Australia’sNationalScienceAgency Conceptual arrangementsand costingsof hypothetical irrigation developmentsin theVictoria and Southern Gulf catchments A technical reportfromtheCSIROVictoriaandSouthern GulfWaterResourceAssessmentsfor theNationalWater Grid KevinDevlin(Independent consultant) ISBN 978-1-4863-2109-4 (print) ISBN 978-1-4863-2110-0 (online) Citation 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. 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 and Southern Gulf Water Resource Assessments 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 Assessments have been undertaken in conjunction with the Northern Territory and Queensland governments. The Assessments were guided by three committees: i.The 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; NTDepartment 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 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 CouncilShire; Watertrust iii.The Southern Gulf catchments Steering Committee: Amateur Fishermen’s Association of the NT; Austral Fisheries; Burketown Shire; Carpentaria Land Council Aboriginal Corporation; Health and Wellbeing Queensland; National Water Grid (Department of Climate Change, Energy, the Environment and Water); Northern Prawn Fisheries; Queensland Department of Agriculture and Fisheries; NT Department of Environment, Parks and Water Security; NT Department of Industry, Tourism and Trade; Office of Northern Australia; Queensland Department of Regional Development, Manufacturing and Water; Southern Gulf NRM 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 its release. This report was reviewed by Dr Cuan Petheram (CSIRO). 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 Ord Irrigation Area. Source: CSIRO – Nathan Dyer Director’s foreword Sustainable development and regional economic prosperity are priorities for the Australian, Queensland 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 and the Southern Gulf 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 and Southern Gulf catchments. The Assessments focus mainly on the potential for agricultural development, and the opportunities and constraints that development could experience. They also consider 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, Queensland 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 Assessments do not recommend one development over another, nor assume any particular development pathway, nor even assume that water resource development will occur. They provide 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 Assessments will be publicly available. C:\Users\bru119\AppData\Local\Microsoft\Windows\Temporary Internet Files\Content.Word\C_Chilcott_high.jpg Chris Chilcott Project Director The Victoria and Southern Gulf 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, Margaux Dupuy, Geoff Hodgson, Anthony Knapton6, Shane Mule, Stacey Priestley, Jodie Pritchard, Matthias Raiber, Steven Tickell7, Axel Suckow Indigenous water values, rights, interests and development goals Marcus Barber/Kirsty Wissing, Pethie Lyons, Peta Braedon, Kristina Fisher, Petina Pert Land suitability Ian Watson, Jenet Austin, Bart Edmeades7, Linda Gregory, Ben Harms10, Jason Hill7, Jeremy Manders10, Gordon McLachlan, Seonaid Philip, Ross Searle, Uta Stockmann, Evan Thomas10, Mark Thomas, Francis Wait7, Peter L. Wilson, Peter R. Wilson, Peter Zund Surface water hydrology Justin Hughes, Matt Gibbs, Fazlul Karim, Julien Lerat, Steve Marvanek, Cherry Mateo, Catherine Ticehurst, Biao Wang Surface water storage Cuan Petheram, Giulio Altamura8, Fred Baynes9, Jamie Campbell11, Lachlan Cherry11, 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 (Victoria catchment), 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; 10Queensland Government Department of Environment, Science and Innovation; 11Enturaii | Hypothetical irrigation developments Shortened forms For more information on this table please contact CSIRO on enquiries@csiro.au Units For more information on this table please contact CSIRO on enquiries@csiro.au Preface Sustainable development and regional economic prosperity are priorities for the Australian, NT and Queensland governments. In the Queensland Water Strategy, for example, the Queensland Government (2023) looks to enable regional economic prosperity through a vision which states ‘Sustainable and secure water resources are central to Queensland’s economic transformation and the legacy we pass on to future generations.’ Acknowledging the need for continued research, the NT Government (2023) announced a Territory Water Plan priority action to accelerate the existing water science program ‘to support best practice water resource management and sustainable development.’ Governments are actively seeking to diversify regional economies, considering a range of factors, including Australia’s energy transformation. The Queensland Government’s economic diversification strategy for north west Queensland (Department of State Development, Manufacturing, Infrastructure and Planning, 2019) includes mining and mineral processing; beef cattle production, cropping and commercial fishing; tourism with an outback focus; and small business, supply chains and emerging industry sectors. In its 2024–25 Budget, the Australian Government announced large investment in renewable hydrogen, low-carbon liquid fuels, critical minerals processing and clean energy processing (Budget Strategy and Outlook, 2024). This includes investing in regions that have ‘traditionally powered Australia’ – as the North West Minerals Province, situated mostly within the Southern Gulf catchments, has done. For very remote areas like the Victoria and Southern Gulf catchments, the land (Preface Figure 1-1), water and other environmental resources or assets will be key in determining howsustainable regional development might occur. Primary questions in any consideration ofsustainable regional development relate to the nature and the scale of opportunities, and theirrisks. How people perceive those risks is critical, especially in the context of areas such as the Victoria and Southern Gulf catchments, where approximately 75% and 27% of the population (respectively) is Indigenous (compared to 3.2% for Australia as a whole) and where many Indigenous Peoples still live on the same lands they have inhabited for tens of thousands of years. About 31% of the Victoria catchment and 12% of the Southern Gulf catchments are owned by Indigenous Peoples as inalienable freehold. Access to reliable information about resources enables informed discussion and good decision making. Such information includes the amount and type of a resource or asset, where it is found (including 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 possible impacts of development. Most of northern Australia’s land and water resources have not been mapped in sufficient detail to provide the level of information required for reliable resource allocation, to mitigate investment or environmental risks, or to build policy settings that can support good judgments. The Victoria and Southern Gulf Water Resource Assessments aim to partly address this gap by providing data to better inform decisions on private investment and government expenditure, to account for intersections between existing and potential resource users, and to ensure that net development benefits are maximised. Preface Figure 1-1 Map of Australia showing Assessment areas (Victoria and Southern Gulf catchments) and other recent CSIRO Assessments FGARA = Flinders and Gilbert Agricultural Resource Assessment; NAWRA = Northern Australia Water Resource Assessment. The Assessments differ somewhat from many resource assessments in that they consider a wide range of resources or assets, rather than being single mapping exercises of, say, soils. They provide a lot of contextual information about the socio-economic profile of the catchments, and the economic possibilities and environmental impacts of development. Further, they consider many of the different resource and asset types in an integrated way, rather than separately. The Assessments have agricultural developments as their primary focus, but they also consider opportunities for and intersections between other types of water-dependent development. For example, the Assessments explore the nature, scale, location and impacts of developments relating to industrial, urban and aquaculture development, in relevant locations. The outcome of no change in land use or water resource development is also valid. The Assessments were designed to inform consideration of development, not to enable any particular development to occur. As such, the Assessments inform – but do not seek to replace – existing planning, regulatory or approval processes. Importantly, the Assessments do not assume a given policy or regulatory environment. Policy and regulations can change, so this flexibility enables the results to be applied to the widest range of uses for the longest possible time frame. It was not the intention of – and nor was it possible for – the Assessments to generate new information on all topics related to water and irrigation development in northern Australia. Topics For more information on this figure please contact CSIRO on enquiries@csiro.au not directly examined in the Assessments are discussed with reference to and in the context of the existing literature. CSIRO has strong organisational commitments to Indigenous reconciliation and to conducting ethical research with the free, prior and informed consent of human participants. The Assessments allocated significant time to consulting with Indigenous representative organisations and Traditional Owner groups from the catchments to aid their understanding and potential engagement with their requirements. The Assessments did not conduct significant fieldwork without the consent of Traditional Owners. Functionally, the Assessments adopted an activities-based approach (reflected in the content and structure of the outputs and products), comprising activity groups, each contributing its part to create a cohesive picture of regional development opportunities, costs and benefits, but also risks. Preface Figure 1-2 illustrates the high-level links between the activities and the general flow of information in the Assessments. Preface Figure 1-2 Schematic of the high-level linkages between the eight activity groups and the general flow of information in the Assessments Assessment reporting structure Development opportunities and their impacts are frequently highly interdependent and, consequently, so is the research undertaken through these Assessments. While each report may be read as a stand-alone document, the suite of reports for each Assessment most reliably informs discussion and decisions concerning regional development when read as a whole. For more information on this figure please contact CSIRO on enquiries@csiro.au The Assessments have produced a series of cascading reports and information products: •Technical reports present scientific work with sufficient detail for technical and scientific expertsto reproduce the work. Each of the activities (Preface Figure 1-2) has one or more correspondingtechnical reports. •Catchment reports, one for each of the Victoria and Southern Gulf catchments, synthesise keymaterial from the technical reports, providing well-informed (but not necessarily scientificallytrained) users with the information required to inform decisions about the opportunities, costsand benefits associated with irrigated agriculture and other development options. •Summary reports, one for each of the Victoria and Southern Gulf catchments, provide a shortersummary and narrative for a general public audience in plain English. •Summary fact sheets, one for each of the Victoria and Southern Gulf catchments, provide keyfindings for a general public audience in the shortest possible format. The Assessments have also developed online information products to enable users to better access information that is not readily available in print format. All of these reports, information tools and data products are available online at https://www.csiro.au/victoriariver and https://www.csiro.au/southerngulf. The webpages give users access to a communications suite including fact sheets, multimedia content, FAQs, reports and links to related sites, particularly about other research in northern Australia. Executive summary This report seeks to highlight the types of considerations necessary in designing potential irrigation schemes in northern Australia by developing four conceptual arrangements of hypothetical irrigation schemes in the Victoria and Southern Gulf catchments and developing estimates of their cost. For comparison, conceptual arrangements and costings for two water harvesting schemes were also developed. Importantly, the intention is to define what a possible development might look like and cost based on the information available rather than to define the optimum development for each area. A summary of the hypothetical irrigation schemes, two water-harvesting schemes and two hypothetical irrigation schemes assessed as part of the Victoria, Roper and Southern Gulf Water Resource Assessments are summarised in Table 1-1. Table 1-1 Summary of hypothetical irrigation schemes in the Victoria, Roper and Southern Gulf catchments CATCHMENT POTENTIAL DAM SITE. SCHEME CHARACTERISTICS SERVICED AREA (HA) LOCAL DEVELOPMENT UNIT COST ($/HA) TOTAL SCHEME DEVELOPMENT UNIT COST ($/HA) Victoria Wickham River Pipeline-based system, involving pumping to high-level balancing storages Two re-regulation weirs in Wickham River Two pump stations serving three discrete areas 17,953 16,200 104,931 Leichhardt Creek Channel-based system, involving supply from an offstream storage One re-regulation weir on West Baines River Low-lift pump station supplying the offstream storage 3,780 3,351 104,761 Flood harvesting along West Baines River Channel-based system with water- harvesting supply Low-level weir on Wickham River Pump station and inlet channel leading to storage cells Four large storage cells with centrally located pump transfer box Small main channel system 2,000 18,300 18,300 Southern Gulf Gunpowder Creek Pipeline-based system, with low boost pumping at offtake Re-regulation weir on Gunpowder Creek Low-lift (8 m) pump station supplying pipeline distribution system 11,734 27,200 93,077 CATCHMENT POTENTIAL DAM SITE. SCHEME CHARACTERISTICS SERVICED AREA (HA) LOCAL DEVELOPMENT UNIT COST ($/HA) TOTAL SCHEME DEVELOPMENT UNIT COST ($/HA) Gregory River FSL 145 mEMG96 Channel-based system, to maximum serviced area Re-regulation weir on Gregory River Pump station serving start of channel system 19,710 3,180 Not calculated Gregory River FSL 138 mEMG96 Channel-based system, to lower level of development based on dam not encroaching on national park Re-regulation weir on Gregory River Pump station serving start of channel system 11,398 3,336 62,259 Flood harvesting along the Gregory River Channel-based system, with water- harvesting supply Pump station supplying directly to storage cells by five rising mains Four large storage cells, with transfer box pumps separating the northern three cells Dual channel system, located on the high ground to the south and west of the serviced area 2,000 15,913 15,913 Roper Waterhouse River Fully piped system directly from the dam site to areas riparian to Waterhouse River Pump station providing 10 m boost at dam site 48.5 km pipeline system to areas on both sides of the river 9,560 41,680 Not calculated Flying Fox Creek Channel-based system, supplied from a re-regulation weir at AMTD 36 km on Flying Fox Creek, some 53 km below the dam site (not included in costs) Pump station and 2.6 km rising main to head of channel system 21 km channel system featuring three siphons 5,200 10,046 Not calculated Scheme costs on a per hectare basis varied from $3180/ha to $41,580/ha. It was found that channel-based schemes were significantly less costly to develop than piped schemes in the same catchment, based on locally derived costs, though scheme-scale costs were small relative to the cost of the potential dams servicing the hypothetical irrigation areas. Once potential water storage (i.e. instream dam or earth embankment ringtank) costs were included in the calculation, water-harvesting schemes were found to have significantly lower development costs per hectare. x | Hypothetical irrigation developments Contents Director’s foreword .......................................................................................................................... i The Victoria and Southern Gulf Water Resource Assessment Team ............................................. ii Shortened forms .............................................................................................................................iii Units ............................................................................................................................... iv Preface ............................................................................................................................... v Executive summary ......................................................................................................................... ix Contents .............................................................................................................................. xii Part I Introduction and overview 1 1 Potential irrigation development in the Victoria and Southern Gulf catchments ............. 