountered when sowing a rainfed crop at the start of April or later. This constraint is much more severe for sandier soils, which have less capacity to store PAW (like Kandosols in the Victoria catchment, Figure 4-7a), compared to finer textured soils (like the alluvial Vertosols in the Victoria catchment, Figure 4-7b). (a) Kidman Springs Kandosol (sandy loam, PAWC 129 mm) (b) Kidman Springs Vertosol (high clay, PAWC 213 mm) Figure 4-7 Influence of planting date on rainfed grain sorghum yield at Kidman Springs for a (a) Kandosol and (b) Vertosol Estimates are from Agricultural Production Systems Simulator simulations with planting dates on the 1st and 15th of each month. PAWC values are the plant available water capacities of the soil profiles. The shaded band around the median line indicates the 80% to 20% exceedance probability range in year-to-year variation. Soil is seldom uniform within a single paddock, let alone across entire districts. Without the homogenising input of irrigation to alleviate water limitations (and associated high inputs of fertilisers to alleviate nutrient limitations), yields from low-input rainfed cropping are typically much more variable (both across years and locations) than yields from irrigated agriculture. Furthermore, the capacity of the soil to supply stored water varies with soil type, and it also depends on crop type and variety because each crop’s root system has a different ability to access water, particularly deep in the profile. This makes it harder to make generalisations about the viability of rainfed cropping in the Victoria catchment as farm performance (e.g. yields and GMs) is much more sensitive to slight variations in local conditions. Rigorous estimates of rainfed crop performance on which investment decisions could be confidently made would require detailed localised soil mapping and crop trials before investment decisions could be confidently made. Despite the challenges described above, recent efforts in the NT have identified potential opportunities for rainfed farming using higher-value crops, such as pulses or cotton. A preliminary APSIM assessment of the potential for rainfed cotton in the region suggested that mean lint yields of 2.5 to 3.5 bales per ha may be possible at a range of locations in the vicinity of the Victoria catchment (Yeates and Poulton, 2019). However, there was very high variability in median yields between farms (1–5 bales/ha), depending on management and soil type. 4.3.4 Irrigated crop response and performance metrics Crops that are fully irrigated can yield substantially more than rainfed crops. Figure 4-8 shows how yields for grain sorghum grown on a Kandosol in the Victoria catchment increase as more water becomes available to alleviate water limitations and meet increasing proportions of crop demand. With sufficient irrigation, yields are highest for (wet-season sown) crops grown over the dry season when radiation tends to be less limiting (comparing plateau of lines in Figure 4-8a and b). For wet-season sowing, unirrigated yields can approach fully irrigated yields in good years (yields exceeded in the top 20% of years, marked by the upper shaded range in Figure 4-8a). However, Graph of sorghum yield versus planting date of sorghum on a Kandosol \\fs1-cbr.nexus.csiro.au\{lw-rowra}\work\5_Agriculture_economics\2_Victoria\4_Data\2_APSIMmodelling\ViWRA-Charts_APSIM_v0_YO.xlsx For more information on this figure please contact CSIRO on enquiries@csiro.au Graph of sorghum yield versus planting date of sorghum on a Vertosol \\fs1-cbr.nexus.csiro.au\{lw-rowra}\work\5_Agriculture_economics\2_Victoria\4_Data\2_APSIMmodelling\ViWRA-Charts_APSIM_v0_YO.xlsx For more information on this figure please contact CSIRO on enquiries@csiro.au irrigation allows greater flexibility in sowing dates, allows sowing in the dry season too (for crops that would then grow through the wet season) and generates more reliable (and higher median) yields. (a) 1 February sowing (wet season) (b) 1 August sowing (dry season) Figure 4-8 Influence of available irrigation water on grain sorghum yields for planting dates of (a) 1 February and (b) 1 August, for a Kandosol with a Kidman Springs climate Estimates are from 100-year Agricultural Production Systems Simulator simulations. The shaded band around the median line indicates the 80% to 20% exceedance probability range in year-to-year variation. Rainfed production is indicated by the zero point, where no allocation is available for irrigation. The simulations did not seek to ‘optimise’ supplemental irrigation strategies in years where available water was insufficient to maximise crop yields; irrigators would need to make those decisions in years where available water was insufficient to fully meet crop demand. A key advantage of irrigated dry-season cropping in northern Australia is that the availability of water in the soil profile and surface water storages for growing the crop is largely known at the time of planting (near the start of the wet season; Table 4-5). This means irrigators have good advance knowledge for planning how much area to plant, which crops to grow and which irrigation strategies to use, particularly in years where they have insufficient water to fully irrigate all fields. A mix of irrigation approaches could be used, such as expanding the scale of a core irrigated cropping area with other less intensively farmed areas, opportunistic rainfed cropping, opportunistic supplemental irrigation, opportunistic sequential cropping and/or adjusting the area of fully irrigated crops grown to match available water supplies that year. Measures of farm performance (in terms of yields, water use and GMs) are presented for the 20 cropping options that were evaluated (Table 4-4). Given the limited commercial irrigated farming currently occurring in the Victoria catchment that can provide real-world data, estimates of crop water use and yields should be considered as indicative, and to have at least a 20% margin of error at the catchment scale (with further variation expected between farms and fields). The measures of performance should be considered as an upper bound of what could be achieved under best- practice management after learning and adapting to location-specific conditions. GMs are a key partial metric of farm performance but should not be treated as fixed constants determined by the cropping system alone. They are a product of the farming and business management decisions made by individual farmers, input prices, commodity prices and market opportunities (details on calculation of GMs are in Webster et al., 2024). As such, the GMs Graph of 1st February sorghum yield versus Irrigation water application on a Kandosol \\fs1-cbr.nexus.csiro.au\{lw-rowra}\work\5_Agriculture_economics\2_Victoria\4_Data\2_APSIMmodelling\ViWRA-Charts_APSIM_v0_YO.xlsx For more information on this figure please contact CSIRO on enquiries@csiro.au Graph of 1st August sorghum yield versus Irrigation water application on a Kandosol \\fs1-cbr.nexus.csiro.au\{lw-rowra}\work\5_Agriculture_economics\2_Victoria\4_Data\2_APSIMmodelling\ViWRA-Charts_APSIM_v0_YO.xlsx For more information on this figure please contact CSIRO on enquiries@csiro.au presented in Table 4-6 should be treated as indicative of what might be attained for each cropping option once its sustainable agronomic potential has been achieved. Any divergence from assumptions about yields and costs would flow through to GM values, as would the consequences of any underperformance or overperformance in farm management. It is unrealistic to assume that the levels of performance in the results below would be achieved in the early years of newly established farms, and allowance should be made for an initial period of learning when yields and GMs are below their potential (Chapter 6). Collectively however, the GMs and other performance metrics presented here provide an objective and consistent comparison across a suite of likely cropping options for the Victoria catchment, and indicate a maximum performance that could be achievable for greenfield irrigated development for each of the groupings of crops below. 4.3.5 Irrigated broadacre crops Table 4-6 shows the farm performance (yields, water use and GMs) for the ten broadacre cropping options that were evaluated. For crops that were simulated with APSIM, estimates are provided for locations with three different soil types associated with four climates in the Victoria catchment (Vertosol at Timber Creek, Red Dermosol at Kidman Springs, Vertosol at Montejinni and Red Kandosol at Wave Hill) and include measures of variability (expressed in terms of years with yield exceedance probabilities of 80%, 50% (median) and 20%). For other crops, yield and water use estimates (and resulting GMs) were estimated based on expert experience and climate-informed extrapolation from the most similar analogue locations in northern Australia where commercial production currently occurs. The broadacre cropping options with the best GMs (>$2000/ha) were cotton (both wet-season and dry-season cropping), forages (Rhodes grass (Chloris gayana)) and peanuts. These suggest GMs of $4000/ha to $5000/ha might be achievable for broadacre cropping in the Victoria catchment, although not necessarily at scale. Grain sorghum, mungbean, soybean and maize had intermediate GMs (about $1500/ha). Simulated yields (and consequent GMs) were generally lowest on the Kandosol and highest on the Vertosol because of the increased buffering capacity that a high PAWC clay soil provides against hot weather, which triggers water stress even in irrigated crops. The Dermosol yields and GMs were slightly lower than the Vertosol due to its lower PAWC. A breakdown of the variable costs for growing broadacre crops shows that the largest two costs are the costs of inputs (mean 31%) and farm operations (mean 32%) (Table 4-7). Both of these cost categories would have similar dollar values when growing the same crop in southern parts of Australia, but the cost category that is higher and thus puts northern growers at a disadvantage is market costs (mean 26%, for freight and other costs involved in selling the crop). Total variable costs consume 77% of the gross revenue generated, which leaves sufficient margin for profitable farms to be able to temporarily absorb small declines in commodity prices or yields without creating severe cashflow problems. Table 4-6 Performance metrics for broadacre cropping options in the Victoria catchment: applied irrigation water, crop yield and gross margin (GM) for four environments Performance metrics indicate the upper bound that could be achieved after best management practices for Victoria catchment environments had been identified and implemented. All options are for dry-season (DS) irrigated crops sown between mid-March and the end of April (end of the wet season (WS)), except for the WS cotton, sown in early February. Variance in yield estimates from Agricultural Production Systems sIMulator (APSIM) simulations is indicated by providing 80%, 50% (median, highlighted) and 20% probability of exceedance values (Y80%, Y50% and Y20%, respectively), together with associated applied irrigation water (including on-farm losses) and GMs in those years. ‘na’ indicates 20% and 80% exceedance estimates that were not applicable because APSIM outputs were not available and expert estimates of just the median yield and applied irrigation water were used instead. Peanut is omitted for the Vertosol location because of the practical constraints of harvesting root crops on clay soils. Freight costs assume processing near Katherine for cotton and peanut, and that hay is sold locally. No crop model was available for sesame or hemp, so indicative estimates for the catchment were used. Cotton yields and prices are for lint bales (227 kg after ginning), not tonnes. PAWC = plant available water capacity. For more information on this figure or table please contact CSIRO on enquiries@csiro.au For more information on this figure or table please contact CSIRO on enquiries@csiro.au For more information on this figure or table please contact CSIRO on enquiries@csiro.au Table 4-7 Breakdown of variable costs relative to revenue for broadacre crop options The first eight crops (Cotton (WS) to Rhodes grass) are for the Dermosol (intermediate performance), and the last three crops are for general catchment estimates. ‘Input’ costs are mainly for fertilisers, herbicides and pesticides; the cost of farm ‘operations’ includes harvesting; ‘labour’ costs are the variable component (mainly seasonal workers) not covered in fixed costs (mainly permanent staff); ‘market’ costs include levies, commission and transport to the point of sale. WS = wet season; DS = dry season. For more information on this figure or table please contact CSIRO on enquiries@csiro.au Risk analyses were conducted for the two broadacre crops with the highest GMs: cotton and forages. The risk analysis used a narrative approach, where variable values with the potential to be different from those used in the GMs were varied and new GMs calculated. The narrative approach allows the impact of those variables to be determined. The cotton analysis explored the sensitivity of GMs to opportunities and challenges created by changes in cotton lint prices, crop yields and distance to the nearest gin (Table 4-8). Results show that high recent cotton prices (about $800/bale through 2022) have created a unique opportunity for those looking to establish new cotton farms in NT locations like the Victoria catchment, since growers could transport cotton to distant gins or produce suboptimal yields and still generate GMs above $3000/ha. At lower cotton lint prices, a local gin becomes more important for farms to remain viable. High cotton prices and the opening of a cotton gin 30 km north of Katherine in December 2023 have reduced some of the risk involved in learning to grow cotton as GMs increase from both these developments. At high yields and prices, the returns per megalitre of irrigation water may favour growing a single cotton crop per year, instead of committing limited water supplies to sequential cropping with a dry-season crop (that would likely provide lower returns per megalitre and be operationally difficult/risky to sequence). Table 4-8 Sensitivity of cotton crop gross margins ($/ha) to variation in yield, lint prices and distance to gin The base case is the Timber Creek Vertosol (Table 4-6) and is highlighted for comparison. The gin locations considered are a local gin near a new cotton farming region in the Victoria catchment, the new gin in Katherine, and two other potential gins in the NT (Adelaide River) and north-west Queensland (Richmond). Cotton lint prices include a low price for 2015–2020 ($500/bale), a mean price for 2020–2024 ($700/bale) and a high price for 2015–2020 ($800/bale). Effects of a lower yield are also tested (the 6.5 bales/ha estimated as the dry-season yield for this location versus the base case of 11.4 bales/ha for wet-season cropping). For more information on this figure or table please contact CSIRO on enquiries@csiro.au For more information on this figure or table please contact CSIRO on enquiries@csiro.au The narrative risk analysis for irrigated forages also looked at the sensitivity of farm GMs to variations in hay price and distance to markets, but here focuses on the issues of local supply and demand (Table 4-9). Forages, such as Rhodes grass, are a forgiving first crop to grow on greenfield farms as new farmers gain experience of local cropping conditions and ameliorate virgin soils while producing a crop with a ready local market in cattle. While there are limited supplies of hay in the region, growers may be able to sell hay at a reasonable price, given the large amount of beef production in the Victoria and challenges of maintaining livestock condition through the dry season, when the quality of native pastures is low. The scale of unmet local demand for hay limits opportunities for expansion of hay production without depressing local prices and/or having to sell hay further away, both of which lead to rapid declines in GMs (to below zero in many cases; Table 4-9). Another opportunity for hay is for feeding to cattle during live export, which could be integrated into an existing beef enterprise to supply their own live export livestock; this would require the hay to be pelleted. Section 4.3.9 considers how forages could be integrated into local beef production systems for direct consumption by livestock within the same enterprise. Table 4-9 Sensitivity of forage (Rhodes grass) crop gross margins ($/ha) to variation in yield and hay price The base case is the Timber Creek Vertosol (Table 4-8) and is highlighted for comparison. Transporting the hay further distances would increase opportunities for finding counter-seasonal markets paying higher prices, but this would be rapidly offset by higher freight costs. FREIGHT COST/TONNE (DISTANCE TO DELIVER) FORAGE CROP GROSS MARGIN ($/ha) HAY PRICE/TONNE $150 $220 $300 $20 (local) 1,600 4,702 8,247 $46 (300 km to Katherine) 448 3,550 7,095 $308 (2000 km to Richmond) –11,160 –8,059 4,514 4.3.6 Irrigated horticultural crops Table 4-10 shows estimates of potential performance for a range of horticultural crop options in the Victoria catchment. Upper potential GMs for annual horticulture (about $4000 per ha per year) were less than upper potential GMs for farming perennial fruit trees (about $6000 per ha per year). Capital costs of farm establishment and operating costs increase as the intensity of farming increases, so ultimate farm financial viability is not necessarily better for horticulture compared to broadacre crops with lower GMs (Chapter 6). Note also that perennial horticulture crops typically require more water than annual crops because irrigation occurs for a longer period each year (mean of 9.0 compared to 4.8 ML per ha per year, respectively in Table 4-10); this also, indirectly, affects capital costs of development since perennial crops require a larger investment in water infrastructure compared to annual crops to support the same cropped area. Table 4-10 Performance metrics for horticulture options in the Victoria catchment: annual applied irrigation water, crop yield and gross margin Applied irrigation water includes losses of water during application. Horticulture is most likely to occur on well-drained Kandosols. Product unit prices listed are for the dominant top grade of produce, but total yield was apportioned among lower graded/priced categories of produce as well in calculating total income. Transport costs assume sales of total produce are split among southern capital markets in proportion to their size. Applied irrigation water accounts for application losses assuming efficient pressurised micro irrigation systems. KP = Kensington Pride mangoes. PVR = new high-yielding mango varieties with plant variety rights (e.g. Calypso). CROP APPLIED IRRIGATION WATER CROP YIELD PRICE PRICING UNIT VARIABLE COSTS TOTAL REVENUE GROSS MARGIN (ML/ha/y) (t/ha/y) ($/unit) (unit) ($/ha/y) ($/ha/y) ($/ha/y) Row crop fruit and vegetables, annual horticulture (less capital intensive) Rockmelon 5.3 25.0 28 15 kg tray 43,699 44,000 301 Watermelon 6.0 47.0 450 500 kg box 53,449 42,300 –11,149 Capsicum 3.2 32.0 19 8 kg carton 71,959 76,000 4,041 Onion 4.7 30.0 15 10 kg bag 37,607 41,850 4,243 Fruit trees, perennial horticulture (more capital intensive) Mango (KP) 7.8 9.3 24 7 kg tray 22,242 28,398 6,156 Mango (PVR) 7.8 17.5 21 7 kg tray 43,257 47,250 3,993 Lime 11.4 28.5 18 5 kg carton 95,666 100,890 5,224 Crop yields and GMs can vary substantially among varieties, as is demonstrated here for mangoes (Mangifera indica). Mango production is well established in multiple regions of northern Australia, including in the Darwin, Douglas–Daly and Katherine regions of the NT, with a smaller area of orchards at Mataranka in the Roper catchment. For example, the well-established Kensington Pride mangoes typically produce 5 to 10 t/ha while newer varieties can produce 15 to 20 t /ha. New varieties of mango (such as Calypso) are likely to be released with plant variety rights (PVR) accreditation and are denoted as such. Selection of varieties also needs to consider consumer preferences and timing of harvest relative to seasonal gaps in market supply that can offer premium prices. Prices received for fresh fruit and vegetables can be extremely volatile (Figure 4-9) because produce is perishable and expensive to store, and because regional weather patterns can disrupt target timing of supply, causing unintended overlaps or gaps in combined supply between regions. This creates regular fluctuations between oversupply and undersupply, against inelastic consumer demand, to the extent that prices can fall so low at times that it would cost more to pick, pack and transport produce than farms receive in payment. Within this volatility are some counter-seasonal windows in southern markets (where prices are typically higher) that northern Australian growers can target. Volatility in seedless water melon prices at Melbourne markets https://www.agriculture.gov.au/abares/data/weekly-commodity-price-update/australian-horticulture-prices#daff-page-main For more information on this figure please contact CSIRO on enquiries@csiro.au Figure 4-9 Fluctuations in seedless watermelon prices at Melbourne wholesale markets from April 2020 to February 2023 Percentage change information available; however, prices are commercially sensitive and not available Source: ABARES (2023) Horticultural enterprises typically run on very narrow margins, where about 90% of gross revenue would be required just to cover variable costs of growing and marketing a crop grown in the Victoria catchment. This makes crop GMs extremely sensitive to fluctuations in variable costs, crop yield and produce prices, amplifying the effect of already volatile prices for fresh fruit and vegetables. Most of the variable costs of horticultural production occur from harvest onwards, mainly in freight, labour and packaging. This affords the opportunity to mitigate losses if market conditions are unfavourable at the time of harvest, since most costs can be avoided (at the expense of foregone revenue) by not picking the crop. A narrative risk analysis for horticulture used the crop with the lowest GM (watermelons (Citrullus lanatus);(Table 4-8) to illustrate how opportunities for reducing freight costs and targeting periods of higher produce prices could improve GMs to find niches for profitable farms (Table 4-11). Reducing freight costs by finding backloading opportunities or concentrating on just the smaller closest southern capital city market of Adelaide would substantially improve GMs. The base case already assumed that growers in the Victoria catchment would target the predictable seasonal component of watermelon price fluctuations (Figure 4-9), but any further opportunity to attain premiums in pricing could help convert an unprofitable baseline case into a profitable one. This example also highlights the issue that while there may be niche opportunities that allow an otherwise unprofitable enterprise to be viable, the scale of those niche opportunities also then limits the scale to which the industry in that location could expand, for example: (i) there is a limit to the volume of backloading capacity at cheaper rates, (ii) supplying produce to only the closest market excludes the largest markets (e.g. accessing the larger Sydney and Melbourne markets remains non-viable except when prices are high; Table 4-11) and (iii) chasing price premiums restricts the seasonal windows into which produce is sold or restricts markets to smaller niches that target specialised product specifications. Niche opportunities are seldom scalable, particularly in horticulture, which is partly why horticulture in any region usually involves a range of different crops (often on the same farm). Table 4-11 Sensitivity of watermelon crop gross margins ($/ha) to variation in melon prices and freight costs The base case (Table 4-10) is highlighted for comparison. FREIGHT COST/TONNE WATERMELON PRICE (PERCENTAGE DIFFERENCE FROM BASE PRICE) (MARKET LOCATION) $225 (–50%) $337 (–25%) $450 (BASE PRICE) $675 (+50%) $900 (+100%) $350 (backloading to Adelaide) –20,150 –11,096 –1,961 16,228 34,417 $440 (close market: Adelaide) –24,380 –15,326 –6,191 11,998 30,187 $550 (all capital cities) –29,550 –20,496 –11,361 6,828 25,017 $616 (Sydney) –32,652 –23,598 –14,463 3,726 21,915 $584 (Melbourne) –31,308 –22,254 –13,119 5,070 23,259 The risk analysis also illustrates just how much farm financial metrics like GMs amplify fluctuations to input costs and commodity prices to which they are exposed. For horticulture, far more than broadacre agriculture, it is very misleading to look just at a single ‘median’ GM for the crop, because that is a poor reflection of what is going on within an enterprise. For example, the –50% to +100% variation in watermelon prices would result in theoretical annual GMs fluctuating between –$29,550/ha and $25,017/ha (Table 4-11). Although, in practice, potentially negative GMs could be greatly mitigated (by not harvesting the crop), this still creates cashflow challenges in managing years of negative returns between years of windfall profits. This amplified volatility is another reason that horticulture farms often grow a mix of produce (as a means of spreading risk). For row crop production, another common way of mitigating risk is using staggered planting through the season, so that subsequent harvesting and marketing are spread out over a longer target window to smooth out some of the price volatility. 4.3.7 Plantation tree crops Estimates of annual performance for African mahogany (Khaya ivorensis) and sandalwood (Santalum album) are provided in Table 4-12. The best available estimates were used in the analyses, but information on plantation tree production in northern Australia is often commercially sensitive and/or not independently verified. The measures of performance presented therefore have a low degree of confidence and should be treated as broadly indicative, noting that actual commercial performance could be either lower or higher. Table 4-12 Performance metrics for plantation tree crop options in the Victoria catchment: annual applied irrigation water, crop yield and gross margin Yields are values at final harvest and for sandalwood are just for the heartwood component. African mahogany pricing unit is for an 800 kg cube, and 10% of the African mahogany yield is marketable cubes. Other values are annual averages assuming a 20-year life cycle of the crop (representing the idealised ultimate steady state of an operating farm that was set up with staggered plantings for a steady stream of harvests). No discounting is applied to account for the substantial timing offset between when costs are incurred and income is received; any investment decision would need to take that into account. African mahogany performance is for unirrigated production. CROP CROP LIFE CYCLE APPLIED IRRIGATION WATER CROP YIELD AT HARVEST PRICE PRICING UNIT VARIABLE COSTS TOTAL REVENUE GROSS MARGIN (y) (ML/ha/y) (t/ha) ($/unit) ($/ha/y) ($/ha/y) ($/ha/y) African mahogany 20 unirrigated 160 4000 cube 980 4000 3020 Sandalwood 20 4.7 4 8800 t heartwood 1100 1760 660 Plantation forestry has long life cycles with low-intensity management during most of the growth cycle, so variable costs typically consume less of the gross revenue (27%) than for broadacre or horticultural farming. However, production systems with long life cycles have additional risks over annual cropping. There is a much longer period between planting and harvest for adverse events to affect the yield quantity and/or quality, and prices of inputs and harvested products could change substantially over that period. Market access and arrangements with buyers could also change. The long lags from planting to harvest also mean that potential investors need to consider other similar competing pipeline developments (that may not be obvious because they are not yet selling product) and long-term future projections of supply and demand (for when their own plantation will start to be harvested and enter supply chains). The cashflow challenges are also significant given the long-term outlay of capital and operating costs before any revenue is generated. Carbon credits might be able to assist with some early cashflow (if the ‘average’ state of the plantation, from planting to harvest, stores more carbon than the vegetation it replaced). 4.3.8 Cropping systems This section evaluates the types of cropping systems (crop species × growing season × resource availability × management options) that are most likely to be profitable in the Victoria catchment based on the above analyses of GMs, information from companion technical reports in this Assessment, and cropping knowledge from climate-analogous regions (relative to local biophysical conditions). Cropping system choices could include growing a single crop during a 12-month period, or growing more than one crop, commonly referred to as sequential, double or rotational cropping. Since many of the issues for single cropping options were covered earlier, this section focuses on sequential cropping systems and the mix of cropping options that might be grown in sequence on a unit of land in the Victoria catchment. Cropping system considerations In addition to the challenges of choosing an individual crop to farm in the Victoria catchment, selecting two or more crops to grow in sequence increases the complexity. The rewards from successfully growing crops in sequence (versus single cropping) can be substantial if additional net annual revenue can be generated from the same initial capital investment (to establish the farm). Markets Whether growing a single crop or doing sequential cropping, the choice of crop(s) to grow is market driven. As the price received for different crops fluctuates, so too will the crops grown. In the Victoria catchment, freight costs, determined by the distance to selected markets, must also be considered. A critical scale of production may be needed for a new market opportunity or supply chain to be viable (e.g. exporting grains from Darwin would require sufficient economies of scale for the required supporting port infrastructure, and shipping routes to be viable). Crops such as cotton, peanut and sugarcane (Saccharum officinarum) require a processing facility. A consistent and critical scale of production is required for processing facilities to be viable. From 2024 cotton will have the advantage of local processing, with a gin operational 30 km north of Katherine. Transporting raw cotton from the Victoria catchment to this gin would go a long way to improving the viability of cotton production (Table 4-8). Most horticultural production from the Victoria catchment would be sent to capital city markets, often using refrigerated transport. Victoria catchment horticultural production would have to accept a high freight cost compared to the costs faced by producers in southern parts of Australia. The competitive advantage of horticultural production in the Victoria catchment is that higher market prices can be achieved from ‘out of season’ production compared to large horticultural production areas in southern Australia. Annual horticultural row crops, such as melons, would be grown sequentially, for example with fortnightly planting over 3 to 4 months, to reduce risk of exposure to low market prices and to make it more likely that very high market prices would be achieved for at least some of the produce. Operations Sequential cropping can require a trade-off against sowing at optimal times to allow crops to be grown in a back-to-back schedule. This trade-off could lead to lower yields from planting at suboptimal times. For annual horticulture crops there would be an additional limitation on the seasonal window over which produce can be sent to market (reducing opportunities to target peak prices and/or mitigate risks from price fluctuations). Growing crops sequentially depends on timely transitions between the crops, and selecting crops with growing seasons that will reliably fit into the available cropping windows. In the Victoria catchment’s variable and often intense wet season, rainfall increases operational risk because of reduced trafficability and the subsequent limited ability to conduct timely operations. A large investment in machinery (either multiple or larger machines) could increase the area that could be planted per day when fields are trafficable within a planting window. With sequential cropping, additional farm machinery and equipment may be required where there are crop-specific machinery requirements, or to help complete operations on time when there is tight scheduling between crops. Any additional capital expenditure on farm equipment would need to be balanced against the extra net farm revenue generated. Sequential cropping can also lead to a range of cumulative issues that need careful management, for example: (i) build-up of pests, diseases (particularly if the sequential cropping is of the same species or family) and weeds; (ii) pesticide resistance; (iii) increased watertable depth; and (iv) soil chemical and structural decline. Many of these challenges can be anticipated before beginning sequential cropping. Integrated pest, weed and disease management would be essential when multiple crop species are grown in close proximity (adjacent fields or farms). Many of these pests and controls are common to several crop species where pests (e.g. aphids) move between fields. Such situations are exacerbated when the growing seasons of nearby crops partially overlap or when sequential crops are grown, because both scenarios create ‘green bridges’ that facilitate the continuation of pest life cycles. When herbicides are required, it is critical to avoid products that could damage a susceptible crop the following season or sequentially. Water Sequential cropping leads to a higher annual crop water demand because: (i) the combined period of cropping is longer (compared with single cropping), (ii) it includes growing during the Victoria catchment’s dry season and (iii) PAW at planting will have been depleted by the previous crop. Typically, an additional 1 ML/ha on well-drained soils, and 1.5 ML/ha on clays, is required for sequential cropping relative to the combined water requirements of growing each of those crops individually (with the same sowing times). This additional water demand needs consideration during development where on-farm water storage is required or dry-season water extraction is necessary. Irrigating using surface water in the Victoria catchment would face issues with the reliability and the timing of water supplies. Monitored river flows need to be sufficient to allow pumping into on- farm storages for irrigation (i.e. to meet environmental flow and river height requirements). The timing of water availability is analysed in the companion technical report on river model scenario analysis (Hughes et al., 2024). The timing of water availability is therefore not well suited to crops that would need to be reliably sown by March (e.g. wet-season grain sorghum, soybean and sesame), and it would push cotton planting to the later part of the wet-season window (Figure 4-5). The availability of water for extraction each wet season reduces the options for sequencing a second crop. Soils The largest arable areas in the Victoria catchment are loamy Kandosols on the deep low-relief Tertiary sediments in the south-western, southern and south-eastern (Sturt Plateau) parts of the catchment (SGGs 4.1 and 4.2, marked ‘A’ in Figure 4-3) and the cracking clay Vertosols on the alluvial plains of the major rivers, basalt and limestone landscapes (SGG 9, marked ‘B’, ‘C’ and ‘E’ in Figure 4-3). There are good analogues of these Victoria catchment environments in successful irrigated farming areas in other parts of northern Australia: Katherine is indicative of farming systems and potential crops grown on well-drained loamy soils irrigated by pressurised systems and the Ord River Irrigation Area is indicative of furrow irrigation on heavy clay soils. The good wet-season trafficability of the well-drained loamy Kandosols (Figure 4-6) permits timely cropping operations and would enhance the implementation of sequential cropping systems. However, Kandosols also present some constraints for farming. Kandosols are inherently low in organic carbon, nitrogen, phosphorus, sulfur, zinc and potassium, and supplementation with other micronutrients (molybdenum, boron and copper) is often required. Very high fertiliser inputs are therefore required at first cultivation. Due to the high risk of leaching of soluble nutrients (e.g. nitrogen and sulfur) during the wet season, in-crop application (multiple times) of the majority of crop requirement for these nutrients is necessary. In addition, high soil temperatures and surface crusting combined with rapid drying of the soil at seed depth reduce crop establishment and seedling vigour for many broadacre species sown during the wet season and early dry season (e.g. maize, soybean and cotton). In contrast, the cracking clay Vertosols have poor trafficability following rainfall (Figure 4-6) or irrigation, disrupting cropping operations. Farm design is a major factor on cracking clay soils to minimise flooding of fields from nearby waterways, ensure prompt runoff from fields after irrigation or rain events, and maintain trafficability of farm roads. Timely in-field bed preparation can reduce delays in planting. Clay soils also have some advantages, particularly in costs of farm development by allowing lower-cost surface irrigation (versus pressurised systems) and on-farm storages (where expensive dam lining can be avoided if soils contain sufficient clay). Clay soils also typically have greater inherent fertility than Kandosols (but initial sorption by clay means that phosphorus requirements can be high for virgin soils in the first 2 years of farming). Potentially suitable cropping systems Crop species that could potentially be grown as a single crop per year were identified and rated for the Victoria catchment (Table 4-13) based on indicators of farm performance presented above (yields, water use and GMs) and considerations of growing season, experiences at climate- analogous locations, past research, and known market and resource limitations and opportunities. Annual horticulture, cotton, peanut and forages are the most likely to generate returns that could exceed farm development and growing costs (Table 4-13). Table 4-13 Likely annual irrigated crop planting windows, suitability, and viability in the Victoria catchment Crops are rated on likelihood of being financially viable: *** = likely at low-enough development costs; ** = less likely for single cropping (at current produce prices); * S = marginal but possible in a sequential cropping system. Rating qualifiers are coded as L development limitation, M market constraint, P depends on sufficient scale and distance to local processor, and B depends on distance to and type of beef (livestock production) activity it is supporting. Farm viability depends on the cost at which land and water can be developed and supplied (Chapter 6). na = not applicable. For more information on this figure or table please contact CSIRO on enquiries@csiro.au Due to good wet-season trafficability on loamy soils, there are many possible sequential cropping options for the Victoria catchment Kandosols (Table 4-14). Due to the predominance of broadleaf and legume species in many of the sequences, a grass species is desirable as an early wet-season cover crop. Although annual horticulture and cotton could individually be profitable, an annual sequence of the two would be very tight operationally. Cotton would be best grown from late January with the need to pick the crop by early August, then destroy cotton stubble, prepare land and remove volunteer cotton seedlings. That scheduling would make it challenging to fit in a late- season melon crop, which would need to be sown by late August to early September. Similar challenges would occur with cotton followed by mungbean or grain sorghum. Table 4-14 Sequential cropping options for Kandosols WET-SEASON PLANTING, DECEMBER TO EARLY MARCH DRY-SEASON PLANTING, MARCH TO AUGUST CROP GROWING SEASON CROP GROWING SEASON Mungbean Early February to late April Annual horticulture Mid-May to late October Sorghum (grain) January to April Peanut (not on clay) January to April or February to May Cotton Late January to early August Mungbean Mid-August to late October Sorghum (grain) Mid-August to mid-November Forage/silage Mid-August to early November; cut then retained as wet-season cover crop Mungbean Early February to late April Cotton Early May to early November Mungbean Peanut Sesame Soybean Early February to late April Early January to late April Early January to late April Early January to late April Maize May to October Sesame or Sorghum (grain) January to late April Chickpea May to August Mungbean Sesame Soybean Early February to late April January to late April January to late April Grass forage/silage May to early November; cut then retained as wet-season cover crop Fully irrigated sequential cropping on the Victoria catchment Vertosols would likely be opportunistic and favour combinations of short-duration crops that can be grown when irrigation water reliability is greatest (March to October), for example, annual horticulture (melons), mungbean, chickpea and grass forages (growing season 2 to 4 months). Following an unirrigated (rainfed) wet-season grain crop with an irrigated dry-season crop could also be possible. However, seasonally dependent soil wetting and drying would limit timely planting and the area planted, which means that farm yields between years would be very variable. Grain sorghum, mungbean and sesame are the species most adapted to rainfed cropping due to favourable growing season length, and their tolerance to water stress, and higher soil and air temperatures. 4.3.9 Integrating forage and hay crops into existing beef cattle enterprises A commonly held view within the northern cattle industry is that the development of water resources would allow graziers to integrate irrigated forages and hay into existing beef cattle enterprises, thereby improving their production and, potentially, their profitability. Currently, cattle graze on native pastures, which rely solely on rainfall and any consequent overland flow. During the dry season, the total standing biomass and the nutritive value of the vegetation decline. Changes in cattle liveweight closely follow this pattern, with higher growth rates over the wet season than the dry season. In many cases, cattle lose liveweight and body condition throughout the dry season until the next pulse of growth initiated by wet-season rains. Theoretically, producing on-farm irrigated forage and hay would give graziers greater options for marketing cattle, such as meeting market liveweight specifications for cattle at a younger age, meeting the specifications required for markets not typically targeted by cattle enterprises in the Victoria catchment and providing cattle that meet market specification at a different time of the year. Forages and hay may also allow graziers to implement management strategies, such as early weaning or weaner feeding, which should have flow-on benefits throughout the herd, including increased reproductive rates. Some of these strategies are already practised within the Victoria catchment but in most instances rely on hay or other supplements purchased on the open market. By growing hay on-farm, the scale of these management interventions might be increased, at reduced net cost. The addition of irrigated feeds may also allow graziers to increase the total number of cattle that can be sustainably carried on a property. Very few graziers use irrigated hay or forage production to feed cattle on-farm in the Victoria catchment (Cowley, 2014). In fact, very few cattle enterprises in northern Australia are set up to integrate on-farm irrigation, notwithstanding the theoretical benefits. Despite its apparent simplicity, fundamentally altering an existing cattle enterprise in this way brings in considerable complexity, with a range of unknowns about how best to increase productivity and profitability. There is still much to be learned about the most appropriate forage and hay species to grow, how best to manage the forages and hay to ensure high-quality feed, which cohort(s) of cattle to feed, how the feeding should be managed and which market specifications should be targeted to obtain maximum return. Because there are so few on-ground examples, modelling has been used in a number of studies to consider the integration of forages and hay into cattle enterprises (Watson et al., 2021). The most comprehensive guide to what might be possible to achieve by integrating forages into cattle enterprises can be found in the guide by Moore et al. (2021), who used a combination of industry knowledge, new research and modelling to consider the costs, returns and benefits. Bio-economic modelling was used in the Assessment to consider the impact of growing irrigated forages and hay on a representative beef cattle enterprise on the black soils of the Ivanhoe land system (Pettit, undated), using Kidman Springs as the rainfall record (see the companion technical report on agricultural viability and socio-economics (Webster et al., 2024) for more detail). The enterprise was based on a self-replacing cow–calf operation, focused on selling into the live export market. Broadly speaking, these enterprise characteristics can be thought of as an owner– manager small cattle enterprise within the Victoria catchment. Cattle numbers are lower than that of the average property in the Victoria catchment but can be scaled to represent larger herds, notwithstanding that economies of scale will result in reduced costs per head in the larger enterprises. More detail on the beef industry in the Victoria catchment can be found in Section 3.3.3. The modelling considered a number of management options: (i) a base enterprise; (ii) base enterprise plus buying in hay to feed weaners; growing forage sorghum, an annual forage grass species, and feeding either as (iii) stand and graze or (iv) as hay; (v) growing lablab (Lablab purpureus), an annual legume, and feeding as stand and graze; and (vi) growing Rhodes grass, a perennial tropical grass, and feeding as hay. Ideally, production would increase by allowing cattle to reach minimum selling weight at a younger age and allowing for greater weight gain during the dry season when animals on native pasture alone either lose weight or gain very little weight. The addition of forages and hay also allows more cattle to be carried, while still maintaining a utilisation rate of native pastures at around 20%. A GM per adult equivalent (AE) was calculated as the total revenue from cattle sales minus total variable costs (Table 4-15). A profit metric, earnings before interest, taxes, depreciation and amortisation (EBITDA), was also calculated as income minus variable and overhead costs, which allows performance to be compared independently of financing and ownership structure (McLean and Holmes, 2015) and is used in the analysis of net present value (NPV). Three sets of beef prices were considered: • LOW beef price. Beef prices were set to 275c/kg for males between 12 and 24 months old, declining across age and sex classes to 134c/kg for cows older than 108 months. • MED beef price. Beef prices were set to 350c/kg for males between 12 and 24 months old, declining across age and sex classes to 170c/kg for cows older than 108 months. • HIGH beef price. Beef prices were set to 425c/kg for males between 12 and 24 months old, declining across age and sex classes to 206c/kg for cows older than 108 months. At all three beef prices, total income was highest for the four irrigated forage or hay scenarios compared to the two baseline scenarios, but the higher costs for the irrigated scenarios led to similar or lower GMs (Table 4-15). Table 4-15 Production and financial outcomes from the different irrigated forage and beef production options for a representative property in the Victoria catchment Details for LOW, MED and HIGH beef prices are in the text above. Descriptions of the six management options are in the companion technical report on agricultural viability and socio-economics (Webster et al., 2024). AE = adult equivalent; EBITDA = earnings before interest, taxes, depreciation and amortisation. Cattle are sold twice per year for all options. Cattle are sold in May for all options. Cattle are sold in September for the two base enterprises and for lablab stand and graze. Cattle are sold in October for forage sorghum stand and graze and the two hay options. BASE ENTERPRISE BASE ENTERPRISE PLUS HAY FORAGE SORGHUM – STAND AND GRAZE FORAGE SORGHUM – HAY LABLAB – STAND AND GRAZE RHODES GRASS – HAY Forage/hay None Bought hay Forage sorghum Forage sorghum Lablab Rhodes grass Maximum number of breeders 2050 2100 2230 2380 2290 2788 Mean of herd size (AE) across calendar year 2525 2553 2943 3084 2999 3094 Pasture utilisation (%) 20.1 20.1 20.1 20.1 20.0 20.1 BASE ENTERPRISE BASE ENTERPRISE PLUS HAY FORAGE SORGHUM – STAND AND GRAZE FORAGE SORGHUM – HAY LABLAB – STAND AND GRAZE RHODES GRASS – HAY Weaning rate (%) 59.2 60.4 62.6 64.6 63.8 64.6 Mortality rate (%) 6.8 6.8 6.6 6.3 6.2 6.2 Percentage of ‘one-year-old castrate males’ (8–11 or 8–12 months old) sold in September or October 0.0 0.0 8.8 78.4 62.8 78.9 Percentage of ‘one-and-a-half-year-old castrate males’ (15–19 months old) sold in May 77.5 86.8 79.4 20.3 27.6 19.9 Percentage of ‘two-year-old castrate males’ (20–23 or 20–24 months old) sold in September or October 9.1 6.7 11.8 1.3 9.7 1.2 Percentage of ‘two-and-a-half-year-old castrate males’ (27–31 months old) sold in May 13.4 6.6 0.0 0.0 0.0 0.0 Liveweight sold per year (kg) 343,106 351,446 415,624 468,346 443,607 471,258 Gross margin ($/AE) (LOW beef price) 133 120 –6 103 30 115 Profit (EBITDA) ($) (LOW beef price) 72,596 40,766 –282,084 52,172 –173,157 91,099 Gross margin ($/AE) (MED beef price) 219 206 79 171 119 183 Profit (EBITDA) ($) (MED beef price) 288,753 262,178 –32,710 262,928 93,007 303,166 Gross margin ($/AE) (HIGH beef price) 305 294 164 239 208 252 Profit (EBITDA) ($) (HIGH beef price) 504,910 487,103 216,664 473,683 359,172 515,232 At MED beef prices, EBITDA was highest for Rhodes grass hay ($303,166/year) and the lowest for forage sorghum stand and graze (–$32,710). The Rhodes grass hay option and the forage sorghum hay option produced the most liveweight sold per year and the two highest incomes. An NPV analysis allows consideration of the capital costs involved in development, which are not captured in the gross margin or EBITDA. The analysis used two costings ($15,000 and $25,000/ha) for the capital costs of development used in the NPV analysis. The NPV analysis showed that none of the options had a positive NPV (see the companion technical report on agricultural viability and socio-economics, Webster et al., 2024). Note that cost of capital theory is complex and investors need to understand their weighted average cost of capital and the relative risk of the project compared to the enterprise’s existing project portfolio before drawing their own conclusion from an NPV analysis. A significant proportion of the animal production increases due to the irrigated forage options came from the increased number of breeders that could be carried, while still keeping the utilisation rate of native pastures at about 20% (Table 4-15). The Rhodes grass hay option allowed the highest number of breeders to be carried (2788) compared with 2050 for the base enterprise. This flowed through to the total number of AE carried. The AE for Rhodes grass hay was 22% higher than that of the base enterprise and the total liveweight sold was on average 37% higher. The irrigated options increased the herd’s weaning rate by 3.4% to 5.4% compared to the base enterprise without weaner feeding. Even an increase of several per cent is known to have lifetime benefits throughout a herd. The most obvious biophysical impact of the various feeding strategies was the increase in liveweight compared to that of the base enterprise. This allowed a greater proportion of the animals to be sold earlier. For example, for the two hay options, nearly 79% of the ‘one-year-old castrate males’ (8–12 months old) were sold in October at a minimum weight of 280 kg, while no animals from the same cohort under the two base enterprise options met the minimum weight at that time (Table 4-15). Over 77% of these animals were retained for an additional wet-season, and sold in the following May as one-and-a-half year olds’ (15–19 months old). Keeping the utilisation rate at 20.0% meant that carrying these animals for the extra period lowered the number of breeders that could be carried and the overall stocking rate (AE). In summary, three patterns of growth to reach sale weight (280 kg) occurred: • For the two base enterprises, no animals reached sale weight in September as ‘one year olds’. By the following May 77.5% (base enterprise) or 86.8% (base enterprise plus hay) had reached sale weight. The following September 9.1% (base enterprise) or 6.7% (base enterprise plus hay) were sold as ‘two-year-olds’. The remaining 13.4% (base enterprise) or 6.6% (base enterprise plus hay) were then sold in the following May as ‘two-and-a-half year olds’. • By contrast, the majority of animals in the forage sorghum hay, lablab stand and graze, and Rhodes grass hay options were sold as ‘one year olds’ in September or October. The majority of the rest (20.3%, 27.6% and 19.9%, respectively) were sold in the following May. The remainder, less than 10%, were sold in the next September or October. None of this cohort remained for sale in the following May as ‘two-and-a-half year olds’. • The forage sorghum stand and graze option sat between these two extremes. Very few were sold as ‘one year olds’ in October, most were sold as ‘one-and-a-half year olds’ in the following May (79.4%) with all of the remainder sold in the following September. While there are advantages to some form of irrigated forage or hay production, the introduction of irrigation to an existing cattle enterprise requires additional skills and resources. The options here range from an area that would require 2.25 pivots of 40 ha each to an area that would require eight 40 ha pivots. A water allocation of about 1.5 to 2.2 GL would be required to provide sufficient irrigation water. The capital cost of development would range between $1,350,000 for 90 ha of Rhodes grass hay, at a development cost of $15,000/ha, to $8,000,000 for 320 ha of lablab at a development cost of $25,000/ha. In addition, the grazing enterprise would need to develop the expertise and knowledge required to run a successful irrigation enterprise of that scale, which is quite a different enterprise to one of grazing only. This is a constraint recognised by graziers elsewhere in northern Australia (McKellar et al., 2015) and almost certainly contributes to the lack of uptake of irrigation in the Victoria catchment. 4.4 Crop synopses 4.4.1 Introduction The estimates for land suitability in these synopses represent the total areas of the catchment unconstrained by factors such as water availability, landscape complexity, land tenure, environmental and other legislation and regulations, and a range of biophysical risks such as cyclones, flooding and secondary salinisation. These are addressed elsewhere by the Assessment. The land suitability maps are designed to be used predominantly at the regional scale. Farm-scale planning would require finer-scale, more localised assessment. 4.4.2 Cereal crops Cereal production is well established in Australia. The area of land devoted to producing grass grains (e.g. wheat, barley (Hordeum vulgare), grain sorghum, maize, oats (Avena sativa), triticale (× Triticosecale)) each year has stayed relatively consistent at about 20 million ha over the decade from 2012–13 to 2021–22, yielding over 55 Mt with a value of $19 billion in 2021–22 (ABARES, 2022). Production of cereals greatly exceeds domestic demand, and in 2021–22 the majority (82% by value) ted (ABARES, 2022). Significant export markets exist for wheat, barley and grain sorghum, with combined exports valued at $15 billion in 2021–22. There are additional niche export markets for grains such as maize and oats. Among the cereals, sorghum (grain) is promising for the Victoria catchment. Sorghum is grown over the summer period, coinciding with the Victoria catchment wet season. Sorghum can be grown opportunistically using rainfed production, although the years in which this could be successfully achieved will be limited. Cereal crop production is higher and more consistent when irrigation is used. From a land suitability perspective, selected cereal crops are included in Crop Group 7 (Table 4-2; Figure 4-10). Cracking clays (Vertosols) make up nearly 12% of the Victoria catchment; they are found on alluvial plains, relict alluvial plains, and on level to gently undulating plains on basalt (marked CA1, CA2, CB1 and CB2 on Figure 2-5). These soils have very high water-holding capacity but the non-basalt Vertosols may have a restricted rooting depth due to salt levels in the subsoil. Vertosols generally have moderate to high agricultural potential, but inadequate drainage and deep gilgais in some areas reduce the prospects for furrow irrigation. Poor drainage and low permeability will cause waterlogging in the wet season, especially along the Baines, lower West Baines and East Baines rivers. Loamy soils, mostly red loams, make up more than 18% of the catchment. These soils dominate the deeply weathered sediments of the Sturt Plateau in the east to south-east (marked K1 and K2 on Figure 2-5) and other deeply weathered landscapes to the south and west of Kalkarindji. Loamy soils are typically nutrient deficient and have low to high water-holding capacity. Irrigation potential is limited to spray- and trickle-irrigated crops on the moderately deep to deep soils. In parts of the catchment, loamy soils are found on narrow flat areas dissected by stream channels and deep gullies, making the land difficult to develop for broadacre cropping. Shallow and/or rocky soils make up a little more than 57% of the catchment and are unsuitable by definition. Assuming unconstrained development, approximately 2.9 million ha of the Victoria catchment is considered to be suitable with moderate limitations (Class 3; Table 4-1) or better (Class 2 or Class 1) for irrigated cereal cropping (Crop Group 7; Table 4-2) using spray irrigation in the dry season. For spray irrigation in the wet season, nearly 2.7 million ha is suitable with moderate limitations (Class 3) or better. Land considered suitable with moderate limitations for furrow irrigation is limited to about 625,500 ha in the dry season and 423,500 ha in the wet season, due to inadequate soil drainage in clay soils (and/or because gilgais are too deep) and because the loamy soils are too permeable. There is potential for rainfed cereal production in the wet season over an area of about 880,000 ha. Note that from a land suitability perspective, Crop Group 7 contains cereal crops and cotton; the latter is considered under industrial (cotton) in these crop synopses (Section 4.4.6). The ‘winter cereals’ such as wheat and barley are not well adapted to the climate of the Victoria catchment. To grow cereal crops, farmers will require access to tillage, fertilising, planting, spraying and harvesting equipment. Harvesting is often a contract operation, and in larger growing regions other activities can also be performed under contract. Because of the low relative value of cereals, good returns are made through production at a large scale. This requires machinery to be large so that operations can be completed in a timely way. Table 4-16 provides summary information relevant to the cultivation of cereals, using sorghum (grain) (Figure 4-11) as an example. The companion technical report on agricultural viability and socio-economics (Webster et al., 2024) provides greater detail for a wider range of cereal crops. Crop suitability map – grain sorghum, maize \\FS1-CBR.nexus.csiro.au\{lw-rowra}\work\10_Reporting\2_Victoria\1_GIS\1_Map_Docs\CR-V-Ch4_501_Suit_Sorghum_Grain_Maize_Grain_v3.mxd For more information on this figure please contact CSIRO on enquiries@csiro.au Figure 4-10 Modelled land suitability for Crop Group 7 (e.g. sorghum (grain) or maize) using furrow irrigation in the (a) wet season and (b) dry season These land suitability maps do not consider flooding, risk of secondary salinisation or availability of water. The methods used to derive the reliability data in the inset maps are outlined in the companion technical report on digital soil mapping and land suitability (Thomas et al., 2024). Table 4-16 Summary information relevant to the cultivation of cereals, using sorghum (grain) as an example For more information on this figure, table or equation please contact CSIRO on enquiries@csiro.au Figure 4-11 Sorghum (grain) Photo: CSIRO 4.4.3 Pulse crops (food legume) Pulse production is well established in Australia. The area of land devoted to production of pulses (mainly chickpea, lupin (Lupinus spp.) and field pea (Pisum sativum)) each year has varied from 1.1 to 2.0 million ha over the decade from 2012–13 to 2021–22, yielding over 3.8 Mt with a value of $2.5 billion in 2021–22 (ABARES, 2022). The vast majority of pulses in 2021–22 (93% by value) were exported (ABARES, 2022). Pulses produced in the Victoria catchment would most likely be exported, although there is presently no cleaning or bulk-handling facility. Pulses often have a short growing season. They are suited to opportunistic rainfed production over the wet season or more continuous irrigated production, often in rotation with cereals. Not all pulse crops are likely to be suited to the Victoria catchment. Those that are ‘tender’, such as field peas and beans, may not be well suited to the highly desiccating environment and periodically high temperatures. Direct field experimentation in the catchment is required to confirm this for these and other species. In the Victoria catchment, mungbean and chickpea are likely to be well suited. From a land suitability perspective, pulse crops are included in Crop Group 10 (Table 4-2; Figure 4-12). Cracking clays (Vertosols) make up nearly 12% of the Victoria catchment; they are found on alluvial plains, relict alluvial plains, and on level to gently undulating plains on basalt (marked CA1, CA2, CB1 and CB2 on Figure 2-5). These soils have very high water-holding capacity but the non- basalt Vertosols may have a restricted rooting depth due to salt levels in the subsoil. Vertosols generally have moderate to high agricultural potential, but inadequate drainage and deep gilgais in some areas reduce the prospects for furrow irrigation. Poor drainage and low permeability will mean waterlogging in the wet season, especially along the Baines, lower West Baines and East Baines rivers. Loamy soils, mostly red loams, make up more than 18% of the catchment. These soils dominate the deeply weathered sediments of the Sturt Plateau (marked K1 and K2 on Figure 2-5) in the east to south-east and other deeply weathered landscapes to the south and west of Kalkarindji. Loamy soils are typically nutrient deficient and have low to high water-holding capacity. Irrigation potential is limited to spray- and trickle-irrigated crops on the moderately deep to deep soils. In parts of the catchment, loamy soils are found on narrow flat areas dissected by stream channels and deep gullies, making the land difficult to develop for broadacre cropping. Shallow and/or rocky soils make up a little more than 57% of the catchment, and are unsuitable by definition. Assuming unconstrained development, approximately 2.6 million ha of the Victoria catchment is considered to be suitable with moderate limitations (Class 3; Table 4-1) or better (Class 2 or Class 1) for irrigated pulse cropping (Crop Group 10; Table 4-2) using spray irrigation in the dry season, most of this being Class 2. Land considered suitable with moderate limitations for furrow irrigation is limited to about 395,000 ha in the dry season, due to inadequate soil drainage in clay soils (and/or because gilgais are too deep) and because the loamy soils are too permeable. There is potential for rainfed pulse production in the wet season over an area of about 570,000 ha. From a land suitability perspective, Crop Group 10 includes the pulse crops mungbean and chickpea, while soybean is considered under oilseed in these crop synopses. Pulses are often advantageous in rotation with other crops because they provide a disease break and, being legumes, can provide nitrogen for subsequent crops. Even where this is not the case, their ability to meet their own nitrogen needs can be beneficial in reducing costs of fertiliser and associated freight. Pulses such as mungbean and chickpea can also be of high value (historical prices have reached >$1000/t), so the freight costs as a percentage of the value of the crop are lower than for cereal grains. To grow pulse crops, farmers will require access to tillage, fertilising, planting, spraying and harvesting equipment. Harvesting is generally a contract operation, and in larger growing regions other activities can also be performed under contract. The equipment required for pulse crops is the same as is required for cereal crops, so farmers intending on a pulse and cereal rotation would not need to purchase pulse-specific equipment. Table 4-17 provides summary information relevant to the cultivation of many pulses, using mungbean (Figure 4-13) as an example. The companion technical report on agricultural viability and socio-economics (Webster et al., 2024) provides greater detail for a wider range of crops. Crop suitability map – mungbean \\FS1-CBR.nexus.csiro.au\{lw-rowra}\work\10_Reporting\2_Victoria\1_GIS\1_Map_Docs\CR-V-Ch4_502_Suit_Mungbean_Mungbean_v2.mxd For more information on this figure please contact CSIRO on enquiries@csiro.au Figure 4-12 Modelled land suitability for mungbean (Crop Group 10) in the dry season using (a) furrow irrigation and (b) spray irrigation These land suitability maps do not consider flooding, risk of secondary salinisation or availability of water. The methods used to derive the reliability data in the inset maps are outlined in the companion technical report on digital soil mapping and land suitability (Thomas et al., 2024). Figure 4-13 Mungbean Photo: CSIRO Table 4-17 Summary information relevant to the cultivation of pulses, using mungbean as an example For more information on this figure, table or equation please contact CSIRO on enquiries@csiro.au 4.4.4 Oilseed crops The area of land devoted to production of oilseed (predominantly canola, Brassica napus) each year has varied between 2.1 and 3.4 million ha over the decade from 2012–13 to 2021–22, yielding over 8.4 Mt with a value of $6.1 billion in 2021–22 (ABARES, 2022). Most oilseed produced in 2021–22 (98% by value) was exported (ABARES, 2022). Canola dominates Australian oilseed production, accounting for 98% of the gross value of oilseed in 2021–22. Soybean, sunflower (Helianthus annuus) and other oilseed (including peanuts) each accounted for less than 1%. Soybean, canola and sunflower are oilseed crops used to produce vegetable oils and biodiesel, and as high-protein meals for intensive animal production. Soybean is also used in processed foods such as tofu. It can provide both green manure and soil benefits in crop rotations, with symbiotic nitrogen fixation adding to soil fertility and sustainability in an overall cropping system. Soybean is used commonly as a rotation crop with sugarcane in northern Queensland, providing a disease break and nitrogen to the soil. Summer oilseed crops such as soybean, sesame and sunflower are more suited to tropical environments than are winter-grown oilseed crops such as canola. Cottonseed is also classified as an oilseed and is used for animal production. Soybean is sensitive to photoperiod (day length) and requires careful consideration in selection of the appropriate variety for a particular sowing window. From a land suitability perspective, soybean is included in Crop Group 10 (Table 4-2; Figure 4-14). Cracking clays (Vertosols) make up nearly 12% of the Victoria catchment; they are found on alluvial plains, relict alluvial plains, and on level to gently undulating plains on basalt (marked CA1, CA2, CB1 and CB2 on Figure 2-5). These soils have very high water-holding capacity but the non- basalt Vertosols may have a restricted rooting depth due to salt levels in the subsoil. Vertosols generally have moderate to high agricultural potential, but inadequate drainage and deep gilgais in some areas reduce the prospects for furrow irrigation. Poor drainage and low permeability will mean waterlogging in the wet season, especially along the Baines, lower West Baines and East Baines rivers. Loamy soils, mostly red loams, make up more than 18% of the catchment. These soils dominate the deeply weathered sediments of the Sturt Plateau (marked K1 and K2 on Figure 2-5) in the east to south-east and other deeply weathered landscapes to the south and west of Kalkarindji. Loamy soils are typically nutrient deficient and have low to high water-holding capacity. Irrigation potential is limited to spray- and trickle-irrigated crops on the moderately deep to deep soils. In parts of the catchment, loamy soils are found on narrow flat areas dissected by stream channels and deep gullies, making the land difficult to develop for broadacre cropping. Shallow and/or rocky soils make up a little more than 57% of the catchment, and are unsuitable by definition. Assuming unconstrained development, approximately 2.6 million ha of the Victoria catchment is considered to be suitable with moderate limitations (Class 3; Table 4-1) or better (Class 2 or Class 1) for irrigated pulse cropping (Crop Group 10; Table 4-2) using spray irrigation in the dry season, most of this being Class 2. Land considered suitable with moderate limitations for furrow irrigation is limited to about 395,000 ha in the dry season, due to inadequate soil drainage in clay soils (and/or because gilgais are too deep) and because the loamy soils are too permeable. There is potential for rainfed pulse production in the wet season over an area of about 570,000 ha. From a land suitability perspective, soybean is in Crop Group 10, which contains the pulse crops. Two of these, mungbean and chickpea, are considered under pulse crops (food legume) in these crop synopses. To grow oilseed crops, farmers will require access to tillage, fertilising, planting, spraying and harvesting equipment. Harvesting is generally a contract operation, and in larger growing regions other activities can also be performed under contract. The equipment required for oilseed crops is the same as is required for cereal crops, so farmers intending on an oilseed and cereal rotation would not need to purchase oilseed-specific equipment. Table 4-18 provides summary information relevant to the cultivation of oilseed crops using soybean (Figure 4-15) as an example. The companion technical report on agricultural viability and socio-economics (Webster et al., 2024) provides greater detail for a wider range of crops. Crop suitability map – soybean \\FS1-CBR.nexus.csiro.au\{lw-rowra}\work\10_Reporting\2_Victoria\1_GIS\1_Map_Docs\CR-V-Ch4_503_Suit_Soybean_Soybean_v2.mxd For more information on this figure please contact CSIRO on enquiries@csiro.au Figure 4-14 Modelled land suitability for soybean (Crop Group 10) in the dry season using (a) furrow irrigation and (b) spray irrigation These land suitability maps do not consider flooding, risk of secondary salinisation or availability of water. The methods used to derive the reliability data in the inset maps are outlined in the companion technical report on digital soil mapping and land suitability (Thomas et al., 2024). Figure 4-15 Soybean Photo: CSIRO Table 4-18 Summary information relevant to the cultivation of oilseed crops, using soybean as an example For more information on this figure, table or equation please contact CSIRO on enquiries@csiro.au 4.4.5 Root crops, including peanut Root crops, including peanut, sweet potato (Ipomoea batatas) and cassava (Manihot esculenta), are potentially well suited to the lighter soils found across the Victoria catchment. Root crops such as these are not suited to growing on heavier clay soils because they need to be pulled from the ground for harvest, and the heavy clay soils, such as cracking clays, are not conducive to mechanical pulling. While peanut is technically an oilseed crop, it has been included in the root crop category due to its similar land suitability and management requirements (i.e. the need for it to be pulled from the ground as part of the harvest operation). The most widely grown root crop in Australia, peanut is a legume crop that requires little or no nitrogen fertiliser and is very well suited to growing in rotation with cereal crops, as it is frequently able to fix atmospheric nitrogen in the soil for following crops. The Australian peanut industry currently produces approximately 15,000 to 20,000 t/year from around 11,000 ha, which is too small an industry to be reported separately in Australian Bureau of Agricultural and Resource Economics and Sciences statistics (ABARES, 2022). The Australian peanut industry is concentrated in Queensland. In northern Australia, a production area is present on the Atherton Tablelands, and peanuts could likely be grown in the Victoria catchment. The Peanut Company of Australia established a peanut-growing operation at Katherine in 2007 and examined the potential of both wet- and dry-season peanut crops, mostly in rotation with maize. Due to changing priorities within the company, coupled with some agronomic challenges (Jakku et al., 2016), the company sold its land holdings in Katherine in 2012 (and Bega bought the rest of the company in 2018). For peanuts to be successful, considerable planning would be needed in determining the best season for production and practical options for crop rotations. The nearest peanut-processing facilities to the Victoria catchment are Tolga on the Atherton Tablelands and Kingaroy in southern Queensland. From a land suitability perspective, peanut is included in Crop Group 6 (Table 4-2; Figure 4-16). Cracking clays (Vertosols) make up nearly 12% of the Victoria catchment (Figure 2-5). These soils have very high water-holding capacity but the non-basalt Vertosols may have a restricted rooting depth due to salt levels in the subsoil. Vertosols generally have moderate to high agricultural potential, but these heavier-textured soils are generally unsuited to root crops due to difficulties with pulling of crops from these soils during harvest. Loamy soils, mostly red loams, make up more than 18% of the catchment. These soils dominate the deeply weathered sediments of the Sturt Plateau in the east to south-east (marked K1 and K2 on Figure 2-5) and other deeply weathered landscapes to the south and west of Kalkarindji. Loamy soils are typically nutrient deficient and have low to high water-holding capacity. Irrigation potential is limited to spray- and trickle- irrigated crops on the moderately deep to deep soils. In parts of the catchment, loamy soils are found on narrow flat areas dissected by stream channels and deep gullies, making it difficult to develop for broadacre cropping. Shallow and/or rocky soils make up a little more than 57% of the catchment and are unsuitable by definition. Assuming unconstrained development, approximately 2.3 million ha of the Victoria catchment is considered to be suitable with moderate limitations (Class 3; Table 4-1) or better (Class 2 or Class 1) for irrigated root crops (Crop Group 6; Table 4-2) using spray irrigation in the dry season, most of this being Class 2. For spray irrigation in the wet season, nearly 1.9 million ha is suitable with moderate limitations (Class 3) or better, again most being Class 2. Furrow irrigation is not suited to either season, with wetness on the heavier-textured soils being the limitation and the lighter textured soils being too permeable, therefore furrow irrigation was not considered in the land suitability analysis. To grow root crops, farmers will require access to tillage, fertilising, planting, spraying and harvesting equipment. The harvesting operation requires specialised equipment to pull the crop from the ground, and then to pick it up after a drying period. Peanuts are usually dried soon after harvest in industrial driers. Table 4-19 provides summary information relevant to the cultivation of root crops, using peanut (Figure 4-17) as an example. The companion technical report on agricultural viability and socio- economics (Webster et al., 2024) provides greater detail for a wider range of crops. P2015#yIS1 Figure 4-16 Modelled land suitability for peanut (Crop Group 6) using spray irrigation in the (a) wet season and (b) dry season These land suitability maps do not consider flooding, risk of secondary salinisation or availability of water. The methods used to derive the reliability data in the inset maps are outlined in the companion technical report on digital soil mapping and land suitability (Thomas et al., 2024). P2018#yIS1 Figure 4-17 Peanut Photo: Shutterstock Table 4-19 Summary information relevant to the cultivation of root crops, using peanut as an example For more information on this figure, table or equation please contact CSIRO on enquiries@csiro.au 4.4.6 Industrial (cotton) Rainfed and irrigated cotton production are well established in Australia. The area of land devoted to cotton production varies widely from year to year, largely in response to availability of water. It varied from 70,000 to 600,000 ha between 2012–13 and 2021–22; a mean of 400,000 ha/year has been grown over the decade (ABARES, 2022). Likewise, the gross value of cotton lint production varied greatly between 2012–13 and 2021–22, from $0.3 billion in 2019–20 to $5.2 billion in 2021– 22. Genetically modified cotton varieties were introduced in 1996 and now account for almost all cotton produced in Australia (over 99%). Australia was the fourth largest exporter of cotton in 2022, behind the United States, India and Brazil. Cottonseed is a by-product of cotton processing and is a valuable cattle feed. Mean lint production in Australia in 2015–16 was 8.8 bales/ha (ABARES, 2022). Commercial cotton has a long but discontinuous history of production in northern Australia, including in Broome, the Fitzroy River and the Ord River Irrigation Area in WA; in Katherine and Douglas–Daly in the NT; and near Richmond and Bowen in northern Queensland. An extensive study undertaken by the Australian Cotton Cooperative Research Centre in 2001 (Yeates, 2001) noted that past ventures suffered from: • a lack of capital investment • too rapid a movement to commercial production • a failure to adopt a systems approach to development • climate variability. Mistakes in pest control were also a major issue in early projects. Since the introduction of genetically modified cotton in 1996, yields and incomes from cotton crops have increased in most regions of Australia. The key benefits of genetically modified cotton over conventional cotton are savings in insecticide and herbicide use, and improved tillage management. In addition, farmers can now forward-sell their crop as part of a risk management strategy. Growers of genetically modified cotton are required to comply with the approved practices for growing the genetically modified varieties, including preventative resistance management. Research and commercial test farming have demonstrated that the biophysical challenges are manageable if the growing of cotton is tailored to the climate and biotic conditions of northern Australia (Yeates et al., 2013). In recent years, irrigated cotton crops achieving more than 10 bales/ha have been grown successfully in the Burdekin irrigation region and experimentally in the Gilbert catchment of northern Queensland. New genetically modified cotton using CSIRO varieties that are both pest- and herbicide-resistant are an important component of these northern cotton production systems. Climate constraints will continue to limit production potential of northern cotton crops when compared to cotton grown in more favourable climate regions of NSW and Queensland. On the other hand, the low risk of rainfall occurring during late crop development favours production in northern Australia, as it minimises the likelihood of late-season rainfall, which can downgrade fibre quality and price. Demand for Australian cotton exhibiting long and fine attributes is expected to increase by 10% to 20% of the market during the next decade and presents local producers with an opportunity to target production of high-quality fibre. From a land suitability perspective, cotton is included in Crop Group 7 (Table 4-2; Figure 4-18). Cracking clays (Vertosols) make up nearly 12% of the Victoria catchment; they are found on alluvial plains, relict alluvial plains, and on level to gently undulating plains on basalt (marked CA1, CA2, CB1 and CB2 on Figure 2-5). These soils have very high water-holding capacity but the non- basalt Vertosols may have a restricted rooting depth due to salt levels in the subsoil. Vertosols generally have moderate to high agricultural potential, but inadequate drainage and deep gilgais in some areas reduce the prospects for furrow irrigation. Poor drainage and low permeability will cause waterlogging in the wet season, especially along the Baines, lower West Baines and East Baines rivers. Loamy soils, mostly red loams, make up more than 18% of the catchment. These soils dominate the deeply weathered sediments of the Sturt Plateau in the east to south-east (marked K1 and K2 on Figure 2-5) and other deeply weathered landscapes to the south and west of Kalkarindji. Loamy soils are typically nutrient deficient and have low to high water-holding capacity. Irrigation potential is limited to spray- and trickle-irrigated crops on the moderately deep to deep soils. In parts of the catchment, loamy soils are found on narrow flat areas dissected by stream channels and deep gullies, making the land difficult to develop for broadacre cropping. Shallow and/or rocky soils make up a little more than 57% of the catchment, and are unsuitable by definition. Assuming unconstrained development, approximately 2.9 million ha of the Victoria catchment is considered to be suitable with moderate limitations (Class 3; Table 4-1) or better (Class 2 or Class 1) for irrigated cotton (Crop Group 7; Table 4-2) using spray irrigation in the dry season. For spray irrigation in the wet season, nearly 2.7 million ha is suitable with moderate limitations (Class 3) or better. Land considered suitable with moderate limitations for furrow irrigation is limited to about 625,500 ha in the dry season and 423,500 ha in the wet season, due to inadequate soil drainage in clay soils (and/or because gilgais are too deep) and because the loamy soils are too permeable. There is potential for rainfed cotton production in the wet season over an area of about 880,000 ha. From a land suitability perspective, Crop Group 7 contains both cotton and cereal crops; the latter are considered in Section 4.4.2. In addition to a normal row planter and spray rig equipment used in cereal production, cotton requires access to suitable picking and module or baling equipment, as well as transport to processing facilities. Decisions on initial development costs