Water Availability in the Border Rivers

Transcription

1 Water Availability in the Border Rivers A report to the Australian Government from the CSIRO Murray-Darling Basin Sustainable Yields Project November 27

2 Murray-Darling Basin Sustainable Yields Project acknowledgments The Murray-Darling Basin Sustainable Yields project is being undertaken by CSIRO under the Australian Government's Raising National Water Standards Program, administered by the National Water Commission. Important aspects of the work were undertaken by Sinclair Knight Merz; Resource & Environmental Management Pty Ltd; Department of Water and Energy (New South Wales); Department of Natural Resources and Water (Queensland); Murray-Darling Basin Commission; Department of Water, Land and Biodiversity Conservation (South Australia); Bureau of Rural Sciences; Salient Solutions Australia Pty Ltd; ewater Cooperative Research Centre; University of Melbourne; Webb, McKeown and Associates Pty Ltd; and several individual sub-contractors. Murray-Darling Basin Sustainable Yields Project disclaimers Derived from or contains data and/or software provided by the Organisations. The Organisations give no warranty in relation to the data and/or software they provided (including accuracy, reliability, completeness, currency or suitability) and accept no liability (including without limitation, liability in negligence) for any loss, damage or costs (including consequential damage) relating to any use or reliance on that data or software including any material derived from that data and software. Data must not be used for direct marketing or be used in breach of the privacy laws. Organisations include: Department of Water, Land and Biodiversity Conservation (South Australia), Department of Sustainability and Environment (Victoria), Department of Water and Energy (New South Wales), Department of Natural Resources and Water (Queensland), Murray-Darling Basin Commission. 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. Data is assumed to be correct as received from the Organisations. Citation CSIRO (27). Water availability in the Border Rivers. A report to the Australian Government from the CSIRO Murray-Darling Basin Sustainable Yields Project. CSIRO, Australia. 144pp Publication Details Published by CSIRO 27 all rights reserved. This work is copyright. Apart from any use as permitted under the Copyright Act 1968, no part may be reproduced by any process without prior written permission from CSIRO. ISSN X Photo on cover: Macintyre River upstream of Holdfast crossing, courtesy of CSIRO Land and Water

3 Director s Foreword Following the November 26 Summit on the Southern Murray-Darling Basin, the Prime Minister and Murray-Darling Basin state Premiers commissioned CSIRO to report on sustainable yields of surface and groundwater systems within the Murray-Darling Basin. This report from the CSIRO Murray-Darling Basin Sustainable Yields Project details the assessments for one of 18 regions that encompass the Basin. The CSIRO Murray-Darling Basin Sustainable Yields Project is providing critical information on current and likely future water availability. This information will help governments, industry and communities consider the environmental, social and economic aspects of the sustainable use and management of the precious water assets of the Murray-Darling Basin. The project is the first rigorous attempt worldwide to estimate the impacts of catchment development, changing groundwater extraction, climate variability and anticipated climate change, on water resources at a basin-scale, explicitly considering the connectivity of surface and groundwater systems. To do this, we are undertaking the most comprehensive hydrologic modelling ever attempted for the entire Basin, using rainfall-runoff models, groundwater recharge models, river system models and groundwater models, and considering all upstream-downstream and surfacesubsurface connections. We are complementing this work with detailed surface water accounting across the Basin never before has surface water accounting been done in such detail in Australia, over such a large area, and integrating so many different data sources. To deliver on the project CSIRO is drawing on the scientific leadership and technical expertise of national and state government agencies in Queensland, New South Wales, Victoria, the Australian Capital Territory and South Australia, as well as the Murray-Darling Basin Commission and Australia s leading industry consultants. The project is dependent on the cooperative participation of over 15 government and private sector organisations contributing over 1 individuals. The project has established a comprehensive but efficient process of internal and external quality assurance on all the work performed and all the results delivered, including advice from senior academic, industry and government experts. The project is led by the Water for a Healthy Country Flagship, a CSIRO-led research initiative which was set up to deliver the science required for sustainable management of water resources in Australia. The Flagship goal is to achieve a tenfold increase in the social, economic and environmental benefits from water by 225. By building the capacity and capability required to deliver on this ambitious goal, the Flagship is ideally positioned to accept the challenge presented by this complex integrative project. CSIRO has given the Murray-Darling Basin Sustainable Yields Project its highest priority. It is in that context that I am very pleased and proud to commend this report to the Australian Government. Dr Tom Hatton Director, Water for a Healthy Country National Research Flagships CSIRO

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5 Executive Summary Background The CSIRO Murray-Darling Basin Sustainable Yields Project is providing governments with a robust estimate of water availability for the entire Murray-Darling Basin (MDB) on an individual catchment and aquifer basis, taking into account climate change and other risks. This report describes the assessment undertaken for the Border Rivers region. While key aspects of the assessment and modelling methods used in the project are contained in this report, fuller methodological descriptions will be provided in a series of project technical reports. The Border Rivers region is in southern Queensland and northeastern New South Wales and represents 4 percent of the total area of the MDB. The region is based around the Macintyre Brook and Dumaresq Rivers which join the Macintyre River and continue to become the Barwon River. The population is around 5, or 2.5 percent of the MDB total, concentrated in the major centres of Glen Innes, Inverell, Tenterfield, Stanthorpe, Inglewood, Mungindi and Goondiwindi. The dominant land use is broadacre livestock grazing, particularly on the tablelands. There is a shift to cropping on the slopes and plains. There were approximately 75,3 ha of irrigated cropping in the year 2. Cotton accounted for over 75 percent of this area. The region includes a small area of commercial forestry plantations and large numbers of farm dams and ring tanks. The nationally significant wetland Morella Watercourse/Boobera Lagoon/Pungbougal Lagoon 6 km south-west of Goondiwindi in New South Wales is considered to be one of the most important Aboriginal places in eastern Australia. Executive Summary The region uses 4.4 percent of the total surface water diverted for irrigation in the MDB and 2 percent of the MDB groundwater resource. A number of major water storages constructed since the late 196s enable irrigated agriculture on the plains. Over 9 percent of the water used for irrigation is diverted from surface water resources. However, groundwater use is high in some parts of the region. Key Messages The key messages relating to climate, surface water resources, groundwater and the environment are presented below for scenarios of current and possible future conditions. The scenarios assessed are defined in Chapter 1. Historical climate and current development (Scenario A) The average annual rainfall for the Border Rivers region is 641 mm. Modelled average annual runoff is 32 mm. Rainfall is generally higher in the summer half of the year and runoff is relatively uniform through the year. The region generates 4.7 percent of the total runoff of the MDB. Current average surface water availability is 128 GL/year comprised of 95 GL/year in the Macintyre and Dumaresq rivers, 242 GL/year in the Weir River and 61 GL/year in Whalan Creek. Average diversions are 34 percent of average available water. This is a high level of use which has reduced the reliability of supply for water users in the region and has reduced end-of-system flows. New South Wales general security water is highly utilised 82 percent of the available water is utilised. Queensland medium security water in the Glenlyon system is also highly utilised 73 percent of the available water is used. (The river model used assumes that Queensland medium security water is fully utilised in the Coolmunda system.) River flows are highly regulated Glenlyon Dam regulates 88 percent of inflows under current levels of development and Pindari Dam regulates 7 percent of inflows. Of the constructed storage capacity in the region around 4 percent is in the form of on-farm ring tanks. The environment flow objective of the Water Resource (Border Rivers) Plan 23 requires an end-of-system flow at Mungindi, of at least 6.8 percent of the without development flow in preparing the first resource operations plan. Thus the upstream diversions should not reduce flows at Mungindi by more than 39.2 percent of the average without development flow for the simulation period used in developing the plan. Given current surface water entitlements in Border Rivers, considering equilibrium surface groundwater exchanges and for the common modelling period of this CSIRO 27 November 27 Water availability in the Border Rivers

6 project, the flows at Mungindi are 59.5 percent of the without development flow. This indicates that the end-of-system target is sensitive to the climatic period used for modelling and to the inclusion of surface groundwater exchanges. Groundwater extraction in the Border Rivers region is estimated to be 34.3 GL/year. About 37 percent of this is from the New South Wales and Queensland Border Rivers Alluvium (BRA) groundwater management units (GMUs). Groundwater modelling of the BRA GMU in the Dumaresq River area indicates that current extraction (~11.2 GL/year in the modelled area) is about 75 percent of groundwater recharge. This is a high level of extraction. The current spatial pattern of groundwater extraction is expected to lead to large reductions in groundwater levels. As groundwater levels fall, responses would be expected from both groundwater users and resource managers. These responses would reduce groundwater extraction in areas of falling groundwater levels. Executive Summary Current groundwater extraction affects flows in the Dumaresq River. Over the calibration period of the groundwater model (196 to 1999), and in across the modelled portion of the BRA GMUs, the Dumaresq River gains 4.4 GL/year on average. However, after prolonged groundwater extraction at 23/4 levels the river is predicted to eventually lose 5.2 GL/year on average. This means that once equilibrium is reached, there will be a potential double accounting error of around 9.6 GL/year inherent in any separate surface and groundwater assessments. A period of about 2 years is required before half of the final impact on streamflow eventuates. However, it may require more than 1 years for groundwater levels to reach dynamic equilibrium. Future water planning should consider these equilibrium surface groundwater exchanges. Current groundwater extraction in the Miscellaneous Alluvium of the Barwon Region GMU exceeds recharge; this is a very high level of development. In the other GMUs in the region current development is low. The anabranches and billabongs of the Macintyre River floodplain are important environmental assets. Hydrologic connections between these systems and the main river affect ecological processes in the main river. Water resource development has increased the average period between flows that connect these anabranches and billabongs to the main river by about 22 percent and has reduced the average volume of individual events by about 8 percent. These changes are likely to have caused changes to all these riverine ecosystems. Recent climate and current development (Scenario B) The average annual rainfall and runoff over the ten-year period 1997 to 26 are within 1 percent of the long-term (1895 to 26) average values. A scenario based on the last ten years was therefore not modelled for this region. Future climate and current development (Scenario C) Rainfall-runoff modelling with climate change projections from global climate models indicates that future runoff in the Border Rivers region is more likely to decrease than to increase. The best estimate (median) 23 climate shows a 9 percent reduction in average annual runoff. The extreme estimates, which come from a high global warming scenario, range from a 28 percent reduction to a 2 percent increase in average annual runoff. By comparison, the range from a low global warming scenario is from a 9 percent reduction to a 5 percent increase in average annual runoff. Under the best estimate 23 climate average water availability would be reduced by 1 percent, end-of-system flows by 12 percent lower and total diversions by 2 percent. However, the impacts on diversions would differ by water product : in New South Wales both general security and supplementary use would fall by 1 percent. In Queensland, both medium security and unsupplemented use would fall by 3 percent. Town water supply would be unaffected. Under the wet extreme 23 climate there would increases in: water availability (18 percent), total diversions (8 percent), and end-of-system flows (26 percent); and under the dry extreme decreases in: water availability (26 percent), total diversions (17 percent), and end-of-system flows (34 percent). High security town water use is maintained at current levels under all 23 climate change scenarios. Under the best estimate 23 climate current Border Rivers entitlements would reduce flows at Mungindi to 52.9 percent of the without development flow, well below the target of 6.8 percent required under the current Water Resource Plan. The Queensland Water Act 2 allows for reviews and/or amendments to be made to water resource plans where there is new evidence indicating that the objectives of the plan are either no longer appropriate or are no longer being met. The impact of climate change on surface-groundwater exchanges is relatively small. Under the best estimate (median) 23 climate the net surface groundwater flux would be unaffected by any climate changes. Water availability in the Border Rivers November 27 CSIRO 27

7 The best estimate 23 climate scenario would increase the average period between events inundating the anabranches and billabongs of the Macintyre River by a further 26 percent above current conditions; the average period would then be 5 percent greater than pre-development. Further small reductions in the average volumes of individual events would also occur. The dry extreme 23 climate scenario would lead to major additional increases in the period between events and major additional reductions the average volume of individual events, while the wet extreme 23 climate would return the average period and event volumes back close to the pre-development values. The hydrologic changes under best estimate 23 climate and the dry extreme 23 climate would be likely to affect in-stream processes due to changes in the availability of dissolved organic carbon, and this in turn would be likely to affect fish and other aquatic animals. Future climate and future development (Scenario D) There is negligible projected growth in commercial forestry plantations in the Border Rivers region. The total farm dam storage volume over the entire Border Rivers region is projected to increase by 12.8 GL. About 85 percent of the increased volume is in the New South Wales part of the Border Rivers region, where the growth would represent a 14 percent increase over current farm dam storage volume. The projected increase in farm dams will reduce mean annual runoff by about 1 percent. This is relatively small compared to the best estimate climate change impact on runoff (9 percent). The best estimate of the combined impact of climate change and farm dam development is a 1 percent reduction in mean annual runoff, with extreme estimates ranging from a 28 percent reduction to 19 percent increase. Future (23) groundwater extraction is projected to be 23 GL/year in the modelled area of the BRA GMUs, compared to the extraction limit of 3 GL/year. This level of extraction (assuming the current spatial pattern of groundwater bores) could not be sustained as large reductions in groundwater levels would occur. This would be most likely to lead to responses from groundwater users and resource managers that would reduce groundwater extraction in the affected areas. Without such responses projected future extraction could lead to complete drying of the aquifer, thus forcing a reduction in extraction. It is predicted that prolonged extraction at these future levels would eventually remove another 8.9 GL/year from the river through induced leakage to groundwater. However, the model is likely to overestimate the real impact. Executive Summary Under the best estimate 23 climate and with projected 23 groundwater extraction, groundwater use would represent 28 percent of the total annual water use in the region on average, and 67 percent in the driest year within the 111 year modelling period. These values compare to 8 percent on average or 26 percent in the driest year under current conditions. Groundwater use in other GMUs in New South Wales is expected to increase nearly 6-fold overall and 27-fold in the New England Fold Belt GMU. Projected increases in extraction in the Miscellaneous Alluvium of Barwon Region GMU would further increase the already very high level of development. The total impact of this additional groundwater use on river inflows is estimated to be 3 GL/year. River modelling, with 6 percent of the inflow reduction due to additional groundwater use together with the minor impacts of farm dam growth, reduces surface water availability by about 22 GL/year in addition to the impacts of the best estimate 23 climate. Of this, about 55 percent is due to farm dam increases and about 45 percent is due to additional groundwater use outside the BRA GMU. The predicted additional river leakage of 8.9 GL/Year due to increases in groundwater extraction in the BRA GMU would further reduce surface water availability. Uncertainty The runoff estimates for the Border Rivers region are relatively good because there are many gauged catchments in the region from which to estimate the model parameter values. Rainfall-runoff model verification analyses for the MDB indicate that the mean annual runoff estimated for ungauged catchments using optimised parameter values from a nearby catchment have an error of less than 2 percent in more than half the catchments and less than 5 percent in almost all the catchments. The largest source of uncertainty for future climate results are the climate change projections (global warming level) and the modelled implications of global warming on regional rainfall. A wide range of the best available climate modelling was used but there is considerable scope for improvement in those global models at predicting regional rainfall. CSIRO 27 November 27 Water availability in the Border Rivers

8 Improvements in the ability to predict the hydrological consequences of climate change would have substantial benefits for water management. There are considerable uncertainties associated with the future development projections for commercial forestry plantations and farm dams and the impact of these developments on runoff. Uncertainty around farm dam projections is higher for New South Wales than for Queensland, since current New South Wales policy does not prevent construction of farm dams for irrigation. Future development could be very different should governments impose different policy controls on these activities. Overall, the internal uncertainty in the river model used is less than the external uncertainty associated with climate change projections. The river model predicts supply of water to the majority of water uses well. As such it is considered suitable for the purposes of this project as well as for water resource planning. However, caution is advised when interpreting end-of-system flow characteristics at Mungindi (particularly the magnitude of peak flows). Executive Summary The current form of the groundwater model of the Border Rivers Alluvium GMUs produces results that have a high level of uncertainty due to its poor conceptualisation and the lack of a suitable calibration. It is considered unsuitable for use as a water allocation tool due to its inability to implement local management rules. Further model calibration is required once a larger stress is placed on the aquifer via pumping, and the measured aquifer response is incorporated into the model. The model is not expected to accurately represent the drawdowns in the deeper aquifer once pressure levels drop. Notwithstanding the level of uncertainty surrounding the model, the level of analysis for the Border Rivers Alluvium GMU is commensurate with the priority ranking of these GMU given the project objectives. There is considerable uncertainty in the groundwater assessments outside of the Border Rivers Alluvium GMUs, especially in the unincorporated areas in Queensland and the Great Artesian Basin Intake Beds in Queensland for which there is no reliable information on current or future extraction. There is also considerable uncertainty in the future projections of groundwater development outside of the Border Rivers Alluvium GMU, but the estimates indicate the importance of development in these areas. The groundwater projections are considered to generally represent the upper limit of groundwater development as it can be constrained by pumping rules, groundwater quality and land suitability. However, the assessments of development impacts are generally underestimates due to the use of entitlements in determining stream impacts and the use of connectivity estimates based on conservative best guesses. The environmental assessments consider only a subset of the important assets for this region and are based on limited hydrology parameters with no direct quantitative relationships for environmental responses. Considerably more detailed investigation is required to provide the necessary information for informed management of the environmental assets of the region. Water availability in the Border Rivers November 27 CSIRO 27

9 Table of Contents 1 Introduction Background Project methodological framework Climate and development scenarios Rainfall-runoff modelling River system modelling Monthly water accounts Groundwater modelling Environmental assessment References Overview of the region The region Environmental description Surface water resources Groundwater References Rainfall-runoff modelling Summary Modelling approach Modelling results Discussion of key findings References River system modelling Summary Modelling approach Modelling results Discussion of key findings References Uncertainty in surface water modelling results Summary Approach Results Discussion of key findings References Groundwater assessment Summary Groundwater management units in the region Surface water groundwater connectivity Groundwater modelling approach Modelling results and discussion Water balances for lower priority groundwater management units Conjunctive water use indicators Discussion of key findings References Environment Summary Approach Results Discussion of key findings References Appendix A Rainfall-runoff results for all subcatchments Appendix B River water modelling reach mass balances Appendix C River system model uncertainty assessment by reach Erratum sheets, issued May 29, reissued May 21, inside back CSIRO 21 Reissue page, May 21 Water availability in the Border Rivers

10 Tables Table 1-1. River system models in the Murray-Darling Basin...7 Table 2-1. Summary of land use in the year 2 within the Border Rivers region...15 Table 2-2. Ramsar wetlands and wetlands of national significance located within the Border Rivers region...18 Table 2-3. Summary of surface water sharing arrangements within New South Wales...21 Table 2-4. Summary of surface water sharing arrangements within Queensland...22 Table 2-5. Groundwater extraction, entitlement and recharge summary...25 Table 2-6. Groundwater sharing arrangements within the Border Rivers region...27 Table 3-1. Summary results from the 45 Scenario C simulations (numbers show percentage change in mean annual rainfall and runoff under Scenario C relative to Scenario A)...37 Table 3-2. Water balance over the entire region by scenario...39 Table 4-1. Storages in the river system model...47 Table 4-2. Modelled water use configuration...47 Table 4-3. Model water management...48 Table 4-4. Model setup information...49 Table 4-5. Rainfall, evaporation and flow factors for model robustness test...5 Table 4-6. River system model average annual water balance under scenarios O, AO, A, C and D...51 Table 4-7. Annual water availability for pre-development Scenario A and relative change under pre-development scenarios C and D...53 Table 4-8. Details of Glenlyon Dam behaviour...54 Table 4-9. Details of Pindari Dam behaviour...54 Table 4-1. Details of Coolmunda Dam behaviour...55 Table Details of Boggabilla Weir behaviour...55 Table Change in total diversions in each subcatchment relative to Scenario A...57 Table Relative level of use under scenarios A, C and D...59 Table Indicators of use during dry periods under scenarios A, C and D...59 Table Average reliability of water products under Scenario A, and relative change under scenarios C and D...6 Table Summary of average allocated water and diverted water for NSW general security licences and Queensland medium security licences...63 Table Daily flow event frequency under scenarios P, A, C and D...65 Table Percentage of time flow occurs at the end-of-system under scenarios P, A, C and D...68 Table Relative level of available water not diverted for use under scenarios A, C and D...69 Table 5-1. Possible framework for considering implications of assessed uncertainties...74 Table 5-2. Comparison of water accounting reaches with river model reaches...75 Table 5-3. Some characteristics of the gauging network of the Border Rivers region (43,633 km 2 ) compared with the entire MDB (1,62,443 km 2 )...78 Table 5-4. Gauges for which streamflow data were used in model calibration, and rating of data quality...81 Table 5-5. Definition of model performance qualifiers used (NSW DNR)...82 Table 5-6. Indicators of model performance in reproducing stream flow patterns. Between brackets performance before the storage and diversion models were included, where this differs from the overall qualification...83 Table 5-7. Indicators of model performance in reproducing storage behaviour. Between brackets terms are the best performance without including the diversion and planted area models, where these differ from the overall qualification Table 5-8. Indicators of model performance in reproducing diversion patterns and planted areas. Between brackets performance before the planting area model was included, where this differs from the overall qualification...85 Table 5-9. Regional water balance modelled and estimated on the basis of water accounting...87 Table 6-1. Groundwater management units of the Border Rivers region and associated data...95 Table 6-2. Summary results from the 45 Scenario C simulations (numbers show percentage change in mean annual rainfall and recharge under Scenario C relative to Scenario A). Those in bold type were selected for further modelling...13 Table 6-3. Summary results of the scenarios for modelling mean annual recharge for each groundwater management unit in the Border Rivers region...13 Table 6-4. Median groundwater level over 111 years under Scenario A and the difference in level from Scenario A for scenarios C and D...15 Table 6-5. Annual average combined recharge and net loss of river flow...17 Table 6-6. Dumaresq River average annual modelled groundwater balance...18 Table 6-7. Definition of groundwater indicators...19 Table 6-8. Groundwater indicators under scenarios A, C and D...19 Table 6-9. Estimated groundwater extraction for the Border Rivers region...11 Table 6-1. Scaled recharge under scenarios A and C Table Comparison of groundwater extraction with scaled rainfall recharge Water availability in the Border Rivers November 27 CSIRO 27