2 1.1 Scope of report ...................................................................................................... 2 1.2 Selection of development area ............................................................................. 5 1.3 Learnings from other northern Australian irrigation developments .................... 6 Part II Victoria catchment 9 2 Potential dam site on Wickham River AMTD 63 km ........................................................ 10 2.1 Options evaluated ............................................................................................... 10 2.2 Layout for re-regulation with piped distribution ................................................ 12 2.3 Piped reticulation design capacities .................................................................... 13 2.4 System pipe sizing ............................................................................................... 15 2.5 The Wickham River potential dam site pumping requirements ......................... 16 2.6 The Wickham River potential dam site reticulation costing ............................... 16 3 Potential dam site on Leichhardt Creek AMTD 26 km ..................................................... 18 3.1 Identification of potential lands for development .............................................. 18 3.2 Selection of area for development ...................................................................... 20 3.3 Operation of potential scheme ........................................................................... 21 3.4 Elements of potential scheme ............................................................................. 21 3.5 Area irrigated ....................................................................................................... 23 3.6 Design capacities ................................................................................................. 24 3.7 The Leichhardt Creek potential dam site channel reticulation costing .............. 25 4 Water-harvesting options along West Baines River ......................................................... 27 4.1 Evaluation of water-harvesting options .............................................................. 27 4.2 Details of water-harvesting operation ................................................................ 28 4.3 Major elements of the notional water-harvesting scheme ................................ 30 4.4 Likely scope of development – furrow-irrigated water-harvesting-based scheme ............................................................................................................................. 32 4.5 Water-harvesting cost estimation ....................................................................... 34 Part III Southern Gulf catchments 37 5 Potential dam site on Gunpowder Creek AMTD 66 km ................................................... 38 5.1 Re-regulation weir for Gunpowder Creek potential dam site ............................ 40 5.2 Irrigation layout ................................................................................................... 41 5.3 Piped reticulation design ..................................................................................... 42 5.4 Pipe system type.................................................................................................. 43 5.5 System pipe sizing ............................................................................................... 45 6 Potential dam site on Gregory River AMTD 174 km ......................................................... 48 6.1 Conceptual irrigation scheme arrangement for Gregory River potential dam with FSL 145 mEMG96 ...................................................................................................... 48 6.2 Conceptual irrigation scheme arrangement for Gregory River potential dam with FSL 138 mEMG96 ...................................................................................................... 55 7 Water-harvesting options along the Gregory River ......................................................... 59 7.1 Major elements of the notional water-harvesting scheme ................................ 59 7.2 Water-harvesting cost estimation ....................................................................... 60 Part IV Discussion 63 8 Discussion ......................................................................................................................... 64 References ............................................................................................................................. 68 Part IV Appendices 69 Roper catchment dam site developments, updated cost estimates .................. 70 Figures Preface Figure 1-1 Map of Australia showing Assessment areas (Victoria and Southern Gulf catchments) and other recent CSIRO Assessments ........................................................................ vi Preface Figure 1-2 Schematic of the high-level linkages between the eight activity groups and the general flow of information in the Assessments ..................................................................... vii Figure 1-1 Selected potential dam sites and hypothetical irrigation areas in the Victoria catchment ....................................................................................................................................... 3 Figure 1-2 Selected potential dam sites and hypothetical irrigation areas in the Southern Gulf catchment ....................................................................................................................................... 4 Figure 2-1 Potential development areas for the Wickham River potential dam site ................... 10 Figure 2-2 Piped reticulation layout for Wickham River potential dam site ................................ 13 Figure 3-1 Potential development areas for the Leichhardt Creek potential dam site ................ 19 Figure 3-2 Adopted layout for furrow irrigation to Area 4 for the Leichhardt Creek potential dam site ................................................................................................................................................. 23 Figure 3-3 Adopted gradeline for the Leichhardt Creek potential dam site Area 4 main channel ....................................................................................................................................................... 24 Figure 4-1 Notional water-harvesting layout for full development of Area C .............................. 30 Figure 4-2 Flood-harvesting channel and pipeline layout ............................................................ 32 Figure 4-3 Layout for furrow irrigation development................................................................... 33 Figure 5-1 The Gunpowder Creek potential dam site and potential diversion locations ............ 38 Figure 5-2 Potential development areas for Dam site 28 ............................................................. 39 Figure 5-3 Targeted development area (reduced Area B) and pipeline infrastructure for potential Dam site 28 .................................................................................................................... 42 Figure 6-1 The Gregory River potential dam site and potential diversion and development areas ....................................................................................................................................................... 49 Figure 6-2 Channel layout and serviced areas .............................................................................. 50 Figure 6-3 Adopted gradeline for Gregory River potential dam site main channel ..................... 52 Figure 6-4 Adopted gradeline for Gregory River potential dam site lateral channel ................... 52 Figure 6-5 Area for reduced development ................................................................................... 56 Figure 6-6 Main channel profile for the 131 GL development ..................................................... 57 Figure 6-7 Lateral channel profile for the 131 GL development .................................................. 57 Figure 7-1 Layout of water-harvesting scheme ............................................................................ 59 Tables Table 1-1 Summary of hypothetical irrigation schemes in the Victoria, Roper and Southern Gulf catchments ...................................................................................................................................... ix Table 1-1 Selected soil generic groups (SGGs) descriptions ........................................................... 6 Table 2-1 Evaluation of development options .............................................................................. 11 Table 2-2 Adopted flow-rates for the piped reticulation ............................................................. 14 Table 2-3 Adopted pipe requirements .......................................................................................... 15 Table 2-4 Pump station details for the Wickham River potential dam site .................................. 16 Table 2-5 Cost summary for the Wickham River potential dam site reticulation infrastructure . 17 Table 3-1 Details and comparison of potential development areas below the Leichhardt Creek potential dam site ......................................................................................................................... 19 Table 3-2 Channel flow-rate determination ................................................................................. 24 Table 3-3 Adopted main channel parameters .............................................................................. 25 Table 3-4 Leichhardt Creek potential dam site reticulation costing ............................................. 26 Table 4-1 Evaluation of water-harvesting options ........................................................................ 27 Table 4-2 Furrow-irrigation water-harvesting cost estimate ....................................................... 35 Table 5-1 Evaluation of alternative development areas for potential Dam site 28 ..................... 39 Table 5-2 Adopted flow-rates for piped reticulation .................................................................... 43 Table 5-3 Adopted pipe requirements .......................................................................................... 45 Table 5-4 Cost summary for the Gunpowder Creek potential dam site reticulation ................... 46 Table 5-5 Factors against open-channel reticulation and potential strategies to negate ........... 47 Table 6-1 Channel flow-rate determination ................................................................................. 51 Table 6-2 Adopted main channel parameters .............................................................................. 53 Table 6-3 Adopted lateral channel parameters ............................................................................ 53 Table 6-4 The Gregory River potential dam site channel reticulation costing ............................. 55 Table 6-5 Adopted main channel parameters .............................................................................. 56 Table 6-6 Adopted lateral channel parameters ............................................................................ 57 Table 6-7 The Gregory River potential dam site channel reticulation costing – reduced area .... 58 Table 7-1 Furrow-irrigation water-harvesting cost estimate ....................................................... 60 Table 8-1 Key characteristic for reticulation sites examined ........................................................ 64 PartIIntroduction and overview 1 Potential irrigation development in the Victoria and Southern Gulf catchments 1.1 Scope of report Potential water storage sites for irrigation development have been identified in both the catchment of the Victoria River and the catchments of the Southern Gulf rivers, that is Settlement Creek, Gregory–Nicholson River and Leichhardt River, the Morning Inlet catchments and the Wellesley island groups (see companion technical report on surface water storage, Yang et al., 2024). For this report and highlighting the types of considerations necessary in designing potential irrigation schemes in northern Australia, two potential dam sites in each study area were select upon which to develop conceptual arrangements of hypothetical irrigation schemes and estimate their cost. In the Victoria catchment, these sites are on Leichhardt Creek adopted middle thread distance (AMTD) 26 km, a tributary of the West Baines River and the Wickham River AMTD 63 km upstream of the Victoria River junction (Figure 1-1). In the Southern Gulf catchments these sites are on the Gregory River AMTD 174 km and Gunpowder Creek AMTD 66 km (Figure 1-2). This report examines the scope for broad-scale irrigation development serviced by each of those storages. The intention is to define what a possible development might look like from the information available rather than to define the optimum development for the areas. Indicative costings are presented for each of the hypothetical developments. For the site on the Wickham River in the Victoria catchment and the site on the Gregory River in the Southern Gulf catchments, the costs of potential flood harvesting developments are provided for comparative purposes. This information is presented by way of comparison with dam-based options only, and it does not represent the extent of water-harvesting possibilities in the two study areas. It should be noted that development decisions will be influenced by laws, policies and regulations about land tenure, land ownership, land use, water management and environmental protection, as well as by production costs and market demands. In reality, the nature and scale of potential future development will depend heavily upon community and government values about desirable forms of development and the balance of potential benefits and impacts, including impacts to communities and water-dependent ecosystems. Figure 1-1 Selected potential dam sites and hypothetical irrigation areas in the Victoria catchment The black circles and squares indicates the general location of the two potential dam sites (A and B) and the general location of their associated hypothetical irrigation areas (AA and BB) overlaid on versatile agricultural land (see companion technical report on digital soil mapping and land suitability, Thomas et al., 2024a). A is Leichhardt Creek AMTD 26 km; B is Wickham River AMTD 63km. For more information on this figure please contact CSIRO on enquiries@csiro.au Figure 1-2 Selected potential dam sites and hypothetical irrigation areas in the Southern Gulf catchment The black circles and squares indicates the general location of the two potential dam sites (A and B) and the general location of their associated hypothetical irrigation areas (AA and BB) overlaid on versatile agricultural land (see companion technical report on digital soil mapping and land suitability, Thomas et al., 2024b). A is Gregory River AMTD 