and scale of establishing cotton production in the catchment would need to consider the need to source external contractors; this could provide an opportunity to develop local contract services to support a growing industry. Cotton production is also highly dependent on access to processing plants (cotton gins). The first cotton gin in the NT opened in December 2023 and is the closest processing facility for cotton grown in the Victoria catchment (30 km north of Katherine, approximately 140 km east of the Victoria catchment boundary). A cotton gin has also been proposed for Kununurra. Niche industrial crops, such as guar (Cyamopsis tetragonoloba) and chia (Salvia hispanica), may be feasible for the Victoria catchment, but verified agronomic and market data on these crops are limited. Past research on guar has been conducted in the NT, and trials are currently underway. Hemp is a photoperiod-sensitive summer annual with a growing season between 70 and 120 days depending on variety and temperature. Hemp is well suited to growing in rotation with legumes, as hemp can use the nitrogen fixed by the legume crop. Industrial hemp can be harvested for grain with modifications to conventional headers, otherwise all other farming machinery for ground preparation, fertilising and spraying can be used. There are legislative restrictions to growing hemp in Australia, and jurisdictions including the NT are implementing industrial hemp legislation to license growing of industrial hemp to facilitate development of the industry. The companion technical report on agricultural viability and socio-economics (Webster et al., 2024) provides greater detail for a wider range of industrial crops. Table 4-20 describes some key considerations relating to cotton production (Figure 4-19). P2090#yIS1 Figure 4-18 Modelled land suitability for cotton (Crop Group 7) using furrow irrigation in the (a) wet season and (b) dry season These land suitability maps do not consider flooding, risk of secondary salinisation or availability of water. The methods used to derive the reliability data in the inset maps are outlined in the companion technical report on digital soil mapping and land suitability (Thomas et al., 2024). Cotton P2093#yIS1 Figure 4-19 Cotton Photo: CSIRO Table 4-20 Summary information relevant to the cultivation of cotton For more information on this figure, table or equation please contact CSIRO on enquiries@csiro.au 4.4.7 Forages Forage, hay and silage are crops that are grown specifically for consumption by animals. Forage is consumed in the paddock in which it is grown, which is often referred to as ‘stand and graze’. Hay is cut, dried, baled and stored before being fed to animals at a time when natural pasture production is low (generally towards the end of the dry season). Silage use resembles that for hay, but crops are stored wet, in anaerobic conditions where fermentation occurs, to preserve the feed’s nutritional value. Rainfed and irrigated production of forage crops is well established throughout Australia, with over 20,000 producers, most of whom are not specialist forage crop producers. Approximately 85% of forage production is consumed domestically, with the rest primarily used on live export ships often in a pelleted form. The largest consumers are the horse, dairy and beef feedlot industries. Forage crops are also widely used in horticulture for mulches and for erosion control. While there is already consumption use of forages by the northern beef industry, forage costs constitute less than 5% of beef production costs (Gleeson et al., 2012), so there is likely room for further expansion of forage production. Non-leguminous forage, hay and silage The Victoria catchment is suited to rainfed or irrigated production of non-leguminous forage, hay and silage. A significant amount of rainfed hay production occurs in the Douglas–Daly region, south of Darwin. Most of the hay produced in the NT is to locally feed cattle destined for live export or used as part of feed pellets used on boats carrying live export cattle. Forage crops, both annual and perennial, include sorghum (Sorghum spp.), Rhodes grass, maize and Jarra grass (Digitaria milanjiana ‘Jarra’), with particular cultivars specific for forage. These grass forages require considerable amounts of water and nitrogen as they can be high yielding (20 to 40 t dry matter per ha per year). Given the rapid growth of grass forages, crude protein levels can decrease very quickly, reducing their value as a feed for livestock. To maintain high nutritive value, high levels of nitrogen must be applied, and in the case of hay the crop needs to be cut every 45 to 60 days. After cutting, the crop grows back without the need for resowing. The rapid growth of forage during the wet season can make it challenging to match animal stocking rates to forage growth so that it is kept leafy and nutritious, and does not become rank and of low quality. Producing rainfed hay from perennials gives producers the option of irrigating when required or, if water becomes limiting, allowing the pasture to remain dormant before water again becomes available. Silage can be made from a number of crops, such as grasses, maize and forage sorghum. From a land suitability perspective, Rhodes grass is included in Crop Group 14 (Table 4-2; Figure 4-20). Cracking clays (Vertosols) make up nearly 12% of the Victoria catchment; they are found on alluvial plains, relict alluvial plains, and on level to gently undulating plains on basalt (marked CA1, CA2, CB1 and CB2 on Figure 2-5). These soils have very high water-holding capacity but the non- basalt Vertosols may have a restricted rooting depth due to salt levels in the subsoil. Vertosols generally have moderate to high agricultural potential, but inadequate drainage and deep gilgais in some areas reduce the prospects for furrow irrigation. Poor drainage and low permeability will cause waterlogging in the wet season, especially along the Baines, lower West Baines and East Baines rivers. Loamy soils, mostly red loams, make up more than 18% of the catchment. These soils dominate the deeply weathered sediments of the Sturt Plateau in the east to south-east (marked K1 and K2 on Figure 2-5) and other deeply weathered landscapes to the south and west of Kalkarindji. Loamy soils are typically nutrient deficient and have low to high water-holding capacity. Irrigation potential is limited to spray- and trickle-irrigated crops on the moderately deep to deep soils. In parts of the catchment, loamy soils are found on narrow flat areas dissected by stream channels and deep gullies, making the land difficult to develop for broadacre cropping. Shallow and/or rocky soils make up a little more than 57% of the catchment, and are unsuitable by definition. Assuming unconstrained development, approximately 2.9 million ha of the Victoria catchment is considered to be suitable with moderate limitations (Class 3; Table 4-1) or better (Class 2 or Class 1) for irrigated cropping of annual forages (Crop Group 12; Table 4-2) using spray irrigation in the dry season, most of this being Class 2. For spray irrigation in the wet season, nearly 2.7 million ha is suitable with moderate limitations (Class 3) or better, again the majority being Class 2. Land considered suitable with moderate limitations for furrow irrigation of annual forages is limited to about 625,000 ha in the dry season and about 420,000 ha in the wet season, due to inadequate soil drainage in clay soils (and/or because gilgais are too deep) and because the loamy soils are too permeable. There is potential for rainfed production of annual forages in the wet season over an area of about 850,000 ha. For the perennial Rhodes grass, about 2.9 million ha are suitable with moderate or minor limitations under spray irrigation and about 620,000 ha under furrow irrigation. Apart from irrigation infrastructure, the equipment needed for forage production is machinery for planting and fertilising. Spraying equipment is also desirable but not necessary. Cutting crops for hay or silage requires more-specialised harvesting, cutting, baling and storage equipment. Table 4-21 describes Rhodes grass production (Figure 4-21) for hay over 1 year of a 6-year cycle. Information similar to that in Table 4-21 for grazed forage crops is presented in the companion technical report on agricultural viability and socio-economics (Webster et al., 2024). P2160#yIS1 Figure 4-20 Modelled land suitability for Rhodes grass (Crop Group 14) using (a) spray irrigation and (b) furrow irrigation These land suitability maps do not consider flooding, risk of secondary salinisation or availability of water. The methods used to derive the reliability data in the inset maps are outlined in the companion technical report on digital soil mapping and land suitability (Thomas et al., 2024). Rhodes grass P2163#yIS1 Figure 4-21 Rhodes grass Photo: CSIRO Table 4-21 Rhodes grass production for hay over 1 year of a 6-year cycle For more information on this figure, table or equation please contact CSIRO on enquiries@csiro.au Forage legume The use of forage legumes is similar to that of forage grasses. They are generally grazed by animals but can also be cut for silage or hay. Some forage legumes are well suited to the Victoria catchment and would be considered among the more promising opportunities for irrigated agriculture (Figure 4-22). Forage legumes are desirable because of their high protein content and their ability to fix atmospheric nitrogen. The nitrogen fixed during a forage legume phase is often in excess of that crop’s requirements, which leaves the soil with additional nitrogen. Forage legumes are being used by the northern cattle industry, and farmers primarily engaged in extensive cattle production could use irrigated forage legumes to increase the capacity of their enterprise, turning out more cattle from the same area. Cavalcade (Centrosema pascuorum ‘Cavalcade’) and lablab are currently grown in northern Australia and would be well suited to the Victoria catchment. Hay crops are commonly used as a component of forage pellets that are used to feed live export cattle in holding yards and on boats during transport. From a land suitability perspective, forage legumes such as Cavalcade and lablab are included in Crop Group 13 (Table 4-2; Figure 4-22). Cracking clays (Vertosols) make up nearly 12% of the Victoria catchment; they are found on alluvial plains, relict alluvial plains, and on level to gently undulating plains on basalt (marked CA1, CA2, CB1 and CB2 on Figure 2-5). These soils have very high water-holding capacity but the non-basalt Vertosols may have a restricted rooting depth due to salt levels in the subsoil. Vertosols generally have moderate to high agricultural potential, but inadequate drainage and deep gilgais in some areas reduce the prospects for furrow irrigation. Poor drainage and low permeability will cause waterlogging in the wet season, especially along the Baines, lower West Baines and East Baines rivers. Loamy soils, mostly red loams, make up more than 18% of the catchment. These soils dominate the deeply weathered sediments of the Sturt Plateau in the east to south-east (marked K1 and K2 on Figure 2-5) and other deeply weathered landscapes to the south and west of Kalkarindji. Loamy soils are typically nutrient deficient and have low to high water-holding capacity. Irrigation potential is limited to spray- and trickle- irrigated crops on the moderately deep to deep soils. In parts of the catchment, loamy soils are found on narrow flat areas dissected by stream channels and deep gullies, making the land difficult to develop for broadacre cropping. Shallow and/or rocky soils make up a little more than 57% of the catchment, and are unsuitable by definition. Assuming unconstrained development, approximately 2.9 million ha of the Victoria catchment is considered to be suitable with moderate limitations (Class 3; Table 4-1) or better (Class 2 or Class 1) for irrigated forage legumes (Crop Group 13; Table 4-2) using spray irrigation in the dry season, most of this being Class 2. For spray irrigation in the wet season, nearly 2.4 million ha is suitable with moderate limitations (Class 3) or better, again the majority being Class 2. Land considered suitable with moderate or minor limitations for furrow irrigation is limited to about 620,000 ha in the dry season and 360,000 ha in the wet season, due to inadequate soil drainage in clay soils (and/or because gilgais are too deep) and because the loamy soils are too permeable. There is potential for rainfed forage legume production in the wet season over an area of about 670,000 ha. The equipment needed for grazed forage legume production is similar to that for forage grasses: a planting method, with fertilising and spraying equipment, is desirable but not essential. Cutting crops for hay or silage requires more-specialised harvesting, cutting, baling and storage equipment. Table 4-22 describes Cavalcade production over a 1-year cycle. The comments could be applied equally to lablab production (Figure 4-23). P2228#yIS1 Figure 4-22 Modelled land suitability for Cavalcade (Crop Group 13) in the wet season using (a) spray irrigation and (b) furrow irrigation These land suitability maps do not consider flooding, risk of secondary salinisation or availability of water. The methods used to derive the reliability data in the inset maps are outlined in the companion technical report on digital soil mapping and land suitability (Thomas et al., 2024). Lablab P2231#yIS1 Figure 4-23 Lablab Photo: CSIRO Table 4-22 Cavalcade production over a 1-year cycle For more information on this figure, table or equation please contact CSIRO on enquiries@csiro.au 4.4.8 Horticulture Horticulture is an important and widespread Australian industry, occurring in every state. Horticulture production encompasses a very wide range of intensive cultivated food and ornamental crops, including a vast range of fruit and vegetable crops. Horticultural production varied between 2.9 and 3.3 Mt per year between 2012–13 and 2021–22, of which 65% to 70% was vegetables (ABARES, 2022). Unlike broadacre crops, most horticultural produce in Australia is consumed domestically. The total gross value of horticultural production was $13.2 billion in 2021–22 (up from $9.3 billion in 2012–13), of which 24% was from exports (ABARES, 2022). Horticulture is also an important source of jobs, employing approximately one-third of all people employed in agriculture. Production of horticultural crops is highly seasonal, and individual farms may grow a range of crops or the same crop with sequential planting dates. The importance of freshness in many horticultural products means seasonality of supply is important in the market. The value of horticulture crops can vary widely, with price changes occurring over very short periods of time (weeks). Part of the attraction of growing horticulture crops in the Victoria catchment is to supply southern markets when southern growing regions are unable to produce due to climate restrictions. Transport of horticulture produce can involve significant costs, so achieving a price premium for ‘out of season’ production will be required for successful production in the Victoria catchment. This requires a heightened understanding of risks, markets, transport and supply chain issues. Horticultural production systems are generally more intensive than broadacre farming, requiring higher capital investment in establishing farm infrastructure and higher ongoing inputs for production. Picking and packing operations involve significant labour. Attracting sufficient seasonal workers to the Victoria catchment for harvesting season would need consideration. Horticulture (row crops) Horticulture row crops are generally short-lived, annual crops, grown in the ground, such as watermelon, rockmelon (Cucumis melo var. cantalupensis) and sweet corn (Zea mays). Almost all produce is shipped to major markets (cities) where central markets are located. Row crops such as watermelon and rockmelon use staggered plantings over a season (e.g. every 2 to 3 weeks) to extend the period over which harvested produce is sold. This strategy allows better use of labour and better management for risks of price fluctuations. Often only a short period of time with very high prices is enough to make melon production a profitable enterprise. Horticultural row crops are well established throughout the NT. The NT melon industry, consisting of watermelons (Citrullus lanatus) alongside some varieties of rockmelon (Cucumis melo) and honeydew melons (Cucumis melo), produces approximately 25% of Australia’s melons. Melon production is well suited across many parts of the NT and would be well suited to the Victoria catchment. From a land suitability perspective, intensive horticulture row crops such as rockmelon are included in Crop Group 3 (Table 4-2). Cracking clays (Vertosols) make up nearly 12% of the Victoria catchment; they are found on alluvial plains, relict alluvial plains, and on level to gently undulating plains on basalt (marked CA1, CA2, CB1 and CB2 on Figure 2-5). These soils have very high water- holding capacity but the non-basalt Vertosols may have a restricted rooting depth due to salt levels in the subsoil. Vertosols generally have moderate to high agricultural potential, but inadequate drainage and deep gilgais in some areas reduce the prospects for furrow irrigation. Poor drainage and low permeability will cause waterlogging in the wet season, especially along the Baines, lower West Baines and East Baines rivers. In addition, disease risk is very high for horticulture row crops in the wet season. Loamy soils, mostly red loams, make up more than 18% of the catchment. These soils dominate the deeply weathered sediments of the Sturt Plateau in the east to south-east (marked K1 and K2 on Figure 2-5) and other deeply weathered landscapes to the south and west of Kalkarindji. Loamy soils are typically nutrient deficient and have low to high water-holding capacity. Irrigation potential is limited to spray- and trickle-irrigated crops on the moderately deep to deep soils. Shallow and/or rocky soils make up a little more than 57% of the catchment, and are unsuitable by definition. A wide range of horticultural row crops are considered in the land suitability analysis (crop groups 3, 4, 5, 6 and 18; Table 4-2; Figure 4-24). Assuming unconstrained development, between about 2.5 million ha and 3.1 million ha of the Victoria catchment is considered to be suitable with moderate limitations (Class 3; Table 4-1) or better (Class 2 or Class 1) using spray or trickle irrigation in the dry season. Land considered suitable with moderate limitations for furrow irrigation of sweet corn (Crop Group 18) is limited to about 750,000 ha in the dry season and 420,000 ha in the wet season, due to inadequate soil drainage in clay soils (and/or because gilgais are too deep) and because the loamy soils are too permeable. Horticulture typically requires specialised equipment and a large labour force. Therefore, a system for attracting, managing and retaining sufficient staff is also required. Harvesting is often by hand, but packing equipment is highly specialised. Irrigation is mostly with micro or trickle equipment, but overhead spray is also feasible. Leaf fungal diseases need to be more carefully managed with spray irrigation. Micro spray equipment has the advantage of also being a nutrient delivery (fertigation) mechanism, as fertiliser can be delivered with the irrigation water. Table 4-23 describes some key considerations relating to row crop horticulture production, with rockmelon (Figure 4-25) as an example. P2298#yIS1 Figure 4-24 Modelled land suitability for (a) cucurbits (e.g. rockmelon, Crop Group 3) using trickle irrigation in the dry season and (b) root crops such as onion (Crop Group 6) using spray irrigation in the wet season These land suitability maps do not consider flooding, risk of secondary salinisation or availability of water. The methods used to derive the reliability data in the inset maps are outlined in the companion technical report on digital soil mapping and land suitability (Thomas et al., 2024). P2301#yIS1 Figure 4-25 Rockmelon Photo: Shutterstock Table 4-23 Summary information relevant to row crop horticulture production, with rockmelon as an example For more information on this figure, table or equation please contact CSIRO on enquiries@csiro.au Horticulture (tree crops) Some fruit and tree crops, such as mango and citrus (Citrus spp.), are well suited to the climate of the Victoria catchment. Other species, such as avocado (Persea americana) and lychee (Litchi chinensis), are not likely to be as well adapted to the climate due to high temperatures and low humidity. Tree crops are generally not well suited to cracking clays, which make up some of the suitable soils for irrigated agriculture in the Victoria catchment. Fruit production shares many of the marketing and risk features of horticultural row crops, such as a short season of supply and highly volatile prices as a result of highly inelastic supply and demand. Managing these issues requires a heightened understanding of risks, markets, transport and supply chain issues. The added disadvantage of fruit tree production is the time lag between planting and production, meaning decisions to plant need to be made with a long time frame for production and return in mind. Mango production in the NT is buffered somewhat against large- scale competition as its crop matures earlier than the main production areas in Queensland and it can achieve high returns. Mango production in the NT had a gross value of $129 million in 2020, accounting for 38% of the $341 million total value of horticultural production in the NT and half of mangoes produced in Australia (Sangha et al., 2022). The perennial nature of tree crops makes a reliable year-round supply of water essential. However, some species, such as mango and cashew (Anacardium occidentale), can survive well under mild water stress until flowering (generally August to October for most fruit trees). It is critical for optimum fruit and nut production that trees are not water stressed from flowering through to harvest. This is the period approximately beginning in August to November and carrying through to February, depending on the species. Very little rain falls in the Victoria catchment over this period, and farmers would need to have a system in place to access irrigation water during this time. From a land suitability perspective, intensive horticultural tree crops such as mango are included in Crop Group 1, the monsoonal tropical tree crops (Table 4-2). Cracking clays (Vertosols) make up nearly 12% of the Victoria catchment. They are found on alluvial plains, relict alluvial plains, and on level to gently undulating plains on basalt (marked CA1, CA2, CB1 and CB2 on Figure 2-5). These soils have very high water-holding capacity but the non-basalt Vertosols may have a restricted rooting depth due to salt levels in the subsoil. Vertosols generally have moderate to high agricultural potential, but inadequate drainage and deep gilgais in some areas reduce the prospects for horticultural tree crops. Loamy soils, mostly red loams, make up more than 18% of the catchment. These soils dominate the deeply weathered sediments of the Sturt Plateau in the east to south-east (marked K1 and K2 on Figure 2-5) and other deeply weathered landscapes to the south and west of Kalkarindji. Loamy soils are typically nutrient deficient and have low to high water-holding capacity. Irrigation potential is limited to spray- and trickle-irrigated crops on the moderately deep to deep soils. Shallow and/or rocky soils make up a little more than 57% of the catchment and are unsuitable by definition. A wide range of horticultural tree crops are considered in the land suitability analysis (crop groups 1, 2, 20 and 21; Table 4-2; Figure 4-26). Assuming unconstrained development, between about 650,000 ha (papaya/cashew/macadamia) and 2.6 million ha (e.g. mango) of the Victoria catchment is considered to be suitable with moderate limitations (Class 3; Table 4-1) or better (Class 2 or Class 1) using spray or trickle irrigation. Furrow irrigation was not considered for horticultural tree crops. Fruit and nut tree production requires specialised equipment. The requirement for a timely and significant labour force necessitates a system for attracting, managing and retaining sufficient staff. Tree-pruning and packing equipment is highly specialised for the fruit industry. Optimum irrigation is usually using micro spray. This equipment is also able to deliver fertiliser directly to the trees through fertigation. Table 4-24 describes some key considerations relating to mango production (Figure 4-27) in the Victoria catchment, as an exemplar of the conditions relating to tree crop production more broadly. Similar information for other fruit tree crops is described in the companion technical report on agricultural viability and socio-economics (Webster et al., 2024). P2358#yIS1 Figure 4-26 Modelled land suitability for (a) mango (Crop Group 1) and (b) lime (Crop Group 2), both grown using trickle irrigation These land suitability maps do not consider flooding, risk of secondary salinisation or availability of water. The methods used to derive the reliability data in the inset maps are outlined in the companion technical report on digital soil mapping and land suitability (Thomas et al., 2024). P2361#yIS1 Figure 4-27 Mango Photo: Shutterstock Table 4-24 Summary information relevant to tree crop horticulture production, with mango as an example For more information on this figure, table or equation please contact CSIRO on enquiries@csiro.au For more information on this figure, table or equation please contact CSIRO on enquiries@csiro.au PVR = plant variety rights. 4.4.9 Plantation tree crops (silviculture) Of the potential tree crops that could be grown in the Victoria catchment, Indian sandalwood and African mahogany are the only two that would be considered economically feasible. Many other plantation species could be grown, but returns are much lower than for these two crops. African mahogany is well established in commercial plantations near Katherine, and Indian sandalwood is also grown in Katherine, the Ord River Irrigation Area (WA) and in northern Queensland. Plantation timber species require over 15 years to grow, but once established can tolerate prolonged dry periods. Irrigation water is critical in the establishment and first 2 years of a plantation. In the case of Indian sandalwood, the provision of water is for not only the trees themselves but also the leguminous host plant associated with Indian sandalwood, as it is a hemiparasite. From a land suitability perspective, plantation tree crops such as Indian sandalwood, African mahogany and teak (Tectona grandis) are included in crop groups 15, 16 and 17 (Table 4-2). Cracking clays (Vertosols) make up nearly 12% of the Victoria catchment and are found on alluvial plains, relict alluvial plains, and on level to gently undulating plains on basalt (marked CA1, CA2, CB1 and CB2 on Figure 2-5). These soils have very high water-holding capacity but the non-basalt Vertosols may have a restricted rooting depth due to salt levels in the subsoil. Vertosols generally have moderate to high agricultural potential, but inadequate drainage and deep gilgais in some areas reduce the prospects for plantation tree crops. Loamy soils, mostly red loams, make up more than 18% of the catchment. These soils dominate the deeply weathered sediments of the Sturt Plateau in the east to south-east and other deeply weathered landscapes to the south (marked K1 and K2 on Figure 2-5) and west of Kalkarindji. Loamy soils are typically nutrient deficient and have low to high water-holding capacity. Irrigation potential is limited to spray- and trickle-irrigated crops on the moderately deep to deep soils. Shallow and/or rocky soils make up a little more than 57% of the catchment and are unsuitable by definition. Depending on the specific tree species being planted and their tolerance to poorly drained soils and waterlogging, the suitable areas vary considerably. A range of silviculture trees were considered in the land suitability analysis (crop groups 15, 16 and 17; Table 4-2). Assuming unconstrained development, between about 1.9 million ha (teak) and 2.7 million ha (African mahogany) of the Victoria catchment is considered to be suitable with moderate limitations (Class 3; Table 4-1) or better (Class 2 or Class 1) using trickle irrigation (Figure 4-28). Furrow irrigation was considered for Indian sandalwood only, and 170,000 ha was assessed as suitable with moderate limitations. Table 4-25 describes Indian sandalwood (Figure 4-29) production. P2422#yIS1 Figure 4-28 Modelled land suitability for Indian sandalwood (Crop Group 15) grown using (a) trickle or (b) furrow irrigation These land suitability maps do not consider flooding, risk of secondary salinisation or availability of water. The methods used to derive the reliability data in the inset maps are outlined in the companion technical report on digital soil mapping and land suitability (Thomas et al., 2024). P2425#yIS1 Figure 4-29 Indian sandalwood and host plants Indian sandalwood trees are those with a darker trunk and leaves in a line left of centre in the image. Photo: CSIRO Table 4-25 Summary information for Indian sandalwood production For more information on this figure, table or equation please contact CSIRO on enquiries@csiro.au For more information on this figure, table or equation please contact CSIRO on enquiries@csiro.au 4.4.10 Niche crops Niche crops such as guar, chia, quinoa (Chenopodium quinoa), bush products and others may be feasible in the Victoria catchment, but limited verified agronomic and market data are available for these crops. Niche crops are niche due to the limited demand for their products. As a result, small-scale production can lead to very attractive prices, but only a small increase in productive area can flood the market, leading to greatly reduced prices and making production unsustainable. There is growing interest in bush products but insufficient publicly available information for inclusion with the analyses of irrigated crops options in this Assessment. Bush product production systems could take many forms, from culturally appropriate wild harvesting targeting Indigenous consumers to modern mechanised farming and processing, like macadamia (Macadamia integrifolia) farming. The choice of production system would have implications for the extent of Indigenous involvement throughout the supply chain (farming, processing, marketing and/or consumption), the scale of the markets that could be accessed (in turn affecting the scale of the industry for that bush product), the price premiums that produce may be able to attract and the viability of those industries. The current publicly available information on bush products mainly focuses on eliciting Indigenous aspirations, biochemical analysis (for safety, nutrition and efficacy of potential health benefits) and considerations of safeguarding Indigenous intellectual property. Analysing bush products in a comparable way to other crop options in this report would first require these issues to be resolved, for communities to agree on the preferred type of production systems (and pathways for development), and for agronomic information on yields, production practices and costs to be publicly available. Past research on guar has been conducted in the NT, and trials are underway in northern Queensland, which could prove future feasibility. There is increasing interest in non-leguminous, small-seeded crops such as chia and quinoa, which have high nutritive value. The market size for these niche crops is quite small compared with cereals and pulses, so the scale of production is likely to be small in the short to medium term. There is a small, established chia industry in the Ord River Irrigation Area of WA, but its production and marketing statistics are largely commercial in confidence. Nearly all Australian production of chia is contracted to The Chia Company of Australia or is exported to China. In Australia, The Chia Company produces whole chia seeds, chia bran, ground chia seed and chia oil for wholesale and retail sale, and it exports these products to 36 countries. The growing popularity of quinoa in recent years is attached to its marketing as a superfood. It is genetically diverse and has not been the subject of long-term breeding programs. This diversity means it is well suited to a range of environments, including northern Australia, where its greatest opportunity is as a short-season crop in the dry season under irrigation. It is a high-value crop with farm gate prices of about $1000/t. Trials of quinoa production have been conducted at the Katherine Research Station (approximately 140 km from the eastern edge of the Victoria catchment), with reasonable yields being returned. More testing is required in the northern environments of the Victoria catchment before quinoa could be recommended for commercial production. 4.5 Aquaculture 4.5.1 Introduction There are considerable opportunities for aquaculture development in northern Australia given its natural advantages of a climate suited to farming valuable tropical species, large areas identified as suitable for aquaculture, political stability and proximity to large global markets. The main challenges to developing and operating modern and sustainable aquaculture enterprises are regulatory issues, global cost competitiveness and the remoteness of much of the suitable land area. A comprehensive situational analysis of the aquaculture industry in northern Australia (Cobcroft et al., 2020) identifies key challenges, opportunities and emerging sectors. This section draws on a recent assessment of the opportunities for aquaculture in northern Australia in the Northern Australia Water Resource Assessment technical report on aquaculture (Irvin et al., 2018), summarising the three most likely candidate species (Section 4.5.2), overviewing production systems for candidate species (Section 4.5.3), land suitability for aquaculture within the Victoria catchment (Section 4.5.4) and the financial viability of different options for aquaculture development (Section 4.5.5). 4.5.2 Candidate species The three species with the most aquaculture potential in the Victoria catchment are black tiger prawns, barramundi and red claw. The first two species are suited to many marine and brackish water environments of northern Australia and have established land-based culture practices and well-established markets for harvested products. Prawns could potentially be cultured in either extensive (low density, low input) or intensive (higher density, higher input) pond-based systems in northern Australia, whereas land-based culture of barramundi would likely be intensive. Red claw is a freshwater crayfish that is currently cultured by a much smaller industry than the other two species. Black tiger prawns Black tiger prawns (Figure 4-30) are found naturally at low abundances across the waters of the western Indo-Pacific region, with wild Australian populations making up the southernmost extent of the species. Within Australia, the species is most common in the tropical north, but does occur at lower latitudes. Tiger prawns P2498#yIS1 Figure 4-30 Black tiger prawns Photo: CSIRO Barramundi Barramundi (Figure 4-31) is the most highly produced and valuable tropical fish species in Australian aquaculture. Barramundi inhabit the tropical north of Australia from the Exmouth Gulf in WA through to the Noosa River on Queensland’s east coast. It is also commonly known as the ‘Asian sea bass’ or ‘giant sea perch’ throughout its natural areas of distribution in the Persian Gulf, the western Indo-Pacific region and southern China (Schipp et al., 2007). The attributes that make barramundi an excellent aquaculture candidate are fast growth (reaching 1 kg or more in 12 months), year-round fingerling availability, well-established production methods, and hardiness (i.e. they have a tolerance to low oxygen levels, high stocking densities and handling, as well as a wide range of temperatures) (Schipp et al., 2007). In addition, barramundi are euryhaline (able to thrive and be cultured in fresh and marine water), but freshwater barramundi can have an earthy flavour. Barramundi P2503#yIS1 Figure 4-31 Barramundi Photo: CSIRO Red claw Red claw is a warm-water crayfish species that inhabits still or slow-moving water bodies. The natural distribution of red claw is from the tropical catchments of Queensland and the NT to southern New Guinea. The name ‘red claw’ is derived from the distinctive red markings present on the claws of the male crayfish. The traits of red claw that make them attractive for aquaculture production are a simple life cycle, which is beneficial because complex hatchery technology is not required (Jones et al., 1998); their tolerance of low oxygen levels (<2 mg/L), which is beneficial in terms of handling, grading and transport (Masser and Rouse, 1997); their broad thermal tolerance, with optimal growth achievable between 23 and 31 °C; and their ability to remain alive out of water for extended periods. 4.5.3 Production systems Overview Aquaculture production systems can be broadly classified into extensive, semi-intensive and intensive systems. Intensive systems require high inputs and expect high outputs: they require high capital outlay and have high running costs; they require specially formulated feed and specialised breeding, water quality and biosecurity processes; and they have high production per hectare (in the order of 5000 to 20,000 kg per ha per crop). Semi-intensive systems involve stocking seed from a hatchery, routine provision of a feed, and monitoring and management of water quality. Production is typically 1000 to 5000 kg per ha per crop. Extensive systems are characterised by low inputs and low outputs: they require less-sophisticated management and often require no supplementary feed because the farmed species live on naturally produced feed in open-air ponds. Extensive systems produce about half the volume of global aquaculture production, but there are few commercial operations in Australia. Water salinity and temperature are the key parameters that determine species selection and production potential for any given location. Suboptimal water temperature (even within tolerable limits) will prolong the production season (because of slow growth) and increase the risk of disease, reducing profitability. The primary culture units for land-based farming are purpose-built ponds. Pond structures typically include an intake channel, production pond, discharge channel and a bioremediation pond (Figure 4-32). The function of the pond is to be a containment structure, an impermeable layer between the pond water and the local surface water and groundwater. Optimal sites for farms are flat and have sufficient elevation to enable ponds to be completely drained between seasons. It is critical that all ponds and channels can be fully drained during the off (dry-out) season to enable machinery access to sterilise and undertake pond maintenance. P2513#yIS1 Figure 4-32 Schematic of marine aquaculture farm Most production ponds in Australia are earthen. Soils for earthen ponds should have low permeability and high structural stability. Ponds should be lined if the soils are permeable. Synthetic liners have a higher capital cost but are often used in high-intensity operations, which require high levels of aeration – conditions that would lead to significant erosion in earthen ponds. Farms use aerators (typically electric paddlewheels and aspirators) to help maintain optimal water quality in the pond, provide oxygen and create a current that consolidates waste into a central sludge pile (while keeping the rest of the pond floor clear). A medium-sized (50 ha) prawn farm in Australia uses around 4 GWh annually, accounting for most of an enterprise’s energy use (Paterson and Miller, 2013). Backup power capacity sufficient to run all the aerators on the farm, usually with a diesel generator, is essential to be able to cope with power failures. Extensive production systems do not require aeration in most cases. Black tiger prawns For black tiger prawns, a typical pond in the Australian industry is rectangular in shape, about 1 ha in area and about 1.5 m in depth. The ponds are either wholly earthen, lined on the banks with black plastic and earthen bottoms or (rarely in Australia) fully lined. Pond grow-out of black tiger prawns typically operates at stocking densities of 25 to 50 individuals per square metre (termed ‘intensive’ in this report). These pond systems are fitted with multiple aeration units, which could double from 8 to 16 units as the biomass of the prawn crop increases (Mann, 2012). At the start of each prawn crop, pond bottoms are dried, and unwanted sludge from the previous crop is removed. If needed, additional substrate is added. Before filling the ponds, lime is often added to buffer pH, particularly in areas with acid-sulfate soils. The ponds are then filled with filtered seawater and left for about 1 week prior to postlarval stocking. Algal blooms in the water are encouraged through addition of organic fertiliser to provide shading for prawns, discourage benthic algal growth and stimulate growth of plankton as a source of nutrition (QDPIF, 2006). Postlarvae are purchased from hatcheries and grow rapidly into small prawns in the first month after stocking, relying mainly on the natural productivity (zooplankton, copepods and algae) supported by the algal bloom for their nutrition. Approximately 1 month after the prawns are stocked, pellet feed becomes the primary nutrition source. Feed is a major cost of prawn production; around 1.5 kg of feed is required to produce 1 kg of prawns. Prawns typically reach optimal marketable size (30 g) within 6 months. After harvest, prawns are usually processed immediately, with larger farms having their own production facilities that enable grading, cooking, packaging and freezing. Effective prawn farm management involves maintaining optimal water quality conditions, which becomes progressively complex as prawn biomass and the quantity of feed added to the system increase. As prawn biomass increases, so too does the biological oxygen demand of the microbial population within the pond that is breaking down organic materials. This requires increases in mechanical aeration and water exchanges (either fresh or recycled from a bioremediation pond). In most cases water salinity is not managed, except through seawater exchange, and will increase naturally with evaporation and decrease with rainfall and flooding. Strict regulation of the quality and volume of water that can be discharged means efficient use of water is standard industry practice. Most Australian prawn farms allocate up to 30% of their productive land for water treatment by pre-release containment in settlement systems. Barramundi The main factors that determine productivity of barramundi farms are water temperature, dissolved oxygen levels, effectiveness of waste removal, expertise of farm staff and the overall health of the stock. Barramundi are susceptible to a variety of bacterial, fungal and parasitic organisms. They are at highest risk of disease when exposed to suboptimal water quality conditions (e.g. low oxygen or extreme temperatures). Due to the cost and infrastructure required, many producers elect to purchase barramundi fingerlings from independent hatcheries, moving fish straight into their nursery cycle. Regular size grading is essential during the nursery stage to minimise aggressive and cannibalistic behaviour: size grading helps to prevent mortalities and damage from predation on smaller fish, and it assists with consistent growth. Ponds are typically stocked to a biomass of about 3 kg per 1000 L. Under optimal conditions barramundi can grow to over 1 kg in 12 months and to 3 kg within 2 years (Schipp et al., 2007). The two largest Australian aquafeed manufacturers (located in Brisbane and Hobart) each produce a pellet feed that provides a specific diet promoting efficient growth and feed conversion. The industry relies heavily on these mills to provide a regular supply of high-quality feed. Cost of feed transport would be a major cost to barramundi production in the Victoria catchment. As a carnivorous species, high dietary protein levels, with fishmeal as a primary ingredient, are required for optimal growth. Barramundi typically require between 1.2 and 1.5 kg of pelleted feed for each kilogram of body weight produced. Warm water temperatures in northern Australia enable fish to be stocked in ponds year-round. Depending on the intended market, harvested product is processed whole or as fillets and delivered fresh (refrigerated or in ice slurry) or frozen. Smaller niche markets for live barramundi are available for Asian restaurants in some capital cities. Red claw Water temperature and feed availability are the variables that most affect crayfish growth. Red claw are a robust species but are most susceptible to disease (including viruses, fungi, protozoa and bacteria) when conditions in the production pond are suboptimal (Jones, 1995). In tropical regions, mature females can be egg-bearing year round. Red claw breed freely in production ponds, so complex hatchery technology (or buying juvenile stock) is not required. However, low fecundity and the associated inability to source high numbers of quality selected broodstock are an impediment to intensive expansion of the industry. Production ponds are earthen, rectangular in design and on average 1 ha in size. They slope in depth from 1.2 to 1.8 m. Sheeting is used on the pond edge to keep the red claw in the pond (they tend to migrate), and netting surrounds the pond to protect stock from predators (Jones et al., 2000). At the start of each crop, ponds are prepared (as for black tiger prawns above), then filled with fresh water and left for about 2 weeks before stocking. During this period, algal blooms in the water are encouraged through addition of organic fertiliser. Ponds are then stocked with about 250 females and 100 males that have reached sexual maturity. Natural mating results in the production of around 20,000 advanced juveniles. Red claw are omnivorous, foraging on natural production such as microbial biomass associated with decaying plants and animals. Early-stage crayfish rely almost solely on natural pond productivity (phytoplankton and zooplankton) for nutrition. As the crayfish progress through the juvenile stages, the greater part of the diet changes to organic particulates (detritus) on the bottom of the pond. Very small quantities of a commercial feed are added daily to assist with the weaning process and provide an energy source for the pond bloom. Providing adequate shelters (net bundles) is essential at this stage to improve survival (Jones, 2007). Approximately 4 months after stocking, the juveniles are harvested and graded by size and sex for stocking in production ponds. Juveniles are stocked in production ponds at 5 to 10 per square metre. Shelters are important during the grow-out stage, with 250/ha recommended. During the grow-out phase, pellet feed becomes an important nutrition source, along with the natural productivity provided by the pond. Current commercial feeds are low cost and provide a nutrition source for natural pond productivity as much as for the crayfish. Most Australian farmers use diets consisting of 25% to 30% protein. Effective farm management involves maintaining water quality conditions within ranges optimal for crayfish growth and survival as pond biomass increases. As with barramundi, management involves increasing aeration and water exchanges, while strictly managing effluent discharges. Red claw are harvested within 6 months of stocking to avoid reproduction in the production pond. At this stage the crayfish will range from 30 to 80 g. Stock are graded by size and sex into groups for market, breeding or further grow-out (Jones, 2007). Estimated water use An average crop of prawns farmed in intensive pond systems (8 t/ha over 150 days) is estimated to require 127 ML of marine water, which equates to 15.9 ML of marine water for each tonne of harvested product (Irvin et al., 2018). For pond culture of barramundi (30 t/ha over 2 years), 562 ML of marine water, or fresh water, is required per crop, equating to 18.7 ML of water for each tonne of harvested fish. For extensive red claw culture (3 t/ha over 300 days), 240 ML of fresh water is required per pond crop, equating to 16 ML of water for each harvested tonne of crayfish (Irvin et al., 2018). 4.5.4 Aquaculture land suitability The suitability of areas for aquaculture development was also assessed from the perspective of soil and land characteristics using the set of five land suitability classes in Table 4-1. The limitations considered include clay content, soil surface pH, soil thickness and rockiness. Limitations mainly relate to geotechnical considerations (e.g. construction and stability of impoundments). Other limitations, including slope, and the likely presence of gilgai microrelief and acid-sulfate soils, are indicative of more difficult, expensive and therefore less suitable development environments, and a greater degree of land preparation effort. More detail can be found in the companion technical report on digital soil mapping and land suitability (Thomas et al., 2024). Suitability was assessed for lined and earthen ponds, with earthen ponds requiring soil properties that prevent pond leakage. Soil acidity (pH) was also considered for earthen ponds, as some aquaculture species can be affected by unfavourable pH values exchanged into the water column (i.e. biological limitation). Two aquaculture species were selected to represent the environmental needs of marine species (represented by prawns) and freshwater species (red claw). Additionally, barramundi and other euryhaline species, which can tolerate a range of salinity conditions, may be suited to either marine or fresh water, depending on management choices. Except for aquaculture of marine species, which for practical purposes is restricted by proximity to sea water, no consideration was given in the analysis to proximity to suitable water for aquaculture of fresh and euryhaline species. It was not possible to include proximity to fresh water due to the large number of potential locations where water could be captured and stored within the catchment. Note also that the estimates for land suitability presented below represent the total areas of the catchment unconstrained by factors such as water availability, land tenure, environmental and other legislation and regulations, and a range of biophysical risks such as cyclones and flooding. These are addressed elsewhere by the Assessment. The land suitability maps are designed to be used predominantly at the regional scale. Planning at the enterprise scale would demand more localised assessment. Analysis of suitability of land for marine aquaculture has been restricted to locations within 2 km of a marine water source. Suitable land for aquaculture in lined ponds is restricted to the areas under tidal influence and the river margins where cracking clay and seasonally or permanently wet soils dominate (Figure 4-33a). These soils show the desired land surface characteristics such as no rockiness, suitable slope and sufficient soil thickness, but have the risk of acid-sulfate soils and must be managed accordingly. Approximately 48,500 ha (0.6% of the catchment) is suited (Class 2) to marine aquaculture in lined ponds and 67,300 ha (0.8%) as Class 3 (Table 4-1). The land suitability patterns for marine species in earthen ponds (Figure 4-33b) closely mirror those of the marine species in lined ponds, although areas are restricted to slowly permeable cracking clay soils. Approximately 4100 ha (0.05% of the catchment) is mapped as suitability Class 2 and 88,700 ha (1%) as Class 3. P2537#yIS1 Figure 4-33 Land suitability in the Victoria catchment for marine species aquaculture in (a) lined ponds and (b) earthen ponds These land suitability maps do not consider flooding, risk of secondary salinisation or availability of water. The methods used to derive the suitability data are outlined in the companion technical report on digital soil mapping and land suitability (Thomas et al., 2024). The map of aquaculture land suitabilities for freshwater species (Figure 4-34) shows significant tracts of lands with soil attributes suitable for freshwater aquaculture in lined ponds (Figure 4-34a). The large tracts of suitability Class 2 (suitable with minor limitations) coincide with level plains with deep soils and no rock. These characteristics are associated with the marine plains, alluvial plains and the level lateritic Tertiary sedimentary plains physiographic units. The Class 3 suitability areas (suitable with moderate limitations) coincide with limestone gentle plains and various gentle plains on basalt. Approximately 3170 ha (0.04% of the catchment) is highly suited (Class 1) for freshwater lined aquaculture, 1,596,200 ha (19%) is mapped as Class 2 and 1,639,000 ha (20%) is mapped as Class 3. In comparison, opportunities for freshwater species in earthen ponds in the Assessment area are fewer (Figure 4-34b), being restricted to level plains with deep impermeable, rock free clay soils. Moderately to highly permeable soils are unsuited to earthen ponds. There are minor areas of Class 2 associated with cracking clay soils mainly on the alluvial plains physiographic unit. Areas of Class 3 suitability on slowly permeable clays are found on alluvial plains, limestone gentle plains and some gentle plains on basalt. There are also significant areas of the coastal plain near the river mouth of Class 3 suitability on slowly permeable seasonally or permanently wet soils and cracking clay soils. These coastal plains have potential acid-sulfate soils that would require appropriate management. Land suitability for freshwater species using earthen ponds shows a small proportion of Class 2 suitability totalling 69,800 ha (0.85% of the catchment) and 887,500 ha (11%) as Class 3. P2542#yIS1 Figure 4-34 Land suitability in the Victoria catchment for freshwater species aquaculture in (a) lined ponds and (b) earthen ponds These land suitability maps do not consider flooding, risk of secondary salinisation or availability of water. The methods used to derive the suitability data are outlined in the companion technical report on digital soil mapping and land suitability (Thomas et al., 2024). 4.5.5 Aquaculture viability This section provides a brief, generic analysis of what would be required for new aquaculture developments in the Victoria catchment to be financially viable. First, indicative costs are provided for a range of four possible aquaculture enterprises that differ in species farmed, scale and intensity of production. The cost structure of the enterprises was based on established tools available from the Queensland Government for assessing the performance of existing or proposed aquaculture businesses (Queensland Government, 2024). Based on the ranges of these indicative capital and operating costs, gross revenue targets that a business would need to attain to be commercially viable are then calculated. Enterprise-level costs for aquaculture development Costs of establishing and running a new aquaculture business are divided here into the initial capital costs of development and ongoing operating costs. The four enterprise types analysed were chosen to portray some of the variation in cost structures between potential development options, not as a like-for-like comparison between different types of aquaculture (Table 4-26). Capital costs include all land development costs, construction, and plant and equipment accounted for in the year production commences. The types of capital development costs are largely similar across the aquaculture options with costs of constructing ponds and buildings dominating the total initial capital investment. Indicative costs were derived from the case study of Guy et al. (2014), and consultation with experts familiar with the different types of aquaculture, including updating to December 2023 dollar values (Table 4-26). Operating costs cover both overheads (which do not change with output) and variable costs (which increase as the yield of produce increases). Fixed overhead costs in aquaculture are a relatively small component of the total costs of production. Overheads consist of costs relating to licensing, approvals and other administration (Table 4-26). The remaining operating costs are variable (Table 4-26). Feed, labour and electricity typically dominate the variable costs. Aquaculture requires large volumes of feed inputs, and the efficiency with which this feed is converted to marketed produce is a key metric of business performance. Labour costs consist of salaries of permanent staff and casual staff who are employed to cover intensive harvesting and processing activities. Aerators require large amounts of energy, increasing as the biomass of produce in the ponds increases, which accounts for the large costs of electricity. Transport, although a smaller proportional cost, is important because this puts remote locations at a disadvantage relative to aquaculture businesses that are closer to feed suppliers and markets. In addition, transport costs may be higher at times if roads are cut (requiring much more expensive air freight or alternative, longer road routes) or if the closest markets become oversupplied. Packing is the smallest component of variable costs in the breakdown categories used here. Revenue for aquaculture produce typically ranges from $10 to $20 per kg (on a harvested mass basis), but prices vary depending on the quality and size classes of harvested animals and how they are processed (e.g. live, fresh, frozen or filleted). Farms are likely to deliver a mix of products targeted to the specifications of the markets they supply. Note that the mass of sold product may be substantially lower than the harvested product (e.g. fish fillets are about half the mass of harvested fish), so prices of sold product may not be directly comparable to the costs of production in Table 4-26, which are on a harvest mass basis. Table 4-26 Indicative capital and operating costs for a range of generic aquaculture development options Costs are provided both per hectare of grow-out pond and per kilogram of harvested produce, although capital costs scale mostly with the area developed and operating costs scale mainly with crop yield at harvest. Capital costs have been converted to an equivalent annualised cost assuming a 10% discount rate and that a quarter of the developed infrastructure was for 15-year life span assets and the remainder for 40-year life span assets. Indicative breakdowns of cost components are provided on a proportional basis. Costs derived from Guy et al. (2014) and adjusted to December 2023 dollar values. PARAMETER UNIT PRAWN (EXTENSIVE) PRAWN (INTENSIVE) BARRAMUNDI RED CLAW (SMALL SCALE) Scale of development Grow-out pond area ha 20 100 30 4 Total farm area ha 25 150 100 10 Yield at harvest t/y 30 800 600 32 Yield at harvest per pond area t/ha/y 1.5 8.0 20.0 3.0 Capital costs of development (scale with area of grow-out ponds developed) Land and buildings % 56 26 23 30 Vehicles % 5 2 2 11 Pond-related assets % 27 67 70 41 Other infrastructure and equipment % 11 6 5 17 PARAMETER UNIT PRAWN (EXTENSIVE) PRAWN (INTENSIVE) BARRAMUNDI RED CLAW (SMALL SCALE) Total capital cost (year 0) $/ha 74,000 142,000 147,000 163,000 Equivalent annualised cost $/kg 5.41 1.94 0.81 5.95 $/ha/y 8,108 15,558 16,106 17,859 Operating costs (vary with yield at harvest, except overheads) Nursery/juvenile costs % 12 9 7 1 Feed costs % 0 26 30 8 Labour costs % 47 13 12 57 Electricity costs % 16 24 30 9 Packing costs % 2 4 3 2 Transport costs % 6 16 16 11 Overhead costs (fixed) % 17 8 1 12 Total annual operating costs $/kg 19.31 12.47 12.46 17.80 $/ha/y 28,966 99,783 249,211 53,402 Total costs of production Total annual cost $/kg 24.72 14.42 13.27 23.75 $/ha/y 37,100 115,300 265,300 71,300 Commercial viability of new aquaculture developments Capital and operating costs differ between different types of aquaculture enterprises (Table 4-27), but these costs may differ even more between locations (depending on case-specific factors such as remoteness, soil properties, distance to water source and type of power supply). Furthermore, there can be considerable uncertainty in some costs, and prices paid for produce can fluctuate substantially over time. Given this variation among possible aquaculture developments in the Victoria catchment, a generic approach was taken to determine what would be required for new aquaculture enterprises to become commercially viable. The approach used here was to calculate the gross revenue that an enterprise would have to generate each year to achieve a target internal rate of return (IRR) for given operating costs and development costs (both expressed per hectare of grow-out ponds). Capital costs were converted to annualised equivalents on the assumption that developed assets equated to a mix of 25% 15-year assets and 75% assets with a 40-year life span (using a discount rate matching the target IRR). The target gross revenue is the sum of the annual operating costs and the equivalent annualised cost of the infrastructure development (Table 4-27). Table 4-27 Gross revenue targets required to achieve target internal rates of return (IRR) for aquaculture developments with different combinations of capital costs and operating costs All values are expressed per hectare of grow-out ponds in the development. Gross revenue is the yield per hectare of pond multiplied by the price received for produce (averaged across products and on a harvest mass basis). Capital costs were converted to an equivalent annualised cost assuming a quarter of the developed infrastructure was assets with a 15-year life span and the remainder for a 40-year life span. Targets would be higher after taking into account risks such as initial learning and market fluctuations. OPERATING COSTS ($/ha/y) GROSS REVENUE REQUIRED TO ACHIEVE TARGET IRR ($/ha/y) CAPITAL COSTS OF DEVELOPMENT ($/HA) 60,000 70,000 80,000 90,000 100,000 110,000 125,000 150,000 175,000 7% target IRR 20,000 25,022 25,859 26,696 27,533 28,371 29,208 30,463 32,556 34,648 50,000 55,022 55,859 56,696 57,533 58,371 59,208 60,463 62,556 64,648 100,000 105,022 105,859 106,696 107,533 108,371 109,208 110,463 112,556 114,648 150,000 155,022 155,859 156,696 157,533 158,371 159,208 160,463 162,556 164,648 200,000 205,022 205,859 206,696 207,533 208,371 209,208 210,463 212,556 214,648 250,000 255,022 255,859 256,696 257,533 258,371 259,208 260,463 262,556 264,648 10% target IRR 20,000 26,574 27,669 28,765 29,861 30,956 32,052 33,695 36,434 39,174 50,000 56,574 57,669 58,765 59,861 60,956 62,052 63,695 66,434 69,174 100,000 106,574 107,669 108,765 109,861 110,956 112,052 113,695 116,434 119,174 150,000 156,574 157,669 158,765 159,861 160,956 162,052 163,695 166,434 169,174 200,000 206,574 207,669 208,765 209,861 210,956 212,052 213,695 216,434 219,174 250,000 256,574 257,669 258,765 259,861 260,956 262,052 263,695 266,434 269,174 14% target IRR 20,000 28,776 30,238 31,701 33,163 34,626 36,089 38,283 41,939 45,596 50,000 58,776 60,238 61,701 63,163 64,626 66,089 68,283 71,939 75,596 100,000 108,776 110,238 111,701 113,163 114,626 116,089 118,283 121,939 125,596 150,000 158,776 160,238 161,701 163,163 164,626 166,089 168,283 171,939 175,596 200,000 208,776 210,238 211,701 213,163 214,626 216,089 218,283 221,939 225,596 250,000 258,776 260,238 261,701 263,163 264,626 266,089 268,283 271,939 275,596 In order for an enterprise to be commercially viable, the volume of produce grown each year multiplied by the sales price of that produce would need to match or exceed the target values provided above. For example, a proposed development with capital costs of $125,000/ha and operating costs of $200,000 per ha per year would need to generate gross revenue of $213,695 per ha per year to achieve a target IRR of 10% (Table 4-27). If the enterprise received $12/kg for produce (averaged across product types, on a harvest mass basis), then it would need to sustain mean long-term yields of 18 t/ha (= $213,695 per ha per year ÷ $12/kg × 1 t/1000 kg) from the first harvest. However, if prices were $20/kg, mean long-term yields would require 11 t/ha (= $213,695 per ha per year ÷ $20/kg × 1 t/1000 kg) for the same $125,000 capital costs per hectare, or only 6 t/ha harvests if the capital costs decreased to $100,000/ha (= $113,695 per ha per year ÷ $20/kg × 1 t/1000 kg). Target revenue would be higher after taking into account risks such as learning and adapting to the particular challenges of a new location, and periodic setbacks that could arise from disease, climate variability, changes in market conditions or new legislation. Key messages From this analysis, a number of key points about achieving commercial viability in new aquaculture enterprises are apparent: • Operating costs are very high, and the amount spent each year on inputs can exceed the upfront (year zero) capital cost of development (and the value of the farm assets). This means that the cost of development is a much smaller consideration for achieving profitability than ongoing operations and costs of inputs. • High operating costs also mean that substantial capital reserves are required, beyond the capital costs of development, as there will be large cash outflows for inputs in the start-up years before revenue from harvested product starts to be generated. This is particularly the case for larger size classes of product that require multi-year grow-out periods before harvest. Managing cashflows would therefore be an important consideration at establishment and as yields are subsequently scaled up. • Variable costs dominate the total costs of aquaculture production, so most costs will increase as yield increases. This means that increases in production, by itself, would contribute little to achieving profitability in a new enterprise. What is much more important is increasing production efficiency, such as feed conversion rate or labour efficiency, so inputs per unit of produce are reduced (and profit margins per kilogram are increased). • Small changes in quantities and prices of inputs and produce would have a relatively large impact on net profit margins. These values could differ substantially between different locations (e.g. varying in remoteness, available markets, soils and climate) and depend on the experience of managers. Even small differences from the indicative values provided in Table 4-27 could render an enterprise unprofitable. • Enterprise viability would therefore be very dependent on the specifics of each particular case and how the learning, scaling up and cashflow were managed during the initial establishment years of the enterprise. It would be essential for any new aquaculture development in the Victoria catchment to refine the production system and achieve the required levels of operational efficiency (input costs per kilogram of produce) using just a few ponds before scaling any enterprise. 4.6 References ABARES (2022) Agricultural commodities: September quarter 2022. Australian Bureau of Agricultural and Resource Economics and Sciences, Canberra. September CC BY 4.0. DOI: doi.org/10.25814/zs85-g927. ABARES (2023) Australian horticulture prices. Australian Bureau of Agricultural and Resource Economics and Sciences, Canberra. 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DOI: 10.1071/CP13220. 5 Opportunities for water resource development in the Victoria catchment Authors: Justin Hughes, Andrew R Taylor, Cuan Petheram, Ang Yang, Steve Marvanek, Lee Rogers, Anthony Knapton, Geoff Hodgson, Fred Baynes Chapter 5 examines the opportunities, risks and costs for water resource development in the catchment of the Victoria River. Evaluating the possibilities for water resource development and irrigated agriculture requires an understanding of the development-related infrastructure requirements, how much water can be supplied and at what reliability, and the associated costs. The key components and concepts of Chapter 5 are shown in Figure 5-1. Figure 5-1 Schematic of key engineering and agricultural components to be considered in the establishment of a water resource and greenfield irrigation development For more information on this figure please contact CSIRO on enquiries@csiro.au Numbers in blue refer to sections in this report. 5.1 Summary This chapter provides information on a variety of potential options to supply water, primarily for irrigated agriculture. The methods used to generate these results included a mixture of field surveys and desktop analysis. The potential water yields reported in this chapter are based largely on physically plausible volumes. They do not consider economic, social, environmental, legislative or regulatory factors, which will inevitably constrain many developments. In some instances, the water yields are combined with land suitability information from Chapter 4 so as to provide estimates of areas of land that could potentially be irrigated close to the water source or storage. 5.1.1 Key findings Water can be sourced and stored for irrigation in the Victoria catchment in a variety of ways. If the water resources of the Victoria catchment are further developed for consumptive purposes, it is likely that a number of the options below may have a role to play in maximising the cost- effectiveness of water supply in different parts of the catchment. Groundwater extraction Groundwater is already widely used in parts of the Victoria catchment for a variety of purposes (community water supplies, and stock and domestic uses) and offers some year-round niche opportunities that are geographically distinct from surface water development opportunities. The two most productive groundwater systems in the Victoria catchment are the regional-scale Cambrian Limestone Aquifer (CLA) in the east of the catchment and the local- to intermediate- scale Proterozoic dolostone aquifers (PDAs) in the centre and south of the catchment. There are currently no licensed groundwater entitlements from the CLA in the Victoria catchment. However, three licensed entitlements totalling 7.4 GL/year from the CLA are available for use in agriculture about 150 km to the north-east of the Victoria catchment, in the proposed Flora Tindall Water Allocation Plan area. However, actual groundwater use is less. There is currently very little development of groundwater from the PDAs other than stock and domestic bores, and the community water supply at Timber Creek, and no water allocation plan exists. With appropriately sited borefields, up to 10 GL/year could potentially be extracted from the CLA to the south of Top Springs (i.e. groundwater extraction occurring between 20 and 80 km to the south toward Cattle Creek). Due to the time lags associated with groundwater flow, the additional hypothetical extraction will result in between an 11% and 14% reduction in modelled groundwater discharge to spring complexes and groundwater-fed vegetation near Top Springs. The modelled reduction in groundwater levels ranges from about 15 m at the centre of the hypothetical developments to 0.5 m up to 20 km away by about 2060. Under a projected dry future climate (10% reduction in rainfall) and no future hypothetical groundwater development (Scenario Cdry), groundwater recharge to the CLA near Top Springs was projected to reduce by 32%. The equivalent reduction in modelled discharge to the spring complexes nearby was estimated to be 33%. The modelled changes in the water balance from a projected drier future climate are larger than for the modelled future hypothetical groundwater development. This highlights the sensitivity of groundwater storage in and discharge from the CLA near Top Springs to natural variations in climate. Based on conservative annual recharge fluxes to the PDAs there may be potential to extract up to about 20 GL/year from the outcropping and subcropping parts of the aquifers in the centre and south of the catchment. However, these aquifers, while prospective, are data sparse, and understanding how water balance of these aquifers may change under future hypothetical groundwater development or projected future climates would require more detailed hydrogeological investigations. The actual scale of potential future groundwater development will depend upon community and government acceptance of potential impacts to groundwater- dependent ecosystems (GDEs) and existing groundwater users. Opportunities for potential future groundwater development from aquifers hosted in other hydrogeological units (Cambrian basalt, Devonian–Carboniferous sandstone and Proterozoic sandstone) are most likely to be limited to use for stock and domestic purposes, and occasional community water supply. The Quaternary alluvium may offer some potential opportunities, but this requires further investigation. Major dams Indigenous customary residential and economic sites are usually concentrated along major watercourses and drainage lines. Consequently, potential instream dams are more likely to have an impact on areas of high cultural significance than are most other infrastructure developments of comparable size. This has particular significance to the Victoria catchment. Based on topography and hydrology, there is considerable physical potential for large instream dams in the Victoria catchment. However, their utility is low due to the absence of large areas of contiguous soils suitable for irrigated agriculture downstream and the lack of electrical transmission infrastructure that could transmit hydro-electric power to potential markets. In the Victoria catchment, potential dams upstream of the larger contiguous areas of soil suitable for irrigated agriculture, and in areas of favourable topography for reticulation infrastructure, yield modest quantities of water due to the limited size of their headwater catchments. A potential large instream dam, located on Leichhardt Creek 85 km from the Victoria Highway, could yield 64 GL in 85% of years and cost $396 million (−20% to +50%) to construct, assuming favourable geological conditions. This equates to a unit capital cost of $6188/ML, making it one of the more cost-effective potential large instream dams in the Victoria catchment. A nominal 4000 ha reticulation scheme associated with the potential dam was estimated to cost an additional $12.67 million or $3168/ha (excluding farm development and infrastructure). The potential for large instream dams to mitigate flooding to very remote communities in the Victoria catchment is limited, and it would be more cost-effective to raise or relocate existing infrastructure. Water harvesting and offstream storage Water harvesting, where water is pumped from a major river into an offstream storage such as a ringtank, is a cost-effective option of capturing and storing water from the Victoria River and its major tributaries. Approximately 8% of the catchment (540,000 ha) was modelled as being likely to be suitable or possibly suitable for ringtanks. However, unlike many large catchments in northern Australia, contiguous areas of soil suitable for irrigation within 5 km of the river are more limiting than surface water along the Victoria River and its major tributaries, except the West Baines River, for which irrigation is water limited. Along the West Baines River, the soils are most suitable for irrigated agriculture upstream of the Victoria Highway. Upstream of the highway it is physically possible to extract 100 GL in 75% of years by pumping or diverting water from the river to offstream storages such as ringtanks for irrigating dry-season crops. Downstream of the highway the soils become increasingly less versatile due to wetness and flooding. This would make irrigation establishment and operation costs higher due to the need for drainage and ensuring infrastructure has sufficient flood immunity. These problems would ultimately make potential water-harvesting enterprises less viable. Nonetheless, it would be possible to physically extract an additional 300 GL in 75% of years downstream of the highway for irrigation of broadacre crops during the dry season. Along the Victoria River and its other major tributaries apart from the West Baines, water harvesting is limited due to narrow floodplains, sandy levee soils and increasing elevation with distance from the river resulting in higher reticulation infrastructure costs (e.g. pumps and pipelines). Nonetheless, across the entire Victoria catchment it is physically possible to extract 690 GL per year in 75% of years. This volume could irrigate approximately 50,000 ha (0.6% of catchment area) of broadacre crops such as cotton on the clay alluvial soil during the dry season. In this situation, water from the Victoria River and its major tributaries would be pumped or diverted and stored in offstream storages such as ringtanks. This scenario results in a modelled reduction in the mean and median annual discharges from the Victoria catchment of about 9% and 12%, respectively. Managed aquifer recharge The Assessment indicates there are few opportunities for managed aquifer recharge (MAR) in the Victoria catchment. The basic requirements for a MAR scheme are the presence of a suitable aquifer with sufficient storage capacity, soils with moderate to high permeability, landscapes with low to moderate slope (i.e. 10% or less) and a source of water. In the majority of those parts of the catchment where the soils, slope and hydrogeology are potentially suitable for MAR (i.e. where the CLA occurs along the eastern margin of the catchment), the rivers and streams are highly intermittent, so there is no reliable source of water for MAR. Furthermore, the soils are unsuitable for the construction of offstream storages. Approximately 64,500 ha (0.8%) of the Victoria catchment was identified as having potential for aquifers, groundwater and landscape characteristics suitable for infiltration MAR techniques within 5 km of a river with a median annual flow of greater than 20 GL and from which water could potentially be sourced for recharge (though in the headwaters of these rivers the reliability of flow would need to be locally assessed). Within 1 km, the equivalent area was around 24,000 ha (0.3%) of the catchment. However, 60% of the area within 1 km of the river was Quaternary alluvium aquifers for which there was no water- level data, little bore log data and consequently considerable uncertainty regarding their potential suitability for MAR. Jointly considering the location of areas potentially suitable for MAR and the location of soils potentially suitable for irrigated agriculture, opportunities for MAR-based irrigated agriculture in the Victoria catchment are highly limited. Gully dams and weirs Suitably sited, large farm-scale gully dams are a relatively cost-effective method of supplying water. The topography of the Victoria catchment is highly suitable for large farm-scale gully dams, and opportunities are scattered throughout the catchment. The major limitation is that the soil in many places is rocky and shallow, meaning that access is required to a nearby clay borrow pit for the cut-off trench and core zone. These sites will be less economically viable than sites with more suitable soil. Nonetheless, numerous favourable gully dam locations occur across the catchment near soils that are suitable for irrigated agriculture. Furthermore, the quantity of water that could potentially be supplied by gully dams is likely to be commensurate to the (limited) extent of contiguous soils suitable for irrigated agriculture scattered throughout the Victoria catchment. The other sources of water and storage options, namely weirs and natural water bodies, can reliably supply considerably smaller volumes of water than major instream dams. Sourcing water from natural water bodies, although the most cost-effective option, is highly contentious, and irrigated agriculture would be limited to small-scale operations (e.g. tens of hectares), such as trialling irrigation prior to scaling up. Summary of investigative, capital, and operation and maintenance costs of different water supply options and potential scale of unconstrained development Table 5-1 summarises indicative investigative, capital, and operation and maintenance costs of different water supply options and estimates of the potential scale of unconstrained development. The development of any of these options will affect existing uses, including ecological systems, to varying degrees depending on the level of development. This is examined in Section 7.2. All of the water source options reported in Table 5-1 are considerably cheaper than the cost of desalinisation. The initial cost of constructing four large desalinisation plants (capacity of 90 to 150 GL/year) in Australia between 2010 and 2012 ranged from $19,000 to $31,000/ML (AWA, 2018), indexed to 2023. This does not include the cost of ongoing operation (e.g. energy) and maintenance or the cost of conveying water to the demand. Table 5-1 Summary of capital costs, yields and costs per megalitre of supply, including operation and maintenance (O&M) Costs and yields are indicative. Values are rounded. Capital costs are the cost of construction of the water storage/source infrastructure. They do not include the cost of constructing associated infrastructure for conveying water or irrigation development. Water supply options are not independent of one another, and the maximum yields and areas of irrigation cannot be added together. Equivalent annual cost assumes a 7% discount rate over the service life of the infrastructure. Total yields and areas are indicative and based on physical plausibility unconstrained by economic, social, environmental, legislative or regulatory factors, which will inevitably constrain many developments. WATER SOURCE/ STORAGE GROUND- WATER† MANAGED AQUIFER RECHARGE‡ MAJOR DAM WEIR§ LARGE FARM- SCALE RINGTANK LARGE FARM- SCALE GULLY DAM NATURAL WATER BODY Cost and service life of individual representative unit Capital cost ($ million) 3.9 1.1 396 5–40 2.95 1.65 0.02 O&M cost ($ million/y)* 0.1 0.07 1.0 0.05–0.8 0.125 0.045 ~0 Assumed service life (y) 50 50 100 50 40 30 15 Potential yield of individual representative unit at water source Yield at source (GL)†† 2 0.6 64 0.1–10 2.4 3 0.125–0.5 Unit cost ($/ML)‡‡ 1,950 1,830 6,190 6,500 1,040 570 100 Levelised cost ($/ML)§§ 190 250 460 600 130 60 10 Potential yield of individual representative unit at paddock WATER SOURCE/ STORAGE GROUND- WATER† MANAGED AQUIFER RECHARGE‡ MAJOR DAM WEIR§ LARGE FARM- SCALE RINGTANK LARGE FARM- SCALE GULLY DAM NATURAL WATER BODY Assumed conveyance efficiency to paddock (%)††† 95 90 63 80 90 90 90 Yield at paddock (GL) 1.9 0.54 40 0.8–12 2.16 2.7 0.11–0.45 Unit cost ($/ML)‡‡ 2050 2,040 9,820 8,125 1,160 630 110 Levelised cost ($/ML) 200 280 730 750 145 65 12 Total potential yield and area (unconstrained) Total potential yield (GL/y) at source ≥75% reliability‡‡‡ 20 <10 600 <100 415 <50 <25 Potential area that could be irrigated at ≥75% reliability (ha)§§§ 3,000 <1,500 50,000 <10,000 50,000 <5,000 <2,500 †Value assumes extraction from the Cambrian Limestone Aquifer with a mean bore yield of 25 L/s to meet mean peak evaporative demand over a 3- day period for 500 ha. Assumes a mean depth of 60 m and a drilling failure rate of 50%. ‡Based on recharge weir. §Sheet piling weir. *Annual cost of operating and maintaining infrastructure. It includes the cost of pumping groundwater, assuming groundwater is 10 to 20 m below ground level, and the cost of pumping water into ringtank. ††Yield at dam wall (considering net evaporation from surface water storages prior to release) or at groundwater bore. Value assumes large farm- scale ringtanks do not store water past August. ‡‡Capital cost divided by the yield. §§Assumes 7% discount rate. †††Conveyance efficiency between dam wall or groundwater bore and edge of paddock (does not include field application losses). ‡‡‡Actual yield will depend upon government and community acceptance of impacts to water-dependent ecosystems and existing users. Yields are not additive. Likely maximum cumulative yield at the dam wall or groundwater bore. §§§Likely maximum area that could be irrigated (after conveyance and field application losses) in at least 75% of years. Assumes a single crop. Areas provided for each water source are not independent and hence are not additive. Actual area will depend upon government and community acceptance of impacts to water-dependent ecosystems and existing users. 