11 Table Estimation of the impacts of future groundwater extraction on streamflow outside of the Border Rivers Alluvium GMUs Table Ratio of groundwater extraction to total water (surface and groundwater) under different scenarios and for low flow periods Table 7-1. Definitions of environmental indicators Table 7-2. Environmental indicator values under scenarios P and A, and percentage changes (from Scenario A) in environmental indicators under scenarios C and D Figures Figure 1-1. Region by region map of the Murray-Darling Basin...2 Figure 1-2. Methodological framework for the Murray-Darling Basin Sustainable Yields Project...3 Figure 1-3. Timeline of groundwater use and resultant impact on river...8 Figure annual and monthly rainfall averaged over the region (the curve on the annual graph shows the low frequency variability)...14 Figure 2-2. Map of dominant land uses of the Border Rivers region with inset showing the region s location within the Murray-Darling Basin...16 Figure 2-3. Historical surface water diversions for Queensland and New South Wales Border Rivers region...23 Figure 2-4. Map of groundwater management units within the Border Rivers region...26 Figure 2-5. Historical groundwater diversions for Queensland and New South Wales Border Rivers region...28 Figure 3-1. Map of modelling subcatchments and calibration catchments...33 Figure 3-2. Modelled and observed monthly runoff and daily flow duration curve for the calibration catchments...34 Figure 3-3. Spatial distribution of mean annual rainfall and modelled runoff averaged over Figure annual rainfall and modelled runoff series averaged over the region (the curve shows the low frequency variability)...35 Figure 3-5. Mean monthly rainfall and modelled runoff (averaged over for the region)...36 Figure 3-6. Percentage change in mean annual runoff under the 45 Scenario C simulations (15 GCMs and three global warming scenarios) relative to Scenario A runoff...37 Figure 3-7. Mean annual rainfall and modelled runoff under scenarios A, Cdry, Cmid and Cwet...38 Figure 3-8. Mean monthly rainfall and modelled runoff under scenarios A, C and D averaged over across the region (C range is based on the consideration of each month separately - the lower and upper limits in C range are therefore not the same as scenarios Cdry and Cwet)...4 Figure 3-9. Daily flow duration curves under scenarios A, C and D averaged over the region (C range is based on the consideration of each rainfall and runoff percentile separately - the lower and upper limits in C range are therefore not the same as scenarios Cdry and Cwet)...4 Figure 4-1. River system map showing major rivers, and model subcatchments, reaches, calibration reaches, inflow gauges, nodes and links...47 Figure 4-2. Transect of Dumaresq-Macintyre average annual river flow under pre-development scenarios A and C...52 Figure 4-3. Pre-development Scenario A water availability...53 Figure 4-4. Time series of change in total water availability relative to pre-development scenario A under (a) pre-development scenario C and (b) pre-development scenario D...54 Figure 4-5. Glenlyon Dam behaviour over the maximum days between spills under Scenario A with change in storage behaviour under (a) Scenario C and (b) Scenario D...55 Figure 4-6. Pindari Dam behaviour over the maximum days between spills under Scenario A with change in storage behaviour under (a) Scenario C and (b) Scenario D...56 Figure 4-7. Coolmunda Dam behaviour over the maximum days between spills under Scenario A with change in storage behaviour under (a) Scenario C and (b) Scenario D...56 Figure 4-8. Boggabilla Weir behaviour over the maximum days between spills under Scenario A with change in storage behaviour under (a) Scenario C and (b) Scenario D...56 Figure 4-9. Total average annual diversions for subcatchments under (a) scenarios A and C and (b) scenarios A and D...57 Figure 4-1. Total diversions for (a) Scenario A and difference between total water use under (b) Scenario Cwet; (c) Scenario Cmid; (d) Scenario Cdry; (e) Scenario Dwet; (f) Scenario Dmid; and (g) Scenario Ddry...58 Figure New South Wales general security reliability under scenarios (a) A; (b) Cwet and Dwet; (c) Cmid and Dmid; (d) Cdry and Dry...6 Figure Queensland Glenlyon medium security reliability under scenarios (a) A; (b) Cwet and Dwet; (c) Cmid and Dmid; (d) Cdry and Ddry...61 Figure Coolmunda system medium security reliability under scenarios (a) A; (b) Cwet and Dwet; (c) Cmid and Dmid; (d) Cdry and Ddry...62 Figure Reliability of unsupplemented and supplemented access water for (a) Queensland irrigators under Scenario C, (b) New South Wales irrigators and town water supplies under Scenario C, (c) Queensland irrigators under Scenario D and (d) New South Wales irrigators and town water supplies under Scenario D...63 Figure Daily flow duration curves under scenarios P, A, C and D at Boggabilla gauge (4162)...64 CSIRO 27 November 27 Water availability in the Border Rivers

12 Figure Average monthly flow at the end of the gaining reach under scenarios P, A, C and D...64 Figure Daily flow duration curves under scenarios A, P and C for lower end of flows for each end-of-system flow gauge (a) Mungindi Gauge; (b) Boomi at Neeworra and (c) Little Weir River...65 Figure Daily flow duration curves under scenarios A, P and D for lower end of flows for each end-of-system flow gauge (a) Mungindi Gauge; (b) Boomi at Neeworra and (c) Little Weir River...66 Figure Seasonal flow curves under scenario A, P and C at (a) Mungindi Gauge; (b) Boomi at Neeworra and (c) Little Weir River...67 Figure 4-2. Seasonal flow curves under scenarios A, P and D at (a) Mungindi Gauge; (b) Boomi at Neeworra and (c) Little Weir River...68 Figure Comparison of state use and non-diverted shares of water under scenarios P, A, C and D...69 Figure 5-1. Map showing the subcatchments used in modelling, the reaches for which river water accounts were developed ( accounting reach ) and gauged head water catchments ( contributing catchment ). Shaded areas ( floodplain and wetlands ) were classified as subject to periodic inundation. Black dots and red lines are nodes and links in the river model respectively...76 Figure 5-2. Map showing the rainfall, stream flow and evaporation observation network, and the subcatchments used in modelling...79 Figure 5-3. Patterns of indicators of the fraction of inflows/gains, outflows/losses and the total of water balance components that is (a) gauged or (b) could be attributed in the water accounts...86 Figure 5-4. Patterns in different measures of model efficiency (the relative performance of the river model in explaining observed streamflow patterns) along the length of the river...88 Figure 5-5. Comparison of modelled (model) and observed (gauged) monthly flows at the end of the Border Rivers system at Mungindi...89 Figure 5-6. Comparison of modelled (model) and recorded (accounts) diversions in Border Rivers accounting reaches. Note that no data were available for Queensland diversions prior to 1993/ Figure 5-7. Pattern along the river of the ratio of the projected change over the river model uncertainty under the different scenarios modelled for (a) annual and (b) monthly flows...9 Figure 6-1. Map of groundwater management units in the Border Rivers region...96 Figure 6-2. Map of surface groundwater connectivity...98 Figure 6-3. Comparison of levels of the Dumaresq River and adjacent groundwater levels...99 Figure 6-4. Mass balance for the calibration model...11 Figure 6-5. Percentage change in mean annual recharge from the 45 Scenario C simulations (15 GCMs and three global warming scenarios) relative to Scenario A recharge...12 Figure 6-6. Annual net river loss for the Dumaresq River model under Scenario A over the 222-year simulation period...14 Figure 6-7. Combined recharge compared to groundwater extraction under Scenario A...16 Figure 6-8. Groundwater system inflows and outflows under scenarios A, Cmid and Dmid...17 Figure 6-9. Annual total recharge exceedence curves for the second 111 years of scenarios (a) A and C, and (b) A and D...18 Figure 6-1. Daily flow duration curves for gauges (a) 4168, (b) 4161, (c) 41621, (d) and (e) The scenarios shown are Cmid (climate change impacts only), Dmid (climate change and future farm dam impacts) and Dmid-modified (climate change, future farm dams and future groundwater extraction impacts) Figure 7-1. Satellite image (22) indicating (within yellow polygons) the anabranches of the lower river floodplain of the Macintyre and Barwon rivers from Goondiwindi to Mungindi. Bright green areas indicate irrigated land Water availability in the Border Rivers November 27 CSIRO 27

13 1 Introduction 1.1 Background Australia is the driest inhabited continent on Earth, and in many parts of the country including the Murray-Darling Basin water resources water for rural and urban use is comparatively scarce. Into the future, climate change and other risks (including catchment development) are likely to exacerbate this situation and hence improved water resource data, understanding and planning and management are of high priority for Australian communities, industries and governments. On 7 November, 26, the Prime Minister of Australia met with the First Ministers of Victoria, New South Wales, South Australia and Queensland at a water summit focussed primarily on the future of the Murray-Darling Basin (MDB). As an outcome of the Summit on the Southern Murray-Darling Basin, a joint communiqué called for CSIRO to report progressively by the end of 27 on sustainable yields of surface and groundwater systems within the MDB, including an examination of assumptions about sustainable yield in light of changes in climate and other issues. The subsequent Terms of Reference for what became the Murray-Darling Basin Sustainable Yields Project specifically asked CSIRO to: 1 Introduction estimate current and likely future water availability in each catchment and aquifer in the MDB considering: o climate change and other risks o surface-groundwater interactions compare the estimated current and future water availability to that required to meet the current levels of extractive use. The Murray-Darling Basin Sustainable Yields Project is reporting progressively on each of 18 contiguous regions that comprise the entire MDB. These regions are primarily the drainage basins of the Murray and the Darling rivers - Australia s longest inland rivers, and their tributaries. The Darling flows southwards from southern Queensland into New South Wales west of the Great Dividing Range into the Murray River in southern New South Wales. At the South Australian border the Murray turns south-westerly eventually winding to the mouth below the Lower Lakes and the Coorong. The regions for which the project assessments are being undertaken and reported are the Paroo, Warrego, Condamine-Balonne, Moonie, Border Rivers, Gwydir, Namoi, Macquarie-Castlereagh, Barwon-Darling, Lachlan, Murrumbidgee, Murray, Ovens, Goulburn-Broken, Campaspe, Loddon-Avoca, Wimmera and Eastern Mount Lofty Ranges (see Figure 1-1). CSIRO 27 November 27 Water availability in the Border Rivers 1

14 1 Introduction Figure 1-1. Region by region map of the Murray-Darling Basin The Murray-Darling Basin Sustainable Yields Project will be the most comprehensive MDB-wide assessment of water availability undertaken to-date. For the first time: daily rainfall-runoff modelling has been undertaken at high spatial resolution for a range of climate change and development scenarios in a consistent manner for the entire MDB the hydrologic subcatchments required for detailed modelling have been precisely defined across the entire MDB the hydrologic implications for water users and the environment by 23 of the latest Intergovernmental Panel on Climate Change climate projections, the likely increases in farm dams and commercial forestry plantations and the expected increases in groundwater extraction have been assessed in detail (using all existing river system and groundwater models as well new models developed within the project) river system modelling has included full consideration of the downstream implications of upstream changes between multiple models and between different States, and quantification of the volumes of surfacegroundwater exchange detailed analyses of monthly water balances for the last ten to twenty years have been undertaken using available streamflow and diversion data together with additional modelling including estimates of wetland evapotranspiration and irrigation water use based on remote sensing imagery (to provide an independent crosscheck on the performance of river system models). 2 Water availability in the Border Rivers November 27 CSIRO 27

15 The successful completion of these outcomes, among many others, relies heavily on a focussed collaborative and teamoriented approach between CSIRO, State government natural resource management agencies, the Murray-Darling Basin Commission, the Bureau of Rural Sciences, and leading consulting firms each bringing their specialist knowledge and expertise on the MDB to the project. 1.2 Project methodological framework The methodological framework for the project is shown in the diagram below (Figure 1-2). This also indicates in which chapters of this report the different aspects of the project assessments and results are presented. 1 Introduction Figure 1-2. Methodological framework for the Murray-Darling Basin Sustainable Yields Project The first steps in the sequence of the project are definition of the reporting regions and their composite subcatchments, and definition of the climate and development scenarios to be assessed (including generation of the time series of climate data that describe these scenarios). The second steps are rainfall-runoff modelling and rainfall-recharge modelling for which the inputs are the climate data for the different scenarios. Catchment development scenarios for farm dams and commercial forestry plantations are modifiers of the modelled runoff time series. Next, the runoff implications are propagated through river system models and the recharge implications propagated through groundwater models for the major groundwater resources or considered in simpler assessments for minor groundwater resources. The connectivity of surface and groundwater is assessed and the actual volumes of surfacegroundwater exchange under current and likely future groundwater extraction are quantified. Uncertainty levels of the river system models are then assessed based on monthly water accounting. The results of scenario outputs from the river system model are used to make limited hydrological assessments of ecological relevance to key environmental assets. Finally, the implications of the scenarios for water availability and water use under current water sharing arrangements are assessed, synthesised and reported. CSIRO 27 November 27 Water availability in the Border Rivers 3

16 1.3 Climate and development scenarios The project is assessing the following four scenarios of historical and future climate and current and future development, all of which are defined by daily time series of climate variables based on different scalings of the climate: historical climate and current development recent climate and current development future climate and current development future climate and future development. These scenarios are described in some detail below with full details provided in Chiew et al. (27a). 1 Introduction Historical climate and current development Historical climate and current development referred to as Scenario A is the baseline against which other climate and development scenarios are compared. The historical daily rainfall time series data that are used are taken from the SILO Data Drill of the Queensland Department of Natural Resources and Water database which provides data for a.5 o x.5 o (5 km x 5 km) grid across the continent (Jeffrey et al., 21; and Areal potential evapotranspiration (PET) data are calculated from the SILO climate surface using Morton s wet environment evapotranspiration algorithms ( and Chiew and Leahy, 23). Current development for the rainfall-runoff modelling is the average of 1975 to 25 land use and small farm dam conditions. Current development for the river system modelling is the dams, weirs and licence entitlements in the latest State agency models, updated to 25 levels of large farm dams. Current development for groundwater models is 24 to 25 levels of licence entitlements. Surface-groundwater exchanges in the river and groundwater models represent an equilibrium condition for the above levels of surface and groundwater development Recent climate and current development Recent climate and current development referred to as Scenario B is used for assessing future water availability should the climate in the future prove to be similar to that of the last ten years. Climate data for 1997 to 26 is used to generate stochastic replicates of 112-year daily climate sequences. The replicate which best produces a mean annual runoff value closest to the mean annual runoff for the period 1997 to 26 is selected to define this scenario. Scenario B is only analysed and reported upon where the mean annual runoff for the last ten years is statistically significantly different to the long-term average Future climate and current development Future climate and current development referred to as Scenario C is used to assess the range of likely climate conditions around the year 23. Three global warming scenarios are analysed in 15 global climate models (GCM) to provide a spectrum of 45 climate variants for the 23. The scenario variants are derived from the latest modelling for the fourth assessment report of the Intergovernmental Panel on Climate Change (IPCC, 27). Two types of uncertainties in climate change projections are therefore taken into account: uncertainty in global warming mainly due to projections of greenhouse gas emissions and global climate sensitivity to the projections; and uncertainty in GCM modelling of climate over the MDB. Results from each GCM are analysed separately to estimate the change per degree global warming in rainfall and other climate variables required to calculate PET. The change per degree of global warming is then scaled by a high, medium and low global warming by 23 relative to 199 to obtain the changes in the climate variables for the high, medium and low global warming scenarios. The future climate and current development Scenario C considerations are therefore for 112-year rainfall and PET series for a greenhouse enhanced climate around 23 relative to 199 and not for a forecast climate at Water availability in the Border Rivers November 27 CSIRO 27

17 The method used to obtain the future climate and current development Scenario C climate series also takes into account different changes in each of the four seasons as well as changes in the daily rainfall distribution. The consideration of changes in the daily rainfall distribution is important because many GCMs indicate that extreme rainfall in an enhanced greenhouse climate is likely to be more intense, even in some regions where projections indicate a decrease in mean seasonal or annual rainfall. As the high rainfall events generate large runoff, the use of traditional methods that assumes the entire rainfall distribution to change in the same way will lead to an underestimation of mean annual runoff in regions where there is an increase, and an overestimation of the decrease in mean annual runoff where there is a decrease (Chiew, 26). All 45 future climate and current development Scenario C variants are used in rainfall-runoff modelling; however, three variants a dry, a mid (best estimate median) and a wet variant are presented in more detail and are used in river and groundwater modelling Future climate and future development Future climate and future development referred to as Scenario D considers the dry, mid and wet climate variants from the future climate and current development Scenario C together with likely expansions in farm dams and commercial forestry plantations and the changes in groundwater extractions anticipated under existing groundwater plans. 1 Introduction Farm dams here refer only to dams with their own water supply catchment, not those that store water diverted from a nearby river, as the latter require licenses and are usually already included within existing river system models. A 23 farm dam development scenario for the MDB has been developed by considering current distribution and policy controls and trends in farm dam expansion. The increase in farm dams in each subcatchment is estimated using simple regression models that consider current farm dam distribution, trends in farm dam (Agrecon, 25) or population growth (Australian Bureau of Statistics, 24; and Victorian Department of Sustainability and Enviroment (DSE), 24) and current policy controls (Queensland Government, 2; New South Wales Government, 2; Victoria Government, 1989; South Australia Government, 24). Data on the current extent of farm dams is taken from the 27 Geosciences Australia Man-made Hydrology GIS coverage and from the 26 VicMap 1:25, topographic GIS coverage. The former covers the eastern region of Queensland MDB and the north-eastern and southern regions of the New South Wales MDB. The latter data covers the entire Victorian MDB. A 23 scenario for commercial forestry plantations for the MDB has been developed using regional projections from the Bureau of Rural Sciences which takes into account trends, policies and industry feedbacks. The increase in commercial forestry plantations is then distributed to areas adjacent to existing plantations (which are not natural forest land use) with the highest biomass productivity estimated from the PROMOD model (Battaglia and Sands, 1997). Growth in groundwater extractions has been considered in the context of existing groundwater planning and sharing arrangements and in consultation with State agencies. For groundwater the following issues have been considered: growth in groundwater extraction rates up to full allocation improvements in water use efficiency due to on-farm changes and lining of channels water buy-backs. 1.4 Rainfall-runoff modelling The adopted approach provides a consistent way of modelling historical runoff across the MDB and assessing the potential impacts of climate change and development on future runoff. The lumped conceptual daily rainfall-runoff model, SIMHYD, with a Muskingum routing method (Chiew et al., 22; Tan et al., 25), is used to estimate daily runoff at.5 o grids (~ 5 km x 5 km) across the entire MDB for the four scenarios. The model is calibrated against 1975 to 26 streamflow data from about 2 unregulated catchments of 5 km 2 to 2 km 2 across the MDB (calibration catchments). Although unregulated, streamflow in these catchments for the calibration period may reflect low levels of water diversion and the effects of historical land use change. The calibration period is a compromise between a shorter period that would better represent current development and a longer period CSIRO 27 November 27 Water availability in the Border Rivers 5

18 that would better account for climatic variability. In the model calibration, the six parameters in SIMHYD are optimised to maximise an objective function that incorporates the Nash-Sutcliffe efficiency (Nash and Sutcliffe, 197) of monthly runoff and daily flow duration curve, together with a constraint to ensure that the total modelled runoff over the calibration period is within five percent of the total recorded runoff. The resulting optimised model parameters are therefore identical for all cells within a calibration catchment. The runoff for non-calibration catchments is modelled using optimised parameter values from the geographically closest calibration catchment, provided there is a calibration catchment point within 25 km. Once again the parameter values for each grid cell within a non-calibration catchment are identical. For catchments more than 25 km from a calibration catchment default point the parameter values are used. The default parameter values are taken from the entire MDB modelling run (identical parameters across the entire MDB are chosen to ensure a realistic runoff gradient across the drier parts of the MDB) which best matched observed flows at calibration points. The places these default values are used are therefore all areas of very low runoff. 1 Introduction As the parameter values come from calibration against streamflow from 5 km 2 to 2 km 2 catchments, the runoff defined here is different, and can be much higher, than streamflow recorded over very large catchments where there can be significant transmission losses (particularly in the western and north-western parts of the MDB). Almost all of the catchments available for model calibration are in the higher runoff areas in the eastern and southern parts of the MDB. Runoff estimates are therefore generally good in the eastern and southern parts of the MDB and are comparatively poor elsewhere. The same model parameter values are used for all the simulations. The future climate Scenario C simulations therefore do not take into account the effect on forest water use of global warming and enhanced atmospheric CO 2 concentrations. There are compensating positive and negative global warming impacts on forest water use, and it is difficult to estimate the net effect because of the complex climate-biosphere-atmosphere interactions and feedbacks. This is discussed in Marcar et al. (26) and in Chiew et al. (27b). Bushfire frequency is also likely to increase under the future climate Scenario C. In local areas where bushfires occur, runoff would reduce significantly as forests regrow. However, the impact on runoff averaged over an entire reporting region is unlikely to be significant (see Chiew et al., 27b). For the Scenario D (future climate and future development scenario) the impact of additional farm dams on runoff is modelled using the CHEAT model (Nathan et al., 25) which takes into account rainfall, evaporation, demands, inflows and spills. The impact of additional plantations on runoff is modelled using the FCFC model (Forest Cover Flow Change), Brown et al. (26) and The rainfall-runoff model SIMHYD is used because it is simple and has relatively few parameters and, for the purpose of this project, provides a consistent basis (that is automated and reproducible) for modelling historical runoff across the entire MDB and for assessing the potential impacts of climate change and development on future runoff. It is possible that, in data-rich areas, specific calibration of SIMHYD or more complex rainfall-runoff models based on expert judgement and local knowledge as carried out by some state agencies would lead to better model calibration for the specific modelling objectives of the area. Chiew et al. (27b) provide a more detailed description of the rainfall-runoff modelling, including details of model calibration, cross-verification and regionalisation with both the SIMHYD and Sacramento rainfall-runoff models and simulation of climate change and development impacts on runoff. 1.5 River system modelling The project is using river system models that encapsulate descriptions of current infrastructure, water demands, and water management and sharing rules to assess the implications of the changes in inflows described above on the reliability of water supply to users. Given the time constraints of the project and the need to link the assessments to State water planning processes, it is necessary to use the river system models currently used by State agencies, the Murray-Darling Basin Commission and Snowy Hydro Ltd. The main models in use are IQQM, REALM, MSM-Bigmod, WaterCRESS and a model of the Snowy Mountains Hydro-electric Scheme. The modelled runoff series from SIMHYD are not used directly as subcatchment inflows in these river system models because this would violate the calibrations of the river system models already undertaken by State agencies to different runoff series. Instead, the relative differences between the daily flow duration curves of the historical climate Scenario A 6 Water availability in the Border Rivers November 27 CSIRO 27

19 and the remaining scenarios (Scenarios B, C and D respectively) are used to modify the existing inflows series in the river system models (separately for each season). The Scenarios B, C and D inflow series for the river system modelling therefore have the same daily sequences but different amounts as the Scenario A river system modelling series. Table 1-1. River system models in the Murray-Darling Basin Model Description Rivers modelled IQQM Integrated Quantity-Quality Model: hydrologic modelling tool developed by the NSW Government for use in planning and evaluating water resource management policies. Paroo, Warrego, Condamine-Balonne (Upper, Mid, Lower), Nebine, Moonie, Border Rivers, Gwydir, Peel, Namoi, Castlereagh, Macquarie, Marthaguy, Bogan, Lachlan, Murrumbidgee, Barwon-Darling REALM Resource Allocation Model: water supply system simulation tool package for modelling water supply systems configured as a network of nodes and carriers representing reservoirs, demand centres, waterways, pipes, etc. MSM-BigMod Murray Simulation Model and the daily forecasting model Murray BigMod: purpose-built by the Murray-Darling Basin Commission to manage the Murray River system. MSM is a monthly model that includes the complex Murray accounting rules. The outputs from MSM form the inputs to BigMod, which is the daily routing engine that simulates the movement of water. Ovens (Upper, Lower), Goulburn, Wimmera, Avoca, ACT water supply. 1 Introduction WaterCRESS Water Community Resource Evaluation and Simulation System: PC-based water management platform incorporating generic and specific hydrological models and functionalities for use in assessing water resources and designing and evaluating water management systems. Eastern Mt Lofty Ranges (six separate catchments) SMHS Snowy Mountains Hydro-electric Scheme model: purpose built by Snowy Hydro Ltd to guide the planning and operation of the SMHS. Snowy Mountains Hydro-electric Scheme A few areas of the MDB have not previously been modelled and hence some new IQQM or REALM models have been implemented. In some cases ancillary models are used to estimate aspects of water demands of use in the river system model. An example is the PRIDE model used to estimate irrigation for Victorian REALM models. River systems that do not receive inflows or transfers from upstream or adjacent river systems are modelled independently. This is the case for most of the river systems in the MDB and for these rivers the modelling steps are: model configuration model warm-up to set initial values for all storages in the model, including public and private dams and tanks, river reaches and soil moisture in irrigation areas using scenario climate and inflow time series, run the river model for all climate and development scenarios where relevant, extract initial estimates of surface-groundwater exchanges and provide this to the groundwater model where relevant, use revised estimates of surface-groundwater exchanges from groundwater models and re-run the river model for all scenarios. For river systems that receive inflows or transfers from upstream or adjacent river systems, model inputs for each scenario were taken from the upstream models. In a few cases several iterations were required between upstream and downstream models because of the complexities of the water management arrangements. An example is the connections between the Murray, Murrumbidgee and Goulburn regions and the Snowy Mountains Hydro-electric Scheme. CSIRO 27 November 27 Water availability in the Border Rivers 7