174 km; B is Gunpowder Creek AMTD 66km. For more information on this figure please contact CSIRO on enquiries@csiro.au 1.2 Selection of development area An investigation into the suitability of the soils of the Victoria catchment and Southern Gulf catchments (see companion technical reports on land suitability in the Victoria and Southern Gulf catchments, Thomas et al., 2024a,b) indicated that there were relatively small areas of suitable soils in the immediate vicinity of potential storage sites. Hence, the areas to be serviced by potential dams were selected using the following criteria: •Suitable soils are present in aggregations rather than isolated patches. Thus, the main targets ofpotential development will be the alluvial soils downstream of the storage site on the banks ofthe streams being impounded and adjacent areas of suitable soils within practical reach of theriver channel. •The development area is close to the storage site. The storages identified are relatively modestin size, the Leichhardt Creek and Gunpowder C potential sites being particularly so. Proximity ofsoils suitable for irrigated agriculture is important for two main reasons. It limits the capital costof transfer infrastructure to transfer the water from the source impoundment, whether that beby connector pipeline or channel or by downstream regulating structure and re-lift. Also, it limitslosses in transferring the water from source to point of use in all cases other than the fully pipedoption. These losses arise mainly from accessions to the riverbed and operational losses, such asthat resulting from rain rejection (i.e. when irrigation demand reduces following rainfall, afterwater has been released from the storage in anticipation of demand). •Planned development is compatible with topography, not requiring extreme land levelling orexpensive reticulation to adjacent subcatchments. In both cases, the hypothetical storages arelocated in sections of the river where the stream is relatively incised, and distribution byreleases to the downstream stream, or by channel conveyance, will only potentially serve areasdown the catchment. Distribution by pipeline has the potential to reach downstream adjacentsubcatchments but at the expense of additional re-lift pumping. In all the hypotheticaldevelopments, the targeted area is downstream of the dam site, and adjacent to the stream. •Soils in the development area are compatible with a range of crop types rather than a limitedsuite of crops. The inescapable conclusion for the potential dam sites is that the potential for irrigation development in the immediate proximity to the dam sites is minimal. Hence, the most crucial consideration will be how the water is conveyed from the storage to the development area. 1.2.1 Soil generic groups The soils of the Victoria and Southern Gulf catchments are presented in a soil generic group (SGG) classification (Table 1-1). These are described in detail in the companion technical reports on land suitability in the Victoria and Southern Gulf catchments (Thomas et al., 2024a,b). These groupings provided the Assessment with a means of aggregating soils with broadly similar properties and management considerations. The distinctive groupings have different potential for agriculture, some with almost no potential, such as the shallow and/or rocky soils (SGG 7), and some with moderate to high potential (e.g. SGG 9) assuming other factors such as flooding and the amount of salt in the profile are not limiting. Selected SGGs discussed in this report are listed in Table 1-1. Table 1-1 Selected soil generic groups (SGGs) descriptions Partially reproduced from Thomas et al. (2024a,b). SGG SGG OVERVIEW GENERAL DESCRIPTION 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 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 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 9 Cracking clay soils Clay soils with shrink–swell properties that cause cracking when dry. Usually alkaline and moderately deep to very deep 1.3 Learnings from other northern Australian irrigation developments A number of schemes have seen larger scale irrigation developments in the northern part of Australia in recent decades, and these hold potential lessons for any potential irrigation development in the Victoria and Southern Gulf catchments. This analysis draws on such lessons from: •the Emerald Irrigation Scheme in Central Queensland, which involves both in-situ derivedbasaltic soils and associated alluvial deposits along the Negoa River •the Burdekin Irrigation Scheme in north Queensland, which involves a range of soil types on theBurdekin and Haughton River floodplain, and associated upslope areas •the Ord River Irrigation Scheme – Stage 2 in the Kimberley region of WA, which involves mostlyclay alluvium deposits on the Weaber Plain •cane supplementation schemes, in particular by the Pioneer Valley Water Board and theProserpine Water Board, which involve pumping from rivers and piped reticulation. Pumping pools are important for any river re-lift pumps to ensure adequate submergence and avoid complications from flood siltation. The total river flow for a good proportion of the year will only comprise the irrigation releases, and at least for the smaller Leichhardt and Gunpowder creeks storages is likely to only average around 200 or 900 ML/day, respectively, at the dam, and be decreasing downstream. Therefore providing adequate submergence will normally mean either a flow constriction or a constructed re-regulating weir. For all potential dam sites, the solutions examined in detail involve one or two discrete re-lift points rather than the alternative of multiple pump installations along the river course. The reasons are slightly different for each catchment but can be summarised as follows: •The Leichhardt Creek downstream area is very small, and the key to achieving acceptabletransmission efficiencies will be a steady release pattern and pumping at one site. •For the Wickham River site, the targeted areas are in three separate areas spread out over45 km of the river. Cost effectiveness and efficiencies of operation will dictate the minimum number of re-regulation weirs and pump sites. Accordingly, the nominal conceptual arrangement involves two potential weirs for this site. • The Gunpowder Creek sections offer limited sites for effective re-lift pools. • The Gregory River site has a likely serviced area generally falling away from the river re-lift point. It is important to align infrastructure to cater for flood flows in internal and adjacent catchments. This is more of an issue for schemes involving open-channel reticulation than those involving piped and pumped schemes, but it will apply to some degree for all schemes, such as those where the primary soils to be developed are riparian alluvia. It is particularly important in this instance for the Gregory River and Leichhardt Creek developments where the areas targeted are floodplain soils, but it will also apply to the Wickham River development if water-harvesting storages are constructed. It is less critical, but still important for both the Gunpowder Creek and Wickham River developments. Irrigation design is best shaped by existing topography and soils distribution, not the other way around, where excessive land levelling and manipulation of soil profiles is used to give a particular irrigation layout. This is especially the case for spray irrigation systems, where spray system design can cater for reasonably irregular layouts. Hydrogeology is critical to long-term sustainability, and any irrigation system must contain a mechanism to cater for the increased accessions to groundwater that are an unavoidable part of irrigation. This is mainly because accessions from rainfall are greater in irrigated areas than in dryland, due to the higher mean antecedent moisture profile in the soil. In this situation, riparian lands, above but adjacent to a river system, are normally better situated to avoid long-term salinisation than isolated lands without drainage incisions. Natural landscape slope also plays a part in this requirement. Water use efficiency needs to be designed in at the start, for example, by incorporating high- quality flow measurement, and supervisory control of channel or pipeline structures, such as Total Channel Control (a proprietary open water control system from Rubicon Water). This particularly applies to the downriver releases but is also important for open-channel distribution systems. Long systems involving substantial travel time can be inefficient and waste valuable water in operational overflows if the above components are not included. PartIIVictoria catchment 2 Potential dam site on Wickham River AMTD 63 km 2.1 Options evaluated The Wickham River potential dam site has an annual water yield of some 196 GL at 85% annual reliability. If water from the storage is distributed downstream by river releases to a re-regulation point, this water could irrigate up to 20,000 ha, assuming piped reticulation from the river re-regulation point to the field. More than that amount of land seems to be available, but it is in a number of discrete parcels (Figure 2-1). Figure 2-1 Potential development areas for the Wickham River potential dam site Development areas are overlaid on levels of suitability for dry-season spray-irrigated cotton or grains, green Class 2, yellow Class 3. Numbers are the gross area of soils (ha) suitable for dry-season spray-irrigated cotton in the particular potential development area (A to G). Red dotted lines are prior stream remnants that will complicate irrigation development. If distribution occurred via a channel network, the lower efficiency of that distribution may mean that slightly less than 20,000 ha could be irrigated. However, the major difference between the piped reticulation and channel network options is that it is probably not practical to have a channel system on both sides of the river, which would limit development to the southern side of the river. Nevertheless, the gross suitable area on the southern side would still fully utilise the above yield. Development on the southern side would also avoid conflict with the Yarralin town and surrounds and the infrastructure around the Victoria River Downs homestead. For more information on this figure please contact CSIRO on enquiries@csiro.au A third option is that the development may involve flood harvesting to offstream storages. This option would not involve a major storage at the Wickham River potential dam site but would have a small storage in the river to provide a suitable pumping pool and individual offstream storage systems serviced by pump stations on the river bank. A water-harvesting option based on Area C is discussed further in Section 4. Details of the two reticulation options for the Wickham River potential dam site, and their advantages and disadvantages, are presented in Table 2-1. Table 2-1 Evaluation of development options For more information on this table please contact CSIRO on enquiries@csiro.au Given the above, the following conclusions can be drawn: •The option offering the most potential is a piped reticulation system to the south of the riveronly based on a re-regulation weir at the upper site. An interconnecting pipeline will beevaluated against a second re-lift point to service Area C. •The piped reticulation option is likely to result in better use of the available resource, both interms of the amount of land serviced and the reliability of the resulting irrigation operation. The piped reticulation option from a potential dam at the Wickham River potential dam site is examined below. 2.2 Layout for re-regulation with piped distribution As summarised above, a piped distribution system from a re-regulation point (or points) would allow utilisation of the full yield of the potential storage, less distribution losses to the re-regulation point(s). Also, it avoids the difficulty of the major soil types encountered on any likely alignment being unsuitable for earth channel construction without lining, either by over-excavation and backfill or membrane lining. The major elements of the piped reticulation option, and the reasons for those choices, are as follows: •The scheme will only target suitable lands on the southern side of the river. Areas to the northare more fragmented and have greater complications from prior streams and existinginfrastructure. The total area of suitable soils on the southern side is sufficient to fully utilise theavailable yield from the Wickham River potential dam site. •Two pumping sites could be constructed: one near the downstream end of Area A and the othertowards the upper end of Area C (across the river from the Victoria River Downs homestead). This will require two re-regulating weirs, but both are on existing rock features in the riverbed, meaning lower constructed height, and less expensive bed protection. The locations are shownin Figure 2-2. Both weirs will only be of nominal height, sufficient only to provide pumpsubmergence, and both are located on significant existing waterholes. •The operational strategy used for both pump stations and the associated reticulation networksis to pump to an elevated balance tank, and then supply the serviced area by flow from thebalance tank, and to pump from the river as required. The main reason for this arrangement isto create an open system to limit transient pressure surges that would otherwise dominate thedesign of these systems. This is because being spray irrigated implies re-pumping at the offtaketo a particular paddock, and these offtakes will be subject to power failure if they are electricallydriven. In a long, closed system, this would create a major pressure transient in the pipelinenetwork. Even if the individual offtakes were diesel powered, starting and stopping the riverpumps could also induce major pressure transients if the system was fully closed. The adopted layout is shown in Figure 2-2. This site has the potential to serve up to 17,350 ha, assuming: •Dam yield at 85% annual reliability is 196 GL/year. •Crop demand assuming dry-season field crops or perennial trees under spray is 8 ML/ha. •Irrigation efficiency for spray application is 85%. •Irrigation efficiency for trickle application is 90%. •Distribution efficiency for piped reticulation is 98%. •River reticulation efficiency is 85%. •Net area irrigated is 95% of gross area. The total area identified in Figure 2-2 is 17,953 ha. Note that part of Area D has been removed compared to Figure 2-1 to give the reduced area. While this is slightly larger than the figure of 17,350 ha derived above, it is appropriate since some of the irrigation may be by trickle. Figure 2-2 Piped reticulation layout for Wickham River potential dam site Main pipelines, pump stations and balancing storage sites are overlaid on levels of suitability for dry-season spray- irrigated cotton or grains. Nomenclature for serviced areas is A Sub B, where A refers to the gross areas from Figure 2-1 and the Sub B is the section used for flow calculations. Red dot locations are used in the flow calculations below. 