5.2 Introduction 5.2.1 Contextual information Irrigation during the dry season and other periods when soil water is insufficient for crop growth requires sourcing water from a suitable aquifer or from a surface water body. However, decisions regarding groundwater extraction, river regulation and water storage are complex, and the consequences of decisions can be inter-generational, where even relatively small inappropriate releases of water may preclude the development of other, more appropriate (and possibly larger) developments in the future. Consequently, governments and communities benefit by having a wide range of reliable information available prior to making decisions, including the ways by which water can be sourced and stored, as this can have long-lasting benefits and facilitate an open and transparent debate. More detailed information can be found in the companion technical reports. Sections 5.3 and 5.4 examine the nature and scale of groundwater and surface water storage opportunities, respectively, in the Victoria catchment. Section 5.5 discusses the conveyance of water from the storage and its application to the crop. Transmission and field application efficiencies and associated costs and considerations are examined. All costs presented in this chapter are indexed to December 2023. Concepts The following concepts are used in sections 5.3 and 5.4. • Each of the water source and storage sections is structured around: (i) an opportunity- or reconnaissance-level assessment and (ii) a pre-feasibility-level assessment: – Opportunity-level assessments involved a review of the existing literature and a high-level desktop assessment using methods and datasets that could be consistently applied across the entire Assessment area. The purpose of the opportunity-level assessment is to provide a general indication of the likely scale of opportunity and geographic location of better options. – Pre-feasibility-level assessments involved a more detailed desktop assessment of sites/geographic locations that were considered more promising. This involved a broader and more detailed analysis including the development of bespoke numerical models, site-specific cost estimates and site visits. Considerable field investigations were undertaken for the assessment of groundwater development opportunities (Section 5.3.2). • ‘Yield’ is a term used to report the performance of a water source or storage. It is the amount of water that can be supplied for consumptive use at a given reliability. For dams, an increase in water yield results in a decrease in reliability. For groundwater, an increase in water yield results in an increase in the ‘zone of influence’ and can result in a decrease in reliability, particularly in local- and intermediate-scale groundwater systems. • Equivalent annual cost is the annual cost of owning, operating and maintaining an asset over its entire life. Equivalent annual cost allows a comparison of the cost-effectiveness of various assets that have unequal service lives/life spans. • Levelised cost is the equivalent annual cost divided by the amount of water that can be supplied at a specified reliability. It allows a comparison of the cost-effectiveness of various assets that have unequal service lives/life spans and water supply potential. Other economic concepts reported in this chapter, such as discount rates, are outlined in Chapter 6. 5.3 Groundwater and subsurface water storage opportunities 5.3.1 Introduction The Assessment undertook a catchment-wide reconnaissance assessment and, at selected locations, a pre-feasibility assessment of: • opportunities for groundwater resource development (Section 5.3.2) • MAR opportunities (Section 5.3.3). Groundwater, where the aquifer is relatively shallow and of sufficient yield to support irrigation, is often one of the cheapest sources of water available, particularly where pumping costs are reduced because groundwater levels are close to the land surface. Even the cheapest forms of MAR, infiltration-based techniques, are usually considerably more expensive than developing a groundwater resource. Further to this, in northern Australia many unconfined aquifers, which are best suited to infiltration-based MAR, either have large areas with no ‘free’ storage capacity at the end of the wet season (because groundwater levels have risen to near the ground surface) or, where storage capacity is available, are often at uneconomically viable distances (i.e. greater than 5 km) from a reliable source of water to recharge the aquifer. Therefore, MAR will inevitably only be developed following development of a groundwater system, where groundwater extraction may create additional storage capacity within the aquifer (by lowering groundwater levels) to allow additional recharge, and hydrogeological information is more readily available to evaluate the local potential of MAR. However, if developed, MAR can increase the quantity of water available for extraction and help mitigate impacts to the environment. Note that where water uses have a higher value than irrigation (e.g. mining, energy operations, town water supply), other more expensive but versatile forms of MAR, such as aquifer storage and recovery, can be economically viable and should be considered. 5.3.2 Opportunities for groundwater development Introduction Planning future groundwater resource developments and authorising licensed groundwater entitlements require value judgments about acceptability of impacts to receptors such as environmental assets or existing users at a given location. These decisions can be complex, and they typically require considerable input from a wide range of stakeholders, particularly government regulators and communities. Scientific information to help inform these decisions includes: (i) identifying aquifers that may be potentially suitable for future groundwater resource development; (ii) characterising their depth, spatial extent, saturated thickness, hydraulic properties and water quality; (iii) conceptualising the nature of their flow systems; (iv) estimating aquifer water balances; and (v) providing initial estimates of potential extractable volumes and associated drawdown in groundwater level over time and distance relative to existing water users and GDEs. The changes in groundwater levels over time at different locations provide information on the potential risks of changes in aquifer storage and therefore water availability to existing groundwater users or the environment. Unless stated otherwise, the material presented in Section 5.3.2 has been summarised from the companion technical report on groundwater characterisation (Taylor et al., 2024) and the companion technical report on groundwater modelling (Knapton et al., 2024). Opportunity-level assessment of groundwater resource development opportunities in the Victoria catchment The hydrogeological units of the Victoria catchment (Figure 5-2) contain a variety of local-, intermediate- and regional-scale aquifers that host localised to regional-scale groundwater flow systems. The intermediate- to regional-scale limestone and dolostone aquifers are present in the subsurface across moderate areas, collectively occurring beneath about 24% of the catchment. Given their moderate spatial extent, they underlie and partially coincide with areas of soil suitable for irrigated agriculture (Section 4.2). They contain mostly fresh water (<1000 mg/L total dissolved solids, TDS) and have potential to yield water at a sufficient rate to support irrigation development (>10 L/s) with appropriately constructed and sited bores. These aquifers contain larger volumes of groundwater in storage (tens to hundreds of gigalitres) than local-scale aquifers, and their storage and discharge characteristics are often less affected by short-term (yearly) variations in recharge rates caused by inter-annual variability in rainfall. Furthermore, their moderate spatial extent provides greater opportunities for groundwater resource development away from existing water users and GDEs at the land surface, such as springs, spring-fed vegetation and surface water, which can be ecologically and culturally significant. In contrast, local-scale aquifers in the Victoria catchment, such as fractured and weathered rock and alluvial aquifers, host local-scale groundwater systems that are highly variable in composition, salinity and yield. They also have a small and variable spatial extent and less storage compared to the larger aquifers, limiting groundwater resource development to localised opportunities such as stock and domestic use or in some instances as a conjunctive water resource (i.e. combined use of groundwater with surface water or rainwater). The Assessment identified six hydrogeological units hosting aquifers that may have potential for future groundwater resource development in the Victoria catchment (Table 5-2): • Cambrian limestone • Proterozoic dolostone • Cambrian basalt • Devonian–Carboniferous sandstone • Proterozoic sandstone • Quaternary alluvium. Table 5-2 Opportunity-level estimates of the potential scale of groundwater resource development in the Victoria catchment For locations of the hydrogeological units see Figure 5-2. Indicative scale of the resource is based on a combination of numerical modelling, estimates of mean annual recharge, and conceptualisation of the aquifers hosted in different hydrogeological units. The actual scale will depend upon government and community acceptance of potential impacts to groundwater-dependent ecosystems (GDEs) and existing groundwater users. For more information on this table please contact CSIRO on enquiries@csiro.au For more information on this table please contact CSIRO on enquiries@csiro.au †Actual scale will depend upon government and community acceptance of impacts to GDEs and existing water users. Stratigraphic cross sections on hydrogeology map \\FS1-CBR.nexus.csiro.au\{lw-rowra}\work\11_Groundwater\2_Victoria\1_GIS\1_Map_docs\Gr-V-542_GW_opportunities_hydrogeology_v03_CR.mxd For more information on this figure please contact CSIRO on enquiries@csiro.au Figure 5-2 Key hydrogeological units of the Victoria catchment The spatial extent of the outcropping and subcropping component of each hydrogeological unit is presented with the majority of overlying Cretaceous and Cenozoic cover removed (except the alluvium). Right inset shows the spatial extent of the Cambrian limestone and Proterozoic dolostone that extend outside the Victoria catchment. Groundwater development costs The cost of groundwater development is the cost of the infrastructure plus the cost of the hydrogeological investigations required to understand the resource and risks associated with its development. This section presents information relevant to the cost of further developing the groundwater resources of the CLA, including but not limited to: (i) the depth to groundwater-bearing rock/and or sediments in the subsurface (hydrogeological unit), which influences the cost of drilling; and (ii) the depth to groundwater, which influences the cost of pumping. For example, in unconfined aquifers, the depth to groundwater can be greater than the depth to the top of the aquifer and will change over time due to groundwater recharge and/or groundwater pumping. Information on the spatial extent of changes in groundwater levels is also presented. This is relevant to the potential hydraulic impact of future groundwater development on receptors such as existing licensed groundwater users, and culturally and ecologically important GDEs. Aquifer yield information is presented in Section 2.5.2. At a local development scale, individual proponents will need to undertake sufficient localised investigations to provide confidence around aquifer properties and bore performance. This information will also form part of an on-site hydrogeological assessment required by the regulator to grant an authorisation to extract groundwater. Key considerations for an individual proponent include: •determining the locations to drill production bores •testing the production bores •determining the location and number of monitoring bores required •conducting a hydrogeological assessment as part of applying for an authorisation to extractgroundwater. Estimates of costs associated with these local-scale investigations are summarised in Table 5-3. Table 5-3 Summary of estimated costs for a 250 ha irrigation development using groundwater Assumes a mean bore yield of 25 L/s and that 16 production bores are required to meet peak evaporative demands of an area of 250 ha. Does not include operating and maintenance costs. DRILLING, CONSTRUCTION, INSTALLATION AND TESTING OF BORES ESTIMATED COST ($) Production bores 2,044,500† Monitoring bores 226,500‡ Submersible pumps 1,360,000§ Mobilisation/demobilisation 15,000§§ Aquifer testing 168,000* Hydrogeological assessment 100,000†† †Value assumes 16 production bores drilled and constructed at a mean depth of 80 m at a cost per bore of $750/m, constructed with 200 mm steel casing at a cost of $82/m and 18 m stainless steel wire-wound screen at a cost of $150/m. Assumes on average of two drill-holes needed for every cased production bore to account for the variability in the nature of the aquifer at each location. ‡Value assumes six monitoring bores drilled and constructed at a mean depth of 80 m at a cost of $500/m, constructed with 150 mm PVC and machine-slotted 5 m screen at a cost of $50/m. §Value assumes a pump that is rated to draw water at a rate of up to 60 L/second and from depths of up to 50 m below ground level (mBGL). Value based on 16 pumps. §§Value assumes a mobilisation/demobilisation rate of $10/km from Darwin to south of Top Springs and return (approximately 1500 km round trip). *Value assumes six 72-hour constant-rate discharge tests (48 hours pumping, 24 hours recovery) at a cost of $500/h and $4000 mobilisation/demobilisation. ††Indicative cost to proponent. Value assumes a small-scale development away from existing groundwater users and GDEs. Assumes the regulator has already characterised the aquifers at an intermediate to regional scale to better understand the resource potential under cumulative extraction scenarios and under current and future constraints to development. Pre-feasibility-level assessment of groundwater resource development opportunities and risks associated with the Cambrian Limestone Aquifer The Assessment identified the CLA along the east of the catchment to be the most promising regional-scale aquifer with potential for future groundwater resource development. The CLA is hosted mostly in the Montejinni Limestone and is almost exclusively unconfined in the Victoria catchment. This means the CLA outcrops at the land surface or is within tens of metres of the land surface and is directly recharged via outcrop areas or via overlying variably permeable Cretaceous claystone, siltstone and sandstone, and Cenozoic sand, silt and clay, across its extent in the Victoria catchment (see Figure 2-25 in Section 2.2.5). The thickness of the CLA varies spatially beneath the eastern part of the Victoria catchment. It is influenced by historical weathering of the limestone in places and by changes in the topography of the underlying volcanic rocks (Figure 5-3). The CLA is generally about 50 to 120 m thick beneath the eastern part of the Victoria catchment and over 120 m thick in the Wiso Basin to the north-west of the catchment boundary. The saturated thickness (amount of saturated rock) also varies spatially and is an important characteristic, along with aquifer hydraulic properties, in relation to groundwater storage and flow. In some parts of the western Wiso Basin beneath the eastern part of the Victoria catchment, the saturated thickness can be thin (<20 m), or unsaturated, as shown by the mixed success of historical drilling (dry holes or bores with little water). Along the eastern margin of the Victoria catchment, the saturated thickness is variable, ranging between about 10 and 100 m (Figure 5-3). See Figure 2-4 in Section 2.2.3 for an overview of the spatial extent of the different geological basins in the Victoria catchment. For more information on this figure please contact CSIRO on enquiries@csiro.au Figure 5-3 Hydrogeological cross-section through the Cambrian Limestone Aquifer in the east of the Victoria catchment See Figure 5-2 for the spatial location of the cross-section. The CLA beneath the Victoria catchment is generally flat. Depth to the top of the CLA in the subsurface along the eastern margin of the Victoria catchment is generally shallow (<50 mBGL) as the aquifer outcrops across large areas (Figure 5-5). To the north-east of Top Springs, depth to the top of CLA increases to about 120 mBGL where overlying Cretaceous rocks are more extensive (Figure 5-3 and Figure 5-5). Depth to the top of the CLA generally increases (>150 mBGL) east of the catchment boundary out into the central Wiso Basin where the overlying Cretaceous rocks are thicker. Depth to the CLA also increases (>150 mBGL) where the aquifer dips below mean sea level in the Daly Basin in the far north (Figure 5-5). See Figure 2-25 in Section 2.5.2 for information on the spatial occurrence and extent of the geological basins. Changes in the depth to groundwater across the CLA, also referred to as depth to standing water level (SWL), exhibit similar spatial patterns to the depth to the top of the aquifer. For example, groundwater is shallow (<10 mBGL) along the western margin of the aquifer around and to the south of Top Springs (Figure 5-6) where groundwater discharges by: (i) intermittent lateral outflow to streams (Armstrong River, and Bullock, Cattle and Montejinni creeks), where they are incised into the aquifer outcrop; (ii) perennial localised spring discharge at spring complexes (Old Top, Lonely, Palm and Horse springs); and (iii) evapotranspiration from groundwater-dependent vegetation in nearby groundwater-fed streams and springs. For this reason, GDEs associated with the CLA in the Victoria catchment are largely limited to the western margin of the aquifer around Top Springs (see conceptual model in Figure 5-7). Depth to groundwater then increases subtly to depths ranging from 40 to 50 mBGL in a somewhat radial pattern north-east, east and south-east from the western aquifer boundary towards the eastern margin of the Victoria catchment. Beyond the eastern margin of the catchment, the depth to groundwater often exceeds 70 mBGL (Figure 5-6). For more information on this figure please contact CSIRO on enquiries@csiro.au Figure 5-4 Groundwater pumps powered by the wind provide water points for cattle Photo: CSIRO – Nathan Dyer Depth to CLA map \\FS1-CBR.nexus.csiro.au\{lw-rowra}\work\11_Groundwater\2_Victoria\1_GIS\1_Map_docs\Gr-V-544_CLA_DtoAq_surfaces_v01_CR.mxd For more information on this figure please contact CSIRO on enquiries@csiro.au Figure 5-5 Depth to the top of the Cambrian Limestone Aquifer Only a partial spatial extent of the CLA is shown beyond the Victoria catchment boundary. Depths are in metres below ground level (mBGL). Stratigraphic data points represent a bore with stratigraphic data that provides information about changes in geology with depth. Aquifer extent data source: Knapton (2020) SWL CLA Wiso map \\FS1-CBR.nexus.csiro.au\{lw-rowra}\work\11_Groundwater\2_Victoria\1_GIS\1_Map_docs\Gr-V-568_CLA_SWL_Map_WISO_CR.mxd For more information on this figure please contact CSIRO on enquiries@csiro.au Figure 5-6 Depth to standing water level (SWL) of the Cambrian Limestone Aquifer Only a partial spatial extent of the CLA is shown beyond the Victoria catchment boundary. Depths are in metres below the land surface. Aquifer extent data sources: Knapton (2020) For more information on this figure please contact CSIRO on enquiries@csiro.au Figure 5-7 Conceptual block model of part of the Cambrian Limestone Aquifer near Top Springs along the eastern margin of the Victoria catchment Large blue arrows represent groundwater flow directions. Larger blue sections associated with streams represent perennial reaches where groundwater discharge supports surface water flow. Texture in the hydrogeological units represent fractured and/or karstic rocks. Impacts of extracting groundwater from the Cambrian Limestone Aquifer to groundwater-dependent ecosystems and existing groundwater users The Assessment used a groundwater model which covers part of the CLA in the Victoria catchment (see companion technical report on groundwater modelling in the Victoria catchment, Knapton et al., 2024), based on the revised conceptual model (e.g. Figure 5-7), to evaluate the impacts of incrementally larger groundwater extractions on localised perennial groundwater discharge to the spring complexes around Top Springs and existing groundwater users under historical and future climates. The results, detailed in the report by Knapton et al. (2024), are summarised in Table 5-4 and Table 5-5. The potential impacts, in terms of groundwater drawdown, of three hypothetical annual groundwater extraction quantities (3, 4 and 5 GL) at three hypothetical locations within the CLA are reported at ten stock and domestic bores (each with a registered number, RN) installed in a range of different hydrogeological settings and proximities to existing users. The three hypothetical extraction locations, located to the south of Top Springs, were selected considering the location of existing groundwater users, suitability of soil for irrigated agriculture, suitable hydrogeological properties for groundwater extraction and distance from ecologically and culturally important GDEs (see Knapton et al. (2024) for more detail). The locations of the hypothetical groundwater extractions and the reporting sites are shown in Figure 5-8, along with the location of numerous spring complexes along the western margin of the CLA. A picture of Old Top Spring is shown in Figure 5-9. Hypothetical extraction \\FS1-CBR.nexus.csiro.au\{lw-rowra}\work\11_Groundwater\2_Victoria\1_GIS\1_Map_docs\Gr-V-551_GW_modelling_sites_v02_CR.mxd For more information on this figure please contact CSIRO on enquiries@csiro.au Figure 5-8 Location of hypothetical groundwater extraction sites in relation to modelled groundwater level reporting sites and modelled discharge at key springs for the Cambrian Limestone Aquifer For more information on this figure please contact CSIRO on enquiries@csiro.au Figure 5-9 Perennial localised discharge from the Cambrian Limestone Aquifer to Old Top Spring Photo: CSIRO The CLA is a regional-scale groundwater system, which means that changes in climate and increases in groundwater extraction can take many hundreds of years to fully propagate through the system. Consequently, the results are sensitive to the reporting time period. All model results are reported at 2060 (~40 years). This is considered a pragmatic time period over which to consider the impacts of changes in climate and groundwater extraction because it is: (i) equivalent to more than twice the length of the investment period of a typical agricultural enterprise, (ii) roughly equivalent to the service life of a commissioned groundwater borefield and (iii) consistent with the time period over which future climate projections have been evaluated. Note that this time period is about four times the length of the current period over which NT water licences are assigned. Importantly, in reporting the results of the hypothetical groundwater development scenarios, no judgment is made about acceptability of the impact of the modelled groundwater-level drawdown to receptors such as groundwater-dependent environmental assets or existing users. Drawdown in groundwater levels in the CLA under the three hypothetical annual extraction scenarios – B9 (3 × 3 GL extraction), B12 (3 × 4 GL extraction) and B15 (3 × 5 GL extraction) – is concentric around the three hypothetical groundwater extraction sites (Figure 5-10). At the smallest cumulative hypothetical extraction rate (9 GL/year, Scenario B9) the maximum modelled drawdown in groundwater level after the 40-year period (~2060) is about 14 m in the centre of each of the three hypothetical extraction sites (Figure 5-10). At RN026109, which is about 6 km from the epi-centre of the three hypothetical extraction sites (Figure 5-8), the maximum modelled drawdown in groundwater level is about 4 m under Scenario B9 after 40 years (Table 5-4). At the largest cumulative extraction rate (15 GL/year, Scenario B15), the modelled drawdown in groundwater level at the centre of each of the three hypothetical extraction sites after the 40-year period (~2060) was 26 m (Figure 5-10). At RN026109, (Figure 5-8), the maximum modelled drawdown in groundwater level is about 7 m under Scenario B9 after 40 years ( Table 5-4 Mean modelled groundwater levels at ten locations within the Cambrian Limestone Aquifer under extraction scenarios A, B, C and D Locations are shown in Figure 5-8 All results are reported for approximately 2060. Values shown are the differences in modelled groundwater level relative to Scenario A (a negative value is a decrease; a positive value is an increase). Additional maps of groundwater drawdown are provided in the companion technical report on groundwater modelling (Knapton et al., 2024). SCENARIO MODELLED GROUNDWATER LEVEL (m) RN000594 (~13 km east of Lonely Spring) RN005578 (~45 km north- east of Old Top Spring) RN020020 (~15 km east of Old Top Spring) RN026109 (~20 km south-east of Palm Spring) RN026490 (~56 km south of Palm Spring) RN035496 (~58 km south- east of Palm Spring) RN026441 (~26 km south of Palm Spring) RN026552 (~15 km south- east of Lonely Spring) RN037936 (~26 km east of Old Top Spring) RN042219 (~27 km south- east of Old Top Spring) A 0 0 0 0 0 0 0 0 0 0 B9 –2.2 – –0.2 –4.3 –1.3 –0.8 –0.5 –1.9 –0.2 –0.9 B12 –2.9 – –0.3 –5.7 –1.7 –1.1 –0.7 –2.5 –0.3 –1.2 B15 –3.6 – –0.3 –7.1 –2.1 –1.4 –0.8 –3.2 –0.4 –1.5 Cdry –5.7 –2.3 –0.5 –1.6 – – –0.1 –4.0 –1.3 –0.7 Cmid –1.3 –1.0 –0.1 –0.4 – – – –0.9 –0.4 –0.2 Cwet +7.6 +2.2 +0.6 +2.2 – – +0.2 +5.3 +1.7 +1.0 Ddry9 –7.9 –2.3 –0.7 –5.7 –1.2 –0.8 –0.6 –5.9 –1.5 –1.6 Dmid9 –3.5 –1.0 –0.4 –4.6 –1.2 –0.8 –0.5 –2.8 –0.6 –1.1 Dwet9 +5.4 +2.2 +0.4 –2.0 –1.2 –0.8 –0.3 +3.4 +1.5 +0.1 Ddry12 –8.7 –2.3 –0.8 –7.1 –1.7 –1.1 –0.8 –6.5 –1.6 –1.9 Dmid12 –4.2 –1.0 –0.4 –6.0 –1.7 –1.1 –0.7 –3.5 –0.6 –1.4 Dwet12 +4.8 +2.2 +0.3 –3.5 –1.7 –1.1 –0.5 +2.8 +1.4 –0.2 Ddry15 –9.4 –2.3 –0.8 –8.5 –2.1 –1.4 –0.9 –7.2 –1.7 –2.2 Dmid15 –4.9 –1.0 –0.5 –7.3 –2.1 –1.4 –0.8 –4.1 –0.7 –1.7 Dwet15 +4.1 +2.2 +0.3 –4.9 –2.1 –1.4 –0.6 +2.2 +1.3 –0.5 Scenario A baseline is 0 m. – represents no modelled change. A negative value represents a decrease in groundwater level relative to Scenario A. A positive value represents an increase relative to Scenario A. For more information on this figure please contact CSIRO on enquiries@csiro.au Figure 5-10 Modelled drawdown in groundwater level in the Cambrian Limestone Aquifer (CLA) under scenarios (a) B9, (b) B12 and (c) B15 in approximately 2060 Drawdown contours relate to drawdown in groundwater level. The darker shade of pink represents the extent of the CLA. For more detail see companion technical report on groundwater modelling (Knapton et al., 2024). Under Scenario B9, the modelled mean groundwater discharge (i.e. total of evapotranspiration) and localised spring discharge) from the CLA is 9.9 GL/year, a reduction in modelled discharge of 11% compared to under Scenario A (11.1 GL/year) (Table 5-5). Under Scenario B15, the modelled mean groundwater discharge from the CLA is 9.1 GL/year (Table 5-5). This is 2.0 GL/year less (18% reduction) than the mean modelled groundwater discharge under Scenario A (Table 5-5). The reductions in mean modelled groundwater discharge under groundwater extraction scenarios B9, B12 and B15 are due to the small spatial extent of the CLA in the Victoria catchment (12,000 km2) and the short distance (about 15 km) between the closest hypothetical groundwater extraction site relative to the spring complexes around Top Springs (Figure 5-8). The three hypothetical extraction sites are between about 15 and 80 km from the discharge areas of the aquifer. This highlights that changes in the CLA’s water balance depend on a range of factors, including the location, magnitude and duration of extraction, and the nature of the aquifer’s hydrogeological properties (saturated aquifer thickness, aquifer hydraulic properties, hydrogeological conceptual model) on spatial and temporal changes in groundwater flow in an aquifer. Table 5-5 Mean modelled groundwater discharge by evapotranspiration and localised spring discharge from the Cambrian Limestone Aquifer at spring complexes along its western margin near Top Springs For more information on this figure, table or equation please contact CSIRO on enquiries@csiro.au †A negative value represents a decrease in groundwater discharge relative to Scenario A. A positive value represents an increase relative to Scenario A. The mean modelled groundwater discharge from the CLA at spring complexes along the western margin of the CLA (Figure 5-8) in the Victoria catchment under projected future climate scenarios C and D are summarised in Table 5-5. Under Scenario Cdry (projected future dry climate with no groundwater development), the reduction in groundwater recharge to the aquifer will result in a larger reduction in groundwater discharge via evapotranspiration and localised spring discharge than groundwater extraction. This is because the CLA outcrops near Top Springs, where it receives localised recharge, and the groundwater system has relatively short groundwater flow paths to the spring complexes. Consequently, inter-annual variations in climate are evident in inter-annual variations in discharge. Based on these findings, with appropriately sited borefields up to 10 GL/year could potentially be extracted from the CLA to the south of Top Springs (i.e. groundwater extraction occurring between 20 and 80 km to the south toward Cattle Creek) (Table 5-2). However, this would depend upon government and community acceptance of potential impacts to GDEs and existing groundwater users, as well as approval of licenses to extract groundwater. Groundwater resource development opportunities and risks associated with the Proterozoic dolostone aquifers The Assessment also identified the PDAs in the centre and south of the catchment that host intermediate-scale aquifers as having potential for future groundwater resource development. The PDAs, despite being data sparse, appear to offer some opportunities for potential future groundwater resource development but require further investigation. The aquifers outcrop, subcrop and are unconfined in the centre and south of the Victoria catchment (Figure 5-11). This means they outcrop at the surface or close to the surface (within tens of metres of it) and are directly recharged by outcrop areas or vertical leakage through a thin (<20 m) and patchy veneer of overlying, variably permeable Cenozoic sediments and rocks (black soil plains, laterite, silcrete, sand, gravel and clay). Dolostone aquifer springs \\FS1-CBR.nexus.csiro.au\{lw-rowra}\work\11_Groundwater\2_Victoria\1_GIS\1_Map_docs\Gr-V-543_DepthToSWL_ProtDolostone_V02_CR.mxd For more information on this figure please contact CSIRO on enquiries@csiro.au Figure 5-11 Outcropping and subcropping areas of the Proterozoic dolostone aquifers in the Victoria catchment The spatial extent of the outcropping and subcropping component of the Proterozoic dolostone is presented with the majority of overlying Cretaceous and Cenozoic cover removed (except the alluvium). mBGL = metres below ground level. While pre-feasibility information about the dolostone aquifers is limited, the following factors indicate they offer potential for future development: • The spatial extent to which their outcropping/subcropping area (7000 km2, Figure 5-11) coincides with cracking clay soils and red loamy soils potentially suitable for agricultural intensification (Section 2.3.2) is moderate. • The aquifers can be intersected by drilling at relatively shallow depths in the outcropping and subcropping areas (mostly <100 mBGL, Figure 5-12). • Their potential to achieve high bore yields (>20 L/s) indicates that they have potential to yield water at a sufficient rate for groundwater-based irrigation. • The depth to pump groundwater to the surface is less than 50 mBGL across most areas except for in the far south, west of Kalkarindji (>75 mBGL, Figure 5-11). • They host fresh water suitable for a variety of irrigated crops (mostly <500 mg/L TDS). Insufficient information exists to develop geological models and water balance models for the PDAs. However, an indicative scale of the resource can be derived by applying the estimated recharge rates for the aquifers (Section 2.5.3) to the outcropping and subcropping areas of these aquifers to assess the potential recharge component of the water balance for these aquifers. Given the likelihood that the water balance for the PDAs will be sensitive to climate variability similar to that of the CLA, a conservative approach of using the 95th percentile exceedance of the estimated range in annual recharge rates to the outcropping and subcropping areas of the PDAs (see Section 2.5.3) results in a conservative estimate for the annual recharge flux of 105 GL/year. Assuming 20% of the conservative recharge flux may potentially be available for future groundwater resource development, an indicative scale of the groundwater resource in the PDAs was estimated to be less than or equal to 20 GL/year (Table 5-2). However, this requires further hydrogeological investigations (drilling and pump testing), and hydrological risk assessment modelling is needed to evaluate groundwater extraction and climate variability impacts to existing groundwater users and GDEs. If and how much groundwater is licensed will ultimately depend upon government and community acceptance of impacts to GDEs and existing groundwater users. Recharge rates are challenging to estimate, especially in karstic aquifers, and despite applying only the 5th percentile recharge rate (95th percentile exceedance) in this Assessment these initial estimates of annual recharge and the indicative scale of the resource require further investigation. In addition, as is the case for the CLA, climate variability is likely to influence the magnitude of annual recharge fluxes to the aquifers. Furthermore, temporal water level information for the aquifers is sparse, and it is unclear if the aquifers can accept this magnitude of annual recharge flux. The aquifers dip steeply in the subsurface, indicating they shift across different areas from unconfined to confined conditions, which influences the nature and timescale of groundwater flow (Figure 5-12). The aquifers host numerous ecologically and culturally important springs (Figure 5-13), and support Timber Creek’s water supply. For more information on this figure please contact CSIRO on enquiries@csiro.au Figure 5-12 North-west to south-east cross-section traversing the dolostone aquifers hosted in the Bullita Group Vertical axis is exaggerated. See Figure 5-2 for the spatial location of the cross-section B–B′. AHD = Australian Height Datum. Groundwater resource development opportunities and risks associated with aquifers in other hydrogeological units Opportunities for potential future groundwater resource development from aquifers hosted in other hydrogeological units (Cambrian basalt, Devonian–Carboniferous sandstone and Proterozoic sandstone) across the Victoria catchment are most likely to be limited to use for stock and domestic purposes and occasional community water supply. Productive local-scale aquifers hosted in the Quaternary alluvium occurring in patches associated with the streambed, stream channel and floodplain of major streams and their tributaries may offer some opportunities; these will require local investigation. The largest occurrences of the alluvium are in the north of the catchment along the lower reaches of the Angalarri, Victoria and West Baines rivers (Figure 5-2). Indicative bore yield data indicate bore yields can be as high as 11 L/s, but the aquifer is currently sparsely tested. Water quality can vary from fresh to brackish, but it is also sparsely tested. However, in places the aquifers may offer potential for small-scale (<1.0 GL/y) localised developments or as a conjunctive water resource. Opportunities are likely to be limited where the alluvium is: (i) storage limited (thin saturated thickness <15 m), (ii) made up mostly of fine- textured sediments (clay lenses), (iii) regularly flooded and (iv) highly connected to perennial reaches of streams such that development may limit water availability to GDEs. For more information on this figure please contact CSIRO on enquiries@csiro.au Figure 5-13 Water sampling at Kidman Springs Photo: CSIRO 5.3.3 Opportunities for managed aquifer recharge Introduction MAR is the intentional recharge of water to aquifers for subsequent recovery or environmental benefit (NRMMC-EPHC-NHMRC, 2009). Importantly for northern Australia, which has high intra- annual variability in rainfall, MAR can contribute to planned conjunctive use, whereby excess surface water can be stored in an aquifer in the wet season for subsequent reuse in the dry season (Evans et al., 2013; Lennon et al., 2014). Individual MAR schemes are typically small- to-intermediate-scale storages with annual extractable volumes of up to 20 GL/year. In Australia, they currently operate predominantly within the urban and industrial sectors, but they also operate in the agricultural sector. This scale of operation can sustain rural urban centres, contribute to diversified supply options in large urban centres and provide localised water management options, and it is suited to mosaic-type irrigation developments. The basic requirements for a MAR scheme are the presence of a suitable aquifer for storage, availability of an excess water source for recharge and a demand for water. The presence of suitable aquifers is determined from previous regional-scale hydrogeological and surface geological mapping (see companion technical report on hydrogeological assessment (Taylor et al., 2024)). Source water availability is considered in terms of presence or absence rather than volumes with respect to any existing water management plans. Pre-feasibility assessment was based on MAR scheme entry-level assessment in the Australian guidelines for water recycling: managed aquifer recharge (NRMMC-EPCH-NHMRC, 2009) – referred to as the MAR guidelines. The MAR guidelines provide a framework to assess feasibility of MAR, incorporating four stages of assessment and scheme development: (i) entry-level assessment (pre-feasibility), (ii) investigations and risk assessment, (iii) MAR scheme construction and commissioning, and (iv) operation of the scheme. There are numerous types of MAR (Figure 5-15), and the selection of MAR type is influenced by the characteristics of the aquifer, the thickness and depth of low-permeability layers, land availability and proximity to the recharge source. Infiltration techniques can be used to recharge unconfined aquifers, with water infiltrating through permeable sediments beneath a dam, river or basin. If infiltration is restricted by superficial clay, the recharge method may involve a pond or sump that penetrates the low-permeability layer. Bores are used to divert water into deep or confined aquifers. Infiltration techniques are typically lower cost than bore injection (Dillon et al., 2009; Ross and Hasnain, 2018) and are generally favoured in this Assessment. The challenge in northern Australia is to identify a suitable unconfined aquifer with capacity to store more water when water is available for recharge. Unless stated otherwise, the material presented in this section has been summarised from the Northern Australia Water Resource Assessment technical report on MAR (Vanderzalm et al., 2018). For more information on this figure please contact CSIRO on enquiries@csiro.au Figure 5-14 The Ord River Irrigation Area 290 km west of Timber Creek has a similar climate and some similar soils and climate setting to the Victoria catchment Photo: CSIRO – Nathan Dyer Figure 5-15 Types of managed aquifer recharge ASR = aquifer storage and recovery; ASTR = aquifer storage, transfer and recovery. Groundwater level indicated by triangle. Arrows indicate nominal movement of water. Dashed arrows indicate recovered water. Source: Adapted from NRMMC-EPHC-NHMRC (2009) Opportunity-level assessment of infiltration-based managed aquifer recharge in the Victoria catchment The most promising aquifers for infiltration-based MAR in the Victoria catchment are within limestones and dolostones because these formations host the major aquifer systems in the Victoria catchment: the CLA and PDAs respectively (Figure 5-2). Available geological mapping indicates that some of the major drainage lines of the Victoria catchment are accompanied by narrow strips of Quaternary alluvium. In some instances, these could be used for MAR provided there is sufficient depth of alluvium and available storage capacity. Groundwater-level data are currently very sparse within the Quaternary alluvium. Groundwater extraction lowers groundwater levels and therefore creates storage capacity in the aquifer, which is required for MAR. However, the challenge remains to target aquifers with storage capacity at the end of the wet season, or to identify an available recharge source when there is sufficient storage capacity (i.e. early in the dry season). Infiltration techniques recharging unconfined aquifers are generally favoured for producing cost-effective water supplies, hence the initial focus on recharge techniques and limitations for unconfined aquifers. Water-level data for stock and domestic bores across the Victoria catchment provide some insight into the potential for aquifers to store additional water. A watertable level deeper than 4 m is recommended in order to have sufficient storage capacity for MAR. Sufficient aquifer storage space is indicated where depth to water is either greater than 4 m at the end of the wet season (i.e. available for recharge year round) or greater than 4 m at the end of the dry season (i.e. available for seasonal recharge). Bores recording depth to water of less than 4 m at the end of the dry season could be considered to have no storage space at any time of year. Only sparse water- level information is available for aquifers hosted in the Quaternary alluvium. While water-level data for the CLA and PDAs indicate that sufficient storage capacity is available (Figure 5-16), there is no source water over most of the CLA along the eastern margin of the Victoria catchment, as the drainage lines in this part of the catchment are highly intermittent, and the soils are unlikely to be suitable for the construction of offstream storages (Section 5.4.4). MAR opportunity maps were developed from the best available data at the catchment scale using the method outlined in the Northern Australia Water Resource Assessment technical report on managed aquifer recharge (Vanderzalm et al., 2018). This method uses four suitability classes for the more promising aquifers for MAR: • Class 1 – highly permeable and low slope (<5%) • Class 2 – highly permeable and moderate slope (5% to 10%) • Class 3 – moderately permeable and low slope (<5%) • Class 4 – moderately permeable and moderate slope (5% to 10%). Class 1 is considered most suitable for MAR and Class 4 least suitable. All areas not classified into one of classes 1, 2, 3 and 4 are considered unsuitable. Figure 5-16 shows the suitability map for MAR in the Victoria catchment, with classes 1 and 2 considered potentially suitable for MAR and classes 3 and 4 considered to be poorly suitable. Figure 5-17 shows areas of classes 1 to 4 that occur within 5 km of a drainage line with a median annual flow greater than 20 GL. MAR map \\FS1-CBR.nexus.csiro.au\{lw-rowra}\work\11_Groundwater\2_Victoria\1_GIS\1_Map_docs\Gr-V-550_Victoria_MAR_suitabilitly_v01_CR.mxd For more information on this figure please contact CSIRO on enquiries@csiro.au Figure 5-16 Managed aquifer recharge opportunities for the Victoria catchment, independent of distance from a water source for recharge Analysis based on soil permeability (Thomas et al., 2024) and terrain slope (Gallant et al., 2011) datasets and limited to the following aquifer formations: Cambrian limestone, Proterozoic dolostone and Quaternary alluvium (Figure 5-2). The opportunity assessment (Figure 5-17) indicates approximately 64,500 ha (0.8%) of the Victoria catchment may have aquifers (including areas of Quaternary alluvium) with potential for MAR within 5 km of drainage lines with a median annual flow greater than 20 GL. Approximately 24,000 ha (~0.3%) of the catchment is considered Class 1 or Class 2 and is within 1 km of drainage lines with a median annual flow greater than 20 GL. However, 60% of this area is underlain by Quaternary alluvium aquifers for which the storage capacity and water level are unknown. Opportunities for MAR that coincide with soils that may be suitable for irrigated agriculture appear to be limited to small parts of the West Baines River catchment. However, Quaternary alluvium is a potential aquifer for MAR although considerable additional investigations would be required. For more information on this figure please contact CSIRO on enquiries@csiro.au Figure 5-17 Managed aquifer recharge (MAR) opportunities in the Victoria catchment (a) within 5 km of major rivers Analysis based on the permeability (Thomas et al., 2024) and terrain slope (Gallant et al., 2011) datasets and limited to the following aquifer formations (b): Cambrian limestone, Proterozoic dolostone and Quaternary alluvium (Figure 5-2). See the Northern Australia Water Resource Assessment technical report on MAR schemes in northern Australia (Vanderzalm et al., 2018) for detailed costings on ten hypothetical MAR schemes in northern Australia. 5.4 Surface water storage opportunities 5.4.1 Introduction In a highly seasonal climate, such as that of the Victoria catchment, and in the absence of suitable groundwater, surface water storages are essential to enable irrigation during the dry season and other periods when soil water is insufficient for crop growth. The Assessment undertook a pre-feasibility-level assessment of three types of surface water storage options. These were: • major dams that could potentially supply water to multiple properties (Section 5.4.2) • re-regulating structures such as weirs (Section 5.4.3) • large farm-scale or on-farm dams, which typically supply water to a single property (Section 5.4.4 and Section 5.4.5). Both major dams and large farm-scale dams can be further classified as instream or offstream water storages. In the Assessment, instream water storages are defined as structures that intercept a drainage line (creek or river) and are not supplemented with water from another drainage line. Offstream water storages are defined as structures that: (i) do not intercept a drainage line or (ii) intercept a small drainage line and are largely supplemented with water extracted from another larger drainage line. Ringtanks and turkey nest tanks are examples of offstream storages with a continuous embankment; the former are the focus in the Assessment due to their higher storage-to-excavation ratios relative to the latter. The performance of a dam is often assessed in terms of water yield. This is the amount of water that can be supplied for consumptive use at a given reliability. For a given dam and reservoir capacity, an increase in water yield results in a decrease in reliability. Importantly, the Assessment does not seek to provide instruction on the design and construction of farm-scale water storages. Numerous books and online tools provide detailed information on nearly all facets of farm-scale water storage (e.g. IAA, 2007; Lewis, 2002; QWRC, 1984). Siting, design and construction of weirs, large farm-scale ringtanks and gully dams are heavily regulated in most jurisdictions across Australia and should always be undertaken in conjunction with a suitably qualified professional and tailored to the nuances at every site. Major dams are complicated structures and usually involve a consortium of organisations and individuals. Unless otherwise stated, the material in Section 5.4 originates from the companion technical report on surface water storage (Yang et al., 2024). 5.4.2 Major dams Introduction Major dams are usually constructed from earth, rock and/or concrete materials, and typically act as a barrier wall across a river to store water in the reservoir created. They need to be able to safely discharge the largest flood flows likely to enter the reservoir, and the structure has to be designed so that the dam meets its purpose, generally for at least 100 years. Some dams, such as the Kofini Dam in Greece and the Anfengtang Dam in China, have been in continuous operation for over 2000 years, with Schnitter (1994) consequently coining dams as ‘the useful pyramids’. An attraction of major dams over farm-scale dams is that if the reservoir is large enough relative to the demands on the dam (i.e. water supplied for consumptive use and ‘lost’ through evaporation and seepage), when the reservoir is full, water can last 2 or more years. This has the advantage of mitigating against years with low inflows to the reservoir. For this reason, major dams are sometimes referred to as ‘carry-over storages’. Major instream versus offstream dams Offstream water storages were among the first man-made water storages (Nace, 1972; Scarborough and Gallopin, 1991) because people initially lacked the capacity to build structures that could block rivers and withstand large flood events. One of the advantages of offstream storages is that, if properly designed, they can cause less disruption of the natural flow regime than large instream dams. Less disruption occurs if water is extracted from the river using pumps, or if there is a diversion structure with gates that can be raised, to allow water and aquatic species to pass through when not in use. In the very remote environments of northern Australia, the period in which these gates need to be operated is also the period in which it is difficult to move around wet roads and flooded waterways. The primary advantage of large instream dams is that they provide a very efficient way of intercepting the flow in a river, effectively trapping all flow until the full supply level (FSL) is reached. For this reason, however, they also provide a very effective barrier to the movement of fish and other species within a river system, alter downstream flow patterns and can inundate large areas of land upstream of the dam. Types of major dams Two types of major dams are particularly suited to northern Australia: embankment dams and concrete gravity dams. Embankment dams are usually the most economic, provided suitable construction materials can be found locally, and are best suited to smaller catchment areas where the spillway capacity requirement is small. Concrete gravity dams with a central overflow spillway are generally more suitable where a large-capacity spillway is needed to discharge flood inflows, as is the case in most large catchments in northern Australia. Traditionally, concrete gravity dams were constructed by placing conventional concrete in formed ‘lifts’. Since 1984 in Australia, however, roller compacted concrete (RCC) has been used, where low-cement concrete is placed in continuous thin layers from bank to bank and compacted with vibrating rollers. This approach allows large dams to be constructed in a far shorter time frame than required for conventional concrete construction, often with large savings in cost (Doherty, 1999). RCC is best used for high dams where a larger-scale plant can provide significant economies of scale. This is now the favoured type of construction in Australia whenever foundation rock is available within reasonable depth, and where a larger-capacity spillway is required. In those parts of the Victoria catchment with topography and hydrology most suited to large instream dams, RCC was deemed to be the most appropriate type of dam. Opportunity-level assessment of potential major dams in the Victoria catchment A promising dam site requires inflows of sufficient volume and frequency, topography that provides a constriction of the river channel and, critically, favourable foundation geology. The only study identified in the literature that looked at surface water storage in the Victoria catchment was undertaken in 1995 by the NT Government (Tickell and Rajaratnam, 1995) who undertook a water resource survey of Legune Station in the Victoria catchment. This study evaluated small gully dams, excavated tanks and modified waterholes on Legune Station. No studies of large dams in the Victoria catchment have been identified. Consequently an opportunity-level assessment of potential major dams in the Victoria catchment was undertaken using a bespoke computer model, the DamSite model (Petheram et al., 2017a, Petheram et al., 2017b), to assess over 50 million sites in the study area for their potential as major offstream or instream dams. Broad-scale geological considerations Favourable foundation conditions include a relatively shallow layer of unconsolidated materials, such as alluvium, and rock that is relatively strong, resistant to erosion, non-permeable or capable of being grouted. Geological features that make dam construction challenging include the presence of faults, weak geological units, landslides and deeply weathered zones. Potentially, feasible dam sites occur where resistant ridges of rock that have been incised by the river systems outcrop on both sides of river valleys. The rocks are generally weathered to varying degrees, and the depth of weathering, the amount of outcrop on the valley slopes, the occurrence of dolomitic rocks (which may contain solution features), and the width and depth of alluvium in the base of the valley are fundamental controls on the suitability of the potential dam sites. Where the rocks are relatively unweathered and outcrop on the abutments of the potential dam site, less stripping (removal of material) will be required to achieve a satisfactory founding level for the dam. In general, where stripping removes the more weathered rock, it is anticipated that the Proterozoic sandstones, siltstones, mudstones and conglomerates will form a reasonably watertight dam foundation, requiring conventional grout curtains and foundation preparation. However, because dolostones are soluble over a geological timescale, it is possible that, where they occur within the Proterozoic sequences, potentially leaky dam abutments and reservoir rims may be present, which would require specialised and costly foundation treatment such as extensive grouting. The extent and depth of the Cenozoic or Quaternary alluvial sands and gravels in the floor of the valley are also important geological controls on dam feasibility, as these materials will have to be removed to achieve a satisfactory founding level for the dam. Where rivers are tidal (e.g. lower Victoria River), the presence of soft estuarine sediments has the potential to make dam design more challenging and construction more expensive, which may compromise the feasibility of a dam. Sites potentially topographically suitable for large storages for water supply Figure 5-18 displays the most promising sites across the Victoria catchment in terms of topography, assessed in terms of approximate cost of construction per unit of storage volume. Favourable locations with a small catchment area and adjacent to a large river may be suitable as major offstream storages. Potential storage sites cost per ML map \\FS1-CBR.nexus.csiro.au\{lw-rowra}\work\4_Water_storage\1_Victoria\1_GIS\1_Map_docs\WS506-V_Storage_Unit_cost_map_v2_CR.mxd For more information on this figure please contact CSIRO on enquiries@csiro.au Figure 5-18 Topographically more favourable potential storage sites in the Victoria catchment based on minimum cost per megalitre storage capacity This figure can be used to identify locations where topography is suitable for large offstream storages. At each location the minimum cost per megalitre storage capacity is displayed. The smaller the minimum cost per megalitre storage capacity ($/ML) the more suitable the site for a large offstream storage provided a source of water was nearby. Analysis does not take into account geological considerations, hydrology or proximity to water. Only sites with a minimum cost-to-storage-volume ratio of less than $5000/ML are shown. Costs are based on unit rates and quantity of material and site establishment for a roller compacted concrete dam. Insets display height and width of dam wall at full supply level at the minimum cost per megalitre storage capacity. For more detail see companion technical report on surface water storage (Yang et al., 2024). In Figure 5-18, only those locations with a ratio of cost to storage of less than $5000/ML are shown. This is a simple way to display those locations in the Victoria catchment with the most favourable topography for a large reservoir relative to the size (i.e. cost) of the dam wall necessary to construct the reservoir. This figure can be used to help identify more promising sites for offstream storage (i.e. where some or all of the water is pumped into the reservoir from an adjacent drainage line). The threshold value of $5000/ML is nominal and was used to minimise the amount of data displayed. This analysis does not consider open water evaporation, hydrology or geological suitability for dam construction. Figure 5-18 shows that the parts of the Victoria catchment with the most favourable topography for storing water are predominantly along the lower Victoria, East Baines and Wickham rivers. The topography of the West Baines River is less suitable for large instream dams. There is little favourable topography for large instream dams on the Sturt Plateau in the east of the catchment or the deeply weathered landscapes to the south of Kalkarindji. Major instream dams for water and irrigation supply In addition to suitable topography (and geology), instream dams require sufficient inflows to meet a potential demand. Potential dams that command smaller catchments with lower runoff have smaller yields. Results concerning this criterion are presented in terms of minimum cost per unit yield, where the smaller the cost per megalitre yield ($/ML) the more favourable the site for a large instream dam The potential for major instream dams to cost-effectively supply water is presented in Figure 5-19. No values greater than $10,000/ML are shown. The most cost-effective potential dam sites are along the lower reaches of the Victoria River. However, as shown by the versatile land map in Figure 5-19, very little land is suitable for irrigated agriculture below these potential dam sites. The results presented in Figure 5-19 do not consider the geological suitability of a site for dam construction. Based on this analysis and a broad-scale desktop geological evaluation, four of the more cost- effective, larger-yielding sites in distinct geographical areas that are proximal to soils suitable for irrigated agriculture were selected for pre-feasibility analysis (see companion technical report on surface water storage (Yang et al., 2024)) to explore the potential opportunities and risks of water supply dams in the Victoria catchment. The locations of these pre-feasibility potential dam sites are denoted in Figure 5-19 by black circles and the letters ‘A’, ‘B’, ‘C’ and ‘E’. Two additional sites were short-listed for pre-feasibility analysis – one to provide a commentary on the potential for large dams to generate hydro-electric power in the Victoria catchment (denoted by a black circle and the letter ‘D’) and the second to explore the potential for large dams in the Victoria catchment to mitigate the impacts of flooding on very remote communities downstream (denoted by a black circle and the letter ‘F’). Potential storage sites min cost per ML at dam wall map \\FS1-CBR.nexus.csiro.au\{lw-rowra}\work\4_Water_storage\1_Victoria\1_GIS\1_Map_docs\WS507-V_Yield_Unit_cost_map_CR_v6.mxd For more information on this figure please contact CSIRO on enquiries@csiro.au Figure 5-19 Topographically and hydrologically more favourable potential storage sites in the Victoria catchment based on minimum cost per megalitre yield at the dam wall This figure indicates those sites more suitable for major dams in terms of cost per ML yield at the dam wall in 85% of years overlain on versatile land surface (see companion technical report on land suitability, Thomas et al., 2024). At each location the minimum cost per ML storage capacity is displayed. Only sites with a minimum cost-to-yield ratio less than $10,000/ML are shown. Costs are based on unit rates and quantity of material required for a roller compacted concrete dam with a flood design of 1 in 10,000. Right inset displays height of full supply level (FSL) at the minimum cost per megalitre yield and left inset displays width of FSL at the minimum cost per megalitre yield. Letters indicate potential dams listed in Table 5-6 and Table 5-7: A – Bullo River adopted middle thread distance (AMTD) 57 km; B – Leichhardt Creek AMTD 26 km; C – Gipsy Creek AMTD 56 km; D – Victoria River AMTD 97 km; E – Wickham River AMTD 63 km; F –Victoria River AMTD 283 km; G – Victoria River AMTD 320 km. For more detail see companion technical report on surface water storage (Yang et al., 2024). Along the Victoria River downstream of the junction with the Wickham River is a relatively large area of soil potentially suitable for irrigated agriculture that could potentially be supplied water from a large instream dam denoted by the letter ‘G’ in Figure 5-19. However, irrigated agriculture would be expensive to establish at this location as the landscape (soils and topography) is complex and an extensive network of pumps and pipelines would be required to distribute water across the area. Consequently this site was not short-listed. Key parameters and performance metrics are summarised in Table 5-6 and an overall summary comment is recorded in Table 5-7. More detailed analysis of the six pre-feasibility sites is provided in the companion technical report on surface water storage (Yang et al., 2024). Hydro-electric power generation potential in the Victoria catchment The potential for major instream dams to generate hydro-electric power is presented in Figure 5-20, following an assessment of more than 50 million potential dam sites in the Victoria catchment (Yang et al., 2024). This figure provides indicative estimates of hydro-electric power generation potential but does not consider the existence of supporting infrastructure (e.g. transmission lines) or geological suitability for dam construction. No values greater than $20,000/ML are shown. The only sites that meet this criteria in the Victoria catchment are on the lower reaches of the Victoria River near Timber Creek and upstream of Victoria River Roadhouse, where high dam walls could potentially be constructed to provide the necessary elevation head. As discussed in Section 3.3.4, however, the Victoria catchment is in a very remote part of the NT that does not have access to major electricity networks, and the small communities rely on diesel generators or hybrid diesel – solar systems provided by Power and Water Corporation. Due to the high cost of electrical infrastructure to support hydro-electric power generation in the Victoria catchment, investigations into hydro-electric power generation were not progressed further. For more details on the hydro-electric power generation capacity of one of the more favourable potential sites on the Victoria River see the companion technical report on river modelling simulation (Hughes et al., 2024b). Potential storage sites hydro power map \\FS1-CBR.nexus.csiro.au\{lw-rowra}\work\4_Water_storage\1_Victoria\1_GIS\1_Map_docs\WS508-V_Hydropower_Unit_cost_map_CR_v5.mxd For more information on this figure please contact CSIRO on enquiries@csiro.au Figure 5-20 Victoria catchment hydro-electric power generation opportunity map Costs are based on unit rates and quantity of material required for a roller compacted concrete dam with a flood design of 1 in 10,000. Data are underlain by a shaded topographic relief map. ‘D’ indicates location of hypothetical hydro-electric power development on the Victoria River. Right inset displays height of full supply level (FSL) at the optimal cost per megawatt hour and left inset displays width of FSL at the optimal cost per megawatt hour. For more detail see companion technical report on surface water storage (Yang et al., 2024). Pre-feasibility-level assessment of potential major dams in the Victoria catchment Six potential dam sites in the Victoria catchment were examined as part of this pre-feasibility assessment. They are summarised Table 5-6 and Table 5-7. More detailed descriptions of the six potential dam sites, including impacts on migratory species and ecological impacts of reservoir inundation, are provided in the companion technical report on surface water storage (Yang et al., 2024). Table 5-6 Potential dam sites in the Victoria catchment examined as part of the Assessment All numbers have been rounded. Locations of potential dams are shown in Figure 5-19. AMTD = adopted middle thread distance; EB = embankment dam; FSL = full supply level; RCC = roller compacted concrete. For more information on this table please contact CSIRO on enquiries@csiro.au *The height of the dam abutments and saddle dams will be higher than the spillway height. **Water yield is based on 85% annual time-based reliability using a perennial demand pattern for the baseline river model under Scenario A. This is yield at the dam wall (i.e. does not take into account distribution losses or downstream transmission losses). These yield values do not take into account downstream existing entitlement holders or environmental considerations. # Indicates manually derived preliminary manual cost estimate, which is likely to be –10% to +50% of ‘true cost’.  Indicates modelled preliminary cost estimate, which is likely to be –25% to +100% of ‘true’ cost. If site geotechnical investigations reveal unknown unfavourable geological conditions, costs could be substantially higher. ##This is the unit cost of annual water supply and is calculated as the capital cost of the dam divided by the water yield at 85% annual time reliability. ###Assumes a 7% real discount rate and a dam service life of 100 years. Includes operation and maintenance costs, assuming these costs are 0.4% of the total capital cost. §This site was evaluated to investigate the potential for hydro-electric power in the Victoria catchment. The yield at this site greatly exceeds the quantity of water required to irrigate the limited area of soil suitable for irrigated agriculture immediately downstream of this potential dam site. §§This potential dam site was evaluated to investigate the potential for dams to mitigate the impacts of flooding to remote communities in the Victoria catchment. For this potential dam the spillway height is actually 23 m, however, the storage capacity is only 10 m. &Includes cost of power station. Does not include cost of other energy infrastructure such as transmission lines or substations. Table 5-7 Summary comments for potential dams in the Victoria catchment Locations of potential dams are shown in Figure 5-19. AMTD = adopted middle thread distance. For more information on this table please contact CSIRO on enquiries@csiro.au The investigation of a potential large dam site generally involves an iterative process of increasingly detailed studies over a period of years, occasionally over as few as 2 or 3 years but often over 10 years or more. It is not unusual for the cost of the geotechnical investigations for a potential dam site alone to exceed several million dollars. For any of the options in this report to advance to construction, far more comprehensive studies would be needed, including not just bio- physical studies such as geotechnical investigations, field measurements of sediment yield, archaeological surveys and ground-based vegetation and fauna surveys, but also extensive consultations with Traditional Owners (e.g. see companion technical report on Indigenous aspirations, interests and water values (Barber et al., 2024)) and other stakeholders. Studies at that level of detail are beyond the scope of this regional-scale resource assessment. The companion technical report on surface water storage (Yang et al., 2024) outlines the key stages in investigation of design, costing and construction of large dams. More comprehensive descriptions are provided by Fell et al. (2005), while Indigenous Peoples’ views on large-scale water development in the catchment can be found in the companion technical report on Indigenous aspirations, interests and water values (Barber et al., 2024). Other important considerations Cultural heritage considerations Indigenous Peoples traditionally situated their campsites, and hunting and foraging activities, along major watercourses and drainage lines. Consequently, dams are more likely to affect areas of high cultural significance than are most other infrastructure developments (e.g. irrigation schemes, roads). No field-based cultural heritage investigations of potential dam and reservoir locations were undertaken in the Victoria catchment as part of the Assessment. However, based on existing records and statements from Indigenous participants in the Assessment, it is highly likely such locations will contain heritage sites of cultural, historical and wider scientific significance. Information relating to the cultural heritage values of the potential major dam sites is insufficient to allow full understanding or quantification of the likely impacts of water storages on Indigenous cultural heritage. The cost of cultural heritage investigations associated with large instream dams that could potentially impound large areas is high relative to other development activities. Ecological considerations of the dam wall and reservoir The water impounded by a major dam inundates an area of land, drowning not only instream habitat but surrounding flora and fauna communities. Complex changes in habitat resulting from inundation could create new habitat to benefit some of these species, while other species would be affected by loss of habitat. For instream ecology, the dam wall acts as a barrier to the movements of plants, animals and nutrients, potentially disrupting connectivity of populations and ecological processes. There are many studies linking water flow with nearly all the elements of instream ecology in freshwater systems (e.g. Robins et al., 2005). The impact of major dams on the movement and migration of aquatic species will depend upon the relative location of the dam walls in a catchment. For example, generally a dam wall in a small headwater catchment will have less of an impact on the movement and migration of species than a dam lower in the catchment. A dam also creates a large, deep lake, a habitat that is in stark contrast to the usually shallow and often flowing, or ephemeral, habitats it replaces. This lake-like environment favours some species over others and will function completely differently to natural rivers and streams. The lake-like environment of an impoundment is often used by sports anglers to augment natural fish populations by artificial stocking. Whether fish stocking is a benefit of dam construction is a matter of debate and point of view. Stocked fisheries provide a welcome source of recreation and food for fishers, and no doubt an economic benefit to local businesses, but they have also created a variety of ecological challenges. Numerous reports of disruption of river ecosystems (e.g. Drinkwater and Frank, 1994; Gillanders and Kingsford, 2002) highlight the need for careful study and regulatory management. Impounded waters may be subject to unauthorised stocking of native fish and releases of exotic flora and fauna. Further investigation of any of these potential dam sites would typically involve a thorough field investigation of vegetation and fauna communities. Ecological assets in the Victoria catchment are discussed in Section 3.2 and described in more detail in the companion technical reports on ecological assets (Stratford et al., 2024) and surface water storage (Yang et al., 2024). Potential changes to instream, riparian and near-shore marine species arising from changes in flow are discussed in Section 7.2. Sedimentation Rivers carry fine and coarse sediment eroded from hill slopes, gullies and banks, and sediment stored within the channel. The delivery of this sediment into a reservoir can be a problem because it can progressively reduce the volume available for active water storage. The deposition of coarser-grained sediments in backwater (upstream) areas of reservoirs can also cause back- flooding beyond the flood limit originally determined for the reservoir. Although infilling of the storage capacity of smaller dams has occurred in Australia (Chanson, 1998), these dams had small storage capacities, and infilling of a reservoir is generally only a potential problem where the volume of the reservoir is small relative to the catchment area. Sediment yield is strongly correlated to catchment area (Tomkins, 2013; Wasson, 1994). Sediment yield to catchment area relationships developed for northern Australia (Tomkins, 2013) predicted lower sediment yield values than global relationships. This is not unexpected given the antiquity of the Australian landscape (i.e. it is flat and slowly eroding under ‘natural’ conditions). Using the relationships developed by Tomkins (2013), potential major dams for water supply in the Victoria catchment were estimated to have about 2% or less sediment infilling after 30 years and less than 7% sediment infilling after 100 years. Exploration of two potential dam sites in the Victoria catchment Two potential dam sites on different rivers are summarised here. These sites are described because they are among the most cost-effective sites in close proximity to relatively large continuous areas of land suitable for irrigated agriculture in the Victoria catchment. More detailed descriptions of the six sites selected for pre-feasibility assessment are provided in the companion technical report on surface water storage (Yang et al., 2024). Potential dam on Leichhardt Creek AMTD 26 km for water supply This potential dam site is 15 km upstream of a floodplain above the junction with the West Baines River. An advantage of this potential dam site over other sites in the Victoria catchment is its proximity to the Victoria Highway and the regional service centre Kununurra. Access to the potential dam would partly be along an 85 km road constructed for the potential dam branching from Highway 1 east of the West Baines River crossing. The total distance from the site to Kununurra would be some 375 km. Although data from the NT cultural heritage sites register were not made available to the Assessment, it is likely that the site and parts of the potential inundation area would contain cultural heritage sites of significance. Given the potential for significant flooding during construction and the spillway capacity required, an RCC gravity dam could have a 70 m wide central uncontrolled spillway. The FSL is nominally at an elevation of 122 mEGM96 (Earth Gravitational Model 1996), (i.e. approximately 45 m above the river bed). A 50 m wide hydraulic jump-type spillway basin would be provided to protect the river bed against erosion during spillway overflows. Releases downstream of the dam would be made through pipework installed in a diversion conduit located in the right abutment of the dam. A fish- lift transfer facility would also be installed in the right abutment of the dam. Based on geological mapping and satellite imagery, the potential dam site is located on Proterozoic rocks of the Jasper Gorge Sandstone, which consists of medium quartz sandstone with minor siltstone. There appear to be gently dipping outcrops on both of the abutments. The river bed is approximately 30 m wide, with ponded water approximately 20 m wide. In the river bed are possible rock bars, and the alluvium appears to be shallow. The foundations appear to be suitable for an RCC dam and the estimated depth of alluvium is approximately 5 m. It is estimated that 5 m of stripping would be required on the dam abutments. The storage area appears stable and watertight. The floodplain downstream of the potential dam is dominated by red loamy soils (soil generic group (SGG) 4.1; see Section 2.3) and friable non-cracking clay loam to clay soils (SGG 2). These soils are suitable, with minor limitations (suitability Class 2, see Section 5.3.3), for dry-season, trickle-irrigated intensive horticulture such as cucurbits and dry-season, spray-irrigated root crops such as sweet potato (Ipomoea batatas) and peanut (Arachis hypogaea). The red loamy soils are also suitable, with minor limitations (Class 2), for spray-irrigated perennial grasses such as Rhodes grass (Chloris gayana) and pulse crops such as mungbean (Vigna radiata), soybean (Glycine max) and chickpea (Cicer arietinum). The friable non-cracking clay loam to clay soils are also suitable, with moderate limitations (Class 3), for spray-irrigated perennial grasses and pulse crops. Approximately 4% of the catchment upstream of this potential dam site (5372 ha) is modelled as having suitable habitat for at least 40% of the 11 mobile or migratory species modelled (Figure 5-21). Some of these species are also found in neighbouring streams. However, the modelledsuitable habitat for these water-dependent species upstream of the potential dam site is small; depending on the species, it ranges from zero % to 1.5% of its total modelled suitable habitat inthe Victoria catchment. The potential for ecological change as a result of changes to thedownstream flow regime is examined in Section 7.2. Modelled yield and cost versus dam FSL are shown in Figure 5-22. At a nominal FSL 122 mEGM96 (23 m above river bed), the reservoir of the dam would inundate 2024 ha at full supply and have a capacity of 193 GL (Figure 5-22). At this FSL the reservoir could yield 64 GL of water in 85% of years at the dam wall. A manual cost estimate undertaken as part of the Assessment for an RCC dam on Leichhardt Creek with FSL 122 mEGM96 found the dam would cost approximately $396 million. Setting an (environmental) transparent flow threshold of 20% or 40% of mean daily inflows (i.e. daily inflows up to 20% (or 40%) of mean daily flow are allowed to pass through the dam) reduces the yield of the reservoir to 61 or 59 GL in 85% of years, respectively. Water-dependent assets Leichhardt Creek dam site map \\FS1-CBR.nexus.csiro.au\{lw-rowra}\work\4_Water_storage\1_Victoria\1_GIS\1_Map_docs\WS527-V_Dam140_Ecology_v02_CR.mxd For more information on this figure please contact CSIRO on enquiries@csiro.au Figure 5-21 EPBC and NT listed species, water-dependent assets and aggregated modelled habitat in the vicinity of the potential dam site on Leichhardt Creek AMTD 26 km AMTD = adopted middle thread distance; FSL = full supply level. Under this hypothetical conceptual arrangement, water could be released from the storage into Leichhardt Creek where approximately 50 km downstream it could be impounded by a low concrete gravity weir of sufficient height (i.e. 0.75 m above river bed) to create submergence for pumping infrastructure. Water would then be pumped to an offstream storage of approximately 5 GL capacity. The offstream storage would form a buffer to releases from the dam and the actual irrigation demand. It is estimated that under this arrangement this potential dam could support an irrigated area of about 4000 ha, depending upon the cropping mix. The total cost of the reticulation infrastructure is estimated to be $12.67 million or $3168/ha (see companion technical report on irrigation scheme design and costs for the Victoria and Southern Gulf catchments (Devlin, 2024)). For more information on this figure please contact CSIRO on enquiries@csiro.au Figure 5-22 Potential dam site on Leichhardt Creek AMTD 26 km: cost and yield at the dam wall (a) Dam width and modelled dam cost versus full supply level (FSL), and (b) dam yield and yield/$ million at 75% and 85% annual time reliability. Modelled cost estimates will differ from more detailed manual cost estimates presented in Table 5-6. AMTD = adopted middle thread distance. Potential dam on Victoria River AMTD 283 km for flood mitigation In 2023, flooding in the upper Victoria River resulted in the relocation of community members from Kalkarindji and Nitjpurru (Pigeon Hole) to Darwin. These events were modelled to have an annual exceedance probability (AEP) of 1.7% and 1.1% at Kalkarindji and Nitjpurru (Pigeon Hole), respectively, noting the paucity of stream gauge data in the upper reaches of the Victoria catchment (see companion technical report on river model calibration in the Victoria catchment (Hughes et al., 2024a)). Based on only the observed record (1953 to 2023), this event had AEP of 2.6% at Coolibah Homestead streamflow gauge, which is downstream of Kalkarindji and Nitjpurru (Pigeon Hole). The potential Victoria River dam site is an instream development approximately 15 km upstream of Kalkarindji that was investigated for its potential to provide a flood mitigation benefit to Kalkarindji, Nitjpurru (Pigeon Hole) and other communities downstream. A flood mitigation dam at this site could also potentially provide a limited water supply to meet local needs at Kalkarindji (e.g. town water supply, market gardens). Access to the dam would be partly along a 5 km new road branching from the Buntine Highway 13 km south-west of Kalkarindji. The total distance from the site to Kununurra would be some 524 km. Alternatively, the distance to Katherine via Delamere would be 462 km. No site-specific evaluation of cultural heritage considerations was possible at this site, as pre- existing Indigenous cultural heritage site records were not made available to the Assessment. Land tenure and native title information were derived from regional land councils and the National Native Title Tribunal. There is a high likelihood of unrecorded sites of cultural significance in the inundation area. Based only on geological maps and satellite imagery, the dam site is located on Cambrian rocks of the Antrim Plateau Volcanics, which consist of basalts with some minor sediments. There appears to be some outcrop on the abutments, but the basalts are likely to be deeply weathered. In the river bed is a 250 m wide area of pooled water and gravel bars. The foundations may not be stiff enough for an RCC dam and are thought to be more suitable for a concrete-faced rockfill dam or an embankment dam, with a separate lined chute spillway on either abutment. The depth of alluvium in the river bed is estimated to be 5 to 10 m, and it is estimated that 5 to 10 m of stripping on the abutments would be required. Storage appears stable and watertight. Based on the anticipated foundation conditions, a concrete-faced rockfill embankment dam is assumed. Diversion of flows during construction would be through a tunnel constructed through the left abutment of the dam. Reinforced steel mesh protection on the downstream face of the embankment would be used as a protection against overtopping during construction. An uncontrolled, fully lined spillway channel would be excavated through the right abutment, with placement of the crest structure delayed until the embankment is raised to a safe height. The potential for a dam on the Victoria River AMTD 283 km to mitigate flooding at Kalkarindji is moderate and negligible at Nitjpurru (Pigeon Hole). Under this conceptual arrangement, the spillway is nominally at an elevation of 200 mEGM96 (i.e. approximately 23 m above the river bed), which would inundate an area of 4177 ha at full capacity (Figure 5-23). The dam could potentially store water to a level 10 m above bed level, with the storage to the spillway crest level serving as a temporary flood storage compartment. Under this configuration the reservoir could supply 17 GL of water in 85% of years. By way of context, if the potential dam were used for water supply purposes rather than for flood mitigation, the reservoir could yield 70 GL in 85% of years at the dam wall. "\\FS1-CBR.nexus.csiro.au\{lw-rowra}\work\4_Water_storage\1_Victoria\3_Plotting_scripts\1_output\figure2\short_listed_dam_122_Figure2.png" For more information on this figure please contact CSIRO on enquiries@csiro.au Figure 5-23 Potential dam site on Victoria River AMTD 283 km: cost and yield at the dam wall (a) Dam width and modelled roller compacted concrete dam cost versus full supply level (FSL), and (b) dam yield and yield/$ million at 75% and 85% annual time reliability. Modelled cost estimates will differ from more detailed manual cost estimates presented in Table 5-6. AMTD = adopted middle thread distance Approximately 20 km below the potential dam site, the Victoria River is deeply incised into a gently undulating basalt landscape. Moderately deep (0.5–1 m), slowly permeable neutral-to- alkaline cracking clay soils (SGG 9) with a high (100–250 mm) water-holding capacity (within 1 m of the surface) dominate the gently undulating plains. Soils have varying levels of surface and profile rock, limiting the extent suitable for agricultural development. Approximately 2% of the catchment upstream of the potential dam (8137 ha) is modelled as having suitable habitat for at least 40% of the 11 ‘mobile’ species modelled (Figure 5-24). The modelled suitable habitat for these water-dependent species upstream of the potential dam site is relatively small; depending on the species, it ranges from 0.04% to 6.8% of its total modelled suitable habitat in the Victoria catchment. The potential for ecological change as a result of changes to the downstream flow regime is examined in Section 7.2. Water-dependent assets Vic Riv dam site map \\FS1-CBR.nexus.csiro.au\{lw-rowra}\work\4_Water_storage\1_Victoria\1_GIS\1_Map_docs\WS526-V_Dam122_Ecology_v02_CR.mxd For more information on this figure please contact CSIRO on enquiries@csiro.au Figure 5-24 Listed species, water-dependent assets and aggregated modelled habitat in the vicinity of the potential dam site on the Victoria River AMTD 283 km AMTD = adopted middle thread distance; FSL = full supply level. 