20 1.5.1 Surface-groundwater interactions The project is explicitly considering and quantifying the water exchanges between rivers and groundwater systems. The approaches used are described below. The river models used by State agencies have in turn typically been calibrated by State agencies to achieve mass balance within calibration reaches over relatively short time periods. When the models are run for extended periods the relationships derived during calibration are assumed to hold for the full modelling period. In many cases however, the calibration period is a period of changing groundwater extraction and a period of changing impact of this extraction on the river system. That is, the calibration period is often one of changing hydrologic relationships, a period where the river and groundwater systems have not fully adjusted to the current level of groundwater development. To provide a consistent equilibrium basis for scenario comparisons it is necessary to determine the equilibrium conditions of surface and groundwater systems considering their interactions and the considerable lag times involved in reaching equilibrium. 1 Introduction Figure 1-3 shows an indicative timeline of groundwater use, impact on river, and how this has typically been treated in river model calibration, and what the actual equilibrium impact on the river would be. By running the groundwater models until a dynamic equilibrium is reached, a reasonable estimate of the ultimate impact on the river of current groundwater use is obtained. A similar approach is used to determine the ultimate impact of future groundwater use. Figure 1-3. Timeline of groundwater use and resultant impact on river For some groundwater management units particularly fractured rock aquifers there is significant groundwater extraction but no model available for assessment. In these cases there is the potential for considerable impacts on streamflow. At equilibrium, the volume of water extracted must equal the inflows to the aquifer from diffuse recharge, lateral flows and flows from overlying rivers. The fraction that comes from the overlying rivers is determined using a connectivity factor that is estimated from the difference in levels between the groundwater adjacent to the river and the river itself, the conductance between the groundwater pump and the river, and the hydrogeological setting. Given the errors inherent in this method, significant impacts are deemed to be those about 2 GL/year for a subcatchment, which given typical connectivity factors translates to groundwater extraction rates of around 4 GL/year for a subcatchment. 8 Water availability in the Border Rivers November 27 CSIRO 27

21 1.6 Monthly water accounts Monthly water accounts provide an independent set of the different water balance components by river reach and by month. The water accounting differs from the river modelling in a number of key aspects: the period of accounting extends to 26 where possible, which is typically more recent than the calibration and evaluation periods of the river models assessed. This means that a comparison can produce new insights about the performance and assumptions in the river model, as for example associated with recent water resources development or the recent drought in parts of the MDB the accounting is specifically intended to estimate, as best as possible, historical water balance patterns, and used observed rather than modelled data wherever possible (including recorded diversions, dam releases and other operations). This reduces the uncertainty associated with error propagation and assumptions in the river model that were not necessarily intended to reproduce historical patterns (e.g. differences in actual historical and potential future degree of entitlement use) the accounting uses independent, additional observations and estimates on water balance components not used before such as actual water use estimates derived from remote sensing observations. This can help to constrain the water balance with greater certainty. Despite these advantages, it is emphasised that the water accounting methodology invokes models and indirect estimates of water balance components where direct measurements are not available. Because of this, these water accounts are not an absolute point of truth. Rather, they provide an estimate of the degree to which the river water balance is understood and gauged, and a comparison between river model and water account water balances provides one of several lines of evidence to inform our (inevitably partially subjective) assessment of model uncertainty and its implications for the confidence in our findings. The methods for water accounting are based on existing methods and those used by Kirby et al. (26) and Van Dijk et al. (27) and are described in detail in Kirby et al. (27). 1 Introduction Wetland and irrigation water use An important component of the accounting is an estimate of actual water use based on remote sensing observations. Spatial time series of monthly net water use from irrigation areas, rivers and wetlands are estimated using interpolated station observations of rainfall and climate combined with remote sensing observations of surface wetness, greenness and temperature. Net water use of surface water resources is calculated as the difference between monthly rainfall and monthly actual evapotranspiration (AET). AET estimates are based on a combination of two methods. The first method uses surface temperature remotely sensed by the AVHRR series of satellite instruments for the period 199 to 26 and combines this with spatially interpolated climate variables to estimate AET from the surface energy balance (McVicar and Jupp, 22). The second method loosely follows the FAO56 crop factor approach and scales interpolated potential evaporation (PET) estimates using observations of surface greenness and wetness by the MODIS satellite instrument (Van Dijk et al., 27). The two methods are constrained using direct on-ground AET measurements at seven study sites and catchment stream flow observations from more than 2 catchments across Australia. Both methods provide AET estimates at 1 km resolution. The spatial estimates of net water use are aggregated for each reach and separately for all areas classified as either irrigation area or floodplains and wetlands. The following digital data sources were used: land use grids for 2/21 and 21/2 from the Bureau of Rural Sciences (adl.brs.gov.au/mapserv/landuse/) NSW wetlands maps from the NSW Department of Environment and Conservation, (NSW DEC) hydrography maps, including various types of water bodies and periodically inundated areas, from Geoscience Australia (GA maps; Topo25K Series 3) long-term rainfall and AET grids derived as outlined above LANDSAT satellite imagery for the years 1998 to 24. CSIRO 27 November 27 Water availability in the Border Rivers 9

22 The reach-by-reach estimates of net water use from irrigation areas and from floodplains and wetlands are subject to the following limitations: 1 Introduction partial validation of the estimates suggested an average accuracy in AET estimation within 15 percent, but probably decreasing with the area over which estimates are averaged. Uncertainty in spatial estimates originates from the interpolated climate and rainfall data as well as from the satellite observations and the method applied errors in classification of irrigation and floodplain/wetland areas may have added an unknown uncertainty to the overall estimates, particularly where subcatchment definition is uncertain or wetland and irrigation areas are difficult to discern estimated net water use cannot be assumed to have been derived from surface water in all cases as vegetation may also have access to groundwater use, either directly or through groundwater pumping estimated net water use can be considered as an estimate of water demand that apparently is met over the long-term. Storage processes, both in irrigation storages and wetlands, need to be simulated to translate these estimates in monthly (net) losses from the river main stem. Therefore, the AET and net water use estimates are used internally to conceptual water balance models of wetland and irrigation water use that include a simulated storage as considered appropriate based on ancillary information Calculation and attribution of apparent ungauged gains and losses In a river reach, ungauged gains or losses are the difference between the sum of gauged main stem and tributary inflows, and the sum of main stem and distributary outflows and diversions. This would be equal to measured main stem outflows and water accounting could occur with absolute certainty. The net sum of all gauged gains and losses provides an estimate of ungauged apparent gains and losses. There may be differences between apparent and real gains and losses for the following reasons: apparent ungauged gains and losses will also include any error in discharge data that may originate from errors in stage gauging or from the rating curves associated to convert stage height to discharge ungauged gains and losses can be compensating and so appear smaller than in reality. This is more likely to occur at longer time scales. For this reason water accounting was done on a monthly time scale changes in water storage in the river reach, connected reservoirs, or wetlands, can lead to apparent gains and losses that become more important as the time scale of analysis decreases. A monthly time scale has been chosen to reduce storage change effects, but they can still occur. The monthly pattern of apparent ungauged gains and losses are evaluated for each reach in an attempt to attribute them to real components of water gain or loss. The following techniques are used in sequence: analysis of normal (parametric) and ranked (non-parametric) correlation between apparent ungauged gains and losses on one hand, and gauged and estimated water balance components on the other hand. Estimated components included SIMHYD estimates of monthly local inflows and remote sensing-based estimates of wetland and irrigation net water use visual data exploration: assessment of temporal correlations in apparent ungauged gains and losses to assess trends or storage effects, and comparison of apparent ungauged gains and losses and a comparison with a time series of estimated water balance components. Based on the above information, apparent gains and losses are attributed to the most likely process, and an appropriate method was chosen to estimate the ungauged gain or loss using gauged or estimated data. 1 Water availability in the Border Rivers November 27 CSIRO 27

23 The water accounting model includes the following components: a conceptual floodplain and wetland running a water balance model that estimates net gains and losses as a function of remote sensing-based estimates of net water use and main stem discharge observations a conceptual irrigation area running a water balance model that estimates (net) total diversions as a function of any recorded diversions, remote sensing-based estimates of irrigated area and net crop water use, and estimates of direct evaporation from storages and channels a routing model that allows for the effect of temporary water storage in the river system and its associated water bodies and direct open water evaporation a local runoff model that transforms SIMHYD estimates of local runoff to match ungauged gains. These model components are will be described in greater detail in Kirby et al. (27) and are only used where the data or ancillary information suggests their relevance. Each component has a small number of unconstrained or partially constrained parameters that need to be estimated. A combination of direct estimation as well as step-wise or simultaneous automated optimisation is used, with the goal to attribute the largest possible fraction of apparent ungauged gains and losses. Any large residual losses and gains suggest error in the model or its input data. 1.7 Groundwater modelling 1 Introduction Groundwater assessment, including groundwater recharge modelling, is undertaken to assess the implications of the climate and development scenarios on groundwater management units (GMUs) across the MDB. A range of methods are used appropriate to the size and importance of different GMUs. There are over 1 GMUs in the MDB, and the choice of methods was based on an objective classification of the GMUs as high, medium or low priority. Rainfall-recharge modelling is undertaken for all GMUs. For dryland areas, daily recharge was assessed using a model that considered plant physiology, water use and soil physics to determine vertical water flow in the unsaturated zone of the soil profile at a single location. This model is run at multiple locations across the MDB in considering the range of soil types and land uses to determine scaling factors for different soil and land use conditions. These scaling factors are used to scale recharge for given changes in rainfall for all GMUs according to local soil types and land uses. For many of the higher priority GMUs, recharge is largely from irrigation seepage. In New South Wales this recharge has been embedded in the groundwater models as a percentage of the applied water. For irrigation recharge, information was collated for different crop types, irrigation systems and soil types, and has been used for the scenario modelling. For high priority GMUs numerical groundwater models are being used. In most cases these already exist but often require improvement. In some cases new models are being developed. Although the groundwater models have seen less effort invested in their calibration than the existing river models, the project has invested considerable effort in model calibration and various cross-checks to increase the level of confidence in the groundwater modelling. For each groundwater model, each scenario is run using river heights as provided from the appropriate river system model. For recent and future climate scenarios, adjusted recharge values are also used, and for future development the 23 groundwater extractions levels are used. The models are run for two consecutive 111-year periods. The average surface-groundwater flux values for the second 111-year period are passed back to the river models as the equilibrium flux. The model outputs are used to assess indicators of groundwater use and reliability. For lower priority GMUs no models are available and the assessments are limited to simple estimates of recharge, estimates of current and future extraction, allocation based on State data, and estimates of the current and future impacts of extraction on streamflow where important. 1.8 Environmental assessment Environmental assessments on a region by region basis consider the environmental assets already identified by State governments or the Australian Government that are listed in the Directory of Important Wetlands in Australia (Environment Australia, 21) or the updated on-line database of the directory. From this directory, environmental assets CSIRO 27 November 27 Water availability in the Border Rivers 11

24 are selected for which there exists sufficient publicly available information on hydrological indicators (such as commenceto-fill levels) which relate to ecological responses such as bird breeding events. Information sources include published research papers and reports, accessible unpublished technical reports, or advice from experts currently conducting research on specific environmental assets. In all cases the source of the information on the hydrological indicators used in each assessment is cited. The selection of the assets for assessment and hydrologic indicators was undertaken in consultation with State governments and the Australian Government through direct discussions and through reviews by the formal internal governance and guidance structures of the project. 1 Introduction The Directory of Important Wetlands in Australia (Environment Australia, 21) lists over 2 wetlands in the MDB. Information on hydrological indicators of ecological response adequate for assessing scenario changes only exists for around one-tenth of these. More comprehensive environmental assessments are beyond the terms of reference for the project. The Australian Department of Environment and Water Resources has separately commissioned a compilation of all available information on the water requirements of wetlands in the MDB that are listed in the Directory of Important Wetlands in Australia. For regions where the above selection criteria identify no environmental assets, the river channel itself is considered as an asset and ecologically-relevant hydrologic assessments are reported for the channel. The locations for which these assessments are provided are guided by prior studies. In the Victorian regions for example, detailed environmental flow studies have been undertaken which have identified environmental assets at multiple river locations with associated hydrological indicators. In these cases a reduced set of locations and indicators has been selected in direct consultation with the Victorian Department of Sustainability and Environment. In regions where less information is available, hydrological indicators may be limited to those that report on the water sharing targets that are identified in water planning policy or legislation. Because the environmental assessments are a relatively small component of the project, a minimal set of hydrological indicators are used in assessments. In most cases this minimum set includes change in the average period between events and change in the maximum period between events as defined by the indicator. A quality assurance process is applied to the results for the indicators obtained from the river system models which includes checking the consistency of the results with other river system model results, comparing the results to other published data and with the asset descriptions, and ensuring that the river system model is providing realistic estimates of the flows required to evaluate the particular indicators. 1.9 References Agrecon (25) Agricultural Reconnaissance Technologies Pty Ltd Hillside Farm Dams Investigation. MDBC Project 4/4677DO. Australian Bureau of Statistics (24) Population projections for Statistical Local Areas 22 to 222. Available at: Battaglia M and Sands P (1997) Modelling site productivity of Eucalyptus globulus in response to climatic and site factors. Australian Journal of Plant Physiology 24, Brown AE, Podger PM, Davidson AJ, Dowling TI and Zhang L (26) A methodology to predict the impact of changes in forest cover on flow duration curves. CSIRO Land and Water Science Report 8/6. CSIRO, Canberra. Chiew et al. (27a) Climate data for hydrologic scenario modelling across the Murray-Darling Basin. A report to the Australian Government from the CSIRO Murray-Darling Basin Sustainable Yields Project. CSIRO, Australia. In prep. Chiew et al. (27b) Rainfall-runoff modelling across the Murray-Darling Basin. A report to the Australian Government from the CSIRO Murray-Darling Basin Sustainable Yields Project. CSIRO, Australia. In prep. Chiew FHS (26) An overview of methods for estimating climate change impact on runoff. Paper prepared for the 3th Hydrology and Water Resources Symposium, December 26, Launceston. Chiew FHS and Leahy C (23) Comparison of evapotranspiration variables in Evapotranspiration Maps of Australia with commonly used evapotranspiration variables. Australian Journal of Water Resources 7, Chiew FHS, Peel MC and Western AW (22) Application and testing of the simple rainfall-runoff model SIMHYD. In: Singh VP and Frevert DK (Ed.s), Mathematical Models of Small Watershed Hydrology and Application. Littleton, Colorado, pp DSE (24) Victoria in Future 24 Population projections. Department of Sustainability and Environment, Victoria. Available at: Environment Australia (21) A Directory of Important Wetlands in Australia. Available at: IPCC (27) Climate Change 27: The Physical Science Basis. Contributions of Working Group 1 to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press. Jeffrey SJ, Carter JO, Moodie KB and Beswick AR (21) Using spatial interpolation to construct a comprehensive archive of Australian climate data. Environmental Modelling and Software 16, Water availability in the Border Rivers November 27 CSIRO 27

25 Kirby J, Mainuddin M, Podger G and Zhang L (26) Basin water use accounting method with application to the Mekong Basin. In: Sethaputra S and Promma K (eds) Proceedings on the International Symposium on Managing Water Supply for Growing Demand, Bangkok, Thailand, 16 2 October 26. Jakarta: UNESCO Kirby J et al. (27) Uncertainty assessments for scenario modelling. A report to the Australian Government from the CSIRO Murray- Darling Basin Sustainable Yields Project, CSIRO Australia. In prep. Marcar NE, Benyon RG, Polglase PJ, Paul KI, Theiveyanathan S and Zhang L (26) Predicting the Hydrological Impacts of Bushfire and Climate Change in Forested Catchments of the River Murray Uplands: A Review. CSIRO Water for a Healthy Country. McVicar TR and Jupp DLB (22) Using covariates to spatially interpolate moisture availability in the Murray-Darling Basin. Remote Sensing of Environment 79, Nash JE and Sutcliffe JV (197) River flow forecasting through conceptual models 1: A discussion of principles. Journal of Hydrology 1, Nathan RJ, Jordan PW and Morden R (25) Assessing the impact of farm dams on streamflows 1: Development of simulation tools. Australian Journal of Water Resources 9, New South Wales Government (2) Water Management Act 2 No 92. Queensland Government (2) Water Act 2. South Australia Government (24) Natural Resources Management Act 24. Tan KS, Chiew FHS, Grayson RB, Scanlon PJ and Siriwardena L (25) Calibration of a daily rainfall-runoff model to estimate high daily flows. Paper prepared for the Congress on Modelling and Simulation (MODSIM 25), December 25. Melbourne, Australia. pp Van Dijk A et al. (27) Reach-level water accounting for across the Murray-Darling Basin. A report to the Australian Government from the CSIRO Murray-Darling Basin Sustainable Yields Project. CSIRO, Australia. In prep. Victoria Government (1989) Water Act 1989, Act Number 8/ Introduction CSIRO 27 November 27 Water availability in the Border Rivers 13

26 2 Overview of the region 2 Overview of the region The Border Rivers region is in southern Queensland and northeastern New South Wales and represents 4 percent of the area of the Murray-Darling Basin (MDB). The region is based around the Macintyre Brook and the Dumaresq River which joins the Macintyre River that ultimately becomes the Barwon River. The population is around 5, or 2.5 percent of the MDB total, concentrated in the major centres of Glen Innes, Inverell, Tenterfield, Stanthorpe, Inglewood, Mungindi and Goondiwindi. The dominant land use is broadacre livestock grazing, particularly on the tablelands, with a shift to cropping on the slopes and plains. In the year 2, there were approximately 75,3 ha of irrigated cropping with cotton accounting for over 75 percent of this area. There is a small amount of commercial plantation forestry and large numbers of farm dams and ring tanks in the region. The nationally significant wetland Morella Watercourse/Boobera Lagoon/Pungbougal Lagoon 6 km south-west of Goondiwindi in New South Wales is considered to be one of the most important Aboriginal places in eastern Australia. The region uses 4.4 percent of the surface water diverted for irrigation and slightly less than 2 percent of the MDB groundwater resource that is used. A number of major water storages constructed since the late 196s enable irrigated agriculture on the plains. There are seven groundwater management units (GMUs) in the southern part of the region. Over 9 percent of the water used for irrigation is diverted from surface water resources. However, groundwater use is high, and is a particularly important resource in dry years. The following sections summarise the region s biophysical features including rainfall, topography, land use and the environmental assets of significance. It outlines the institutional arrangements for the region s natural resources and presents key features of the surface and groundwater resources of the region including historical water use. 2.1 The region The Border Rivers region covers 43,633 km 2 or 4 percent of the area of the MDB. The region is bounded to the east by the Great Dividing Range, to the north by the Condamine-Balonne and Moonie regions, to the south by the Gwydir region and to the west by the Barwon-Darling region. In this project, the region terminates at three points being the Barwon River at Mungindi, the Boomi River at Neeworra and at Gil Gil Creek at Weemalah. Major water resources in the Border Rivers region include Macintyre Brook, Dumaresq River and the Macintyre River which continues to become the Barwon River, the Great Artesian Basin, alluvial aquifers, wetlands and water storages. Private and public infrastructure including Pindari, Glenlyon and Coolmunda dams are associated with these water resources. Annual rainfall (mm) Mean monthly rainfall (mm) J F M A M J J A S O N D Figure annual and monthly rainfall averaged over the region (the curve on the annual graph shows the low frequency variability) 14 Water availability in the Border Rivers November 27 CSIRO 27

27 The mean annual rainfall is 641 mm varying from 12 mm in the east to 5 mm in the west. Summer is typically the wettest season. The region s average annual rainfall has remained relatively consistent over the past 111 years (Figure 2-1). The mean annual rainfall for 1997 to 26 was not significantly different from the long-term mean. The Border Rivers region contributes about 5 percent of the total runoff in the MDB. The mean annual modelled runoff over the region for the 111-year period is 32 mm. This level of runoff is four times higher than that modelled for the northwestern regions of the MDB. The mean annual runoff over the ten-year period 1997 to 26 is similar to the longterm mean. The runoff estimates in the Border Rivers region, particularly the eastern half of the region, are relatively good because there are many gauged catchments from which model parameter values are estimated. The region has approximately 5, people which is 2.5 percent of the total MDB population. The major towns are Glen Innes, Inverell, Tenterfield, Stanthorpe, Inglewood, Mungindi and Goondiwindi. The dominant land use is broadacre livestock grazing, particularly on the tablelands, with a shift to cropping on the slopes. There is an increasing use of irrigation on the western plains, which has caused intensification of farming enterprises predominantly cotton. Irrigation is mostly from surface water diversions although groundwater is used predominantly in the Dumaresq River valley and around Croppa Creek to irrigate fodder crops. Irrigated crop production covered 75,3 ha in 2. Small-scale crops such as grapes, stone fruit, vegetables and apples are grown on the upland areas. Mixed cash crops are grown in the middle reaches of the region and cotton growing is dominant in the lower reaches downstream of Boggabilla (DNRM, 22). Cotton accounted for over 75 percent of the irrigated crop area in 2. The land use area (Table 2-1) and land use map (Figure 2-2) are based on the 2 land use of the MDB grid, derived from 21 Bureau of Rural Sciences AgCensus data. Irrigation estimates are based on crop areas recorded as irrigated in the census. 2 Overview of the region Table 2-1. Summary of land use in the year 2 within the Border Rivers region Land use Area percent ha Dryland crops 13.1% 572,2 Dryland pasture 63.6% 2,774,8 Irrigated crops 1.7% 75,3 Cereals 7.2% 5,4 Cotton 76.1% 57,3 Horticulture 3.9% 2,9 Orchards 5.6% 4,2 Pasture and hay 6.4% 4,9 Vine fruits.8% 6 National parks and State forests 21.2% 921,7 Plantation forests.1% 3,5 Urban.2% 1,2 Water.1% 3,1 Total 1.% 4,36,8 Source: BRS (2) CSIRO 27 November 27 Water availability in the Border Rivers 15

28 2 Overview of the region Figure 2-2. Map of dominant land uses of the Border Rivers region with inset showing the region s location within the Murray-Darling Basin Within the New South Wales part of the region, a regional catchment plan the Border Rivers-Gwydir Catchment Action Plan provides a strategy for managing natural resources in the region. It was prepared under the Catchment Management Authorities Act 23 and commenced in June 26 for a period of ten years. The plan is structured around four themes: community, biodiversity and native vegetation, water, and soils and land use. Under each theme, the plan provides an indication of the current resource condition, the pressures or challenges faced by the resource and how the targets determined by the Authority will achieve improvements in the resource (BRGCMA, 26). The water catchment target within this plan is: by 215 to maintain or improve the condition of all subcatchments across the catchment based on the scores from the 21 Riverine Condition Assessment (RCA) index. The intent of this target is to improve the condition of individual subcatchments in the region leading to an overall improvement in the RCA Index. There are 15 of the 5 subcatchments in the Plan area that have been rated as either in fair or poor condition. The development of the Border Rivers-Gwydir Catchment Action Plan considers the State Water Management Outcomes Plan and is consistent with water sharing plans gazetted under the Water Management Act 2. The Queensland Murray-Darling Committee Incorporated is the regional body for the Border Rivers Maranoa-Balonne natural resource management region. This committee and South West Natural Resource Management Limited, in consultation with local communities, developed a joint regional plan that covers both the Border Rivers Maranoa-Balonne and South West Queensland natural resource management regions. 16 Water availability in the Border Rivers November 27 CSIRO 27