2.3 Piped reticulation design capacities Flow-rates for the reticulation pipelines were based on the following calculation. Daily crop demand was based on 𝐸𝐸𝑡𝑡 =𝑝𝑝×𝑓𝑓1 ×0.8 × 𝐸𝐸0 (1) where: •p is climate factor, assumed as 0.7 •f1 is crop factor, assumed as 1.0 •E0 is assumed at 11.475 mm/day, based on values from the Scientific Information for LandOwners (SILO) database for Victoria River Downs (99th percentile (P99) of 4-day mean E0). Victoria River Downs Station is virtually in the middle of the serviced area, and while only having53 years of evaporation data, is the closest site with relevant climate data. The other station inthe vicinity (Kidman Springs) gave similar results. Et is therefore 6.43 mm/day. Irrigation demand is 7.56 mm per day per hectare, assuming spray irrigation. No diversity factor was applied, as the total area is small and soil types are reasonably uniform. For more information on this figure please contact CSIRO on enquiries@csiro.au The adopted flow-rates are as shown in Table 2-2. Table 2-2 Adopted flow-rates for the piped reticulation Nomenclature follows Figure 2-2. For more information on this table please contact CSIRO on enquiries@csiro.au Some assumptions made in deriving the capacities in Table 2-2 are as follows: •In general, capacities are calculated assuming the flow is coming from the pump stations, notthe balancing storage. In practical terms this is reasonable, since this will be the case at full flow. The main roles of the balancing storage are to have a stable method of controlling the pumpflow and to reduce the potential for destructive pressure surges due to rapid flow changes. •Flow changes are generally at the centroid of the serviced areas. This is an approximation, and inany final design, the capacities would be more closely tied to the actual locations of individualofftakes from the mainline. It is, however, an acceptable approximation of the actualrequirements. •The flow capacity of the final link to the balancing storage will limit the rate of filling of thebalancing storage. However, if the storage is being filled without major demand to the rest ofthe serviced area, there will be significant additional head to be dissipated across this last leg, sothe flow able to be delivered will be significantly higher than the nominal capacity noted above. When storage fill corresponds to a period of heavy demand on the system, the storage will fillslowly. However, this will not be an operational limitation as the primary purpose will be flow- rate setting in response to level change in the storage. 2.4 System pipe sizing Pipelines were designed for the above network to meet a number of criteria, including the following: •Two different approaches were used for sizing the pipelines. In general, pipelines supplied directly from the balancing storages (such as Area B and legs H–K and H–I–J) were designed as simple gravity lines from the lower operational level of the storage. The remaining lines were designed as pump rising mains, for which the combined variable capital cost of the pipeline and pump installation were combined with the capitalised cost of annual energy for the pump station to give the best economic option, subject to the other limitations noted below. •Preference was given to lower pumping heads if the life cycle costs outlined above are similar, since this avoids high pipeline pressures and consequent transient pressure issues on power failure. •Likewise, pipeline velocity at full flow was limited to below 2 m/second to also help moderate transient pressures on pump power failure or abrupt changes of demand. An exception was short lateral channels, where slightly higher velocities (up to 2.2 m/second) were allowed. •Pipelines were designed to produce a minimum of 2 m residual head at the take-off point. This is conservative, as there will be some re-pumping at this point for travelling irrigators or filtering for trickle, but it ensured that there was some flexibility in the location of the re-pumping. •In general, glass-reinforced plastic (GRP) pipelines were considered for this project as they represent the minimum cost solution for the pressures and flow-rates involved. In some cases of relatively smaller flow-rates, it was possible that high-density polyethylene (HDPE) lines could be used but installed costs were similar. The use of GRP pipe throughout was selected, mainly driven by the large diameters required. An effective roughness of k = 0.06 mm was assumed; this represents an achievable long-term value. Head loss was calculated using the Colebrook–White equation. The results of this analysis are shown in Table 2-3. Table 2-3 Adopted pipe requirements Area and reach refer to the points defined in Figure 2-2. 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 2.5 The Wickham River potential dam site pumping requirements Details of the two pump stations required for the layout shown in Figure 2-2 are given in Table 2-4. Table 2-4 Pump station details for the Wickham River potential dam site For more information on this table please contact CSIRO on enquiries@csiro.au Of particular note in Table 2-4 are the installed power figures. These effectively mean that this type of installation will only be practical with access to a mains electricity supply. As outlined above, both sites will require augmentation of the existing waterholes to provide adequate submergence for what are very significant pump stations. Estimates for the cost of these structures are only approximate, but have been based on the following assumptions: •Upper pump site –The assumed submergence required is 2 m. –The existing pool provides at least 0.5 m of reliable water depth. –The re-regulating weir provides an additional 1.5 m of water depth. •Lower pump site –The assumed submergence required is 1.75 m. –The existing pool is very substantial and is likely to provide at least 1.0 m of reliable waterdepth. –The re-regulation weir provides an additional 0.75 m of water depth. 2.6 The Wickham River potential dam site reticulation costing The above works were costed (Table 2-5) based on a number of assumptions, including: •Pipelines were costed at unit rates derived by Rider Levett Bucknall (RLB) (2024) and adjustedwhere necessary for actual sizes and pressure classes. A percentage allowance was made for normal pipeline appurtenances, such as air valves, scours, swabbing facilities, thrust blocks, specials and valving. •The three balancing storages are only of nominal size and were costed as membrane-lined paneltanks. This is the likely solution for tanks B and C, since the soils at those locations are likely tobe minimal and permeable, but Tank A is located in suitable soils and could potentially be asmall earth tank. In any event, the impact on scheme pricing is small. •The pump stations are substantial structures. Each requires multiple pump units in a range ofsizes, both to meet the total capacity requirement and to allow the necessary downturn to meetlow-demand periods. To date, little is known about the actual site, so it was not feasible to makeany sort of preliminary design. Therefore, some costing curves derived from investigatingSunWater pump stations of a range of sizes in north Queensland were used to estimate likelycost ranges. •Costs for both re-regulating weirs were based on using a low-level reinforced concrete slab withupstands. The total capital cost of the Wickham River potential dam site reticulation infrastructure (Table 2-5) represents a development cost of some $16,200 per spray-irrigated hectare for the backboneinfrastructure only. The total cost to move the water to the paddock will also include distributionfrom the main reticulation network to the individual irrigators required for the irrigated area. Table 2-5 Cost summary for the Wickham River potential dam site reticulation infrastructure For more information on this table please contact CSIRO on enquiries@csiro.au 3 Potential dam site on Leichhardt Creek AMTD 26 km Leichhardt Creek potential dam site is a very small site of only some 60 GL annual water yield, and it is located a significant distance upstream of any significant areas of soil suitable for irrigated development. Nevertheless, the site was examined in a similar method to that used for the Wickham River potential dam site to ascertain what development, if any, would be feasibly fed from that site. Given the small yield, and the distance to potential serviced lands, a targeted development of less than 4000 ha will be likely. 3.1 Identification of potential lands for development Lands potentially suited for development serviced from the Leichhardt Creek potential dam site were selected on the following bases: •The area is relatively close to the river course below the dam. A feature of the river networkbelow the dam site is a multi-branched channel with multiple flood runners. The areas betweenthe major channels were avoided as being too flood prone. •The soils involved are uniform in their soil generic group (SGG) classification (see Thomas et al., 2024). In some cases, the complexity meant that two SGG classifications were involved, andareas of highly complex distributions were excluded. Preference was given in the evaluation tothe more uniform soil types within a particular area to aid irrigation management. •Soils are suitable for a range of crop options. The most likely appear to be either cucurbits underdry-season trickle irrigation, or cotton or grains under dry-season spray irrigation. •Topography is not complicated; for example, it lacks features such as prior streams or overbankflow paths. The four areas identified for further study are shown in Figure 3-1. Details of the selected areas, and their advantages and disadvantages, are presented in Table 3-1. Figure 3-1 Potential development areas for the Leichhardt Creek potential dam site Development areas are overlaid on levels of suitability for dry-season spray-irrigated cotton or grains and Google imagery. Table 3-1 Details and comparison of potential development areas below the Leichhardt Creek potential dam site For more information on this table please contact CSIRO on enquiries@csiro.au †SGG = soil generic group. For more information on this figure please contact CSIRO on enquiries@csiro.au For more information on this table please contact CSIRO on enquiries@csiro.au 3.2 Selection of area for development Table 3-1 shows that each identified area has significant limitations. However, since there are no alternative areas closer to the dam site, and since other more uniform areas will be even further downstream from the dam, an assessment was required to compare the limitations of the four areas. The following comments, while subjective, can be made: •Area 1 has limitations that probably rule it out from contention. It is too small to fully utilise thepotential yield, has diverse soil types, and has prior streams that make it too flood prone fordevelopment. •Area 3 is too far from the dam site and has flood runners that will be difficult to divert around inany large-scale irrigation development. It is also probably ruled out for those reasons. •Area 4, despite being the most uniform area, also suffers from being a long way downstream. Ithas the best crop flexibility of the four areas. One advantage it has over the other areas is thatthe soils are all suitable for ringtank construction. A mechanism whereby releases are passeddown the river in substantial slug flows and picked up and stored on-site in an offstream storagefor gradual release to irrigation demand is possible. This would reduce the challenges posed bythe distance from the Leichhardt Creek potential dam site. The practicality of this option isdiscussed below. •Area 2 seems the most attractive at first: it is almost large enough and has the best suitability(most Class 2 soils) of the four areas. However, the need for a 10 km rising main will be a seriouslimitation to the development of this area. At 50.5 km downstream, it has only a very marginaladvantage over Area 4 at 66 km. Furthermore, it has no area suitable for ringtank constructionto mitigate that distribution distance. Considering all the above points, Area 4 was the one targeted for derivation of a development option. 3.3 Operation of potential scheme Area 4 is far from ideal for development because of the long distance from the potential storage at the Leichhardt Creek potential dam site to the likely re-regulation point and re-lift from the river. Additionally, the upper 40 km of that river channel was predicted to be SGG 4.1 (the red loamy soils), which would result in significant accessions from the bed to underlying strata. Three different approaches could address these issues: •Release down the river to a re-regulation point that will be of sufficient capacity to handle any ‘rain rejection’ inflows. This refers to potential losses that can occur if significant rain falls in the irrigated area when an irrigation release is underway, cancelling the need for irrigation that cycle. If the water on its way down the river is not stored somewhere then it is lost downriver, adding to system losses. A normal allowance would be to make the river storage equal to at least twice the design release rate by the likely transit time. In this case, where the transit time is likely to be of the order of 2 days, the operating volume required will be some 1200 ML. With a bed slope of about 0.045%, this will be very difficult to achieve, given the friable banks noted above and the consequent need to limit afflux for any instream structure. Instream storages above about 400 ML will be difficult and expensive. •Release down the river to a smaller re-regulation storage but with the ability to re-pump to an offstream storage that would form a buffer between the releases from the dam and the actual irrigation demand. This can easily and cost effectively be a much larger storage than would be possible in the river. Indeed, the area immediately next to the river lends itself to a storage of some 5000 ML. In this option, the river pumps have only to be sized to the maximum irrigation demand, and the re-regulation weir can be sized only to provide the required pump submergence. •The final variation is to have the release in higher slugs, rather to the maximum irrigation demand, in the hope that this will reduce the transmission losses from the dam to the re-regulation re-pumping. However, a couple of factors make this approach difficult. First, the river channel capacity is very limited before it braids significantly, limiting the amount of any slug flow. Second, there is no real evidence that higher slugs will significantly reduce transmission losses. In fact, some factors, such as the need for wetting flows, and the likely higher losses at higher stages indicate that this may be counterproductive. Finally, as noted in the first option above, there will be real limits to the height of any practical re-regulation weir, so achieving pump submergence will be more difficult for the larger extraction flows necessary for this option. Considering the above, the second approach was chosen for further development: release down the river to a smaller re-regulation storage but with the ability to re-pump to an offstream storage. 3.4 Elements of potential scheme General details of the major elements of the scheme and further details of the sizing of some of those elements are provided below: •Re-regulation weir. This is at a point where the banks are high from some remnant hills on thenorthern side and a localised high point on the southern side. The practical limit of any storage will be limited by the friable nature of the banks, however, and it is assumed that any attempt to construct a weir greater than 1 m operating height will be problematic due to the amount of protection required downstream. A sheet piling structure or a low concrete slab structure, with significant rock mattress protection to the abutments and downstream, will be required. No specific allowance will be made for releases due to the small nature of the storage. An effective height of only 0.75 m is assumed. •Pump site. This is chosen as an apparently stable section of river bank close to both the re-regulation point and the offstream storage. The pump station would feature bank-mounted axial-flow pump units at 30 degrees with control equipment located on an elevated platform out of flood reach on the upper river bank. •Offstream storage. This is sized at 4000 ML, which provides a working range of at least one irrigation watering for the potential irrigation area, and sited immediately adjacent to the river to minimise works from the river to the storage. The storage will be constructed from banks formed from material won from within the storage area, taken from strata that do not affect the low permeability of these cracking clay soils. The banks will require water and compaction during construction, not just cross dozing as commonly used for smaller storages. The inner batters will need to be flat enough to handle the relatively rapid filling and emptying of the storage. Ratios of 1 vertical: 3 horizontal internal and 1:2 external will be used for the preliminary costing. •Final targeted area. The area immediately downslope of the above offstream storage is targeted for development, but with a few modifications to the gross area identified in Figure 3-1. The area is reduced to be parallel sided in the north–south direction to facilitate a furrow-irrigated layout. The total targeted area is reduced to about 3900 ha to allow for the likely limit of serviced area taking into account the available water, net of transmission, distribution and irrigation losses. •Main distribution channel. The mechanism for delivery of irrigation water from the offstream storage to the individual paddocks is a main distribution open channel down the middle of the serviced area. Regardless of whether the irrigation is by furrow or spray, this is a sensible method of distribution as the grade downslope is 0.08%, making distribution by pipeline uneconomic. This, of course, could be changed by re-pumping at the storage, but that solution is unlikely to be adopted early in the development. Main channel distribution by open channel, and then lateral distribution by either open channels cross slope or pipelines, depending on the final method of irrigation, will be the mechanism detailed below. In summary, the scheme described below features releases downriver to a pump station near the top of the area that is fed by a small re-regulation structure in the river. The pumps deliver water to a balancing storage on the left bank of the river with releases to a main channel down the middle of the area. Distribution from the main channel will depend on the crop type and irrigation method chosen and will not be detailed for this analysis. Details of those costs will be included with the land development component. 