5.4.3 Weirs and re-regulating structures Re-regulating structures, such as weirs, are typically located downstream of large dams. They allow for more efficient releases from the storages and for some additional yield from the weir storage itself, thereby reducing the transmission losses normally involved in supplemented river systems. As a rule of thumb, weirs are constructed to one-half to two-thirds of the river bank height. This height allows the weirs to achieve maximum capacity, while ensuring the change in downstream hydraulic conditions does not result in excessive erosion of the toe of the structure. It also ensures that large flow events can still be passed without causing excessive flooding upstream. Broadly speaking, there are two types of weir structure: concrete gravity type weirs and sheet piling weirs. These are discussed below. For each type of weir, rock-filled mattresses are often used on the stream banks, extending downstream of the weir to protect erodible areas from flood erosion. A brief discussion on sand dams is also provided. Weirs, sand dams and diversion structures obstruct the movement of fish in a similar way to dams during the dry season. Concrete gravity type weirs Where rock bars are exposed at bed level across a stream, concrete gravity type weirs have been built on the rock at numerous locations across northern Queensland. This type of construction is less vulnerable to flood erosion damage both during construction and in service. Indicative costs are provided for a small weir structure with only sufficient height (e.g. 0.75 m above river bed) to submerge pumping infrastructure. Assuming exposed bedrock across the river bed, and rock for aggregates and mattresses, are available locally, the cost of a low reinforced concrete slab with upstand (i.e. 0.75 m above river bed, nominally 150 m width along crest) for the purpose of providing pump station submergence is estimated to cost about $13 million. Nominal allowances were made for site access, services and construction camp costs on the basis that more substantial site establishment costs would be incurred by the nearby irrigation development. Sheet piling weirs Where rock foundations are not available, stepped steel sheet piling weirs have been successfully used in many locations across Queensland. No sheet piling weirs have been constructed in the NT. These weirs consist of parallel rows of steel sheet piling, generally about 6 m apart, with a step of about 1.5 to 1.8 m high between each row. Reinforced concrete slabs placed between each row of piling absorb much of the energy as flood flows cascade over each step. The upstream row of piling is the longest, driven to a sufficient depth to cut off the flow of water through the most permeable material (Figure 5-25). Indicative costs are provided in Table 5-8. It should be noted, however, that in recent years Queensland Department of Agriculture and Fisheries have not approved stepped weirs in Queensland on the basis that the steps result in fish mortalities. Sheet piling weirs would therefore have to have a sloping face with a more extensive dissipator at bed level. For more information on this figure please contact CSIRO on enquiries@csiro.au Figure 5-25 Schematic cross-section diagram of sheet piling weir FSL = full supply level. Source: Petheram et al. (2013) Table 5-8 Estimated construction cost of 3 m high sheet piling weir Cost indexed to 2023. For more information on this table please contact CSIRO on enquiries@csiro.au Sand dams Because many of the large rivers in northern Australia are very wide (e.g. >300 m), weirs are likely to be impractical and expensive at many locations. Alternative structures are sand dams, which are low embankments built of sand on the river bed. They are constructed at the start of each dry season during periods of low or no flow when heavy earth-moving machinery can access the bed of the river. They are constructed to form a pool of depth sufficient to enable pumping (i.e. typically greater than 4 m depth) and are widely used in the Burdekin River near Ayr in Queensland, where the river is too wide to construct a weir. Typically, sand dams take three to four large excavators about 2 to 3 weeks to construct, and no further maintenance is required until they need to be reconstructed again after the wet season. Bulldozers can construct a sand dam more quickly than can a team of excavators but have greater access difficulties. Because sand dams only need to form a pool of sufficient size and depth from which to pump water, they usually only partially span a river and are typically constructed immediately downstream of large, naturally formed waterholes. The cost of 12 weeks of hire for a 20 t excavator and float (i.e. transportation) is approximately $100,000. Although sand dams are cheap to construct relative to a weir, they require annual rebuilding and have very high seepage losses beneath and through the dam wall. No studies are known to have quantified losses from sand dams. The application of sand dams in the Victoria catchment is likely to be limited. 5.4.4 Large farm-scale ringtanks Large farm-scale ringtanks are usually fully enclosed circular earthfill embankment structures constructed close to major watercourses/rivers to minimise the cost of pumping infrastructure by ensuring long ‘water harvesting’ windows. For this reason, they are often subject to reasonably frequent inundation, usually by slow-moving flood waters. In some exceptions embankments may not be circular; rather, they may be used to enhance the storage potential of natural features in the landscape such as horseshoe lagoons or cut-off meanders adjacent to a river (see Section 5.4.6 for discussion on extracting water from persistent waterholes). An advantage of ringtanks over gully dams is that the catchment area of the former is usually limited to the land that it impounds, so costs associated with spillways, failure impact assessments and constructing embankments to withstand flood surges are considerably less than those for large farm-scale gully dams. Another advantage of ringtanks is that unless a diversion structure is utilised in a watercourse to help ‘harvest’ water from a river, a ringtank and its pumping station do not impede the movement of aquatic species or transport of sediment in the river. Ringtanks have to be sited adjacent to major watercourses to ensure there are sufficient days available for pumping. While this limits where they can be sited, it means that because they can be sited adjacent to major watercourses (on which gully dams would be damaged during flooding – large farm-scale gully dams are typically sited in catchments of areas less than 40 km2), they often have a higher reliability of being filled each year than gully dams. However, operational costs of ringtanks are usually higher than those of gully dams because water must be pumped into the structure each year from an adjacent watercourse, typically using diesel-powered pumps. (Solar and wind energy do not generate sufficient power to operate high-volume axial flow or centrifugal pumps.) Even where diversion structures are utilised to minimise pumping costs, the annual cost of excavating sediment and debris accumulated in the diversion channel can be in the order of tens of thousands of dollars. For more information on ringtanks in the Victoria catchment, refer to the companion technical reports on surface water storage (Yang et al., 2024). river modelling simulation (Hughes et al., 2024b) and pump stations (Devlin, 2023). Also of relevance is the Northern Australia Water Resource Assessment technical report on large farm-scale dams (Benjamin, 2018). A rectangular ringtank in the catchment of the Flinders River (Queensland) is pictured in Figure 5-26. In this section, the following assessments of ringtanks in the Victoria catchment are reported: • suitability of land for large farm-scale ringtanks • reliability with which water can be extracted from different reaches • indicative evaporative and seepage losses from large farm-scale ringtanks • indicative capital, operation and maintenance costs of large farm-scale ringtanks. Figure 5-26 Rectangular ringtank and 500 ha of cotton in the Flinders catchment (Queensland) The channel along which water is diverted from the Flinders River to the ringtank can be seen in the background. Photo: CSIRO Suitability of land for ringtanks in the Victoria catchment Figure 5-27 displays the broad-scale suitability of land for large farm-scale ringtanks in the Victoria catchment. Approximately 8% of the Victoria catchment (488,000 ha) is classed as being potentially suitable. Several land types are likely to be suitable for ringtanks. These include the poorly drained coastal marine clay plains, the cracking clay soils on the alluvial plains of the Victoria River and tributaries, the Cenozoic clay plains of the upper catchment and the black and red Vertosols on the Cambrian basalts. Very poorly drained saline coastal marine clay plains The very poorly drained saline coastal marine plains subject to tidal inundation have very deep, strongly mottled, grey non-cracking and cracking clay soils with potential acid-sulfate deposits in the profile. They are likely to be suitable for ringtanks but are subject to storm surge from cyclones. Very deep alluvial clay plains The very deep (>1.5 m) alluvial clay plains of the Victoria and upper Baines rivers are predominantly impermeable, imperfectly drained to moderately well-drained grey and brown, hard-setting, cracking clay soils, frequently with small (<0.3 m) normal gilgai depressions. These soils on the Baines River alluvial plains grade to seasonally wet soils along the lower reaches of the river and may be subject to regular flooding. Soils are usually strongly sodic at depth. The clay soils of the middle Victoria River alluvial plains are frequently dissected by severe gully erosion adjacent to the stream channels. For more information on this figure please contact CSIRO on enquiries@csiro.au \\FS1-CBR.nexus.csiro.au\{lw-rowra}\work\4_Water_storage\1_Victoria\1_GIS\1_Map_docs\1_Exports\WS501-V-RingTank_Suitability_v4.png Figure 5-27 Suitability of land for large farm-scale ringtanks in the Victoria catchment Soil and subsurface data were only available to a depth of 1.5 m, hence the Assessment does not consider the suitability of subsurface material below this depth. This figure does not consider the availability of water. Data are overlaid on a shaded relief map. The results presented in this figure are only indicative of suitable locations for siting a ringtank; site-specific investigations by a suitably qualified professional should always be undertaken prior to ringtank construction. Cenozoic clay plains of the upper catchment The Cenozoic clay plains are dominated by strongly sodic, impermeable, imperfectly drained self- mulching, grey cracking clay soils grading to moderately well-drained grey-brown clay soils in the lower-rainfall southern parts of the catchment. This relict alluvium deposited over a diverse range of geologies frequently has shallow (0.1 to 0.2 m) normal to linear gilgai and surface gravels/stones of various lithology. It frequently occurs in drainage depressions, enabling collection and storage of overland flows. Black and red Vertosols on Cambrian basalts The moderately deep to deep (0.5 to <1.5 m), gilgaied, slowly permeable, non-sodic brown, black and red Vertosols on Cambrian basalts are predominantly gravelly/stony, with slopes greater than 2%, but small areas of ‘less rocky’ soils occasionally occur on level to very gently undulating plains (slopes <1%) and are likely to be suitable for ringtanks. These less rocky soils are moderately well- drained self-mulching, brown and black cracking clay soils in the north-eastern and far western parts of the catchment, grading to well-drained brown and red clay soils in the lower-rainfall southern part of the catchment. However, such areas are usually small and fragmented. Reliability of water extraction The reliability at which an allocation or volume of water can be extracted from a river depends upon a range of factors including the: • quantity of discharge and the natural inter- and intra-variability of a river system (Section 2.5.5) • capacity of the pumps or diversion structure (expressed here as the number of days taken to pump an allocation) • quantity of water being extracted by other users and their locations • conditions associated with a licence to extract water, such as: – a minimum threshold (i.e. water height level/discharge) at which pumping can commence (pump start threshold) – a ‘diversion commencement requirement’, which is the minimum flow that must pass a specified node in the river model before pumping can commence each water year (1 September to 31 August). In the Victoria catchment, this is the point at which the Victoria River discharges into the Joseph Bonaparte Gulf, referred to hereafter as the ‘end- of-system’. Licence conditions can be imposed on a potential water user to ensure downstream entitlement holders are not affected by new water extractions and to minimise environmental change that may arise from perturbations to streamflow. In some cases a pump start threshold may be a physical threshold below which it is difficult to pump water from a natural pumping pool, but it can also be a regulatory requirement imposed to minimise impacts to existing downstream users and mitigate changes to existing water-dependent ecosystems. The reliability of water extraction under different conditions and at different locations in the Victoria catchment is detailed in the companion technical report for river modelling (Hughes et al., 2024b). A selection of plots from that report are provided below to illustrate key concepts. Figure 5-28 can be used to explore the reliability of extracting (‘harvesting’) or diverting increasing volumes of water at five locations in the Victoria catchment under varying pump start thresholds. The left vertical axis (y1-axis) indicates the system target volume, which is the maximum volume of water extracted across the whole catchment each season (nominal catchment-wide entitlement volume). The right vertical axis (y2-axis) is the maximum volume of water extracted in that reach each season (nominal reach entitlement volume). This example assumes a 30-day pump capacity, that is, the system and reach target volumes (i.e. nominal entitlement volume) that can be pumped in 30 days (not necessarily consecutive). This means an irrigator with a 3 GL ringtank would need a pump capacity of 100 ML/day to fill their ringtank in 30 days. In this example there is no end-of-system flow requirement. The impacts of pump start thresholds and end-of-system flow requirements on extraction reliability are explored because these environmental flow provisions are among the least complex to regulate and ensure compliance in very remote areas. Although more-targeted environmental flow provisions may be possible, these are inevitably more complicated for irrigators to adhere to (usually requiring many dozens of pump operations during the course of a single season) and more difficult for regulators to ensure compliance. Within each river reach, water could be harvested by one or more hypothetical water harvesters and the water nominally stored in ringtanks adjacent to the river reach. The locations of the hypothetical extractions are illustrated in the map in the bottom right corners of Figure 5-28 to Figure 5-34. Their relative proportions of the total system allocation (left vertical axis) were assigned based on joint consideration of area of crop versatility, broad-scale flooding, ringtank suitability and river discharge (see companion technical report on river modelling (Hughes et al., 2024b)). At the smallest pump start threshold examined, 200 ML/day (nominally representative of a lower physical pumping limit), more than 800 GL of water can be extracted in the Victoria catchment in 75% of years. However, insufficient soil is suitable for irrigated agriculture in close proximity (~5 km) to the rivers to fully use this volume of water for irrigated agriculture. The hashed shading (diagonal white lines) in Figure 5-28 indicates where the system target volumes are in excess of that required to irrigate the area of land suitable for irrigated agriculture (assuming 10 ML is required to be extracted per hectare). This figure shows that, as the total system and reach targets increase, the extraction reliability for the full system and reach targets decreases. Similarly, as the pump start threshold increases, the extraction reliability for the full system and reach targets decreases. "\\fs1-cbr.nexus.csiro.au\{lw-rowra}\work\2_Hydrology\101_Victoria\5_River_model\4_sim_cal3\8_water_harvest\5_plots\5_catchReportPlots\plot1_thresh_v_alloc_0eos_rate30days_v2.png" Figure 5-28 Annual reliability of diverting annual system and reach target volumes for varying pump start thresholds No end-of-system flow requirement before pumping can commence. Cross-shading indicates volumes of water for which there is insufficient soil suitable for irrigated agriculture in close proximity to the river. Eight-digit numbers refer to model node locations. For more detail see companion technical report on river modelling (Hughes et al., 2024b). The data presented in Figure 5-30 and Figure 5-31 are similar to those presented in Figure 5-28, but in Figure 5-30 and Figure 5-31 an additional extraction condition is imposed: 500 GL (Figure 5-30) and 700 GL (Figure 5-31), respectively, have to flow past the end of the system (node 81100000) each wet season before any water can be extracted. These figures show that increasing the end-of-system flow requirement reduces the extraction reliability for the system and reach targets. Figure 5-32 and Figure 5-33 show how median (50% exceedance) annual streamflow and 80% exceedance annual streamflow vary under different levels of extraction and different end-of- system flow requirements. These plots show median annual flow is sensitive to irrigation target and insensitive to end-of-system requirements (Figure 5-32). However, 80% exceedance annual flows are sensitive to both irrigation target volumes and end-of-system requirements (Figure 5-33) illustrating that end-of-system requirements have some utility in ‘preserving’ flow in drier years. Figure 5-34 shows the relationship between the reliability of achieving system and reach target volumes and pump capacity, expressed in days to pump target. With a pump start threshold of 1000 ML/day and an annual end-of-system flow requirement of 500 GL, large pump capacities (i.e. 10 days or less) are required to extract the system and reach targets in 75% of years or greater. For more information on this figure please contact CSIRO on enquiries@csiro.au Figure 5-29 Victoria River has the second largest median annual streamflow of any river in the NT Photo: CSIRO – Nathan Dyer "\\fs1-cbr.nexus.csiro.au\{lw-rowra}\work\2_Hydrology\101_Victoria\5_River_model\4_sim_cal3\8_water_harvest\5_plots\5_catchReportPlots\plot3_thresh_v_alloc_500eos_rate30days_v2.png" Figure 5-30 Annual reliability of diverting annual system and reach target volumes for varying pump start thresholds assuming end-of-system flow requirement before pumping can commence is 500 GL Assumes pumping capacity of 30 days (i.e. system and reach targets can be pumped in 30 days). Diagonal white lines indicates volumes of water for which there is insufficient soil suitable for irrigated agriculture in close proximity to the river. Eight-digit numbers refer to model node locations. For more detail see companion technical report on river modelling (Hughes et al., 2024b). "\\fs1-cbr.nexus.csiro.au\{lw-rowra}\work\2_Hydrology\101_Victoria\5_River_model\4_sim_cal3\8_water_harvest\5_plots\5_catchReportPlots\plot4_thresh_v_alloc_700eos_rate30days_v2.png" Figure 5-31 Annual reliability of diverting annual system and reach target volumes for varying pump start thresholds assuming end-of-system flow requirement before pumping can commence is 700 GL Assumes pumping capacity of 30 days (i.e. system and reach targets can be pumped in 30 days). Diagonal white lines indicates volumes of water for which there is insufficient soil suitable for irrigated agriculture in close proximity to the river. Eight-digit numbers refer to model node locations. For more detail see companion technical report on river modelling (Hughes et al., 2024b). "\\fs1-cbr.nexus.csiro.au\{lw-rowra}\work\2_Hydrology\101_Victoria\5_River_model\4_sim_cal3\8_water_harvest\5_plots\5_catchReportPlots\catchRep_50annual_residiual_flow_v4.png" Figure 5-32 50% annual exceedance (median) streamflow relative to Scenario A in the Victoria catchment for varying end-of-system (EOS) requirements assuming a pump start threshold of 1000 ML/day and a pump capacity of 30 days Diagonal white lines indicates volumes of water for which there is insufficient soil suitable for irrigated agriculture in close proximity to the river. Eight-digit numbers refer to model node locations. For more detail see companion technical report on river modelling (Hughes et al., 2024b). "\\fs1-cbr.nexus.csiro.au\{lw-rowra}\work\2_Hydrology\101_Victoria\5_River_model\4_sim_cal3\8_water_harvest\5_plots\5_catchReportPlots\catchRep_80annual_residual_flow_v3.png" Figure 5-33 80% annual exceedance streamflow relative to Scenario A in the Victoria catchment for varying end-of- system (EOS) requirements assuming a pump start threshold of 1000 ML/day and a pump capacity of 30 days Diagonal white lines indicates volumes of water for which there is insufficient soil suitable for irrigated agriculture in close proximity to the river. Eight-digit numbers refer to model node locations. For more detail see companion technical report on river modelling (Hughes et al., 2024b). "\\fs1-cbr.nexus.csiro.au\{lw-rowra}\work\2_Hydrology\101_Victoria\5_River_model\4_sim_cal3\8_water_harvest\5_plots\5_catchReportPlots\plot2_pumpRate_v_alloc_500eos_1000MLthresh.png" Figure 5-34 Annual reliability of diverting annual system and reach targets for varying pump rates assuming a pump start flow threshold of 1000 ML/day End-of-system flow requirement before pumping can commence is 500 GL. Diagonal white lines indicates volumes of water for which there is insufficient soil suitable for irrigated agriculture in close proximity to the river. Eight-digit numbers refer to model node locations. For more detail see companion technical report on river modelling (Hughes et al., 2024b). Evaporation and seepage losses Losses from a farm-scale dam occur through seepage and evaporation. A study of 138 farm dams ranging in capacity from 75 to 14,000 ML from southern NSW to central Queensland by the Cotton Catchment Communities CRC (2011) found mean seepage and evaporation rates of 2.3 and 4.2 mm/day, respectively. Of the 138 dams examined, 88% had seepage values of less than 4 mm/day and 64% had seepage values of less than 2 mm/day. These results largely concur with those of the Irrigation Association of Australia (IAA, 2007), which states that reservoirs will have seepage losses equal to or less than 1 to 2 mm/day if constructed on suitable soils and greater than 5 mm/day if sited on less suitable (i.e. permeable) soils. When calculating evaporative losses from farm dams it is important to calculate net evaporation (evaporation minus rainfall) rather than just evaporation. Ringtanks with greater mean water depths lose a lower percentage of their total storage capacity to evaporation and seepage; however, they have a smaller ratio of storage capacity to excavation. In Table 5-9, effective volume refers to the actual volume of water that could be used for consumptive purposes after losses due to evaporation and seepage. For example, if water is stored in a ringtank with mean water depth of 3.5 m from April until January and the mean seepage loss is 2 mm/day, more than half the stored volume (56%) would be lost to evaporation and seepage. The example provided in Table 5-9 is for a 4000 ML storage but the effective volume expressed as a percentage of the ringtank capacity is applicable to any storage (e.g. ringtanks or gully dams) of any capacity for mean water depths of 3.5, 6.0 and 8.5 m. Table 5-9 Effective volume after net evaporation and seepage for hypothetical ringtanks of three mean water depths, under three seepage rates, near the Victoria River Downs in the Victoria catchment Effective volume refers to the actual volume of water that could be used for consumptive purposes as a result of losses due to net evaporation and seepage, assuming the storage capacity is 4000 ML. For storages of 4000 ML capacity and mean water depths of 3.5, 6.0 and 8.5 m, reservoir surface areas are 110, 65 and 45 ha, respectively. Effective volumes are calculated based on the 20% exceedance net evaporation. For more detail see companion technical report on surface water storage (Yang et al., 2024). S:E ratio = storage capacity to excavation ratio. MEAN WATER DEPTH† (m) S:E RATIO SEEPAGE LOSS (mm/day) EFFECTIVE VOLUME (ML) EFFECTIVE VOLUME AS PERCENTAGE OF CAPACITY (%) EFFECTIVE VOLUME (ML) EFFECTIVE VOLUME AS PERCENTAGE OF CAPACITY (%) EFFECTIVE VOLUME (ML) EFFECTIVE VOLUME AS PERCENTAGE OF CAPACITY (%) 5 months (April to August) 7 months (April to October) 10 months (April to January) 3.5 14:1 1 2923 73 2393 60 1777 44 14:1 2 2756 69 2159 54 1441 36 14:1 5 2254 56 1456 36 435 11 6 7.5:1 1 3359 84 3044 76 2676 67 7.5:1 2 3260 82 2906 73 2478 62 7.5:1 5 2964 74 2490 62 1883 47 8.5 5:1 1 3554 89 3335 83 3079 77 5:1 2 3486 87 3239 81 2941 74 5:1 5 3281 82 2952 74 2530 63 †Mean water depth above ground surface. Strategies to minimise evaporation include liquid and solid barriers, but these are typically expensive per unit of inundated area (e.g. $12 to $40 per m2). In non-laboratory settings, liquid barriers such as oils are susceptible to being dispersed by wind and have not been shown to reduce evaporation from a water body (Barnes, 2008). Solid barriers can be effective in reducing evaporation but are expensive, at approximately two to four times the cost of constructing a ringtank. Evaporation losses from a ringtank can also be reduced slightly by subdividing the storage into multiple cells and extracting water from each cell in turn to minimise the total surface water area. However, constructing a ringtank with multiple cells requires more earthworks and incurs higher construction costs than outlined in this section. Capital, operation and maintenance costs of ringtanks Construction costs of a ringtank may vary considerably, depending on its size and the way the storage is built. For example, circular storages have a higher ratio of storage volume to excavation cost than rectangular or square storages. As discussed in the section on large farm-scale gully dams (Section 5.4.5), it is also considerably more expensive to double the height of an embankment wall than double its length due to the low angle of the walls of the embankment (often at a 3:1 ratio, horizontal to vertical). Table 5-10 provides a high-level breakdown of the capital and operation and maintenance (O&M) costs of a large farm-scale ringtank, including the cost of the water storage, pumping infrastructure, up to 100 m of pipes, and O&M costs of the scheme. In this example it is assumed that the ringtank is within 100 m of the river and pumping infrastructure. The cost of pumping infrastructure and conveying water from the river to the storage is particularly site specific. In flood-prone areas where flood waters move at moderate to high velocities, riprap (rocky material) protection may be required, and this may increase the construction costs presented in Table 5-10 and Table 5-11 by 10% to 20% depending upon the volume of rock required and proximity to a quarry with suitable rock. For a more detailed breakdown of ringtank costs and pumping infrastructure costs see the Northern Australia Water Resource Assessment technical report on large farm-scale dams (Benjamin, 2018) and the Victoria and Southern Gulf Water Resource Assessment technical report on pumping infrastructure (Devlin, 2023). Table 5-10 Indicative costs for a 4000 ML ringtank Assumes a 4.25 m wall height, 0.75 m freeboard, 3:1 ratio on upstream slope, 3:1 ratio on downstream slope and crest width of 3.1 m, approximately 60% of material can be excavated from within storage, and costs of earthfill and compacted clay are $5.40/m3 and $7/m3, respectively. Earthworks costs include vegetation clearing, mobilisation/demobilisation of machinery and contractor accommodation. Costs indexed to 2023. Pump station operation and maintenance (O&M) costs assume cost of diesel of $1.49/L. SITE DESCRIPTION/ CONFIGURATION EARTHWORKS COSTS ($) GOVERNMENT PERMITS AND FEES ($) INVESTIGATION AND DESIGN FEES ($) PUMP STATION ($) TOTAL CAPITAL COST ($) O&M COSTS OF RINGTANK ($/y) O&M COSTS OF PUMP STATION ($/y) TOTAL O&M COSTS ($/y) 4000 ML ringtank 2,000,000 43,000 92,000 380,000 2,515,000 21,000 92,000 113,000 The capital costs can be expressed over the service life of the infrastructure (assuming a 7% discount rate) and combined with O&M costs to give an equivalent annual cost for construction and operation. This enables infrastructure with differing capital and O&M costs and service lives to be compared. The total equivalent annual costs for the construction and operation of a 1000 ML ringtank with 4.25 m high embankments and 55 ML/day pumping infrastructure is about $143,600 (Table 5-11). For a 4000 ML ringtank with 4.25 m high embankments and 160 ML/day pumping infrastructure, the total equivalent annual cost is about $301,550. For a 4000 ML ringtank with 6.75 m high embankments and 160 ML/day pumping infrastructure, the total equivalent annual cost is about $457,600. Table 5-11 Annualised cost for the construction and operation of three ringtank configurations Assumes freeboard of 0.75 m, pumping infrastructure can fill ringtank in 25 days and assumes a 7% discount rate. Costs based on those provided for 4000 ML provided in Northern Australia Water Resource Assessment technical report on large farm-scale dams (Benjamin, 2018). Costs indexed to 2023. Pump station operation and maintenance (O&M) costs assume cost of diesel of $1.49/L. CAPACITY AND EMBANKMENT HEIGHT ITEM CAPITAL COST ($) LIFE SPAN (y) ANNUALISED CAPITAL COST ($) ANNUAL O&M COST ($) 1000 ML and 4.25 m Ringtank 1,075,000 40 80,480 10,700 Pumping infrastructure† 245,000 15 26,900 4,500 Pumping cost (diesel) NA NA NA 21,000 4000 ML and 4.25 m Ringtank 2,000,000 40 150,000 17,250 Pumping infrastructure† 380,000 15 41,700 7,600 Pumping cost (diesel) NA NA NA 85,000 4000 ML and 6.75 m Ringtank 3,863,000 40 290,000 33,300 Pumping infrastructure† 380,000 15 41,700 7,600 Pumping cost (diesel) NA NA NA 85,000 NA = data not available. †Costs include short rising main, large-diameter concrete or multiple strings of high-density polypipe, control valves and fittings, concrete thrust blocks and headwalls, dissipator, civil works and installation. Although ringtanks with an mean water depth of 3.5 m (embankment height of 4.25 m) lose a higher percentage of their capacity to evaporation and seepage than ringtanks of equivalent capacity with mean water depth of 6 m (embankment height of 6.75 m) (Table 5-9); their annualised unit costs are lower (Table 5-12) due to the considerably lower cost of constructing embankments with lower walls (Table 5-11). In Table 5-12 the levelised cost (equivalent annual cost per unit of water) supplied from the ringtank takes into consideration net evaporation and seepage from the storage, which increase with the length of time water is stored (i.e. crops with longer growing seasons will require water to be stored longer). In this table, the results are presented for the equivalent annual cost of water yield from a ringtank of different seepage rates and lengths of time for storing water. Table 5-12 Levelised costs for two hypothetical ringtanks of different capacities under three seepage rates near Victoria River Downs in the Victoria catchment Assumes a 0.75 m freeboard, 3:1 ratio on upstream slope, 3:1 ratio on downstream slope. Crest widths are 3.1 and 3.6 m for embankments with heights of 4.25 and 6.75 m, respectively, and assuming earthfill and compacted clay costs of $5/m3 and $6.50/m3, respectively. Earthwork costs include vegetation clearing, mobilisation/demobilisation of machinery and contractor accommodation. 1000 ML ringtank reservoir has surface area of 27 ha and storage volume to excavation ratio of about 7:1. 4000 ML ringtank and 4.25 m embankment height reservoir has surface area of 110 ha and storage volume to excavation ratio of about 14:1. 4000 ML ringtank with 6.75 m embankment height reservoir has surface area of 64 ha and storage volume to excavation ratio of about 7.5:1. Annualised cost indexed to 2023 and assumes a 7% discount rate. For more information on this table please contact CSIRO on enquiries@csiro.au 5.4.5 Large farm-scale gully dams Large farm-scale gully dams are generally constructed of earth, or earth and rockfill embankments with compacted clay cores, and usually to a maximum height of about 20 m. Dams with a crest height of over 10 or 12 m typically require some form of downstream batter drainage incorporated into embankments. Large farm-scale gully dams typically have a maximum catchment area of about 40 km2 due to the challenges in passing peak floods from large catchments (large farm-scale gully dams are generally designed to pass an event with an annual exceedance probability of 1%), unless a site has an exceptionally good spillway option. Like ringtanks, large farm-scale gully dams are a compromise between best-practice engineering and affordability. Designers need to follow accepted engineering principles relating to important aspects of materials classification, compaction of the clay core and selection of an appropriate embankment cross-section. However, costs are often minimised where possible; for example, by employing earth bywashes and grass protection for erosion control rather than more expensive concrete spillways and rock protection as found on major dams. This can compromise the integrity of the structure during extreme events and the longevity of the structure, as well as increase the ongoing maintenance costs, but can considerably reduce the upfront capital costs. In this section the following assessments are reported: •suitability of the land for large farm-scale gully dams •indicative capital and O&M costs of large farm-scale gully dams. Net evaporation and seepage losses also occur from large farm-scale gully dams. The analysis presented in Section 5.4.4 is also applicable to gully dams. Suitability of land for large farm-scale gully dams Figure 5-36 indicates those locations where it is more topographically and hydrologically favourable to construct large farm-scale gully dams in the Victoria catchment and the likely density of options. This analysis considers those sites likely to have more favourable topography. It does not explicitly consider those sites that are underlain by soil suitable for the construction of the embankment and to minimise seepage from the reservoir base. This is shown in Figure 5-37. In reality, dams can be constructed on eroded or skeletal soils provided there is access to a clay borrow pit nearby for the cut-off trench and core zone. However, these sites are likely to be less economically viable. These figures indicate that those parts of the Victoria catchment that are more topographically suitable as large-scale gully dam sites generally do not coincide with areas with soils that are moderately suitable for irrigated agriculture. Furthermore, in many areas topographically suitable for gully dams, dam walls would need to be constructed from rockfill, cement and imported clay soils, increasing the cost of their construction. Figure 5-35 Julius Dam on the Leichhardt River Photo: CSIRO Most economical gully dam map \\FS1-CBR.nexus.csiro.au\{lw-rowra}\work\4_Water_storage\1_Victoria\1_GIS\1_Map_docs\WS560-V_GullyDam_Damsite_Land_Versatile_V3_CR.mxd For more information on this figure please contact CSIRO on enquiries@csiro.au Figure 5-36 Most economically suitable locations for large farm-scale gully dams in the Victoria catchment Gully dam data overlaid on agricultural versatility data (see Section 4.2.3). Agricultural versatility data indicate those parts of the catchment that are more or less versatile for irrigated agriculture. For the gully dam analysis, soil and subsurface data were only available to a depth of 1.5 m, hence this Assessment does not consider the suitability of subsurface material below this depth. Sites with catchment areas greater than 40 km2 or yield to excavation ratio less than 10 are not displayed. The results presented in this figure are modelled and consequently only indicative of the general locations where siting a gully dam may be most economically suitable. This analysis may be subject to errors in the underlying digital elevation model, such as effects due to the vegetation removal process. An important factor not considered in this analysis was the availability of a natural spillway. Site-specific investigations by a suitably qualified professional should always be undertaken prior to dam construction. Most economical gully dam soil suit map \\FS1-CBR.nexus.csiro.au\{lw-rowra}\work\4_Water_storage\1_Victoria\1_GIS\1_Map_docs\WS561-V_GullyDam_Suitability_Damsite_V4_CR.mxd For more information on this figure please contact CSIRO on enquiries@csiro.au Figure 5-37 Suitability of soils for construction of gully dams in the Victoria catchment Capital, operation and maintenance costs of large farm-scale gully dams The cost of a large farm-scale gully dam will vary depending upon a range of factors, including the suitability of the topography of the site, the size of the catchment area, quantity of runoff, proximity of site to good quality clay, availability of durable rock in the upper bank for a spillway and the size of the embankment. The height of the embankment, in particular, has a strong influence on cost. An earth dam to a height of 8 m is about 3.3 times more expensive to construct than a 4 m high dam, and a dam to a height of 16 m will require 3.6 times more material than the 8 m high dam, but the cost may be more than 5 times greater, due to design and construction complexity. As an example of the variability in unit costs of gully dams, actual costs for four large farm-scale gully dams in northern Queensland are presented in Table 5-13. Table 5-13 Actual costs of four gully dams in northern Queensland Sourced from Northern Australia Water Resource Assessment technical report on farm-scale design and costs (Benjamin, 2018). Costs indexed to 2023. DAM NAME LOCATION CAPACITY (ML) YIELD (ML/y) COST ($) UNIT COST ($/ML) COMMENTS Sharp Rock Dam Lakelands 3300 1070 400,700 374 Chimney filter and drainage under- blanket. Two-stage concrete sill spillway. No fishway. Pump station not included Dump Gully Dam Lakelands 1450 420 975,600 2,323 Deep and wet cut-off. Chimney filter and downstream under drainage. No fishway. Pump station was $91,000 Spring Dam #2 Lakelands 2540 1377 1,111,600 807 Chimney filter and drainage under- blanket. Two-stage rock excavation. Spillway with fishway. Fishway was $36,500. Pump station not included Ronny’s Dam Georgetown 9975 1700 555,900 327 Very favourable site. Low embankment and 450 ha ponded area. Natural spillway. No pump station, gravity supply by pipe Performance and cost of three hypothetical farm-scale gully dams in northern Australia A summary of the key parameters for three hypothetical 4 GL (4000 ML) capacity farm-scale gully dam configurations is provided in Table 5-14 and a high-level breakdown of the major components of the capital costs for each of the three configurations is provided in Table 5-15. Detailed costs for the three hypothetical sites are provided in the Northern Australia Water Resource Assessment technical report on large farm-scale dams (Benjamin, 2018). Table 5-14 Cost of three hypothetical large farm-scale gully dams of capacity 4 GL Costs include government permits and fees, investigation and design, and fish passage. For a complete list of costs and assumptions see the Northern Australia Water Resource Assessment technical report on farm-scale dams (Benjamin, 2018). Costs indexed to 2023. O&M = operation and maintenance; S:E ratio = storage capacity to excavation ratio. SITE DESCRIPTION/ CONFIGURATION CATCH- MENT AREA (km2) EMBANK- MENT HEIGHT (m) EMBANK- MENT LENGTH (m) S:E RATIO MEAN DEPTH (m) RESERVOIR SURFACE AREA (ha) TOTAL CAPITAL COST ($) O&M COST ($) Favourable site with large catchment, suitable topography and simple spillway (e.g. natural saddle) 30 9.5 1100 29:1 5.0 80 1,600,000 70,000 Less favourable site with small catchment, challenging topography and limited spillway options (e.g. steep gully banks, no natural saddle) 15 14 750 21:1 6.3 63 1,844,000 44,000 Less favourable site with moderate catchment, challenging topography and limited spillway options (e.g. steep gully banks, no natural saddle) 20 14 750 21:1 6.3 63 1,937,000 50,000 Table 5-15 High-level breakdown of capital costs for three hypothetical large farm-scale gully dams of capacity 4 GL Earthworks include vegetation clearing, mobilisation/demobilisation of equipment and contractor accommodation. Investigation and design fees include design and investigation of fish passage device and failure impact assessment (i.e. investigation of possible existence of population at risk downstream of site). Costs indexed to 2023. SITE DESCRIPTION/CONFIGURATION EARTHWORKS COST ($) GOVERNMENT PERMITS AND FEES ($) INVESTIGATION AND DESIGN FEES ($) TOTAL CAPITAL COST ($) Favourable site with large catchment, suitable topography and simple spillway (e.g. natural saddle) 1,447,000 46,000 107,000 1,600,000 Less favourable site with small catchment, challenging topography and limited spillway options (e.g. steep gully banks, no natural saddle) 1,677,000 50,000 117,000 1,844,000 Less favourable site with moderate catchment, challenging topography and limited spillway options (e.g. steep gully banks, no natural saddle) 1770,000 50,000 117,000 1,937,000 Table 5-16 presents calculations of the effective volume for three configurations of 4 GL capacity gully dams (varying mean water depth/embankment height) for combinations of three seepage losses and water storage capacities over three time periods in the Victoria catchment. Table 5-16 Effective volumes and cost per megalitre for three 4 GL gully dams with various mean depths and seepage loss rates based on climate data at Victoria River Downs Station in the Victoria catchment Time periods of 4, 6 and 9 months refer to length of time water is stored or required for irrigation. MEAN DEPTH AND MAXIMUM RESERVOIR SURFACE AREA CONSTRUC- TION COST ($) COST ($/ML) SEEPAGE LOSS (mm/d) EFFECTIVE VOLUME (ML) EFFECTIVE VOLUME AS PERCENT- AGE OF CAPACITY (%) EFFECTIVE VOLUME (ML) EFFECTIVE VOLUME AS PERCENT- AGE OF CAPACITY (%) EFFECTIVE VOLUME (ML) EFFECTIVE VOLUME AS PERCENT- AGE OF CAPACITY (%) 5 months (April to August) 7 months (April to October) 10 months (April to January) 3 m and 133 ha 1,250,000 250 1 3087 77 2639 66 2113 53 1,250,000 250 2 2946 74 2441 61 1830 46 1,250,000 250 5 2522 63 1847 46 979 24 6 m and 66 ha 1,900,000 375 1 3545 89 3321 83 3057 76 1,900,000 375 2 3475 87 3223 81 2917 73 1,900,000 375 5 3265 82 2929 73 2496 62 9 m and 44 ha 2,500,000 500 1 3692 92 3540 88 3361 84 2,500,000 500 2 3644 91 3474 87 3266 82 2,500,000 500 5 3503 88 3276 82 2983 75 Based on the information presented in Table 5-14, an equivalent annual unit cost including annual O&M cost for a 4 GL gully dam with a mean depth of about 6 m is about $220,000 (Table 5-17 and Table 5-18). Table 5-17 Cost of construction and operation of three hypothetical 4 GL gully dams Assumes operation and maintenance (O&M) cost of 3% of capital cost and a 7% discount rate. Figures have been rounded. Costs indexed to 2023. MEAN DEPTH AND MAXIMUM RESERVOIR SURFACE AREA ITEM CAPITAL COST ($) ANNUALISED CAPITAL COST ($) ANNUAL O&M COST ($) EQUIVALENT ANNUAL COST ($/y) 3 m and 133 ha Low embankment, wide gully dam 1,250,000 107,000 37,500 144,800 6 m and 66 ha Moderate embankment, gully dam 1,900,000 163,000 57,000 220,000 9 m and 44 ha High embankment, narrow gully dam 2,500,000 214,500 75,000 290,000 Table 5-18 Equivalent annualised cost and effective volume for three hypothetical 4 GL gully dams with various mean depths and seepage loss rates based on climate data at Victoria River Downs Station in the Victoria catchment Dam details are in Table 5-17. Annual cost assumes a 7% discount rate. Time periods of 4, 6 and 9 months refer to length of time water is stored or required for irrigation. MEAN DEPTH AND MAXIMUM RESERVOIR SURFACE AREA EQUIVALENT ANNUAL COST ($/y) SEEPAGE LOSS (mm/d) UNIT COST ($/ML) LEVELISED COST ($/ML) UNIT COST ($/ML) LEVELISED COST ($/ML) UNIT COST ($/ML) LEVELISED COST ($/ML) 5 months (April to August) 7 months (April to October) 10 months (April to January) 3 m and 133 ha 144,800 1 405 47 474 55 592 69 144,800 2 424 49 512 59 683 79 144,800 5 496 57 677 78 1277 148 6 m and 66 ha 220,000 1 536 62 572 66 622 72 220,000 2 547 63 590 68 651 75 220,000 5 582 67 649 75 761 88 9 m and 44 ha 290,000 1 677 78 706 82 744 86 290,000 2 686 79 720 83 765 89 290,000 5 714 83 763 88 838 97 Where the topography is suitable for large farm-scale gully dams and a natural spillway is present, large farm-scale gully dams are typically cheaper to construct than a ringtank of equivalent capacity. 5.4.6 Natural water bodies Wetland systems and waterholes that persist throughout the dry season are natural water bodies characteristic of large parts of the northerly draining catchments of northern Australia. Many property homesteads in northern Australia use natural waterholes for stock and domestic purposes. However, the quantities of water required for stock and domestic supply are orders of magnitude less than those required for irrigated cropping, and it is partly for this reason that naturally occurring persistent water bodies in northern Australia are not used to source water for irrigation. For example, a moderately sized (5 ha) rectangular water body of mean depth 3.5 m may contain about 175 ML of water. Based on the data presented in Table 5-9 and assuming minimal leakage (i.e. 1 mm/day), approximately 74%, 61% and 50% of the volume would be available if a crop were to be irrigated until August, October and January, respectively. Assuming a crop or fodder with a 6-month growing season requires 5 ML/ha of water before losses, and assuming an overall efficiency of 80% (i.e. the waterhole is adjacent to land suitable for irrigation, 95% conveyance efficiency and 85% field application efficiency), a 175 ML waterhole could potentially be used to irrigate about 20 ha of land for half a year if all the water was able to be used for this purpose. A large natural water body of 20 ha and mean depth of 3.5 m could potentially be used to irrigate about 80 ha of land if all the water was able to be used for this purpose. Although the areas of land that could be watered using natural water bodies are likely to be small, the costs associated with storing water are minimal. Consequently, where these waterholes occur at sufficient size and adjacent to land suitable for irrigated agriculture, they can be a very cost- effective source of water. It would appear that where natural water bodies of sufficient size and suitable land for irrigation coincide, natural water bodies may be effective in staging a development (Section 6.3), where several hectares could potentially be developed, enabling lessons learned and mistakes made on a small-scale area before more significant capital investments are undertaken (noting that staging and learning are best to occur over multiple scales). In a few instances it may be possible to enhance the storage potential of natural features in the landscape such as horseshoe lagoons or cut-off meanders adjacent to a river. The main limitation to the use of wetlands and persistent waterholes for the consumptive use of water is that they have considerable ecological significance (e.g. Kingsford, 2000; Waltham et al., 2013), and in many cases there is a limited quantity of water contained within the water bodies. In particular, water bodies that persist throughout the dry season are considered key ecological refugia (Waltham et al., 2013). For a water body situated in a sandy river, a waterhole is likely to be connected to water within the bedsands of the river. Hence, during and following pumping water within the bedsands of a river, the bedsands may in part replenish the waterhole and vice versa. While water within the bedsands of the river may in part replenish a depleted waterhole, in these circumstances it also means that pumping from a waterhole will have a wider environmental impact than just on the waterhole from which water is being pumped. 5.5 Water distribution systems – conveyance of water from storage to crop 5.5.1 Introduction In all irrigation systems, water needs to be conveyed from the water source through artificial and/or natural water distribution systems before ultimately being used on-field for irrigation. This section discusses water losses during conveyance and application of water to a crop, and the associated costs. Costs of reticulation infrastructure are highly site specific. Examples for two locations in the Victoria catchment are provided in the companion technical report on irrigation scheme design and costs (Devlin, 2024). 5.5.2 Conveyance and application efficiencies Some water diverted for irrigation is lost during conveyance to the field before it can be used by a crop. These losses need to be taken into account when planning irrigation systems and developing likely irrigated areas. The amount of water lost during conveyance depends on the: • river conveyance efficiency, from the water storage to the re-regulating structure or point of extraction • channel distribution efficiency, from the river offtake to the farm gate • on-farm distribution efficiency, in storing (using balancing storages) and conveying water from the farm gate to the field • field application efficiency, in delivering water from the edge of the field and applying it to the crop. The overall or system efficiency is the product of these four components. Little research on irrigation systems has been undertaken in the Victoria catchment. The time frame of the Assessment did not permit on-ground research into irrigation systems. Consequently, a brief discussion on the components listed above is provided based on relevant literature from elsewhere in Australia and overseas. Table 5-19 summarises the broad range of efficiencies associated with these components. The total conveyance and application efficiency of the delivery of water from the water storage to the crop (i.e. the overall or system efficiency) depends on the product of the four components in Table 5-19. For example, if an irrigation development has a river conveyance efficiency of 80%, a channel distribution efficiency of 90%, an on-farm distribution efficiency of 90% and a field application efficiency of 85%, the overall efficiency is 55% (80% × 90% × 90% × 85%). This means only 55% of all water released from the dam can be used by the crop. Table 5-19 Summary of conveyance and application efficiencies For more information on this table please contact CSIRO on enquiries@csiro.au †River conveyance efficiency varies with a range of factors (including distance) and may be lower than the range quoted here. Under such circumstances, it is unlikely that irrigation would proceed. It is also possible for efficiency to be 100% in gaining rivers. Achieving higher efficiencies requires a re-regulating structure (Section 5.4.3). River conveyance efficiency The conveyance efficiency of rivers is difficult to measure and even more difficult to predict. Although there are many methods for estimating groundwater discharge to surface water, there are few suitable methods for estimating the loss of surface water to groundwater. In the absence of existing studies for northern Australia, conveyance efficiencies as nominated in water resource plans and resource operation plans for four irrigation water supply schemes in Queensland were examined collectively. The results are summarised in Table 5-20. The conveyance efficiencies in Table 5-20 are from the water storage to the farm gate and are nominated efficiencies based on experience delivering water in these supply schemes. These data can be used to estimate conveyance efficiency of similar rivers elsewhere. Table 5-20 Water distribution and operational efficiency as nominated in water resource plans for four irrigation water supply schemes in Queensland For more information on this table please contact CSIRO on enquiries@csiro.au †Ignores differences in efficiency between high- and medium-priority users and variations across the scheme zone areas. ‡Channel conveyance efficiency only. Channel distribution efficiency Across Australia, the mean water conveyance efficiency from the river to the farm gate has been estimated to be 71% (Marsden Jacob Associates, 2003). For heavier-textured soils and well- designed irrigation distribution systems, conveyance efficiencies are likely to be higher. In the absence of larger scheme-scale irrigation systems in the Victoria catchment, it is useful to look at the conveyance efficiency of existing irrigation developments to estimate the conveyance efficiency of irrigation developments in the study area. Australian conveyance efficiencies are generally higher than those found in similarly sized overseas irrigation schemes (Bos and Nugteren, 1990; Cotton Catchment Communities CRC, 2011). The most extensive review of conveyance efficiency in Australia was undertaken by the Australian National Commission on Irrigation and Drainage, which tabulated system efficiencies across irrigation developments in Australia (ANCID, 2001). Conveyance losses were reported as the difference between the volume of water supplied to irrigation customers and the water delivered to the irrigation system. For example, if 10,000 ML of water was diverted to an irrigation district and 8000 ML was delivered to irrigators, then the conveyance efficiency was 80% and the conveyance losses were 20%. Figure 5-38 shows reported conveyance losses across irrigation areas of Australia between 1999 and 2000, along with the supply method used for conveying irrigation water and associated irrigation deliveries. There is a wide spread of conveyance losses both between years and across the various irrigation schemes. Factors identified by Marsden Jacob Associates (2003) that affect the variation include delivery infrastructure, soil types, distance that water is conveyed, type of agriculture, operating practices, infrastructure age, maintenance standards, operating systems, in- line storage, type of metering used, and third-party impacts such as recreational, amenity and environmental demands. Differences across irrigation seasons are due to variations in water availability, operational methods, climate and customer demands. For more information on this figure please contact CSIRO on enquiries@csiro.au 0% 15% 30% 45% 60% 0100,000200,000300,000400,000500,000600,000700,000800,000Losses 1999 to 2000 (percent) Irrigation deliveries 1999 to 2000 (ML) NSWQldSATasVicWA Figure 5-38 Reported conveyance losses from irrigation systems across Australia The shape of the marker indicates the supply method for the irrigation scheme: square (▪) indicates natural carrier, circle (•) indicates pipe and diamond (♦) indicates channel. The colour of the marker indicates the location of the irrigation system (by state), as shown in the legend. Source: ANCID (2001) Based on these industry data, Marsden Jacob Associates (2003) concluded that, on average, 29% of water diverted into irrigation schemes is lost in conveyance to the farm gate. However, some of this ‘perceived’ conveyance loss may be due to meter underestimation (about 5% of water delivered to provider (Marsden Jacob Associates, 2003)). Other losses were from leakage, seepage, evaporation, outfalls, unrecorded usage and system filling. On-farm distribution efficiency On-farm losses are losses that occur between the farm gate and delivery to the field. These losses usually take the form of evaporation and seepage from on-farm storages and delivery systems. Even in irrigation developments where water is delivered to the farm gate via a channel, many farms have small on-farm storages (i.e. less than 250 ML for a 500 ha farm). These on-farm storages enable the farmer to have a reliable supply of irrigation water with a higher flow rate, and also enable recycling of tailwater. Several studies have been undertaken in Australia for on- farm distribution losses. Meyer (2005) estimated an on-farm distribution efficiency of 78% in the Murray and Murrumbidgee regions, while Pratt Water (2004) estimated on-farm efficiencies to be 94% and 88% in the Coleambally Irrigation and Murrumbidgee Irrigation areas, respectively. For nine farms in these two irrigation areas, however, Akbar et al. (2000) measured channel seepage to be less than 5%. Field application efficiency After water is delivered to a field, it needs to be applied to the crop using an irrigation system. The application efficiency of irrigation systems typically varies between 60% and 90%, with more expensive systems usually resulting in higher efficiency. Three types of irrigation system can potentially be applied in the Victoria catchment: surface irrigation, spray irrigation and micro irrigation (Figure 5-39). Irrigation systems applied in the Victoria catchment need to be tailored to the soil, climate and crops that may be grown in the catchment and matched to the availability of water for irrigation. This is taken into consideration in the land suitability assessment figures presented in Section 4.2. System design will also need to consider investment risk in irrigation systems as well as likely returns, degree of automation, labour availability and O&M costs (e.g. the cost of energy). Irrigation systems have a trade-off between efficiency and cost. Table 5-21 summarises the different types of irrigation systems, including their application efficiency, indicative cost and limitations. Across Australia the ratio of areas irrigated using surface, spray and micro irrigation is 83:10:7, respectively. Irrigation systems that allow water to be applied with greater control, such as micro irrigation, cost more (Table 5-21) and as a result are typically used for irrigating higher- value crops such as perennial horticulture and vegetables. For example, although only 7% of Australia’s irrigated area uses micro irrigation, it generates about 40% of the total value of produce grown using irrigation (Meyer, 2005). Further details on the three types of irrigation systems follow Table 5-21. (a) (b) (c) Figure 5-39 Efficiency of different types of irrigation system (a) For bankless channel surface irrigation systems, application efficiencies range from 60% to 85%. (b) For spray irrigation systems, application efficiencies range from 75% to 90%. (c) For pressurised micro irrigation systems on polymer-covered beds, application efficiencies range from 80% to 90%. Photos: CSIRO Table 5-21 Application efficiencies for surface, spray and micro irrigation systems Application efficiency is the efficiency with which water can be delivered from the edge of the field to the crop. Costs indexed to 2023. For more information on this table please contact CSIRO on enquiries@csiro.au Adapted from Hoffman et al. (2007), Raine and Bakker (1996) and Wood et al. (2007). †Sources: DEEDI (2011a, 2011b, 2011c). Surface irrigation systems Surface irrigation encompasses basin, border strip and furrow irrigation, as well as variations such as bankless channel systems. In surface irrigation, water is applied directly to the soil surface, with check structures (banks or furrows) used to direct water across a field. Control of applied water is dictated by the soil properties, soil uniformity and the design characteristics of the surface system. Generally, fields are prepared by laser levelling to increase the uniformity of applied water and allow ease of management of water and adequate surface drainage from the field. The uniformity and efficiency of surface systems are highly dependent on the system design and soil properties, timing of the irrigation water and the skill of the individual irrigator in operating the system. Mismanagement can severely degrade system performance and lead to systems that operate at poor efficiencies. Surface irrigation has the benefit that it can generally be adapted to almost any crop and usually has a lower capital cost compared with alternative systems. Surface irrigation systems perform better when soils are of uniform texture as infiltration characteristics of the soil play an important part in the efficiency of these systems. Therefore, surface irrigation systems should be designed into homogenous soil management units and layouts (run lengths, basin sizes) tailored to match soil characteristics and water supply volumes. High application efficiencies are possible with surface irrigation systems, provided soil characteristic limitations, system layout, water flow volumes and high levels of management are applied. On ideal soil types and with systems capable of high flow rates, efficiencies can be greater than 85%. On poorly designed and managed systems on soil types with high variability, efficiencies can be less than 60%. Generally, the major cost in setting up a surface irrigation system is land grading and levelling, with costs directly associated with the volume of soil that must be moved. Typical earth-moving volumes are in the order of 800 m3/ha but can exceed 2500 m3/ha. Volumes greater than 1500 m3/ha are generally considered excessive due to costs (Hoffman et al., 2007). Surface irrigation systems are the dominant form of irrigation type used throughout the world. Their potential suitability in the Victoria catchment would be due to their generally lower set-up costs and adaptability to a wide range of irrigated cropping activities. They are particularly suited to the heavier-textured soils on the alluvial soils adjacent to the Victoria River and its major tributaries, which reduce set-up or establishment costs of these systems. With surface irrigation, little or no energy is required to distribute water throughout the field, and this ‘gravity-fed’ approach reduces energy requirements of these systems. Surface irrigation systems generally have lower applied irrigation water efficiency than spray or micro systems when compared across an industry and offer less control of applied water; however, well-designed and well-managed systems can approach efficiencies of alternative irrigation systems in ideal conditions. Spray irrigation systems In the context of the Victoria catchment, spray irrigation refers specifically to lateral move and centre pivot irrigation systems. Centre pivot systems consist of a single sprinkler, laterally supported by a series of towers. The towers are self-propelled and rotate around a central pivot point, forming an irrigation circle. Time taken for the pivot to complete a full circle can range from as little as half a day to several days depending on crop water demands and application rate of the system. Lateral or linear move systems are similar to centre pivot systems in construction but, rather than move around a pivot point, the entire line moves down a field perpendicular to the lateral direction. Water is supplied by a lateral channel running the length of the field. Lateral lengths are generally in the range of 800 to 1000 m. Their advantage over surface irrigation systems is they can be utilised on rolling topography and generally require less land forming. Both centre pivot and lateral move irrigation systems have been extensively used for irrigating a range of annual broadacre crops and are capable of irrigating most field crops. They are generally not suitable for tree crops or vine crops, or for saline irrigation water applications in arid environments, which can cause foliage damage. Centre pivot and lateral move systems usually have higher capital costs but are capable of very high efficiencies of water application. Generally, application efficiencies for these systems range from 75% to 90% (Table 5-21). They are used extensively for broadacre irrigated cropping situations in high evaporative environments in northern NSW and South West Queensland. These irrigation developments have high irrigation crop water demand requirements, which are similar to those found in the Victoria catchment. A key factor in the suitable use of spray systems is sourcing the energy needed to operate these systems, which are usually powered by electricity or diesel depending on available costs and infrastructure. Where available, electricity is considerably cheaper than diesel for powering spray systems. For pressurised systems such as spray or micro irrigation systems, water can be more easily controlled, and potential benefits of the system through fertigation (application of crop nutrients through the irrigation system (i.e. liquid fertiliser)) are also available to the irrigator. Micro irrigation systems For high-value crops, such as horticultural crops where yield and quality parameters dictate profitability, micro irrigation systems should be considered suitable across the range of soil types and climate conditions in the Victoria catchment. Micro irrigation systems use thin-walled polyethylene pipe to apply water to the root zone of plants through small emitters spaced along the drip tube or micro sprinklers. These systems are capable of precisely applying water to the plant root zone, thereby maintaining a high level of irrigation control and applied irrigation water efficiency. Historically, micro irrigation systems have been extensively used in tree, vine and row crops, with limited applications in complete-cover crops such as grains and pastures due to the expense of these systems. Micro irrigation is suitable for most soil types and can be practised on steep slopes. Micro irrigation systems are generally of two varieties: above-ground and below-ground (where the drip tape is buried beneath the soil surface). Below-ground micro irrigation systems offer advantages in reducing evaporative losses and improving trafficability. However, below-ground systems are more expensive and require higher levels of expertise to manage. Properly designed and operated micro irrigation systems are capable of very high application efficiencies, with field efficiencies of 80% to 90% (Table 5-21). In some situations, micro irrigation systems offer water and labour savings and improved crop quality (i.e. more marketable fruit through better water control). Management of micro irrigation systems, however, is critical. To achieve these benefits requires a much greater level of expertise than for other traditional systems such as surface irrigation systems, which generally have higher margins of error associated with irrigation decisions. Micro irrigation systems also have high energy requirements, with most systems operating at pressure ranges from 135 to 400 kPa, with diesel or electric pumps most often used. 5.6 References Akbar S, Beecher HG, Cullis B and Dunn B (2000) Using of EM surveys to identify seepage sites in on-farm channel and drains. Proceedings of the Irrigation Australia 2000 Conference, Australia. ANCID (2001) Australian irrigation water provider benchmarking report for 1999/2000. An ANCID initiative funded by Land and Water Australia and Department of Agriculture, Fisheries and Forestry−Australia, Australia. AWA (2018) Desalinisation factsheet. Australia Water Association. Viewed 10 April 2018, http://www.awa.asn.au/AWA_MBRR/Publications/Fact_Sheets/Desalination_Fact_Sheet.aspx. Barber M, Fisher K, Wissing K, Braedon P and Pert P (2024) Indigenous water values, rights, interests and development goals in the Victoria catchment. 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In: Horton AJ and Jobling GA (eds) Farm Water Supplies Section, Irrigation Branch, Queensland Water Resources Commission. Raine SR and Bakker DM (1996) Increased furrow irrigation efficiency through better design and management of cane fields. Proceedings Australian Society of Sugar Cane Technologists 1996, 119–124. Robins JB, Halliday IA, Staunton-Smith J, Mayer DG and Sellin MJ (2005) Freshwater-flow requirements of estuarine fisheries in tropical Australia: a review of the state of knowledge and application of a suggested approach. Marine and Freshwater Research 56, 343–360. Ross A and Hasnain S (2018) Factors affecting the cost of managed aquifer recharge (MAR) schemes. Sustainable Water Resources Management. DOI: 10.1007/s40899-017-0210-8. Scarborough VL and Gallopin G (1991) A water storage adaptation in the Maya Lowlands. Science 251(4), 658–662. DOI:10.1126/science.251.4994.658. Schnitter NJ (1994) A history of dams: the useful pyramids. AA Balkema, Rotterdam, Brookfield. 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A technical report from the CSIRO Victoria River Water Resource Assessment for the National Water Grid. CSIRO, Australia. Tickell SJ and Rajaratnam LR (1995) Water resources survey of the western Victoria River District, Legune Station. Report 31/1995D, Power and Water Authority, Water Resources Division. Tomkins K (2013) Estimated sediment infilling rates for dams in northern Australia based on a review of previous literature. A technical report to the Australian Government from the CSIRO Flinders and Gilbert Agricultural Resource Assessment, part of the North Queensland Irrigated Agriculture Strategy. CSIRO Water for a Healthy Country and Sustainable Agriculture flagships, Australia. Vanderzalm JL, Page DW, Gonzalez D, Barry KE, Dillon PJ, Taylor AR, Dawes WR, Cui T and Knapton A (2018) Assessment of managed aquifer recharge (MAR) opportunities in the Fitzroy, Darwin and Mitchell catchments. 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Wood M, Wang Q and Bethune M (2007) An economic analysis of conversion from border-check to centre-pivot irrigation on dairy farms in the Murray dairy region. Irrigation Science 26(1), 9–20. Yang A, Petheram C, Marvanek S, Baynes F, Rogers L, Ponce Reyes R, Zund P, Seo L, Hughes J, Gibbs M, Wilson PR, Philip S and Barber M (2024) Assessment of surface water storage options in the Victoria and Southern Gulf catchments. A technical report from the CSIRO Victoria River and Southern Gulf Water Resource Assessments for the National Water Grid. CSIRO Australia. Part IV Economics of development and accompanying risks Chapters 6 and 7 describe economic opportunities for water development in the Victoria catchment, and the associated constraints and risks: • economic opportunities and constraints (Chapter 6) • a range of risks to development (Chapter 7). Young cattle being finished on feed before sale at the Victoria River Research Station. Photo: CSIRO – Nathan Dyer 6 Overview of economic opportunities and constraints in the Victoria catchment Authors: Chris Stokes, Shokhrukh Jalilov, Diane Jarvis Chapter 6 examines the types of opportunities for the development of irrigated agriculture in the catchment of the Victoria River that are most likely to be financially viable. The chapter considers the costs of building the required infrastructure (both within the scheme and beyond), the financial viability of various types of schemes (including lessons learned from past large dam developments in Australia), and the regional economic impacts (the direct and flow-on effects for businesses across the catchment) (Figure 6-1). The chapter focuses on costs and benefits that are the subject of normal market transactions, but it does not provide a full economic analysis. Commercial factors are likely to be among the most important criteria in deciding between potential development opportunities. Options clearly identifiable at the pre-feasibility stage as not being commercially viable could be deprioritised. More-detailed and Assessment-specific agronomic, ecological, social, cultural and regulatory assessments could then focus on those opportunities identified as showing the most commercial promise. The non-market impacts and risks associated with any financially viable development opportunities, discussed in Chapter 7, must also be considered. Figure 6-1 Schematic diagram of key components affecting the commercial viability of a potential greenfield irrigation development "\\fs1-cbr.nexus.csiro.au\{lw-rowra}\work\10_Reporting\1_All\9_Graphics_artist\3_Vic and SoG\C Bruce Vic CR Chp6_8_2024.jpg" 6.1 Summary 6.1.1 Key findings Scheme-scale financial viability New investment in irrigation development in the Victoria catchment would depend on finding viable combinations of low-cost water sources, low-cost farming development opportunities, and high-productivity farms; finding opportunities for reducing cropping costs and attracting price premiums for produce; and managing a wide range of risks. Financial analyses have indicated that large dams in the Victoria catchment are unlikely to be viable if public investors target full cost recovery at a 7% internal rate of return (IRR) and do not provide assistance, which would make water from the most cost-effective dam sites too expensive for irrigators. However, large dams could be marginally viable if public investors accepted a 3% IRR. On-farm water sources provide better prospects than large dams: where sufficiently cheap water development opportunities can be found, they could support viable broadacre farms and horticulture with low development costs. Horticulture with high development costs (e.g. fruit orchards) in the Victoria catchment would be more challenging unless farm financial performance could be boosted by (i) finding niche opportunities for premium produce prices, (ii) making savings in production and marketing costs, and/or (iii) obtaining high yields. Farm performance can be affected by a number of risks, including water reliability, climate variability, price fluctuations, and the need to adapt farming practices to new locations. Setbacks that occur soon after an irrigation scheme has been established have the largest effect on scheme viability. There is a strong incentive for choosing well-proven crops and technologies when starting any new irrigation development, and for being thoroughly prepared for those agronomic risks of establishing new farmland that can be anticipated. Risks that cannot be avoided must be managed, mitigated where possible, and accounted for when determining the realistic returns that may be expected from a scheme and the capital buffers that would be required. Cost–benefit analysis of large public dams A review of recent large public dams built in Australia has highlighted some areas where cost– benefit analyses (CBAs) for water infrastructure projects could be improved upon, particularly the need for more-realistic forecasting of the demand for water. This chapter provides information for benchmarking a number of the processes commonly used in such CBAs, including demand forecasting. These processes can then act as a check when proposals for new dams are being unrealistically optimistic (or pessimistic). Regional economic impacts Any new irrigated agriculture development and its supporting infrastructure will have knock-on benefits to the regional economy beyond direct economic growth from the new farms and construction. The initial construction phase of a new irrigation development in the Victoria catchment could provide an additional (approximately) $1.1 million of indirect regional benefits, over and above the direct benefits, for each million dollars spent on construction within the local region. The ongoing production phase of a new irrigation development could provide an additional (approximately) $0.46 to $1.82 million of indirect regional benefits for each million dollars of direct benefits from the increased agricultural activity (gross revenue), depending on the type of agricultural industry. The indirect regional benefits would be reduced if some of the extra expenditure generated by a new development was leaked to outside the catchment. Each $100 million increase in agricultural activity could create approximately 100 to 852 jobs. 6.2 Introduction Large new infrastructure projects in Australia are expected to be increasingly more accountable and transparent. This trend extends to the planning and building of new water infrastructure, and the way water resources are managed and priced (e.g. Infrastructure Australia, 2021a, 2021b; NWGA, 2022, 2023), and includes greater scrutiny of the costs and benefits of potential large new public dams. The difficulty in accurately estimating costs and the chance of incurring unanticipated expenses during construction, or of not meeting the projected water demands or achieving revenue trajectories when completed, put the viability of developments at risk if they are not thoroughly planned and assessed. For example, in a global review of dam-based megaprojects, Ansar et al. (2014) found that the forecast costs were systematically biased downwards, with three-quarters of projects running over budget and the mean of the actual costs being almost double the initial estimates. This is typical for most types of large infrastructure projects, not just dams (see review in Section 6.4.1). Ultimately, economic factors are likely to be among the most important criteria in deciding the scale and types of potential development opportunities in the Victoria catchment. An assessment of 13 agricultural developments in northern Australia found that, while the natural environments were challenging for agriculture, the most important factors determining the viability of developments were management, planning and finances (Ash et al., 2014). At the pre-feasibility stage, options that can be clearly identified as not being financially viable could be deprioritised. The expensive, more-detailed and project-specific agronomic, ecological, social, cultural and regulatory assessments could then focus on the more promising opportunities. This chapter aims to assist future planning and evaluation of investments in new irrigated agriculture developments by highlighting the types of projects that are more likely to be viable, and quantifying the costs, benefits and risks involved. It provides a generic information resource that is broadly applicable to a variety of irrigated agriculture development opportunities but does not examine any specific options in detail. The results are presented in a way that allows readers to identify the costs, risks, and farm productivity values specific to the project opportunities in which they are interested, to evaluate their likely financial viability. The information also provides a set of benchmarks for establishing realistic assumptions and the thresholds of financial performance required for water and farm developments, individually and in combination, to be financially viable. This chapter builds on earlier material in Chapter 4 (assessing the viability of new irrigated agriculture opportunities in the Victoria catchment at the enterprise level) and in Chapter 5 (assessing the opportunities for developing water sources to support those farms). Section 6.3 provides information, within a financial analysis framework, for determining whether those farming options and water sources can be paired into viable developments. It presents the financial criteria that would have to be met for new farms to be able to cover the development costs. Section 6.3 highlights some key considerations for evaluating the costs and benefits of new publicly funded dams, including lessons learned from recent large dam projects in Australia. Section 6.4 also provides indicative costs for some of the additional enabling infrastructure required (typically additional to the costs included in project CBAs). Finally, Section 6.5 explores the knock-on effects of any new irrigated development in the Victoria catchment, quantifying the regional economic impacts using regional input–output (I–O) analysis. Rather than analysing the cost–benefit of specific irrigation scheme proposals, this chapter presents generic tables for evaluating multiple alternative development configurations, providing the threshold farm gross margins and water costs and pricing that would be required in order to cover infrastructure costs. These tables serve as tools that allow users to answer their own questions about agricultural land and water development. Examples of the questions that can be asked, and which tables provide the answers, are given in Table 6-1. Table 6-1 Types of questions that users can answer using the tools in this chapter For each question, the relevant table number is given, together with an example answer for a specific development scenario. More questions can be answered with each tool by swapping around the factors that are known and the factor being estimated. (All initial estimates assume farm performance is 100% in all years, i.e. before accounting for risks. See Table 6-3 for the supporting generalised assumptions.) QUESTION (WITH EXAMPLE ANSWER) RELEVANT TABLE 1) How much can various types of farms afford to pay per ML of water they use? Table 6-4 A broadacre farm with a gross margin (GM) of $4000/ha and water consumption of 8 ML/ha could afford to pay $135/ML while achieving a 10% internal rate of return (IRR). 