29 This Regional Natural Resource Management Plan 24 (NRM Plan) is a framework to guide coordinated and holistic planning and on-ground action to improve the management and condition of the natural resources in the region (QMDC and SWNRM, 24). The NRM Plan identifies resource condition targets and prioritises innovative management strategies to improve catchment health and protect regional assets. The aspirational resource condition and management action targets for water are primarily based on the principles in the Queensland Water Resource Plans. These plans are discussed in more detail in the following sections. The aspirational targets for water are: water is efficiently used by 235 groundwater is sustainably managed for long-term environmental, production and social values by 235 surface water is sustainably managed for long-term environmental, production and social values by 235. The statutory responsibility for the development of a water resource plan in the Queensland section of the Border River sits with the Queensland Department of Natural Resources and Water. In developing the Water Resource Plan for the region, the Department engaged a range of stakeholders in the plan area including the Queensland Murray-Darling Committee. The resource condition targets seek to incorporate the objectives from the Strategic Management Plan for the Great Artesian Basin (GABCC, 2) and the objectives from the Water Resource Plan. 2.2 Environmental description The Border Rivers region spans the high country in the east to the wide alluvial western plains and contains distinct tablelands, slopes and plains landforms. There are four main bioregions within the region and the vegetation varies from high altitude areas in the east, consisting of patches of extensively forested areas to the graduation west of more open forest, shrublands and grassy plains. The tablelands area lies east of Texas and Ashford and is characterised by granite and basalt tablelands. The slopes region lies west of Ashford and Texas to below Boggabilla and is characterised by undulating country with numerous permanent and semi-permanent billabongs. The plains region is downstream of Boggabilla where the terrain is undulating to flat. Floodplains stretch west towards Mungindi. 2 Overview of the region The Border Rivers are made up of a number of streams which provide a wide range of aquatic habitats. Thoms et al. (1997, cited in Markham (1999)) identified five broad river reach types throughout the catchment, these being pools, constrained reaches, armoured reaches, mobile reaches and anabranching reaches. The anabranching reach downstream of Goondiwindi is the longest and contains large areas of anabranches and billabongs (Thoms et al., 25). Current water resource development and river operations have decreased the average frequency of inundation of a range of billabongs on the Macintyre River floodplain by between 12 and 17 percent (Thoms et al., 25); see also Chapter 7. The riparian vegetation of the lower portions of the Border Rivers is dominated by River Red Gum (Eucalyptus camaldulensis), Coolabah (E coolabah) and River Oak (Casuarina cunninghamiana), with Weeping Bottlebrush (Callistemon viminalis) a common understorey (McCosker, 1999). The floodplain between Goondiwindi and Mungindi contains large areas of anabranches and billabongs. When flooded, these provide large amounts of organic carbon, which is essential to aquatic ecosystem functioning. Downstream from Goondiwindi small effluent creeks such as Boomi, Callandoon, Dingo and Whalan break off from the main channel and meander across the region forming a complex floodplain of billabongs and wetlands that rely on over-bank flows (Kingsford, 1999). These wetlands support the breeding of waterbirds listed under the New South Wales Threatened Species Conservation Act (1995) including Brolgas, Black-necked Storks and Magpie Geese. The single wetland within the region that is listed in the Directory of Wetlands in Australia as having national importance (Environment Australia, 21) is detailed in Table 2-2. Wetlands may be nationally or regionally significant depending on more locally specific criteria. All wetlands are important for a variety of ecological reasons or because they bear historical significance or have high cultural value, particularly to Aboriginal people. CSIRO 27 November 27 Water availability in the Border Rivers 17

30 Table 2-2. Ramsar wetlands and wetlands of national significance located within the Border Rivers region Site code Directory of Important Wetlands of Australia Area* (ha) RAMSAR sites NSW95 Morella Watercourse/Boobera Lagoon/Pungbougal Lagoon 46 No * Wetland areas have been extracted from the Australian Wetlands Database and are assumed to be correct as provided from State and Territory agencies Source: Environment Australia (21) 2 Overview of the region The Morella Watercourse/Boobera Lagoon/Pungbougal Lagoon is located on the Macintyre River floodplain. This area floods from the river approximately once in ten years on average (Environment Australia, 21). Boobera Lagoon is considered to be one of the most important Aboriginal places in eastern Australia. Local Aboriginal people believe the lagoon is the resting place of the rainbow serpent and the immediate area contains numerous Aboriginal artefacts. The lagoon remains important to Aboriginal people today (Environment Australia, 21). McCosker (1999) also identified Maynes, Telephone, Callendoon and Serpentine lagoons as significant wetlands within the region. A number of Identified Ecological Features are listed in the draft Water Sharing Plan for the New South Wales Border Rivers Regulated Water Source (DWE, 27a). Some dryland salinity occurs in the Border Rivers alluvial landscape and the interface with the Brigalow Plains to the north is identified as a key hazard area. The extensive irrigation of sodic and saline clays in some areas could increase salt leaching. Associated deep drainage could elevate watertables. Monitoring bores on the Macintyre River floodplains downstream of Goondiwindi indicate groundwater at depths of 1 m to 25 m with salinity ranging from 14, to 45, µs/cm. Several older bores close to broadacre irrigation areas show rising groundwater trends. Overall stream salinity in the Border Rivers region is rated as either low (<2 µs/cm) or low to moderate (2 to 4 µs/cm) according to the NRM Plan. 2.3 Surface water resources Rivers and storages The Border Rivers region includes a number of rivers that generally flow from the east and northeast in a westerly direction. Principal streams are the Macintyre River and Severn River (NSW) in the south-east, the Dumaresq River and Severn River (Qld) in the east, Macintyre Brook in the north and the Weir River in the north-west. The state border follows the Dumaresq River and the Macintyre River below its junction with the Dumaresq River downstream to Mungindi. This is referred to as the common trunk stream. The Macintyre River drains in a northwesterly direction through large areas of relatively flat terrain except around Ashford and to the east, where hilly to steep slopes predominate. The Severn River in New South Wales which is the Macintyre s principal tributary originates in the elevated region between Emmaville and Ben Lomond. The Macintyre River joins the Dumaresq River 16 km upstream of Boggabilla. The Dumaresq River begins at the junction of the Severn River (Qld), the Mole River and Pike Creek about 5 km west of Tenterfield. Tenterfield Creek flows into the Severn River (Qld) just above this junction. The principal tributaries of the Dumaresq River are the Beardy River and Ottley s Creek. About halfway between Texas and Boggabilla the Dumaresq is joined by its last major tributary, the Macintyre Brook, located entirely in Queensland. The Dumaresq River becomes the Macintyre River below its junction with Macintyre Brook. In the lower catchment there are a number of distributary streams and lagoon systems that flow away from the trunk stream only when certain river levels are reached. These include Whalan, Callandoon and Dingo Creeks, the Boomi River and the Little Weir River. The only significant tributary downstream of Boggabilla is the Weir River. For its entire length it flows through Queensland and joins the Macintyre River 23 km upstream of Mungindi. At Newinga the Weir River and Macintyre River almost join. When there is a sizable flow event in the Macintyre, water can flow from it into the lower Weir River. An event in the Weir River reverses the situation. The Macintyre River becomes the Barwon River at its junction with the Weir River. It flows past Mungindi, the end of the Border Rivers system, and becomes the Darling River below Brewarrina and upstream of Bourke. Major water storages 18 Water availability in the Border Rivers November 27 CSIRO 27

31 exist on each of the major rivers. These include the Pindari Dam on the Severn River (NSW), the Glenlyon Dam on the Dumaresq River and Coolmunda Dam on the headwaters of Macintyre Brook. The area of irrigation substantially expanded within the Border Rivers region with the construction of the Pindari Dam in 1969 and of Glenlyon Dam in Small scale irrigation of tobacco, lucerne and other crops commenced many years earlier. The storage capacity of the major dams within the region is estimated to be 641 GL. Pindari Dam had an initial capacity of 38 GL and was enlarged in 1994 to 312 GL. Glenlyon Dam has a capacity 254 GL and Coolmunda Dam has a capacity of 75 GL. Flows from these dams are regulated to Mungindi. A shift towards using unregulated stream systems for irrigation and water harvesting, including harvesting of on-farm overland flow, occurred in the 199s with onfarm storage increasing in Queensland from 185 GL in 1991/92 to 35 GL in 1998/99 (DNRM, 2). The storage capacity of weirs and dams is estimated at 15 GL for weirs, 459 GL for ring tanks and 119 GL for hillside dams across the region (MDBC, 27a). A subsequent study in New South Wales estimates the storage capacity of farm dams at 77 GL (Geosciences Australia, 27) Surface water management institutional arrangements The New South Wales Queensland Border Rivers Agreement 1946 and subsequent amendments provides the basis for the sharing of the surface water resources between the two states. The Dumaresq Barwon Border Rivers Commission was established under this Agreement in 1946 to coordinate management of the rivers. Each state created a New South Wales Queensland Border Rivers Act that ratified the New South Wales Queensland Border Rivers Agreement. This respective state legislation contains the management arrangements for the surface and groundwater resources that the states are entitled to use. The Water Management Act 2 in New South Wales requires the implementation of ten-year plans defining water sharing arrangements between the environment and water users and amongst water user groups. The plans aim to protect rivers and aquifers and their dependent ecosystems, and to provide water users with clarity and certainty regarding water access rights. 2 Overview of the region Water access is based on a long-term average annual extraction limit. The basic rights (native title and domestic and stock) and access licences for domestic and stock use and local water utilities are volumetric and are granted highest access priority. High and general security access licences are based on shares of the water available, with high security having priority over general security. Most general security access licences are expressed as a relative unit share of the available water rather than as an annual volume. Licensing continues under the Water Act 1912 in areas where water sharing plans are not gazetted. A draft Water Sharing Plan for the New South Wales part of the Border Rivers was exhibited until mid-october 27 and applies to all regulated river sections in the New South Wales Border Rivers Water Management Area. This includes Pindari Dam downstream to the junction of the Severn River (NSW) with the Macintyre River, the Macintyre River to the junction of the Barwon River and the Barwon River downstream to Mungindi Weir. The Dumaresq River from the junction of Pike Creek to the junction of the Macintyre River is supplied from Glenlyon Dam and forms part of the New South Wales Border Rivers Regulated River Water Source and the Water Sharing Plan (DWE, 27b). The objectives of the draft Water Sharing Plan regarding the Border Rivers Regulated River Water Source are (DWE, 27a): ensure equitable sharing of water between all uses implement environmental flow rules that protect, maintain and enhance the environmental, cultural and heritage values maintain and where feasible improve the flow related water quality preserve and provide for basic landholder rights preserve and enhance cultural and heritage values provide a market-based trading of surface water entitlements. In 1995 the state governments in the MDB and the Federal Government agreed that a cap should be placed on future surface water diversions. The New South Wales Border Rivers is a special case with regard to cap management because the Pindari Dam enlargement was under construction prior to the cap benchmark year of 1993/94, but was not completed until after the cap was applied to other catchments. CSIRO 27 November 27 Water availability in the Border Rivers 19

32 Hence the cap for the New South Wales Border Rivers is based on the long-term annual average water diversions given the 1993/94 level of development and management, plus an allowance for the enlarged Pindari Dam. The cap is aimed at preventing further growth in diversions and further deterioration in river flow regimes. The Water Sharing Plan defines specific environmental flow rules to improve flow regimes and provide a better balance between river health and water diversions. A water sharing plan limit prevents erosion of environmental flow rules. The limit corresponds with the November 1999 water use and must not exceed the MDB cap. 2 Overview of the region The New South Wales Water Management Act 2 recognises two classes of environmental water, planned environmental water and adaptive environmental water. Planned environmental water is water committed by management plans for fundamental ecosystem health or other specific environmental purposes. Adaptive environmental water is water committed by conditions of access licences for specified environmental purposes. The rules for managing planned environmental water are detailed in Table 2-3. These include a minimum daily release from Pindari dam, translucent flows and stimulus flows. There were no access licences related to adaptive environmental water committed for environmental purposes at the commencement of the draft Water Sharing Plan (DWE, 27a). A water sharing plan for the Tenterfield Creek Water Source 23 (DNRM, 23a), prepared under the New South Wales Water Management Act 2, covers a corresponding area of land within the Border Rivers water management area. Its strategies are to: establish cease and commence to pump levels and flow classes limit the amount of water that can be extracted on a daily basis from different flow classes limit the long-term average diversion of water clearly define access rules and conditions for diverting water from this water source establish rules for determining the water available from time to time under access licences establish water allocation accounting rules specify access licence dealing rules that maximise flexibility for water users without adversely impacting on this water source. Volumetric allocation and metering of regulated streams commenced when licences were issued. These include licence embargoes, maximum annual use limited to nominal allocation, a supplementary water use limit in New South Wales and compliance with the North West Unregulated Flow Management Plan for downstream stock and domestic supplies, algal management and fish migration. In contrast, the unregulated systems are not volumetrically allocated or metered, although programs to convert these area-based licences to volumetric licences have commenced (McCollum, 2). A moratorium was placed on new water entitlements in the region in September 2. Water resources within Queensland are managed under the Water Act 2. The two-tier planning regime involves development of a Water Resource Plan, which sets the strategic rules for water management in a catchment, and a Resource Operations Plan which sets the operational rules. The Water Resource (Border Rivers) Plan 23 covers the entirety of the Queensland portions of the Border Rivers region including the Severn River, Pike Creek, Macintyre Brook, Weir River, and the Queensland portions of the Dumaresq River and Macintyre River to Mungindi (DNRM, 23b). The draft Border Rivers Resource Operations Plan 26 describes the practical implementation of the objectives and outcomes specified in the Water Resource (Border Rivers) Plan 23. The intent of the plan is to provide enhanced certainty and security for water users and the natural environment (DNRM, 26a). The objectives for the water resource plan include objectives for environmental flow and water allocation security. The environmental flow objective includes that the end-of-system flow should be at least 6.8 percent of the pre-development flow pattern in the first Resource Operations Plan. There are ten key locations or nodes on the Barwon, Weir, Macintyre, Dumaresq, Macintyre Brook and Severn rivers where the pre-development indicator reported in the amended Water Resource Plan is used as a performance benchmark. Future allocation decisions regarding security are limited to include: the annual volume probability for a water allocation group be not less than the annual volume probability for the group immediately before the decision is made, and the 45 percent annual volume probability for a water allocation group be not less than the 45 percent annual volume probability for the group immediately before the decision is made. 2 Water availability in the Border Rivers November 27 CSIRO 27

33 Queensland Water Resource Plans do not establish specific environmental water allocations, rather environmental water is protected via water access rules such as pumping thresholds. The Water Resource (Border Rivers) Plan 23 (DNRM, 23b) establishes the following performance indicators for environmental flow objectives: end-of-system flow low flow summer flow beneficial flooding flow one in two-year flood. Water allocated for the Border Rivers region is detailed in Table 2-3 for New South Wales and Table 2-4 for Queensland. A volume of 5 ML of unallocated water is currently held as a strategic reserve within the Stanthorpe Shire in Queensland (DNRM, 23b). There is 35 ML of the total held for irrigation and associated industry use and 15 ML held for town water supply. Water source plan Table 2-3. Summary of surface water sharing arrangements within New South Wales Draft Border Rivers water sharing plan Tenterfield Creek Water products Priority of access Allocated entitlement Allocated entitlement Basic rights ML/y* ML/day Stock and domestic rights Native title Extraction shares Total licensed (long term) extraction limit Annual volumetric extraction limit not quantified Local water utilities high 62 High security access high 1233 unit shares General security A access medium 21, unit shares General security B access medium 244, unit shares Supplementary access low 12, unit shares Domestic and stock 125 not specified Environmental provisions *** ** * Preliminary volumes as Border Rivers Water Sharing Plan is in preparation. ** Environmental provisions are the daily flow minus the total daily extraction limit and basic stock and domestic extraction rights. *** Environmental provisions are based on three components: (i) maintain a minimum release of 1 ML/day from Pindari Dam (ii) translucence flows as follows: pass inflows up to 5 ML/day during September to May pass inflows up to 2 ML/day during June to August. (iii) stimulus flow arrangements as follows: A stimulus flow shall be released on 1st September in any one year, triggered by an inflow greater than 12 ML/day into Pindari Dam in the preceding months of April, May, June, July or August. The stimulus flow shall consist of a total of 4 ML over a seven (7) day release. 2 Overview of the region CSIRO 27 November 27 Water availability in the Border Rivers 21

34 Table 2-4. Summary of surface water sharing arrangements within Queensland 2 Overview of the region Water products Priority of access Allocated entitlement Total licensed (long-term) extraction limit 287,43 Annual volumetric extraction limit ML not specified Supplemented access high 3654 Supplemented access medium 19,965 Domestic and stock * Unallocated irrigation and associated industry 3,5 Unallocated town water supply 1,5 Unsupplemented access low 168,811 Environmental provisions ** * Domestic and stock allocations have been converted to nominal allocations ** Environmental Provisions are taken into consideration when setting the conditions of extraction on the entitlement to ensure there is a volume of water available for the environment. Source: Draft Border Rivers Resource Operations Plan 26 (DNRM, 26a) Water products and use Water users get water from regulated and unregulated streams and the lower floodplains within the Border River region. This includes: the New South Wales regulated system supplied by Pindari Dam, a share of Glenlyon Dam, and tributary inflows the Queensland Border Rivers Water Supply Scheme regulated system, supplied by a share of Glenlyon Dam and tributary inflows the Queensland Macintyre Brook Water Supply Scheme regulated system, supplied by Coolmunda Dam New South Wales unregulated tributaries, primarily the Mole River, Tenterfield Creek, Upper Macintyre River, Beardy River and Ottleys Creek New South Wales unregulated distributary streams, primarily Whalan Creek and the Boomi River Queensland unregulated tributaries, principally the Severn River and tributaries and the Weir River which enter the system near its end point at Mungindi, and also is interconnected with the trunk system by Newinga Breakout overland flows. The surface water diversions for irrigation were 535 GL in 2/1 (MDBC, 27b) or 4.4 percent of the total surface water diversions within the MDB. The surface water diversions within New South Wales were stable at around 2 GL/year prior to 22/3. Diversions reduced to around 125 GL/year over the three years to 24/5. The annual diversions in Queensland were less stable and generally ranged between 5 GL/year and 2 GL/year. 22 Water availability in the Border Rivers November 27 CSIRO 27

35 Water use (GL/y) Total surface water diversions Qld surface water diversions NSW surface water diversions Figure 2-3. Historical surface water diversions for Queensland and New South Wales Border Rivers region Source: 83/84 (AWRC, 1987); 1988, 1994 (MDBMC, 1995); 1994/95 24/5 (MDBC, 27a) (Note: the data in different years are not always comparable, because the areas defined in each catchment changed, as did the definitions of water uses. Even where data sets should refer to the same records, data from state and MDBC data bases often vary. Differences are typically less than 1 percent but differences of more than 5 percent have been found in some cases.) 2.4 Groundwater Groundwater management units the hydrogeology and connectivity 2 Overview of the region Groundwater occurs in aquifers in the Queensland and New South Wales highlands, the Great Artesian Basin (GAB), and in alluvial deposits associated with the Dumaresq River in Queensland and the Macintyre River in New South Wales. A number of rock types provide groundwater of variable yield and quality in the New South Wales and Queensland highlands, including porous sandstones, fractured granites, other sedimentary rocks and volcanic rocks. Reliable groundwater supplies are also found in highland alluvial deposits which are generally less than 15 m thick. Groundwater in the highlands is mainly for domestic and stock use. Little is known of the recharge and flow mechanisms in these areas. Multi-layered sandstones and mudstones of the GAB aquifer system occur across much of the central and western parts of the region, outcropping in many areas on the western flanks of the highlands. These are an important water resource primarily for stock and domestic use. The outcropping Intake Beds allow recharge from rainfall and river flow to the deeper confined GAB aquifers further west. In other areas, the GAB sequence is overlain by relatively thick layers of more recent alluvium, which themselves contain groundwater of variable quality and bore yield. Groundwater flow in the GAB in the region is initially to the west, and then towards the south where bores become artesian. Water quality decreases further along the flow path with fresher groundwater occurring in the upper aquifers. Groundwater salinity levels are usually less than 1 mg/l total dissolved salts (TDS) in the upper aquifers in the east, but become more saline with depth and to the west. The water resources within these aquifers are not considered in this assessment except where intake beds for the GAB outcrop within the region, since groundwater in these areas has the potential to be connected with surface water systems. There is no licensed groundwater extraction from the GAB Intake beds in Queensland, however, groundwater from these units is used for stock and domestic supply. The major source of high yielding groundwater in the region is the alluvial deposits associated with the Dumaresq and Macintyre Rivers. These sediments are deposited in a narrow valley which broadens downstream near Keetah. The Gunnedah Formation (also known as Unit B in the region) overlies the highland and GAB aquifers and comprises fluviolacustrine sands, gravels and clays up to 7 m thick. The coarser sediments form a palaeochannel which meanders through the incised valley. Useable groundwater resources are restricted to those areas upstream of Keetah that contain fresh groundwater. Downstream of Keetah the only occurrence of fresh groundwater is associated with raised water levels in the region of the Boggabilla Weir. CSIRO 27 November 27 Water availability in the Border Rivers 23

36 The Narrabri Formation (also known as Unit C in the region) overlies the Gunnedah Formation and comprises alluvial sands, gravels and silts forming an unconfined aquifer. These sediments are generally 1 to 3 m thick, and form the ground surface in the valley. The two units are separated by 2 to 15 m of semi-permeable clay that controls leakage between the two aquifers. Aquifer transmissivities and groundwater quality decrease markedly from the east to the west of the region. Groundwater in the Narrabri Formation is mostly recharged by stream losses, although diffuse recharge from rainfall and excess irrigation are also likely to contribute minor amounts. Recharge to the deeper Gunnedah Formation aquifers is by cross-formational flow, upward leakage from underlying aquifers, and infiltration of rainfall and runoff. Groundwater salinity is generally less than 1 mg/l TDS in the eastern and central part of the region, but increases in the western area. 2 Overview of the region Groundwater levels, salinity and isotopic signatures indicate connection between the Dumaresq River and the alluvial aquifers. In the upper reaches, the Dumaresq is a low gaining river. However, throughout much of the Border Rivers Alluvial GMUs, where most groundwater extraction occurs, the Dumaresq is classified as high losing. The middle reaches of the Dumaresq are classified as medium losing to low gaining. The Macintyre River is also low gaining in the upper reaches, low gaining to medium losing in the middle reaches, and low losing in the lower reaches. For management purposes, the aquifers within the region are divided into a number of groundwater management units (GMUs). These units are three dimensional in nature, allowing for the layered nature of geological formations at different depths. Different GMUs cover all the New South Wales portion of the region, but only a small part of the Queensland portion of the region, except for the GAB GMU which lies at greater depths under the region. The area of the sediments lying above the GAB in Queensland not covered by a GMU is referred to as an unincorporated area. The degree of development of the groundwater source in each GMU and the unincorporated area varies considerably between areas of intensive extraction for irrigation to areas of broad scale stock and domestic use. The GMUs in the region are assessed as low to very low priority in the context of the overall project on the basis of the size of the aquifers, the level of development and the assumed degree of connectivity with the surface water system. The priority ranking provides a basis for focussing efforts to those aquifers affecting most the total resource across the MDB. Available groundwater extraction, entitlement and recharge data are itemised for each GMU in the region (Table 2-5). A large part of the region in Queensland has no data available as it is an unincorporated area. Within the Queensland unincorporated area, groundwater with salinity levels considered suitable for irrigation purposes (<15 mg/l TDS) occur along the eastern margin of the region such as those drawn from the Ruby Creek Granite and the Stanthorpe Adamellite. This zone is composed largely of granites and other fractured rock aquifers. These aquifers possess limited resource potential and groundwater use is largely restricted to stock and domestic supplies. In addition, some reliable groundwater supplies are also taken from alluvium associated with the area s surface drainage systems. Groundwater quality is variable within these alluvial aquifers. Further west, the unincorporated areas have higher salinity levels and are considered marginal for irrigation purposes, however, very localised pockets of fresh water do exist and may be utilised. No information for the GAB GMU in Queensland is included. 24 Water availability in the Border Rivers November 27 CSIRO 27

37 Table 2-5. Groundwater extraction, entitlement and recharge summary Code GMU Priority Total entitlement Current extraction (3) Long-term average extraction limit GL/y Recharge (4) Q73 Border Rivers Alluvium (Qld) low (2) 14.6 (2) (5) 7.31 N22 Border Rivers Alluvium (NSW) low (1) 15. (1) (5) 7.31 N23 Miscellaneous Alluvium of the Barwon Region (NSW) low N63 GAB Alluvial (NSW) low N61 GAB Intake Beds (NSW) very low N83 Inverell Basalt (NSW) low N85 New England Fold Belt (NSW) low na Unincorporated Areas <15 mg/l na na stock and domestic only na GAB Intake Beds (Qld) na na stock and domestic only na na (6) 2.48 (6) 43.1 (1) Supplied by NSW DWE (2) Supplied by QNRM (3) Current groundwater extraction for Macro Groundwater Sharing Plan areas is based on metered and estimated data provided by NSW DWE. Data quality is variable depending on the location of bores and the frequency of meter reading. (4) This value represents only rainfall recharge in Macro Groundwater Sharing Plan areas. The volume of recharge does not include recharge to national park areas, which has generally been allocated to environmental purposes and is not available for consumptive use. (5) Taken from model. (6) Recharge to unincorporated areas is calculated from deep drainage rates assigned to a region based on mapped classifications of land use and soil type. 2 Overview of the region CSIRO 27 November 27 Water availability in the Border Rivers 25