3.5 Area irrigated This site is of modest size and suffers from the long downriver release path, which leads to high losses. Using similar criteria to those developed for the Leichhardt Creek potential dam site, it has the potential to serve up to 4000 ha, depending on the distribution and irrigation method chosen, assuming: •Dam yield at 85% annual reliability is 60 GL/year. •Crop demand assuming dry-season field crops is 8 ML/ha. •Irrigation efficiency for spray application is 85%. •Irrigation efficiency for trickle application is 90%. •Irrigation efficiency for furrow irrigation is 80%. •Distribution efficiency for open-channel distribution is 90%. •Distribution efficiency for piped reticulation is 98%. •River reticulation efficiency is 70%. •Net area irrigated is 95% of gross area. Targeted gross areas are therefore between 3780 ha (open channel and furrow) and 4252 ha (piped and spray). The layout of the above infrastructure, plus the land parcels assumed for the flow calculations are shown in Figure 3-2. Figure 3-2 Adopted layout for furrow irrigation to Area 4 for the Leichhardt Creek potential dam site Layout is overlaid on SGG predictions. Individual fields and reach points on the reticulation are labelled for flow calculation purposes. Re-regulation, pump site and offstream storage sites shown. For more information on this figure please contact CSIRO on enquiries@csiro.au 3.6Design capacities Flow-ratesforthereticulationpipelineswerebased on thefollowingcalculation. Dailycropdemandwasbasedon 𝐸𝐸𝑡𝑡=𝑝𝑝×𝑓𝑓1×0.8×𝐸𝐸0(2) where: •pisclimatefactor,assumedas0.7 •f1iscrop factor, assumedas 1.0 •E0isassumedat11.825mm/day,basedonSILOvaluesfor Rosewood Station(P99of 4-day meanE0).Rosewood Station issome85kmwest-southwest of theservicedareaand gaveslightlyhighervaluesthanthoseused in Section 2.3for Victoria River Downs. Etistherefore6.62mm/day. Irrigationdemandis8.28mmperdayperhectare,assumingfurrowirrigation. Nodiversityfactor wasapplied,asthetotal areaissmall andsoil typesarereasonablyuniform. Theadopted flow-rates areas showninTable3-2. Table3-2Channelflow-ratedetermination CHANNELREACHLENGTH(M) CUMULATIVECHAINAGE(M) INCREMENTALAREASERVICED(HA) CUMULATIVEGROSS AREASERVICED(HA) NETCUMULATIVEAREASERVICED(HA) DESIGN FLOWRATE(M3/S) MainlineA–B 2395 2395 0 4230 4019 3.9 B–C 2003 4398 937 For more information on this table please contact CSIRO on enquiries@csiro.au 3128 3.0 C–D2270 6668 1043 2250 2138 2.0 D–E2016 8684 920 1330 1264 1.2 Theadopted gradelinefromtheearthworkrunsforthemainchannel isshown inFigure3-3. Area 4 Main ChannelProfile 02000400060008000Chainage (m) Main channel natural surfaceReach pointsDesignflowlevelBed ABCDE354555Elevation(m) Figure3-3Adopted gradeline for the Leichhardt Creekpotential dam siteArea4 main channel Reachpointsrefertothe locationsshowninFigure3-2. 24|Hypothetical irrigationdevelopments In the derivation of the earthworks required for the above channel profiles: •The profile, consisting of deep cracking clay soils, is assumed to be suitable for bank constructionwithout modification or lining of the cut profile following over-excavation. •Minimums have been assumed for water depth (for reasons of weed control) and bed width (toallow practical construction by scraper). In some cases, the actual capacity is above thenominated capacity due to the above minimums. •Design flow levels are adjusted so there is no net borrow requirement within each of the abovereaches. Some minor additional excavation will be necessary to ensure longitudinal drainage onthe high side of the channel (particularly in reach A–B), but this will be costed separately to themain channel profile. Adopted parameters are shown in Table 3-3. Table 3-3 Adopted main channel parameters For more information on this table please contact CSIRO on enquiries@csiro.au 3.7 The Leichhardt Creek potential dam site channel reticulation costing A number of assumptions and choices were made for the costings detailed in Table 3-4, of which the more important are: •At each drop in design flow level noted above (Figure 3-3), a control structure is located on theupstream side of an access crossing. A conventional outlet structure is used on the outlet side. This arrangement achieves both flow control and cross-channel access at the same location. Rubicon FlumeGates will be assumed to be the flow control device. •The storage is designed as a single water body. This is probably realistic, but a more cautiousdesign would include a wave break barrier in the middle to limit wind-induced wave fetch. •No specific allowance is made for borrow, which reflects the basis of selection of design flowlevels noted above. •A separate allowance will be made for any necessary longitudinal catch drainage excavation andbanks, particularly for Reach A–B. Note that the costs used for this estimate were those appropriate for a corporate-scale irrigation project. This total development, at approximately 4000 ha, is not beyond the scope of a single farming entity. In that case, the design reliability of the supply and the standard of the works might both be less than presented here. This represents an internalising of risk not possible or practical for a larger scale corporate development. In a single enterprise case, it is expected that these costs may overestimate the expenditure required. The total capital cost represents a development cost of some $3350 per irrigated hectare for furrow irrigation for the backbone infrastructure only. As outlined above, the total cost to move the water to the paddock will also include distribution from the main channel to the paddock, depending on the type of irrigation adopted. Table 3-4 Leichhardt Creek potential dam site reticulation costing For more information on this table please contact CSIRO on enquiries@csiro.au †Refers to the channel control system – supervisory control and data acquisition. 4 Water-harvesting options along West Baines River This section examines the potential for flood harvesting, but only in the areas examined above for service from the two dam sites being investigated in the catchment of the Victoria River. Leichhardt Creek potential dam site can effectively be discounted, as the area serviceable from the dam is small and that able to be serviced from a water-harvesting operation would be even smaller. This leaves the areas targeted downstream from the Wickham River potential dam site. 4.1 Evaluation of water-harvesting options Examining the potential to service the areas identified in Figure 2-1 gave the two water-harvesting options outlined in Table 4-1. Table 4-1 Evaluation of water-harvesting options 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 The following conclusions can be drawn: •A water-harvesting operation, based on a minor instream storage to provide a suitable pumpingpool, at the lower alternative site, with major offstream storage complexes on both sides of theriver is the more practical option. Based on rough rules of thumb, full development of theseareas is likely to involve about 3 km2 of storage cells on the north bank and 9 km2 on thesouthern side. •Scale 2 is discounted due to the lack of sites for storage construction. •Water-harvesting options are likely to cost less than the dam and reticulation options canvassedabove and may be more likely to achieve regulatory approval, given the lower impact on theriver environment. As a result, Scale 1 water harvesting was examined further below. 4.2 Details of water-harvesting operation While the nominated water-harvesting (Scale 1) scheme is described in Table 4-1, this discussion of major elements is based on the following assumptions: •Development of the full Scale 1 area will be problematic due to the conflict with infrastructurearound Victoria River Downs, so this discussion refers to the development of the area to thesouth of the river only. This is essentially Area C in Figure 2-1. •The pumping pool will be formed by a low weir constructed at the natural rocky constrictionsome 4 km below the Victoria River Downs homestead. Weir height is based on the requiredpump submergence discussed below. •The pump submergence required will assume bank-mounted inclined 24-inch flood lifters, arranged as a bank of pumps on the southern bank. Pumps will be uncontrolled, and flow will bedetermined by the number of pumps started. While larger diameter flood-lifter pumps areavailable, they would require greater submergence, which would be difficult in this river. Twenty-four-inch pumps are commonly used for larger water-harvesting operations. Assuming a 30-degreeinstallation,minimumsubmergencerequirementswill bearound1.5m,withafurther0.3mbelow thepumps.Thisgives1.8mtotal.Othertypesof pumpssuchassubmersiblemixed-flow volutetypeswould betheoreticallypossiblebut arenot favouredastheywouldrequireevengreatersubmergence.Based on an assumedexistingwaterholedepthat thissiteof1m,a small weirwilllikelyberequiredatthissite,dependingonthelikelystartingflowrequirementsfor water-harvestingdiversions.To keepcostestimatesconservative,thesameweir costsasdevelopedfor thedam-based developmentsat thissitewillbeassumed(Table2-5). •Pumpssites: –must beon theexistingVictoria RiverDownslagoon(tominimisetheheight of weir) –must beinarelativelystablesectionofbank –must beinproximitytoanareaofcrackingclaysoilsforstorageconstruction –ifpossible,mustbeinproximitytoanareaofclaysoilsfor constructionofa lead-inchannel tothestorages.Notethisisa secondorder requirement,asclaymaterialcouldbeimportedforthispurpose. •Storagesarebasedon: –an effectivewaterdepth of up to7mwithafurther1mof freeboard.Thisavoidsthemandatoryfailureimpact assessmentandreferabledamprocesses.Itisalsothecommonlimitforstoragesconstructed without fullyengineered embankments.Material for thebankswillbesourcedfrom borrowareaswithinthestoragearea andsobecomepartofthestoredvolume.Notethatthisrepresentstheupperlimit of storagedepth,ascellcost increasesrapidlywithoverall depth,andsmaller developmentswillfavour lowerheightcells –amaximum fetchof1.5km,tolimitwave-inducederosiondamage.Thiswill alsotieinwiththeaim ofproducinga matrixofstoragesto minimise evaporativelossesbypumpingtoasmallernumber ofstoragesasavailablesupplydecreases.For thesereasons,thestorageswillbeassumedtobecellsof up to1.2by1.2kmand 7meffectivestorage.Thecapacity ofeachstoragecellwill beuptoabout9900ML. •TheamountofstoragenecessarytofullydevelopAreaCwilldepend heavilyon arangeoffactorssuch asthearealost tostoragecells,thetimingand duration of flood flows,and thecroptiming,whichwill determineevaporativelosses.Asaninitial indicativeestimate,upto60,000MLof grossstoragewouldappeartobetheupperlimit of viablestorageat thissite.Thisimpliesatleastsixcellsofstorage,whichwill beconfirmedbystreamflowanalysisoncethemajor elementsaresited.However,thefullarea will includesubstantialareasthat canonly beeffectivelyirrigatedbyspraytechniques.An initialdevelopmentwould undoubtedlyfocusonthecrackingclayareasabletobefloodirrigated,tolimittotal expenditure.Thiswill beasubstantiallysmallerenterprise. •Storageswillbesited entirelywithin thecrackingclaySGG9unit,limitingthepotential sites.Anotionalareaof2.5 by3.7kmwillberequired forthefulldevelopment. •Given theneed tolimitthelength of theinletchanneland keepthestoragesnearthepump site, thesitechosen forinvestigationistheoneshowninFigure4-1. Chapter4 Water-harvestingoptions alongWestBaines River|29 Figure 4-1 Notional water-harvesting layout for full development of Area C Development area is overlaid on SGG predictions and Google imagery. The boundaries of areas C and F as per Figure 2-1 are also shown. 4.3 Major elements of the notional water-harvesting scheme While it is noted that full development of Area C under a water-harvesting scheme is unlikely due to the total cost, the major elements of such a scheme are briefly described to highlight the salient differences to a more likely scheme that focuses on the cracking clay areas. Major elements of the total development scheme for Area C are: •a pump pool weir on the Wickham River, noted as ‘Pumping weir’ on Figure 4-1 •a pump station complex of axial-flow flood-lifter-type pumps located on the river bank at thelocation, noted as ‘Pump station’ on Figure 4-1 •an inlet channel some 1.1 km in length that leads to storage cell 1. The channel is assumed to bean earth channel formed from local borrow. It will have a design flow level at the storage ofEL 92 m (elevation), equivalent to 1.0 to 3 m above natural surface •a low-head pump station at the end of the inlet channel to lift the water to the storage at higherelevations •a system of up to six storage cells, arranged as shown in Figure 4-1. The full supply levels of thecells will decrease west to east for the six-cell case For more information on this figure please contact CSIRO on enquiries@csiro.au •asystem ofaxial-flow box-mounted pumpstoallow both interconnectionofthecellsandtransfer fromanyonecell toanadjacentcell.Thesearelocated at thepointslabelled Aand BonFigure4-1 •asystemof channelsorpipelinestoconveythestored watertoindividualirrigation paddocks. Thiswilldependon thecropandirrigationtechniquechosen,butgeneral commentscanbemadeon thisaspect.Themajorityofthesuitablearea iscrackingclaysoils(classifiedSGG9,seeThomasetal.,2024a),whicharepotentiallysuited tofurrow irrigation dependingonthecrop. However,notallareasofSGG9totheeast of thepotentialstoragecellsarerated suitableforfurrowirrigation,duetoslope.Thiscould beremediedbyextensivelandlevelling.AlikelyarrangementisthattheareasofSGG9tothewest of thestoragecellswould bedesignedforfurrowirrigation,aswouldoneblocktotheeastof thestoragecells.Thebalanceoftheservicedarea,consistingofredloamysoils,gradingtofriablenon-crackingclays, or clayloams,gradingtocrackingclays, willbebest irrigatedbysprayand would beserved byapipelinesystem •the existingdrainagefeaturetothesouth ofthearea. Thiswillbeutilisedasthedrainagemechanismforthetotal area. Itlendsitselftoa tailwater returnsystem dischargingbacktothestorages. A total grossareaofsome4460ha was identified in thelayout inFigure4-2,beingabout 40% furrow and60% spray.Somearea waslostduetoirregular shapes,soaneffectivegrossareaof4200hawasassumed.Forthepurposesofthisfeasibilitydesign,thiswasdivided into1700ha furrow and2500ha spray. Thesupplysystemtomoveirrigationwater fromthestoragestothefieldisonlydetailedasfar asthemaininfrastructure,asfortheWickhamRiverpotential dam siteandthe LeichhardtCreekpotential dam sitedevelopmentsoutlined in sections2and3,respectively.Channeland pipelinealignmentsareshowninFigure4-2. Chapter4 Water-harvestingoptions alongWestBaines River|31 Figure 4-2 Flood-harvesting channel and pipeline layout Furrow area shown in light green shading, spray area in light blue shading. Channel alignments shown in purple, and pipelines in red. 4.4 Likely scope of development – furrow-irrigated water-harvesting- based scheme As outlined above, a development focusing on furrow irrigation of lands in reasonable proximity to the storage cells is more likely to be economically attractive