2) How much would the operator of a large off-farm dam have to charge for water? Table 6-6 If off-farm water infrastructure had a capital cost of $5000 for each ML/y supply capacity (yield) at the dam wall, the (public) water supplier would have to charge $537 for each ML to cover its costs (at a 7% target IRR). 3) For an on-farm dam with a known development cost, what is the equivalent $/ML price of water? Table 6-8 If a farm dam had a capital development cost of $1500 for each ML/y supply capacity (yield), water could be purchasable at a cost of $190 for each ML (at a 10% target IRR). 4) (a) What farm GM would be required to fully cover the costs of an off-farm dam? (b) What proportion of the costs of off-farm water infrastructure could farms cover? Table 6-5 If off-farm infrastructure had a capital cost of $50,000/ha to build, broadacre farms would need to generate a GM of $5701/ha in order to fully cover the water supplier costs (while meeting a target 7% IRR for the water supplier (public investor) and a 10% IRR for the irrigator (private investor)). With the same target IRRs, a broadacre farm with a GM of $4000/ha could contribute the equivalent of $20,000 to $30,000 per ha towards the capital costs of building the same $50,000/ha dam (~50% of the full costs of building and operating that infrastructure). 5) What GM would be required in order to cover the costs of developing a new farm, including a dam orbores? Table 6-7 A horticultural farm with low overheads ($1500/ha) that cost $40,000/ha to develop (e.g. $30,000/ha to establish the farm and $10,000/ha to build the on-farm water supply for irrigating it) would require a GM of $6702/ha to attain a 10% IRR. 6) How would risks associated with water reliability affect the farm GMs above? Table 6-9 If an on-farm dam could fully irrigate the farm in 70% of years and could irrigate 50% of the farm in the remaining years, all farm GMs in the answers above would need to be multiplied by 1.18 (i.e. would be 18% higher), and the price irrigators could afford to pay for water would need to be divided by 1.18. For example, in Q4, the GM required in order to cover the costs of the farm development would increase from $5825/ha to $6874/ha after accounting for the risks of water reliability. QUESTION (WITH EXAMPLE ANSWER) RELEVANT TABLE 7) How would the risks associated with ‘learning’ (initial farm underperformance) affect estimates? Table 6-11 If a farm with a 10% target IRR achieved a GM that was 50% of its full potential in the first year, and gradually improved to achieve its full potential over 10 years, then the GMs above would need to be multiplied by a factor of 1.26 (i.e. would be 26% higher). For example, in Q6, the required farm GM would increase to $8661/ha after accounting for the risks of both water reliability and learning (a combined 49% higher than the value before accounting for risks). 6.3 Balancing scheme-scale costs and benefits Designing a new irrigation development in the Victoria catchment would require balancing three key determinants of irrigation scheme financial performance to find combinations that might collectively constitute a viable investment. The determinants are: • farm financial performance (relative to development costs and water use) (Chapter 4) • capital cost of development, for both water resources and farms (Chapter 5 and Section 6.3.1) • risks (and the associated required level of investment return) (Section 6.3.5). The determinants considered have been limited to those with greater certainty and/or lower sensitivity, so that the results can be applied to a wide range of potential developments. A key finding of the irrigation scheme financial analyses is that no single factor within the above list is likely to be able to provide a silver bullet for meeting the substantial challenge of designing a commercially viable new irrigation scheme. Balancing the benefits to meet costs in order to identify viable investments would likely require contributions from each of the above factors and careful selection to piece together a workable combination. This section provides background information on the analysis approach used, to help readers understand how these factors influence irrigation scheme financial performance. 6.3.1 Approach and terminology Scheme financial evaluations use a discounted cashflow framework to evaluate the commercial viability of irrigation developments. The framework, detailed in the companion technical report on agricultural viability and socio-economics (Webster et al., 2024), is intended to provide a purely financial evaluation of the conditions required to produce an acceptable return from an investor’s perspective. It is not a full economic evaluation of the costs and benefits to other industries, nor does it consider ‘unpriced’ impacts that are not the subject of normal market transactions, or the equity of how costs and benefits are distributed. For the discussion that follows, the costs and benefits of an irrigation scheme were taken to include all those from the development of the land and water resources to the point of sale for farm produce. This section explains the terminology and standard assumptions used. A ‘discounted cashflow analysis’ considers the lifetime of costs and benefits following capital investment in a new project. Costs and benefits that occur at various times are expressed in constant real dollars (December 2023 Australian dollars), with a discount rate being applied to streams of costs and benefits. The ‘discount rate’ is the percentage by which future costs and benefits are discounted each year (compounded) to convert them to their equivalent present value. For an entire project, the ‘net present value’ (NPV) can be calculated by subtracting the present value of the stream of all costs from the present value of the stream of all benefits. The ‘benefit to cost ratio’ (BCR) of a project is the present value of all the benefits of a project divided by the present value of all the costs involved in achieving those benefits. To be commercially viable (at the nominated discount rate), a project would require an NPV that is greater than zero (in which case the BCR would be greater than one). The IRR is the discount rate at which the NPV is zero (and the BCR is one). For a project to be considered commercially viable, it needs to meet its target IRR, and the NPV has to be greater than zero at a discount rate appropriate to the risk profile of the development and alternative investment opportunities available to investors. A target IRR of 7% is typically used when evaluating large public investments (with the sensitivity analysis set at 3% and 10%) (Infrastructure Australia, 2021b). Private agricultural developers usually target an IRR of 10% or more (to compensate for the investment risks involved). A back-calculation approach is used in the tables below to present the threshold GMs and water prices that would be required in order for investors to achieve specified target IRRs (the NPV would be equivalent to zero at these discount rates). The ‘project evaluation periods’ used in this chapter matched the ‘life spans’ of the main infrastructure assets: 100 years for large off-farm dams and 40 years for on-farm developments. To simplify the tracking of asset replacements, four categories of life spans were used: 15 and 40 years for farms and 25 and 100 years for off-farm infrastructure. It was assumed that the shorter-life-span assets would be replaced at the end of their life, and that costs would have been accounted for in full by the actual year of their replacement. At the end of the evaluation period, a ‘residual value’ was calculated to account for any shorter-life-span assets that have not reached the end of their working life. Residual values were calculated as the proportional asset life remaining multiplied by the original asset price. The ‘capital costs’ of infrastructure were assumed to be the costs at completion (accounted for in full in the year of delivery), such that the assets commenced operations the following year. In some cases, the costs of developing the farmland and setting up the buildings and equipment were considered separately from the costs of the water source, so that various water source options could be compared on a like-for-like basis. Where an off-farm water source was used, the separate investor in that water source would receive payments for water at a price that the irrigator could afford to pay. The main ‘costs for operating’ a large dam and the associated water distribution infrastructure are (i) fixed costs for administering and maintaining the infrastructure, expressed here as percentage of the original capital cost, and (ii) variable costs associated with pumping water into distribution channels. At the farm scale, fixed overhead costs are incurred each year, whether or not a crop is planted in a particular field that year. ‘Fixed costs’ are dominated by the fixed component of labour costs, but also include maintenance, insurance, professional services, and registrations. An additional allowance is made for annual operation and maintenance (O&M), budgeted at 1% of the original capital value of all assets (with an additional variable component in maintenance costs when machinery is used for cropping operations). A ‘farm annual gross margin’ (GM) is the difference between the gross income from crop sales and variable costs of growing a crop each year. ‘Net farm revenue’ is calculated by subtracting the fixed overhead costs from the GM. ‘Variable costs’ vary in proportion to the area of land planted, the amount of crop harvested and/or the amount of water and other inputs applied. Farm GMs can vary substantially within and between locations, as described in Chapter 4. The GMs presented here are the values obtained before subtracting the variable costs of supplying water to farms; these water supply costs are, instead, accounted for in the capital costs of developing water resources. (The equivalent unit costs of supplying each ML of water are presented separately below.) The CBA analyses first considered the case of irrigation schemes built around public investment in a large off-farm dam in the Victoria catchment and then considered the case developments using on-farm dams and bores. Cost and benefit streams, totalled across the scheme, were tracked in separate components, allowing for both on-farm and off-farm sources of new water development. For farms, these streams were: (i) the capital costs of land development, farm buildings and equipment (including replacement costs and residual values), (ii) the fixed overhead costs, applied to the full area of developed farmland, and (iii) the total farm GM (across all farms in the scheme), applied to the mean proportion of land in production each year. If an ‘on-farm water source’ was being considered, then those costs were added to the farm costs. Farm developers were treated as private investors who would seek a commercial return. When an ‘off-farm water source’ (large dam >25 GL/year) was evaluated, its investor was treated as a separate public investor to whom payment was made by farmers for water supplied (which served as an additional stream of costs for farmers, and a stream of benefits for the water supplier, at their respective target IRRs). For the public off-farm developer, the streams of costs were: (i) the capital costs of developing the water and associated enabling infrastructure (including replacement costs and residual values), and (ii) the costs of maintaining and operating those assets. Threshold gross margins and water pricing to achieve target internal rate of return New irrigation schemes in the Victoria catchment would be costly to develop, so many technically feasible options are unlikely to be profitable at the returns and over the time periods expected by many investors. The results presented below suggest it would be difficult for any farming options to fully cover the costs of a large off-farm dam development. However, there is greater prospect of viable developments using on-farm sources of water for broadacre and cost-efficient horticulture. The costs of developing water and land resources for a new irrigation development vary widely, depending on a range of case-specific factors that are dealt with in other parts of this Assessment. These factors include the type and nature of the water source, the type of water storage, geology, topography, soil characteristics, water distribution system, type of irrigation system, type of crop to be grown, local climate, land preparation requirements, and level to which infrastructure is engineered. The financial analyses, therefore, have used a generic approach for exploring the consequences for the development costs of this variation, and other key factors that determine whether or not an irrigation scheme would be viable (e.g. farm performance and the level of returns sought by investors). The analyses used the discounted cashflow framework described above to back- calculate and fit the water prices and farm GMs that would be required for respective public (off- farm) and private investors (irrigators) to achieve their target IRRs. The results are summarised in tables showing the thresholds that must be met for a particular combination of water development and farm development options to meet the investor’s target returns. The tables allow viable pairings to be identified based on either threshold costs of water or required farm GMs. Financial viability for these threshold values was defined and calculated as investors achieving their target IRR (or, equivalently, that the investment would have an NPV of zero and a BCR of one at the target discount rate). Assumptions Analyses first considered the case of irrigation schemes built around public investment in a large off-farm dam in the Victoria catchment. The analyses then considered the case of developments using on-farm dams and bores. To keep the results as relevant as possible to a wide range of different development options and configurations, the analyses here do not assume the scale at which a water development would be undertaken. Instead, all costs are expressed per hectare of irrigated farmland and per ML per year of water supply capacity, facilitating comparisons between scenarios (which can differ substantially in size). To illustrate how this slightly abstract generic approach can be applied to specific development projects, a worked example shows the indicative off-farm infrastructure costs that would be involved in development of a representative dam site in the Victoria catchment (Table 6-2). Table 6-2 Indicative capital costs for developing a representative irrigation scheme in the Victoria catchment The dam costings already allow for a road; an indicative allowance has been added for a bitumen road to the irrigation development from the Victoria Highway, a transmission line from Kununurra, and electricity distribution lines to which farms can connect. For more information on this figure or table please contact CSIRO on enquiries@csiro.au Source: Dam and weir costings are based on data from the companion technical report on surface water storage for the Victoria catchment (Yang et al., 2024), and reticulation costings based on a per hectare rate from Devlin (2024) and include contingencies; see those reports for full details of cost breakdowns and assumptions To enhance like-for-like comparisons across the various development scenarios, a set of standard assumptions have been made about the breakdown of development costs (by life span) and associated ongoing operating costs (Table 6-3). Three indicative types of farming enterprise represent different levels of capital investment, associated with the intensity of production and the extent to which farming operations are performed on-farm or outsourced ( Table 6-3 Assumed indicative capital and operating costs for new off- and on-farm irrigation infrastructure Three types of farming enterprise represent a range of increasing intensity, value and cost of production. Indicative base capital costs for establishing new farms (excluding water costs) allow on- and off-farm water sources to be added and compared on an equal basis. Annual operation and maintenance (O&M) costs are expressed as a percentage of the capital costs of assets. The Horticulture-H farm, with higher development costs, includes on-farm packing facilities, cold storage, and accommodation for seasonal workers. The Horticulture-L farm, with lower development costs, does not include these assets and would have to outsource these services if required (reducing the farm gross margin). IRR = internal rate of return. SCHEME COMPONENT ITEM VALUE UNIT O&M COST (% capital cost/y) Off-farm infrastructure development capital and operating costs (large dam and enabling infrastructure) Capital costs Total capital costs (split by life span below) Indicative >50,000 (analysed range: 20,000–150,000) $/ha Longer-life-span infrastructure (100 y) 85 % 0.4 Shorter-life-span infrastructure (40 y) 15 % 1.6 Operating O&M (by life-span categories) % capital cost $/ha/y Off-farm water source pumping costs ~2 (additional) $/ML/ Target IRR Base (with sensitivity range) 7 % Farm development capital and operating costs Broadacre Horticulture-L (low capital) Horticulture-H (high capital) Capital costs Base (excluding water source) 9000 25,000 70,000 $/ha Water source (on- or off-farm) Indicative >4000 (analysed range: 3000 to 15,000) $/ha Longer-life-span infrastructure (40 y) 50 50 50 % 1.0 Shorter-life-span infrastructure (15 y) 50 50 50 % 1.0 Operating O&M (by life-span categories) % capital cost $/ha/y Farm water source pumping costs ~2 (additional) $/ML/ Fixed costs 600 1,500 6,500 $/ha/y Water use Crop water use (before losses) 6 6 6 ML/ha On-farm water use efficiency 70 90 90 % Gross margin Indicative gross margin 4,000 7,000 11,000 $/ha/y Target IRR Base (with sensitivity range) 10 10 10 % For consistency, all costs of delivering water to the farm at the level of the soil surface are treated as the costs of the water source (so the costs of the various water source options can be compared on a like-for-like basis). Subsequent farm pumping costs of distributing and applying the supplied water to crops are treated as part of the variable costs of growing crops and are already accounted for in the crop GMs presented in Chapter 4. The pumping costs for the water supplier are highly situation-specific for the various water sources. In particular, these pumping costs are affected by the elevation of the water source relative to the point of distribution to the farm: for example, the height water needs to be pumped from a weir to a distribution channel, or from a farm dam to a field; or the dynamic head required to lift bore water to the field surface. For this reason, water source pumping costs have not been included in the summary tables of water pricing, but should be added separately as required at a cost of approximately $2 per ML per m dynamic head. This is mainly a consideration for groundwater bores, but also applies when water needs to be lifted from rivers or irrigation channels. For more information on water infrastructure costs, see Chapter 5 (and the companion technical reports referenced there). For more information on crop GMs, see Chapter 4 (and the companion technical reports referenced there). The analyses presented below consider (i) the case of irrigation schemes built around a large dam and its associated supporting off-farm infrastructure (Section 6.3.3); (ii) the case of self-contained, modular farm developments with their own on-farm source of water (Section 6.3.4). For both cases, the water price that irrigators can afford to pay provides a useful common point of reference for identifying suitable water sources for various types of farm developments (Section 6.3.2). The initial analyses assumed that all farmland was in full production and performed at 100% of its potential (and assumed 100% reliable water supplies) from the start of the development. Section 6.3.5 provides a set of adjustment factors that quantify the risks of various sources of underperformance that can be anticipated. 6.3.2 Price irrigators can afford to pay for a new water source Table 6-4 shows the price that the three different types of farms could afford to pay for water, while meeting a target 10% IRR, for different levels of farm water use and productivity. For prices to be sustained at this level throughout the life of the water source, the associated farm GM (in the first column of Table 6-4) would also need to be maintained over this period. The table is therefore most useful when assessing the long-term price that can be sustained to pay off long- lived water infrastructure (rather than temporary spikes in farm GMs during runs of favourable years). The lowest GM in the first column of Table 6-4 for each farm is the value below which the farm would not be viable, even if water was free. This does not necessarily mean that such GMs could readily be achieved in practice: for the capital-intensive Horticulture-H farm, in particular, it would be challenging in the Victoria catchment to reach the $17,000 per ha per year GM to cover the farm’s other costs, even before considering the costs of water. These water prices are likely to be most useful for public investors in large dams, because the sequencing of development creates asymmetric risks between the water supplier and the irrigators. Irrespective of the planned water pricing for a dam project, once the dam is built, irrigators have the choice of whether to develop new farms; they are unlikely to act to their own detriment by making an investment if they cannot do so at a water price that will allow them to obtain a commercial rate of return. These water prices, together with estimates of likely attainable farm GMs (available in Chapter 4), provide a useful benchmark for checking assumptions about any potential public dam developments in the Victoria catchment. For on-farm water sources, these water prices can assist in planning water development options that cropping operations could reasonably be expected to afford. The tables in the next sections allow comparisons of water development options by converting capital costs of developing on- and off-farm water sources to volumetric costs ($ per ML supplied). All water prices are based on volumes supplied to the farm gate or surface (after losses in transit) per metered ML supplied. Table 6-4 Price irrigators can afford to pay for water, based on the type of farm, the farm water use and the farm annual gross margin (GM), while meeting a target 10% internal rate of return (IRR) Analyses assume water volumes are measured on delivery to the farm gate or surface: pumping costs involved in getting water to the farmland surface would be an additional cost of supplying the water (indicatively $2 per ML per m dynamic head), while pumping costs in distributing and applying the water to the crop are considered part of the variable costs included in the GM. Indicative GMs that the three types of farms could attain in the Victoria catchment are $4000 and $7000 per ha per year for Broadacre and Horticulture-L farms, respectively (blue-shaded rows), and $11,000 per ha per year for Horticulture-H (Table 6-3, Chapter 4). Note that the Horticulture-H farm cannot pay anything for water until it achieves a GM above $17,000 per ha per year. GROSS MARGIN PRICE IRRIGATORS CAN AFFORD TO PAY ($/ha/y) ($/ML at farm gate/surface) Farm water use (ML/ha including on-farm distribution and application losses) 4 5 6 7 8 9 10 12 Broadacre ($9,000/ha development costs, $600/ha/y fixed costs, 70% on-farm efficiency) 2,000 25 20 17 14 12 11 10 8 2,500 86 69 57 49 43 38 34 29 3,000 147 118 98 84 74 65 59 49 3,500 209 167 139 119 104 93 83 70 4,000 270 216 180 154 135 120 108 90 5,000 392 314 262 224 196 174 157 131 Horticulture-L ($25,000/ha development costs, $1,500/ha/y fixed costs, 90% on-farm efficiency) 5,000 39 31 26 22 19 17 16 13 6,000 241 193 161 138 121 107 97 80 7,000 444 355 296 254 222 197 178 148 8,000 646 517 431 369 323 287 259 215 10,000 1051 841 701 601 526 467 421 350 12,000 1456 1165 971 832 728 647 583 485 Horticulture-H ($70,000/ha development costs, $6,500/ha/y fixed costs, 90% on-farm efficiency) 17,000 203 162 135 116 101 90 81 68 20,000 810 648 540 463 405 360 324 270 25,000 1823 1458 1215 1042 911 810 729 608 30,000 2835 2268 1890 1620 1418 1260 1134 945 40,000 4860 3888 3240 2777 2430 2160 1944 1620 50,000 6885 5508 4590 3934 3443 3060 2754 2295 6.3.3 Financial targets required to cover full costs of large, off-farm dams The first generic assessment considered the case of public investment in a large dam in the Victoria catchment and whether the costs of that development could be covered by water payments from irrigators (priced at their capacity to pay). The public costs of development include the cost of the dam and water distribution, and of any other supporting infrastructure required. Costs are standardised per unit of farmland developed, noting that a smaller area could be developed for a crop with a higher water use (so the water development costs per hectare would be higher). Target farm gross margins for off-farm public water infrastructure shows what farm annual GM would be required for various costs of water infrastructure development at the public investors’ target IRR. As expected, higher farm GMs are required in order to cover higher capital costs and attain a higher target IRR. The tables in this section can be used to assess whether water development opportunities and farming opportunities in the Victoria catchment are likely to combine in financially viable ways. Indicative farm GMs that could be achieved in the Victoria catchment are approximately $4000, $7000 and $11,000 per ha per year for Broadacre, less-capital-intensive Horticulture-L (including penalising GMs if outsourcing occurs) and capital-intensive Horticulture-H, respectively (Table 6-3). A dam and supporting infrastructure would likely require at least $50,000/ha of capital investment (Table 6-2). None of the three farming types is likely to be viable at these farm GMs and water development costs (at a 7% target IRR for the public investor). However, Broadacre and Horticulture-L farming might be marginally viable at a 3% target IRR for the public investor. Broadacre and lower-cost Horticulture- L could both achieve a target 10% IRR for the farm investments while contributing $20,000 to $30,000 per ha (25%–38%) towards the cost of a dam (including enabling infrastructure and ongoing O&M costs) that cost $80,000/ha to build. That is a higher proportion of costs than irrigators have historically contributed towards irrigation schemes in some other parts of Australia (approximately a quarter of capital costs (Vanderbyl, 2021)), and would involve a decision for the Australian and NT governments in accordance with their expectations, priorities and investment criteria. Table 6-5 Farm gross margins (GMs) required in order to cover the costs of off-farm water infrastructure (at the supplier’s target internal rate of return (IRR)) Assumes 100% farm performance on all farmland in all years, once construction is complete. Costs of supplying water to farms are consistently treated as costs of water source development (and not part of the farm GM calculation). Risk adjustment multipliers are provided in Section 6.3.5. Blue-shaded cells indicate the capital costs that could be afforded by farms with GMs of $4000 (Broadacre), $7000 (Horticulture-L) and $11,000 (Horticulture-H) per ha per year. Blue-shaded column headers indicate the most cost-effective dam development options in the Victoria catchment (Table 6-2). TARGET IRR FARM GROSS MARGIN REQUIRED IN ORDER TO PAY FOR OFF-FARM WATER INFRASTRUCTURE (%) ($/ha/y) Total capital costs of off-farm water infrastructure ($/ha) 20,000 30,000 40,000 50,000 70,000 100,000 125,000 150,000 Broadacre ($9,000/ha development costs, $600/ha/y fixed costs, 70% on-farm efficiency) 3 2,604 3,016 3,428 3,840 4,664 5,900 6,930 7,960 5 2,977 3,569 4,160 4,751 5,933 7,707 9,185 10,663 7 3,359 4,139 4,920 5,701 7,263 9,605 11,558 13,510 10 3,941 5,013 6,085 7,157 9,301 12,516 15,196 17,876 12 4,333 5,601 6,869 8,137 10,673 14,478 17,648 20,818 Horticulture-L ($25,000/ha development costs, $1,500/ha/y fixed costs, 90% on-farm efficiency) 3 5,584 5,996 6,408 6,820 7,645 8,881 9,911 10,941 5 5,985 6,576 7,167 7,759 8,941 10,715 12,193 13,671 7 6,370 7,150 7,931 8,712 10,274 12,616 14,569 16,521 10 6,952 8,024 9,096 10,168 12,312 15,528 18,208 20,887 12 7,345 8,613 9,881 11,149 13,685 17,489 20,659 23,829 Horticulture-H ($70,000/ha development costs, $6,500/ha/y fixed costs, 90% on-farm efficiency) 3 16,618 17,068 17,518 17,967 18,867 20,217 21,342 22,467 5 17,164 17,789 18,413 19,038 20,288 22,162 23,724 25,286 7 17,610 18,416 19,222 20,027 21,638 24,055 26,070 28,084 10 18,215 19,301 20,387 21,472 23,644 26,901 29,615 32,330 12 18,607 19,884 21,161 22,438 24,992 28,823 32,015 35,207 Target water pricing for off-farm public water infrastructure Table 6-6 shows the price that a public investor in off-farm water infrastructure would have to charge to fully cover the costs of development of off-farm water infrastructure, expressed per unit of supply capacity at the dam wall. Pricing assumes that the full supply of water (i.e. reservoir yield) would be used and paid for every year over the entire lifetime of the dam, after accounting for water losses between the dam and the farm. It can be challenging for farms to sustain the high levels of revenue over such long periods (100 years) to justify the costs of building expensive dams. For these base analyses, the water supply is assumed to be 100% reliable; risk adjustment multipliers to account for reliability of supply are provided in Section 6.3.5. For example, in the Victoria catchment, one of the most cost-effective dam opportunities would cost approximately $9,000 per ML per year of supply capacity at the dam wall after including the required supporting off-farm water infrastructure (Table 6-2). This would require farms to pay $966 per ML extracted to fully cover the costs of the public investment at the base 7% target IRR for public investments (read from value between 8,000 and 10,000 in Table 6-6). Comparisons with what irrigators can afford to pay (Table 6-4) show that it is unlikely any farming options could cover the costs of a dam in the Victoria catchment at the GMs farms are likely to be able to achieve (Table 6-3, Chapter 4). When a scheme is not viable (BCR < 1), the water cost and pricing tables can be used as a quick way of estimating the BCR and the likely proportion of public development costs that farms would be able to cover. For example, a Broadacre farm that uses 8 ML/ha (measured at delivery to the farm) with a GM of $4000 per ha per year could afford to pay $135/ML extracted (Table 6-4), which would cover 13% ($135/$966) of the $966/ML price (Table 6-6) required to cover the full costs of the public development. The BCR would, therefore, be 0.13 (the ratio of the amount the net farm benefits can cover to the full costs of the scheme). As for the example in Table 6-5, it would be a decision for the public investor as to what proportion of the capital costs of infrastructure projects they would realistically expect to recover from users. Table 6-6 Water pricing required in order to cover costs of off-farm irrigation scheme development (dam, water distribution, and supporting infrastructure) at the investors target internal rate of return (IRR) Assumes the conveyance efficiency from dam to farm is 70% and that supply is 100% reliable. Risk adjustment multipliers for water supply reliability are provided in Table 6-9. Pumping costs between the dam and the farm would need to be added (e.g. ~$30/ML extra to lift water ~15 m from the weir pool to distribution channels). ‘$ CapEx per ML/y at dam’ is the capital expenditure on developing the dam and supporting off-farm infrastructure per ML per year of the dam’s supply capacity measured at the dam wall. Blue-shaded cells indicate $/ML cost of water. Blue-shaded column headers are indicative of the most cost-effective large dam options available in the Victoria catchment (Table 6-2). TARGET IRR WATER PRICE THAT WOULD NEED TO BE CHARGED IN ORDER TO COVER OFF-FARM INFRASTRUCTURE COSTS (%) ($/ML charged at farm gate) Capital costs of off-farm infrastructure ($ CapEx per ML/y at dam) 3,000 4,000 5,000 6,000 8,000 10,000 12,000 14,000 16,000 3 162 215 269 323 431 538 646 754 861 5 239 319 399 479 638 798 958 1117 1277 7 322 429 537 644 859 1073 1288 1502 1717 10 448 598 747 897 1196 1495 1794 2093 2392 6.3.4 Financial targets required in order to cover costs of on-farm dams and bores The second generic assessments considered the case of on-farm sources of water. Indicative costs for on-farm water sources, including supporting on-farm distribution infrastructure, vary between $4,000 and $15,000 per ha of farmland. Costs depend on the type of water source, how favourable the local conditions are for its development, and the irrigation requirement of the farming system. Since the farm and water source would be developed by a single investor, the first analyses considered the combined cost of all farm development together (without separating out the water component). Target farm gross margins required in order to cover full costs of greenfield farm development with water source Table 6-7 shows the farm GMs that would be required in order to cover different costs of farm development at the investor’s target IRR. Note that private on-farm water sources are typically engineered to a lower standard than public water infrastructure and have lower upfront capital costs, higher recurrent costs (higher O&M and asset replacement rates) and lower reliability. Based on the indicative farm GMs provided earlier (Table 6-3) and a 10% target IRR, a Broadacre farm with a $4000 per ha per year GM could cover total on-farm development capital costs of approximately $20,000/ha. A lower capital cost Horticulture-L farm with a GM of $7000 per ha per year could afford approximately $40,000/ha of initial capital costs, and a capital-intensive Horticulture-H farm with a GM of $11,000 per ha per year could pay approximately $30,000/ha for farm development (Table 6-7). This indicates that on-farm water sources may have better prospects of being viable than large public dams in the Victoria catchment, particularly for broadacre farms and horticulture with lower development costs, if good sites can be identified for developing sufficient on-farm water resources at a low-enough cost. Table 6-7 Farm gross margins (GMs) required in order to achieve target internal rates of return (IRR), given various capital costs of farm development (including an on-farm water source) Assumes 100% farm performance on all farmland in all years, once construction is complete. Risk adjustment multipliers are provided in Section 6.3.5. Blue-shaded cells indicate the capital costs that could be afforded by farms with GMs of $4000 (Broadacre), $7000 (Horticulture-L) and $11,000 (Horticulture-H) per ha per year. TARGET IRR FARM GROSS MARGIN REQUIRED IN ORDER TO ACHIEVE THE FARMER'S TARGET IRR (%) ($/ha/y) Total capital costs of farm development, including water source ($ CapEx/ha) 10,000 15,000 20,000 30,000 40,000 50,000 70,000 100,000 Broadacre ($600/ha/y fixed costs, 70% on-farm efficiency) 5 1,516 1,957 2,398 3,279 4,160 5,042 6,804 9,449 7 1,669 2,181 2,694 3,718 4,742 5,767 7,815 10,888 10 1,923 2,554 3,185 4,447 5,709 6,972 9,496 13,282 12 2,105 2,821 3,537 4,968 6,400 7,832 10,696 14,991 15 2,389 3,238 4,087 5,785 7,483 9,181 12,578 17,672 20 2,882 3,963 5,044 7,206 9,368 11,530 15,854 22,340 TARGET IRR FARM GROSS MARGIN REQUIRED IN ORDER TO ACHIEVE THE FARMER'S TARGET IRR (%) ($/ha/y) Total capital costs of farm development, including water source ($ CapEx/ha) 10,000 15,000 20,000 30,000 40,000 50,000 70,000 100,000 Horticulture-L ($1,500/ha/y fixed costs, 90% on-farm efficiency) 5 2,469 2,909 3,350 4,231 5,113 5,994 7,757 10,401 7 2,637 3,149 3,661 4,685 5,710 6,734 8,783 11,856 10 2,915 3,546 4,177 5,439 6,702 7,964 10,488 14,274 12 3,114 3,830 4,546 5,978 7,409 8,841 11,705 16,001 15 3,424 4,273 5,122 6,820 8,519 10,217 13,613 18,708 20 3,962 5,043 6,124 8,286 10,448 12,610 16,934 23,420 Horticulture-H ($6,500/ha/y fixed costs, 90% on-farm efficiency) 5 7,760 8,201 8,642 9,523 10,404 11,286 13,048 15,692 7 8,012 8,524 9,036 10,060 11,085 12,109 14,158 17,231 10 8,427 9,058 9,689 10,951 12,213 13,475 15,999 19,785 12 8,720 9,436 10,152 11,584 13,016 14,448 17,312 21,607 15 9,177 10,026 10,875 12,573 14,271 15,970 19,366 24,461 20 9,963 11,044 12,125 14,287 16,449 18,611 22,935 29,421 Volumetric water cost equivalent for on-farm water source Table 6-8 converts the capital cost of developing an on-farm water source (per ML of annual supply capacity) into an equivalent cost for each individual megalitre of water supplied by the water source. The table can be used to estimate how much a farm could spend on developing required water resources by comparing the costs per ML with what farms can afford to pay for water (Table 6-4). For example, a Broadacre farm with a GM of $4000 per ha per year, an annual farm water use of 8 ML/ha and a target 10% IRR could afford to pay $135/ML for its water supply (Table 6-4), which would allow capital costs of up to $1000 for each ML/year supply capacity for developing an on-farm supply (Table 6-8). Approximate indicative costs for developing on-farm water sources range from $500/ML to $2000/ML (based on the range of per hectare costs above), which confirms, by this alternative approach, that there are likely to be viable farming opportunities using on-farm water development in the Victoria catchment. Table 6-8 Equivalent costs of water per ML for on-farm water sources with various capital costs of development, at the internal rate of return (IRR) targeted by the investor Assumes the water supply is 100% reliable. Risk adjustment multipliers for water supply reliability are provided in Table 6-9. Pumping costs to the field surface would be extra (e.g. ~$2 per ML per m dynamic head for bore pumping). Blue-shaded cells indicate $/ML cost of water. TARGET IRR WATER VOLUMETRIC COST EQUIVALENT UNIT FOR VARIOUS CAPITAL COSTS OF WATER SOURCE (%) ($/ML) Capital costs for on-farm water infrastructure ($ CapEx per ML per y at farmland surface) 300 400 500 700 1000 1250 1500 1750 2000 3 22 29 37 51 74 92 110 129 147 5 26 35 44 61 87 109 131 153 175 7 31 41 51 72 102 128 154 179 205 10 38 51 63 89 127 159 190 222 254 12 43 58 72 101 144 180 216 252 288 15 51 68 85 120 171 213 256 299 342 20 65 87 109 152 217 271 326 380 434 6.3.5 Risks associated with variability in farm performance This section assessed the impacts of two types of risks on scheme financial performance: those that reduce farm performance through the early establishment and learning years, and those occurring periodically throughout the life of the development. The effect of these risks is to reduce the expected revenue and expected GM. Setbacks that occur soon after a scheme is established were found to have the largest effect on scheme viability, particularly at higher target IRRs. There is a strong incentive to start any new irrigation development with well-established crops and technologies, and to be thoroughly prepared for those agronomic risks of establishing new farmland that can be anticipated. Analyses showed that delaying full development for longer periods than the learning time had only a slight negative effect on IRRs, whereas proceeding to full development before learning was complete had a much larger impact. This implies that it is prudent to err on the side of delaying full development (particularly given that, in practice, it is only possible to know when full performance has been achieved in retrospect). An added benefit of staging is the limiting of losses when small- scale testing proves initial assumptions of benefits to be overoptimistic and that full-scale development could never be profitable (even after attempts to overcome unanticipated challenges). For an investment to be viable, farm GMs must be sustained at high levels over long periods. Thus, variability in farm performance poses risks that must be considered and managed. GMs can vary between years because of either short-term initial underperformance or periodic shocks. Initial underperformance is likely to be associated with learning as farming practices are adapted to local conditions, overcoming initial challenges to reach their long-term potential. Further unavoidable periodic risks are associated with water reliability, climate variability, flooding, outbreaks of pests and diseases, periodic technical or equipment failures, and fluctuations in commodity prices and market access. Unreliability of water supply is less easy to avoid than other periodic risks. Risks that cannot be avoided must be managed, mitigated where possible and accounted for in determining the realistic returns that can be expected from an irrigation development. This would include having adequate capital buffers for survival through challenging periods. Another perceived risk for investors is the potential future policy changes and delays in regulatory approvals. Reducing this, or any other sources of risk, in the Victoria catchment would help make marginal investment opportunities more attractive. The results of the analyses of both the periodic and the learning risks are shown below. The right to farm and other sovereignty risks, especially with regard to access to water, may become key factors in future years, based on experience from elsewhere, but these are not the subject of the risk discussion presented here. Throughout this section, farm performance in a given year is quantified as the proportion of the long-term mean GM that a farm attains; 100% performance is when this level is reached and zero % equates to a performance in which revenues only balance variable costs (GM = zero). Risks from periodic underperformance The analyses considered periodic risks generically, without assuming any of the particular causes listed above. To quantify their effects on scheme financial performance, periodic risks were characterised by three components: • reliability – the proportion of ‘good’ years, in which the ‘full’ 100% farm performance was achieved, with the remainder of years being termed ‘failed’ years, in which some negative impact was experienced • severity – the farm performance in a ‘failed’ year, in which some type of setback occurred • timing – in ‘early’ timing (in relation to a 10-year cycle), the ‘failed’ years came early in each 10- year cycle (e.g. 80% reliability meant that ‘failed’ years occurred in the first 2 years of the scheme and in the first 2 years of each 10-year cycle after that). In ‘late’ timing, the ‘failed’ years came at the end of each 10-year cycle. In ‘random’ timing, each year was allocated the long- term mean farm performance of ‘good’ and ‘failed’ years (frequency weighted). Table 6-9 summarises the effects of a range of reliabilities and severities for periodic risks on scheme viability. Periodic risks had a consistent proportional effect on target GMs, irrespective of development options or costs, so the results were simplified as a set of risk adjustment multipliers. The multipliers can, therefore, be applied to the target farm GMs in Section 6.3.2 (the GMs required in order to cover capital costs of development at the investor’s target IRRs at 100% farm performance) to account for the effects of various risks. These same adjustment factors can be applied to the water prices that irrigators can afford to pay (Table 6-4), but would be used as divisors to reduce the price that irrigators could pay for water. As expected, the greater the frequency and severity of ‘failed’ years, the greater the impact on the scheme viability and the greater the increase in farm GMs required in order to offset these impacts. As an example, the reliability of water supply is one of the more important sources of unavoidable variability in the productivity of irrigated farms. Water reliability (proportion of ‘good’ years, in which the full supply of water is available) is shown as ‘reliability’ in Table 6-9, and the mean percentage of water available in a ‘failed’ year (in which less than the full supply of water is available) is shown as the ‘failed year performance’ in Table 6-9 (assuming the area of farmland planted is reduced in proportion to the amount of water available). For example, if a water supply was 85% reliable and provided a mean of 75% of its full supply in ‘failed’ years, a risk adjustment factor of 1.04 ( For crops for which the quality of the produce is more important than the quantity, such as horticulture, the approach of reducing planted land area in proportion to available water in ‘failed’ years would be reasonable. However, for perennial horticulture or tree crops, it may be difficult to reduce (or increase) areas on an annual basis. Farmers of these crops would, therefore, tend to opt for systems with a high degree of reliability of water supply (e.g. 95%). For many broadacre crops, deficit irrigation could partially mitigate impacts on farm performance in years with reduced water availability, as could carryover effects from inputs (such as fertiliser) in a ‘failed’ year that reduce input costs the following year (see Section 4.3.4). Table 6-9 Risk adjustment factors for target farm gross margins (GMs), accounting for the effects of the reliability and severity (level of farm performance in ‘failed’ years) of the periodic risk of water reliability Results are not affected by discount rates. ‘Good’ years = 100% farm performance; ‘failed’ years = <100% performance. ‘Failed year performance’ is the mean farm GM in years in which some type of setback is experienced relative to the mean GM when the farm is running at ‘full’ performance. FAILED YEAR PERFORMANCE (%) RISK ADJUSTMENT MULTIPLIER FOR TARGET FARM GROSS MARGINS (VS BASE 100% RELIABILITY TABLES) (unitless ratio) Reliability (proportion of ‘good’ years) 1.00 0.90 0.85 0.80 0.70 0.60 0.50 0.40 0.30 0.20 85 1.00 1.02 1.02 1.03 1.05 1.06 1.08 1.10 1.12 1.14 75 1.00 1.03 1.04 1.05 1.08 1.11 1.14 1.18 1.21 1.25 50 1.00 1.05 1.08 1.11 1.18 1.25 1.33 1.43 1.54 1.67 25 1.00 1.08 1.13 1.18 1.29 1.43 1.60 1.82 2.11 2.50 0 1.00 1.11 1.18 1.25 1.43 1.67 2.00 2.50 3.33 5.00 Table 6-10 shows how the timing of periodic impacts affects scheme viability, providing risk adjustment factors for a range of reliabilities for an impact that had 50% severity, with late timing, early timing and random (long-term frequency, weighted mean performance) timing. These results indicate that any negative disturbances that reduce farm performance will have a larger effect if they occur soon after the scheme is established, and that this effect is greater at higher target IRRs. For example, at a 7% target IRR and 70% reliability with ‘late’ timing (in which setbacks occur in the last 3 of every 10 years), the GM multiplier is 1.13, meaning the annual farm GM would need to be 13% higher than if farm performance were 100% reliable. In contrast, for the same settings with ‘early’ timing, the GM multiplier is 1.23, meaning the farm GM would need to be 23% higher than if farm performance were 100% reliable. The impacts of early setbacks are more severe than the impacts of late setbacks. Table 6-10 Risk adjustment factors for target farm gross margins (GMs) accounting for the effects of reliability and the timing of periodic risks Assumes 50% farm performance during ‘failed’ years, in which 50% farm performance means 50% of the GM at ‘full’ potential production. IRR = internal rate of return. TARGET IRR (%) TIMING OF FAILED YEARS RISK ADJUSTMENT MULTIPLIER FOR TARGET FARM GROSS MARGINS (VS BASE 100% RELIABILITY TABLES) (unitless ratio) Reliability (proportion of ‘good’ years) 1.00 0.90 0.80 0.70 0.60 0.50 0.40 0.30 0.20 3 Late 1.00 1.05 1.10 1.16 1.22 1.30 1.39 1.50 1.63 Random – no bias 1.00 1.05 1.11 1.18 1.25 1.33 1.43 1.54 1.67 Early 1.00 1.06 1.13 1.20 1.28 1.37 1.47 1.58 1.70 7 Late 1.00 1.04 1.08 1.13 1.19 1.26 1.35 1.46 1.59 Random – no bias 1.00 1.05 1.11 1.18 1.25 1.33 1.43 1.54 1.67 Early 1.00 1.07 1.15 1.23 1.32 1.41 1.51 1.62 1.74 10 Late 1.00 1.03 1.07 1.12 1.17 1.24 1.32 1.42 1.56 Random – no bias 1.00 1.05 1.11 1.18 1.25 1.33 1.43 1.54 1.67 Early 1.00 1.08 1.16 1.25 1.35 1.45 1.55 1.66 1.77 Risks from initial ‘learning’ period Another form of risk arises from the initial challenges in establishing new agricultural industries in the Victoria catchment; it includes setbacks from delays, such as gaining regulatory approvals, and adapting farming practices to conditions in the Victoria catchment. Some of these risks are avoidable if investors and farmers learn from past experiences of development in northern Australia (e.g. Ash et al., 2014), avoid previous mistakes and select farming options that are already well proven in analogous northern Australian locations. However, even well-prepared developers are likely to face initial challenges in adapting to the unique circumstances of a new location. Newly developed farmland can take some time to reach its productive potential as soil nutrient pools are established, soil limitations are ameliorated, suckers and weeds are controlled, and pest and disease management systems are established. ‘Learning’ (used here to broadly represent all aspects of overcoming initial sources of farm underperformance) was assessed in terms of two simplified generic characteristics: • initial level of performance – the proportion of the long-term mean GM that the farm achieves in its first year • time to learn – the number of years taken to reach the long-term mean farm performance. Performance was represented as increasing linearly over the learning period from the starting level to the long-term mean performance level (100%). The effect of learning on scheme financial viability was considered for a range of initial levels of farm performance and learning times. As described above, learning had consistent proportional effects on target GMs, so the results were simplified as a set of risk adjustment factors (Table 6- 11). As expected, the impacts on scheme viability are greater the lower the starting level of farm performance and the longer it takes to reach the long-term performance level. Since these impacts, by their nature, are weighted to the early years of a new development, they have more impact at higher target IRRs. To minimise the risks of learning impacts, there is a strong incentive to start any new irrigation development with well-established crops and technologies, and to be thoroughly prepared for those agronomic risks of establishing new farmland that can be anticipated. Higher-risk options (e.g. novel crops, equipment or practices that are not currently in profitable commercial use in analogous environments) could be tested and refined on a small scale until locally proven. As indicated in the examples above, the influence of each risk individually can be quite modest. However, the combined influence of all foreseeable risks must be accounted for in planning, and the cumulative effect of these risks can be substantial. For example, the last question in Table 6-1 shows that the combined effect of just two risks requires farm GMs to be approximately 50% higher than they would be without the risks. See Stokes and Jarvis (2021) for the effects of a common suite of risks on the financial performance of a Bradfield-style irrigation scheme. Table 6-11 Risk adjustment factors for target farm gross margins (GMs), accounting for the effects of learning risks Learning risks were expressed as the level of initial farm underperformance and time taken to reach full performance levels. Initial farm performance is the initial GM as a percentage of the GM at ‘full’ performance. IRR = internal rate of return. TARGET IRR (%) INITIAL FARM PERFORMANCE (%) RISK ADJUSTMENT MULTIPLIER FOR TARGET FARM GROSS MARGINS (VS BASE 100% RELIABILITY TABLES) (unitless ratio) Learning time (years to 100% performance) 2 4 6 8 10 15 3 85 1.01 1.02 1.03 1.03 1.04 1.05 75 1.02 1.03 1.04 1.05 1.07 1.10 50 1.04 1.06 1.09 1.12 1.14 1.21 25 1.06 1.10 1.14 1.19 1.23 1.35 0 1.08 1.14 1.20 1.26 1.33 1.53 7 85 1.02 1.03 1.04 1.05 1.05 1.07 75 1.03 1.05 1.06 1.08 1.09 1.13 50 1.06 1.10 1.13 1.17 1.21 1.29 25 1.09 1.15 1.22 1.28 1.35 1.51 0 1.12 1.21 1.31 1.41 1.52 1.83 10 85 1.02 1.03 1.05 1.06 1.07 1.09 75 1.04 1.06 1.08 1.10 1.11 1.15 50 1.08 1.12 1.17 1.21 1.26 1.35 25 1.12 1.20 1.28 1.36 1.44 1.65 0 1.16 1.28 1.41 1.55 1.69 2.10 6.4 Cost–benefit considerations for water infrastructure viability 6.4.1 Lessons from recent Australian dams CBA is widely used to help decision makers evaluate the net benefits likely to arise from implementing a proposed project, particularly for investments in large-scale public infrastructure. Despite this wide usage of CBAs, there are few examples for which the estimated costs and benefits used to justify the project have been revisited at a later date. Such ex-post evaluations allow the outcomes of completed projects to improve planning, management and risk mitigation in future projects (Infrastructure Australia, 2021a). The few examples in which water infrastructure CBAs have been evaluated have focused on exploring the accuracy of the forecast capital costs. An international study of large water infrastructure projects showed that actual construction costs exceeded contracted costs by a mean of 96% (Ansar et al., 2014). Similarly, an Australian-focused study found mean cost overruns of 120% (Petheram and McMahon, 2019). There is evidence of a systematic tendency across a range of large infrastructure projects for proponents to substantially under estimate development costs (Ansar et al., 2014; Flyvbjerg et al., 2002; Odeck and Skjeseth, 1995; Wachs, 1990; Western Australian Auditor General, 2016). Ex-post evaluations of project benefits are even scarcer. One international study found that large dam developments frequently underperformed, whereby ‘irrigation services have typically fallen short of physical targets, did not recover their costs and have been less profitable in economic terms than expected’ (World Commission on Dams, 2000). In particular, this study highlighted inaccurate and overestimated forecasting of future irrigation demand for water from dam developments. Review of recent Australian dams The Roper River Water Resource Assessment technical report on agricultural viability and socio- economics (Stokes et al., 2023) conducted a systematic review of the five most recently built dams in Australia (Figure 6-2, Table 6-12) to address the gap in the ex-post evaluations. The goal was to assess how well Australian dam projects have achieved their anticipated benefits and to make the learnings available for future planning. These lessons provide context for interpreting CBAs from project proponents, independent analysts, and the financial analyses provided in the previous section. The key lessons from that review are summarised below, and the full details are reported in Webster et al. (2024). Locations of five dams used in costing review map \\FS1-CBR.nexus.csiro.au\{lw-rowra}\work\5_Agriculture_economics\2_Victoria\1_GIS\1_Map_docs\Se-V-503_Map_Australia_and_river_basins_new dams_V1.mxd For more information on this figure please contact CSIRO on enquiries@csiro.au Figure 6-2 Locations of the five dams used in this review The dams are numbered in blue as 1: New Harvey Dam, 2: Paradise Dam, 3: Meander Dam, 4: Wyaralong Dam and 5: Enlarged Cotter Dam. Table 6-12 Summary characteristics of the five dams used in this review Documents reviewed for each dam are cited in the companion technical report on agricultural viability and socio- economics (Webster et al., 2024). CBA = cost–benefit analysis. NEW HARVEY DAM PARADISE DAM MEANDER DAM WYARALONG DAM ENLARGED COTTER DAM State/territory WA Qld Tas Qld ACT Date completed 2002 2005 2008 2011 2012 Capacity (GL) 59 300 43 103 78 New dam or redevelopment of existing dam? Replaces Harvey weir (built 1916, extended 1931), capacity of ~10 GL New New New Replaces original Cotter Dam (built 1915, extended 1951), capacity of ~4 GL Primary use(s) proposed for water from dam Irrigated agriculture Irrigated agriculture, water supply Irrigated agriculture, environmental flows, hydro- electric power Water supply to south-east Queensland Water supply for Canberra Type of key project documents used for this review Proposed water allocation plans (no CBA available) CBA and economic impact assessment CBA Environmental Impact Statement (EIS) (no CBA available) EIS (which included CBA information, but the actual CBA report was unavailable) Summary of key issues identified This review highlighted a number of issues with the historical use of CBAs for recently built dams in Australia together with ways they could be more rigorously addressed (Table 6-13). These issues arise because of the complexity of the forecasts and estimates required to plan large infrastructure projects and because of pressures on proponents that can introduce systematic biases. However, this report acknowledges that flaws with the use of CBAs in large public infrastructure investment decisions are not unique to regional Australia or to water infrastructure – they are systemic and occur in many different types of infrastructure globally. Under such circumstances it would be inequitable to apply more rigor to CBAs only for some select investments, geographic regions and infrastructure classes before the same standards are routinely applied in all cases. And there is no incentive for individual proponents to apply more rigor to CBAs if those proposals would suffer from unfavourable comparisons to alternative or competing investments with exaggerated cost–benefit ratios (CBRs). Table 6-13 Summary of key issues and potential improvements arising from a review of recent dam developments KEY ISSUE POTENTIAL IMPROVEMENTS 1 There is a lack of clear documentary evidence regarding the actual outcome of dam developments compared with the assumptions made in ex-ante proposals, Environmental Impact Statements (EISs) and cost– benefit analyses (CBAs). Ex-post evaluations or post- completion reviews have either not been prepared or not been made publicly available. Conducting ex-post evaluations of developments and making these publicly available (as recommended by 2021 guidance from Infrastructure Australia (Infrastructure Australia, 2021a, 2021b) and in the 2022 National Water Grid Investment Framework (NWGA 2022)) would enable lessons learned to be shared and benefit future developments. 2 Predicted increases in water demand from specific developments generally do not appear to arise at the scale and/or within the time frame forecast. While the reasons for this are varied and context-dependent, there does appear to be a systematic bias towards overestimation of the magnitude and rate at which new benefit would flow. Recognising the tendency towards a systematic bias of overstating benefits and understating costs, CBAs in project proposals could be improved by: (i) further efforts to present unbiased financial analysis (e.g. independent review) and ensuring appropriate sensitivity analysis is included in all proposals, (ii) developing broadly applicable and realistically achievable benchmarks for evaluating proponents’ assumptions and financial performance claims, (iii) using past experiences and lessons learned from previous projects with a similar context to inform the analysis presented in the proposals (building on Issue 1 above), and (iv) presenting a like-for-like comparison of cost-to-benefit ratios (CBRs) for the proposed case vs standard alternatives (such as water buybacks or a smaller dam, possibly better matched to realistic future demand). 3 The systematic bias towards optimism in proposals is exacerbated by mismatches between forecast demand and the full supporting infrastructure required to enable this demand to be realised, resulting in additional capital investment (pipelines, treatment plants, etc.) being required that was not costed in the original proposal. The same improvements as for Issue 2 (recognising and addressing inherent bias) apply here. 4 Developments are justified based on a complex mix of multiple market and non-market benefits, many of which are hard to monetise and capture in a single net present value (NPV) figure. CBAs could be improved by presenting clear information on the full portfolio of benefits (and costs and disbenefits) anticipated to arise from a project. While the quantitative part of the CBA would analyse the easily monetised costs and benefits (with metrics such as CBR and NPV), benefits that are hard to monetise could also be formally presented in whatever form is most appropriate to the magnitude and nature of that particular benefit. This presentation would enable the relative importance of each element of the mix to be weighed and given appropriate consideration, rather than attention being focused on a single NPV figure, which may have omitted key elements of the project. KEY ISSUE POTENTIAL IMPROVEMENTS 5 Improved water security and reliability of supply is often the most important benefit offered by dam developments, while also being the hardest to monetise. Dams provide a form of insurance against the risk that water may not be available when needed in the future. Assessing the value of this insurance requires consideration of the cost of lack of water supply when needed and the likelihood that this could occur. CBAs could be improved by providing clear information on exactly how the development will serve to improve water security, the likelihood that such insurance will be required (i.e. an estimate of the risk), and the estimated social and economic impacts if the insurance was not there when required. Such information could be presented alongside, and given equal prominence with, other information regarding the proposal, including the estimated NPV. This is preferable to attempting to ‘force’ the benefit into an NPV calculation that is ill equipped to deal with such a benefit. In the short term, the main value of the information provided here is to enable more critically interpretation and evaluation of CBAs so that more-informed decisions can be made about the likely viability (and relative ranking) of projects in practice. In particular, it highlights several aspects of CBAs regarding which the claims of proponents warrant critical scrutiny. The longer term value of this analysis is that it has identified many issues similar to those raised in past review cycles of Infrastructure Australia’s CBA best-practice guidelines and the recommendations that are being progressively added to those guidelines to improve how large public investments are evaluated (Infrastructure Australia, 2021a, 2021b). 6.4.2 Demand trajectories for high-value water uses For irrigated agriculture to expand in the Victoria catchment, additional water will be required. Forecasting that growth in demand is essential, both for planning new water infrastructure and for evaluating individual water infrastructure proposals. This will ensure assumed demand trajectories for water, and the associated value that can be generated from irrigated agriculture to justify the costs of that infrastructure, are reasonable. Australian Bureau of Statistics data series on historical agricultural production and water use were analysed to derive trends and relationships for benchmarking realistic growth trajectories in the NT (Figure 6-3). (a) Australia (b) Northern Territory Trend in value of Aust ag \\fs1-cbr.nexus.csiro.au\{lw-rowra}\work\5_Agriculture_economics\2_Victoria\4_Data\3_Economic\ViWRA-Charts_Economic.xlsx For more information on this figure please contact CSIRO on enquiries@csiro.au 010,00020,00030,0001981–901991–002001–102011–21GVAP ($M) DecadeCrops (horticulture)Crop (other)Livestock Trend in value of NT ag \\fs1-cbr.nexus.csiro.au\{lw-rowra}\work\5_Agriculture_economics\2_Victoria\4_Data\3_Economic\ViWRA-Charts_Economic.xlsx For more information on this figure please contact CSIRO on enquiries@csiro.au 02004006001981–901991–002001–102011–21GVAP ($M) DecadeCrops (horticulture)Crop (other)Livestock Figure 6-3 Trends in gross value of agricultural production (GVAP) in (a) Australia and (b) the NT over 40 years (1981–2021) Data points are decade averages of annual values. The ‘Crop (other)’ category is predominantly broadacre farming. Source: (ABS, 2022) Horticultural produce is typically perishable and expensive to store and transport, and must meet stringent phytosanitary (plant health) standards for export, so most Australian horticultural produce (~70%) is sold domestically for consumption shortly after harvest. Growth in horticultural industries is, therefore, constrained by growth in demand from local consumers. The current rate of growth in the value of Australian horticulture is $2.7 billion per decade, and for the NT it is $35 million per decade (step changes in gross value of agricultural production (GVAP) from 1981– 90 to 2011–21 are shown in Figure 6-3). Any new irrigated development would compete for some share of that growth, providing a benchmark guide for the scale of new horticulture that could realistically be included in any new irrigation scheme. It also provides a benchmark for the trajectory at which high-value horticulture (and the associated demand for high-priority water) could grow towards the ultimate scheme potential. In addition, the scale of new horticultural expansion for any single crop is limited by seasonal gaps in supply, so horticulture in any single location is typically a mix of products that fill the niche market gaps that the location can supply (usually dictated by climate, but sometimes a result of other factors such as backloading opportunities; see Chapter 4), rather than being a monoculture of the most valuable crop alone. Data on how the value of irrigated agriculture has increased with increasing irrigation water availability over time provide an indicative benchmark of how much gross value such a mix of new agricultural activities could generate for each new GL of irrigation water that becomes available (Figure 6-4). Based on the trendlines in Figure 6-4, each extra new GL of water use could produce either: • an extra $2.9 million of gross value from mixed fruit industries • an extra $7.9 million of gross value from mixed vegetable industries • an extra $3.8 million of gross value from mixed horticulture (combined), or • an extra $1.2 million of gross value from a typical mix of agriculture overall. Growth trends in the value of broadacre crops are stronger than those for horticulture (Figure 6- 3); they are a combination of increases in both product volumes and the value per unit product. Unlike horticultural crops, bulk broadacre commodities are stored and traded on large global markets (with multiple competing international buyers), which could easily absorb the scale of increases in production that would be possible from the Victoria catchment. However, supply chains, rather than markets, pose a challenge for new broadacre production. Despite northern Australia being geographically closer than southern Australia to many key markets, the supply chains for northern Australian produce are longer, because most agricultural exports leave through southern ports. For example, Darwin Port currently does not handle bulk food-grade containers (for either import or export). The challenge is to develop transport and handling capacity for exports and balance that with compatible imports to avoid the added cost of dead freighting empty containers (CRCNA, 2020). (a) Fruits (c) Fruits and vegetables combined (b) Vegetables (d) Total agriculture Trend in fruit GVIAP to available water \\fs1-cbr.nexus.csiro.au\{lw-rowra}\work\5_Agriculture_economics\2_Victoria\4_Data\3_Economic\ViWRA-Charts_Economic.xlsx For more information on this figure please contact CSIRO on enquiries@csiro.au Trend in fruit and vegetable GVIAP to available water \\fs1-cbr.nexus.csiro.au\{lw-rowra}\work\5_Agriculture_economics\2_Victoria\4_Data\3_Economic\ViWRA-Charts_Economic.xlsx For more information on this figure please contact CSIRO on enquiries@csiro.au Trend in vegetable GVIAP to available water \\fs1-cbr.nexus.csiro.au\{lw-rowra}\work\5_Agriculture_economics\2_Victoria\4_Data\3_Economic\ViWRA-Charts_Economic.xlsx For more information on this figure please contact CSIRO on enquiries@csiro.au Trend in total agriculture GVIAP to available water \\fs1-cbr.nexus.csiro.au\{lw-rowra}\work\5_Agriculture_economics\2_Victoria\4_Data\3_Economic\ViWRA-Charts_Economic.xlsx For more information on this figure please contact CSIRO on enquiries@csiro.au Figure 6-4 National trends for increasing gross value of irrigated agricultural production (GVIAP) as available water supplies have increased for (a) fruits, (b) vegetables, (c) fruits and vegetables combined, and (d) total agriculture Source: (ABS, 2022) 6.4.3 Costs of enabling infrastructure A range of infrastructure would be required to support the development of a new irrigation scheme in the Victoria catchment, both within the scheme itself and beyond. Any infrastructure that is not included in the initial water development contract but is required to enable the new water resources to be used effectively (and to achieve their anticipated benefits) will require construction after the contracted project is complete, often at public expense. The types of infrastructure addressed here are those that would not typically be included in a formal CBA or be built by the water infrastructure developer or farmers. Within the context of a large irrigation development, such enabling infrastructure can be considered ‘hard’ or ‘soft’, which can be broadly defined as follows: • Hard infrastructure refers to the physical assets necessary for a development to function. It can include water storage, roads, irrigation supply channels, energy, and processing infrastructure, such as sugar mills, cotton gins, abattoirs and feedlots. • Soft infrastructure refers to the specialised services required for maintaining the economic, health, cultural and social standards of a population. These are indirect costs of a development and are usually less obvious than hard infrastructure costs. They can include expenses that continue after the construction of a development has been completed. Soft infrastructure can include: – physical assets, such as community infrastructure (e.g. schools, hospitals, housing) – non-physical assets, such as institutions, supporting rules and regulations, compensation packages, and law enforcement and emergency services. New processing infrastructure and community infrastructure are particularly pertinent to large, remote, greenfield developments, and these costs to other providers of infrastructure can be substantial, even after a new irrigation scheme has been developed. For example, a review of the Ord-East Kimberley Development Plan (for expansion of the Ord irrigation system by ~15,000 ha) found additional costs of $114 million to the WA Government beyond the planned $220 million state investment in infrastructure already provided to directly support the expansion (Western Australian Auditor General, 2016). This section provides an indication of the additional public and private infrastructure required to support a new irrigation development (once the main water infrastructure and farms are built) and the costs of the additional investments required. The intention is to highlight potentially overlooked costs of infrastructure that is required to realise the benefits of development and population growth in a region, rather than to diminish the potential benefits. Costs of hard infrastructure Establishing new irrigated agriculture in the Victoria catchment would involve the initial costs of land development, water infrastructure (which could include distribution and re-regulation or balancing of storages), and farm set-up (for equipment and facilities on each new farm). It may also involve costs associated with constructing processing facilities, extending electricity networks, and upgrading road transport. The costs of water storage and conveyance are provided in Chapter 5. Indicative costs for processing facilities are provided in Table 6-14, and indicative costs for roads and electricity infrastructure are provided in Table 6-15. Indicative costs for transporting goods to key markets are listed in Table 6-16. All tables are summarises of information provided in the companion technical report on agricultural viability and socio-economics (Webster et al., 2024). Table 6-14 Indicative costs of agricultural processing facilities ITEM CAPITAL COST OPERATING COST COMMENT Meatworks $33 to $100 million $330/head Operational capacity 100,000 head/y Cotton gin $34 to $37 million $1.1 million/y plus $24 to $35 per bale Operational capacity of 80,000 to 95,000 bales/yr Operating costs depend on the scale of the gin, and the source of energy Sugar mill $469 million $39 million/y Operational capacity of 1000 t cane/h, 6-month crushing season Basic mill producing sugar only (no electricity or ethanol) Table 6-15 Indicative costs of road and electricity infrastructure ITEM CAPITAL COST COMMENT Roads Seal dirt road $0.31 to $2.4 million per km Upgrade and widen dirt road to sealed road New bridges and floodway $27.4 million Costs of bridges and floodways vary widely Electricity New generation capacity may also be required Transmission lines $0.34 to $1.57 million per km High-voltage lines deliver bulk flow of electricity from generators over long distances Distribution lines $0.22 to $0.49 million per km Lower-voltage lines distribute power from substations over shorter distances to end users Substation $1.3 to $12.2 million Transformers and switchgear connect transmission and distribution networks Table 6-16 Indicative road transport costs between the Victoria catchment and key markets and ports The top section of the table gives trip costs from the Victoria River Roadhouse to key destinations. The bottom section gives distance-based costs of getting goods from within the catchment to the Victoria River Roadhouse (on unsealed roads) and approximate distance-based costs of getting goods from the Victoria River Roadhouse on sealed roads to other destinations (not specifically listed). DESTINATION TRANSPORT COST Unrefrigerated Refrigerated Cattle Transport costs from Victoria River Roadhouse ($/t) Adelaide 440 515 396 Brisbane 515 604 463 Cairns 393 487 354 Darwin 78 92 70 Fremantle 536 639 482 Karumba 306 368 275 Melbourne 584 654 526 Port Hedland 285 344 257 Sydney 616 692 555 Townsville 354 426 319 Wyndham 65 77 59 Transport costs by distance ($/t/km) Properties to Victoria River Roadhouse 0.32 0.38 0.29 Victoria River Roadhouse to key markets/ports 0.15 0.18 0.14 Costs of soft infrastructure The availability of community services and facilities would play an important role in attracting people to (or deterring them from) living in a new development in the Victoria catchment. If local populations increase as a result of new irrigated developments, then the demand for public services would increase, and provision of those services would need to be anticipated and planned for. Indicative costs for constructing a variety of facilities that may be required for supporting population growth are listed in Table 6-17. Each 1000 people in Australia require 2.3 (in ‘Major cities’) to 4.0 (in ‘Remote and Very remote areas’) hospital beds, served by 16 full-time equivalent (FTE) hospital staff and $3.5 million/year funding to maintain current mean national levels of hospital service (AIHW, 2023). Health care services in remote locations generally focus on providing primary care and some secondary care. More specialised tertiary services tend to be concentrated in referral hospitals, which are generally located in large cities but also serve the surrounding area. Primary schools tend to be smaller and more widespread than secondary schools, which are larger and more centralised. Table 6-17 Indicative costs of community facilities Costs are quoted for Darwin as a reference capital city for northern Australia. Costs in remote parts of northern Australia, including the Victoria catchment, are estimated to be approximately 30% to 60% higher than those quoted for Darwin. School costs were estimated separately based on a number of locations across northern Australia. See the companion technical report on agricultural viability and socio-economics (Webster et al., 2024) for details. ITEM CAPITAL COST COMMENT Hospital $0.2 to $0.5 million per bed Higher end costs include a major operating theatre and a larger hospital area per bed School $27,000 to $35,000 per student Secondary schools tend to be larger and more centralised than primary schools House (each) $585,000 to $850,000 Single- or double-storey house, 325 m2 Unit (each) $230,000 to $395,000 Residential unit (townhouse), 90 to 120 m2 Offices $2400 to $3450 per m2 1 to 3 storeys, outside central businesses district The demand for community services is growing, both from population increases in Australia and rising community expectations. New infrastructure would be built to service that demand, irrespective of any development in the Victoria catchment. However, if new irrigation projects encourage people to live in the Victoria catchment, this could then shift the locations at which some services would be delivered and the associated infrastructure built. The costs of delivering services and building infrastructure are generally higher in very remote locations like the Victoria catchment. The net cost of any new infrastructure built to support development in the Victoria catchment is the difference in the cost of shifting some infrastructure to this very remote location (rather than the full cost of the facilities (Table 6-17), which would otherwise have been built elsewhere). 6.5 Regional-scale economic impact of irrigated development New irrigated development in the Victoria catchment could provide economic benefits to the region in terms of both increased economic activity and jobs. The size of the total economic benefit experienced would depend on the scale of the development, the type of agriculture that was established, and how much spending from the increased economic activities occurred within the region. Regional economic impacts are an important consideration for evaluating potential new water development projects. It was estimated that each million dollars spent on construction within the Victoria catchment would generate an additional $1.06 to $1.09 million of indirect benefits ($2.06 to $2.18 million total regional benefits, including the direct benefit of each million dollars spent on construction). It was estimated that each million dollars of direct benefit from new agricultural activity would generate an additional $0.46 to $1.82 million in regional economic activity (depending on the particular agricultural industry). The full, catchment-wide impact of the economic stimulus provided by an irrigated agriculture or aquaculture development project extends far beyond the impact on those businesses and workers directly involved in either the short term (construction phase) or the longer term (operational phase). Businesses directly benefiting from the project would need to increase their purchases of the raw materials and intermediate products used by their growing outputs. Should any of these purchases be made within the surrounding region, this would provide a stimulus to those businesses from which they purchase, contributing to further economic growth within the region. Furthermore, household incomes would increase as a result of the employment of local residents as a consequence of the direct and/or production-induced business stimuli. As a proportion of this additional household income would be spent in the region, economic activity within the region would be further stimulated. Accordingly, the larger the initial amount of money spent within the region, and the larger the proportion of that money re-spent locally, the greater the overall benefits that would accrue to the region. The size of the impact on the local regional economy can be quantified by regional economic multipliers (derived from I–O tables that summarise expenditure flows between industry sectors and households within the region): a larger multiplier indicates larger regional benefits. These multipliers can be used to estimate the value of increased regional economic activity likely to flow from a stimulus to particular industries, focusing on construction in the short term and various types of agriculture in the longer term. It is also possible to estimate the increase in household incomes in the region, and then estimate the approximate number of jobs represented by the increased economic activity, including both those directly related to the increase in agriculture and those generated indirectly within other industries in the region. Not all expenditure generated by a large-scale development will occur within the local region. The greater the leakage (i.e. the amount of direct and indirect expenditure occurring outside the region), the smaller the resulting economic benefit enjoyed by the region. Conversely, the greater the retention of the initial expenditure and subsequent indirect expenditure within the region, the greater the economic benefit and the number of jobs created within the local region. However, a booming local economy can also bring with it a number of issues that can place upward pressure on prices (including materials, houses and wages) in the region, negating some of the positive impacts of the development. If some of the unemployed or underemployed people within the Victoria catchment could be engaged as workers during the construction or operational phases of the development, this could reduce pressure on local wages and reduce the leakage resulting from the use of fly-in fly-out (FIFO) or drive-in drive-out (DIDO) workers, retaining more of the benefit from the project within the local region. However, the current low unemployment rate within the Victoria catchment (Chapter 3) suggests there may be difficulties in sourcing local workers from within the region. The overall regional benefit created by a particular development depends on both the one-off benefits from the construction phase and the ongoing annual benefits from the operational phase. The benefits from the operational phase may take a number of years to reach the expected level, as new and existing agricultural enterprises learn and adapt to make full use of the new opportunities presented by the development. It is important to note that the results presented here are based on illustrative scenarios incorporating broad assumptions, are derived from an I–O model developed for an I–O region that is much larger than the Victoria catchment study area, and are subject to the limitations of the method. 