38 2 Overview of the region Figure 2-4. Map of groundwater management units within the Border Rivers region Water management institutional arrangements The New South Wales and Queensland Border Rivers Acts empower the respective controlling authorities to manage their groundwater entitlements. The Water Management Act 2 in New South Wales requires the implementation of ten-year plans defining water sharing arrangements between the environment and groundwater users and amongst water user groups in a similar way to that required for surface water diversions. Water sharing plans are prepared for the more highly developed GMUs to protect rivers and aquifers and their dependent ecosystems, and to provide water users with clarity and certainty regarding water access rights. The Border Rivers GMUs in New South Wales do not have water sharing plans. Groundwater extraction is controlled by macro water sharing plans in those areas of New South Wales not covered by water sharing plans. These plans provide a groundwater extraction limit and environmental provisions. Groundwater extraction records for the macro water sharing plans regions are generally poor. The annual extraction limit is set as a proportion of recharge to the system. The macro planning process does not discount the extraction limit for salinity. As such, the limits reflect groundwater availability in volumetric terms only. The environmental provisions are 3 to 5 percent of the rainfall recharge. The macro water sharing plans are intended to commence in 29. The water entitlement provisions for the individual macro groundwater plans are aggregated for the region in Table 2-6. The only GMU in Queensland is the area of the Border Rivers Alluvium that occurs on the northern side of the state border. The Water Act 2 provides the primary framework for water management in Queensland. Water resource plans provide the means for integrating surface water and groundwater management into a regulatory framework. A water resource plan is gazetted for the Border Rivers region but does not currently apply to groundwater extraction. 26 Water availability in the Border Rivers November 27 CSIRO 27

39 The large unincorporated area of the region above the GAB aquifer in Queensland is not gazetted under the Water Act for groundwater management purposes. Groundwater may be used in this part of the region but its use is not managed or monitored. Table 2-6. Groundwater sharing arrangements within the Border Rivers region Description Border Rivers Alluvium (NSW) Border Rivers Alluvium (Qld) Remaining GMUs (NSW only) Name of Plan no plan no plan Macro Groundwater Sharing Plan GAB Intake Beds (NSW) Water Sharing Plan for the Great Artesian Basin Groundwater Sources GAB Intake Beds (Qld) Water Resource (Great Artesian Basin) Plan 26 Year of plan no plan no plan * Environmental provisions Planned share not available not available 4 to 5% of recharge 3% of recharge Adaptive provisions not available not available none left or taken as required on an access licence Basic rights Domestic and stock rights.36 GL/y not available 6.42 GL/y 1.27 GL/y Native title GL/y not available none Access Licences Urban.5 GL/y not available.67 GL/y.4 GL/y 2 Overview of the region Planned share 14.6 not available 9.34 GL/y 3.59 GL/y Announced Allocation not available not available none Supplementary provisions not available not available none none * NSW DWE advise that the Macro Water Sharing Plans are proposed to commence in 29 The water resources within the Queensland GAB aquifers are administered by the Water Resource (Great Artesian Basin) Plan 26. This plan provides a framework for sustainably allocating and managing water in the GAB (GABCC, 2). A Resource Operations Plan details the arrangements for implementing the water resource plan (GABCC, 26). In New South Wales the water resources within the GAB aquifers are controlled by the Water Sharing Plan for the New South Wales Great Artesian Basin Groundwater Resources 27. The vision for this plan is to achieve equitable, viable and sustainable management of the Great Artesian Basin in New South Wales for the benefit of the community and the biodiversity of the region Water products and use The groundwater extraction potential of the alluvial aquifers was discovered in 1985, but by the early 199s only about 1 percent of total water use in the region was from groundwater. Groundwater use increased significantly in the mid- 199s and early 2s. Groundwater extraction within the Border Rivers region accounts for 2 percent of the total groundwater extraction throughout the MDB or GL excluding stock and domestic extractions and extractions in unincorporated areas. There are over 2378 groundwater licences in the New South Wales portion of the region. Groundwater entitlements in the Border Rivers Alluvium GMU were set at 3 GL/year which has been split to allow 15 GL/year for entitlement in each of New South Wales and Queensland. Groundwater extractions from the alluvium are currently about half of the level of entitlement and in 24/5 were 6.2 GL in New South Wales and 6.3 GL in Queensland (Figure 2-5). CSIRO 27 November 27 Water availability in the Border Rivers 27

40 Groundwater extraction (GL/y) Total NSW Qld Overview of the region Figure 2-5. Historical groundwater diversions for Queensland and New South Wales Border Rivers region Notes (1) 198 and 1987 were for use between Keetah and Glenlyon Dam: dates unknown. (2) Prior to 2/3 recording date was for Oct Sep. O2/3 was for Oct 2 June 3. Subsequently for financial years. (3) 3.5 GL allocation from shallow aquifer; use unknown. (4) Area used for recording not consistent over time. Sources 198 and 1987 figures: A review of the groundwater resources of the Dumaresq-Macintyre Border Rivers System: Border Rivers groundwater sub-committee Border Rivers Commission Annual Reports 1989/9 to 1996/ Border Rivers Commission Annual Statistics onwards Data on groundwater levels are available for the alluvial aquifer along the Dumaresq River. Groundwater levels in the Narrabri Formation have shown a long-term decline since 199, with the greatest declines of up to 1 m occurring in the upper reaches of the alluvium. Seasonal drawdown is as much as 2 m. In the Gunnedah Formation groundwater levels show long-term declines of between 5 and 1 m since 199. Seasonal drawdown can be in the order of 1 to 3 m, although recovery is generally rapid. As a result of concentrated pumping, three cones of depression have formed in the alluvium, near Bonshaw Weir, Texas and Cunningham Weir. Both aquifers are affected at all three locations. In the lower reaches of the region, where irrigation of cotton occurs but groundwater quality is poor, groundwater levels have risen up to 2 metres since the 199s. There is insufficient information to assess the water level trends in the highland fractured rock aquifers. GAB aquifers have shown a long-term decrease in pressure. Most groundwater extraction for irrigation occurs along the Dumaresq River for horticultural crops such as potatoes, for fodder crops including lucerne and for livestock pasture. Viticulture and horticulture crops are expanding enterprises in the upper catchment region. 2.5 References AWRC (1987) 1985 Review of Australia's Water Resources and Water Use. Australian Water Resources Council. Department of Primary Industries and Energy/Australian Government Publishing Service, Canberra, Vol. 2 (reported on at BRGCMA (26) Border Rivers Gwydir Catchment Action Plan Border Rivers Gwydir Catchment Management Authority. BRS (2) Land use data. Available at: DNRM (2) Supporting Documents to Water Resources Plan. DNRM (22) Overview report for the Draft Border Rivers Water Resource Plan. Queensland Department of Natural Resources and Mines. DNRM (23a) Water Sharing Plan for the Tenterfield Creek Water Source 23. Queensland Department of Natural Resources and Mines. DNRM (23b) Water Resource (Border Rivers) Plan 23. Queensland Department of Natural Resources and Mines. DNRM (26a) Draft Border Rivers Resource Operations Plan 26. Queensland Department of Natural Resources and Mines. 28 Water availability in the Border Rivers November 27 CSIRO 27

41 DWE (27a) Draft Water Sharing Plan New South Wales Border Rivers Regulated River Water Source Part A Background Document August 27. DWE (27b) Draft Water Sharing Plan New South Wales Border Rivers Regulated River Water Source Guide August 27. Environment Australia (21) A Directory of Important Wetlands in Australia. Third Edition. Environment Australia, Canberra. Available at: GABCC (2) Water Resource (Great Artesian Basin) Pan 2. GABCC (26) Resource Operations (Great Artesian Basin) Plan 26. Geosciences Australia (27) Man-made hydrology GIS coverage. Kingsford RT (1999) Managing the water of the Border Rivers in Australia: irrigation, government and the wetland environment. Wetlands Ecology and Management 7, Markham A (1999) Fluvial Geomorphology. in Current Ecological Condition of Streams in the Border Rivers Catchment. Department of Natural Resources (Queensland) and Department of Land and Water Conservation (New South Wales). McCollum B (2) Review of Operations of the Cap - Response sheet for comments on Draft report to New South Wales IPART July 2. Border Rivers Food and Fibre Goondiwindi, Queensland. McCosker R (1999) Floodplan and Riparian Vegetation. in Current Ecological Condition of Streams in the Border Rivers Catchment. Department of Natural Resources (Queensland) and Department of Land and Water Conservation (New South Wales). MDBC (27a) State of the Darling Hydrology Report. Prepared by Webb, McKeown & Associates Pty Ltd for the Murray Darling Basin Commission. MDBC Publication No. 7/7. MDBC (27b) Water Audit Monitoring Reports, to 24-5, MDBC, Canberra. MDBMC (1995) An Audit of Water Use in the Murray-Darling Basin, Murray-Darling Basin Commission, Canberra. MDBC (1998) Floodplain Wetlands Management Strategy. MDB Ministerial Council; Canberra. ISBN Murray-Darling Basin Commission. NSW DEC (unknown) Warrego River. Available at: QMDC and SWNRM (24) Regional Natural Resource Management Plan 24 (NRM), Queensland Murray Darling Committee Inc. and South West Natural Resource Management Group Inc. Thoms MC, Southwell M and McGinness HM (25) Floodplain-river ecosystems: Fragmentation and water resources development. Geomorphology 71, Overview of the region CSIRO 27 November 27 Water availability in the Border Rivers 29

42 3 Rainfall-runoff modelling This chapter includes information on the climate and rainfall-runoff modelling for the Border Rivers region. It has four sections: a summary an overview of the regional modelling approach a presentation and description of results a discussion of key findings. 3.1 Summary 3 Rainfall-runoff modelling Issues and observations The methods used for climate scenario and rainfall-runoff modelling across the Murray-Darling Basin (MDB) are described in Chapter 1. There are no significant differences in the methods used to model the Border Rivers region Key messages The mean annual rainfall and modelled runoff averaged over the Border Rivers region are 641 mm and 32 mm respectively. Rainfall is generally higher in the summer half of the year and runoff is relatively uniform through the year. The Border Rivers region covers 4.1 percent of the MDB and contributes 4.7 percent of the total runoff in the MDB. The mean annual rainfall and runoff over the ten-year period 1997 to 26 are within 1 percent of the long-term (1895 to 26) means. Rainfall-runoff modelling with climate change projections from global climate models indicate that future runoff in the Border Rivers region is more likely to decrease than increase. Two-thirds of the results show a decrease in runoff and one-third of the results show an increase in runoff. The best estimate (median) is a 9 percent reduction in mean annual runoff by ~23 relative to ~199. The extreme estimates, which come from the high global warming scenario, range from a 28 percent reduction to a 2 percent increase in mean annual runoff. By comparison, the range from the low global warming scenario is from a 9 percent reduction to a 5 percent increase in mean annual runoff. There is negligible projected growth in commercial forestry plantations in the Border Rivers region. The total farm dam storage volume over the entire Border Rivers region is projected to increase by 12.8 GL. About 85 percent of the increased volume is in the New South Wales part of the Border Rivers region. The projected increase in farm dams will reduce mean annual runoff by about 1 percent. This is relatively small compared to the best estimate climate change impact on runoff (9 percent). The best estimate of the combined impact of climate change and farm dam development is therefore a 1 percent reduction in mean annual runoff, with extreme estimates ranging from a 28 percent reduction to a 19 percent increase Uncertainty Scenario A historical climate and current development The runoff estimates in the Border Rivers region are relatively good because there are many gauged catchments in the region from which to estimate model parameter values. Rainfall-runoff model verification analyses for the MDB indicate that the mean annual runoff estimated for ungauged catchments, using optimised parameter values from a nearby catchment have an error of less than 2 percent in more than half the catchments and less than 5 percent in almost all the catchments. 3 Water availability in the Border Rivers November 27 CSIRO 27

43 Scenario C future climate and current development The biggest uncertainty in Scenario C modelling is in the global warming projections and the modelled implications of global warming on regional rainfall. The uncertainty in the rainfall-runoff modelling of climate change impact on runoff is small compared to the climate change projections. This project takes into account the current uncertainty in climate change projections explicitly by considering results from 15 global climate models and three global warming scenarios based on the Intergovernmental Panel on Climate Change Fourth Assessment Report. The results are then presented as a median estimate of climate change impact on runoff and as the range of the extreme estimates. Scenario D future climate and future development After the uncertainty in the climate change projections, the biggest uncertainty in Scenario D modelling is in the projections of future increases in commercial forestry plantations and farm dam development and the impact of these developments on runoff. The impact of commercial forestry plantations on runoff is not modelled because the Bureau of Rural Sciences projections indicate negligible growth in commercial forestry plantations in the Border Rivers region. The increase in farm dams is estimated by considering trends in historical farm dam growth and current policy controls in New South Wales and Queensland and there is uncertainty both as to how land holders will respond to these policies and how governments may set policies in future. However, the uncertainties in the farm dam projections are considerably greater for New South Wales than for Queensland, as unlike current Queensland policy, current New South Wales policy does not prevent the development of farm dams for irrigation use. 3.2 Modelling approach Rainfall-runoff modelling general approach 3 Rainfall-runoff modelling The general rainfall-runoff modelling approach is described more fully in Chapter 1 and in detail in Chiew et al. (27). A brief summary is given below. The lumped conceptual daily rainfall-runoff model, SIMHYD, with a Muskingum routing method is used to estimate daily runoff at.5 o grids (~ 5 km x 5 km) across the entire MDB for the four scenarios. The rainfall-runoff model is calibrated against 1975 to 26 streamflow from about 18 small and medium size unregulated catchments (5 km 2 to 2 km 2 ). In the model calibration, the six parameters of SIMHYD are optimised to maximise an objective function that incorporates the Nash-Sutcliffe efficiency of monthly runoff and daily flow duration curve, together with a constraint to ensure that the total modelled runoff over the calibration period is within five percent of the total recorded runoff. The runoff for a.5 o grid cell in an ungauged subcatchment is modelled using optimised parameter values for a calibration catchment closest to that subcatchment. The rainfall-runoff model SIMHYD is used because it is simple and has relatively few parameters, and for the purpose of this project, provides a consistent basis (that is automated and reproducible) for modelling historical runoff across the entire MDB and for assessing the potential impacts of climate change and development on future runoff. In data-rich areas, specific calibration of SIMHYD or more complex rainfall-runoff models based on expert judgement and local knowledge as carried out by some state agencies, may lead to better model calibration for the specific modelling objectives of the area Rainfall-runoff modelling for the Border Rivers region The rainfall-runoff modelling was undertaken to estimate runoff in.5 o grid cells in 53 subcatchments as defined for the river system modelling in Chapter 4 for the Border Rivers region (Figure 3-1). Optimised parameter values from ten calibration catchments were used. Nine of these calibration catchments are in the Border Rivers region and their optimised parameter values were used for the subcatchments in the middle and eastern parts of the region. The other calibration catchment is in the Condamine-Balonne region north-west of the Border Rivers region (not shown in Figure 3-1) and its optimised parameter values were used for the subcatchments in the northern and western parts of the Border Rivers region. CSIRO 27 November 27 Water availability in the Border Rivers 31

44 Scenario B modelling was not undertaken for the Border Rivers region because the mean annual rainfall and modelled runoff for the ten-year period 1997 to 26 are not significantly different (at statistical significance level of α =.2 with the Student-t and Rank-Sum tests) from the long-term 1895 to 1996 means (Section 3.3.1). The impact of commercial plantation forestry on runoff was not modelled because the Bureau of Rural Sciences projections that take into account industry information indicate negligible growth in commercial plantation forestry in the Border Rivers region. The increase in farm dams in each subcatchment was estimated based on extrapolation of historical farm dam growth rate and current policy control. This resulted in an estimated 12.8 GL increase in farm dam storage volume by ~23 over the entire Border Rivers region, 85 percent of which are in the New South Wales part of Border Rivers (1.8 GL in New South Wales and 2 GL in Queensland). The projected increases in farm dam storage volume for each subcatchment are given in Appendix A. 3 Rainfall-runoff modelling The farm dam projection for the New South Wales part of the Border Rivers region is dependent on three factors: current farm dam storage volume, growth rate of farm dams, and maximum harvestable right under the New South Wales Water Management Act (2). The current farm dam storage volume was estimated from the satellite imagery captured between 24 and 26 (Geosciences Australia, 27). The limited farm data from Agrecon (25) for 1999 to 24, which covers less than 1 percent of New South Wales, indicates a growth rate of up to 4 percent in north-east New South Wales and about.6 percent elsewhere. A growth rate of 4 percent is unlikely because it is not economically viable to sustain significant on-farm irrigation enterprise (D. Black and R. Beecham, pers. comm.), and for this reason, a rate of.6 percent was used to model farm dam growth in New South Wales. The maximum harvestable right volume is estimated by multiplying the area of each land parcel by the harvestable right dam capacity per unit area multiplier for that property (New South Wales Department of Natural Resources, 27) and then aggregating the values for all of the individual properties across the reporting region. The maximum harvestable right across rural land in the New South Wales part of the Border Rivers region is 1.3 GL. The estimate of current farm dam storage volume over the New South Wales part of the entire Border Rivers is 77 GL, with these farm dams utilising about 31 GL of the harvestable right. There are farm dams capturing more than the maximum harvestable right volume that was later defined by the Water Management Act 2. The available harvestable right is therefore about 72 GL. The projection of 11 GL increase in farm dam storage volume over the New South Wales part of the Border Rivers region by ~23 is therefore an increase of about 14 percent of the current farm dam storage volume and about 15 percent of the available harvestable right. For Queensland catchments in the MDB, future development of farm dams is limited to those for stock and domestic purposes (Queensland Government, 2). The increase in farm dams in each subcatchment in the Queensland part of the Border Rivers region is estimated by multiplying the projected increase in rural population (using data from Australian Bureau of Statistics (24)) by the current average storage volume of stock and domestic farm dams over rural parts of the Queensland MDB of.32 ML/person, giving an increase in farm dam storage volume over the Border Rivers of about 2 GL. 32 Water availability in the Border Rivers November 27 CSIRO 27

45 3 Rainfall-runoff modelling Figure 3-1. Map of modelling subcatchments and calibration catchments Model calibration Figure 3-2 compares the modelled and observed monthly runoff and the modelled and observed daily flow duration curves for the ten calibration catchments. The results indicate that the SIMHYD calibration can reasonably reproduce the observed monthly runoff series (Nash-Sutcliffe E values generally greater than.7) and the daily flow duration characteristic (Nash Sutcliffe E values generally greater than.8). The volumetric constraint used in the model calibration ensures that the total modelled runoff is within 5 percent of the total observed runoff. The calibration to optimise Nash-Sutcliffe E means that more importance is placed on the simulation of high runoff, and therefore SIMHYD modelling of the medium and high runoff are considerably better than the simulation of low runoff. Nevertheless, an optimisation to reduce overall error variance will result in some underestimation of high runoff and overestimation of low runoff, as shown in some of the scatter plots comparing the modelled and observed monthly runoff and many of the daily flow duration curves. The disagreement between the modelled and observed daily runoff characteristics is discernable for runoff that is exceeded less than.1 or 1 percent of the time. This is accentuated in the plots because of the linear scale on the y-axis and normal probability scale on the x-axis. The runoff estimates for the Border Rivers region are relatively good because there are many calibration catchments in the region from which to estimate the parameter values. The rainfall-runoff model verification analyses for the MDB with data from about 18 catchments indicate that the mean annual runoffs for ungauged catchments are under or overestimated (when using optimised parameter values from a nearby catchment) by less than 2 percent in more than half the catchments and by less than 5 percent in almost all the catchments. CSIRO 27 November 27 Water availability in the Border Rivers 33

46 3 Rainfall-runoff modelling Figure 3-2. Modelled and observed monthly runoff and daily flow duration curve for the calibration catchments 3.3 Modelling results Scenario A historical climate and current development Figure 3-3 shows the spatial distribution of mean annual rainfall and modelled runoff for 1895 to 26 across the Border Rivers region, Figure 3-4 shows the 1895 to 26 annual rainfall and modelled runoff series averaged over the region, and Figure 3-5 shows the mean monthly rainfall and runoff averaged over the region for 1895 to Water availability in the Border Rivers November 27 CSIRO 27

47 The mean annual rainfall and modelled runoff averaged over the Border Rivers region are 641 mm and 32 mm respectively. The mean annual rainfall varies from about 85 mm in the east to 5 mm in the west. The modelled mean annual runoff varies from 7 mm in the east to 15 mm in the west (Figure 3-3). Rainfall is generally higher in the summer half of the year. Runoff is fairly uniform throughout the year with the highest runoff averaged across the region occurring in January and February (Figure 3-5). The Border Rivers region covers about 4.1 percent of the MDB and contributes about 4.7 percent of the total runoff in the MDB. Rainfall and runoff can vary considerably from year to year with long periods over several years or decades that are considerably wetter or drier than others (Figure 3-4). The coefficients of variation of annual rainfall and runoff averaged over the Border Rivers region are.22 and.71 respectively. The 1th percentile, median and 9th percentile values across the 18 MDB regions are.22,.26 and.36 respectively for rainfall and.54,.75 and 1.19 for runoff. The interannual rainfall variability in the Border Rivers region is therefore amongst the lowest in the MDB and the inter-annual runoff variability is about the median runoff variability in the MDB. The mean annual rainfall and modelled runoff over the ten-year period 1997 to 26 are within 1 percent of the long-term (1895 to 26) mean values. Potter et al. (27) present a more detailed analysis of recent rainfall and runoff across the MDB. 3 Rainfall-runoff modelling Figure 3-3. Spatial distribution of mean annual rainfall and modelled runoff averaged over Annual rainfall (mm) Annual runoff (mm) Figure annual rainfall and modelled runoff series averaged over the region (the curve shows the low frequency variability) CSIRO 27 November 27 Water availability in the Border Rivers 35

48 Mean monthly rainfall (mm) J F M A M J J A S O N D Mean monthly runoff (mm) J F M A M J J A S O N D 3 Rainfall-runoff modelling Figure 3-5. Mean monthly rainfall and modelled runoff (averaged over for the region) Scenario C future climate and current development Figure 3-6 shows the percentage change in the modelled mean annual runoff averaged over the Border Rivers region for Scenario C relative to Scenario A for the 45 scenarios 15 Global Climate Models (GCMs) for each of the high, medium and low global warming scenarios. The percentage change in the mean annual runoff and the percentage change in mean annual rainfall from the corresponding GCMs are also tabulated in Table 3-1. The plot and table indicate that the potential impact of climate change on runoff may be significant. Although there is considerable uncertainty in the estimates, the results indicate that runoff in ~23 in the Border Rivers region is more likely to decrease than increase. Rainfall-runoff modelling with climate change projections from two-thirds of the GCMs show a reduction in mean annual runoff, and rainfall-runoff modelling with climate change projections from one-third of the GCMs show an increase in mean annual runoff. Because of the large variation between GCM simulations and the method used to obtain the climate change scenarios, the biggest increase and biggest decrease in runoff come from the high global warming scenario. For the high global warming scenario, rainfall-runoff modelling with climate change projections from more than half the GCMs indicate a decrease in mean annual runoff greater than 1 percent, and rainfall-runoff modelling with climate change projections from 2 percent of the GCMs indicate an increase in mean annual runoff greater than 1 percent. In subsequent reporting here and in other chapters, only results from an extreme dry, mid and extreme wet variant are shown (referred to as Cdry, Cmid and Cwet). For the Cdry scenario, results from the second highest reduction in mean annual runoff from the high global warming scenario are used. For the Cwet scenario, results from the second highest increase in mean annual runoff from the high global warming scenario are used. These are shown in bold in Table 3-1, with the Cdry, Cmid and Cwet scenarios indicating a -28, -9 and +2 percent change in mean annual runoff. By comparison, the range based on the low global warming scenario is -9 to +5 percent change in mean annual runoff. Figure 3-7 shows the mean annual runoff across the Border Rivers region for Scenario A and for the Cdry, Cmid and Cwet scenarios. 36 Water availability in the Border Rivers November 27 CSIRO 27