than one focusing on developing all of Area C. Assumed details of a furrow-irrigated water-harvesting-based scheme are as follows: •Total gross area serviced as shown in Figure 4-3 is 2181 ha, but this is assumed to be 2000 ha forthe purposes of determining channel capacities due to irregular shapes. •Gross water demand allowing for storage purposes to irrigate this serviced area can be assumedto be 21,000 ML out of the storages, based on: –crop demand of 8 ML/ha –furrow irrigation efficiencies of 80% –channel efficiencies of 95%. •Four storage cells will have a notional capacity of 27,400 ML at 5 m depth to allow forevaporation and seepage. Note that this is a notional allowance, as the relative timing of thepumping window, and subsequent irrigation demand, along with soil and climate data willrequire a full hydrological simulation in later stages of design. For more information on this figure please contact CSIRO on enquiries@csiro.au •Pump capacity at the river will be based on full demand over 50 days, which gives 6.5 m3/second against an assumed static lift of 9 m during flow conditions. Pumps will be assumed to be axial-flow flood lifters, installed on the river bank. •The intake channel will be at the same level and freeboard as the west end storage cells. This is possible in this instance as the cells are lower than that assumed for the full development case. A control structure at the downstream end will allow distribution to, and isolation from, the storages cells. •The capacities of the channels, calculated using the method outlined in Section 2.3, are as follows: –channel B–C is 0.9 m3/second–channel C–D is 0.1 m3/second–channel E–F is 0.9 m3/second. The assumed layout for the furrow-irrigated development as described is given in Figure 4-3. Figure 4-3 Layout for furrow irrigation development Serviced area shown in light pink. Main channels shown as purple dashed lines. For more information on this figure please contact CSIRO on enquiries@csiro.au 4.5 Water-harvesting cost estimation Final details of any design will be heavily dependent on the crop type and irrigation method. However, to allow some meaningful comparison with the dam-fed irrigation layouts derived for this area in Section 2, cost estimates (Table 4-2) were prepared on the basis of the following assumptions: •The area of soils targeted for development is the SGG 9 unit, and channels were only defined for costing to the extent of primary infrastructure as defined in Section 4.4. This is to keep assumptions in line with those used in sections 2 and 3. Other distribution to individual fields will be required, but these will be assessed under the ‘farm development cost’ category. •Water-harvesting developments by their nature are more likely to be sole-enterprise developments, which can tolerate a lower standard of design than is possible in larger dam-based irrigation developments. This has a consequence for the method of construction of the major storage cells, which are mostly constructed by cross dozing from borrow from within the ponded area near the alignment. For lower storage levels, this is invariably associated with dozer-only compaction. For the levels assumed in this case, side dozing and compaction by vibratory compactor will be assumed. This is still a much cheaper method of construction than that of conventional channels, which entail excavation and hauling with pushed scrapers, and moisture conditioning, compacting and trimming with water trucks, compactors and graders. The cheaper construction results in a greater potential failure rate for the storages, but the higher maintenance is accepted as a necessary trade-off for the lower capital cost. •The arrangement shown in Figure 4-3 will feature a second pump at location A. This will be a box-mounted column-less axial-flow diaphragm pump that will allow gravity diversion between all cells and pumped diversions from either eastern cell back to either western cell. It will also allow pumping between the two western cells. In this way, water held at the end of the growing period can be moved progressively to a smaller number of cells to limit evaporative losses. •All pumping will be diesel powered. 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 PartIIISouthernGulfcatchments - 5 Potential dam site on Gunpowder Creek AMTD 66 km The Gunpowder Creek potential dam site has an annual water yield of approximately 129 GL at 85% annual reliability. On this basis, and taking into account transmission losses and other factors, the serviced area will be around 10,000 ha (depending on crop type and method of distribution). The site is further limited by the fact that the first 15 km downstream of the dam is much incised, with typical side gradients above likely flood levels of above 1 in 3. This effectively rules out distribution by open-channel or flume systems, and pipelines would be very expensive in that terrain. Tunnelling would be possible but at even greater expense. The inescapable conclusion is that distribution via river releases to a downstream re-regulation and pumping point is the only practical alternative. Both sites identified in Figure 5-1 are on the downstream end of significant existing waterholes where pump submergence could be achieved with a very modest weir height at the natural restriction. Alternative 2 has the additional advantage that there is only one active watercourse at this point, while Alternative 1 has a high-level flood runner to the immediate south. It is notable that Alternative 2 is presently used for a station track crossing. For more information on this figure please contact CSIRO on enquiries@csiro.au Figure 5-1 The Gunpowder Creek potential dam site and potential diversion locations Taking into account the likely location of a downstream re-regulation and pumping point, the area examined below was limited to that potentially serviced by releases to Gunpowder Creek down to the junction with the Leichhardt River. Three major areas of potentially suitable soils, identified as A, B and C in Figure 5-2 and the discussion below, met the criterion outlined above. The three potential serviced areas are compared in Table 5-1. For more information on this figure please contact CSIRO on enquiries@csiro.au Figure 5-2 Potential development areas for Dam site 28 Development areas are overlaid on levels of suitability for dry-season spray-irrigated cotton or grains. Table 5-1 Evaluation of alternative development areas for potential Dam site 28 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 Note that other areas of large aggregations of cracking clay were present both immediately upstream of the Gunpowder Creek – Leichhardt River junction and on the east side of the Leichhardt River alignment. These were not pursued for a number of reasons. The former would require very significant pumping from the river up to the suitable lands. The latter would involve a much more expensive re-regulating structure since it would be in the main Leichhardt River channel. It would also be subject to more losses, being much further downstream. Note, however, that there may be more available yield in this location due to the dam yield being used in conjunction with the natural flow in the Leichhardt River. Given the aim of the study, the upstream areas were favoured. Area B was chosen for further investigation because of the advantages outlined above. It is more than capable of meeting the scope of development supported by the potential dam. 5.1 Re-regulation weir for Gunpowder Creek potential dam site With Area B as the target development area, Alternative 2 in Figure 5-1 was the chosen diversion point. This is still approximately 5 km upstream of the start of the serviced area, but no more favourable sites exist downstream of this diversion point. An indication of the type of structure required is outlined below: •Due to the site being only 35 km below the dam, and the creek section being relatively steep at1:1000, the operational range of the re-regulation storage can be assumed to be modest (0.3 m). •The imagery indicates that existing water depth is at least 1 m with the north abutment about1.5 m high and the south side only 1 m high. If these depths can be assumed as indicative, andassuming that the pumping is only very low head and likely to involve axial-flow pumps, thesubmergence requirements will be modest, and a total water depth of 1.5 m will be adequate. This assumes either angled bank-mounted axial-flow pump units incorporating screening, orvertically mounted axial-flow pumps in a chamber in the bank, with screening on the inlet. Thisimplies a total weir height of about 0.8 m, which should be achievable within the assumedsection with acceptable afflux during flood flow conditions. 5.2 Irrigation layout A number of assumptions and choices were made for the purposes of this study. Piped reticulation from the re-regulation weir pump station was assumed for the following reasons: •The country slope of 1:1000 and steeper will make piped reticulation possible. •The potential for outflows from the main creek line during flood events will require substantialcross-drainage capacity for a channel network. This significant cost involving cross drains orinverted siphons will be avoided for below-ground pipelines. •The likely application methods of spray or trickle will be more amenable to pipe networks than achannel network. This will alleviate the need for tailwater return systems and buffer storages tocater for rain rejection events, which would be a necessary feature of open-channel systems. This site has the potential to serve up to 11,200 ha, assuming: •Dam yield at 85% annual reliability is 119 GL/year. •Crop demand assuming dry-season field crops or perennial trees under spray is 8 ML/ha. •Irrigation efficiency for spray application is 85%. •Irrigation efficiency for trickle application is 90%. •Distribution efficiency for piped reticulation is 98%. •River reticulation efficiency is 85%. •Net area irrigated is 95% of gross area. Targeted gross areas are therefore between 10,500 ha and 11,200 ha, depending on crop type, irrigation method and reticulation arrangement. The total area of Area B is many times the targeted area outlined above. The area selected for notional design was arrived at by: •removing the area of the gully system referred to in Table 4-1 •including enough area to exceed the upper limit of 11,200. The reduced Area B, as shown in Figure 5-3, has a gross area of some 11,700 ha. For more information on this figure please contact CSIRO on enquiries@csiro.au Figure 5-3 Targeted development area (reduced Area B) and pipeline infrastructure for potential Dam site 28 Development area is overlaid on levels of suitability for dry-season spray-irrigated cotton or grains. The notional layout of the pipeline infrastructure (Figure 5-3) was derived on the following basis: •The mainline is positioned so that supply to travelling irrigators or centre pivots will be possibleto both sides of the alignment, with a maximum diameter of the irrigation span of approximately2.5 km. •A lateral is positioned to the east of the above mainline to meet the 2.5 km maximum diameterof the irrigation span criterion. •Both the mainline and lateral channels are orientated primarily downslope to minimise pipediameter. 5.3 Piped reticulation design Flow-rates for the reticulation pipelines were based on the following calculation. Daily crop demand was based on 𝐸𝐸𝑡𝑡 =𝑝𝑝×𝑓𝑓1 ×0.8 × 𝐸𝐸0 (3) where: •p is climate factor, assumed as 0.7 •f1 is crop factor, assumed as 1.0 •E0 is assumed at 12.3 mm/day, based on SILO values for Kamilaroi (P99 of 4-day mean E0). Kamilaroi Station, some 20 km south-east of the serviced area, is the closest site with climatedata. Other more distant meteorological stations in the vicinity gave similar results. Et is therefore 6.89 mm/day. Irrigation demand is 8.1 mm per day per hectare, assuming spray irrigation. No diversity factor was applied, as the total area is small and soil types reasonably uniform. Flow-rate at the head of the system is therefore 10.5 m3/second, with flow decreasing progressively downstream as areas are serviced (Table 5-2). The areas serviced above, assuming 95% utilisation of the gross area, are described in Table 5-2 using the nomenclature of the points in Figure 5-3. For the purposes of this feasibility design, the flow-rate changes were assumed to occur at the mid-point of the area serviced. It can be assumed that any final design will have a more graduated change of flow-rate, but the overall impact will be small. Table 5-2 Adopted flow-rates for piped reticulation For more information on this table please contact CSIRO on enquiries@csiro.au A couple of other assumptions were made prior to the pipeline selection for this area, including: •In this instance, a full gravity pipeline is not possible, and some re-lift must be provided at thepoint of re-regulation. While the re-lift level is optimised to minimise life cycle cost, theminimum re-lift head options are favoured to avoid high pipeline pressures and consequenttransient pressure issues on power failure. •For this exercise, only single re-lift solutions are examined. This is a relatively simple layout, andmultiple re-lift pumps are unlikely to be cost effective. However, the fact that re-pumping forfiltering and/or re-pressurisation for travelling irrigators may be required means that thisconclusion will need to be re-examined in the later stages of the design. 5.4 Pipe system type Two main types of pipeline were considered for this project: high-density polyethylene (HDPE) and glass-reinforced plastic (GRP). While both are considered flexible pipelines for installation purposes under the relevant Australian Standard (AS/NZS 2566), they are quite different in characteristics, as described below. Hence, for some applications one will be more suited than the other. HDPE pipe •HDPE pipe is extruded as a solid wall product from a feedstock normally consisting of pellets orreconstituted polyethylene. All pipe made in Australia currently is formed from PE100 material. This rating relates to the material strength of the pipe and is reflected in the design SDR(standard dimension ratio). A low-pressure pipe such as PN4 (40 m working pressureapproximately) is SDR41, meaning the pipe diameter is 41 times the wall thickness. •Pressure ratings up to PN10 are available for HDPE pipe in the larger diameters required forirrigation projects. However, this pipe (SDR17) is very expensive due to its heavy wall thickness. Supply price for HDPE is closely correlated with the amount of material in the pipe. •Diameters up to DN900 readily available. •Installation to the standard required by AS/NZS 2566 is important for any flexible pipeline, butHDPE is more forgiving than the equivalent GRP product. In higher SDR ratings, it is anextremely flexible product, so correct backfill of bedding and haunch material is crucial toensuring the required limits to deflected shape are achieved to avoid buckling under load. •The product is delivered in individual lengths (12 to 20 m) for larger diameters (smallerdiameters typically come rolled) and is jointed by a hot-fusion welding process either prior toinstallation in the trench or after installation by ‘belling’ the excavation at the joint. Largerdiameter, higher pressure lines are typically installed by ‘belling’, as the pipe flexibility becomesthe limiting factor. GRP pipe •GRP pipe is manufactured by winding glass filaments, resin and sand filler on a spinningmandrel. •Has greater diameters and pressure capability than HDPE. Theoretically available up to DN4000and PN16. Diameters up to DN1700 are available up to PN32. •The product is normally supplied in 12 m nominal lengths. •They are rubber ring jointed in a GRP coupling that is pre-installed on one end of the pipe. •Routinely supplied as two stiffness ratings: SN5,000 and SN10,000. Both ratings are stiffer thanthe equivalent-pressure HDPE pipe, but they are still classified as flexible pipe and installed toAS/NZS 2566. •Equivalent pressure ratings are thinner and lighter than the HDPE pipe. •Bedding is critical to avoid leakage at joint collars, and particular care is required to bed andhaunch. The comparison indicates that GRP will have significant advantages over HDPE for larger flows to be carried by pipelines. The changeover point at which the installation ease of HDPE overcomes the size range and cost competitiveness of GRP will depend on specific site circumstances, but for the purposes of a preliminary design, it will be safe to assume that for sizes above 675 mm diameter, GRP will be cost effective. 