6.5.1 Estimating the size of regional economic benefits To develop regional multipliers for the Victoria catchment, it was necessary to use the available information and models for the Victoria catchment I–O region. Two I–O models were used, one covering the whole of the NT (Murti and NT Office of Resource Development, 2001) and one based on the adjacent catchment of the Daly River (Stoeckl et al., 2011) (Figure 6-5). For more details, see the companion technical report on agricultural viability and socio-economics (Webster et al., 2024). Additional data are presented to show how the economic circumstances of the Victoria catchment compare with those of the two I–O regions (Table 6-18). The Daly I–O region is more similar in some characteristics to the larger NT I–O region than to the Victoria catchment. However, any benefits of development in the Victoria catchment are likely to spill over into the NT’s capital, Darwin, and would be captured in the larger NT I–O model. Typically, smaller and more remote geographic areas have smaller I–O multipliers, as inter-industry linkages tend to be shallow and the area’s capacity to produce a wide variety of goods is low, meaning that inputs and final household consumption are less likely to be locally sourced than in regions with larger urban centres (Stoeckl and Stanley, 2009; Jarvis et al., 2018). Extent of regional input models map \\FS1-CBR.nexus.csiro.au\{lw-rowra}\work\5_Agriculture_economics\2_Victoria\1_GIS\1_Map_docs\Se-V-506_Map_Australia_and_economic_regions_v1.mxd For more information on this figure please contact CSIRO on enquiries@csiro.au Figure 6-5 Regions used in the input–output (I–O) analyses relative to the Victoria catchment Assessment area Table 6-18 Key 2021 data comparing the Victoria catchment with the related I–O analysis regions VICTORIA CATCHMENT† DALY CATCHMENT I–O REGION† NT I–O REGION‡ Land area (km2) 82,232.0 53,088.5 1,348,094.3 Population 1,600 11,233 232,605 Percentage male 50.35% 51.56% 50.53% Percentage Indigenous 74.68% 32.29% 26.27% Median age 25 32 33 Median household income $57,026 $104,505 $107,172 Contribution of agriculture, forestry and fishing to employment in the region 29.2% 6.6% 2.3% Major industries of employment – top three industries in region (by % of employment 2021) Largest employer in region Agriculture, forestry and fishing Public administration and safety Public administration and safety 2nd largest employer in region Public administration and safety Health care and social assistance Health care and social assistance 3rd largest employer in region Education and training Education and training Education and training Gross value of total $110 million $93 million $746 million † Statistics for Victoria catchment (ABS, 2021) and Daly catchment (ABS, 2021) regions have been estimated using the weighted mean of ABS 2021 census data obtained by SA2 statistical region, with weighting based on the proportion of relevant ABS SA2 statistical regions falling within each catchment region. ‡ ABS 2021 census data (ABS, 2021). § ABS Value of agricultural commodities produced 2020–21 by region, report VACPDCASGS202021 (ABS, 2022). There are wide variations in the size of the multipliers for various industries within the NT and Daly I–O regions. Industries with larger local regional multipliers would be expected to benefit more from development within the I–O region. For example, agricultural industries generated smaller multipliers than construction for both I–O models. However, a simple comparison of I–O multipliers can be misleading when considering the different benefits from regional investment, because some impacts provide a short-term, one-off benefit (e.g. the construction phase of a new irrigation development) while others provide a sustained stream of benefits over the longer term (e.g. the production phase of a new irrigation scheme). A rigorous comparison between specific regional investment options would require NPVs of the full cost and benefit streams to be calculated. 6.5.2 Indirect benefits during the construction phase of a development Initially, building new infrastructure (on-farm and off-farm development, including construction of related supporting infrastructure, such as roads, schools and hospitals) comes at a cost. But the additional expenditure within a region (which puts additional cash into people’s and businesses’ pockets) would increase regional economic activity. This creates a fairly short-term economic benefit to the region during the construction phase, provided that at least some of the expenditure occurs within the region and is not all lost from the region due to leakage. The regional impacts of the construction phase of potential developments were estimated using a scenario approach for the scales of development. The analyses modelled regional impacts for five different indicative sizes of developments in the Victoria catchment. Total capital costs, including costs of labour and materials required by the project, ranged from $250 million to $2 billion. The smallest scale of development in Table 6-19, with a capital cost of $250 million, broadly represents approximately 20 new farm developments with their own on-farm water sources enabling approximately 10,000 ha of irrigation for horticulture and broadacre farming (based on costing information from the companion technical report on agricultural viability and socio-economics (Webster et al., 2024)). The second-smallest scenario, with a $500 million capital cost, could represent a similar development to the first but with 20,000 ha of new irrigated farmland; this level of investment could also include a new processing facility (such as a cotton gin) required by (and supported by) this scale of agricultural development. Alternatively, the $500 million development could represent a large off-farm water infrastructure development (e.g. see Table 6- 2) and related farm establishment costs. The larger scales of development, at $1 billion or $2 billion, shown in Table 6-19, indicate outcomes from combining potential developments in various ways (such as one large off-farm dam and multiple on-farm water sources). They also include investment in indirect supporting infrastructure across the region, such as roads, electricity and community infrastructure (see indicative costs in Section 6.4.3). The proportion of expenditure during the construction phase that would be spent within the region depends on the types of costs, including labour, materials and equipment. It is likely that wages would be paid to workers sourced both from within the region and from elsewhere. The likely proportion of labour costs for each source of workers would depend on the availability of appropriately skilled labour within the region. For example, a highly populated region (more than 100,000 people) with a high unemployment rate (more than 10%) and skilled labour force is likely to be able to supply a large proportion of the workers required from within the region. However, a sparsely populated region like the Victoria catchment is more likely to need to attract many workers from outside the region, either on a FIFO or DIDO basis or by encouraging migration to the region. Similarly, some regions may be better able to supply a large proportion of the required materials and equipment from within the region, whereas construction projects in other locations may not be able to source what they need locally and instead need to import a significant proportion into the region from elsewhere. The low representation of the required supplying industries in the Victoria catchment means that most construction supplies would be likely to be sourced from other parts of Australia (and internationally). A review of five large dam projects across the country showed that the proportions of local construction expenditure sourced within a region (as opposed to being imported, with no impact on the local regional economy) varied significantly. Thus, the analyses considered three levels for the proportion spent locally: 65% (i.e. low leakage), 50%, and 35% spent locally (i.e. high leakage). However, note that leakage might be higher (i.e. <35% spent locally) for a very remote region like the Victoria catchment. In cases of high leakage, the knock-on benefits would instead occur in the regions supplying the goods and services (such as in the wider NT I–O region). Table 6-19 shows estimates of the regional economic benefit for the construction phase of a new development for four scales of scheme capital cost ($0.25 billion to $2 billion) and the three levels of leakage described above. These results show that the size of the regional economic benefit experienced increases substantially as the proportion of scheme construction costs spent within the region increases. Given the low urban development within the Victoria catchment and its proximity to Darwin, leakage may be towards the high end of the range examined for the Victoria catchment (but to the middle of the range for the NT I–O region, which includes Darwin). For example, if $500 million was spent on construction for a new dam project and 35% of that was spent within the Victoria catchment (and 50% with the wider NT I–O region), the construction multiplier would only apply to the portion spent locally. This would give an overall regional economic benefit of $380 million within the Victoria catchment based on the Daly I–O model estimate (or $520 million for the wider NT region based on the NT I–O model estimate). Additional benefits would flow to other regions receiving the remaining funds. Table 6-19 Regional economic impact estimated for the total construction phase of a new irrigated agricultural development (based on two independent I–O models) Estimates represent an upper bound, because some assumptions of I–O analysis are violated in the case of such a large public investment in a region where existing irrigated agricultural activity is so low. Leakage to other regions and other countries is accounted for by reducing the proportion of expenditure (and benefits) within the I–O region. I–O = input–output. DEVELOPMENT CAPITAL COST ($ billion) TOTAL REGIONAL ECONOMIC ACTIVITY WITHIN I–O REGION AS A RESULT OF THE CAPITAL COST OF THE DEVELOPMENT ($ billion) Victoria catchment based on NT IO dl Victoria catchment based on Daly catchment IO dl Proportion of total scheme-scale capital cost made locally within the I–O region 65% 50% 35% 65% 50% 35% 0.250 0.33 0.26 0.18 0.35 0.27 0.19 0.500 0.67 0.52 0.36 0.71 0.55 0.38 1.000 1.34 1.03 0.72 1.42 1.09 0.76 2.000 2.68 2.06 1.44 2.83 2.18 1.53 6.5.3 Indirect benefits during the operational phase of a development Regional impacts of irrigation development on the two I–O regions are presented for scenarios using four indicative scales of increase in GVAP ($25, $50, $100 and $200 million per year, indicative of potential outcomes). At the low end ($25 million/year), this could represent 10,000 ha of new plantation timber, while the high end ($200 million/year) could represent 10,000 ha of mixed broadacre cropping and horticulture (based on farm financial estimates for the various crops presented in Chapter 4), with other crop options falling in between. Estimated regional impacts are shown as the total increased economic activity (Table 6-20) in the NT and Daly I–O regions and the associated estimated increases in incomes and employment (Table 6-21) for each category of agricultural activity (beef cattle, agriculture excluding beef cattle, and aquaculture, forestry and fishing for the NT I–O model; and agriculture of all types for the Daly I–O model). As can be seen from the economic impacts (Table 6-20), an irrigation scheme that promotes aquaculture, forestry and fishing could have a larger regional impact in the NT I–O region than a scheme promoting beef cattle or agriculture excluding beef cattle. These differences result from the various industry multipliers estimated for the NT I–O. Table 6-20 Estimated regional economic impact per year in the Victoria catchment resulting from four scales of direct increase in agricultural output (rows) for the different categories of agricultural activity (columns) from two I–O models Increases in agricultural output are net of the annualised value of contribution towards the construction costs. Estimates represent an upper bound because some assumptions of I–O analysis are violated in the case of such a large public investment in a region where existing agricultural activity is so low. Leakage to other regions and other countries is accounted for by reducing the proportion of expenditure (and benefits) within the I–O region. DIRECT INCREASE IN AGRICULTURAL OUTPUT PER YEAR NET OF CONTRIBUTION TO CONSTRUCTION COSTS ($ million) TOTAL ANNUAL VALUE OF INCREASED ECONOMIC ACTIVITY IN I–O REGION– DIRECT, PRODUCTION-INDUCED AND CONSUMPTION-INDUCED ($ million) Victoria catchment based on NT I–O model Victoria catchment based on Daly catchment I–O model Type of agricultural development Beef cattle Agriculture excluding beef cattle Aquaculture, forestry and fishing Agriculture of all types 25 51 37 70 51 50 103 73 141 102 100 205 146 282 203 200 411 292 563 406 Table 6-21 Estimated impact on annual household incomes and full-time equivalent (FTE) jobs within the Victoria catchment resulting from four scales of direct increase in agricultural output (rows) for the various categories of agricultural activity (columns) Increases in agricultural output are assumed to be net of the annualised value of contributions towards the construction costs. Estimates are based on Type ll multipliers determined from two independent I–O models for each year of agricultural production. Estimates represent an upper bound, because some assumptions of I–O analysis are violated in the case of such a large public investment in a region where existing agricultural activity is so low. Leakage to other regions and other countries is accounted for by reducing the proportion of expenditure (and benefits) within the I–O region. DIRECT INCREASE IN AGRICULTURAL OUTPUT PER YEAR NET OF ANY CONTRIBUTION TO CONSTRUCTION COSTS ($ million) TOTAL ANNUAL VALUE OF INCREASED ECONOMIC ACTIVITY IN I–O REGION – DIRECT, PRODUCTION-INDUCED AND CONSUMPTION-INDUCED ($ million or FTE) Victoria catchment based on NT I–O model Victoria catchment based on Daly catchment I–O model Type of agricultural development Beef cattle Agriculture excluding beef cattle Aquaculture, forestry and fishing Agriculture of all types Additional incomes expected to flow to Indigenous households from development ($ million) 25 0.8 0.1 0.9 0.5 50 1.6 0.2 1.7 1.0 100 3.3 0.4 3.4 2.0 200 6.5 0.8 6.8 4.0 Additional incomes expected to flow to non-Indigenous households from development ($ million) 25 7.1 1.7 14.3 6.75 50 14.2 3.3 28.7 13.5 100 28.4 6.7 57.4 27.0 200 56.8 13.4 114.7 54.0 Additional jobs estimated to be created (FTE) 25 108 24 206 98 50 215 48 413 197 100 430 97 825 394 200 860 193 1,650 788 The results for employment (Table 6-21) are closely related to those for impacts on regional economic activity, but the two measures do reveal some differences. Additional FTE jobs arising in the region may require additional community infrastructure (e.g. schools, health services) if workers move to fill these jobs from other parts of the country, resulting in population growth. However, additional infrastructure would not be necessary should these additional jobs be filled by currently unemployed or underemployed local people. Estimates of the expected increases in incomes were divided between Indigenous and non-Indigenous households, using methods outlined in Jarvis et al. (2018), with most increases expected to flow to non-Indigenous households (Table 6-21). For example, if new irrigation development in the Victoria catchment directly enabled an extra $100 million of cropping output per year, the region could benefit from an extra $146 million (NT I–O estimate) to $203 million (Daly I–O estimate) of economic activity recurring annually (Table 6- 20) and generate approximately 100 to 852 new FTE ongoing jobs, depending on the type of agriculture (Table 6-21). 6.6 References ABS (2021) Water account, Australia, 2019–20 financial year. Australian Bureau of Statistics, Canberra. Viewed 19 December 2022, https://www.abs.gov.au/statistics/environment/environmental-management/water- account-australia/latest-release#gross-value-of-irrigated-agricultural-production-gviap-. ABS (2022) Value of agricultural commodities produced, Australia 2021–22. Australian Bureau of Statistics, Canberra. Viewed 19 December 2022, Hyperlink to: Agricultural commodities, Australia . AIHW (2023) Australia’s hospitals at a glance: web report. Australian Institute of Health and Welfare, Canberra. Viewed 1 March 2023, Hyperlink to: Australia's hospitals at a glance: web report . Ansar A, Flyvbjerg B, Budzier A and Lunn D (2014) Should we build more large dams? The actual costs of hydropower megaproject development. Energy Policy 69, 43–56. Hyperlink to: Should we build more large dams? The actual costs of hydropower megaproject development . Ash A, Gleeson T, Cui H, Hall M, Heyhoe E, Higgins A, Hopwood G, MacLeod N, Paini D, Pant H, Poulton P, Prestwidge D, Webster T and Wilson P (2014) Northern Australia: food and fibre supply chains study project report. CSIRO and ABARES, Australia. Viewed 13 September 2024, https://www.csiro.au/en/research/natural-environment/land/food-and-fibre CRCNA (2020). Northern Australian broadacre cropping situational analysis. ST Strategic Services and Pivotal Point Strategic Directions (Issue July). Cooperative Research Centre for Developing Northern Australia, Townsville. Viewed 13 September 2024, https://crcna.com.au/wp-content/uploads/2024/05/NA-Cropping-situational-August.pdf Devlin K (2024) Conceptual arrangements and costings of hypothetical irrigation developments in the Victoria and Southern Gulf catchments. A technical report from the CSIRO Victoria and Southern Gulf Water Resource Assessments for the National Water Grid. CSIRO, Australia. Flyvbjerg B, Holm MS and Buhl S (2002) Underestimating costs in public works projects: error or lie? Journal of the American Planning Association 68(3), 279–295. Hyperlink to: Underestimating costs in public works projects: error or lie? Infrastructure Australia (2021a) Post completion review. Stage 4 of the Assessment Framework. Infrastructure Australia, Canberra. Viewed 1 March 2023, Hyperlink to: Post completion review. Stage 4 of the Assessment Framework . Infrastructure Australia (2021b) Guide to economic appraisal. Technical guide of the Assessment Framework. Infrastructure Australia, Canberra. Viewed 1 March 2023, Hyperlink to: Guide to economic appraisal Jarvis D, Stoeckl N, Hill R and Pert P (2018) Indigenous land and sea management programs: can they promote regional development and help ‘close the (income) gap’? Australian Journal of Social Issues 53(3), 283–303. Hyperlink to: Indigenous land and sea management programs: can they promote regional development and help ‘close the (income) gap’? Murti S and Northern Territory Office of Resource Development (2001) Input–output multipliers for the Northern Territory 1997–1998. Retrieved from Office of Resource Development, Darwin. Hyperlink to: Input–output multipliers for the Northern Territory 1997–1998 NWGA (National Water Grid Authority) (2022) National Water Grid investment framework. Australian Government Department of Climate Change, Energy, the Environment and Water, Canberra. Viewed 1 March 2023, Hyperlink to: National Water Grid Investment Framework . NWGA (National Water Grid Authority) (2023) Project administration manual: National Water Grid Fund. Australian Government Department of Climate Change, Energy, the Environment and Water, Canberra. Viewed 1 March 2023, https://www.nationalwatergrid.gov.au/framework. Odeck J and Skjeseth T (1995) Assessing Norwegian toll roads. Transportation Quarterly 49(2), 89– 98.Viewed 13 September 2024,Hyperlink to: Assessing Norwegian toll roads Petheram C, and McMahon TA (2019) Dams, dam costs and damnable cost overruns. Journal of Hydrology X 3, 100026. Hyperlink to: Dams, dam costs and damnable cost overruns . Stoeckl N and Stanley O (2009) Maximising the benefits of development in Australia’s Far North. Australasian Journal of Regional Studies 15(3), 255–280. Viewed 13 September 2024, https://www.anzrsai.org/assets/Uploads/PublicationChapter/397-153Stoeckl.pdf. Stoeckl N, Esparon M, Stanley O, Farr M, Delisle A and Altai Z (2011) Socio-economic activity and water use in Australia’s tropical rivers: a case study in the Mitchell and Daly river catchments. Charles Darwin University, Darwin. Viewed 15 December 2022, Hyperlink to: Socio-economic activity and water use in Australia’s tropical rivers: a case study in the Mitchell and Daly river catchments . Stokes C and Jarvis D (2021) Economic assessment. In: Petheram C, Read A, Hughes J, Marvanek S, Stokes C, Kim S, Philip S, Peake A, Podger G, Devlin K, Hayward J, Bartley R, Vanderbyl T, Wilson P, Pena Arancibia J, Stratford D, Watson I, Austin J, Yang A, Barber M, Ibrahimi T, Rogers L, Kuhnert P, Wang B, Potter N, Baynes F, Ng S, Cousins A, Jarvis D and Chilcott C. An assessment of contemporary variations of the Bradfield Scheme. A technical report to the National Water Grid Authority from the Bradfield Scheme Assessment. CSIRO, Canberra. 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Hyperlink to: Ethics and advocacy in forecasting for public policy Webster A, Jarvis D, Jalilov S, Philip S, Oliver Y, Watson I, Rhebergen T, Bruce C, Prestwidge D, McFallan S, Curnock M and Stokes C (2024) Financial and socio-economic viability of irrigated agricultural development in the Victoria catchment, Northern Territory. A technical report from the CSIRO Victoria River Water Resource Assessment for the National Water Grid. CSIRO, Australia. Western Australian Auditor General (2016) Ord-East Kimberley Development. Report 20: September 2016. Office of the Auditor General Western Australia, Perth. Viewed 15 December 2022, Hyperlink to: Ord-East Kimberley Development . World Commission on Dams (2000) Dams and development. A new framework for decision making. Retrieved from Earthscan Publications Ltd, UK. Viewed 20 December 2022, Hyperlink to: Dams and development. A new framework for decision making . Yang A, Petheram C, Marvanek S, Baynes F, Rogers L, Ponce Reyes R, Zund P, Seo L, Hughes J, Gibbs M, Wilson PR, Philip S and Barber M (2024) Assessment of surface water storage options in the Victoria and Southern Gulf catchments. A technical report from the CSIRO Victoria River and Southern Gulf Water Resource Assessments for the National Water Grid. CSIRO Australia. 7 Ecological, biosecurity, off-site, downstream and irrigation-induced salinity risks Danial Stratford, Linda Merrin, Simon Linke, Lynn Seo, Rocio Ponce Reyes, Rob Kenyon, Peter R Wilson, Justin Hughes, Heather McGinness, John Virtue, Katie Motson, Nathan Waltham Chapter 7 discusses a range of potential risks to be considered before establishing a greenfield agriculture or aquaculture development. These include ecological implications of altered flow regimes, biosecurity considerations, irrigation drainage and aquaculture discharge water, and irrigation-induced salinity. The key components and concepts of Chapter 7 are shown in Figure 7-1. Figure 7-1 Schematic diagram of the environmental components where key risks can manifest during and after the establishment of a greenfield irrigation or aquaculture development, with numbers in blue specifying sections in this report For more information on this figure please contact CSIRO on enquiries@csiro.au 7.1 Summary This chapter provides information on the potential ecological, biosecurity, off-site, and downstream impacts, as well as the irrigation-induced salinity risks to the catchment of the Victoria River from greenfield agriculture or aquaculture development. It is principally concerned with the potential impact from these developments on the broader environment, but also considers biosecurity risks to the enterprises themselves. The ecological impacts of vegetation clearing associated with irrigated agriculture are not explicitly examined in the Assessment as it is considered of secondary concern to potential impacts on water dependent ecological assets. This is because irrigated agriculture occupies a very small proportion of the landscape (typically less than 0.5%) but can result in a disproportionately high degree of regulation of river flow. Consequently, the Assessment placed greatest effort in understanding the potential ecological impacts of changes in streamflow on aquatic dependent ecosystems. 7.1.1 Key findings Ecological implications of altered flow regimes The flow regime in northern Australia is highly variable with large seasonal and inter-year variability. The natural flow regime is important for supporting species, habitats and a range of ecosystem functions. Species life-histories are often intricately linked to specific flow conditions considering the magnitude, timing and frequency of flow events. The ecological assets considered in this report represent a range of flow dependencies and have different spatial patterns of occurrence across the catchment. For ecology: • High flows provide a range of important functions including providing connectivity for movement, increasing productivity and nutrient exchange, providing cues for spawning and migration, and wetting habitat and supporting vegetation growth and persistence. The magnitude, duration and timing of high flows is important in ecological systems. • Low flows are also an important component of the flow regime with many species adapted to these conditions. Persistent waterholes provide important refuge habitat from environmental conditions and the higher levels of predation that may occur in connected rivers. For many species refuge waterholes function as a source for recolonisation during the wet season. Persistence in low flows during dry periods can help support suitable habitat conditions including thermal and water quality for species in connected rivers and in supporting riparian vegetation and movement and provide a source of water within the broader landscape. • The timing of flow events is important in supporting life-cycle processes including breeding and migration cues for aquatic species. The timing of flood events and the associated increase in productivity supports function in the river channel and connected marine environments. Although irrigated agriculture may occupy only a small percentage of the landscape, relatively small areas of irrigation can use large quantities of water, and the resulting changes in the flow regime can have profound effects on flow-dependent flora and fauna and their habitats. Changes in river flow may extend considerable distances downstream and onto the floodplain, including into the marine environment and their impacts can be exacerbated by other changes, including changes to connectivity, water quality and invasive species. The magnitude and spatial extent of ecological impacts arising from water resource development are highly dependent on the type of development, location, extraction volume and mitigation measures implemented. Ecological impacts, inferred here by calculating change in ecological flow dependency for a range of freshwater-dependent ecological assets. For water harvesting, impacts accumulate downstream, so ecological assets found near the bottom of the catchment experienced the greatest mean catchment impact. The largest catchment mean changes in flow dependencies for assets was for salt flats, mangroves, floodplain wetlands and banana prawns, all with moderate mean change in flow dependencies across their respective nodes. The largest single-site flow change under water harvesting scenarios were major, for assets including for cryptic waders, threadfin, prawns and floodplain wetlands. Mitigation strategies that protect low flows and first flows of a wet season are successful in reducing impacts to ecological assets. These can be particularly effective if implemented for water harvesting developments. At equivalent volumes of water extraction, imposing an end-of-system (EOS) annual flow requirement, where water harvesting can only commence after a specified volume of water has flowed past the EOS and into the Joseph Bonaparte Gulf, is an effective mitigation measure for water harvesting. However, the early wet-season streamflow in the Baines River is only moderately correlated with the early wet-season streamflow in the Victoria River, hence assigning an EOS annual flow requirement for each river may result in better ecological outcomes than a single EOS annual flow requirement for the entire catchment. For EOS annual flow requirements greater than 200 GL, additional mitigation measures (e.g. increasing pump-start capacity or decreasing pump rate) have little additional modelled ecological benefit. A dry future climate has the potential to result in a larger mean change to ecological flow dependencies across the Victoria catchment than the largest physically plausible water resource development scenarios. However, the perturbations to flow arising from a combined drier future climate and water resource development result in greater impacts on ecology–flow dependency than either factor on their own. For instream dams, location matters, and there is potential for high risks of local impacts. Improved outcomes are associated with maintaining attributes of the natural flow regime with transparent flows (flows allowed to ‘pass through’ the dam for ecological purposes). Potential dams located in small headwater catchments may result in a major change in the ecological flow dependency immediately downstream of the dam. However, impacts reduce downstream with the accumulation of additional tributary flows, so when averaged over the entire catchment or measured at the EOS, the change in ecological flow dependency is minor. Providing transparent flows improves flow regimes for ecology by reducing the mean yield of potential dams. Mean outcomes for fish assets can be improved from minor to negligible, and for waterbirds from moderate to minor, at catchment scales for the scale of scenarios explored. Biosecurity considerations Biosecurity is the prevention and management of pests, weeds and diseases, both terrestrial and aquatic, to limit their economic, environmental, social and cultural impacts. Economic impacts include reduced crop yield and product quality, interference with farming operations, loss of market access, and costs of implementing control measures. Environmental impacts include loss of biodiversity and changes to ecosystem processes, such as fire regimes. Social and cultural impacts of pests, weeds and diseases include diminished value of areas for recreational or traditional uses. Despite its relative isolation, there are many human-mediated and natural pathways by which pests, weeds and diseases can spread to and within the Victoria catchment. New pests, weeds and diseases may spread from adjacent regions, other parts of Australia or even neighbouring countries. Biosecurity is a shared responsibility that requires governments, industries and the community to each take steps to limit the introduction and spread of pests, weeds and diseases, to detect and respond to incursions and to manage the impacts of key biological threats. A variety of current and potential pests, weeds and diseases could have an impact on irrigated cropping in the Victoria catchment. These include fall armyworm (Spodoptera frugiperda, which consumes C4 grass crops), cucumber green mottle mosaic virus (Tobamovirus), which infects a wide range of cucurbit crops), incursion risks from overseas, such as citrus canker (Xanthomonas citri subsp. citri), exotic fruit flies, and parthenium weed (Parthenium hysterophorus) (as a competitor, contaminant and allergen). Farm biosecurity planning to identify, prevent, detect and manage key pest, weed and disease threats is fundamental to a successful enterprise. Such planning includes following government and industry best practice regarding movement of plants, plant products and machinery, control of declared species, pesticide use, farm stewardship and market access requirements. Preventive biosecurity practices are crucial in aquaculture facilities as diseases can be difficult to eliminate. There are many diseases of production concern, whether overseas, having entered Australia (e.g. white spot syndrome virus of crustaceans) or naturally occurring in Australian ecosystems. Aquaculture biosecurity planning needs to consider hygiene actions needed for key pathways of disease entry, early detection and diagnosis, quarantining and treatment. Invasive species, whether pest, weed or disease, are commonly characterised as occurring across multiple land uses in a landscape. Their impacts will vary between land uses, but their coordinated control requires action across all tenures. There are various high-impact weeds declared in the NT that are present in or threaten to invade the Victoria catchment, including aquatic plants, grasses, shrubs and trees. There are also pest vertebrates (e.g. large feral herbivores, exotic fish), pest invertebrates (e.g. exotic ants) and plant diseases (e.g. Phytophthora spp.). NT Government legal requirements to control declared pests, weeds and diseases need to be followed. Regional and local irrigation and industry infrastructure development, including road networks, should include prevention and management of invasive species in their environmental planning processes. Choice of crops and aquaculture species should also consider their invasive risk and any management required to prevent their spread into the environment. Off-site and downstream impacts Agriculture can affect the water quality of downstream freshwater, estuarine and marine ecosystems. The principal pollutants from agriculture are nitrogen, phosphorus, total suspended solids, herbicides and pesticides. Most of the science in northern Australia concerned with the downstream impacts of agricultural development has been undertaken in the eastern-flowing rivers that flow into the Great Barrier Reef lagoon. Comparatively little research on the topic has been done in the rest of northern Australia. Degraded water quality can cause a loss of aquatic habitat, biodiversity, and ecosystem services. Increased nitrogen and phosphorus can cause plankton blooms and weed infestation, increase hypoxia (low oxygen levels) and result in fish deaths. Pesticides, used to increase agricultural productivity, can harm downstream aquatic ecosystems, flora and fauna. As with fertiliser nutrients, pesticides can enter surface water bodies and groundwater via infiltration, leaching, and runoff from rainfall events and irrigation. Losses via runoff or deep drainage are the main pathways by which agricultural pollutants enter water bodies. Management of irrigation or agricultural drainage waters is a key consideration when evaluating and developing new irrigation systems, and it should be given careful consideration during the planning and design process. Seasonal hydrology, particularly ‘first-flush’ events following irrigation or significant rainfall, plays a critical role in determining water quality. Studies have shown that pesticide concentrations in runoff are highest following initial irrigation events but decrease in subsequent events. Similarly, nitrogen concentrations in runoff are often higher following early-season rainfall, when crops have not yet fully absorbed available nitrogen, leading to increased transport in runoff. Minimising drainage water by using best-practice irrigation design and management should be a priority in any new irrigation development in northern Australia. While elevated contaminants and water quality parameters can harm the environment and human health, there are several processes by which aquatic ecosystems can partially process contaminants and regulate water quality. Denitrification is a naturally occurring process that can remove and reduce nitrogen concentrations within a water body. Phosphorus, however, does not have a microbial reduction process equivalent to denitrification. Instead, if it is not temporarily taken up by plants, phosphorus can be adsorbed onto the surface of inorganic and organic particles and stored in the soil, or deposited in the sediments of water bodies, such as wetlands. Aquaculture can be impacted by poor water quality and can also contribute to poor water quality unless aquaculture operations are well managed. Aquaculture species are particularly vulnerable to some of the insecticides and other chemicals used in agricultural, horticultural and mining sectors, and in industrial and domestic settings. Aquaculture management is designed to discharge water that contains low amounts of nutrients and other contaminants. The aim is for discharge waters to have similar physiochemical parameters to the source water. Because aquaculture management in northern Australia has largely been developed to ensure that the waters of the Great Barrier Reef lagoon do not receive excessive contaminants they typically operate under world’s best practice. Irrigation-induced salinity Naturally occurring areas of salinity or ‘primary salinity’ occur in the landscape, with ecosystems adapted to the saline conditions. Any change to landscape hydrology, including clearing and irrigation, can mobilise salts, resulting in environmental degradation in the form of ‘secondary salinity’. Rising groundwater can mobilise salts in the soil and substrate materials, moving the salts into the plant root zone and/or discharging salts on lower slopes, in drainage depressions or in nearby streams. Soil knowledge and best-practice management of irrigation timing and application rates can reduce the risk of irrigation-induced salinity. It should be noted that the material in this chapter provides general information regarding soils suitable for irrigation development. The risk of secondary salinisation at a specific location in the Southern Gulf catchments can only be properly assessed by undertaking detailed field investigations at a local scale. Existing salinity is not prominent in the Assessment area apart from the salt plains along the coast, which are not considered for irrigation development. However, the cracking clay soils on the Armraynald Plain, particularly the black soils along the Gregory River backplain, have subsoils that are high in salt and susceptible to irrigation-induced secondary salinity. These cracking clay soils can be successfully irrigated if they can be managed to prevent waterlogging and the mobilisation of salts in the profile. The clay soils (SGG 9) on the Barkly Tableland have low subsoil salt levels. Where they are underlain by porous limestone and dolomite, a build-up of salts due to irrigation is not expected. The sandy, loamy and sand or loam over friable brown, yellow and grey clay soils on the Doomadgee Plain also have negligible salts within the soil profile. However, due to other risk factors, care would need to be exercised when clearing the silver box, bloodwood and broad-leaf paperbark savanna landscapes for rainfed or irrigated cropping. Groundwater aquifers contained by underlying ferricrete, the likelihood of soils having variable depths, and the very gently undulating plain make it difficult to manage irrigation water discharge on lower slopes and in drainage depressions, causing salts to accumulate in these areas in the long term. In places where these soils are shallow, it would be necessary to monitor the depth of watertables and manage irrigation rates accordingly. In addition, over-irrigation is likely to have off-site impacts in the long term, as the lateral flow of water can ‘wick’ from the lower slopes in these landscapes to form scalds. From these scalds, salts can potentially be mobilised towards nearby streams. 7.2 Introduction Water and irrigation development can result in complex and in some cases unpredictable changes to the surrounding environment. For instance, before the construction of the Burdekin Falls Dam, the Burdekin Project Committee (1977) and Burdekin Project Ecological Study (Fleming et al., 1981) concluded that the dam would improve water quality and clarity in the lower river and that para grass (Brachiaria mutica), an invasive weed from Africa that was then present at relatively low levels, could become a useful ecological element as a result of increased water delivery to the floodplain. However, the Burdekin Falls Dam has remained persistently turbid since construction in 1987, greatly altering the water quality and ecological processes of the river below the dam and the many streams and wetlands into which that water is pumped on the floodplain (Burrows and Butler, 2007). Para grass and more recently hymenachne (Hymenachne amplexicaulis), a plant from South America, have become serious weeds of the floodplain wetlands, rendering these wetlands unviable as habitat for most aquatic biota that formerly occurred there (Perna, 2003, 2004; Tait and Perna, 2000). Thus, there are limitations to the level of advice that can be provided in the absence of specific development proposals, so this section provides general advice on those considerations or externalities that are most strongly affected by water resource and irrigation developments. It is not possible to discuss every potential change that could occur. In particular, the ecological impacts of vegetation clearing associated with irrigated agriculture are not explicitly examined as it is considered of secondary concern to potential impacts on water dependent ecological assets. This is because irrigated agriculture occupies a very small proportion of the landscape (typically less than 1%) but can result in a disproportionately high degree of regulation of river flow. Consequently, the Assessment placed greatest effort in understanding the potential ecological impacts of changes in streamflow on aquatic dependent ecosystems. It is noted, however, that areas of high agricultural potential may also be highly valued with respect to biodiversity conservation (Kutt et al., 2009). For these and other reasons the northern jurisdictions have formal processes in place for the approval (or not) of clearing native vegetation. Clearing approvals are only provided by the jurisdictions where they consider the ecological impact to be minimal given the extent and protection of vegetation type in the region. The remainder of the chapter is structured as follows: •Section 7.3 Ecological implications of altered flow regimes: examines how river regulationaffects inland and freshwater assets in the Victoria catchment and marine assets in the near- shore marine environment. It also examines how the impacts can be mitigated. •Section 7.4 Biosecurity considerations: discusses the risks presented to an irrigationdevelopment by diseases, pests and weeds, and the risks new agriculture or aquacultureenterprise in the Victoria catchment may present to the wider industry and broader catchment. •Section 7.5 Off-site and downstream impacts: considers how agriculture can affect the waterquality of downstream freshwater, estuarine and marine ecosystems. •Section 7.5 Irrigation-induced salinity: briefly discusses the risk of irrigation-induced salinity toan irrigation development and the downstream environment in the Victoria catchment. It should be noted that the discussions in section 7.4 to 7.5 are more generalised in nature than the material presented in Section 7.3, as the actual risks tend to be highly scenario- and location- specific, and appropriate data are typically missing. Other externalities associated with water resource and irrigation development discussed elsewhere in this report include the direct impacts of the development of a large dam and reservoir on: •Indigenous cultural heritage (Section 3.4) •the movement of aquatic species and loss of connectivity (Section 5.4) •terrestrial ecosystems within the reservoir inundation area (Section 5.4). These externalities are rarely factored into the true costs of water resource or irrigation development. Even in parts of southern Australia, where data are more abundant, it is very difficult to express these costs in monetary terms, as the perceived changes are strongly driven by values, which can vary considerably within and between communities and fluctuate over time. Therefore, the material in this chapter is presented as a stand-alone analysis to help inform conversations between communities and government, and subsequent decisions. It is important to note that this chapter primarily focuses on key risks resulting from irrigated agriculture and to a lesser extent aquaculture, although the section on biosecurity considers both risks to the enterprise and risks emanating from the enterprise into the broader environment. Additional risks to irrigated agriculture and aquaculture are discussed elsewhere in this report, including risks associated with: •flooding (Section 2.5) •sediment infill of large dams and reservoir inundation (Section 5.4) •reliability of water supply (sections 5.4 and 6.3) •timing of runs of failed years on the profitability of an enterprise (Section 6.3). The material within this chapter is largely based on the companion technical reports on ecology asset analysis (Stratford et al., 2024a) but also draws upon findings presented in the Northern Australia Water Resource Assessment technical reports on agricultural viability (Ash et al., 2018) and aquaculture viability (Irvin et al., 2018). Further information can be found in those reports. 7.3 Ecological implications of altered flow regimes 7.3.1 Water resource development and flow ecology The ecology of a river is intricately linked to its flow regime, with species broadly adapted to the prevailing conditions under which they occur. Flow-dependent flora, fauna and habitats are defined here as those sensitive to changes in flow and those sustained by either surface water or groundwater flows or a combination of these. In rivers and floodplains, the capture, storage, release, conveyance and extraction of water alters the environmental template on which the river functions, and water regulation is frequently considered one of the biggest threats to aquatic ecosystems worldwide (Bunn and Arthington, 2002; Poff et al., 2007). Water resource development can act during both wet and dry periods to change the magnitude, timing, duration and frequency of flows (Jardine et al., 2015; McMahon and Finlayson, 2003). Impacts on fauna, flora and habitats associated with flow regime change often extend considerable distances downstream from the source of the impacts and into near-shore coastal and marine areas as well as onto floodplains (Burford et al., 2011; Nielsen et al., 2020; Pollino et al., 2018). Water resource development can also result in changes to water quality (see Section 7.5). The environmental risks associated with water resource development are complex, and particularly so in northern Australia. This is in part because of the diversity of species and habitats distributed across and within the catchments and the near-shore marine zones, and because water resource development can produce a broad range of direct and indirect environmental impacts. These impacts can include changes to flow regime, loss of habitat, loss of function such as connectivity, changes to water quality, and the establishment of pest species. Instream dams create large bodies of standing water that inundate terrestrial habitat and result in the loss of the original stream and riverine conditions (Nilsson and Berggren, 2000; Schmutz and Sendzimir, 2018). Storages can capture flood pulses and reduce the volume and extent of water that transports important nutrients into estuaries and coastal waters via flood plumes (Burford and Faggotter, 2021; Burford et al., 2016; Tockner et al., 2010). Further, even minor instream barriers can disrupt migration and movement pathways, causing loss of essential habitat for species that need passage along the river at key times, and fragmentation of populations (Crook et al., 2015; Pelicice et al., 2015). With water resource development and irrigation comes increased human activity. This can add additional pressures, including changes in fire regimes, additional harvesting pressures, and biosecurity risks associated with invasive or pest species transferring into new habitats or increasing their advantage in modified habitats (Pyšek et al., 2020). Section 7.3 of this report analyses the risks to flow-dependent freshwater, estuarine and near- shore marine assets, as well as terrestrial systems, resulting from changes in the flow regime change in the catchment of the Victoria River. See the companion technical report on water storages (Yang et al., 2024) for more details on the impacts of habitat loss within potential dam impoundments and connectivity loss due to the development of new instream barriers. Refer to the companion technical report on ecological asset descriptions in the Victoria catchment by Stratford et al. (2024a) for more details on the flow ecology of the Victoria catchment and its ecological values. The asset description report (Stratford et al., 2024a) also qualitatively examines existing and potential threatening processes for freshwater-dependent ecological assets, including possible influences of synergistic impacts. For more details of the ecological asset analysis and details of analysis for all assets, see Stratford et al. (2024b). 7.3.2 Ecology of the Victoria catchment The comparatively intact landscapes of the Victoria catchment hold significant ecological and environmental values and are important for the ecosystem services they provide, including recreational activities, tourism, fisheries (Indigenous, recreational and commercial), military training, and agricultural production (notably cattle grazing on native pastures). The Victoria River is a large river originating to the south of the Judbarra National Park. At over 500 km in length, it is the second longest rivers in the NT with permanent water. The catchment area of 82,400 km2 makes it one of the largest ocean-flowing catchments in the NT, with flows that enter the south- eastern edge of the Joseph Bonaparte Gulf. The catchment and the surrounding marine environment contain a rich diversity of important ecological assets, including species, ecological communities, habitats, and ecological processes and functions. The ecology of the Victoria River is maintained by its flow regime, shaped by the catchment’s complex geomorphology and topography, and driven by patterns of seasonal rainfall, evapotranspiration, and groundwater discharge. The protected areas located in the Victoria catchment include one gazetted national park (Judbarra), a proposed extension to an existing national park (Keep River), the Commonwealth Joseph Bonaparte Gulf Marine Park, two Indigenous Protected Areas and two Directory of Important Wetlands in Australia (DIWA) sites. The two DIWA sites are the Bradshaw Field Training Area and the Legune Wetlands (Figure 7-2). The freshwater sections of the Victoria catchment include diverse habitats such as intermittent and perennial rivers, anabranches, wetlands, floodplains, and groundwater-dependent ecosystems (GDEs). The diversity and complexity of the habitats, and the connections between the habitats within a catchment, are vital for providing the range of habitats needed to support both the aquatic and terrestrial biota (Schofield et al., 2018). In the wet season, flooding connects rivers to floodplains. This exchange of water means that floodplain habitats support higher levels of primary and secondary productivity than surrounding terrestrial areas with less frequent inundation (Pettit et al., 2011). Infiltration of water into the soil during the wet season and along persistent streams enables riparian habitats to form an important interface between the aquatic and terrestrial environments. While riparian habitats often occupy a relatively small proportion of the catchment, they frequently have a higher species richness and abundance of individuals than surrounding habitats. The riparian habitats that fringe the rivers and streams of the Victoria catchment have been rated as having moderate to high cover and structural diversity of riparian vegetation (Kirby and Faulks, 2004). These riparian habitats comprise a Eucalyptus camaldulensis overstorey with Lophostemon grandiflorus, Terminalia platyphylla, Pandanus aquaticus and Ficus spp understorey. The dominant overstorey across many parts of the catchment includes Acacia holosericea and Eriachne festucacea (Kirby and Faulks, 2004). Further away from the creeks and rivers, the overstorey vegetation in the Victoria catchment becomes sparser, opening up into savanna woodlands and various grasslands. In the dry season, biodiversity is supported by perennial rivers, wetlands and the inchannel waterholes that persist in the landscape. In ephemeral rivers, the waterholes that remain become increasingly important as the dry season progresses; they provide important refuge habitat for species and enable recolonisation into surrounding habitats upon the return of larger flows (Hermoso et al., 2013). Waterholes provide habitat for water-dependent species, including fish, sawfish and freshwater turtles, and also provide a source of water for other species more broadly within the landscape (McJannet et al., 2014; Waltham et al., 2013). The mouth and estuary of the Victoria River is up to 25 km wide and includes extensive mudflats and mangrove stands (Kirby and Faulks, 2004). Although mangroves and mudflats are prominent along the coastal margins (Department of Climate Change, Energy, the Environment and Water, n.d.), the mangrove communities along the estuary are recognised as being low in speciesrichness, with approximately ten plant species recorded. Of these, the dominant mangrove speciesin the catchment is Avicennia marina, which is largely confined to the estuary (Kirby and Faulks, 2004). The Legune (Joseph Bonaparte Bay) Important Bird and Biodiversity Area can support over15,000 waterbirds across mudflats, salt flats, and seasonally inundated wetlands (BirdLifeInternational, 2023). Marine habitats in northern Australia are vital for supporting importantfisheries, including banana prawn (Fenneropenaeus merguiensis), mud crab (Scylla spp.) andbarramundi (Lates calcarifer), as well as for supporting biodiversity more generally, includingwaterbirds, marine mammals and turtles. In addition, the natural waterways of the sparselypopulated catchments support globally significant stronghold populations of endangered andendemic species that often use a combination of both marine and freshwater habitats (e.g. sharksand rays). 7.3.3 Scenarios of hypothetical water resource development and future climate This ecology analysis used modelled hydrology to explore the potential ecological risks of water resource development in the Victoria catchment through a series of hypothetical scenarios. It used a purpose built river model for the Victoria catchment – for more detail, see the companion technical report on river model calibration in the Victoria catchment by Hughes et al. (2024a). The scenarios were designed to explore how different types and scales of water resource development might affect selected water-dependent ecosystems across the Victoria catchment. The hypothetical developments assessed included instream infrastructure (i.e. large dams) and water harvesting (i.e. pumping river water into offstream farm-scale storages). In evaluating the likelihood of a development scenario occurring, Section 1.2.2, which discusses the plausibility of development pathways, should be consulted. Broad scenario definitions used in the Assessment are described in Section 1.4.3, with Table 7-1 providing a summary of the specific scenarios used in the ecology analysis. Figure 7-2 shows the location of the river system model nodes used in the ecology analysis and the location of hypothetical water resource developments. Further details of the river system model simulations are provided in the companion technical report on river model simulation (Hughes et al., 2024b). The river models were also used to explore the ways in which dry future climate conditions may have an impact on water-dependent ecosystems (i.e. Scenario C), as well as the interactions between water resource development and a potential dry climate future (i.e. Scenario Ddry). Key terms used in Section 7.3 Water harvesting – an operation where water is pumped or diverted from a river into an offstream storage, assuming there are no instream structures Offstream storages – usually fully enclosed circular or rectangular earthfill embankment structures situated close to major watercourses or rivers so as to minimise the cost of pumping Large engineered instream dams – usually constructed from earth, rock or concrete materials as a barrier across a river to store water in the reservoir created. In the Victoria catchment, most hypothetical dams were assumed to be concrete gravity dams with a central spillway (see companion technical report on water storage) (Yang et al., 2024) Annual diversion commencement flow requirement (DCFR) – also known as an end-of-system requirement, the cumulative flow that must pass the most downstream node (81100000) during a water year (1 September to 31 August) before pumping can commence. It is usually implemented as a strategy for mitigating the ecological impact of water harvesting Pump-start threshold – a daily flow rate threshold above which pumping or diversion of water can commence. It is usually implemented as a strategy for mitigating the ecological impact of water harvesting Pump capacity – the capacity of the pumps, expressed as the number of days it would take to pump the entire node irrigation target Reach irrigation volumetric target – the maximum volume of water extracted in a river reach over a water year. Note, the end use is not necessarily limited to irrigation. Users could also be involved in aquaculture, mining, urban, or industrial activities System irrigation volumetric target – the maximum volume of water extracted across the entire study area over a water year. Note, the end use is not necessarily limited to irrigation. Users could also be involved in aquaculture, mining, urban, or industrial activities Transparent flow – a strategy for mitigating the ecological impacts of large instream dams by allowing all reservoir inflows below a flow threshold to pass ‘through’ the dam Note that each potential water resource development pathway results in different changes to the flow regimes, due to differences and interactions between rainfall and upstream catchment sizes, inflows, the attenuation of flow through the river system (including accumulating inflows with river confluences), and the many ways in which each hypothetical water resource development is implemented. These scenarios were not analysed because they are considered likely or recommended by CSIRO; rather, they were selected to explore some of the interactions between location and the types and scales of development, to provide insights into how different types and scales of water resource development may influence ecology outcomes across the catchment. Some of the hypothetical scenarios listed in Table 7-1 do not provide dedicated environmental provisions and have been optimised for water yield reliability, without considering policy settings or additional restrictions that may help mitigate the impacts to water-dependent ecosystems. These scenarios are useful for considering impacts across various development strategies in the absence of mitigation strategies or policy settings (or could be representative of regulatory non- compliance). Further, as an artefact of the scenario assumptions, modelling hypothetical dam development assumed water from the reservoir was released via a pipe or channel rather than releasing water for irrigation into the downstream river channel. Consequently, the river model calculates and removes the extractive take at the dam node. Furthermore, many of the scenarios explored, while technically feasible, exceed the level of development that would be likely to reasonably occur and are modelled without regulatory requirements and management to mitigate ecological impacts. These scenarios were included as a stress test of the system and can be useful for benchmarking or contrasting various levels of change and different mitigation options. The development scenarios are hypothetical and are for the purpose of exploring a range of options and issues in the Victoria catchment. In the event of any future development occurring, further work would need to be undertaken to assess environmental impacts associated with the specific development across a broad range of environmental considerations. For more information on this figure please contact CSIRO on enquiries@csiro.au Figure 7-2 Map of the Victoria catchment and the marine region showing the locations of the river system modelling nodes at which flow–ecology dependencies were assessed (numbered) and the locations of hypothetical water resource developments Nodes are the locations at which flow–ecology dependencies were assessed and are marked as purple or orange circles. The hypothetical modelled dam locations are shown by the triangles marked A and B, and the water harvesting extraction locations are shown by orange circles. The flow ecology of the ecological assets was assessed in the subcatchments in which they occur, downstream of the river system nodes. The locations of ecological assets across the catchment for modelling are documented in Stratford et al. (2024b). Table 7-1 Water resource development and climate scenarios explored in the ecology analysis Descriptions of the river system modelling scenarios are provided in Hughes et al. (2024b). DCFR = annual diversion commencement flow requirement. FSL = full supply level. GCM = general circulation model. na = not applicable. SCENARIO DESCRIPTION TRANSPARENT FLOW ANNUAL TARGET EXTRACTION VOLUME / YIELD (GL) DCFR (GL) PUMP-START THRESHOLD (ML/D) PUMP CAPACITY (D) Scenario A Historical climate and current levels of development A Historical climate and no development No 0 0 na na Scenario B Historical climate and hypothetical future development B-DLC Single dam on Leichhardt Creek No 60‡ na na na B-DVR Single dam on Victoria River No 500‡ na na na B-D2 Two hypothetical dams, LC, VR No 560‡ na na na B-WV, EF, PT, CR Water harvesting with varying target extraction volume (V), DCR requirements (F), pump- start threshold (T), and/or pump rate (R) na V = 40, 80, …, 960, 1000‡ F = 0, 200, 500, 700, 1000 T = 200, 300, …, 900, 1000 R = 10, 20, 30, 40, 50 Scenario C Future climate and current level of development Cdry Dry GCM§ projection (see Section 2.4.5) No 0 na na na Scenario D Future climate and hypothetical future development D-D2 Two hypothetical dams (same as B-D2), for each Scenario C climate (clim = dry) No 591‡ na na na D-D2T Two hypothetical dams (same as B-D2), for each Scenario C climate (clim = dry) with transparent flows Yes 591‡ na na na D-W150,F,600,c Water harvesting under Scenario C climate (clim = dry) na 680‡ 0 200 30 ‡Target extraction volume applies to water harvesting scenarios. Yield applies to hypothetical dam scenarios and is the amount of water that could be supplied by the dams reservoir in 85% of years. 7.3.4 Ecology outcomes and implications The ecology activity used an asset-based approach for analysis and built upon work presented in Pollino et al. (2018) and Stratford et al. (2024c). For the Victoria catchment, 18 ecological assets were selected for analysis (Table 7-2) across 41 nodes, including the end-of-system node for marine assets (Figure 7-2). Both the ecology asset descriptions technical report (Stratford et al., 2024a) and the ecology asset analysis technical report (Stratford et al., 2024b) should be consulted in conjunction with the material provided here. The selected ecological assets spanned freshwater, marine and terrestrial habitats and included species, species groups, and habitats that depend on river flows. Eighteen assets (shown in Table 7-2) were modelled to investigate the effects of changes to river flow resulting from hypothetical water resource development and a projected dry future climate (as a potential worst- case projected climate scenario). Assets were included if they were distinctive, representative, describable and significant within the catchment. The flow–ecology interactions of the assets, including important flow linkages and relationships, and assessment locations in the catchment were documented in Stratford et al. (2024a), as were species and habitat distribution maps, including species distribution models developed for many of the species. Each asset had different requirements of, and linkages to, the flow regime and was distributed across particular parts of the catchment or the near-shore marine zone. Understanding the flow–ecology interactions of assets and their locations across the catchment was important for identifying the potential risks caused by changes in catchment hydrology. Table 7-2 Ecological assets used in the Victoria Water Resource Assessment Eighteen ecological assets were modelled in the ecology analysis. A description of the ecological assets, their flow ecology, and their distribution is provided in Stratford et al. (2024a). Assets marked with an asterisk are presented in this report. The analyses and interpretations for all assets are provided in Stratford et al. (2024b). For more information on this figure, table or equation please contact CSIRO on enquiries@csiro.au. The flow dependencies (hydrometrics) modelling calculated for each asset an index of flow regime change resulting from the different scenarios using a suite of asset-specific hydrometrics, with metrics based upon those in Kennard et al. (2010). Hydrometrics are statistical measures of the long-term flow regime and can include aspects of flow magnitude, duration, timing, frequency and rate of change (Kennard et al., 2010). As a basis for selecting asset hydrometrics, Stratford et al. (2024a) details each asset’s ecology and relationship to flow, including: • habitat dependencies (e.g. floodplain inundation, refuge, recharging of groundwater) • life-cycle processes (e.g. flow to trigger spawning) • migration and movement pathways (e.g. high flows to enable migration into floodplain wetlands and along the river) • flow to support productivity and food resources (e.g. nutrient plumes into coastal areas). Hydrometrics were calculated for each node under each scenario and used to quantify relative change in important parts of the flow regime as percentile change relative to the distribution of annual values of Scenario A, calculated over the Assessment period (i.e. 1 September 1890 to 31 August 2022). The hydrometric index of change is calculated as: 𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃 𝑐𝑐ℎ𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎= 𝑥𝑥−𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠 𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚 𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠 𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚 × 100 Where x is the median of metric i, for the hypothetical scenario, and all values are for individual nodes. The assets’ important metrics are combined by averaging, with each metric being weighted, considering the knowledge base to support it and its significance to the asset’s ecology. The percentile change is weighted downstream of nodes by the habitat value of each reach in which the asset occurs based upon results of species distribution models, and the change in flow dependency is calculated for each node. The species distribution models were developed using a combination of Random Forests, Generalised Linear Models (GLMs), and Maxent algorithms (see Stratford et al., 2024a). These models were applied to a 2.5 km buffer surrounding the rivers within the catchment to quantify habitat suitability. The change in the flow dependencies was weighted by habitat suitability for each asset between the river system model nodes of each river reach. As such, river reaches with important asset habitat quality or values are weighted higher than marginal habitat. Aggregation of these weighted flow dependency values is undertaken to calculate the catchment means of asset–flow dependencies from the individual node values (see Stratford et al., 2024b for more details). Hydrometrics have been broadly used in ecohydrology assessments in national and international contexts for a range of purposes, including water allocation planning, and in ecohydrology research and literature (Leigh and Sheldon, 2008; Marsh et al., 2012; Olden and Poff, 2003). For this analysis, the flow dependencies modelling considered reach- and catchment-wide changes in the assets’ important flow dependencies across the subcatchments in which the assets occur, including the near-shore marine zone. The impact of a hypothetical development on water- dependent ecological assets is inferred and reported here in terms of a habitat-weighted percentile change in asset-specific important flow dependencies. For interpretation of the results, larger values represent greater change in the parts of the flow regime and across sections of the catchment that are important for the asset, with qualitative descriptors provided in Table 7-3 considering the habitat weighted value of each reach for each asset. At a single location as the values are percentile change from the median of the distribution of Scenario A, the assets flow dependency values can be referenced against this historical variability. For example, a value of 25 for a metric at a single location represents a change from the median (50th percentile of the historical distribution) to the 25th percentile. Using mean annual flow as an example metric, the value of 25 would represent the scenario median now being similar to the driest 25% of years for this metric. Table 7-3 Descriptive qualitative values for the flow dependencies modelling as percentile change of the hydrometrics Values consider the change in mean hydrometric value against the natural distribution observed in the modelled baseline series of 132 years. For more information including metric and habitat weighting see Stratford et al. (2024b). VALUE RATING IMPLICATION >0–2 Negligible The median for the assets’ metrics under the scenario is negligible change, as considered against the modelled historical conditions, and is well within the normal experienced conditions at the model node. The assets’ hydrometrics are within the 2nd percentile of the historical Scenario A median 2–5 Minor The change is minor, with the median for the assets’ metrics for the scenario outside the 2nd and within the 5th percentile of Scenario A and the historical distribution of the hydrometrics 5–15 Moderate The change is moderate, with the median for the assets’ metrics under the scenario outside 5th and within the 15th percentile of Scenario A and the historical distribution of the hydrometrics 15–30 Major The change is major, with the median for the assets’ metrics for the scenario outside the 15th and within the 30th percentile of Scenario A and the historical distribution of the hydrometrics >30 Extreme The change is extreme, with the median for the assets’ metrics under the scenario being extreme change, as considered against the modelled historical conditions, with metrics occurring well outside typical conditions at the modelled node or exceeding that of historical variability. The scenario median is outside the 30th percentile from the historical Scenario A median (or equivalent to the new mean, being typical of the outside 20% of observations from the historical sequence across the metrics important to the asset) In addition to quantifying change relative to the historical variability under Scenario A for each asset, an existing analogue of change in asset–flow dependencies is compared using the level of change in the hypothetical scenarios with models of the Ord River below Lake Kununurra (with and without the Ord River Dam and the Ord Diversion Dam (i.e. Lake Kununurra)), near the end-of- system. This analogue considers the modelled changes in river flow associated with the construction of Lake Kununurra, Ord River Dam and Ord River Irrigation Scheme. In addition to the Ord scheme analogue, three natural periods of low-flow conditions are used as benchmarks and plotted alongside the hypothetical developments and climate scenario values. For the Victoria catchments, these were the periods with the lowest 30-year flow (1905–1934), lowest 50-year flow (1890–1939) and lowest 70-year flow (1890–1959) across the historical climate (Scenario A). These are benchmark comparisons, so flow conditions and outcomes of change in flow dependencies would not necessarily be equivalent to these if development were to occur, but they provide a useful comparison of the potential level of change under the scenarios. It is important to note that this ecological analysis is broad in scale, and the results include significant uncertainty. This uncertainty is due to a range of factors, including, but not limited to, incomplete knowledge, variability within and between catchments, and limitations associated with modelling processes and data. Furthermore, thresholds, temporal processes, interactions, synergistic effects, and feedback responses in the ecology of the system may not be adequately captured in the modelling process. There is also uncertainty associated with the projected future climates, such as rainfall patterns and any additional synergistic and cumulative threatening processes that may emerge and interact across scales of space and time, including the production of potentially novel outcomes. The understanding of freshwater ecology in the Victoria catchment and northern Australia more generally is still developing. Provided below is a sample of outcomes for three representative assets for the Victoria catchment: barramundi; shorebirds; and mangroves. For more details and for results on other assets see Stratford et al. (2024b). Barramundi Barramundi are large opportunistic, predatory fish that inhabit riverine, estuarine and marine waters in northern Australia, including those in the Victoria catchment. Adults mate and spawn in the lower estuary and coastal habitats near river mouths during the late dry season and early wet season. Small juveniles migrate upstream from the estuary to freshwater habitats, where they grow and mature before emigrating downstream to estuarine habitats as adults, where they reside and reproduce. In the Victoria catchment, barramundi occupy relatively pristine habitats in both the freshwater and estuarine reaches, as well as in the coastal marine waters. Their life history renders them critically dependent on river flows (Tanimoto et al., 2012) as new recruits move into supra-littoral estuarine and coastal salt flat habitats, and freshwater riverine reaches and wetland habitats occupied as juveniles (Crook et al., 2016; Russell and Garrett, 1983, 1985). Barramundi are sensitive to changes in flow regime in Australia’s tropical rivers where critical requirements for growth and survival include riverine–wetland connectivity, riverine–estuarine connectivity, passage to spawning habitat, and volume of flood flows (Crook et al., 2016; Roberts et al., 2019). Barramundi are an ecologically important fish species capable of modifying the estuarine and riverine fish and crustacean communities throughout Australia’s wet-dry tropics (Blaber et al., 1989; Brewer et al., 1995; Milton et al., 2005). It is targeted by commercial, recreational and Indigenous fisheries. Barramundi is an important species for Indigenous Peoples in northern Australia, both culturally (Finn and Jackson, 2011; Jackson et al., 2011) and as a food source (Naughton et al., 1986). The analysis here considers change in flow regime and related habitat changes. For consideration of the addition or loss of potential habitat associated with the creation of a dam impoundment or instream structures see Yang et al. (2024). Flow dependencies analysis Barramundi were modelled across a total of 1918 km of assessment reaches in the Victoria catchment and in the marine region, with contributing flows from a total of 41 model nodes (see Stratford et al. (2024b)). Some of the key river reaches for barramundi within the catchment were modelled downstream of nodes 81100070, 81100000 and 81100002. The locations for modelling barramundi in the Victoria catchment were based upon species distribution models (Stratford et al., 2024a). Hypothetical water resource development in the Victoria catchment resulted in varying levels of change to important flow dependencies for barramundi. When considering mean change in flow dependencies across all 41 barramundi reaches and nodes, the effects under the hypothetical dam scenarios ranged from negligible (0.5) to minor (3.2) under scenarios B-DLCT and B-D2, respectively, while for water harvesting the effects were negligible (0.1 to 1.0) under scenarios B-Wv80t200r30f500 and B-Wv800t200r30f0 ( For more information on this figure please contact CSIRO on enquiries@csiro.au Figure 7-3 Habitat weighted change in important flow dependencies for barramundi by scenario across model nodes Colour intensity represents the level of change occurring in important flow metrics as percentile change from the historical conditions weighted by the importance of each reach for barramundi. Equivalent colour intensity (i.e. corresponding to the asset flow dependency change value) for the Ord River below Lake Kununurra shown bottom right. Scenarios are ordered on the left axis by the magnitude of change with the mean across nodes shown on the right axis. Horizontal grey bars and number correspond to the mean change across all model node locations. Only the 30 highest impact nodes are shown (x-axis). Results under Scenario A corresponding to changes in asset flow dependency for the lowest 30-year, 50-year and 70-year time periods provide a reference for the modelled changes under different hypothetical development and projected future climate scenarios. EOS = end-of-system. The mean change in important flow dependencies for barramundi across the Victoria catchment for the lowest 30-year, 50-year and 70-year flows in the historical record are 5, 3.6 and 3.4 respectively. Under Scenario B-DLC, (i.e. a potential dam on Leichhardt Creek without transparent flows) there was a negligible mean change in important flow dependencies (1.1) across the 41 barramundi assessment nodes. When transparent flows were provided to support environmental functions (i.e. Scenario B-DLCT), the change in important flows for barramundi was reduced, remaining negligible (0.5). Under Scenario B-DVR greater change relative to Scenario B-DLC was calculated, with a minor (2.1) mean change in flow dependencies. This was reduced to negligible (1.3) with the provision of transparent flows under Scenario B-DVRT. Under Scenario B-D2, which includes both the B-DLC and B-DVR dams, a minor (3.2) mean change in flow dependencies occurred across the catchment without transparent flows. This was reduced to negligible (1.8) with the provision of transparent flows. Under Scenario B-D2 with multiple dams, there was a greater mean change in flow dependencies across the catchment, relative to either of the single dam scenarios. This was due to the combined effects on flows downstream of the confluence of the two dams and the change in flows affecting a larger portion of the catchment from which flows would be impounded. At the end-of-system node 81100000 the mean impact under the hypothetical dam scenarios in the Victoria catchment was considerably less than at the end-of-system in the Ord. Under Scenario B-D2T, habitat-weighted flow changes for barramundi were greatest at node 81100063 (Figure 7-3), with a major (20.6) change in flow dependencies at this single node. Nodes directly downstream of the dams under scenarios B-DLC and B-DVR resulted in extreme (39.9) and major (26.6) change, respectively. These changes were reduced to major (18.8) and moderate (11.4) with the provision of transparent flows. This reflects a combination of the higher level of change in flows directly downstream of dams, the benefits associated with the provision of transparent flows for riverine resident species, and the importance for barramundi of the habitat at these locations. In years of natural low flows, or flows reduced by anthropogenic activity, the range of facultative habitat and ecosystem processes available to barramundi is reduced, reducing growth and survival (Blaber et al., 1989; Brewer et al., 1995; Milton et al., 2005). For more information on this figure please contact CSIRO on enquiries@csiro.au Figure 7-4 Spatial heatmap of change in important flow dependencies for barramundi, considering their distribution across the catchment Scenarios are: (a) B-Wv80t200r30f0, (b) B-Wv160t200r30f0, (c) B-W160t60r20f0, (d) B-DLC, (e) Cdry and (f) D-dryw160t200r30. See Table 7-1 for a description of the scenarios. River shading indicates the level of flow change of important metrics, weighted by the habitat value of each reach for barramundi. Under the hypothetical water harvesting scenarios, there was a negligible (0.1 to 1.0) mean change in flow dependencies across the barramundi assessment nodes for B-Wv80t200r30f500 and B-Wv800t200r30f0, respectively. Under the water harvesting scenarios the greatest mean changeoccurred at node 81100001, with a moderate (11.8) change occurring at this node under ScenarioB-Wv800t200r30f0. The change in barramundi flow dependencies with water harvesting variesaccording to the extraction targets, pump-start thresholds, pump rates, and locations (Figure 7-3). With a low extraction target of 80 GL under Scenario B-Wv80t200r30f0, the mean weighted changeacross the catchment was negligible (0.3), only increasing to 1.0 with the larger extraction targetof 800 GL under Scenario B-Wv800t200r30f0. Increasing the pump-start threshold from 200 to 600 MLper day (scenarios B-Wv160t200r30f0 and B-Wv160t600r30f0) with a target extraction volume of 160 GLmaintained a negligible change with the mean weighted change reduced from 0.4 to 0.3(Figure 7-3). Increasing the pump-start threshold protected the low flows that are important forbarramundi ecology, such as habitat connectivity and pool refugia water quality, particularly at theend of the annual dry season (Arthington et al., 2005; Crook et al., 2022). The effects of water harvesting were strongly influenced by the node location, relative to the extraction. Nodes downstream of multiple water harvesting locations often had large changes in important flow dependencies (see node 81100001 compared with node 81101135 in Figure 7-5). The benefits associated with having a low system allocation target can be seen when changes in flow dependencies are increased with greater allocation targets (see also nodes 81100001 and 81100180 in Figure 7-5, where change is increased along the plot’s y-axis). Similarly, reductions in change can be seen in association with having higher pump-start thresholds (see node 81101135, where the change in flow dependencies is reduced along the plot’s x-axis). Figure 7-5 demonstrates the large spatial variability in risks associated with water harvesting across the catchment, and that mitigation strategies can be used to reduce flow change, although their success may have local considerations. For more information on this figure please contact CSIRO on enquiries@csiro.au Figure 7-5 The change in barramundi flow dependencies under the various water harvesting scenarios at sample nodes across the catchment, showing response to system targets and pump-start thresholds Colour intensity represents the level of change occurring in the barramundi’s important flow metrics under the scenarios at the important nodes. The results incorporate the habitat-weighted change under each scenario relative to the distribution under Scenario A, with results for no end-of-system (EOS) requirement and a pump rate of 30 days. Scenario Cdry resulted in a moderate mean change in flow dependencies (5.1) for barramundi across the 41 barramundi assessment nodes (Figure 7-3). This level of change accrued, as the new median conditions under this scenario were equivalent to the lowest 30-year flow analogue period for barramundi (Figure 7-3). This analysis indicates that under Scenario Cdry and under the lowest 30-year, 50-year and 70-year flow periods there were on average across all catchment nodesgreater changes to mean asset flow dependencies than under scenarios B-D2T (negligible; 1.8) andB-Wv160t200r30f0 (negligible; 0.4). However, it is important to note that local changes under somewater resource development scenarios can be considerably higher. Under scenarios Dclim-D2T andDdry-Wv160t200r30, there were moderate (7.2 and 5.2) changes, respectively, when weighted acrossall barramundi assessment nodes. These values were higher than any of the analogue low-flowperiods. This shows that the combined impacts under scenarios Dclim-D2T or Ddry-Wv160t200r30 weregreater than under Scenario Cdry or under either scenarios B-D2 or B-Wv160t200r30 alone. Barramundi populations depend on habitat connectivity being maintained throughout the catchment. Access to riverine habitats due to the physical barriers of instream infrastructure (particularly under scenarios B-DVR or B-D2) would limit access to some habitats (see Yang et al. (2024)). Access to upstream habitats and estuarine supra-littoral habitats would be reduced if water harvesting or dam scenarios reduced the inundation level, frequency or duration of overbank flows. High river flows expand the extent of wetland and estuarine-margin habitats, increase connectivity, deliver nutrients from terrestrial landscapes, create hot spots of high primary productivity and food webs, increase prey productivity and availability, and increase migration within the river catchment (Burford and Faggotter, 2021; Burford et al., 2016; Leahy and Robins, 2021; Ndehedehe et al., 2020, 2021). Reduced flow levels under a future drier climate would reduce wetland habitat connectivity and productivity. A wetter climate would likely increase wet-season flow levels and increase wetland–riverine–estuarine connectivity, and it could ameliorate the effects of possible anthropogenic flow reduction compared with current conditions. The difference in flow effects of single dams (negligible or minor) or two dams (minor) are expected, as the single potential dam on Leichhardt Creek has minimal impact on flow at the catchment scale, as it does not affect the majority of subcatchments of the Victoria River. A much larger area of the river catchment is located above the dam on the hypothetical Victoria River (B- DVR). The extent to which the construction of dam infrastructure will reduce barramundi habitat by reducing longitudinal connectivity varies depending upon the potential dam location (see Yang et al. (2024) for changes associated with instream structures). A potential dam on a small headwater catchment such as Leichhardt Creek has minimal impact on longitudinal connectivity of assets compared toa a potential dam on the Victoria River. Across the entire catchment, water extraction of between 80 and 800 GL (i.e. under scenarios B-W v80t200r30f0 to B-W v800t200r30f0) causes a negligible change in flow dependencies for barramundi, including both wet-season high-level flows and low-level flows during September to March prior to the wet season. Barramundi growth and year-class strength are enhanced by large wet-season flows during the wet-season months of January to March (Crook et al., 2022; Leahy and Robins, 2021). Larger flows both preceding and following the wet-season peak flows also enhance barramundi growth and recruitment. Previous studies have shown that reducing high flows lowers the growth rates of barramundi: a model of flow–growth estimates a 12% reduction in barramundi growth under an 18% reduction in the natural flow regime (Leahy and Robins, 2021). Recent research on monsoon- driven habitat use by barramundi has shown that, during drier years with lower river flows, a large proportion of the juvenile barramundi migrate upstream from estuarine spawning habitat to freshwater habitats, probably seeking out riverine and palustrine productive hot spots (Roberts et al., 2023). Hence, maintaining low-level flows would be critical. Negligible change in seasonal flow levels due to water harvesting maintains the natural seasonality of flow patterns and would support barramundi populations within the Victoria River catchment. While two dams within the catchment are modelled to result in a minor change to barramundi flows, mitigation actions (such as transparent flows) can reduce the level of change to negligible. The impacts on barramundi populations from modifying the level and seasonality of flows would be greater under a future dry climate and greatest with water resource development under a dry climate, with results similar to those modelled in other tropical Australian catchments (Plagányi et al., 2024). Shorebirds The shorebirds group consists of waterbirds with a high level of dependence on end-of-system flows and large inland flood events that provide broad areas of shallow-water and mudflat environments (see Stratford et al. (2024a) for a species list). Shorebirds are largely migratory and mostly breed in the northern hemisphere (Piersma and Baker, 2000). They are in significant decline and are of international concern (Clemens et al., 2010; Clemens et al., 2016; Nebel et al., 2008). Shorebirds depend on specific shallow-water habitats in distinct geographic areas, including northern hemisphere breeding grounds, southern hemisphere non-breeding grounds, and stopover sites along migration routes such as the East Asian–Australasian Flyway (Bamford, 1992; Hansen et al., 2016). In northern Australia, this group comprises approximately 55 species from four families, including sandpipers, godwits, curlews, stints, plovers, dotterels, lapwings and pratincoles. Approximately 35 species are common regular visitors or residents. Several species in this group are Endangered globally and nationally, including the bar-tailed godwit, curlew sandpiper (Calidris ferruginea), eastern curlew, great knot (Calidris tenuirostris), lesser sand plover (Charadrius mongolus) and red knot (Calidris canutus). An example species from this group is the eastern curlew, which is listed as Critically Endangered and recognised through multiple international agreements as requiring habitat protection in Australia. Eastern curlews rely on food sources along shorelines, mudflats and rocky inlets, and also need roosting vegetation (Driscoll and Ueta, 2002; Finn et al., 2007; Finn and Catterall, 2022). Developments and disturbances, such as recreational, residential and industrial use of these habitats, have restricted habitat and food availability for the eastern curlew, contributing to population declines. The intertidal mudflats and coastal flats provide important habitat for shorebirds, as do the large open shallow wetlands (Chatto, 2006). Shorebirds rely on the inundation of shallow flat areas such as mudflats and sandflats during seasonal high-level flows to provide invertebrates and other food sources. Without inundation events, these habitats cannot support high densities of shorebird species, and lack of food can increase mortality rates both on-site and during and after migrations (Barbaree et al., 2020; Canham et al., 2021; Durrell, 2000; Kozik et al., 2022; van der Pol, et al., 2024; West et al., 2005). The analysis considers change in flow regime and related habitat changes, and does not consider the addition or loss of potential habitat associated with the creation of a dam impoundment (see Yang et al. (2024) for effects of dam impoundments). Flow dependencies analysis Shorebirds were modelled across a total of 1918 km of assessment reaches in the Victoria catchment and in the marine region, with contributing flows from a total of 41 model nodes, using eastern curlew as a representative species for understanding distribution patterns (see Stratford et al. (2024a)). Some of the key river reaches for shorebirds within the catchment were modelled downstream of nodes 81100180, 81100000 and 81100140, based upon species distribution modelling. The mean change in important flow dependencies for shorebirds across the Victoria catchment for the lowest 30-year, 50-year and 70-year flows in the historical record are 5, 4.5 and 3.6 respectively. Hypothetical water resource development in the Victoria catchment resulted in varying levels of change in flow dependencies for shorebirds that did not exceed any of the analogue low-flow periods from the historical series (Figure 7-6). The mean change in flow dependencies across all 41 shorebird analysis reaches and nodes under the hypothetical dam scenarios ranged from negligible (0.5) to minor (2.9) under scenarios B-DLCT and BD2, respectively, while under water harvesting it was negligible, ranging from 0.2 to 1.5 under scenarios B-Wv80t600t30f500 and B-Wv800t200r30f0, respectively (Figure 7-6). Under Scenario Cdry, there was minor change (4.3) for shorebirds. The resulting spatial change in flows under the dam and water harvesting, varied due to the scale, location and nature of the hypothetical developments. Projected climate scenarios resulted in changes to asset flow dependencies across the entire catchment. Under the hypothetical water harvesting scenarios, there was a mean negligible change in flow dependencies across the shorebirds assessment nodes, ranging from 0.2 to 1.5 under scenarios B-Wv80t600t30f500 and B-Wv800t200r30f0, respectively. Under the water harvesting scenario with the largest change (B--Wv800t200r30f0), the single node with the highest change in flow dependencies was 81100001, with major (16.2) change. The change in important flow dependencies for shorebirds under water harvesting scenarios varies by the extraction targets, pump-start thresholds, pump rates, and location (Figure 7-6). With a low extraction target of 80 GL under ScenarioB-Wv80t200r30f0, the mean weighted change across the catchment was negligible (0.4), increasing slightly (1.5) with an extraction target of 800 GL under Scenario B-Wv800t200r30f0. Increasing the pump-start threshold from 200 ML per day (under Scenario B-Wv160t200r30f0) to 600 ML per day(under Scenario B-Wv160t600r30f0) with a target extraction volume of 160 GL reduced the level of change in shorebird flow dependencies across the assessment nodes from 0.6 to 0.4. Under Scenario Cdry, there were minor mean changes (4.3) for shorebirds across the 41 shorebirds assessment nodes, with a median value that was equivalent to the analogue low-flow time periods (Figure 7-6). This indicates that under the dry climate scenario, there were on average across all catchment nodes greater changes than under scenarios B-D2T (negligible; 1.6) and B-Wv160t200r30f0 (negligible; 0.6). However, it is important to note that local changes under some water resource development scenarios can be greater. Under scenarios Dclim-D2T and Ddry-Wv160t200r30, there were moderate (6.4) and minor (4.6) changes in important flows, respectively, when weighted across all shorebirds assessment nodes. This shows that the combined changes under scenarios Dclim-D2T and Ddry-Wv160t200r30 were greater than under Scenario Cdry or either of scenarios B-D2 or B-Wv160t200r30 alone. 