49 % change in mean annual runoff High global w arming Medium global w arming Low global w arming -4 cnrm giss_aom inmcm iap mpi gfdl mri ipsl csiro ncar_ccsm cccma_t63 miub ncar_pcm cccma_t47 miroc Figure 3-6. Percentage change in mean annual runoff under the 45 Scenario C simulations (15 GCMs and three global warming scenarios) relative to Scenario A runoff Table 3-1. Summary results from the 45 Scenario C simulations (numbers show percentage change in mean annual rainfall and runoff under Scenario C relative to Scenario A) 3 Rainfall-runoff modelling High global warming Medium global warming Low global warming GCM Rainfall Runoff GCM Rainfall Runoff GCM Rainfall Runoff cnrm cnrm -6-2 cnrm -3-1 giss_aom giss_aom Giss_aom -3-9 inmcm inmcm inmcm -2-9 iap iap iap -1-5 mpi mpi ipsl -5 gfdl gfdl -4-1 gfdl -2-5 mri mri -5-1 mpi -2-5 ipsl ipsl -1-9 mri -2-5 csiro -5-7 csiro -3-5 csiro -1-2 ncar_ccsm 2 ncar_ccsm 1-1 Ncar_ccsm -1 cccma_t cccma_t cccma_t miub 3 8 miub 2 5 miub 1 2 ncar_pcm 6 15 ncar_pcm 4 9 ncar_pcm 2 4 cccma_t cccma_t cccma_t miroc miroc 7 21 miroc 3 9 CSIRO 27 November 27 Water availability in the Border Rivers 37

50 3 Rainfall-runoff modelling Figure 3-7. Mean annual rainfall and modelled runoff under scenarios A, Cdry, Cmid and Cwet 38 Water availability in the Border Rivers November 27 CSIRO 27

51 3.3.3 Summary results for all modelling scenarios Table 3-2 shows the mean annual rainfall, modelled runoff and actual evapotranspiration for Scenario A averaged over the Border Rivers region, and the percentage changes in the rainfall, runoff and actual evapotranspiration in scenarios C and D relative to Scenario A. Figure 3-8 shows the mean monthly rainfall and modelled runoff for scenarios A, C and D averaged over 1895 to 26 for the region. Figure 3-9 shows the daily rainfall and flow duration curves for scenarios A, C and D averaged over the region. The modelling results for all the subcatchments in the Border Rivers region are summarised in Appendix A. The Cmid (or Cdry or Cwet) results are from rainfall-runoff modelling using climate change projections from one GCM. As the Cmid scenario is chosen based on mean annual runoff (Section 3.3.2), the comparison of monthly and daily results in Scenario Cmid relative to Scenario A in Figure 3-8 and Figure 3-9 should be interpreted cautiously. However, the C range results shown in Figure 3-8 are based on the second driest and second wettest results for each month separately from the high global warming scenario, and the C range results shown in Figure 3-9 are based on the second lowest and second highest daily rainfall and runoff results at each of the rainfall and runoff percentiles from the high global warming scenario. The lower and upper limits of C range are therefore not the same as the Cdry and Cwet scenarios reported elsewhere and used in the river system and groundwater models. Although two-thirds of the GCMs show a reduction in mean annual rainfall, more than half of the GCMs indicate that the extreme rainfall that is exceeded.1 percent of the time will be more intense (Figure 3-9). Scenario B (recent climate and current development) modelling was not undertaken for the Border Rivers region because the mean annual rainfall and modelled runoff for 1997 to 26 are not statistically significantly different to the long-term means. The Scenario B results would therefore be essentially the same as the Scenario A results. The modelling results indicate a median estimate of -9 percent change in mean annual runoff by ~23 (Scenario C). However, there is considerable uncertainty in the climate change impact estimate with extreme estimates ranging from -28 percent to +2 percent. 3 Rainfall-runoff modelling There is negligible projected growth in commercial forestry plantations in the Border Rivers region. The total farm dam storage volume over the entire Border Rivers region is projected to increase by 12.8 GL by ~23. The median estimate of the combined impact of climate change and farm dam development is a 1 percent reduction in mean annual runoff, with extreme estimates from -28 percent to +19 percent (Scenario D). Table 3-2. Water balance over the entire region by scenario Scenario Rainfall Runoff Evapotranspiration mm A percent change relative to Scenario A B Cdry -1% -28% -9% Cmid -1% -9% % Cwet 9% 2% 8% Ddry -1% -28% -9% Dmid -1% -1% % Dwet 9% 19% 8% CSIRO 27 November 27 Water availability in the Border Rivers 39

52 Mean monthly rainfall (mm) Scenario C range Scenario A Scenario Cmid Mean monthly runoff (mm) Scenario C range Scenario A Scenario Cmid Scenario Dmid J F M A M J J A S O N D J F M A M J J A S O N D 3 Rainfall-runoff modelling Figure 3-8. Mean monthly rainfall and modelled runoff under scenarios A, C and D averaged over across the region (C range is based on the consideration of each month separately - the lower and upper limits in C range are therefore not the same as scenarios Cdry and Cwet) Figure 3-9. Daily flow duration curves under scenarios A, C and D averaged over the region (C range is based on the consideration of each rainfall and runoff percentile separately - the lower and upper limits in C range are therefore not the same as scenarios Cdry and Cwet) 3.4 Discussion of key findings The mean annual rainfall and modelled runoff averaged over the Border Rivers region are 641 mm and 32 mm respectively. The mean annual rainfall varies from about 85 mm in the east to 5 mm in the west. The modelled mean annual runoff varies from 7 mm in the east to 15 mm in the west. Rainfall is generally higher in the winter half of the year and runoff is fairly uniform throughout the year. The Border Rivers region covers 4.1 percent of the MDB and contributes 4.7 percent of the total runoff in the MDB. The mean annual rainfall and modelled runoff over ten-years from 1997 to 26 are within 1 percent of the long-term (1895 to 26) mean values. The runoff estimates for the Border Rivers region are relatively good because there are many calibration catchments in the region from which to estimate the parameter values. Rainfall-runoff modelling with climate change projections from global climate models indicates that future runoff in the Border Rivers region is more likely to decrease than increase. Two-thirds of the modelling results show a decrease in mean annual runoff and one-third show an increase in mean annual runoff. However, although two-thirds of the results indicate a decrease in mean annual rainfall and runoff, more than half of the results also indicate that the extreme rainfall events will be more intense. 4 Water availability in the Border Rivers November 27 CSIRO 27

53 The best estimate is a 9 percent reduction in mean annual runoff by ~23 relative to ~199. However, there is considerable uncertainty in the modelling results with the extreme estimates ranging from -28 percent to +2 percent. These extreme estimates come from the high global warming scenario. For comparison, the range from the low global warming scenario is -9 to +5 percent change in mean annual runoff. The main sources of uncertainty are in the global warming projections and the global climate modelling of local rainfall response to the global warming. The uncertainty in the rainfall-runoff modelling of climate change impact on runoff is small compared to the climate change projections. There is negligible projected growth in commercial forestry plantations in the Border Rivers region. The total farm dam storage volume over the entire Border Rivers region is projected to increase by 12.8 GL by ~23. About 85 percent of the projected increase is in the New South Wales part of the Border Rivers region. The modelled reduction in mean annual runoff from the projected increase in farm dams alone is about 1 percent, which is relatively small compared to the best estimate climate change impact on runoff (9 percent). The median estimate of the combined impact of climate change and farm dam development is a 1 percent reduction in mean annual runoff, with extreme estimates ranging from -28 percent to +19 percent. There is considerable uncertainty in the projection of future increases in farm dam development and the impact of these new farm dams on runoff. The increase in farm dams is estimated by considering trends in historical farm dam growth and current policy controls in New South Wales and Queensland and there is uncertainty both as to how land holders will respond to these policies and how governments may set policies in the future. However, the uncertainties in the farm dam projections are considerably greater for New South Wales than for Queensland, as unlike current Queensland policy, current New South Wales policy does not prevent the development of farm dams for irrigation use. 3.5 References Agrecon (25) Agricultural Reconnaissance Technologies Pty Ltd Hillside Farm Dams Investigation. MDBC Project 4/4677DO. Australian Bureau of Statistics (24) Population projections for Statistical Local Areas 22 to 222. Statistical Consultancy Project by the Australian Bureau of Statistics. Chiew et al. (27) Rainfall-runoff modelling across the Murray-Darling Basin. A report to the Australian government from the CSIRO Murray-Darling Basin Sustainable Yields Project. CSIRO, Australia. In prep. Geosciences Australia (27) Man made hydrology GIS coverage. Potter NJ, Chiew FHS, Frost AJ, Srikanthan R, McMahon TA, Peel MC and Austin JM (27) Characterisation of recent rainfall and runoff across the Murray-Darling Basin. A report to the Australian government from the CSIRO Murray-Darling Basin Sustainable Yields Project. CSIRO, Australia. In prep. Queensland Government (2) Water Act 2. 3 Rainfall-runoff modelling CSIRO 27 November 27 Water availability in the Border Rivers 41

54 4 River system modelling This chapter includes information on the river system modelling for the Border Rivers region. It has four sections: a summary an overview of the regional modelling approach a presentation and description of results a discussion of key findings. 4 River system modelling The information in this chapter is derived from the calibrated IQQM models for the for the Macintyre Brook and Border Rivers systems supplied by the Queensland Department of Natural Resources and Water (DNRW) and New South Wales Department of Water and Energy (DWE). 4.1 Summary Issues and observations River system modelling for the Border Rivers region considers ten modelling scenarios: Scenario O Scenario O represents the original river system model configuration that was used for planning purposes in DNRW and DWE. It is run over the original planning period (1 January 189 to 3 September 2) used by DWE in developing the Border Rivers Water Sharing Plan (DWE, 27) and by DNRW in developing the Border Rivers Draft River Operations Plan (DNRW, 27). Scenario AO Scenario AO is based on the original river system model (Scenario O) but run for a common historical climate period (1 June 1895 to 3 June 26). It includes current levels of development. This scenario does not consider the equilibrium impacts of current groundwater extraction on the river. Scenario A Scenario A is based on Scenario AO with the equilibrium impacts of groundwater extraction on the river. This scenario is the baseline against which all other scenarios are compared. Scenario P Scenario P is based on Scenario A but with all public storages and demand nodes removed from the model to represent pre-development conditions. Natural water bodies, fixed diversion structures and existing catchment runoff characteristics are not altered. Scenarios Cwet, Cmid and Cdry Scenarios Cwet, Cmid and Cdry represent a range of future climate conditions derived by adjusting the historical climate and flow inputs of Scenario A (see Chapter 3). Includes current water resource development. Scenarios Dwet, Dmid and Ddry Scenarios Dwet, Dmid and Ddry is based on the C scenarios but with flow inputs adjusted for estimated impacts of farm dams (see Chapter 3) and groundwater extraction (see Chapter 6) by 23. Includes the equilibrium impacts of groundwater extraction on streamflow. These future scenarios are not of conditions that will eventuate, but describe the range of outcomes that are likely if no management changes were made. Consequently the results highlight pressure points in the system. This assessment does not elaborate on what management actions might be taken to address any of these pressure points. The Border Rivers region is described by two river models: the Macintyre Brook model and the Border Rivers model. The Macintyre Brook model connects to the Border Rivers model at the Booba Sands gauge (416415) on the Macintyre Brook. The Macintyre Brook model: 42 Water availability in the Border Rivers November 27 CSIRO 27

55 is configured to represent the full utilisation of Queensland medium security licences. Consequently the demands generated represent what could be diverted if licences were fully utilised. The observed history of use is smaller than what is reflected in this configuration of the model models irrigation demands using a soil moisture accounting model that is configured with large areas and monthly demand patterns that ensure all available water is utilised. Consequently the demands do not reflect the variation in demands due to climatic influences has fixed modelled crop areas that do not reflect any change in irrigated area as a function of available water includes 6.4 GL/year of medium security entitlement from the Coolmunda system for Queensland irrigators in the Border Rivers. This water is subject to Coolmunda allocations levels and is delivered to downstream users as inflows at Booba Sands. The Border Rivers model: is configured to represent the current level of irrigation infrastructure, areas, crop mix and consequent water use. The model is calibrated to represent farm management practices in relation to on-farm storage use, including floodplain harvesting. The model thus represents current demands. Modelled demands however, differ from the history of use as farm development is not static over time models irrigation demands using a soil moisture accounting model that is configured with areas, crop mixes, farm dams and farm infrastructure that represent current development. The model includes a risk function that adjusts areas planted as a function of available water. The model therefore represents the change in demand as a function of available resource and climatic conditions models town water supplies as a fixed demand. Town water supply is a high security use that is always met except when supply storages reach dead storage capacity 4 River system modelling includes A Class and B Class New South Wales general security licences. A Class entitlements have a higher security rating than B Class entitlements. B Class allocations only occur when A class licences are at full entitlement, and A Class allocations are only restricted when B Class allocations are zero is configured with state sharing. This means that state ownership of inflows is specified as well as capacity shares in Glenlyon Dam and Boggabilla Weir. Surplus events are allocated on a state basis and any underutilised water is shared to the other state with a payback arrangement in Glenlyon Dam. Analysis of the pre-development flows along the Border Rivers system indicates that it changes from a gaining to a losing stream (point of maximum average annual flow) at the Boggabilla gauge (4162). The pre-development average annual flow at this gauge over the modelling period is 95 GL/year. The Weir River and Whalan Creeks also contribute 242 and 61 GL/year respectively, making the total available flow 128 GL/year. The Queensland Water Resource Operations Plan is based on results for the original model (Scenario O) that runs over a different climatic period to the common modelling period used in this study. The difference in modelling period causes a 1.3 percent reduction in the Mungindi end-of-system flows Key messages Current average water availability is 128 GL/year. The current level of use is high 34 percent of average available water is diverted for use. The high level of use has reduced end-of-system flows and has reduced the reliability of supply for water users. New South Wales general security water is highly utilised with 82 percent of the allocated general security water used. Queensland medium security water in the Glenlyon system is also highly utilised 73 percent of the allocated medium security water is used. For the Coolmunda system, the model assumes that all Queensland medium security water that is allocated is used. River flows are highly regulated Glenlyon Dam regulates 88 percent of inflows under current levels of development and Pindari Dam regulates 7 percent of inflows. CSIRO 27 November 27 Water availability in the Border Rivers 43

56 Once current groundwater extraction levels reach equilibrium with the river, the total impact will cause a streamflow reduction of 9.6 GL/year. This will change the Dumaresq River from one which gains water from groundwater to one which loses water to groundwater. This will further reduce the volume of streamflow available for use and further reduce end-of-system flows. Under the best estimate 23 climate scenario, average water availability is reduced by 1 percent and end-of-system flows are reduced by 12 percent. Under the best estimate 23 climate scenario diversions are reduced by 2 percent overall. However, the impacts on diversions would differ by water product : in New South Wales both general security and supplementary use would fall by 1 percent. In Queensland, both medium security and unsupplemented use would fall by 3 percent. Town water supply is not affected. 4 River system modelling The 23 climate extremes indicate: o increases under the wet extreme 23 climate of 18 percent in water availability, 8 percent in total diversions and 26 percent in end-of-system flows o decreases under the dry extreme 23 climate of 26 percent in water availability, 17 percent in total diversions and 34 percent in end-of-system flows o high security town water use is maintained at current levels under all 23 climate change scenarios. The environment flow objective of the Water Resource (Border Rivers) Plan 23 requires an end-of-system flow, at Mungindi, of at least 6.8 percent of the without development flow in preparing the first resource operations plan. Thus the upstream diversions should not reduce flows at Mungindi by more than 39.2 percent of the average without development flow for the simulation period used in developing the plan. Given current surface water entitlements in Border Rivers, considering equilibrium surface groundwater exchanges and for the common modelling period of this project, the flows at Mungindi are 59.5 percent of the without development flow. This indicates that the end-of-system target is sensitive to the climatic period used for modelling and to the inclusion of surface groundwater exchanges.. Under the best estimate 23 climate current Border Rivers entitlements would reduce flows at Mungindi to 52.9 percent of the without development flow. The range for the 23 climate extremes is from 73.6 percent (wet extreme) to 41 percent (dry extreme). Inflows for the best estimate 23 climate with future development are reduced by 41 GL/year, due to additional groundwater use and farm dam growth. This in turn reduces surface water availability by about 22 GL/year. Of this, about 55 percent is due to farm dam increases and 45 percent is due to additional groundwater use. The predicted additional river leakage of around 9 GL/year due to increases in groundwater extraction near the Dumaresq River would further reduce surface water availability Robustness The model was run for an extreme climate scenario to assess how robustly it would behave. Typically the physical processes in the model, such as routing and storage behaviour, work through a full range of flow and storage conditions. However, management rules in the model are closely tied to the historic data set that was used to develop them. When the historic data set is changed to much drier conditions there is no guarantee that models will behave robustly. Therefore it is important to check that models will perform reasonably when allocations and storages are zero or close to empty. During this test scenario, allocations were zero in Queensland and 1 percent in New South Wales. Coolmunda Dam was drawn below dead storage (22 ML) and Glenlyon Dam almost reached dead storage (6 ML). Both models behaved robustly during this extreme test. The model response to increases and decreases in inflow was reasonable, with the change in diversions and end-of-system flows being consistent with the change in inflow. Mass balance over the modelling period was maintained with.1 percent for all scenarios (Appendix B). 44 Water availability in the Border Rivers November 27 CSIRO 27

57 4.2 Modelling approach The following section provides a summary of the generic river modelling approach, a description of the Macintyre Brook and Border Rivers models, and how the river models were developed. Refer to Chapter 1 for more details on the overall project methodology General River system models that encapsulate descriptions of current infrastructure, water demands, and water management and sharing rules are used to assess the implications of changes in inflows on the reliability of water supply to users. Given the time constraints of the project, and the need to link the assessments to state water planning processes, it is necessary to use the river system models currently used by state agencies and the Murray-Darling Basin Commission. The main models in use are IQQM, REALM, MSM-Bigmod, WaterCress and a model of the Snowy Mountains Hydroelectric Scheme. A few areas of the Murray-Darling Basin (MDB) have not previously been modelled, and hence some new IQQM or REALM models have been implemented. In some cases ancillary models are used to estimate aspects of water demands of use in the river system model. A key example is the PRIDE model used to estimate irrigation for Victorian REALM models. River systems that do not receive inflows or transfers from upstream or adjacent river systems are modelled independently. This is the case for most of the river systems in the MDB, and for these rivers the modelling steps are: model configuration model warm-up to set initial values for all storages in the model, including public and private dams and tanks, river reaches and soil moisture in irrigation areas using scenario climate and inflow time series, run river model for all scenarios (historical, recent and future climate as well as future development) where relevant, extract initial estimates of surface-groundwater exchanges and provide to groundwater model where relevant, use revised estimates of surface-groundwater exchanges from groundwater models and re-run river model for all scenarios. 4 River system modelling For river systems that receive inflows or transfer from upstream or adjacent river systems, model inputs for each scenario are taken from the upstream model(s). In a few cases several iterations are required between upstream and downstream models because of the complexities of the water management arrangements. An example is the connections between the Murray, Murrumbidgee and Goulburn regions and the Snowy Mountains Hydro-electric Scheme Model description The Border Rivers region is described by the Border Rivers system model (Figure 4-1). The system is made up of two linked models: the Macintyre Brook model and the Border Rivers model (DLWC, 1999). Macintyre Brook model The Macintyre Brook model is an IQQM V representation of the Macintyre Brook system from Coolmunda Dam to its confluence with the Dumaresq River. The outflows from Macintyre Brook are inflows into the Border Rivers system. This is modelled as two outflow nodes that represent the regulated and unregulated components of flows at the Booba Sands gauge (416415). The model represents the Macintyre Brook system with 4 links and 41 nodes arranged into seven river sections. Coolmunda Dam is the only regulated storage in the model (Table 4-1). Two unregulated weirs, Whetstone and Ben Dor, are also included in the model. Water use is modelled by seven nodes five Queensland medium security irrigators and two Queensland town water supplies (Table 4-2). The Macintyre Brook is operated under an annual accounting scheme. However, 6.4 GL/year of entitlement is delivered to Queensland irrigators in the Border Rivers system. CSIRO 27 November 27 Water availability in the Border Rivers 45

58 Border Rivers model The Border Rivers is modelled by a custom version of IQQM based on IQQM V (DLWC, 1999). The model commences with headwater inflows from Pike Creek into Glenlyon Dam and the Severn River (New South Wales) into the enlarged Pindari Dam. The model ends at three locations Barwon River at Mungindi (4161), Boomi River at Neeworra (41628) and the Little Weir River. These three outflows are inflows into the Barwon-Darling region. The model represents the Border Rivers system with 44 links and 441 nodes arranged into 69 river sections. The natural weir pools and floodplains along the length of the Border Rivers are modelled by 12 storage nodes. Pindari Dam, Glenlyon Dam and Boggabilla Weir are the only regulated storages in the model (Table 4-1). 4 River system modelling Water use is modelled by 115 nodes, comprising 6 Queensland unsupplemented access irrigators, 31 Queensland medium security irrigators, three Queensland town water supplies, 13 New South Wales general security irrigators, five New South Wales unregulated irrigators and three New South Wales high security town water supplies (Table 4-2). The irrigation nodes include 47 GL of farm storage. The model assumes that Pindari Dam will make a seasonal release of inflow of up to 15 ML/day January to March, up to 5 ML/day April to June and up to 15 ML/day July to December. On top of this requirement, a minimum release of 1 ML/day is made. The first 1 ML/day of tributary inflow is not allocated for consumptive use and allowed to flow to the endof the system. The model includes state sharing of Glenlyon Dam and Boggabilla Weir. There is also state sharing of inflows and surplus flows. New South Wales supplementary flow access is constrained by a 12 GL/year cap while Queensland unsupplemented access is constrained as detailed in the Draft Resource Operations Plan (DNRM, 26). Both New South Wales and Queensland regulated users operate under a continuous accounting scheme. New South Wales can hold up to 152 percent of their entitlement in storage but are restricted to use 1 percent of their entitlement within a water year. Queensland is physically constrained to holding 82 percent of their entitlement, due to limited storage in Glenlyon Dam, but can use 1 percent of their entitlement within a water year. 46 Water availability in the Border Rivers November 27 CSIRO 27

59 4 River system modelling Figure 4-1. River system map showing major rivers, and model subcatchments, reaches, calibration reaches, inflow gauges, nodes and links Major supply reservoirs Table 4-1. Storages in the river system model Active storage GL Average annual Inflow Average annual release GL/y Average annual net evaporation Degree of regulation Glenlyon Dam Pindari Dam Coolmunda Dam Boggabilla Weir Private storages On-farm storages 47 Natural water bodies Floodplains 1157 Total High security Table 4-2. Modelled water use configuration Number of nodes Licence GL/y Pump Model notes constraints ML/d Qld town water supply Monthly demand pattern NSW town water supply 3.63 Monthly demand pattern Irrigation Soil moisture accounting single store for each crop type crops CSIRO 27 November 27 Water availability in the Border Rivers 47