5.5 System pipe sizing Pipelines were designed and pipe sizes selected for the network to meet a number of criteria: •The gradeline was selected to produce a hydraulic gradeline (HGL) with sufficient positive headto help avoid negative pressure surges during abrupt flow changes. In effect, the velocitylimitation noted below dominated in most cases, and the HGL selected was the maximumpossible without affecting maximum velocity. •Low-lift pumps were favoured to suit axial-flow pumps whose power demand is practical fordiesel power. Higher lift pumps were able to reduce the life cycle cost of the installation, butthey involve a power demand likely to be beyond the practical limits of readily available dieselpower packs. Low-lift pumps are also more practical in this instance due to the limitedsubmergence available in the pumping pool. •Pipeline velocity at full flow is limited to below 3 m/second to help moderate transient pressureson pump power failure or abrupt changes of demand. •Pipelines are designed to produce a minimum of 2 m residual head at the take-off point. This isconservative, as there will be some re-pumping at this point for travelling irrigators or filteringfor trickle irrigation, but it ensures that there is some flexibility in the location of the re- pumping. •In general, GRP pipelines are favoured for this project because they represent the minimum costsolution for the pressures and flow-rates involved. It is possible that HDPE lines could be used insome cases of relatively smaller flow-rates, but installed costs are estimated to be higher for allthese cases. Thus, GRP pipes are selected for use throughout the project, mainly driven by thelarge diameters required. An effective roughness of k = 0.06 mm is assumed, representing anachievable long-term value. Head loss is calculated using the Colebrook–White equation. The results of this pipe size analysis are shown in Table 5-3. Table 5-3 Adopted pipe requirements Line nomenclature follows Figure 5-3. For more information on this table please contact CSIRO on enquiries@csiro.au 5.6 The Gunpowder Creek potential dam site reticulation costing Costing for the above works necessitated a number of assumptions and choices, of which the more important were: •Pipelines were costed at unit rates derived by Rider Levett Bucknall (2024), adjusted wherenecessary for actual sizes and pressure classes. A percentage allowance was made for normalpipeline appurtenances, such as air valves, scours, swabbing facilities, thrust blocks, specials andvalving. •The pump stations, as detailed above, are low-head structures, suited to axial-flow pumpsmounted on the batter of the river bank. For this exercise, Batescrew axial-flow pump models24/30 (or similar) were assumed. These pumps are mostly used for installations for floodharvesting, but are also quite suitable for this application. Six units were required for thisinstallation, and they are assumed to be diesel powered. Table 5-4 Cost summary for the Gunpowder Creek potential dam site reticulation For more information on this table please contact CSIRO on enquiries@csiro.au The cost calculated in Table 5-4 represents a development cost of some $27,200 per irrigated hectare of spray or trickle irrigation for the backbone infrastructure only. The total cost to move the water to the paddock will also include distribution from the main reticulation network to the individual irrigators required for the irrigated area. This estimated cost is expected to be greater than that feasible for a remote agricultural investment. The main driver for the high cost is the very high cost of large-diameter pipe, such as that detailed for use in this instance. Smaller diameter pipelines would normally be possible but are not used in this instance due to the velocity limits imposed on the design and the fact that high-lift pumps would require more submergence than is achievable in the small stream. The total cost raises the question as to whether an open-channel solution, even though extremely difficult, would be more cost effective in this instance. It is worthwhile revisiting the reasons and assumptions that led to the open-channel solution being discarded to gauge the difficulty in implementing that solution. These factors are discussed in Table 5-5, in which it is assumed that the same alignments would be used. Table 5-5 Factors against open-channel reticulation and potential strategies to negate For more information on this table please contact CSIRO on enquiries@csiro.au The conclusion from the above points is that an open-channel solution should be possible, and it may be possible at significantly less cost than the piped option detailed above. It will service a smaller area due to the reduced transmission efficiency, but at least it may be economically possible, which the piped design is probably not. 6 Potential dam site on Gregory River AMTD 174 km The Gregory River potential dam site was assessed at two full supply levels (FSL), 138 mEMG96 and 145 mEMG96. At a FSL 145 mEMG96, the reservoir would extend into the Boodjamulla National Park and would have an annual water yield of approximately 232 GL at 85% annual reliability. At a FSL of 138 mEMG96 the reservoir does not extend into the national park and the yield is 133 GL at 85% annual time reliability. Both yields take into consideration existing entitlement holders. See companion technical report on river model simulation in the Southern Gulf catchments (Gibbs et al., 2024). Two irrigation scheme conceptual arrangements and costings were prepared: the first, assuming the larger 232 GL yield, was fully examined and preliminary costings were prepared. The second, of 133 GL, was examined on the basis of the changes induced by the lower figure of water availability. The purpose of evaluating irrigation schemes at two different FSL was to understand how the cost of the scheme scales. With the 232 GL yield and taking into account transmission and other losses, the serviced area will be approximately 20,000 ha (depending on crop type and method of distribution). While there is negligible land suited to irrigated agriculture in the immediate vicinity of the dam, the situation changes dramatically some 26 km below the dam, where extensive areas of soils suitable for broad acre irrigation spread out from the river course, especially on the eastern bank. 6.1 Conceptual irrigation scheme arrangement for Gregory River potential dam with FSL 145 mEMG96 6.1.1 Selection of area for development The main factors influencing the selection of the preferred development area were as follows: •The east bank of the river offers more potential than the west side, so attention is focused onthis area. •It will be important not to interfere with the flooding pattern across this land, the definingfeature of which is a slope away from the river, and discrete major outflow points. Twoimportant outflow points in this area are Cartridge Creek to the south and Millar Creek to thenorth. The aim of the potential layout is to leave these waterways unaffected by thedevelopment. •The major roads, the Gregory Downs – Camooweal Road to the west and the WillsDevelopment Road through the middle of the serviced area, will be left intact on their currentalignments. •While the lands are potentially suited to both furrow and spray irrigation, the notional areaswill be selected on the basis of furrow irrigation. This method is the more restrictive in terms ofsuitability, and selecting it will preserve flexibility in development options. The extent of the area for development was derived assuming: •Dam yield at 85% annual reliability is 232 GL/year. •Crop demand assuming dry-season field crops is 8 ML/ha. •Irrigation efficiency for spray application is 85%. •Irrigation efficiency for furrow irrigation is 80%. •Distribution efficiency for open-channel distribution is 90%. •Distribution efficiency for piped reticulation is 98%. •River reticulation efficiency is 85%. •Net area irrigated is 95% of gross area. Targeted gross areas are therefore between 17,750 ha (open channel and furrow irrigation) and 20,500 ha (piped and spray irrigation). The area chosen for further investigation is shown in Figure 6-1. For more information on this figure please contact CSIRO on enquiries@csiro.au Figure 6-1 The Gregory River potential dam site and potential diversion and development areas Shaded area denotes areas targeted for development, serviced from the re-regulation point. The gross total size of the above areas is around the upper limit of the potential development at some 20,236 ha. Allowing for infrastructure losses, this should still yield some 19,200 ha potentially suited for development. 6.1.2 Method of supply The suitable areas for development commence some 35 km downstream of the dam site. This stretch of river is well confined, and the land immediately adjacent to the river becomes increasingly steep nearer to the dam site. Accordingly, it will prove uneconomic to convey water from the dam site to the suitable areas by open channel or bench flume. Rather, a solution involving releases to the river, with re-regulation at the point identified in Figure 6-1, above will be more viable. The re-regulation point is a natural bar in the river with a substantial 2.5 km long pool upstream. The depth of the pool suggests that a very modest piling weir, less than 2 m high, should provide an adequate pumping pool at this point. Reticulation from the re-lift pump point to the area serviced is by open channels constructed from the in-situ cracking clay soils. Two main alignments will be used. The first will follow the north bank of Cartridge Creek, essentially to the eastern extent of the serviced area. The second alignment will follow the Gregory Downs – Camooweal Road for about 20 km to a location south of Gregory Township, where it will cross the road and service the lands to the east. Notional alignments for the above channels are shown in Figure 6-2. Also shown are the parcel boundaries for the calculation of required flow-rates. For more information on this figure please contact CSIRO on enquiries@csiro.au Figure 6-2 Channel layout and serviced areas Channel layout shown as dotted green lines, with the individual areas and points used in the flow calculation. 6.1.3 Channel reticulation design Flow-rates for the main channels were based on the following calculation. Daily crop demand was based on 𝐸𝐸𝑡𝑡 =𝑝𝑝×𝑓𝑓1 ×0.8 × 𝐸𝐸0 (4) where: •p is climate factor, assumed as 0.7 •f1 is crop factor, assumed as 1.0 •E0 is assumed at 11.6 mm/day, based on SILO values for Augustus Downs (P99 of 4-day mean E0). Augustus Downs Station is the closest site with climate data, at some 66 km east of Gregory. Other more distant meteorological stations in the vicinity gave similar results. Et is therefore 6.5 mm/day. Irrigation demand is 8.7 mm per day per hectare, assuming furrow irrigation. No diversity factor was applied, as the total area is small and soil types are reasonably uniform. Flow-rate at the head of the system is therefore 18.9 m3/second, and flow decreases progressively downstream as areas are serviced (Table 6-1). The areas serviced above, assuming 95% utilisation of the gross area are described in Table 6-1 following the nomenclature of Figure 6-2. For the purposes of this feasibility design, the flow-rate change was assumed to occur at the mid-point of the area serviced. It can be assumed that any final design will have a more graduated change of flow-rate, but the overall impact will be small. However, significant drops in design flow level can be expected to correspond to the existing leg boundaries, as some of these correspond to road crossings and other features. So, as a compromise for this preliminary design, the drops were assumed to occur at the existing leg boundaries, but the capacities of the channels designed were weighted to cater for the more likely centre of demand described in Table 6-1. The adopted longitudinal profiles are shown for the main channel in Figure 6-3 and for the lateral channel in Figure 6-4. Table 6-1 Channel flow-rate determination 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 For more information on this figure please contact CSIRO on enquiries@csiro.au Figure 6-3 Adopted gradeline for Gregory River potential dam site main channel Reach points refer to the locations shown in Figure 6-2. For more information on this figure please contact CSIRO on enquiries@csiro.au Figure 6-4 Adopted gradeline for Gregory River potential dam site lateral channel Reach points refer to the locations shown in Figure 6-2. In the derivation of the earthworks required for the above channel profiles: •The profile, consisting of deep cracking clay soils, was assumed to be suitable for bankconstruction without modification or lining of the cut profile following over-excavation. •Freeboards were varied based on the depth of flow. •Design flow levels were adjusted so there was no or negligible borrow requirement within eachreach. •Any borrow required was assumed to be available within close reach of the channel alignment. This reflects the point that some limited longitudinal drainage will be required on the upslopeside of the channel. Adopted parameters are shown in Table 6-2 and Table 6-3. Table 6-2 Adopted main channel parameters For more information on this table please contact CSIRO on enquiries@csiro.au Table 6-3 Adopted lateral channel parameters For more information on this table please contact CSIRO on enquiries@csiro.au Note that sections of both the main channel and the lateral channel feature some very steep sections in which the zero-flow situation will involve dry sections of channel. This creates two issues: it can allow drying of the channel profile, and it may lead to bed erosion on flow start-up. While the extent to which this is a problem is a function of the characteristics of the soil used, it will be prudent to assume a mechanism is used to counter this issue. The normal method of dealing with this problem is to use fixed long-crest weir overflows, so that a series of pools is created in the zero-flow case, and there is minimal head loss in the full flow situation. This solution will be used here. 6.1.4 Channel reticulation costing A number of assumptions were made for the costings detailed in Table 6-4, of which the more important are: •At each drop in design flow level noted above, a control structure is located on the upstreamside of an access crossing. A conventional outlet structure is used on the outlet side. Thisarrangement achieves both flow control and cross-channel access at the same location. Rubicon FlumeGates were assumed to be the flow control device. For larger structures, pre-castconcrete deck units would be used to form the access crossing. •The long-crest weirs detailed above would be used to hold pool level in the long steep reaches. •Road crossings were assumed to be at regulator structures, but incorporated a wider roadcrossing downstream of the control structure regulators. •Regulator gates required (using Rubicon nomenclature) were as follows: –Site B road crossing – three of model FGB-1790-2186 –Site C – two of model FGB-1675-2186 –Site D – two of model FGB-1675-2186 –Site E – three of model FGB-1675-1804 –Site F – two of model FGB-1675-1804 –Site G road crossing – two of model FGB-1675-1587 –Site H – two of model FGB-1675-1587 –Site B lateral – two of model FGB-1675-2186 –Site L – one of model FGB 1675-1804 –Site M – one of model FGB-1485-1437. •The pump station at the river to service this area would be a major structure with installedcapacity of approximately 20 m3/second (without redundancy) and installed motor power of atleast 2.9 MW. This assumed mains supply, and given the paucity of site information, was costedon the basis of the cost curves developed by SunWater for north Queensland river pumpstations. •The re-regulation weir was based on an assumed crest height above existing bed level on arocky outcrop of 1.5 m. The estimate included a basic fish ladder. Table 6-4 The Gregory River potential dam site channel reticulation costing For more information on this table please contact CSIRO on enquiries@csiro.au †Refers to the channel control system – supervisory control and data acquisition. This represents a development cost for the backbone reticulation only of some $3180 per irrigated hectare. To this must be added the cost of the re-regulating weir and any distribution and land development costs downstream of the backbone infrastructure. 