432 | Water resource assessment for the Victoria catchment For more information on this figure please contact CSIRO on enquiries@csiro.au Figure 7-6 Habitat weighted change in important flow dependencies for shorebirds under the various scenarios across the model nodes Colour intensity represents the level of change occurring in important flow metrics as percentile change from the historical conditions weighted by the importance of each reach for shorebirds. Equivalent colour intensity (i.e. corresponding to the asset flow dependency change value) for the Ord River below Lake Kununurra shown bottom right. Scenarios are ordered on the left axis by the magnitude of change with the mean across nodes shown on the right axis. Horizontal grey bars and number correspond to the mean change across all model node locations. Only the 30 highest impact nodes are shown (x-axis). Results under Scenario A corresponding to changes in asset flow dependency for the lowest 30-year, 50-year and 70-year time periods provide a reference for the modelled changes under different hypothetical development and projected future climate scenarios. EOS = end-of-system. Mangroves Mangroves forests include species of shrubs and trees that occupy a highly specialised niche within the intertidal and near-supra-littoral zones along tidal creeks, estuaries and coastlines (Duke et al., 2019; Friess et al., 2020; Layman, 2007). Mangroves are an important and prolific habitat-forming species group in the Victoria River estuary and coastal littoral habitats. Mangrove forests provide a complex habitat that offers a home to many marine species, including molluscs (McClenachan et al., 2021), crustaceans (Guest et al., 2006; Thimdee et al., 2001), reptiles (Fukuda and Cuff, 2013), birds (Mohd-Azlan et al., 2012) and numerous fish species, when connected to coastal waters. During periods of inundation at high tide, species including crustaceans access mangrove forests, which provide settlement substrates and shelter against predation, using the mangroves’ trunks and prop-roots as refugia during postlarval and benthic juvenile phases (Meynecke et al., 2010). Fish and crustaceans also access mangroves and their epiphytes for food (Layman, 2007; Skilleter et al., 2005). Despite occupying saline habitats, mangroves require freshwater inputs from precipitation, groundwater or overbank inundation to thrive (Duke et al., 2017), so reduced flood flows and an increased frequency and duration of no-flow periods or other impacts on hydro-connectivity are key threats to mangroves. Flow dependencies analysis Mangroves were modelled in the marine region with one model node at the end-of-system. The locations for modelling mangroves in the Victoria catchment were based upon habitat maps (see Stratford et al. (2024b)). Hypothetical water resource development in the Victoria catchment resulted in varying levels of change in important flow dependencies for mangroves. The levels of change ranged from negligible (0.8) to moderate (7.4) under hypothetical dam scenarios B-DLCT and B-D2, respectively, while the levels of change in important flow dependencies ranged from negligible (0.7) to moderate (5.7) under the water harvesting scenarios B-Wv80t600t30f500 and B-Wv800t200r30f0, respectively. Under Scenario Cdry, there was moderate change in flows (11.3) formangroves (Figure 7-8). The mean change in important flow dependencies for mangroves acrossthe Victoria catchment for the lowest 30-year, 50-year and 70-year flows in the historical recordare 15.7, 14.3 and 10.1 respectively. For more information on this figure please contact CSIRO on enquiries@csiro.au Figure 7-7 Waterhole fringed by boab trees, Victoria catchment Photo: CSIRO – Nathan Dyer For more information on this figure please contact CSIRO on enquiries@csiro.au Figure 7-8 Change in important mangroves flow dependencies under the various scenarios Colour intensity represents the level of change occurring in important flow metrics as percentile change from the historical conditions for mangroves. Equivalent colour intensity (i.e. corresponding to the asset flow dependency change value) for the Ord River below Lake Kununurra shown bottom right. Scenarios are ordered on the left axis by the magnitude of change with the mean across nodes shown on the right axis. Horizontal grey bars and number correspond to the mean change. Results under Scenario A corresponding to changes in asset flow dependency for the lowest 30-year, 50-year and 70-year time periods provide a reference for the modelled changes under different hypothetical development and projected future climate scenarios. EOS = end-of-system. The hydrological requirements for mangroves are complex: they are influenced by tidal inundation, rainfall, soil water content, groundwater seepage, and evaporation, all of which influence soil salinity, which can have profound effects on mangrove growth and survival. Mangroves require access to fresh water via their roots, though many species occur at their upper salinity threshold (Robertson and Duke, 1990). Sediment delivered to the coast during flood flows helps to sustain mangrove forests, supports their expansion (Asbridge et al., 2016) and increases the accumulation of carbon in sediments (Owers et al., 2022). An overall reduction in freshwater inputs into mangrove systems could contribute to mangrove stress and potentially dieback, as has occurred in the Gulf of Carpentaria (Duke et al., 2019). Under scenarios B-DLC and B-DVR flow-modification changes were negligible and moderate respectively, and under Scenario B-D2 there were moderate flow-modification changes to mangrove flow (Figure 7-8). Water harvesting resulted in moderate negative risks to freshwater service provision to mangroves via flow modification during the year. One dam on a small headwater tributary had little effect in terms of overall catchment flows, in contrast to a potential dam in the mid-reaches of the Victoria River itself, which was associated with a reduction in flow volumes compared to the natural flow regime. Incorporating transparent flows in the potential dam operations only slightly reduced the change in flow dependency for mangroves. Under Scenario B-DVRT, the change in important flow dependency continued to result in a moderate risk to the habitat-forming species group. High-level flows are important for inundating the mangrove forests during the wet season and replenishing the soil water. Water harvesting would extract water during wet-season flows, potentially reducing the magnitude of high flows at the critical period of wet-season ecological replenishment in the wet-dry tropics. In addition, reduction of sediment loads under flow regime change that results in lower flows would be detrimental due to lower levels of coastal deposition to maintain estuarine soils for the benefit of the mangrove community (Asbridge et al., 2016). Overview of the impacts of water resource development on ecology This section provides a high-level overview of the aggregated results (means of assets) arising from the hypothetical development and climate change scenarios and discusses specific differences in the spatial pattern and magnitude of change. Outcomes for specific assets vary depending upon water needs and flow ecology and are discussed with implications and interpretation of results in Stratford et al. (2024b). The values associated with the means include, but do not show, the range in outcomes across assets, where change in flow dependencies for individual assets or at specific locations can be considerably higher or lower than the mean but provide an overview of the potential range of outcomes that may occur. Hypothetical dams and water harvesting resulted in different changes in flows, affecting outcomes for ecology by different magnitudes of change across different parts of the catchment, and in different ways (Figure 7-10 and Figure 7-11). Under a water harvesting scenario, Scenario B-Wv800t200r30f0 (Figure 7-11), the largest catchment mean changes in flow dependencies for assets was for cryptic waders, threadfin, banana prawns and floodplain wetlands, all with moderate mean change in flow dependencies across their respective nodes. The largest single-site flow change under water harvesting scenarios were major, for assets including for floodplain and riparian vegetation, floodplain wetlands, shorebirds and colonial and semi-colonial wading waterbirds. Under Scenario B-D2, 89 nodes were rated as having moderate mean change across all the assets (out of a total potential of 419 asset nodes representing 21%), compared with 43 (10%) under Scenario B-Wv800t200r30f0. Under Scenario B-D2, across all assets there were a total of 16 asset nodes (4%) with extreme levels of change in flow dependencies, which was reduced to none under Scenario B-Wv800t200r30f0. Under Scenario B-D2 with two dams, the largest catchment mean change in flow dependencies for assets were for threadfin, cryptic wading waterbirds, banana prawns and mangroves, each with moderate mean change in flow dependencies across all their assessment nodes. Considering the mean of all assets, the change in flow dependencies under the largest water resource development scenario modelled (B-D2) was lower than that for all three of the benchmark low- flow time periods (Figure 7-11), although individual assets may have differing outcomes (see Stratford et al. (2024b)). Under scenarios with dams, the largest site-based changes in flow for assets were often directly downstream of hypothetical dams and resulted in node impacts with up to extreme change for assets, including floodplain wetlands, colonial and semi-colonial wading 436 | Water resource assessment for the Victoria catchment waterbirds, grunter and sawfish at these impacted downstream nodes (e.g. Figure 7-11d for downstream dam impacts). Under Scenario Cdry, flow regime change impacts on ecology occurred largely across the catchment (Figure 7-10e), and cumulative impacts of water resource development in combination with dry future climate often led to the greatest catchment-level changes in flow ecology (Figure 7-10f showing D-dryw160t200r30 and Figure 7-11). Under the largest hypothetical development scenarios for water harvesting (e.g. B-Wv800t200r30f0) and instream dam (Scenario B-D2) developments, the impacts at the end-of-system node alone were greater under water harvesting than dams for sawfish, shorebirds and salt flats, and inversely greater under dams for mullet, threadfin, barramundi and mangroves. The flow changes under scenarios with a single dam ranged from negligible to moderate at the end-of-system for the mean across assets (negligible under Scenario B-DLC and minor to moderate under Scenario B-DVR). While some assets have extreme change at some nodes downstream of dams, as unimpacted tributary inflows increasingly dominate streamflow patterns with distance downstream from the dam the impact is reduced. For more information on this figure please contact CSIRO on enquiries@csiro.au Figure 7-9 Riverine landscape, Victoria catchment Photo: CSIRO – Nathan Dyer For more information on this figure please contact CSIRO on enquiries@csiro.au Figure 7-10 Spatial heatmap of change to asset–flow dependencies across the Victoria catchment, considering change across all assets in the locations in which each of the assets was assessed Scenarios are: (a) B-Wv80t200r30f0, (b) B-Wv160t200r30f0, (c) B-W160t60r20f0, (d) B-DLC, (e) Cdry and (f) D-dryw160t200r30. See Table 7-1 for descriptions of scenarios. River shading indicates the mean level of flow change of important metrics weighted by the habitat value of each asset for each reach. For more information on this figure please contact CSIRO on enquiries@csiro.au Figure 7-11 Mean change to assets’ important flow dependencies across scenarios and nodes The scenarios (see Table 7-1) are listed on the left vertical axis. The x-axis lists river system model nodes (i.e. locations). Colour intensity represents the mean level of change occurring in the assets’ important flow metrics under the various scenarios, given the habitat importance of each node for each asset. See Table 7-1 for descriptions of the scenarios and Figure 7-2 for a map of the gauge locations. Heatmap shading indicates the mean level of flow change of important metrics, weighted by the habitat value of each asset for each reach. EOS = end-of-system. Horizontal grey bars and number correspond to the mean change across all model node locations. Water harvesting and mitigation of impacts For water harvesting scenarios, measures to mitigate the risks of extraction include limiting the system target thereby reducing extraction across the catchment, providing a pump-start threshold by limiting pumping of water from the river during periods of low river flows, providing an end-of- system requirement for a volume of water to pass the last node in the river system before pumping is allowed to commence that water year, and limiting the pump rate that water can be extracted from the river (see Hughes et al. (2024b) simulation report for more details). Providing reduced limits on system targets improves outcomes for ecological flow dependencies compared with larger targets (Figure 7-12 y-axis); this applies broadly across all asset groups and throughout the range of explored irrigation targets. Larger extraction volumes resulted in increases in mean changes in flow dependencies across asset groups up to moderate change across the catchment’s ecological assets. Some assets, including flow-dependent habitats, the ‘other’ species group and marine assets experienced higher changes in important flow dependencies at some system targets (Figure 7-12). While improvements are likely to occur in conjunction with providing either minimum flow thresholds or end-of-system requirements, greater extraction equates to a greater level of risk due to changes in important ecological flow metrics. Providing minimum flow pump-start thresholds improved ecological flow dependencies across increasing pump-start threshold levels (Figure 7-12 x-axis). Modelled minimum flow thresholds varied incrementally from 200 to over 1000 ML/day and are provided by requiring that flow volume in the river exceeds required thresholds before pumping commences. Increasing pump- start threshold to 1000 ML/day results in a significant reduction in modelled mean change in important flow dependencies compared with only 200 ML/day (Figure 7-12). Increasing the pump- start threshold above 600 ML/day results in incremental improvements to ecological flows with reduced rate of relative improvement to levels of change in important flow dependencies above about 900 ML/day (Figure 7-12). The benefit of higher pump-start thresholds was largest in scenarios with no or low EOS requirements, as the benefit of having higher pump-start thresholds was reduced in combination with scenarios that had greater EOS requirements. This is likely because large flows have already passed the system to the EOS node before the pump-start threshold is triggered. For more information on this figure please contact CSIRO on enquiries@csiro.au Figure 7-12 Mean change to assets’ important flow dependencies across water harvesting increments of system target and pump-start threshold, with no end-of-system (EOS) requirement and a pump rate of 30 days Colour intensity represents the mean level of change occurring in the assets’ important flow metrics under the various scenarios, given the habitat importance of each node for each asset. Instream dams with and without transparent flows Two hypothetical locations for instream dams were selected (Leichhardt Creek and Victoria River) for modelling and analysis (Yang et al., 2024) and simulated following the hydrology modelling approach outlined in Hughes et al. (2024b). The locations are shown in Figure 7-2. The goal of this analysis was to test the effect of different dam locations and configurations on changes to streamflow, to understand the effect on downstream ecology. These hypothetical dams were modelled individually, as well as two dams together, to better understand cumulative impacts. In addition, the hypothetical dams were also modelled incorporating transparent flows. Instream dams create a range of impacts on streamflow associated with the capture and extraction of water, affecting the timing and magnitude of downstream flows. The risks on downstream flow associated with instream dams are explored here across broad asset groups, and the results are presented as the mean of asset values. Impacts associated with loss of connectivity due to the dam wall and loss of habitat associated with the dam inundation extent are discussed in Yang et al. (2024. The dam scenarios and the resulting flow–ecology relationships are discussed in more detail for each asset in Stratford et al. (2024b). Assessment of the individual dams found varying levels of impact on ecology–flow dependencies (Table 7-4). None of the scenarios resulted in changes greater than minor averaged for all assets across the catchment, although local impacts were often considerably higher. The dams varied in size, inflows, and capture volumes, and the location within the catchment, all of which influenced the outcome. Impacts directly downstream of modelled dams can often be high and may cause extreme changes in ecology–flow dependencies. Areas further downstream have contributions from unimpacted tributaries that help support natural flow regimes. Dams further up the catchment may affect a larger proportion of streams and river reaches when considering flow regime change, but they may have lower impacts associated with connectivity. Impacts are not equivalent across assets, and large local impacts may lead to changes in ecology across other parts of the catchment due to the connected nature of ecological systems. Table 7-4 Scenarios of different hypothetical instream dam locations showing end-of-system (EOS) flow and mean changes in ecology flows for groups of assets across each asset’s respective catchment assessment nodes Higher values represent greater change in flows important to the assets of each group. Values are asset means across their respective catchment assessment nodes (see Stratford et al. (2024b)). Some assets are considered in multiple groups, in which cases the mean across the nodes is used. Asset means include values from all nodes that the asset is assessed in, including in reaches that may not be affected by flow regime change. SCENARIO HYPOTHETICAL DAM SCENARIO DESCRIPTION ALL-ASSET MEAN FISH WATERBIRDS OTHER SPECIES HABITATS FRESHWATER ASSETS MARINE ASSETS B-DLC Leichhardt Creek 1.1 1.0 1.0 0.9 1.2 1.2 0.9 B-DLCT Leichhardt Creek with transparent flows 0.6 0.4 0.6 0.6 0.8 0.5 0.7 B-DVR Victoria River 3.6 3.2 3.1 4.3 4.0 2.5 4.5 B-DVRT Victoria River with transparent flows 2.6 1.9 1.9 3.3 3.5 1.4 3.7 B-D2 Both Leichhardt Creek and Victoria River dams 4.5 4.1 4.1 4.9 5.1 3.7 5.2 B-D2T Both Leichhardt Creek and Victoria River dams with transparent flows 2.7 2.0 2.2 3.1 3.9 1.8 3.6 The cumulative change in flow dependencies due to multiple dams (Scenario B-D2) is greater than the change in flow dependencies due to individual dams, considering both change in flow volumes and ecology–flow dependencies (Table 7-4). Cumulative change in flow ecology may be associated with the combination of a larger portion of the catchment being affected by changes in flows across larger parts of the catchment, and residual flows being lower due to the overall greater level of abstraction (Table 7-4). Measures to mitigate the risks of large instream dams, such as transparent flows resulted in reduced ecological change in flows broadly across all assets compared with no transparent flows (Table 7-4). Particularly strong benefits from transparent flows were found for fish (Table 7-4). Instream dams capture inflows and change downstream flow regimes. Transparent flows are a type of environmental flow provided as releases from dams that maintain some aspects of natural flows. Inflow thresholds used in the transparent flows analysis are conceptually similar to the commence-to-pump thresholds used in water harvesting, facilitating comparison. Transparent flows are provided across both dams under Scenario B-D2 (Hughes et al., 2024b). 7.4 Biosecurity considerations 7.4.1 Introduction Biosecurity is the prevention and management of pests, weeds and diseases, both terrestrial and aquatic, to limit the risk of detrimental economic, environmental, social and/or cultural impacts. ‘Pests’ is a broad term encompassing pest insects, other invertebrates (e.g. nematodes, mites, molluscs) and vertebrates (e.g. mammals, birds, fish). Weeds broadly include invasive plants and algae. Diseases are caused by pathogens or parasites such as bacteria, fungi and viruses. Any development of the water resources within the Victoria catchment for plant industries or aquaculture must take account of biosecurity risks that may threaten production or markets. Development in the region may also pose broader biosecurity risks to other industries, the environment or communities, and these risks must be prevented and/or managed. Biosecurity practices to protect the Victoria catchment occur at a range of scales. At the national level, the Australian Government imposes quarantine measures to regulate the biosecurity risks associated with entry of goods, materials, plants, animals and people into Australia. The NT Government also has biosecurity legislation to limit the entry of new pests, weeds and diseases into the jurisdiction, and to require the control of certain species already established within the NT. There can also be requirements at the regional level, such as participating in weed management programs (NT Government, 2021). At the local scale, individual properties ideally follow routine biosecurity protocols, and work with other similar enterprises in implementing industry-wide biosecurity measures. While the Victoria catchment is relatively isolated compared with other regions of Australia, it still has physical connections to the rest of the NT, across northern Australia more broadly, with the rest of the country and with neighbouring countries such as Indonesia. Examples of such connections are the sharing of specialist cropping machinery between agricultural regions, transport of crop products, tourist visits into remote areas, international trade and tourism, mining exploration, shifting cattle between pastoral properties, army training exercises and movements between Indigenous communities. These connections can be pathways for entry of new pests, weeds or diseases. This section introduces the impacts, spread and management of pests, weeds and diseases of irrigated cropping and aquaculture, as well as invasive species that pose a risk to the Victoria catchment. Given the focus on water-intensive primary industries, biosecurity for terrestrial livestock industries is not included. Impacts of pests, weeds and diseases In primary industries, pests, weeds and diseases can cause economic losses by reducing crop yield and product quality, interfering with farm operations and loss of market access, plus the costs of control measures. The national economic impact of established weeds and vertebrate pests on Australian agriculture has been estimated at over $5.3 billion/year (Hafi et al., 2023). Insect pests are also a substantial economic burden nationally (Bradshaw et al., 2021). The environmental impacts of pests, weeds and diseases, collectively termed ‘invasive species’, include loss of native plants and animals (from competition, predation and infection), degradation of habitats and disruption of ecosystem processes (e.g. changed fire or moisture regimes). Invasive species are the greatest threat to Australia’s threatened flora and fauna (Ward et al., 2021). For example, myrtle rust (Austropuccinia psidii) has potential to cause the extinction of some rare, native myrtaceous shrubs and trees (Makinson et al., 2020). Social impacts of pests, weeds and diseases include loss of public amenity and access to outdoor areas, damage to infrastructure and public safety risks. Cultural impacts include a loss of traditional foods, impaired access for hunting and damage to cultural sites. For example, Gamba grass (Andropogon gayanus) is an African grass originally introduced for pasture in the NT that is now a Weed of National Significance (WoNS). WoNS are nationally agreed weed priorities that have been a focus for prevention and improved management (CISS, 2021; Hennecke, 2012). Gamba grass forms tall, dense stands that burn intensely, posing significant risks to public safety, community and primary industries infrastructure, Indigenous heritage sites, native ecosystems and grazing lands (Setterfield et al., 2013). Pathways of movement Pests, weeds and diseases spread by movement of adults and juveniles (e.g. vertebrate pests), with movement of their hosts (e.g. infected aquaculture broodstock or nursery stock for planting, harvested produce infested with insect larvae) and by movement of propagules (e.g. fungal spores, insect eggs, weed seeds, viral particles). Such movements provide many pathways by which pests, weeds and diseases could be introduced to the Victoria catchment, potentially causing new outbreaks. Just as importantly, there is also the potential for pests, weeds and diseases from the Victoria catchment to spread to other areas in the NT and elsewhere in Australia. Human-mediated spread Human activities are the key means of long-distance and local movement. Pests and propagules, including those within transported soil, can ‘hitchhike’ on or in vehicles, construction and farm machinery, shipping containers and other equipment brought into a region. The ease of movement on vehicles and machinery means that the road network (including access roads to camping areas, railways, pipelines and powerlines) can be a frequent source of new infestations. Propagules may contaminate livestock, seed or nursery stock for establishing crops, hay, road base and landscaping supplies (including turf and ornamental plants). Weed infestations can also arise from invasive garden, crop and pasture plants. Aquatic pests and diseases may become established due to deliberate species release into the environment for fishing, inadvertent transport on fishing equipment or vessels, or dumping of aquarium contents. Incursions of new pests, weeds and diseases from overseas are most likely to occur through contamination of imported goods or containers, or be carried by people (e.g. propagules on shoes or clothing, smuggling of seed or fruit). Natural spread Natural dispersal via wind, water and wild animals usually occurs over short distances. Extreme weather events such as floods and cyclones can disperse pests, weeds and diseases over long distances in addition to causing major environmental disturbances that increase the likelihood of invasive species becoming established. Irrigation infrastructure such as dams, pipelines and channels may facilitate distant spread via water movements of some pests, weeds and diseases, within and across catchments. Some animal pests, such as locusts and fall armyworm (Spodoptera frugiperda) naturally migrate long distances. Northern Australia is close to the southern coasts of Indonesia, Timor-Leste and Papua New Guinea (PNG). These neighbouring countries have a range of serious plant pests and diseases that are not present in Australia, including exotic fruit flies and citrus canker (Xanthomonas citri subsp. citri). The likelihood of their arrival by long-distance wind dispersal is uncertain, particularly with regards to novel atmospheric conditions and extreme weather events occurring under climate change. However, their economic consequences in Australia would be severe were they to establish in Australia. Thus, ongoing biosecurity vigilance in northern Australia through government, industry and community surveillance is vital (DAFF, 2024a; PHA, 2021). 7.4.2 Pest, weed and disease threats to the Victoria catchment The Victoria catchment principally faces biosecurity risks from pests, weeds and diseases already present in the catchment, and those that occur in neighbouring regions of northern Australia. However, pests, weeds and diseases could also come from other parts of Australia with similar climates and/or production systems, or from overseas. Examples of pests, weeds and diseases that pose a risk to the Victoria catchment are highlighted in the following sections. Whether any one of these would have a significant impact at the property level depends on the local environment, land use and agricultural or aquatic enterprise. However, there is a legal requirement to prevent and manage any pests, weeds or diseases that are formally ‘declared’ under the NT’s biosecurity legislation, regardless of its local impact. Plant industries The priority pests and diseases for cropping in the Victoria catchment depends on what is grown. Table 7-5 includes some examples of high-impact pest and diseases threats to particular crops, and their current status. The NT Government website provides local plant pest and disease management information (NT Government, 2024a), while the NT Plant Health Manual lists all declared pests and diseases (NT Government, 2023). Plant Health Australia is a centralised resource on exotic (i.e. overseas) biosecurity risks to Australia’s plant industries. Research and development corporations, including the Grains Research and Development Corporation, the Cotton Research and Development Corporation, AgriFutures Australia and Hort Innovation also provide extension publications on identifying and managing biosecurity threats. Many pests and diseases have a high host specificity to a particular crop, but there are also generalists that can use many crops as hosts. Local native species can also pose risks of impacts. For example, naturally occurring pathogens of certain native wild rices may infect cultivated rice (Chapman et al., 2020) or native animals may graze on crops. Irrigation brings the potential for year-round cropping, which can provide a ‘green bridge’ in the dry season to enable pests or diseases, including native insects and diseases, to persist and increase locally, and to potentially spread to other areas. A significant new generalist pest of cropping is fall armyworm, which has become widely established across northern Australia since a national incursion was detected in 2020. It is likely to be present year round in the Victoria catchment, with a lower incidence in the dry season (PHA, 2020). Fall armyworm caterpillars favour C4 grass crops (e.g. maize, sorghum, rice) and pastures but may also feed on broadleaved crops such as soybean, melon, green bean and cotton. Young crops are most at risk of severe damage and can require immediate insecticide treatment if invaded at levels above the damage threshold. Cucumber green mottle mosaic virus (CGMMV) infects a wide range of cucurbit crops, including various melons, cucumber, pumpkin and squash, and can also be hosted by a range of broadleaved crop weeds. It causes plant stunting and fruit discolouration, malformation and rotting. CGMMV is present on a number of farms in the NT and has also been found interstate. Its presence on-farm can make access to interstate markets more difficult as many jurisdictions have imposed quarantine requirements. Infected plants cannot be treated, so preventive farm biosecurity measures are vital (NT Government, 2024a). Types of weed threats differ between plant industries according to production methods. For example, annual grain and cotton crops tend to have annual weeds (grasses and herbs) and herbaceous perennials that persist and spread vegetatively through underground rhizomes. Perennial horticulture disturbs the soil less, so typically has more perennial grasses and perennial broadleaved weeds. The highest priority weeds tend to be those that are most difficult to control, such as herbicide-resistant biotypes or species that are otherwise tolerant to routinely used herbicides. For example, some annual grasses that invade cotton crops have developed resistance to certain herbicides, including barnyard grass (Echinochloa spp.) and feathertop Rhodes grass (Chloris virgata) (CRDC, 2023). Various native vertebrates may consume grain and horticultural crops that are becoming established and damage tree crops. These vertebrate pests, include birds (waterfowl, cockatoos), macropods (kangaroos, wallabies) and rodents. Large flocks of magpie geese (Anseranas semipalmata) can be particularly destructive, by trampling, grazing, uprooting and consuming fruit (Clancy, 2020). Table 7-5 Examples of significant pest and disease threats to plant industries in the Victoria catchment BIOSECURITY THREAT CURRENT STATUS CROPS AT RISK FURTHER INFORMATION INVERTEBRATE PESTS Asian citrus psyllid Diaphorina citri Incursion risk from overseas (including Indonesia and PNG). citrus www.agriculture.gov.au/biosecurity- trade/policy/australia/naqs/naqs-target- lists/pests_of_plants_asian_citrus_psyllid cluster caterpillar Spodoptera litura Widespread in northern Australia. cotton, pulses, brassicas www.business.qld.gov.au/industries/farms-fishing- forestry/agriculture/biosecurity/plants/insects/field- crop/cluster-caterpillar fall armyworm Spodoptera frugiperda Established across northern Australia, following first detection in 2020. grasses (cereal and fodder), cotton, soybean, melon, green beans www.nt.gov.au/industry/agriculture/food-crops- plants-and-quarantine/fall-armyworm fruit flies, various species including: Mediterranean fruit fly Ceratitis capitata melon fruit fly Zeugodacus cucurbitae oriental fruit fly Bactrocera dorsalis New Guinea fruit fly B.trivialis Queensland fruit flyB.tryoni Mediterranean fruit fly established in WA. Queensland fruit fly endemic in NT. Melon, oriental, New Guinea and other exotic fruit fly incursion risks from overseas (including Indonesia, PNG) and the Torres Strait. Various species declared. fruit and fruiting vegetable crops www.agriculture.gov.au/biosecurity-trade/pests- diseases-weeds/fruit-flies-australia www.agriculture.gov.au/biosecurity- trade/policy/australia/naqs/naqs-target-lists/fruit- flies Bollworms Helicoverpa spp. Pectinophora spp. Widespread in northern Australia. cotton, pulses, brassica, sunflower, sorghum, maize www.crdc.com.au/publications/cotton-pest- management-guide guava root-knot nematode Meloidogyne enterolobii Recent detection in Darwin region. Declared. cucurbits, solanaceous crops, sweet potato, cotton, guava, ginger www.nt.gov.au/industry/agriculture/food-crops- plants-and-quarantine/guava-root-knot-nematode Leafminers American serpentine leafminer Liriomyza trifolii serpentine leafminer L.huidobrensis vegetable leafminerL.sativae Serpentine and American serpentine leafminers are recent incursions now present in various locations across Australia. Vegetable leafminer an incursion risk from overseas and Torres Strait and is declared in NT. vegetables, cotton www.business.qld.gov.au/industries/farms-fishing- forestry/agriculture/biosecurity/plants/priority- pest-disease/serpentine-leafminer www.agriculture.gov.au/biosecurity- trade/policy/australia/naqs/naqs-target- lists/vegetable_leaf_miner mango pulp weevil Sternochetus frigidus Incursion risk from overseas (including Indonesia). Declared. mango www.agriculture.gov.au/biosecurity- trade/policy/australia/naqs/naqs-target- lists/mango-pulp-weevil mango shoot looper Perixera illepidaria Recent incursion in Queensland and NT. Not declared. mango, lychee www.nt.gov.au/industry/agriculture/food-crops- plants-and-quarantine/mango-shoot-looper melon thrips Thrips palmi Limited presence in NT north of Alligator township. vegetables www.nt.gov.au/industry/agriculture/food-crops- plants-and-quarantine/plants-and- quarantine/travelling-within-the-nt BIOSECURITY THREAT CURRENT STATUS CROPS AT RISK FURTHER INFORMATION spur-throated locust Austracris guttulosa Native to northern Australia. grasses (cereal and fodder), sunflowers, soybeans, cotton www.agriculture.gov.au/biosecurity-trade/pests- diseases-weeds/locusts/about/spur-throated DISEASES Alternaria leaf blight Alternaria alternata Present in northern Australia. cotton www.crdc.com.au/publications/cotton-pest- management-guide banana freckle Phyllosticta cavendishii Under eradication in NT. Declared. banana www.nt.gov.au/industry/agriculture/food-crops- plants-and-quarantine/banana-freckle brown spot Cochliobolus miyabeanus Endemic on wild rices in northern Australia. rice www.agrifutures.com.au/product/rice-growing- guide-north-queensland citrus canker Xanthomonas citri subsp. citri Eradicated from NT and Queensland. Incursion risk from overseas (including Indonesia, Timor-Leste and PNG). Declared. citrus www.nt.gov.au/industry/agriculture/food-crops- plants-and-quarantine/citrus-canker cucumber green mottle mosaic virus Present in certain areas in NT and other states. cucurbits www.nt.gov.au/industry/agriculture/food-crops- plants-and-quarantine/cucumber-green-mottle- mosaic-virus Fusarium wilt Fusarium oxysporum f. sp. vasinfectum Not present in NT. Declared. cotton www.crdc.com.au/publications/cotton-pest- management-guide Huanglongbing Candidatus Liberibacter asiaticus Incursion risk from overseas (including Indonesia, Timor- Leste and PNG). Declared. citrus www.agriculture.gov.au/biosecurity-trade/pests- diseases-weeds/plant/huanglongbing Panama TR4 Fusarium oxysporum f. sp. cubense Established throughout NT. Declared. banana www.business.qld.gov.au/industries/farms-fishing- forestry/agriculture/biosecurity/plants/priority- pest-disease/panama-disease rice blast Pyricularia oryzae Endemic on wild rices in northern Australia. rice www.dpi.nsw.gov.au/biosecurity/plant/insect-pests- and-plant-diseases/rice-blast Declaration status is under the Plant Health Act 2008 (NT), derived from NT Government (2023). Links to further information are current as of March 2024. PNG = Papua New Guinea. Aquaculture A wide range of diseases and parasites are of concern to Australian aquaculture (DAWE, 2020a), including those not known to be in Australia, those now established (i.e. endemic) in Australia and those native to Australian ecosystems. Barramundi farmers need to consider preventing and managing the biosecurity risks of a range of endemic parasites and viral, bacterial and fungal pathogens that naturally occur in northern Australia (Irvin et al., 2018). In addition, national quarantine measures are vital to prevent exotic disease risks for barramundi from entering Australia (Landos et al., 2019). Prawn aquaculture in northern Australia is most at risk from white spot syndrome virus (WSSV), for which there have been national incursion responses at prawn farms and hatcheries in south- east Queensland and northern NSW. However, there are also many other exotic crustacean diseases (DAWE, 2020a). Endemic viruses (and endemic genotypes of viruses also found overseas) that occur naturally in Australian waters can also trigger mortalities or reduce productivity (Irvin et al., 2018). Invasive species Invasive species, whether pest, weed or disease, are commonly characterised as occurring across multiple land uses in a landscape. Their impacts will vary between land uses, but their coordinated control requires action across all tenures. Weeds Table 7-6 lists regional weed priorities in the Victoria catchment (NT Government, 2021). All of these weeds are currently declared under the Northern Territory Weed Management Act 2001, other than other than coffee bush (Leucaena leucocephala), giant rat’s tail grass (Sporobolus spp.) and yellow oleander (Cascabela thevetia). Many in Table 7-6 are WoNS. These are nationally agreed weed priorities that have been a focus for prevention and improved management (CISS, 2021; Hennecke, 2012). For example, the parthenium weed (Parthenium hysterophorus), one of the WoNS, is a direct competitor to and contaminant in dryland and irrigated crops, and poses a health risk to animals and people as a severe allergen. Aquatic weeds can hamper the efficient function of irrigation infrastructure and cause severe ecological impacts through dense infestations in waterways and wetlands. More-constant water flows from within-stream reservoirs can change riparian conditions from seasonally ephemeral to perennial, predisposing native vegetation to invasion by weeds that thrive in moist environments. Terrestrial vertebrate pests Various large feral herbivores are present in the Victoria catchment, including feral buffalo (Bubalus bubalis), horses (Equus caballus), donkeys (E. asinus), pigs (Sus scrofa) and camels (Camelus dromedarius). They can directly affect agricultural production through grazing impacts, severe soil erosion and damaged infrastructure such as fencing and irrigation channels. Feral animal damage to habitats is a key disturbance mechanism that facilitates weed invasion, particularly in riparian and wetland areas. Feral pigs in particular are a major threat to irrigated cropping. Their daily water requirement means that they concentrate during the dry season around watercourses and man-made water supplies (Bengsen et al., 2014). Cane toads (Rhinella marina) are already established in the Victoria catchment (Kearney et al., 2008), but would likely become more abundant around irrigation developments, where they could access year-round moisture. Aquatic pests Freshwater aquatic pests such as non-native fish, molluscs and crustaceans can affect biodiversity and ecosystem function. While these pests may not directly affect irrigated cropping, the associated infrastructure (e.g. dams, channels, drains) brings increased risk of deliberate release by people for recreational fishing or in the disposal of aquarium contents. This infrastructure can also provide enhanced habitat and pathways for the persistence and dispersal of aquatic pests and weeds in the catchment (Ebner et al., 2020). Table 7-6 Regional weed priorities and their management actions in the Victoria catchment Source: NT Government, 2021; NT Government officers, pers. comm. LIFEFORM AND WEED REGIONAL ACTION HABITATS AT RISK: AQUATIC (e.g. river, wetland, dam) WETTER AREAS (e.g. riparian, floodplain, drain) DRIER AREAS (e.g. grassland, woodland) AQUATIC/SEMI-AQUATIC HERB cabomba Cabomba caroliniana† P ✓ ✓ limnocharis Limnocharis flava P ✓ ✓ sagittaria Sagittaria platyphylla† P ✓ ✓ salvinia Salvinia molesta† P ✓ ✓ water hyacinth Pontederia crassipes† P ✓ ✓ water mimosa Neptunia plena P ✓ ✓ GRASS buffel grass Cenchrus ciliaris, C. pennisetiformis § ✓ gamba grass Andropogon gayanus†‡ E ✓ ✓ giant rat’s tail grass Sporobolus spp. P ✓ grader grass Themeda quadrivalvis‡ C ✓ hymenachne Hymenachne amplexicaulis† P ✓ thatch grass Hyparrhenia rufa P ✓ BROADLEAVED HERB devil’s claw Martynia annua E ✓ Parthenium weed Parthenium hysterophorus† P ✓ ✓ CLIMBER/VINE rubber vine Cryptostegia grandiflora† P ✓ ✓ ornamental rubber vine C. madagascariensis P ✓ ✓ TREE/SHRUB Athel pine Tamarix aphylla†‡ E ✓ bellyache bush Jatropha gossypiifolia†‡ C ✓ calotrope Calotropis procera, C. gigantea M ✓ Chinese apple Ziziphus mauritiana‡ C ✓ ✓ coffee bush Leucaena leucocephala M ✓ lantana Lantana camara† P mesquite Prosopis spp.†‡ E ✓ ✓ mimosa Mimosa pigra†‡ E ✓ neem Azadirachta indica‡ C ✓ parkinsonia Parkinsonia aculeata† M ✓ pond apple Annona glabra† P ✓ ✓ prickly acacia Vachellia nilotica†‡ E ✓ Siam weed Chromolaena odorata P ✓ ✓ yellow oleander Cascabela thevetia M ✓ ✓ OTHER rope cactus Cylindropuntia spp.† P ✓ † On the Weeds of National Significance (WoNS) list. ‡ Have statutory management plans under the Weeds Management Act 2001 (NT). § Declared in 2024 and thus not categorised for management action in the current regional weed management plan (NT Government, 2021). C = strategic control target (control and containment of core infestations, eradication of outlier populations, prevention elsewhere). E = eradication target (few infestations known). M = widely established; regional management focused on protecting assets at risk. P = alert weed for prevention and early intervention. Table 7-7 includes examples of high-risk pest fish for the Victoria catchment. Certain species are formally declared as noxious under the Northern Territory Fisheries Regulations 1992. However, those not declared noxious are still covered by a general precautionary provision that excludes import into the NT and possession of non-native fish that are not on the Australian Government’s list of permitted live freshwater ornamental fish (DAFF, 2023), or otherwise not listed as a permitted import in Schedule 7 of the Regulations. Table 7-7 High-risk freshwater pest fish threats to the Victoria catchment Source: Australian Government and NT Government, n.d.; Queensland Government, 2023 PEST FISH LEGAL STATUS (IF ANY) CURRENT DISTRIBUTION alligator gar Atractosteus spatula N Not known to be in the wild in Australia. black pacu Piaractus brachypomus E Not known to be in the wild in Australia. Risk of incursion from PNG. carp Cyprinus carpio N Not known to be in the wild in NT. cichlids, including tilapia: giant cichlid Boulengerochromis microlepis N Giant cichlid not known to be in the wild in Australia. Jaguar, pearl and Texas cichlid and Mozambique and spotted tilapia present in the wild in Queensland. Mozambique tilapia and pearl cichlid also present in the wild in WA. Not known to be in the wild in NT. Nile tilapia an incursion risk from northern Torres Strait. All tilapia species noxious. jaguar cichlid Parachromis managuensis E Mozambique tilapia Oreochromis mossambicus N Nile tilapia O. niloticus N pearl cichlid Geophagus brasiliensis E spotted tilapia Pelmatolapia mariae N Texas cichlid Herichthys cyanoguttatus E climbing perch Anabas testudineus N Risk of incursion from northern Torres Strait. gambusia / mosquito fish Gambusia holbrooki N Not known to be established in NT (eradicated in Darwin and Alice Springs). Recorded in the wild across Queensland and parts of WA. guppy Poecilia reticulata Recorded in Darwin and Nhulunbuy in NT. Likely to be present elsewhere. marbled lungfish Protopterus aethiopicus N Not known to be in the wild in Australia. oriental weatherloach Misgurnus anguillicaudatus N Not known to be in the wild in NT. oscar Astronotus ocellatus Not known to be in the wild in NT. Present in the wild in Queensland. platy Xiphophorus maculatus Present in the wild in Darwin and Nhulunbuy in NT, and in eastern Queensland. Siamese fighting fish Betta splendens Established in the Adelaide catchment in NT. Not known to be in the wild elsewhere in Australia. spotted gar Lepisosteus oculatus N Not known to be in the wild in Australia. swordtail Xiphophorus hellerii Present in the wild in Darwin and Nhulunbuy in NT, and in eastern Queensland. E = excluded for imports into and possession in the NT. N = noxious under the Northern Territory Fisheries Regulations 1992. n.d. = no date. Terrestrial invertebrates Terrestrial invertebrates can be high-impact invasive species. For example, certain exotic ants form ‘super colonies’ from which they outcompete native ants, consume native invertebrates and seeds, and affect people by stinging them and infesting buildings. Some ant species ‘farm’ sap- sucking scale insects that are pests of horticultural crops and native plants. Non-native ants can be introduced in pot plants, soil or among other materials. Yellow crazy ant (Anoplolepis gracilipes) has been detected in Darwin and Arnhem Land. Browsing ant (Lepisiota frauenfeldi) has been the subject of a national eradication program, including in Darwin and Kakadu in the NT. Other national eradication programs continue for red imported fire ant (Solenopsis invicta) in south-east Queensland and electric ant (Wasmannia auropunctata) in far north Queensland (Outbreak, 2024; Environment and Invasives Committee, 2019). The national eradication program for red imported fire ant has cost $596 million (Outbreak, 2023a). Diseases Examples of diseases that affect multiple species of native, ornamental and crop plants are myrtle rust and phytophthora (Phytophthora spp.). They can cause the death of plants, including established shrubs and trees. 7.4.3 Preventing, responding to and managing biosecurity threats Biosecurity can be categorised into three broad approaches: •Prevention - taking measures to stop movement along pathways of spread, whether that be atthe international or state border, to and within a catchment, or between and within properties •Incursion response - undertaking surveillance to detect new pests, weeds or diseases andattempting eradication upon detection, where feasible and cost-beneficial to do so •Ongoing management – managing a pest, weed or disease that is firmly established in an area(i.e. is not feasible to eradicate), with control measures regularly applied to contain furtherspread and/or mitigate impacts. The invasion curve (Figure 7-13) is commonly used as a visual representation of biosecurity actions taken at various stages of pest invasion. It applies at any scale from national down to an individual property. Prevention and eradication generally cost far less than the ongoing management which is needed for widely established species (i.e. containment and impact mitigation), although improved management tools may substantially reduce long-term costs. For more information on this figure please contact CSIRO on enquiries@csiro.au Figure 7-13 The invasion curve with biosecurity actions taken at various stages Source: J. Virtue Shared responsibility at all levels Effective biosecurity requires a collaborative approach between government, industry and community, from the organisational to the individual level. Such ‘shared responsibility’ includes taking action to limit the risk of entry and spread of new pests, weeds and diseases, routinely looking for incursions and reporting high-risk species if and when detected, and collaborating in coordinated control programs across land tenures. Everyone has a duty of care (whether legal or moral) to not pose a biosecurity risk to others, including to not harbour invasive species that may threaten economic, environmental, social or cultural impacts to neighbouring land uses. The NT’s biosecurity system (NT Government, 2016) is nested in the national biosecurity system of Australia’s border quarantine and states’ and territory’s domestic quarantine and control program arrangements (DAFF, 2022a). Broadly defined, the national biosecurity system consists of the combined Australian, state and territory governments’ biosecurity legislative frameworks that seek to prevent pests, weeds and diseases entering, establishing, spreading and having an impact in Australia. It involves cooperation and collaboration between jurisdictions, and working with and supporting industry and community to involve multiple organisations across Australia as biosecurity partners. Various national agreements, plans and governance arrangements drive this shared responsibility ethos. The following sections describe prevention, incursion response and ongoing management activities for plant industries, aquaculture and invasive species in the Victoria catchment, within local, NT and national contexts. Biosecurity in plant industries Farm biosecurity planning In practice, most plant industry biosecurity activities – whether prevention, preparedness, surveillance, elimination, containment or ongoing management – occur at the property level. This level is where the relationship between expenditure on crop protection and maintaining profit- driven productivity and market access is most direct. Developing and implementing a farm biosecurity plan is an effective means to prevent the introduction and establishment of new pests, weeds and diseases, and to limit the spread and impacts of those that are already established. Standard guidance is available on developing such plans (AHA and PHA, n.d.), which cover hygiene practices for pathways of introduction (e.g. certified seed, machinery and vehicle washdowns, restricted movement of visitors), routine surveillance and quick responses to any on-farm identified biosecurity risks. Associated with implementing these are signage (e.g. Figure 7-14), staff training, mapping, visitor management, record keeping, reporting and annual activity planning. A farm biosecurity plan is informed by the key biosecurity threats to the crops being grown, and broader invasive species risks. A plan should cover both incursion risks and those pests, weeds and diseases already present. It also needs to align with government regulatory requirements and industry standards. For more information on this figure please contact CSIRO on enquiries@csiro.au Figure 7-14 Farm biosecurity signage available through farmbiosecurity website Regulatory prevention Government regulation and policy for plant biosecurity in the Victoria catchment are primarily governed by the Northern Territory Plant Health Act 2008. Specific legal requirements are summarised in the Northern Territory plant health manual (NT Government, 2023), which lists currently declared pests and diseases (and those that must be reported if detected in the NT), and associated entry conditions for all commercial and non-commercial movement of plants and plant products. For example, the NT restricts the entry of maize and soybean seed due to disease risks and the entry of nursery stock due to risk of introducing scale insects and sucking insects. Soil attached to used farm machinery, containers and earth-moving machinery may carry pests or diseases such as nematodes, snails, Phytophthora or Fusarium. Hence these items are legally required to be clean of soil, and a permit may be required for their entry into NT. In relation to used machinery for cotton production, the NT seeks to retain its ‘area freedom’ status for cotton fusarium wilt (Fusarium oxysporum f. sp. vasinfectum), which is established in cotton-growing areas in Queensland and NSW (Le et al., 2020). To access interstate markets, produce must meet the respective quarantine specifications and protocols, so that pests or diseases declared in those jurisdictions are not inadvertently introduced. This typically requires an inspection and the issue of a certificate verifying that conditions have been met, or that the property is in an area known to be free of a specific pest of concern (NT Government, 2023). For example, South Australia has movement restrictions (as of March 2024) on the entry of melons and other hosts of melon thrips (Thrips palmi) from jurisdictions where it is known to occur, including the NT (PIRSA, 2024). Current information on moving plant goods interstate is compiled on the Australian Interstate Quarantine website (Subcommittee on Domestic Quarantine and Market Access, 2024). Exports to overseas markets must meet Australian standards and any additional entry requirements from the importing countries for the products (DAFF, 2024b). This includes certification and supporting documentation relating to area freedom and/or treatments applied for specific pests, weeds and/or diseases. Depending on the country, there also may be maximum residue limits, or even nil tolerances, for specific pesticides. Exports are regulated by the Australian Government through the Commonwealth’s Export Control Act 2020 and associated rules for particular produce and products. Incursion response Most plant industries have national biosecurity, surveillance and/or preparedness plans for high- risk exotic pests and diseases that pose national incursion risks (PHA, 2024a). Entry of these pests and diseases into Australia is prevented by the Australian Government’s pre-border and border quarantine requirements under the Commonwealth Biosecurity Act 2015. The Australian Government’s Northern Australia Quarantine Strategy is an ongoing surveillance program that seeks to detect incursions from countries to Australia’s north (DAFF, 2024a). Plant Health Australia (PHA) is the custodian of the Emergency Plant Pest Response Deed (EPPRD; Anon., 2024), which specifies how governments and affected industries undertake collaborative national eradication responses, including cost sharing and decision making. PLANTPLAN provides accompanying national guidelines for managing responses to emergency plant pest incidents at national, state or territory, and local levels (PHA, 2022). For example, banana freckle (Phyllosticta cavendishii) is currently the subject of an EPPRD national eradication program in the NT (Outbreak, 2023b). Ongoing management Best management practice guides for control of established pests, weeds and diseases are available through the research and development corporations, other industry organisations and state primary industries departments, with some specific to cropping in northern Australia (e.g. NT Government, 2014; NT Farmers, 2022). These extension materials focus on integrated management approaches that combine a range of control practices (e.g. chemical, physical and biological control methods). The cotton industry also has a broader online best management practice assurance system (myBMP, 2024), which includes modules on integrated pest management and pesticide management. Additionally, the Grains Farm Biosecurity Program is an initiative to improve the management of, and preparedness for, biosecurity risks in the grains industry at the farm and industry levels (PHA, 2024b). Pesticides must be approved for use by the Australian Pesticides and Veterinary Medicines Authority (APVMA) and applied in a manner that aligns with requirements of the NT’s Agricultural and Veterinary Chemicals (Control of Use) Act 2004. This includes minimising spray drift, following label requirements for work health and safety, and ensuring appropriate applicator skills and licences. There are maximum permissible levels for certain pesticides in specified agricultural produce, achieved by following pesticide label requirements (or a Australian Pesticides and Veterinary Medicines Authority permit) regarding approved crops, rates and frequency of application, and withholding periods (NT Government, 2024c). A key consideration for ongoing management on-farm is ensuring chemical control tools are used tactically to limit the risk of developing insecticide, herbicide and fungicide resistance (Grains Research and Development Corporation, 2024; CropLife Australia, 2021). For example, growers cultivating Bollgard® 3 and Roundup Ready Flex® cotton must follow on-farm stewardship packages (Bayer, 2023). Growers whose crop production is affected by native animals may require NT Government permits before taking any lethal control measures. On-property storage of harvested grain needs consideration of physical and chemical means to prevent beetle and weevil pests (Grain Storage Extension Project, 2024). Biosecurity in aquaculture Plan for prevention Prevention in aquaculture starts with enterprise-level biosecurity planning. This is vital in protecting aquaculture facilities from diseases and parasites, which can be difficult to eliminate, let alone manage, once established. Planning guides have been developed for various industries, including barramundi (Landos et al., 2019) and oyster hatcheries. Preventing entry of pathogens into facilities is vital. Growers need to understand the various disease risks and where they could come from. Wild-captured broodstock poses a very high risk of introducing endemic diseases; stock known to be free from specific diseases should be sourced (Cobcroft et al., 2020). Diseases may enter a facility through contaminated equipment, workers handling diseased fish, water that is harbouring pathogens, or wild animals such as birds entering ponds (Irvin et al., 2018). Untreated source water is a key pathway for disease entry, with pathogen risks coming from wild stocks or, potentially, a nearby upstream aquaculture facility (Irvin et al., 2018). Pathogen monitoring should be ongoing, and emergency response plans should be developed to isolate any detected disease occurrence and implement thorough disinfestation procedures. Commercial aquaculture is regulated through the Northern Territory Fisheries Act 1998, and the Northern Territory Fisheries Regulations 1992. The Regulations prohibit movement or sale of diseased fish and require reporting of any legally notifiable diseases detected in aquaculture facilities. Movement of all stock is under a permit system, and health assessments are conducted to manage the risk of disease movement through movement of aquaculture stock. Incursion response AQUAPLAN is the national aquatic animal health strategic plan; it aims to improve border, enterprise and regional biosecurity measures, and build surveillance, diagnostic capacity and emergency preparedness (DAFF, 2022b). There is also national policy guidance on minimising the movement of disease when translocating live aquatic animals for aquaculture and other purposes (DAWE, 2020b). The NT Government can declare a control area in the event of an actual or likely notifiable disease outbreak in an aquaculture facility, providing for limits on further fish movement, halting the release of aquaculture water, and/or requiring mandatory treatment or destruction measures for fish and contaminated equipment. Having aquaculture biosecurity plans is not just about protecting the enterprise. There is also a duty of care to protect nearby wild fisheries which may be exposed to disease from discharge waters, escapee infected animals or fish movement via predatory birds. Prompt isolation of affected ponds and preventing water flow from these to the surrounding environment are vital in the event of a disease outbreak. The escape of white spot syndrome virus from prawn farms in Queensland and NSW led to restrictions on commercial and recreational fishing of crustaceans in adjacent catchments, with substantial local economic impacts. Ongoing management Treatment options are limited for aquatic diseases, particularly viral pathogens. Veterinary medicines, such as antibiotics for bacterial disease in barramundi, are available. However, their use can require veterinary permission in order to manage risks of antimicrobial resistance, both in the aquaculture facility itself and the broader food chain. Fungal and external protozoan pathogens may be able to be suppressed using altered salinity bathing. Most fundamentally is the need for a high-quality rearing environment, with optimal water conditions and feed supply, to reduce the risk of stress-induced disease outbreaks (Irvin et al., 2018). Biosecurity for invasive species Irrigation development planning Regional and local irrigation and industry infrastructure development, including road networks, should include prevention and management of invasive species in their environmental planning processes. This includes meeting legal obligations under the various Acts already mentioned, a stocktake of present distribution of declared species, and risk mitigation to limit pathways of introduction of new invasive species during construction and ongoing maintenance. Ongoing monitoring should be implemented for terrestrial and aquatic pests (vertebrate and invertebrate), and weeds. Weeds The Victoria catchment is within the scope of the Katherine Regional Weeds Strategy (NT Government, 2021) which collates the priority declared weed control programs, as coordinated by the NT Government. Under the Northern Territory Weeds Management Act 2001 every landholder is legally obliged to take all reasonable measures to prevent land being infested with a declared weed and to prevent a declared weed from spreading. There are also prohibitions on buying, selling, cultivating, moving or propagating any declared weed, and a legal requirement to notify a declared weed’s presence if it is new to a property. Certain declared plants, such as gamba grass, neem (Azadirachta indica) and bellyache bush (Jatropha gossypiifolia) also have statutory management plans. The NT Government website and other Australian websites (e.g. www.weeds.org.au) provide best management practice information on how to control declared weeds and other invasive plants, including registered herbicides and biological control agents. In particular, much information is available on management on WoNS (CISS, 2021). In selecting new crops and pastures for planting in the Victoria catchment, landholders should consider their crops’ weed risks to the surrounding environment. An example method for considering weed risks is the Western Australian Government’s environmental weed risk assessment process for plant introductions to pastoral lease land (Moore et al., 2022). Many northern Australia pasture grasses can be invasive, and cause significant biodiversity and cultural impacts in the landscape (Australian Government, 2012). Cotton is not considered to pose a significant environmental weed threat in northern Australia (Office of the Gene Technology Regulator, 2024). It has been sporadically recorded across northern Australia on roadsides, near cropping fields, in irrigation drains and adjacent to natural watercourses (Atlas of Living Australia, 2024). However, modern varieties’ ability to establish and reproduce is constrained by dense lint around seeds impeding germination, seed predation, seasonal drought, competition from established plants, herbivory and fire (Eastick and Hearnden 2006; Rogers et al., 2007). Nonetheless, it is recommended that transport of harvested cotton is covered to reduce the likelihood of spread outside cultivation (Addison et al., 2007). Terrestrial vertebrate pests Large feral herbivores are controlled through mustering, trapping, baiting and/or aerial or ground shooting programs, depending on the approved humane control methods for particular species (CISS, 2024; NT Government, 2024d). For long-term suppression, programs need to be conducted over multiple years at a subregional scale across all infested properties, taking account of animal movements and subpopulations. Ongoing control is then needed to maintain low densities. 7.5 Off-site and downstream impacts 7.5.1 Introduction Northern Australian river systems are distinctive as they have highly variable flow regimes, unique species composition, low human population densities and, in some cases, naturally high turbidity (Brodie and Mitchell, 2005). Primary influences on groundwater and surface water quality include increased sediment loads associated with land clearing, grazing, agriculture and late dry-season fires, and nutrient pollution from agricultural and pastoral land use (Dixon et al., 2011). These can affect the water quality of not just groundwater and rivers, lakes and wetlands but also estuarine and marine ecosystems. The principal pollutants from agriculture are nitrogen, phosphorus, total suspended solids, herbicides and pesticides (Lewis et al., 2009; Kroon et al., 2016; Davis et al., 2017). Water losses via runoff or deep drainage are the main pathways by which agricultural pollutants enter water bodies. The type and quantity of pollutants lost from an agricultural system and ultimately the quality of the receiving surface and groundwater is significantly influenced by a wide range of factors, including environment factors such as climate, hydrology, soils, hydro geochemistry and topography as well as land use and management factors such as crops, cropping system, method of application of irrigation water, tailwater management, quality of source water, location and proximity to drainage lines and conservation and irrigation practices. Due to the high dependency of the location, design, implementation and operation of an irrigation development on water quality predicting water quality impacts associated with irrigated agriculture is very difficult. Rather the influence of these environment and management factors on water quality are discussed in more detail in the companion technical report on water quality (Motson et al., 2024). Most of the science in northern Australia concerned with the downstream impacts of agricultural development has been undertaken in the eastern-flowing rivers that flow into the Great Barrier Reef lagoon. Comparatively little research on the topic has been done in the rest of northern Australia and there is need for caution in transposing findings from north-eastern Australia, which is different in terms of climate, geomorphology and patterns of settlement to those parts of northern Australia west of the Great Dividing Range. Nonetheless experience from north-eastern Australia has been that the development of agriculture has been associated with declining water quality (Lewis et al., 2009; Mitchell et al., 2009; De’ath et al., 2012; Waterhouse et al., 2012; Thorburn et al., 2013; Kroon et al., 2016). Pollutant loads in north-eastern Australian rivers (typically those in which agriculture dominates as a land use) are estimated to have increased considerably since European settlement in the 1850s for nitrogen (2 to 9 times baseline levels), phosphorus (3 to 9 times), suspended sediment (3 to 6 times) and pesticides (~17,000 kg) (Kroon et al., 2016). 