60 Number of nodes Licence Pump Model notes constraints Qld medium security On-farm storage at most nodes Qld unsupplemented access 6 unrestricted Area changes based on available resource NSW general security NSW surplus flow access Total Table 4-3. Model water management 4 River system modelling Environmental flow requirements Pindari Dam Pindari Dam Tributary inflow Accounting system NSW: Glenlyon Dam, Boggabilla Weir and Large Pindari Dam QLD: Glenlyon Dam and Boggabilla Weir QLD: Coolmunda system Model setup Seasonal release of inflow, up to 15 ML/d Jan Mar, up to 5 ML/d Apr Jun and up to 15 ML/d Jul Dec Minimum release 1 ML/d 1 ML/d not allocated to consumptive users Continuous accounting 152% max, 1% use/y Continuous accounting 82% max, 1% use/y Continuous accounting The original Macintyre Brook River model and associated IQQM V executable code and Border Rivers model and associated IQQM executable were obtained from DNRW. The agreement for the use of these models was also obtained from DWE. These models were jointly developed by both of these state agencies. The Border Rivers system models were run for the original period of 1 January 189 to 3 September 2 and validated against previous results. The time series rainfall, evaporation and flow inputs to this model were extended to 3 June 26. A pre-development version of the Macintyre Brook and Border Rivers models were created by removing Pindari Dam, Glenlyon Dam, Boggabilla Weir and Coolmunda Dam, all irrigators and fixed demands. Minimum flow requirements were also removed. Natural water storages were not changed as they represent the pre-development physical characteristics of the system. The Border Rivers system contains a large amount of storage. The initial state of this storage can influence the results obtained. As the Border Rivers models start with a warm up period from 1 June 1895 to 3 June 1895 the initial state of Pindari Dam, Glenlyon Dam, Boggabilla Weir, Coolmunda Dam and all natural water body storages needs to be determined. To do this the model was started with all of these storages empty and run up to 31 May 1895 and the final storage volumes were recorded. This was repeated with all of the storages initially full. The results of this analysis are presented in Table 4-4 and show that under both cases the storages converged to a similar result. Each storage was subsequently configured with this storage volume. 48 Water availability in the Border Rivers November 27 CSIRO 27

61 Table 4-4. Model setup information Model setup information Version Start date End date Border Rivers IQQM (special) 1/1/189 3/9/2 Macintyre Brook IQQM /1/189 3/9/2 Connection Baseline models Mungindi gauge Boomi at Neeworra Little Weir River Barwon River outflows to Barwon-Darling Boomi River outflows to Barwon-Darling Little Weir River outflows to Barwon-Darling Warm-up period 1/6/1895 3/6/1895 Border Rivers IQQM (special) 1/6/1895 3/6/26 Macintyre Brook IQQM /6/1895 3/6/26 Connection Mungindi gauge Boomi at Neeworra Little Weir River Border Rivers modifications Barwon River outflows to Barwon-Darling Boomi River outflows to Barwon-Darling Data Extend to 3/6/26 Inflows Groundwater loss nodes Groundwater gain nodes Little Weir River outflows to Barwon-Darling No adjustment required Subcatchments , and Initial storage volume Glenlyon Dam (GL) Initial storage volume Pindari Dam (GL) Initial storage volume Coolmunda Dam (GL) 9.36 Initial storage volume Boggabilla Weir (GL) 3 Warm up test results Setting initial storage volumes Storages commence empty GL n/a Storages commence full Difference Percent Percent of full volume Glenlyon Dam storage volume 31/5/ % -.69% Pindari Dam storage volume 31/5/ % 2.46% Coolmunda Dam storage volume 31/5/ Boggabilla Weir storage volume 31/5/ Natural water bodies storage volume 31/5/1895 Storage volume 3 May ( ) Mean Median Glenlyon Dam Pindari Dam Coolmunda Dam Boggabilla Weir Natural water bodies Robustness test results Minimum allocation (%) 1. NSW: Glenlyon Dam, Boggabilla Weir and Large Pindari Dam 2. Qlld: Glenlyon Dam and Boggabilla Weir % 3. Qld: Coolmunda system % Minimum storage volume (ML) Glenlyon Dam (DSV 6) 6411 Pindari Dam (DSV 8) 21,583 Coolmunda Dam (DSV 22) 21 Boggabilla Weir (DSV 415) 423 GL 1% GL 4 River system modelling CSIRO 27 November 27 Water availability in the Border Rivers 49

62 The model was configured for an extreme dry climate scenario by applying seasonal factors to rainfall, evaporation and inflows (see Table 4-5). The model was run and behaved robustly, allocations in Queensland reached zero percent and in New South Wales reached 1 percent. Coolmunda Dam was the only storage to go below dead storage (22 ML), while Glenlyon Dam was close to dead storage (6 ML). Table 4-5. Rainfall, evaporation and flow factors for model robustness test Season Rainfall Evaporation Flow DJF MAM JJA SON River system modelling 4.3 Modelling results River system water balance The mass balance table (Table 4-6) shows the net fluxes for the Border River system. Scenario O (the original model scenario) fluxes, Scenario AO (without groundwater at dynamic equilibrium) and Scenario A (with groundwater at dynamic equilibrium) fluxes are displayed as GL/year, while all other scenarios are presented as a percentage change from Scenario A. Note the averaging period for Scenario O differs from all other scenarios. The directly gauged inflows represent the inflows into the model that are based on a river gauge. The indirectly gauged inflows represent the inflows that are derived to achieve mass balance between mainstream gauges. Diversions are listed based on the different water products in the reporting region. End-of-system flows are shown for the three end-of-system points and net evaporation is displayed for all the natural water storages. The change in storage between 3 June 1895 and 3 June 26 averaged over the 111-year period is also included. Appendix B contains mass balance tables for the 19 subcatchments in the model. The mass balance of each of these river reaches and the overall mass balance were checked by taking the difference between total inflows and outflows of the system. In all cases the mass balance error was less than.1 percent. 5 Water availability in the Border Rivers November 27 CSIRO 27

63 Table 4-6. River system model average annual water balance under scenarios O, AO, A, C and D Model start date 1/1/189 1/7/1895 Model end date 3/9/2 3/6/26 Storage volume O AO A Cwet Cmid Cdry Dwet Dmid Ddry GL/y Change over period % -27% 38% -7% -14% 41% Inflows Subcatchments Directly gauged % -11% -28% 17% -14% -31% Indirectly gauged % -7% -28% 19% -8% -29% Groundwater inflows % % % % % % Sub-total % -8% -28% 18% -1% -29% Diversions Licensed private diversions NSW general security (entitlement GL/y) % -1% -15% 6% -5% -2% NSW supplementary access % -1% -14% 5% -3% -16% NSW unregulated access % -23% -33% 24% -23% -33% Qld medium security (entitlement 1.77 GL/y) Qld unsupplemented access Border Rivers Qld unsupplemented access Weir River % -3% -25% 3% -8% -29% % -3% -2% 8% -5% -22% % -2% -12% 8% -3% -13% Sub-total % -2% -17% 6% -5% -2% Urban supply NSW town water supply (entitlement.63 GL/y) Qld town water supply (entitlement 2.67 GL/y) % % % % -1% -1% % % % % % -1% Sub-total % % % % -1% -1% Sub-total % -2% -17% 6% -5% -19% Outflows End-of-system outflow to Barwon River at Mungindi gauge % -11% -31% 2% -15% -34% Boomi River at Neeworra % -11% -37% 26% -14% -39% Little Weir River % -19% -48% 34% -21% -49% Sub-total % -12% -34% 23% -15% -37% Net evaporation* Public storages % 4% -1% 9% 1% -13% Natural water bodies and floodplains % 2% -4% 4% 1% -4% Sub-total % 3% -7% 7% 1% -9% Other losses River groundwater loss % % 4% 83% 93% 96% Sub-total % -1% -31% 22% -12% -32% Unattributed fluxes Total % -1% -3% 2% -12% -32% * Evaporation from private licensed storages (GL/year) is not included as it is already accounted in diversions 4 River system modelling Inflows and water availability Inflows There are several ways that the total inflows into the river system can be calculated. The obvious way would be to sum all of the inflows in the model. For the Border Rivers IQQM model this is 286 GL/year (Table 4-6). CSIRO 27 November 27 Water availability in the Border Rivers 51

64 However, the table also shows that a large proportion of the inflow is indirectly gauged and therefore estimated as part of model calibration. The approach used to calibrate these inflows varies considerably between model implementations. In some cases inflows are inflated and subsequently compensated for by loss relationships and in other cases the losses are inherent in the inflows. Because of these different approaches to calibration, totalling inflows does not provide a consistent assessment of total river system inflows across different models. An alternative to simply totalling modelled inflows is to locate the point of maximum average annual flow in the river system under pre-development conditions. As all river models are calibrated to achieve mass balance at mainstream gauges, the gauge with maximum average annual flow is a common reference across all models irrespective of how mass balance is calibrated. The pre-development scenario removes the influences of upstream extractions and regulation and gives a reasonable indication of total inflows without the influence of development. 4 River system modelling This can be repeated for each of the climate scenarios by running the pre-development model with each of the climate scenario inputs. The estimation of the location of maximum annual flow in the Border Rivers is made difficult by the number of anabranches and adjoining tributaries. A transect of the river can be taken from the headwaters of Glenlyon following the Dumaresq river taking into consideration the contribution of Macintyre Brook and the Macintyre River at the Boggabilla gauge. After the Boggabilla gauge the river breaks into various branches that create parallel systems in both New South Wales (Whalan Creek, Croppa Creek and Boomi River) and Queensland (Callandoon and Dingo creeks, Coomongra Creek, Newinga Breakout, Weir River and Little Weir River). Whalan Creek breaks out from the Macintyre River upstream of the Dumaresq River confluence and joins the Boomi River and contributes to the flow at the Boomi end-of-system gauge at Neeworra (41628). Whalan Creek has local inflows form Mobbindry, Tackinbri and Croppa creeks. Only Croppa Creek inflows are gauged and the remaining contributions are estimated by factoring Croppa Creek inflows. The Boomi River receives inflows from the Macintyre River at Boomi Weir, Little Barwon Creek upstream of Kanowna Gauge (41648) and from Boomongerra Creek downstream of Kanowna. Callandoon and Dingo creeks break out of the Macintyre River below Boggabilla gauge and return downstream of the Terrewah gauge. Coomongra Creek breaks out downstream of Terrewah gauge and returns downstream of the Boomi Weir gauge. The Newinga breaks out downstream of Boomi Weir gauge and receives inflows from the Weir River at Tallwood gauge (41622) and the ungauged Yarrilwanna anabranch. The Newinga Breakout and Weir River return to the Macintyre River upstream of the Mungindi gauge. The Little Weir River breaks out upstream of the Mungindi gauge and is an ungauged end-of-system outflow. The point of maximum flow in the Border Rivers can be estimated by plotting gauges from the headwaters of the Dumaresq River to the Macintyre at Boggabilla and then combining end-of-system outflows. Note that by totalling end-of-system flows at Little Weir River, Mungindi Gauge (4161) and Boomi River at Neeworra (41628), contributions on the Weir and Whalan systems are also considered. This transect is presented in Figure 4-2 and shows that the maximum average annual mainstream flow occurs in subcatchment at the Boggabilla gauge (4162) with a value of 94.7 GL/year for the pre-development Scenario A. Annual flow (GL) C range Cmid A EOS total Figure 4-2. Transect of Dumaresq-Macintyre average annual river flow under pre-development scenarios A and C 52 Water availability in the Border Rivers November 27 CSIRO 27

65 Water availability The water availability in the Border Rivers can be estimated by considering the Border Rivers as three parallel systems; the Dumaresq-Macintyre rivers, the Weir River and Whalan Creek. The water availability can be estimated by totalling the points of maximum flows in each of these parallel systems. The point of maximum flow in the Dumaresq-Macintyre rivers was determined to be Boggabilla gauge (Figure 4-2). The Weir River flows are considered as the total of flows at the Tallwood gauge (41622) and the Yarriilwanna anabranch. The Whalan Creek flows are the total of Macintyre breakouts and Mobbindry, Tackinbri and Croppa creek inflows. Table 4-7 shows points of maximum flow for each of these systems as well as the total for the reporting region for the pre-development Scenario A in GL/year and the relative change in pre-development water availability for scenarios C and D. Table 4-7. Annual water availability for pre-development Scenario A and relative change under pre-development scenarios C and D A Cwet Cmid Cdry Dwet Dmid Ddry GL/y Dumaresq-Macintyre % -1% -26% 17% -11% -27% Weir River % -7% -22% 12% -11% -25% Whalan Creek % -16% -38% 21% -24% -44% Total % -1% -26% 16% -11% -28% A time series of total annual water availability under pre-development Scenario A is shown in Figure 4-3. The lowest annual water availability was 188 GL in 1935 while the highest annual water availability was 5592 GL in Figure 4-4 shows the time series change in annual water availability relative to pre-development Scenario A for pre-development Scenario C and pre-development Scenario D. 4 River system modelling Annual water availability (GL) Figure 4-3. Pre-development Scenario A water availability CSIRO 27 November 27 Water availability in the Border Rivers 53

66 (a) (b) 4 River system modelling Annual water availablity (GL) C range Cmid Annual water availablity (GL) D range Dmid Figure 4-4. Time series of change in total water availability relative to pre-development scenario A under (a) pre-development Storage behaviour scenario C and (b) pre-development scenario D The modelled behaviour of major public storages gives an indication of the level of regulation of a system, as well as how reliable the storage is during extended periods of low or no inflows. Table 4-8, Table 4-9, Table 4-1 and Table 4-11 provide indicators that show the lowest recorded storage for Glenlyon Dam, Pindari Dam, Coolmunda Dam and Boggabilla Weir for each of the scenarios. The average and maximum years between spills are also provided. The period between spills commences when the storage exceeds full supply volume and ends when the storage falls below 9 percent of full supply volume. The end condition is applied to remove the periods when the dam is close to full and oscillates between spilling and just below full which distorts the analysis. Table 4-8. Details of Glenlyon Dam behaviour A Cwet Cmid Cdry Dwet Dmid Ddry Minimum storage volume (ML) Minimum storage date 19/1/ /1/ /11/192 28/1/ /1/ /3/193 21/1/1995 Average years between spills Maximum years between spills Table 4-9. Details of Pindari Dam behaviour A Cwet Cmid Cdry Dwet Dmid Ddry Minimum storage volume (ML) Minimum storage date 18/6/ /2/23 18/6/ /3/ /1/ /6/ /3/1989 Average years between spills Maximum years between spills Water availability in the Border Rivers November 27 CSIRO 27

67 Table 4-1. Details of Coolmunda Dam behaviour A Cwet Cmid Cdry Dwet Dmid Ddry Minimum storage volume (ML) Minimum storage date 25/8/1937 5/1/1895 6/1/1895 5/1/1895 5/1/1895 6/1/1895 5/1/1895 Average years between spills Maximum years between spills Table Details of Boggabilla Weir behaviour A Cwet Cmid Cdry Dwet Dmid Ddry Minimum storage volume (ML) Minimum storage date 14/8/192 6/1/1914 1/8/192 6/1/ /8/192 7/8/192 2/8/192 Average years between spills Maximum years between spills The time series of storage behaviour for each storage for the maximum period between spills for Scenario A and the change for the C and D scenarios are shown in Figure 4-5, Figure 4-6, Figure 4-7 and Figure River system modelling (a) (b) Volume (ML) A Cmid Cwet Cdry Volume (ML) A Dwet Dmid Ddry Figure 4-5. Glenlyon Dam behaviour over the maximum days between spills under Scenario A with change in storage behaviour under (a) Scenario C and (b) Scenario D CSIRO 27 November 27 Water availability in the Border Rivers 55

68 (a) (b) Volume (ML) A Cwet Cmid Cdry Volume (ML) A Dwet Dmid Ddry River system modelling Figure 4-6. Pindari Dam behaviour over the maximum days between spills under Scenario A with change in storage behaviour under Volume (ML) (a) A Cwet Cmid Cdry (a) Scenario C and (b) Scenario D Volume (ML) (b) A Dwet Dmid Ddry Figure 4-7. Coolmunda Dam behaviour over the maximum days between spills under Scenario A with change in storage behaviour under (a) Scenario C and (b) Scenario D (a) (b) Volume (ML) A Cwet Cmid Cdry Volume (ML) A Dwet Dmid Ddry 1 1 Jan 1926 Apr 1926 Jul 1926 Oct 1926 Jan 1926 Apr 1926 Jul 1926 Oct 1926 Figure 4-8. Boggabilla Weir behaviour over the maximum days between spills under Scenario A with change in storage behaviour under (a) Scenario C and (b) Scenario D 56 Water availability in the Border Rivers November 27 CSIRO 27

69 4.3.4 Consumptive water use Diversions Table 4-12 shows the total average annual diversions for each subcatchment for Scenario A and the percentage change of all other scenarios compared to Scenario A. Figure 4-9 shows total average annual diversions for all scenarios for the Pindari system, Coolmunda system, Glenlyon Dam to Boggabilla Weir, Weir River and Boggabilla Weir to the end-of-system. Table Change in total diversions in each subcatchment relative to Scenario A Region Reach A Cwet Cmid Cdry Dwet Dmid Ddry Pindari Coolmunda Glenlyon GL/y percent change from Scenario A % % % % % % % % % % % % % 2% -2% 2% -1% -5% % % % % % % % 2% -6% 2% % -1% % 1% -16% 5% 1% -16% % 1% -12% 4% 1% -12% % 1% -17% 5% 1% -17% % % % % % % % % % % % % % -2% -16% 4% -7% -22% % -4% -16% 4% -8% -21% % -1% -17% 5% -4% -21% Weir River % % -9% 5% -1% -1% Boggabilla to EOS % -2% -17% 6% -5% -2% % -4% -21% 8% -7% -24% % -4% -21% 8% -7% -24% % -23% -51% 12% -18% -53% % % % % % % Total % -2% -17% 6% -5% -19% 4 River system modelling (a) (b) Annual diversions (GL) C range Cmid A Annual diversions (GL) D range Dmid A Pindari Coolmunda Glenyon Weir River Bogabilla to EOS Pindari Coolmunda Glenyon Weir River Bogabilla to EOS Figure 4-9. Total average annual diversions for subcatchments under (a) scenarios A and C and (b) scenarios A and D Figure 4-1 shows an annual time series of total diversion for Scenario A and the difference from Scenario A for scenarios C and D. The minimum and maximum diversions for Scenario A are 99 GL in 1915 and 789 GL in 192 respectively. CSIRO 27 November 27 Water availability in the Border Rivers 57

70 (a) (b) Annual diversions (GL) Annual difference (GL) River system modelling Annual difference (GL) (c) Annual difference (GL) (d) (e) (f) Annual difference (GL) Annual difference (GL) (g) Annual difference (GL) Figure 4-1. Total diversions for (a) Scenario A and difference between total water use under (b) Scenario Cwet; (c) Scenario Cmid; (d) Scenario Cdry; (e) Scenario Dwet; (f) Scenario Dmid; and (g) Scenario Ddry 58 Water availability in the Border Rivers November 27 CSIRO 27

71 Level of use The level of use for the region is indicated by the ratio of total net diversions (extraction less any returns) to total inflows. Total net diversions are defined as the net water diverted for the full range of water products. This indicates the share of the available water that is diverted for consumptive use. Once again the most reliable indicator of the total inflow is point of maximum mainstream average annual flow. Net diversions are used to reflect the change in the mass balance of the system. They do not take into consideration the difference in water quality that may exist between diversions and returns. Table 4-13 shows the level of use indicators for each of the scenarios. The level of use is relatively high with 34 percent of the available water being diverted for use. The development of each state is also expressed as a ratio of the total of the water available, not the water available to each state. This shows there is a similar amount of use of the available water between states with New South Wales at 16 percent and Queensland at 18 percent. Table Relative level of use under scenarios A, C and D A Cwet Cmid Cdry Dwet Dmid Ddry New South Wales 16% 15% 17% 18% 14% 17% 18% Queensland 18% 17% 19% 2% 17% 19% 2% Total 34% 31% 37% 38% 31% 37% 38% Use during dry periods 4 River system modelling Table 4-14 shows the average use for all water products, as well as the average annual use for the lowest one, three and five-year periods for Scenario A and the percentage change from Scenario A for each other scenario. These figures indicate the impact on water use during dry periods. Table Indicators of use during dry periods under scenarios A, C and D Annual Diversion A Cwet Cmid Cdry Dwet Dmid Ddry GL/y percent change from Scenario A Lowest 1-year period % -12% -47% 45% -24% -56% Lowest 3-year period % 7% -51% 19% -3% -56% Lowest 5-year period % -3% -46% 21% -1% -51% Average % -2% -17% 6% -5% -19% Reliability The average reliability of water products can be indicated by the ratio of total net diversions to the total long-term average diversion limit or equivalent benchmark. For the Border Rivers region high security town water supply use is compared against the licensed volume of.63 GL for New South Wales and 2.67 GL for Queensland users. General security regulated water use is compared against the licensed volume of GL for New South Wales and medium security licensed volume GL for Queensland users in the Border Rivers and GL for Queensland users in the Coolmunda system. Table 4-15 shows the average reliability for Scenario A and the relative change for scenarios C and D. Note that the New South Wales supplementary access is more reliable than the regulated supply. CSIRO 27 November 27 Water availability in the Border Rivers 59

72 Table Average reliability of water products under Scenario A, and relative change under scenarios C and D A Cwet Cmid Cdry Dwet Dmid Ddry percent relative to Scenario A Licensed private usage NSW general security (entitlement GL).4 7% -1% -15% 6% -5% -2% Qld Glenlyon medium security (entitlement GL).25 1% -6% -31% 2% -15% -39% Qld Coolmunda medium security (entitlement GL).87 5% 1% -17% 5% 1% -17% NSW supplementary flow access (12 GL cap).73 7% -2% -15% 5% -3% -17% Qld unsupplemented access.3 9% -3% -17% 8% -4% -18% NSW town water supply (entitlement.63 GL).98 % % % % -1% -1% Qld town water supply (entitlement 2.67 GL).98 % % % % % -1% 4 River system modelling In most systems there is a difference between the water that is available for use and the water that is actually diverted for use. These differences are due to under utilisation of licenses and water being provided from other sources such as rainfall, surplus flows, on farm storages and groundwater. The difference between available and diverted water will vary considerably across products and time. Figure 4-11, Figure 4-12 and Figure 4-13 show the difference between the maximum yearly allocated general and medium security water and the general and medium security use for each of the scenarios in volume reliability plots. (a) (b) Annual volume (GL) Allocated (A) Diverted (A) Annual volume (GL) Allocated (Cwet) Allocated (Dwet) Diverted (Cwet) Diverted (Dwet) Percent of years exceeded Percent of years exceeded (c) (d) Annual volume (GL) Allocated (Cmid) Allocated (Dmid) Diverted (Cmid) Diverted (Dmid) Annual volume (GL) Allocated (Cdry) Allocated (Ddry) Diverted (Cdry) Diverted (Ddry) Percent of years exceeded Percent of years exceeded Figure New South Wales general security reliability under scenarios (a) A; (b) Cwet and Dwet; (c) Cmid and Dmid; (d) Cdry and Dry 6 Water availability in the Border Rivers November 27 CSIRO 27

73 Note that during periods of low allocation the diversions may exceed the allocations. This is because the New South Wales Border Rivers licence holders have both A and B class entitlements. The allocations that are plotted on this graph are for B class entitlements. When B class allocations reach zero A class entitlements are subject to allocations. During these periods the A class entitlements are fully utilised, that is, allocations match diversions. (a) (b) Annual volume (GL) Annual volume (GL) (c) Percent of years exceeded Allocated (A) Diverted (A) Allocated (Cmid) Allocated (Dmid) Diverted (Cmid) Diverted (Dmid) Annual volume (GL) Annual volume (GL) (d) Allocated (Cwet) Allocated (Dwet) Diverted (Cwet) Diverted (Dwet) Percent of years exceeded Allocated (Cdry) Allocated (Ddry) Diverted (Cdry) Diverted (Ddry) 4 River system modelling Percent of years exceeded Percent of years exceeded Figure Queensland Glenlyon medium security reliability under scenarios (a) A; (b) Cwet and Dwet; (c) Cmid and Dmid; (d) Cdry and Ddry CSIRO 27 November 27 Water availability in the Border Rivers 61

74 (a) (b) 2 2 Annual volume (GL) Allocated (A) Diverted (A) Annual volume (GL) Allocated (Cwet) Allocated (Dwet) Diverted (Cwet) Diverted (Dwet) Percent of years exceeded Percent of years exceeded 4 River system modelling Annual volume (GL) (c) Allocated (Cmid) Allocated (Dmid) Diverted (Cmid) Diverted (Dmid) Annual volume (GL) (d) 5 Allocated (Cdry) Allocated (Ddry) Diverted (Cdry) Diverted (Ddry) Percent of years exceeded Percent of years exceeded Figure Coolmunda system medium security reliability under scenarios (a) A; (b) Cwet and Dwet; (c) Cmid and Dmid; (d) Cdry and Ddry Note in Figure 4-13 the Coolumunda system assumes full utilisation of entitlement, and hence allocation and diverted water are almost equal. Figure 4-14 shows the reliability of unsupplemented water access for Queensland and supplementary access for New South Wales irrigators and town water supplies for each of the scenarios. For the New South Wales supplementary access this graph was drawn based on the water year in the model and region, that is, October to September. A different water year was used to ensure the access is consistent with the annual 12 GL cap for the October to September water year. 62 Water availability in the Border Rivers November 27 CSIRO 27