6.2 Conceptual irrigation scheme arrangement for Gregory River potential dam with FSL 138 mEMG96 This analysis utilised the same method as used in Section 6.1 for the larger yield dam site. While the criteria used for selection of the targeted area were the same as outlined in Section 6.1.1, priority was given to a compact development where supply costs could be minimised. 6.2.1 Selection of area for development Using the criteria outlined in Section 6.1.1, the area for development ranges from 10,175 ha (open channel and furrow irrigation) to 11,770 ha (piped reticulation and spray irrigation). The area shown in Figure 6-5 totals 11,398 ha, and this was used as the gross area to recalculate the design flows for the channel network. For more information on this figure please contact CSIRO on enquiries@csiro.au Figure 6-5 Area for reduced development Showing sub-area labels, location labels and channel alignments overlaid on Google imagery. 6.2.2 Channel design The applicable channel parameters, using the method outlined in Section 6.1.3, are given in Table 6-5 and Table 6-6. Table 6-5 Adopted main channel parameters For more information on this table please contact CSIRO on enquiries@csiro.au Table 6-6 Adopted lateral channel parameters For more information on this table please contact CSIRO on enquiries@csiro.au Adopted longitudinal profiles are shown for the main channel in Figure 6-6 and for the lateral channel in Figure 6-7. For more information on this figure please contact CSIRO on enquiries@csiro.au Figure 6-6 Main channel profile for the 131 GL development Reach points refer to the locations shown in Figure 6-5. For more information on this figure please contact CSIRO on enquiries@csiro.au Figure 6-7 Lateral channel profile for the 131 GL development Reach points refer to the locations shown in Figure 6-5. 6.2.3 Channel reticulation costing – reduced area The estimated costs for the 131 GL scheme are presented in Table 6-7. They were calculated using the method and assumptions outlined in Section 6.1.4, amending the channel, structure and regulator sizes according to the reduced demand. Table 6-7 The Gregory River potential dam site channel reticulation costing – reduced area For more information on this table please contact CSIRO on enquiries@csiro.au †Refers to the channel control system – supervisory control and data acquisition. This represents a development cost for the backbone reticulation only of some $3340 per irrigated hectare. To this must be added the cost of any distribution and land development costs downstream of the backbone infrastructure. Comparing this to the price derived for the larger 232 GL development outlined in Section 6.1 indicates that there may be little penalty attached to smaller scale developments, at least down to the scale of the 131 GL development. 7 Water-harvesting options along the Gregory River Of the two sites investigated in sections 5 and 6 above, only the Gregory River potential dam site in Section 6 lends itself to a water-harvesting option. To allow meaningful comparisons with the Wickham River site detailed in Section 4, the same broad scale of development will be detailed, namely: •storage capacity of about 28,000 ML •irrigated area of about 2000 ha •river pump capacity of 6.5 m3/second. Channel design capacities are calculated using the method outlined in Section 6.1.3. 7.1 Major elements of the notional water-harvesting scheme The adopted layout is shown below in Figure 7-1. For more information on this figure please contact CSIRO on enquiries@csiro.au Figure 7-1 Layout of water-harvesting scheme Irrigated areas shown in red, with channel alignments as green dashed lines and points for flow calculation in green. Major elements of the layout are: •A river pump station, consisting of five axial-flow, two-stage flood-lifter pumps located on theriver bank, and each discharging to a separate rising main some 380 m long with a downstreamflap valve. Pump duty is 1.6 m3/second at 14 m total head. •A system of storage cells, with a full supply level decreasing to the north by approximately 1 to1.2 m between adjacent cells. Water depth at full supply is 5.5 m. •The arrangement shown in Figure 7-1 will feature two minor pump stations at locations X and Y. These will be a box-mounted column-less axial-flow diaphragm pumps that will allow gravitydiversion between adjacent cells and pumped diversions from northern cells back to theadjacent southern cell. In this way, water held at the end of the growing period can be movedprogressively to a smaller number of cells to limit evaporative losses. •Two channel alignments service the supplied area, preserving the natural drainage line betweenthe north and southern sections. As a later addition, a tailwater return system could berelatively easily incorporated into this layout, but is not included in this case. •The channels feature check and drop structures at the mid-point of each of the blocks labelled inFigure 7-1. An automated Rubicon Flume Gate is allowed for each of those structures. 7.2 Water-harvesting cost estimation The same assumptions as outlined for the Wickham River water-harvesting option in Section 4.5 are used for this cost estimate (Table 8-1). Table 7-1 Furrow-irrigation water-harvesting cost estimate 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 The above cost estimate equates to $15,913 per irrigated hectare. As for the Wickham River water-harvesting scheme, it is not valid to compare this directly with the equivalent costs derived in sections 2, 3, 5 and 6 since there is no dam involved in this development. It is also not valid to directly compare the costs per ML of water utilised in the dam and water-harvesting cases, as factors such as differing reliability of supply and differing efficiencies of transfer of water from a dam to the serviced area complicate the issue. The above estimate shows that by far the majority of the costs are associated with the water capture and conservation elements rather than the irrigation reticulation components. Assuming the 21,000 ML effective yield of the system, the cost per ML of annual yield is $1515. PartIV Discussion - 8 Discussion Comparing the results for the notional schemes outlined in sections 2, 3, 4, 5 and 6 is useful to highlight advantages that some schemes offer over others. Also included in the comparison are the schemes in the catchment of the Roper River detailed in Assessment of surface water storage options and reticulation infrastructure in the Roper catchment (Petheram et al., 2022). In the case of these schemes, cost estimates have been updated using rates derived from the companion technical report on water infrastructure related costs for the Victoria and Southern Gulf catchments (Rider Levett Bucknall, 2024), to allow meaningful comparisons with the schemes in this report. See Appendix A for full details of those revised estimates. Table 8-1 Key characteristic for reticulation sites examined 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 The results above imply a very wide range of development costs, but it is important to keep in mind the relevant differences between schemes so meaningful conclusions can be developed. The following conclusions are indicated: • The water-harvesting schemes based on the serviced area alongside the Wickham River, and to the east of the Gregory River clearly represent the better value. This can’t be directly compared to the above sites, as the reliability of the water-harvesting operation is likely to be less than the 85% annual reliability quoted for the dam-based developments. However, given vast disparity of costs, and given that the above development costs include both headworks and reticulation works, they are the more cost effective schemes. • Channel-based schemes are significantly less costly to develop than piped schemes in the same catchment, based on local costs, though scheme scale costs were small relative to the cost of a potential dam. • Of the channel schemes, the potential lower-level dam on the Gregory River at the Gregory River potential dam site appears to offer the most potential. Local development costs for the potential scheme on Leichhardt Creek in the West Baines system are similar, but this development represents higher risk due to a number of factors, including the large distance between the dam and the development area, the risk of flooding and the extremely friable nature of the river at the development site. It is also a very small development. The other channel system scheme is the potential Flying Fox Creek AMTD 105 km in the Roper catchment. This is an expensive scheme, reflecting the long rising main from the weir to the serviced area, and the drainage provisions necessary for the channel constructed on contour. • None of the piped schemes appear to be cost effective, and they all compare unfavourably to flood harvesting and to a lesser extent to channel-based schemes. The reasons are slightly different for each scheme but can be summarised as follows. The Wickham River scheme has more favourable local cost, but once the dam costs are included, shows no advantage over other options. The Gunpowder Creek scheme has low available land gradients, and a fair run of infrastructure before land is serviced. The Waterhouse River scheme is very elongated down the river, and serviced land is on both sides of the river. Another perspective on the above costs is to compare them with irrigation schemes constructed in the last two decades in Tasmania, representing the most intensive irrigation development undertaken in Australia in those decades. However, a number of factors make this comparison less than ideal. Using the example of Midlands Irrigation District, the largest of those schemes, the more important of those factors are: • The irrigation demands are different in nature, with the Tasmanian schemes being more of a supplementary nature, whereas those required for the hypothetical northern Australian schemes, due to the pronounced nature of the dry season, represent the full crop demand. For example, the Midlands scheme supplies a total of 38.5 GL to a total of 105 landholders on over 250,000 ha of existing holdings. By contrast, the Wickham River potential dam site based on reticulation detailed in Section 2 above has 17,900 ha serviced by some 196 GL/year. Since the Midlands scheme is a piped and river reticulated scheme it will bear the most similarities to the Wickham River site, of the schemes examined in this report. • The reliability of the water supplied by the schemes is different, with the Midlands being 95% annual reliability, whereas the Wickham River and other schemes examined in this report are based on 85% annual reliability. • Topography is dramatically different, with Midlands having some excess head from the upper Arthurs Lake hydro-electric storage being dissipated in a mini power station incorporated into the project. By contrast, all the schemes examined in this report are much flatter, with grade induced by pumping. • Crop selection, crop timings and irrigation method will be markedly different for the two areas. Current production in Midlands includes poppies, cereals, canola, pasture seeds, lucerne, potatoes, and pasture for livestock finishing. This involves a reasonably constant demand over the full year, with entitlements differentiated between summer and winter demands. • The geographic environment is quite different between central Tasmania and northern Australia. The former is closely settled, with a fair distribution of services for the existing agriculture and power industries. By contrast, the parts of the catchments of the Victoria River and the catchment of the Southern Gulf rivers (that is Settlement Creek, Gregory–Nicholson River and Leichhardt River, the Morning Inlet catchments and the Wellesley island groups) are extremely remote, and this would be reflected in contract rates for construction. • The irrigation demand, using the same methodology of Section 6.1.3 is significantly less for the Midlands scheme. An E0 of 7.15 mm/day, based on SILO values for York Plains, near the centroid of Midlands Irrigation District (P99 of 4-day mean E0) compares to 11.5 mm/day for the Wickham River catchment scheme. While both climate factor and crop factor may vary for specific crops, the crop mix outlined above would indicate that the values used in Section 2.3 would still be applicable for this design. So, the design capacity of the reticulation infrastructure based on the lower value would be proportionally lower. Given the above factors, it will be of limited value to directly compare the two schemes. Nonetheless, the sensitivity of the Wickham design has been evaluated against the lower evaporative rate to gauge the cost sensitivity to that variable. The comparable numbers to those given in Table 8-1 and in Section 2 are that total capital cost decreases to $211,139,766, or some $11,760 per serviced hectare, compared to $16,200 as per Table 8-1. References Budget Strategy and Outlook (2024) Budget 2024-25. A future made in Australia. Viewed 11 September 2024, https://budget.gov.au/content/factsheets/download/factsheet-fmia.pdf. Department of State Development, Manufacturing, Infrastructure and Planning (2019) North west Queensland economic diversification strategy 2019. Viewed 12 September 2024, https://www.statedevelopment.qld.gov.au/regions/regional-priorities/a-strong-and- prosperous-north-west-queensland/north-west-queensland-economic-diversification- strategy. Gibbs M, Hughes J, Yang A, Wang B, Marvanek S and Petheram C (2024) River model scenario analysis for the Southern Gulf catchments. A technical report from the CSIRO Southern Gulf Water Resource Assessment for the National Water Grid. CSIRO, Australia. 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. Petheram C, Yang A, Seo L, Rogers L, Baynes F, Devlin K, Marvanek S, Hughes J, Ponce Reyes R, Wilson P, Stratford D, Philip S (2022) Assessment of surface water storage options and reticulation infrastructure in the Roper catchment. A technical report from the CSIRO Roper River Water Resource Assessment for the National Water Grid. CSIRO, Australia. Queensland Government (2023) Queensland Water Strategy. Water. Our life resource. Viewed 11 September 2024, https://www.rdmw.qld.gov.au/qld-water-strategy/strategic-direction. 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. Thomas M, Philip S, Zund P, Stockmann U, Hill J, Gregory L, Watson I and Thomas E (2024) Soils and land suitability for the Southern Gulf catchments. A technical report from the CSIRO Southern Gulf 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 PartIV Appendices Roper catchment dam site developments, updated cost estimates A.1 Cost estimate basis These cost estimates take the design outlined in Assessment of surface water storage options and reticulation infrastructure in the Roper catchment (Petheram et al., 2022) and update the costs using rates derived from Water infrastructure related costs for the Victoria and Southern Gulf catchments (Rider Levett Bucknall, 2024). A.1.1 Dam 55 – 10 m boost reticulation costs Apx Table A-1 Dam 55 – 10 m boost reticulation costs For more information on this table please contact CSIRO on enquiries@csiro.au A.1.2 Dam 79 reticulation costs Apx Table A-2Table A2 Dam 79 reticulation costs For more information on this table please contact CSIRO on enquiries@csiro.au As Australia’snational scienceagency and innovation catalyst, CSIRO is solving the greatestchallenges through innovativescience and technology. CSIRO.Unlockingabetterfutureforeveryone. Contact us 1300 363 400+61 3 9545 2176csiroenquiries@csiro.aucsiro.au For further informationEnvironment Dr ChrisChilcott+61 8 8944 8422chris.chilcott@csiro.au Environment DrCuan Petheram+61 467 816 558cuan.petheram@csiro.au Agriculture andFood Dr IanWatson+61 7 4753 8606 Ian.watson@csiro.au