7.5.2 Impacts of changes in water quality on aquatic ecosystems Degraded water quality can cause a loss of aquatic habitat, biodiversity, and ecosystem services. Increased nitrogen and phosphorus can cause plankton blooms and weed infestation, increase hypoxia (low oxygen levels) and result in fish deaths. Pesticides, used to increase agricultural productivity, can harm downstream aquatic ecosystems, flora and fauna. As with fertiliser nutrients, pesticides can enter surface water bodies and groundwater via infiltration, leaching, and runoff from rainfall events and irrigation. These chemicals can be toxic to non-target species, such as aquatic life and humans, affecting nervous systems, immune systems, photosynthesis and growth (Cantin et al., 2007; Kaur et al., 2019; Naccarato et al., 2023). They can be carcinogenic (Mohanty and Jena, 2019) and cause multiple sub-lethal effects that can disrupt the ecological balance of aquatic systems and degrade aquatic communities (Giglio and Vommaro, 2022; Miller et al., 2020; Wang et al., 2022). Other water quality variables that can have a significant effect on the health of aquatic species, communities and ecosystems include salinity, pH, and suspended sediments. Increased salinity, indicated by increased EC and TDS, can interfere with osmoregulatory processes, harming those species not adapted to saline conditions (Hart et al., 2003). Variations in the pH of a water body can negatively affect an organism’s biochemical processes, leading to altered behaviour, functioning, growth, and even survival (U.S. EPA, 2024). In aquatic ecosystems, elevated loads of suspended sediment can smother habitats and benthic invertebrates, affect the feeding and respiratory systems of aquatic species, and reduce light penetration, affecting photosynthetic activity (Chapman et al., 2017). Table 7-8 Water quality variables reviewed – their impacts on the environment, aquatic ecology and human health WATER QUALITY VARIABLE THREATS TO AQUATIC ECOLOGY AND HUMAN HEALTH REFERENCE Nutrients Nitrogen Forms of nitrogen in freshwater systems include: nitrate (NO3), nitrite (NO2), ammonia (NH3) and ammonium (NH4). In excessive quantities, contributes to eutrophication and algal blooms, which can deplete oxygen and create hypoxic/anoxic conditions harmful to aquatic life. Health threat to humans, particularly infants, and mammals Carpenter et al. (1998) Phosphorus High concentrations may lead to eutrophication and algal blooms, which can deplete oxygen and create hypoxic/anoxic conditions harmful to aquatic life Mainstone and Parr (2002) Dissolved Organic Carbon A proxy for dissolved organic matter, affecting water clarity, temperature, biogeochemical processes, food webs and ecosystem productivity. Dissolved Organic Carbon may exacerbate eutrophication and hypoxia in aquatic ecosystems, and cause problems in drinking water treatment processes Palviainen et al. (2022) Pesticide groups Arylurea Includes pesticides such as Diuron® and tebuthiuron. May inhibit photosynthesis in plants and aquatic species. These pesticides are less soluble in water and better absorbed by the soil Cantin et al. (2007), Fojut et al. (2012) Carbamates Broad-spectrum pesticides that affect nerve impulse transmission and are highly toxic to vertebrate species. Suspected carcinogens and mutagens. Relatively low persistence; not easily adsorbed to soil particles Kaur et al. (2019), Rad et al. (2022) Chloroacetanilides Affects cell division, disrupting aquatic plant growth; also toxic to aquatic insects. Persistent. Low binding affinity to soil particles but highly water soluble; therefore, it has a high capacity for leaching into the groundwater and ending up in surface water. Carcinogens with moderate to high chronic toxicity ANZG (2020), Mohanty and Jena (2019) Dinitroanilines Broad-spectrum herbicides with low water solubility; considered non- mobile in soil. Affect seed germination and root growth in plants. Variable, species-specific toxicity ranging from slightly to highly acute. Hazardous to animals and humans in sub-lethal concentrations. Known bioaccumulation in and acute toxicity to aquatic organisms Giglio and Vommaro (2022) Neonicotinoids Highly toxic to invertebrates, particularly aquatic insects. Sub-lethal toxicity in fish. High solubility. High chronic risk to global freshwater ecosystems. Suspected to be carcinogenic Wang et al. (2022) Organochlorines Persistent organic pollutants that can bioaccumulate in fatty tissues. These pesticides are toxic to humans and other animals, and they are highly toxic to most aquatic life DCCEEW (2021) Kaur et al. (2019) Phenylpyrazole These pesticides disrupt nerve impulse transmission. Toxic to aquatic organisms and birds. Phenylpyrazole pesticides, such as Fipronil, have been found to degrade stream communities. Moderate water solubility and hydrophobicity. Slightly mobile in soils. Moderate persistence Gao et al. (2020), Miller et al. (2020) Triazine Inhibits photosynthesis in plants, potentially leading to reduced plant growth and blocks food intake by insect pests. Short to moderate Naccarato et al. (2023) WATER THREATS TO AQUATIC ECOLOGY AND HUMAN HEALTH REFERENCE persistence depending on soil pH. Adverse and sub-lethal effects on terrestrial and aquatic non-target organisms, affecting growth and the nervous and immune systems Salinity Can affect osmoregulatory processes of aquatic species, harming aquatic life not adapted to saline water. Significant increases in salinity may compromise the integrity of freshwater ecosystems Hart et al. (2003) Other Total Suspended Solids Can smother habitats, reduce light penetration (through increasing turbidity), and affect the feeding and respiratory systems of aquatic organisms Chapman et al. (2017) pH Variations can negatively affect aquatic life stages, affecting their biochemical processes. Preferred pH range of 6.4–8.4 for aquatic species U.S. E.P.A (2024) 7.5.3 Impacts of irrigated agriculture on water quality Fertiliser applications in irrigated agriculture can significantly affect nutrient levels in drainage waters, leading to increased concentrations of total phosphorous (TP) and total nitrogen (TN) in surface waters during the irrigation season (Barbieri et al., 2021; Mosley and Fleming, 2010). The type of cropping system employed also plays a crucial role in determining groundwater nutrient concentrations. For example, variations in cropping practices, such as mulch-till versus ridge-till systems, can result in substantial differences in nitrate levels, underscoring the importance of adopting best management practices for protecting groundwater quality (Albus and Knighton, 1998). Surface water quality is similarly affected by nutrient inputs, with concentrations of TP often decreasing as streamflow increases, suggesting a dilution effect (Skhiri and Dechmi, 2012). However, this relationship can be inconsistent, as dilution effects may not be evident when only storm event streamflow is considered. Instead, TP concentrations are influenced by a combination of factors, including rainfall duration and intensity, as well as irrigation and fertiliser application practices. The interplay of these factors highlights the complex interactions between rainfall, irrigation, and nutrient management in determining both surface water and groundwater quality outcomes. Controlled pesticide use is crucial for managing its impact on surface water quality. When pesticide application rates are managed and irrigation schedules are aligned with crop growth stages, their concentrations are typically low. Pesticide-specific application practices also influence runoff concentrations: pesticides that are applied to, and therefore intercepted by, the crop canopy have significantly lower surface water concentrations relative to those applied to bare soil (Moulden et al., 2006). Seasonal hydrology, particularly ‘first-flush’ events following irrigation or significant rainfall, plays a critical role in determining water quality (Davis et al., 2013; Yeates, 2016). Studies have shown that pesticide concentrations in runoff are highest following initial irrigation events but decrease in subsequent events (Davis et al., 2013). Despite this dilution, pesticide concentrations in receiving waters can still exceed recommended levels. Similarly, nitrogen concentrations in runoff are often higher following early-season rainfall, when crops have not yet fully absorbed available nitrogen, leading to increased transport in runoff (Yeates, 2016). These findings underscore the importance of implementing sustainable irrigation management practices and highlight the need for continuous monitoring and adaptive management to mitigate the impacts of agricultural activities on water quality. Ensuring effective management is vital for protecting water resources and maintaining the ecological integrity of aquatic ecosystems and communities amid agricultural intensification. The potential for irrigated agriculture to cause secondary salinisation is discussed in Section 7.6. Managing irrigation drainage Surface drainage water is water that runs off irrigation developments as a result of over-irrigation or rainfall. This is mostly an issue where water is applied using surface irrigation methods (e.g. furrow, flood) rather than spray or micro-irrigation methods (e.g. drip, micro-spray). This excess water can potentially affect the surrounding environment by modifying flow regimes and changing water quality. Hence, management of irrigation or agricultural drainage waters is a key consideration when evaluating and developing new irrigation systems and should be given careful consideration during the planning and design processes. Regulatory constraints on the disposal of agricultural drainage water from irrigated lands are being made more stringent as this disposal can potentially have significant off-site environmental effects (Tanji and Kielen, 2002). Hence, minimising drainage water through the use of best-practice irrigation design and management should be a priority in any new irrigation development in northern Australia. This involves integrating sound irrigation systems, drainage networks and disposal options so as to minimise off-site impacts. Surface drainage networks must be designed to cope with the runoff associated with irrigation, and also the runoff induced by rainfall events on irrigated lands. Drainage must be adequate to remove excess water from irrigated fields in a timely manner and hence reduce waterlogging and potential salinisation, which can seriously limit crop yields. In best-practice design, surface drainage water is generally reused through a surface drainage recycling system where runoff tailwater is returned to an on-farm storage or used to irrigate subsequent fields within an irrigation cycle. The quality of drainage water depends on a range of factors including water management and method of application, soil properties, method and timing of fertiliser and pesticide application, hydrogeology, climate and drainage system (Tanji and Kielen, 2002). These factors need to be taken into consideration when implementing drainage system water recycling and also when disposing of drainage water to natural environments. A major concern with tailwater drainage is the agricultural pollutants derived from pesticides and fertilisers that are generally associated with intensive cropping and are found in the tailwater from irrigated fields. Crop chemicals can enter surface drainage water if poor water application practices or significant rainfall events occur after pesticide or fertiliser application (Tanji and Kielen, 2002). Thus, tailwater runoff may contain phosphate, organic nitrogen and pesticides that have the potential to adversely affect flora and fauna and ecosystem health, on land and in waterways, estuaries or marine environments. Tailwater runoff may also contain elevated levels of salts, particularly if the runoff has been generated on saline surface soils. Training irrigators in responsible application of both water and agrochemicals is therefore an essential component of sustainable management of irrigation. As tailwater runoff is either discharged from the catchment or captured and recycled, it can result in a build-up of agricultural pollutants that may ultimately require disposal from the irrigation fields. In externally draining basins, the highly seasonal nature of flows in northern Australia does offer opportunities to dispose of poor-quality tailwater during high-flow events. However, downstream consequences are possible, and no scientific evidence is available to recommend such disposal as good practice. Hence, consideration should be given to providing an adequate understanding of the downstream consequences of disposing of drainage effluent, and options must be provided for managing disposal that minimise impacts on natural systems. 7.5.4 Natural processing of water contaminants While elevated contaminants and water quality parameters can harm the environment and human health, there are several processes by which aquatic ecosystems can partially process contaminants and regulate water quality. Denitrification, for example, is the process of anaerobic microbial respiration which, in the presence of carbon, reduces nitrogen to nitrous oxide and dinitrogen gas (Martens, 2005). Therefore, denitrification is a naturally occurring process that can remove and reduce nitrogen concentrations within a water body. Pesticides can also be naturally removed from water via chemical oxidation, microbial degradation, or ultraviolet photolysis, although some chemically stable pesticides are highly persistent, and their microbial degradation is slow (Hassaan and El Nemr, 2020). Phosphorus, however, does not have a microbial reduction process equivalent to denitrification. Instead, if it is not temporarily taken up by plants, phosphorus can be adsorbed onto the surface of inorganic and organic particles and stored in the soil, or deposited in the sediments of water bodies, such as wetlands (Finlayson, 2022). This phosphorus can be remobilised into solution and re-adsorbed, resulting in ‘legacy’ phosphorus that can affect water quality for many years (Records et al., 2016). 7.5.5 Water quality considerations relevant to aquaculture Aquaculture can be impacted by poor water quality and can also contribute to poor water quality unless aquaculture operations are well managed. A summary is provided below, however, for more information see Northern Australia Water Resource Assessment report on aquaculture viability (Irvin et al., 2018). Chemical contaminant risk to aquaculture and the environment Hundreds of different chemicals, including oils, metals, pharmaceuticals, fertilisers and pesticides (i.e. insecticides, herbicides, fungicides), are used in different agricultural, horticultural and mining sectors, and in industrial and domestic settings, throughout Australia. Releasing these chemical contaminants beyond the area of target application can contaminate soils, sediments and waters in nearby environments. In aquatic environments, including aquaculture environments, fertilisers have the potential to cause non-point source pollution. Eutrophication is caused by nutrients that trigger excessive growth of plant and algal species, which then form hypoxic ‘dead zones’ and potentially elevated levels of toxic un-ionised ammonia (Kremser and Schnug, 2002). This can have a significant impact on the health and growth of animals in aquaculture operations, as well as in the broader environment. Of concern to aquaculture in northern Australia are the risks posed to crustaceans (e.g. prawns and crabs) by some of the insecticides in current use. These are classified based on their specific chemical properties and modes of action. The different classes of insecticides have broad and overlapping applications across different settings. The toxicity of organophosphate insecticides is not specific to target insects, raising concerns about the impacts on non-target organisms such as crustaceans and fish. Despite concerns about human health impacts and potential carcinogenic risks, organophosphates are still one of the most broadly used types of insecticide globally, and they are still used in Australia for domestic pest control (Weston and Lydy, 2014; Zhao and Chen, 2016). Pyrethroid insecticides have low toxicity to birds and mammals, but higher toxicity to fish and arthropods. Phenylpyrazole insecticides also pose risks to non-target crustaceans (Stevens et al., 2011). Neonicotinoid insecticides are being used in increasing amounts because they are very effective at eliminating insect pests, yet they pose low risks to mammals and fish (Sánchez-Bayo and Hyne, 2014). Monitoring data from the Great Barrier Reef catchments indicate that the concentration of neonicotinoid insecticides in marine water samples is rapidly increasing with widespread use. One significant concern for aquaculture is the risk that different insecticides, when exposed to non-target organisms, may interact to cause additive or greater-than-additive toxicity. Aquaculture discharge water and off-site impacts Discharge water is effluent from land-based aquaculture production (Irvin et al., 2018). It is water that has been used (culture water) and is no longer required in a production system. In most operations (particularly marine), bioremediation is used to ensure that water discharged off-farm into the environment contains low amounts of nutrients and other contaminants. The aim is for discharge waters to have similar physiochemical parameters to the source water. Discharge water from freshwater aquaculture can be easily managed and provides a water resource suitable for general or agriculture-specific irrigation. Discharge water from marine aquaculture is comparatively difficult to manage and has limited reuse applications. The key difference in discharge management is that marine (salty) water must be discharged at the source, whereas the location for freshwater discharge is less restrictive and potential applications (e.g. irrigation) are numerous. Specific water discharge guidelines vary with aquaculture species and jurisdiction. For example, Queensland water discharge policy minimum standards for prawn farming include standards for physiochemical indicators (e.g. oxygen and pH) and nutrients (e.g. nitrogen, phosphorus and suspended solids) and total volume (EHP, 2013). The volume of water required to be discharged or possibly diverted to a secondary application (e.g. agriculture) is equivalent to the total pond water use for the season minus total evaporative losses and the volume of recycled water used during production. A large multidisciplinary study of intensive Australian prawn farming, which assessed the impact of effluent on downstream environments (CSIRO, 2013), found that Australian farms operate under world’s best practice for the management of discharge water. The study found that discharge water had no adverse ecological impact on the receiving environment and that nutrients could not be detected 2 km downstream from the discharge point. While Australian prawn farms are reported as being among the most environmentally sustainable in the world (CSIRO, 2013), the location of the industry adjacent to the World Heritage listed Great Barrier Reef and related strict policy on discharge has been a major constraint to the industry’s expansion. Strict discharge regulation, which requires zero net addition of nutrients in waters adjacent to the Great Barrier Reef, has all but halted expansion in the last decade. An example of the regulatory complexity in this region is the 14-year period taken to obtain approval to develop a site in the Burdekin shire in north Queensland (APFA, 2016). In a report to the Queensland Government (Department of Agriculture and Fisheries Queensland, 2013), it was suggested that less-populated areas in northern Australia, which have less conflict for the marine resource, may have potential as areas for aquaculture development. The complex regulatory environment in Queensland was a factor in the decision by Project Sea Dragon to investigate greenfield development in WA and NT as an alternative location for what would be Australia’s largest prawn farm (Seafarms, 2016). Today, most farms (particularly marine) use bioremediation ponds to ensure that water discharged off-farm into the environment contains low amounts of nutrients and other contaminants. The prawn farming industry in Queensland has adopted a code of practice to ensure that discharge waters do not result in irreversible or long-term impacts on the receiving environment (Donovan, 2011). 7.6 Irrigation-induced salinity Salinity is the presence of soluble salts in soils or water. Salinity is the result of the complex interactions of geophysical and land use factors such as landscape features (geology, landform), climate, soil properties, water characteristics and land management. Salinity becomes a land use issue when the concentration of salts adversely affects plant establishment growth (crops, pastures or native vegetation) or degrades soil or affects water quality (Department of Natural Resources, 1997). The salts in the landscape are derived from salts delivered through rainfall, weathering of primary minerals and origin of the geology such as marine sediments. Most salinity outbreaks result from the imbalances in the hydrological systems of a landscape, including secondary salinity due to man related activities such as clearing of native vegetation, cropping and irrigation. Naturally occurring areas of salinity or ‘primary salinity’ occur in the landscape with ecosystems adapted to these conditions. In a dryland salinity (non-irrigated) hazard mapping of the NT, Tickell (1994) determined that the dryland salinity hazard over most of the NT is low, predominantly due to relatively low salt storages occurring in the landscape were mainly due to small salt inputs from rainfall. Natural salinity in the Victoria catchment is confined to the freshwater springs originating from the dolomites on Kidman Springs; on shales in the West Baines catchment; and on the marine plains at the mouth of the Victoria River which are subject to tidal inundation. The springs and associated discharge areas on Kidman Springs have very high salt concentrations (mainly calcium salts) on the soil surface and are unsuitable for development. All moderately deep to very deep soils developed on the Proterozoic shales in the West Baines catchment are naturally high in subsoil salts with minor natural salinity in scarp retreat areas below quartz sandstone hills and plateaux. In Australia, excessive root-zone drainage through poor irrigation practices, together with leakage of water from irrigation distribution networks and drainage channels, has caused the watertable level to rise under many intensive irrigated areas. Significant parts of all major intensive irrigation areas in Australia are currently either in a shallow watertable equilibrium condition or approaching it (Christen and Ayars, 2001). Where shallow watertables containing salts approach the land surface (in the vicinity of 2–3 m from the land surface), salts can concentrate in the root zone over time through evaporation. The process by which salts accumulate in the root zone is accelerated if the groundwater also has high salt concentrations. In the case of irrigation-induced salinisation in the Victoria catchment, the landscapes suitable for irrigation development but at risk of secondary salinisation are restricted to the extensive Cenozoic clay plains (SGG 9); and the gently undulating plains with Sodosols (SGG 8), Chromosols (SGG 1) and Dermosols (SGG 2) developed on shales in the West Baines catchment. Clay soils (SGG 9) on the alluvial plains overlying the shales may also be at risk. These soils with heavy clay subsoils are naturally high in soluble salts in the subsoils. Irrigation may cause excessive deep drainage and raised watertables resulting in secondary salinisation. Other soils are generally not at risk from irrigation-induced salinity. Generic modelling results evaluating the risk of watertable rise are documented in the Flinders and Gilbert Agricultural Resource Assessment technical report on surface water – groundwater connectivity (Jolly et al., 2013). Further investigations on salinity processes and monitoring of watertables are necessary if these areas are to be developed. 7.7 References AHA and PHA (n.d.) Farm biosecurity action planner. Animal Health Australia and Plant Health Australia, Canberra. Viewed 26 February 2024, Hyperlink to: Farm biosecurity action planner . Albus WL and Knighton RE (1998) Water quality in a sand plain after conversion from dryland to irrigation: tillage and cropping systems compared. Soil and Tillage Research 48(3), 195–206. Anon. (2024) Government and Plant Industry Cost Sharing Deed in respect of Emergency Plant Pest Responses. Viewed 30 September 2024, Hyperlink to: Government and plant industry cost sharing deed in respect of emergency plant pest responses . ANZG (2020) Toxicant default guideline values for aquatic ecosystem protection: Metolachlor in freshwater. Australian and New Zealand Guidelines for Fresh and Marine Water Quality. 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Cotton Research and Development Project: CSP1302. Viewed 8 September 2024, https://www.insidecotton.com/sites/default/files/article-files/CSP1302_Final_Report.pdf. Appendices Skull Creek formation - part of the outcropping Proterozoic dolostone aquifer in the central part of the Victoria catchment Photo: CSIRO - Nathan Dyer Assessment products More information about the Victoria River Water Resource Assessment can be found at https://www.csiro.au/victoriariver. The website provides readers with a communications suite including factsheets, multimedia content, FAQs, reports and links to other related sites, particularly about other research in northern Australia. In order to meet the requirements specified in the contracted ‘Timetable for the Services’, the Assessment provided the following key deliverables: • Technical reports present scientific work at a level of detail sufficient for technical and scientific experts to reproduce the work. Each of the activities of the Assessment has at least one corresponding technical report. • The catchment report (this report) synthesises key material from the technical reports, providing well-informed but non-scientific readers with the information required to make decisions about the opportunities, costs and benefits associated with water resource development. • A summary report is provided for a general public audience. • A factsheet provides key findings for a general public audience. This appendix lists all such deliverables, plus those jointly delivered for the concurrent Southern Gulf Water Resource Assessment. Please cite as they appear. Methods report CSIRO (2021) Proposed methods report for the Victoria catchment. A report from the CSIRO Victoria River Water Resource Assessment for the National Water Grid Authority. CSIRO, Australia. Technical reports Barber M, Fisher K, Wissing K, Braedon P and Pert P (2024) Indigenous water values, rights, interests and development goals in the Victoria catchment. A technical report from the CSIRO Victoria River Water Resource Assessment for the National Water Grid. CSIRO, Australia. Devlin K (2023) Pump stations for flood harvesting or irrigation downstream of a storage dam. A technical report from the CSIRO Victoria and Southern Gulf Water Resource Assessments for the National Water Grid. CSIRO, Australia. Devlin K (2024) Conceptual arrangements and costings of hypothetical irrigation developments in the Victoria and Southern Gulf catchments. A technical report from the CSIRO Victoria and Southern Gulf Water Resource Assessments for the National Water Grid. CSIRO, Australia. Hayward J (2024) Potential for farm-scale hybrid renewable energy supply options in the Victoria and Southern Gulf catchments. A technical report from the CSIRO Victoria and Southern Gulf Water Resource Assessments for the National Water Grid. CSIRO, Australia. Hughes J, Yang A, Marvanek S, Wang B, Gibbs M and Petheram C (2024) River model calibration for the Victoria catchment. A technical report from the CSIRO Victoria River Water Resource Assessment for the National Water Grid. CSIRO, Australia. Hughes J, Yang A, Wang B, Marvanek S, Gibbs M and Petheram C (2024) River model scenario analysis for the Victoria catchment. A technical report from the CSIRO Victoria River Water Resource Assessment for the National Water Grid. CSIRO, Australia. Karim F, Kim S, Ticehurst C, Hughes J, Marvanek S, Gibbs M, Yang A, Wang B and Petheram C (2024) Floodplain inundation mapping and modelling for the Victoria catchment. A technical report from the CSIRO Victoria River Water Resource Assessment for the National Water Grid. CSIRO, Australia. Knapton A, Taylor AR and Crosbie RS (2024) Estimated effects of climate change and groundwater development scenarios on the Cambrian Limestone Aquifer in the eastern Victoria catchment. A technical report from the CSIRO Victoria River Water Resource Assessment for the National Water Grid. CSIRO, Australia. McJannet D, Yang A and Seo L (2023) Climate data characterisation for hydrological and agricultural scenario modelling across the Victoria, Roper and Southern Gulf catchments. A technical report from the CSIRO Victoria River and Southern Gulf Water Resource Assessments for the National Water Grid. CSIRO, Australia. Motson K, Mishra A and Waltham N (2024) A review of water quality studies relevant to northern Australia. A technical report from the CSIRO Victoria and Southern Gulf Water Resource Assessments for the National Water Grid. CSIRO, Australia. Speed R and Vanderbyl T (2024) Regulatory requirements for land and water development in the Northern Territory and Queensland. A technical report from the CSIRO Victoria and Southern Gulf Water Resource Assessments for the National Water Grid. CSIRO, Australia. Stratford D, Kenyon R, Pritchard J, Merrin L, Linke S, Ponce Reyes R, Buckworth R, Castellazzi P, Costin B, Deng R, Gannon R, Gao S, Gilbey S, Lachish S, McGinness H and Waltham N (2024) Ecological assets of the Victoria catchment to inform water resource assessments. A technical report from the CSIRO Victoria River Water Resource Assessment for the National Water Grid. CSIRO, Australia. Stratford D, Linke S, Merrin L, Kenyon R, Ponce Reyes R, Buckworth R, Deng RA, Hughes J, McGinness H, Pritchard J, Seo L and and Waltham N (2024) Assessment of the potential ecological outcomes of water resource development in the Victoria catchment. A technical report from the CSIRO Victoria River Water Resource Assessment for the National Water Grid. CSIRO, Australia. Taylor AR, Pritchard JL, Crosbie RS, Barry KE, Knapton A, Hodgson G, Mule S, Tickell S and Suckow A (2024) Characterising groundwater resources of the Montejinni Limestone and Skull Creek Formation in the Victoria catchment, Northern Territory. A technical report from the CSIRO Victoria River Water Resource Assessment for the National Water Grid. CSIRO, Australia. Thomas M, Philip S, Stockmann U, Wilson PR, Searle R, Hill J, Gregory L, Watson I and Wilson PL (2024) Soils and land suitability for the Victoria catchment, Northern Territory. A technical report from the CSIRO Victoria River Water Resource Assessment for the National Water Grid. CSIRO, Australia. Vanderbyl T (2024) The Northern Territory’s water planning arrangements. A technical report from the CSIRO Victoria River Water Resource Assessment for the National Water Grid. CSIRO, Australia. Waschka M and Macintosh A (2024) CSIRO Water Resource Assessments: Indigenous rights and interests in Queensland and the Northern Territory. A report from Barraband Consulting to CSIRO to inform the CSIRO Victoria, Roper and Southern Gulf Water Resource Assessments. CSIRO, Australia. Webster A, Jarvis D, Jalilov S, Philip S, Oliver Y, Watson I, Rhebergen T, Bruce C, Prestwidge D, McFallan S, Curnock M and Stokes C (2024) Financial and socio-economic viability of irrigated agricultural development in the Victoria catchment, Northern Territory. A technical report from the CSIRO Victoria River Water Resource Assessment for the National Water Grid. CSIRO, Australia. Yang A, Petheram C, Marvanek S, Baynes F, Rogers L, Ponce Reyes R, Zund P, Seo L, Hughes J, Gibbs M, Wilson PR, Philip S and Barber M (2024) Assessment of surface water storage options in the Victoria and Southern Gulf catchments. A technical report from the CSIRO Victoria River and Southern Gulf Water Resource Assessments for the National Water Grid. CSIRO Australia. Catchment report Petheram C, Philip S, Watson I, Bruce C and Chilcott C (eds) (2024) Water resource assessment for the Victoria catchment. A report from the CSIRO Victoria River Water Resource Assessment for the National Water Grid. CSIRO, Australia. Summary report CSIRO (2024) The Victoria River Water Resource Assessment. A summary report from the CSIRO Victoria River Water Resource Assessment for the National Water Grid. CSIRO, Australia. Factsheet on key findings CSIRO (2024) The Victoria River Water Resource Assessment. Key messages of reports to the CSIRO Victoria River Water Resource Assessment for the National Water Grid. CSIRO, Australia. Shortened forms For more information on this figure or equation or table, please contact CSIRO on enquiries@csiro.au For more information on this figure or equation or table, please contact CSIRO on enquiries@csiro.au For more information on this figure or equation or table, please contact CSIRO on enquiries@csiro.au Units SHORT FORM FULL FORM $ dollars % per cent c cents cm centimetre d day dS decisiemens DS dry season g gram GL gigalitre (1,000,000,000 litres) GWh gigawatt hour ha hectare kg kilogram (1000 grams) km kilometre (1000 metres) km2 square kilometre kPa kilopascal kV kilovolt kW kilowatt kWh kilowatt hour L litre m metre m3 cubic metre mBGL metres below ground level mEGM96 metres (Earth Gravity Model of 1996) mg milligram ML megalitre (1,000,000 litres) mm millimetre MW megawatt MWh megawatt hour s second t metric tonne y year °C degrees Celsius List of figures Figure 1-1 Map of Australia showing Assessment area (Victoria catchment) and other recent or ongoing CSIRO Assessments ........................................................................................................... 3 Figure 1-2 Number of large dams constructed in Australia and northern Australia over time ..... 8 Figure 1-3 Schematic of key components and concepts in the establishment of a greenfield irrigation development ................................................................................................................... 9 Figure 1-4 The Victoria catchment ................................................................................................ 13 Figure 2-1 Schematic diagram of key natural components and concepts in the establishment of a greenfield irrigation development ............................................................................................. 19 Figure 2-2 Soil sampling in the West Baines catchment ............................................................... 22 Figure 2-3 Surface geology of the Victoria catchment ................................................................. 24 Figure 2-4 Physiographic units of the Victoria catchment ............................................................ 26 Figure 2-5 Major geological basins and provinces of the Victoria catchment ............................. 28 Figure 2-6 The soil generic groups (SGGs) of the Victoria catchment produced by digital soil mapping ........................................................................................................................................ 31 Figure 2-7 Brown Vertosol SGG 9 soils on alluvial plains along the West Baines River. Gilgai microrelief is evident .................................................................................................................... 35 Figure 2-8 A plain with grey Vertosol SGG 9 soils on relict alluvial plains near Top Springs. Linear gilgai surface microrelief is evident in the mid-left distance ........................................................ 36 Figure 2-9 Well-drained red loamy soils (SGG 4.1) with iron nodules on the Sturt Plateau ........ 37 Figure 2-10 Shallow and rocky soils (SGG 7) on laterite outcrops and scarps of deeply weathered landscapes ..................................................................................................................................... 38 Figure 2-11 (a) Surface soil pH (top 10 cm) of the Victoria catchment as predicted by digital soil mapping and (b) reliability of the prediction ................................................................................ 40 Figure 2-12 (a) Soil thickness of the Victoria catchment as predicted by digital soil mapping and (b) reliability of the prediction ...................................................................................................... 41 Figure 2-13 (a) Soil surface texture of the Victoria catchment as predicted by digital soil mapping and (b) reliability of the prediction ................................................................................ 42 Figure 2-14 (a) Soil permeability of the Victoria catchment as predicted by digital soil mapping and (b) reliability of the prediction ............................................................................................... 43 Figure 2-15 (a) Available water capacity in the upper 100 cm of the soil profile (AWC 100) as predicted by digital soil mapping in the Victoria catchment and (b) reliability of the prediction 44 Figure 2-16 (a) Surface rockiness in soils of the Victoria catchment represented by presence or absence as predicted by digital soil mapping and (b) reliability of the prediction ...................... 45 Figure 2-17 Historical rainfall, potential evaporation and rainfall deficit .................................... 47 Figure 2-18 Historical monthly rainfall (left) and time series of annual rainfall (right) in the Victoria catchment at Auvergne, Yarralin, Kalkarindji and Top Springs ....................................... 50 Figure 2-19 Historical monthly potential evaporation (PE) (left) and time series of annual PE (right) in the Victoria catchment at Auvergne, Yarralin, Kalkarindji and Top Springs .................. 51 Figure 2-20 (a) Coefficient of variation (CV) of annual rainfall and (b) the CV of annual rainfall plotted against mean annual rainfall for 99 rainfall stations around Australia ........................... 52 Figure 2-21 Runs of wet and dry years at Auvergne, Yarralin, Kalkarindji and Top Springs (1890 to 2022) ......................................................................................................................................... 54 Figure 2-22 Percentage change in rainfall and potential evaporation per degree of global warming for the 32 Scenario C simulations relative to Scenario A values for the Victoria catchment ..................................................................................................................................... 55 Figure 2-23 Spatial distribution of mean annual rainfall across the Victoria catchment under scenarios (a) Cwet, (b) Cmid and (c) Cdry ..................................................................................... 56 Figure 2-24 (a) Monthly rainfall and (b) potential evaporation for the Victoria catchment under scenarios A and C .......................................................................................................................... 56 Figure 2-25 Simplified schematic diagram of terrestrial water balance in the Victoria catchment ....................................................................................................................................................... 59 Figure 2-26 Simplified regional geology of the Victoria catchment ............................................. 62 Figure 2-27 Simplified regional hydrogeology of the Victoria catchment .................................... 63 Figure 2-28 Groundwater dependent ecosystems at Kidman Springs ......................................... 64 Figure 2-29 Major types of aquifers occurring beneath the Victoria catchment ......................... 65 Figure 2-30 Simplified regional hydrogeology of the Victoria catchment relative to the entire spatial extent of the Cambrian limestone across large parts of the Northern Territory ............. 67 Figure 2-31 Lonely Spring surrounded by dense spring-fed vegetation ....................................... 68 Figure 2-32 Groundwater bore yields for the major aquifers across the Victoria catchment ..... 69 Figure 2-33 Groundwater salinity for the major aquifers in the Victoria catchment ................... 71 Figure 2-34 Bulls Head Spring surrounded by dense spring-fed vegetation ................................ 72 Figure 2-35 Groundwater bore yields for minor aquifers across the Victoria catchment ........... 74 Figure 2-36 Jasper Gorge a spectacular sandstone gorge dissecting extensive plateau of low open woodlands and spinifex on shallow and rocky soils ............................................................ 75 Figure 2-37 Groundwater salinity for the minor aquifers in the Victoria catchment .................. 76 Figure 2-38 Annual recharge estimates for the Victoria catchment ............................................ 78 Figure 2-39 Summary of recharge statistics to outcropping areas of key hydrogeological units across the Victoria catchment ...................................................................................................... 79 Figure 2-40 Spatial distribution of groundwater discharge classes including surface water – groundwater connectivity across the Victoria catchment............................................................ 80 Figure 2-41 Modelled streamflow under natural conditions ....................................................... 82 Figure 2-42 Streamflow observation data availability in the Victoria catchment ........................ 83 Figure 2-43 Median annual streamflow (50% exceedance) in the Victoria catchment under Scenario A ..................................................................................................................................... 85 Figure 2-44 (a) 20% and (b) 80% exceedance of annual streamflow in the Victoria catchment under Scenario A ........................................................................................................................... 86 Figure 2-45 Catchment area and elevation profile along the Victoria River from upstream of Kalkarindji to its mouth ................................................................................................................. 86 Figure 2-46 Mean annual (a) rainfall and (b) runoff across the Victoria catchment under Scenario A ..................................................................................................................................... 87 Figure 2-47 Annual runoff at (a) 20%, (b) 50% and (c) 80% exceedance across the Victoria catchment under Scenario A ......................................................................................................... 87 Figure 2-48 Runoff in the Victoria catchment under Scenario A showing (a) time series of annual runoff and (b) monthly runoff averaged across the catchment ................................................... 88 Figure 2-49 Flood inundation map of the Victoria catchment ..................................................... 89 Figure 2-50 Flood inundation across the Victoria catchment for a flood event of 1 in 18 annual exceedance probability (AEP) in March 2023 ............................................................................... 90 Figure 2-51 Peak flood discharge and annual exceedance probability (AEP) at (a) gauge 8110006 (West Baines River at Victoria Highway) and (b) gauge 8110007 (Victoria River at Coolibah Homestead) ................................................................................................................................... 91 Figure 2-52 Riparian vegetation along the West Baines River in the Victoria catchment. These areas are subject to regular flooding and the riparian vegetation plays an important role in regulating stream water quality. .................................................................................................. 92 Figure 2-53 Minimum dry-season flow observed at gauging stations 8110006, 8110007 and 8110113 ........................................................................................................................................ 93 Figure 2-54 Minimum monthly flow over 132 years of simulation for October, November and December ...................................................................................................................................... 94 Figure 2-55 Instream waterhole evolution in a reach of the Flinders River ................................. 95 Figure 2-56 Streamflow gauging station in the Victoria catchment ............................................. 95 Figure 2-57 Location of river reaches containing permanent water in the Victoria catchment .. 96 Figure 2-58 Baseflow water quality in the Victoria catchment for parameters (a) electrical conductivity (EC), (b) chloride concentration, (c) total alkalinity, (d) calcium to sodium ratio, (e) silica concentration and (f) turbidity............................................................................................. 97 Figure 3-1 Schematic diagram of key components of the living and built environment to be considered in establishing a greenfield irrigation development ................................................ 103 Figure 3-2 Conceptual diagram of selected ecological values and assets of the Victoria catchment ................................................................................................................................... 108 Figure 3-3 Location of protected areas and important wetlands within the Victoria catchment Assessment area ......................................................................................................................... 110 Figure 3-4 Observed locations of barramundi (Lates calcarifer) and its modelled probability of occurrence in the Victoria catchment ........................................................................................ 119 Figure 3-5 Observed locations of grunters in the Victoria catchment ....................................... 121 Figure 3-6 Red-capped plover walking along a shore ................................................................. 123 Figure 3-7 Distribution of species listed under the Environment Protection and Biodiversity Conservation Act and by the NT Government in the Victoria catchment .................................. 125 Figure 3-8 Boundaries of the Australian Bureau of Statistics Statistical Area Level 2 (SA2) regions used for demographic data in this analysis and the Katherine Daly tourism region ................. 128 Figure 3-9 Land use classification for the Victoria catchment .................................................... 132 Figure 3-10 Regions in the Northern Prawn Fishery ................................................................... 136 Figure 3-11 Main commodity mineral occurrences and exploration tenements in the Victoria catchment ................................................................................................................................... 139 Figure 3-12 Jasper Gorge is seasonally accessible on the Buchanan Highway ........................... 140 Figure 3-13 Road rankings and conditions for the Victoria catchment ...................................... 144 Figure 3-14 Roads accessible to Type 2 vehicles across the Victoria catchment: minor roads are not classified ............................................................................................................................... 145 Figure 3-15 Common configurations of heavy freight vehicles used for transporting agricultural goods in Australia ........................................................................................................................ 146 Figure 3-16 Road condition and distance to market impact the economics of development in the Victoria catchment ............................................................................................................... 146 Figure 3-17 Mean speed achieved for freight vehicles on the Victoria catchment roads ......... 147 Figure 3-18 Annual amounts of trucking in the Victoria catchment and the locations of pastoral properties .................................................................................................................................... 149 Figure 3-19 Electricity generation and transmission network in the Victoria catchment .......... 151 Figure 3-20 Solar photovoltaic capacity factors in the Victoria River catchment ...................... 153 Figure 3-21 Wind capacity factors in the Victoria River catchment ........................................... 154 Figure 3-22 Location, type and volume of annual licensed surface water and groundwater entitlements ................................................................................................................................ 156 Figure 3-23 Colonial frontier massacres in the Victoria catchment ........................................... 161 Figure 3-24 Aboriginal freehold land in the Victoria catchment as at November 2023 ............. 163 Figure 3-25 Native title claims and determinations in the Victoria catchment as at November 2023............................................................................................................................................. 164 Figure 3-26 The Victoria catchment and neighbouring water plans and water control districts ..................................................................................................................................................... 172 Figure 4-1 Schematic of agriculture and aquaculture enterprises as well as crop and/or forage integration with existing beef enterprises to be considered in the establishment of a greenfield irrigation development ............................................................................................................... 192 Figure 4-2 Area (ha) of the Victoria catchment mapped in each of the land suitability classes for 14 selected land use combinations (crop group × season × irrigation type) .............................. 200 Figure 4-3 Agricultural versatility index map for the Victoria catchment .................................. 201 Figure 4-4 Climate comparisons of Victoria catchment sites with established irrigation areas at Katherine (NT) and Kununurra (WA)........................................................................................... 205 Figure 4-5 Annual cropping calendar for irrigated agricultural options in the Victoria catchment ..................................................................................................................................................... 207 Figure 4-6 Soil wetness indices that indicate when seasonal trafficability constraints are likely to occur on Vertosols (high clay), Kandosols (sandy loam) and sand at Kidman Springs for (a) a threshold of 70% of plant available water capacity (PAWC) and (b) 80% of PAWC ................... 208 Figure 4-7 Influence of planting date on rainfed grain sorghum yield at Kidman Springs for a (a) Kandosol and (b) Vertosol ........................................................................................................... 210 Figure 4-8 Influence of available irrigation water on grain sorghum yields for planting dates of (a) 1 February and (b) 1 August, for a Kandosol with a Kidman Springs climate ....................... 211 Figure 4-9 Fluctuations in seedless watermelon prices at Melbourne wholesale markets from April 2020 to February 2023 ....................................................................................................... 220 Figure 4-10 Modelled land suitability for Crop Group 7 (e.g. sorghum (grain) or maize) using furrow irrigation in the (a) wet season and (b) dry season ........................................................ 232 Figure 4-11 Sorghum (grain) ....................................................................................................... 234 Figure 4-12 Modelled land suitability for mungbean (Crop Group 10) in the dry season using (a) furrow irrigation and (b) spray irrigation .................................................................................... 236 Figure 4-13 Mungbean ................................................................................................................ 236 Figure 4-14 Modelled land suitability for soybean (Crop Group 10) in the dry season using (a) furrow irrigation and (b) spray irrigation .................................................................................... 239 Figure 4-15 Soybean.................................................................................................................... 239 Figure 4-16 Modelled land suitability for peanut (Crop Group 6) using spray irrigation in the (a) wet season and (b) dry season ................................................................................................... 242 Figure 4-17 Peanut ...................................................................................................................... 242 Figure 4-18 Modelled land suitability for cotton (Crop Group 7) using furrow irrigation in the (a) wet season and (b) dry season ................................................................................................... 246 Figure 4-19 Cotton ...................................................................................................................... 246 Figure 4-20 Modelled land suitability for Rhodes grass (Crop Group 14) using (a) spray irrigation and (b) furrow irrigation ............................................................................................................. 250 Figure 4-21 Rhodes grass ............................................................................................................ 250 Figure 4-22 Modelled land suitability for Cavalcade (Crop Group 13) in the wet season using (a) spray irrigation and (b) furrow irrigation .................................................................................... 253 Figure 4-23 Lablab ....................................................................................................................... 253 Figure 4-24 Modelled land suitability for (a) cucurbits (e.g. rockmelon, Crop Group 3) using trickle irrigation in the dry season and (b) root crops such as onion (Crop Group 6) using spray irrigation in the wet season ........................................................................................................ 256 Figure 4-25 Rockmelon ............................................................................................................... 257 Figure 4-26 Modelled land suitability for (a) mango (Crop Group 1) and (b) lime (Crop Group 2), both grown using trickle irrigation.............................................................................................. 259 Figure 4-27 Mango ...................................................................................................................... 260 Figure 4-28 Modelled land suitability for Indian sandalwood (Crop Group 15) grown using (a) trickle or (b) furrow irrigation ..................................................................................................... 262 Figure 4-29 Indian sandalwood and host plants ......................................................................... 262 Figure 4-30 Black tiger prawns .................................................................................................... 266 Figure 4-31 Barramundi .............................................................................................................. 266 Figure 4-32 Schematic of marine aquaculture farm ................................................................... 268 Figure 4-33 Land suitability in the Victoria catchment for marine species aquaculture in (a) lined ponds and (b) earthen ponds ...................................................................................................... 272 Figure 4-34 Land suitability in the Victoria catchment for freshwater species aquaculture in (a) lined ponds and (b) earthen ponds ............................................................................................. 273 Figure 5-1 Schematic of key engineering and agricultural components to be considered in the establishment of a water resource and greenfield irrigation development .............................. 281 Figure 5-2 Key hydrogeological units of the Victoria catchment ................................................ 291 Figure 5-3 Hydrogeological cross-section through the Cambrian Limestone Aquifer in the east of the Victoria catchment ............................................................................................................... 293 Figure 5-4 Groundwater pumps powered by the wind provide water points for cattle ............ 294 Figure 5-5 Depth to the top of the Cambrian Limestone Aquifer .............................................. 295 Figure 5-6 Depth to standing water level (SWL) of the Cambrian Limestone Aquifer ............... 296 Figure 5-7 Conceptual block model of part of the Cambrian Limestone Aquifer near Top Springs along the eastern margin of the Victoria catchment.................................................................. 297 Figure 5-8 Location of hypothetical groundwater extraction sites in relation to modelled groundwater level reporting sites and modelled discharge at key springs for the Cambrian Limestone Aquifer ....................................................................................................................... 298 Figure 5-9 Perennial localised discharge from the Cambrian Limestone Aquifer to Old Top Spring ..................................................................................................................................................... 299 Figure 5-10 Modelled drawdown in groundwater level in the Cambrian Limestone Aquifer (CLA) under scenarios (a) B9, (b) B12 and (c) B15 in approximately 2060 .......................................... 301 Figure 5-11 Outcropping and subcropping areas of the Proterozoic dolostone aquifers in the Victoria catchment ...................................................................................................................... 303 Figure 5-12 North-west to south-east cross-section traversing the dolostone aquifers hosted in the Bullita Group ......................................................................................................................... 305 Figure 5-13 Water sampling at Kidman Springs .......................................................................... 306 Figure 5-14 The Ord River Irrigation Area 290 km west of Timber Creek has a similar climate and some similar soils and climate setting to the Victoria catchment .............................................. 307 Figure 5-15 Types of managed aquifer recharge ........................................................................ 308 Figure 5-16 Managed aquifer recharge opportunities for the Victoria catchment, independent of distance from a water source for recharge ............................................................................ 310 Figure 5-17 Managed aquifer recharge (MAR) opportunities in the Victoria catchment (a) within 5 km of major rivers .................................................................................................................... 311 Figure 5-18 Topographically more favourable potential storage sites in the Victoria catchment based on minimum cost per megalitre storage capacity ........................................................... 315 Figure 5-19 Topographically and hydrologically more favourable potential storage sites in the Victoria catchment based on minimum cost per megalitre yield at the dam wall .................... 317 Figure 5-20 Victoria catchment hydro-electric power generation opportunity map................. 319 Figure 5-21 EPBC and NT listed species, water-dependent assets and aggregated modelled habitat in the vicinity of the potential dam site on Leichhardt Creek AMTD 26 km .................. 325 Figure 5-22 Potential dam site on Leichhardt Creek AMTD 26 km: cost and yield at the dam wall ..................................................................................................................................................... 326 Figure 5-23 Potential dam site on Victoria River AMTD 283 km: cost and yield at the dam wall ..................................................................................................................................................... 327 Figure 5-24 Listed species, water-dependent assets and aggregated modelled habitat in the vicinity of the potential dam site on the Victoria River AMTD 283 km ...................................... 328 Figure 5-25 Schematic cross-section diagram of sheet piling weir ............................................ 330 Figure 5-26 Rectangular ringtank and 500 ha of cotton in the Flinders catchment (Queensland) ..................................................................................................................................................... 332 Figure 5-27 Suitability of land for large farm-scale ringtanks in the Victoria catchment ........... 333 Figure 5-28 Annual reliability of diverting annual system and reach target volumes for varying pump start thresholds ................................................................................................................. 336 Figure 5-29 Victoria River has the second largest median annual streamflow of any river in the NT ................................................................................................................................................ 337 Figure 5-30 Annual reliability of diverting annual system and reach target volumes for varying pump start thresholds assuming end-of-system flow requirement before pumping can commence is 500 GL ................................................................................................................... 338 Figure 5-31 Annual reliability of diverting annual system and reach target volumes for varying pump start thresholds assuming end-of-system flow requirement before pumping can commence is 700 GL ................................................................................................................... 339 Figure 5-32 50% annual exceedance (median) streamflow relative to Scenario A in the Victoria catchment for varying end-of-system (EOS) requirements assuming a pump start threshold of 1000 ML/day and a pump capacity of 30 days ........................................................................... 340 Figure 5-33 80% annual exceedance streamflow relative to Scenario A in the Victoria catchment for varying end-of-system (EOS) requirements assuming a pump start threshold of 1000 ML/day and a pump capacity of 30 days.................................................................................................. 341 Figure 5-34 Annual reliability of diverting annual system and reach targets for varying pump rates assuming a pump start flow threshold of 1000 ML/day ................................................... 342 Figure 5-35 Julius Dam on the Leichhardt River ......................................................................... 347 Figure 5-36 Most economically suitable locations for large farm-scale gully dams in the Victoria catchment ................................................................................................................................... 348 Figure 5-37 Suitability of soils for construction of gully dams in the Victoria catchment .......... 349 Figure 5-38 Reported conveyance losses from irrigation systems across Australia .................. 356 Figure 5-39 Efficiency of different types of irrigation system .................................................... 358 Figure 6-1 Schematic diagram of key components affecting the commercial viability of a potential greenfield irrigation development .............................................................................. 367 Figure 6-2 Locations of the five dams used in this review .......................................................... 389 Figure 6-3 Trends in gross value of agricultural production (GVAP) in (a) Australia and (b) the NT over 40 years (1981–2021) ......................................................................................................... 391 Figure 6-4 National trends for increasing gross value of irrigated agricultural production (GVIAP) as available water supplies have increased for (a) fruits, (b) vegetables, (c) fruits and vegetables combined, and (d) total agriculture ............................................................................................ 393 Figure 6-5 Regions used in the input–output (I–O) analyses relative to the Victoria catchment Assessment area ......................................................................................................................... 399 Figure 7-1 Schematic diagram of the environmental components where key risks can manifest during and after the establishment of a greenfield irrigation or aquaculture development, with numbers in blue specifying sections in this report ..................................................................... 407 Figure 7-2 Map of the Victoria catchment and the marine region showing the locations of the river system modelling nodes at which flow–ecology dependencies were assessed (numbered) and the locations of hypothetical water resource developments ............................................. 419 Figure 7-3 Habitat weighted change in important flow dependencies for barramundi by scenario across model nodes .................................................................................................................... 425 Figure 7-4 Spatial heatmap of change in important flow dependencies for barramundi, considering their distribution across the catchment .................................................................. 427 Figure 7-5 The change in barramundi flow dependencies under the various water harvesting scenarios at sample nodes across the catchment, showing response to system targets and pump-start thresholds ................................................................................................................ 429 Figure 7-6 Habitat weighted change in important flow dependencies for shorebirds under the various scenarios across the model nodes ................................................................................. 433 Figure 7-7 Waterhole fringed by boab trees, Victoria catchment .............................................. 434 Figure 7-8 Change in important mangroves flow dependencies under the various scenarios .. 435 Figure 7-9 Riverine landscape, Victoria catchment .................................................................... 437 Figure 7-10 Spatial heatmap of change to asset–flow dependencies across the Victoria catchment, considering change across all assets in the locations in which each of the assets was assessed ...................................................................................................................................... 438 Figure 7-11 Mean change to assets’ important flow dependencies across scenarios and nodes ..................................................................................................................................................... 439 Figure 7-12 Mean change to assets’ important flow dependencies across water harvesting increments of system target and pump-start threshold, with no end-of-system (EOS) requirement and a pump rate of 30 days ................................................................................... 441 Figure 7-13 The invasion curve with biosecurity actions taken at various stages ..................... 453 Figure 7-14 Farm biosecurity signage available through www.farmbiosecurity.com.au ........... 454 List of tables Table 2-1 Victoria catchment physiographic unit descriptions, shortened names, areas and percentage areas ........................................................................................................................... 27 Table 2-2 Soil generic groups (SGGs), descriptions, management considerations and correlations to Australian Soil Classification (ASC) for the Victoria catchment ................................................ 32 Table 2-3 Area and proportions covered by each soil generic group (SGG) in the Victoria catchment ..................................................................................................................................... 34 Table 2-4 Projected sea-level rise for the coast of the Victoria catchment ................................. 57 Table 2-5 Streamflow metrics at gauging stations in the Victoria catchment under Scenario A . 84 Table 3-1 Freshwater, marine and terrestrial ecological assets with freshwater flow dependences ............................................................................................................................... 117 Table 3-2 Definition of threatened categories under the Commonwealth Environment Protection and Biodiversity Conservation Act 1999 and the NT wildlife classification system .. 126 Table 3-3 Major demographic indicators for the Victoria catchment ........................................ 129 Table 3-4 Socio-Economic Indexes for Areas (SEIFA) scores of relative socio-economic advantage for the Victoria catchment .......................................................................................................... 130 Table 3-5 Key employment data for the Victoria catchment ..................................................... 131 Table 3-6 Value of agricultural production for the Victoria catchment (estimated) and the NT for 2020−21 ...................................................................................................................................... 133 Table 3-7 Global water consumption in the mining and refining of selected metals ................ 138 Table 3-8 Overview of commodities (excluding livestock) annually transported into and out of the Victoria catchment ............................................................................................................... 148 Table 3-9 Schools servicing the Victoria catchment ................................................................... 157 Table 3-10 Number and percentage of unoccupied dwellings and population for the Victoria catchment ................................................................................................................................... 158 Table 4-1 Land suitability classes based on FAO (1976, 1985) as used in the Assessment ........ 198 Table 4-2 Crop groups and individual land uses evaluated for irrigation (and rainfed) potential ..................................................................................................................................................... 199 Table 4-3 Qualitative land evaluation observations for Victoria catchment areas A to E shown in Figure 4-3 .................................................................................................................................... 202 Table 4-4 Crop options for which performance was evaluated in terms of water use, yields and gross margins .............................................................................................................................. 204 Table 4-5 Soil water content at sowing, and rainfall for the 90-day period following sowing for three sowing dates, based on a Kidman Springs climate on a Vertosol ..................................... 209 Table 4-6 Performance metrics for broadacre cropping options in the Victoria catchment: applied irrigation water, crop yield and gross margin (GM) for four environments .................. 213 Table 4-7 Breakdown of variable costs relative to revenue for broadacre crop options ........... 217 Table 4-8 Sensitivity of cotton crop gross margins ($/ha) to variation in yield, lint prices and distance to gin ............................................................................................................................. 218 Table 4-9 Sensitivity of forage (Rhodes grass) crop gross margins ($/ha) to variation in yield and hay price ...................................................................................................................................... 218 Table 4-10 Performance metrics for horticulture options in the Victoria catchment: annual applied irrigation water, crop yield and gross margin ................................................................ 219 Table 4-11 Sensitivity of watermelon crop gross margins ($/ha) to variation in melon prices and freight costs ................................................................................................................................. 221 Table 4-12 Performance metrics for plantation tree crop options in the Victoria catchment: annual applied irrigation water, crop yield and gross margin .................................................... 222 Table 4-13 Likely annual irrigated crop planting windows, suitability, and viability in the Victoria catchment ................................................................................................................................... 225 Table 4-14 Sequential cropping options for Kandosols .............................................................. 226 Table 4-15 Production and financial outcomes from the different irrigated forage and beef production options for a representative property in the Victoria catchment ........................... 228 Table 4-16 Summary information relevant to the cultivation of cereals, using sorghum (grain) as an example .................................................................................................................................. 233 Table 4-17 Summary information relevant to the cultivation of pulses, using mungbean as an example ....................................................................................................................................... 237 Table 4-18 Summary information relevant to the cultivation of oilseed crops, using soybean as an example .................................................................................................................................. 240 Table 4-19 Summary information relevant to the cultivation of root crops, using peanut as an example ....................................................................................................................................... 243 Table 4-20 Summary information relevant to the cultivation of cotton .................................... 247 Table 4-21 Rhodes grass production for hay over 1 year of a 6-year cycle ................................ 251 Table 4-22 Cavalcade production over a 1-year cycle ................................................................ 254 Table 4-23 Summary information relevant to row crop horticulture production, with rockmelon as an example ............................................................................................................................. 257 Table 4-24 Summary information relevant to tree crop horticulture production, with mango as an example .................................................................................................................................. 260 Table 4-25 Summary information for Indian sandalwood production ....................................... 263 Table 4-26 Indicative capital and operating costs for a range of generic aquaculture development options .................................................................................................................. 274 Table 4-27 Gross revenue targets required to achieve target internal rates of return (IRR) for aquaculture developments with different combinations of capital costs and operating costs . 276 Table 5-1 Summary of capital costs, yields and costs per megalitre of supply, including operation and maintenance (O&M) ........................................................................................... 285 Table 5-2 Opportunity-level estimates of the potential scale of groundwater resource development in the Victoria catchment ..................................................................................... 289 Table 5-3 Summary of estimated costs for a 250 ha irrigation development using groundwater ..................................................................................................................................................... 292 Table 5-4 Mean modelled groundwater levels at ten locations within the Cambrian Limestone Aquifer under extraction scenarios A, B, C and D Locations are shown in Figure 5-8 ............... 300 Table 5-5 Mean modelled groundwater discharge by evapotranspiration and localised spring discharge from the Cambrian Limestone Aquifer at spring complexes along its western margin near Top Springs ......................................................................................................................... 302 Table 5-6 Potential dam sites in the Victoria catchment examined as part of the Assessment 320 Table 5-7 Summary comments for potential dams in the Victoria catchment .......................... 321 Table 5-8 Estimated construction cost of 3 m high sheet piling weir......................................... 330 Table 5-9 Effective volume after net evaporation and seepage for hypothetical ringtanks of three mean water depths, under three seepage rates, near the Victoria River Downs in the Victoria catchment ...................................................................................................................... 343 Table 5-10 Indicative costs for a 4000 ML ringtank .................................................................... 344 Table 5-11 Annualised cost for the construction and operation of three ringtank configurations ..................................................................................................................................................... 345 Table 5-12 Levelised costs for two hypothetical ringtanks of different capacities under three seepage rates near Victoria River Downs in the Victoria catchment ......................................... 346 Table 5-13 Actual costs of four gully dams in northern Queensland ......................................... 350 Table 5-14 Cost of three hypothetical large farm-scale gully dams of capacity 4 GL ................. 350 Table 5-15 High-level breakdown of capital costs for three hypothetical large farm-scale gully dams of capacity 4 GL ................................................................................................................. 351 Table 5-16 Effective volumes and cost per megalitre for three 4 GL gully dams with various mean depths and seepage loss rates based on climate data at Victoria River Downs Station in the Victoria catchment ............................................................................................................... 351 Table 5-17 Cost of construction and operation of three hypothetical 4 GL gully dams............. 352 Table 5-18 Equivalent annualised cost and effective volume for three hypothetical 4 GL gully dams with various mean depths and seepage loss rates based on climate data at Victoria River Downs Station in the Victoria catchment ................................................................................... 352 Table 5-19 Summary of conveyance and application efficiencies .............................................. 355 Table 5-20 Water distribution and operational efficiency as nominated in water resource plans for four irrigation water supply schemes in Queensland ........................................................... 355 Table 5-21 Application efficiencies for surface, spray and micro irrigation systems ................. 358 Table 6-1 Types of questions that users can answer using the tools in this chapter ................. 370 Table 6-2 Indicative capital costs for developing a representative irrigation scheme in the Victoria catchment ...................................................................................................................... 374 Table 6-3 Assumed indicative capital and operating costs for new off- and on-farm irrigation infrastructure .............................................................................................................................. 375 Table 6-4 Price irrigators can afford to pay for water, based on the type of farm, the farm water use and the farm annual gross margin (GM), while meeting a target 10% internal rate of return (IRR) ............................................................................................................................................. 377 Table 6-5 Farm gross margins (GMs) required in order to cover the costs of off-farm water infrastructure (at the supplier’s target internal rate of return (IRR)) ......................................... 379 Table 6-6 Water pricing required in order to cover costs of off-farm irrigation scheme development (dam, water distribution, and supporting infrastructure) at the investors target internal rate of return (IRR) ........................................................................................................ 380 Table 6-7 Farm gross margins (GMs) required in order to achieve target internal rates of return (IRR), given various capital costs of farm development (including an on-farm water source) .. 381 Table 6-8 Equivalent costs of water per ML for on-farm water sources with various capital costs of development, at the internal rate of return (IRR) targeted by the investor .......................... 383 Table 6-9 Risk adjustment factors for target farm gross margins (GMs), accounting for the effects of the reliability and severity (level of farm performance in ‘failed’ years) of the periodic risk of water reliability ................................................................................................................ 385 Table 6-10 Risk adjustment factors for target farm gross margins (GMs) accounting for the effects of reliability and the timing of periodic risks .................................................................. 386 Table 6-11 Risk adjustment factors for target farm gross margins (GMs), accounting for the effects of learning risks ............................................................................................................... 387 Table 6-12 Summary characteristics of the five dams used in this review................................. 389 Table 6-13 Summary of key issues and potential improvements arising from a review of recent dam developments ..................................................................................................................... 390 Table 6-14 Indicative costs of agricultural processing facilities .................................................. 394 Table 6-15 Indicative costs of road and electricity infrastructure .............................................. 395 Table 6-16 Indicative road transport costs between the Victoria catchment and key markets and ports ............................................................................................................................................ 395 Table 6-17 Indicative costs of community facilities .................................................................... 396 Table 6-18 Key 2021 data comparing the Victoria catchment with the related I–O analysis regions ......................................................................................................................................... 399 Table 6-19 Regional economic impact estimated for the total construction phase of a new irrigated agricultural development (based on two independent I–O models) .......................... 401 Table 6-20 Estimated regional economic impact per year in the Victoria catchment resulting from four scales of direct increase in agricultural output (rows) for the different categories of agricultural activity (columns) from two I–O models ................................................................. 402 Table 6-21 Estimated impact on annual household incomes and full-time equivalent (FTE) jobs within the Victoria catchment resulting from four scales of direct increase in agricultural output (rows) for the various categories of agricultural activity (columns) ........................................... 403 Table 7-1 Water resource development and climate scenarios explored in the ecology analysis ..................................................................................................................................................... 420 Table 7-2 Ecological assets used in the Victoria Water Resource Assessment .......................... 421 Table 7-3 Descriptive qualitative values for the flow dependencies modelling as percentile change of the hydrometrics ........................................................................................................ 423 Table 7-4 Scenarios of different hypothetical instream dam locations showing end-of-system (EOS) flow and mean changes in ecology flows for groups of assets across each asset’s respective catchment assessment nodes ................................................................................... 442 Table 7-5 Examples of significant pest and disease threats to plant industries in the Victoria catchment ................................................................................................................................... 447 Table 7-6 Regional weed priorities and their management actions in the Victoria catchment. 450 Table 7-7 High-risk freshwater pest fish threats to the Victoria catchment .............................. 451 Table 7-8 Water quality variables reviewed – their impacts on the environment, aquatic ecology and human health ....................................................................................................................... 460