75 (a) (b) Annual diversion (GL) C range Cmid A Annual diversion (GL) C range Cmid A % 2% 4% 6% 8% 1% Percent of years equal or exceeded % 2% 4% 6% 8% 1% Percent of years equal or exceeded Annual diversion (GL) (c) D range Dmid A % 2% 4% 6% 8% 1% Percent of years equal or exceeded Annual diversion (GL) (d) D range Dmid A % 2% 4% 6% 8% 1% Percent of years equal or exceeded 4 River system modelling Figure Reliability of unsupplemented and supplemented access water for (a) Queensland irrigators under Scenario C, (b) New South Wales irrigators and town water supplies under Scenario C, (c) Queensland irrigators under Scenario D and (d) New South Wales irrigators and town water supplies under Scenario D Table 4-16 shows the average annual difference between available water and diverted water for each of the general and medium security water products. This table gives an indication of the level of utilisation of the various water products in the Border Rivers region. Table Summary of average allocated water and diverted water for NSW general security licences and Queensland medium security licences A Cwet Cmid Cdry Dwet Dmid Ddry GL/y NSW general security Allocated water Diversion Difference Queensland Border Rivers medium security Allocated water Diversion Difference Queensland Coolmunda medium security Allocated water Diversion Difference CSIRO 27 November 27 Water availability in the Border Rivers 63

76 4.3.5 River flow behaviour There are many ways of considering the flow characteristics in river systems. For this report three different indicators are provided: daily flow duration, seasonal plot and daily event frequency. Mid-river flow characteristics The flow regime will vary depending on which location in the river that is selected. For this analysis the location of the middle of the system is defined as the position where the river changes from a gaining to a losing stream. The selection of this site is discussed in Section For the Border Rivers system this is the Boggabilla gauge (4162). 4 River system modelling Figure 4-15 shows the daily flow duration curves for Scenario A and Scenario P and the range of change for scenarios C and D. For a given flow the flow duration curves show the change in frequency between scenarios for that flow. The vertical difference between flow duration curves shows the change in mass between scenarios although care needs to be taken as the plots use a logarithmic scale that distorts the difference of lower flows. Daily flow (ML) C range Cmid A P Percent time flow is exceeded Daily flow (ML) D range Dmid A P Percent time flow is exceeded Figure Daily flow duration curves under scenarios P, A, C and D at Boggabilla gauge (4162) Figure 4-16 shows the mean monthly flow for Scenario P and Scenario A. This shows that the seasonality in the middle of the river is similar between pre-development and Scenario A with the major difference occurring in December when flows are higher to meet downstream demands. The plots also show that climate change causes the flow to be less in winter when storages are catching water to re-regulate in the summer months. Monthly flow (ML) C range Cmid A P Monthly flow (ML) D range Dmid A P 2 2 J F M A M J J A S O N D J F M A M J J A S O N D Figure Average monthly flow at the end of the gaining reach under scenarios P, A, C and D 64 Water availability in the Border Rivers November 27 CSIRO 27

77 Table 4-17 shows the size of daily events with two, five and ten-year recurrence intervals for scenarios P, A, C and D. Note this analysis estimates the average peak daily flow and not the peak flow for a day, which is considerably higher in most river systems. The table shows that from pre-development to Scenario A there is a 15 percent reduction in the size of two-year events, a 6 percent reduction in the five-year events and a 4 percent reduction in the ten-year events. Table Daily flow event frequency under scenarios P, A, C and D Return interval P A Cwet Cmid Cdry Dwet Dmid Ddry ML/d percent change from Scenario A 2 years % -21% -28% 32% -14% -29% 5 years % -18% -22% 1% -19% -22% 1 years % -16% -21% 23% -16% -21% End-of-system flow characteristics Figure 4-17 and Figure 4-18 show flow duration curves for the three end-of-system locations: Mungindi gauge, Boomi River at Neeworra and Little Weir River. Each of the scenarios is plotted on the same plot. Daily flow (ML) (a) C range Cmid A P Daily flow (ML) (b) C range Cmid A P 4 River system modelling Percent time flow is exceeded Percent time flow is exceeded (c) Daily flow (ML) C range Cmid A P Percent time flow is exceeded Figure Daily flow duration curves under scenarios A, P and C for lower end of flows for each end-of-system flow gauge (a) Mungindi Gauge; (b) Boomi at Neeworra and (c) Little Weir River CSIRO 27 November 27 Water availability in the Border Rivers 65

78 (a) (b) Daily flow (ML) D range Dmid A P Daily flow (ML) D range Dmid A P River system modelling Percent time flow is exceeded (c) 1 Daily flow (ML) Percent time flow is exceeded D range Dmid A P Percent time flow is exceeded Figure Daily flow duration curves under scenarios A, P and D for lower end of flows for each end-of-system flow gauge (a) Mungindi Gauge; (b) Boomi at Neeworra and (c) Little Weir River Figure 4-19 and Figure 4-2 shows the mean monthly flow for the pre-development scenario, Scenario A, Scenario C and Scenario D for each of the end-of-system flow gauges. This shows that the seasonality the end-of-system has not changed in any of the scenarios. It also shows that there has been an overall reduction in flows across all seasons from pre-development and a consistent reduction in winter for all future climate scenarios. 66 Water availability in the Border Rivers November 27 CSIRO 27

79 (a) (b) Monthly flow (GL) C range Cmid A P Monthly flow (GL) C range Cmid A P J F M A M J J A S O N D J F M A M J J A S O N D Monthly flow (GL) (c) 1 C range 8 Cmid 6 A P 4 2 J F M A M J J A S O N D 4 River system modelling Figure Seasonal flow curves under scenario A, P and C at (a) Mungindi Gauge; (b) Boomi at Neeworra and (c) Little Weir River CSIRO 27 November 27 Water availability in the Border Rivers 67

80 (a) (b) Monthly flow (GL) D range Dmid A P Monthly flow (GL) D range Dmid A P J F M A M J J A S O N D J F M A M J J A S O N D 4 River system modelling Monthly flow (GL) (c) D range Dmid A P J F M A M J J A S O N D Figure 4-2. Seasonal flow curves under scenarios A, P and D at (a) Mungindi Gauge; (b) Boomi at Neeworra and (c) Little Weir River The percentage of time that flow occurs for these scenarios is presented in Table Cease-to-flow is considered to occur when model flows are less than 1 ML/day. Table Percentage of time flow occurs at the end-of-system under scenarios P, A, C and D Outflow Name P A Cwet Cmid Cdry Dwet Dmid Ddry Barwon River at Mungindi 95% 93% 95% 93% 91% 93% 89% 87% Boomi River at Neeworra 69% 76% 8% 75% 72% 8% 73% 7% Little Weir River 1% 5% 6% 4% 3% 6% 4% 3% Share of available resource Non-diverted water shares There are several ways of considering the relative level of impact on non-diverted water and diversions. Table 4-19 presents two indicators for relative impact on non-diverted water: the average annual non-diverted water as a proportion of the maximum mainstream average annual flow the average annual non-diverted water as a proportion of Scenario A non-diverted water for the Border Rivers, the current Water Resource (Border Rivers) Plan 23 (DNRM, 23) requires that 6.8 percent of the long-term average end-of-system flows at Mungindi gauge (4161) compared against predevelopment end of system flows. 68 Water availability in the Border Rivers November 27 CSIRO 27

81 Table Relative level of available water not diverted for use under scenarios A, C and D A Cwet Cmid Cdry Dwet Dmid Ddry Relative level of non-diverted water percent Non-diverted water as a percentage of total available water 66% 69% 63% 62% 69% 63% 62% Non-diverted share relative to Scenario A non-diverted share 1% 118% 9% 74% 116% 89% 72% Proportion of pre-development end-of-system flows 59.5% 73.6% 52.9% 41.% 71.3% 5.9% 39.1% Note that the results presented for Scenario A indicate a value less than the 6.8 percent required by the Water Resource (Border Rivers) Plan 23. The difference is due to a different modelling period used in developing the Water Resource Plan (1 January 189 to 3 September 2). During the period from 1 January 189 to 1 June 1895 conditions were wetter and consequently the proportion of flow at Mungindi is higher. In contrast the period from 3 September 2 to 3 June 26 is dry and the proportion of flow at Mungindi is less. The combined impact of this is a smaller proportion of pre-development Mungindi flows in Scenario A compared to the Water Resource Plan modelling. Combined water shares Figure 4-21 combines the results from water availability, use and non-diverted water into a bar chart. The size of the bars indicates total water availability and the sub-division of the bars indicates the diverted (by state) and non-diverted fractions. Annual water (GL) Non-diverted Diverted QLD Diverted NSW P A Cwet Cmid Cdry Dwet Dmid Ddry 4 River system modelling Figure Comparison of state use and non-diverted shares of water under scenarios P, A, C and D 4.4 Discussion of key findings Model configuration The Macintyre Brook river system model is configured to represent the full utilisation of licences. This is achieved by configuring nodes with large irrigation areas and monthly demand patterns. This forces each irrigation node to order water from the Coolmunda Storage up to the full allocation each year. There are several modelling implications of this type of configuration: the irrigation demands do not reflect the change in demand as a function of climatic conditions as there is always a demand for water crop areas are fixed at a large number and do not change as a function of available water resources irrigation usage is not calibrated and consequently modelled usage may be larger than actual usage this means that modelled usage will be more than actual usage even for fully developed farms. CSIRO 27 November 27 Water availability in the Border Rivers 69

82 The Macintyre Brook provides up to 6.4 GL of medium security water to the Border Rivers system. This represents Coolmunda system licences that have been sold to water users in the Border Rivers system. The model does not explicitly represent these licences and simplifies this by treating the regulated inflow from the Macintyre Brook as water that is available to all downstream Queensland irrigators. The net impact of this is to reduce the demand on Glenlyon Dam. This simplification is not likely to have a significant impact on model results Scenarios 4 River system modelling The Macintyre Brook and Border Rivers models were setup up by DNRW and DWE to operate over the period 1 January 189 to 3 September 2. The results from this study are presented for the common modelling period 1 July 1895 to 3 June 26. The water policies developed for the Queensland Draft Resource Operations Plan (DNRM, 26) and the Draft Border Rivers Water Sharing Plan (DWE, 27) are based on the original modelling period. Results presented in this report may differ from numbers published in these reports due to the different modelling period. Table 4-6 shows that there is a 4 percent decrease in inflows for the common modelling period compared to what was used to develop the various water sharing plans. This difference can be attributed to the extremely wet conditions from 189 to Scenarios AO and A are presented so that the impacts of current levels of groundwater development reaching dynamic equilibrium can be considered. The time for this to reach dynamic equilibrium is discussed in Chapter 6. Table 4-6 shows a 9.6 GL/year increase in river loss to groundwater which causes a.7 percent reduction in diversions and end-of-system flows. Additional farm dam development is estimated to cause a 1 percent decrease in inflows into the system (Chapter 3). This equates to 23 GL/year less water entering the system in the best estimate 23 climate with future development scenario. In addition to this, future groundwater development in the headwater catchments causes a further 18 GL/year reduction in inflows (Chapter 6). The combined impact of this and an additional 9 GL/year of river leakage causes a 3 percent reduction in total net diversions and a 3 percent reduction in end-of-system flows. The impacts of the best estimate 23 climate scenario are similar with an 8 percent reduction in inflows. Consequently the combined impacts of development and future climate are 5 percent on total net diversions and 15 percent on end-of-system flows Storage behaviour For current levels of development and historical climate the maximum years between spills for Glenlyon Dam is 52 years and spans the Federation drought. The average number of years between spills is 9.5 years which is reduced by the wetter conditions after 195. In contrast Pindari and Coolmunda dams spill on a much more frequent basis - on average every 2.9 and 2.7 years respectively. Additionally Glenlyon Dam and Pindari Dams respectively regulate 88 percent and 7 percent of the inflows. In both cases this is a high degree of regulation Consumptive use There is no major impact on high security users in Queensland systems as medium security allocations are nearly always above zero (Figure 4-11 and Figure 4-13). When there is a general security or medium security allocation the high security users will receive their full entitlement. However, for the New South Wales Border Rivers system for about 18 percent of the time, general security allocations are zero percent. This changes substantially for dry future climate as water is more fully utilised. Due to carry-over reserve in the resource assessment, sufficient water is reserved such that high security requirements are met in all scenarios. The Border Rivers region is managed under a continuous accounting scheme. Traditionally, many regions operated under annual accounting systems where allocation announcements were made throughout the year to set the proportion of licences made available for general and medium security users. Under continuous accounting, each licence holder has an account balance limited by their share in the storage, being 152 percent for New South Wales licensed entitlement and 82 percent for Queensland entitlements. Users are limited to a maximum usage over a period. For the Border Rivers the limit applies over a year and is 1 percent of licensed entitlement for both New South Wales and Queensland. The model keeps account of each irrigation node s account balance in storages and maintains these balances as water flows into storages and is diverted. Consequently each individual will have a different allocation 7 Water availability in the Border Rivers November 27 CSIRO 27

83 depending on their level of usage compared to licensed entitlement. The model provides an allocation output that represents the aggregation of all water users account balances divided by the licensed entitlement. This aggregated allocation is presented in Figure 4-11, Figure 4-12 and Figure Due to the nature of individual balances, actual usage may exceed allocated water as individual irrigators that have higher allocations than the average divert their water. Hence, in the reliability figures it is possible for diversions to exceed averaged allocations. Also in dry years, when general security allocations are zero, New South Wales irrigators are able to draw on their A Class entitlements, thus allowing usage exceeding the B Class allocations used in deriving this table. The reliability of general and medium security water products in the Border Rivers for current development and historical climate is relatively low at 4 percent for New South Wales general security users and 25 percent for Queensland medium security users Flow behaviour The end-of-system low flows in the Boomi River at Neeworra are larger than pre-development conditions. This is due to the influence of the Boomi Weir regulating water down the Boomi anabranch. However, the total flow leaving the system at all end-of-system gauges is smaller than pre-development conditions as 34 percent of available water is diverted for use under current levels of development. End-of-system cease-to-flow percentiles at Mungindi and Neeworra are largely maintained through all climate change scenarios. This is due to a water management requirement that stops the allocation of the first 1 ML/day of unregulated flow from tributaries being allocated to consumptive users. The minor changes in cease-to-flow are largely due to the variations of unregulated tributary inflows as a function of the climate change scenarios Water Sharing 4 River system modelling The environment flow objective of the Water Resource (Border Rivers) Plan 23 requires an end-of-system flow, at Mungindi, of at least 6.8 percent of the without development flow in preparing the first resource operations plan. Thus the upstream diversions should not reduce flows at Mungindi by more than 39.2 percent of the average without development flow for the simulation period used in developing the plan. Given current surface water entitlements in Border Rivers, considering equilibrium surface groundwater exchanges and for the common modelling period of this project, the flows at Mungindi are 59.5 percent of the without development flow. This indicates that the end-of-system target is sensitive to the climatic period used for modelling and to the inclusion of surface groundwater exchanges. For all of the mid- and dry climate scenarios this target is not met. The Queensland Water Act 2 allows for reviews and/or amendments to be made to water resource plans where there is new evidence indicating that the objectives of the plan are either no longer appropriate or are no longer being met. 4.5 References DLWC (1999) Border Rivers System IQQM Implementation Vol 1-3. Validation report. New South Wales Department of Land and Water Conservation. DWE (27) Draft Water Sharing Plan NSW Border Rivers Regulated River Water Source. Part A: Background document. New South Wales Department of Water and Energy DNRM (23) Water Resource (Border Rivers) Plan 23. Queensland Department of Natural Resources and Mines. DNRM (26) Draft Border Rivers Resource Operations Plan 26. Queensland Department of Natural Resources and Mines. CSIRO 27 November 27 Water availability in the Border Rivers 71

84 5 Uncertainty in surface water modelling results This chapter describes the assessment of uncertainty in the surface water modelling results. It has four sections: a summary an overview of the approach presentation of results discussion of key findings. 5.1 Summary 5 Uncertainty in surface water modelling results The uncertainty that is internal to the river model, as opposed to that associated with the scenarios, and the implications that this has for our confidence in the results and their appropriate use, are assessed using multiple lines of evidence. This involves comparing: (i) the river model to historical gauged main stem flows and diversions, which are its main points of reference to actual conditions, and (ii) ungauged inferred inflows and losses in the model to independent data on inflows and losses to ascertain if they can be attributed to known processes. These two aspects of model performance were then combined with some other measures to assess how well the model might predict future patterns of flow Issues and observations The Border Rivers region is relatively well gauged when compared to other regions in the Murray-Darling Basin (MDB). Streamflow gauging appears generally sufficient with the exception of the lower part of the system, where breakouts and bypass flows create uncertainty in modelling but these are difficult to monitor except with remote sensing. The quality and quantity of data on diversions creates some uncertainty in modelling. Occasionally considerable amounts of irrigation water use are not directly gauged. Groundwater exchanges and conjunctive surface-groundwater use are important sources of uncertainty in the middle part of the system (Holdfast Boggabilla). Monthly water accounts were developed for seven reaches in the Border Rivers region, covering the vast majority of water fluxes in the region, for the period 199/91 to 24/5. They were used to assess model performance in explaining system behaviour for this period, and were combined with earlier model assessments to evaluate whether the model was fit for the purpose of this assessment Key messages The monthly water balances for the reaches examined are well constrained by measurements. For four of the seven reaches examined, more than 9 percent of the water balance can be attributed. The river model reproduces observed monthly and annual flow patterns well in the seven reaches examined. Monthly patterns of flow from Pindari Dam do not correspond well with the model. This is because the model represents the current enlarged dam and full diversions and the accounts are from an earlier period. The mismatch is not a measure of model performance. The lowest two reaches have greater modelling uncertainties due to large unmeasured diversions, unregulated distributary flow and systematic under-prediction of large flow events. This is where most water use takes place and where flows are hardest to measure. Overall, the internal model uncertainty is assessed to be less than the external uncertainty associated with climate change projections. The model predicts supply of water to the majority of water uses well. As such it is considered suitable for the purpose of this project and for water resource planning. 72 Water availability in the Border Rivers November 27 CSIRO 27

85 However, caution should be taken when interpreting indicators of projected change associated with end-ofsystem flow characteristics at Mungindi, particularly the magnitude of peak flows, as the hydrology of this part of the system is complex and the model is not suitable for simulating overbank flood flows accurately. The calibrated climate range of the model is rather narrow 23 percent of years in the historical series were wetter than the calibrated range. This creates uncertainty in model predictions for wet years in particular. However, there has been partial re-calibration since initial model development which extended the calibration range. There is a risk of unpredicted changes in hydrology due to changes in cropping and water use patterns. This causes uncertainty particularly in low and medium flows during the irrigation season. Projected changes to annual flows under future scenarios appear quite distinguishable from the noise of current model uncertainty, with the exception of flows at the end-of-system at Mungindi. Projected changes to monthly flows in future are generally small compared to current model uncertainty. Projected future changes to annual flow patterns appear more significant than the difference between present and pre-development modelled flows. 5.2 Approach General A river model is used in Chapter 4 to analyse expected changes in water balance, flow patterns and consequent water security under climate and/or development change scenarios. Uncertainty in the analysis can be external or internal: External uncertainty is external to the model. It includes uncertainty associated with the forcing data used in the model, determined by processes outside the model such as climate processes, land use and water resources development Internal uncertainty relates to predictive uncertainty in the river model that is an imperfect representation of reality. It can include uncertainty associated with the conceptual model, the algorithms and software code it is expressed in, and its specific application to a region (Refsgaard and Henriksen, 24). Full measurement of uncertainty is impossible. The analysis focuses on internal uncertainty. When scenarios take the model beyond circumstances that have been observed in the past, measurable uncertainty may only be a small part of total uncertainty (Weiss, 23; Bredehoeft, 25). The approach to addressing internal uncertainty involved combining quantitative analysis with qualitative interpretation of the model adequacy (similar to model pedigree, cf. Funtowicz and Ravetz, 199; Van der Sluijs et al., 25) using multiple lines of evidence. The lines of evidence are: 5 Uncertainty in surface water modelling results the quality of the hydrological observation network the components of total estimated streamflow gains and losses that are directly gauged, or can easily be attributed using additional observations and knowledge, respectively, through water accounting characteristics of model conceptualisation, assumptions and calibration the confidence with which the water balance can be estimated, through comparison of water balances from the baseline river model simulations and from water accounting measures of the baseline model s performance in simulating observed streamflow patterns the projected changes in flow pattern under the scenarios compared to the performance of the model in reproducing historical flow patterns. None of these lines of evidence are conclusive in their own right. In particular: the model may be right for the wrong reasons. For example, by having compensating errors there is no absolute reference truth. All observations inherently have errors and the water accounts developed here use models and inference to attribute water balance components that were not directly measured adequate reproduction of historically observed patterns does not guarantee that reliable predictions about the future are produced. This is particularly so if model boundary conditions are outside historically observed conditions, such as in similar climate change studies. CSIRO 27 November 27 Water availability in the Border Rivers 73

86 Qualitative model assessment is preferably done by consulting experts (Refsgaard et al., 26). The timing of the project prevented this. Instead a tentative assessment of model performance is reviewed by research area experts within and outside the project as well as stakeholder representatives. The likelihood that the river model gives realistic estimates of the changes that would occur under the scenarios evaluated is assessed within the above limitations. Overall river model uncertainty is the sum of internal and external uncertainty. The range of results under different scenarios in this project provides an indication of the external uncertainty. River model improvements will reduce overall uncertainty only where internal uncertainty clearly exceeds the external uncertainty. 5 Uncertainty in surface water modelling results The implication of overall uncertainty on the use of the results presented in this project depends on: (i) the magnitude of the assessed change and the level of threat that this implies, and (ii) the acceptable level of risk (Pappenberger and Beven, 26). This is largely a subjective assessment and no attempt is made to judge. A possible framework for considering the implications of the assessed uncertainties is shown in Table 5-1. Low uncertainty High uncertainty Information sources Table 5-1. Possible framework for considering implications of assessed uncertainties Low threat Current water sharing arrangements appear sufficient for ongoing management of water resources. Current water sharing arrangements appear sufficient for ongoing management of water resources, but careful monitoring and adaptive management is recommended. High threat Current water sharing arrangements are likely to be inadequate for ongoing management of water resources, as they do not adequately consider future threats. Current water sharing arrangements may be inadequate for ongoing management of water resources. Further work to reduce the major sources of uncertainty can help guide changes to water sharing arrangements. Information on the gauging network was obtained from the Water Resources Station Catalogue ( the Pinneena 8 database (provided on CDROM by New South Wales) and the Queensland Department of Natural Resources and Water (DNRW) website ( Model calibration reports for three subsystems in the Border Rivers model (DLWC 1999a, b, and c) were provided by the New South Wales Department of Water and Energy. Time series of water balance components as modelled under the baseline scenario (Scenario A) and all other scenarios were derived as described in Chapter 4. The data used in water accounting are described in the following section Water balance accounting Purpose Generic aspects of the water accounting methods are described in Chapter 1. This section includes a description of the basic purpose of the accounts, which is to inform the uncertainty analysis carried out as part of this project using an independent set of the different water balance components by reach and by month. The descriptions in Chapter 1 also cover the aspects of the remote sensing analyses to estimate wetland and irrigation water use, as well as the calculations for attribution of apparent ungauged gains and losses. Aspects of the methods that pertain specifically to the current region are presented below. 74 Water availability in the Border Rivers November 27 CSIRO 27

87 Framework The available streamflow data for this region was deemed sufficiently complete for water accounting for the water years 199/91 to 24/5. Water accounts could be established for seven successive reaches. The associated catchment areas are shown in Figure 5-1 and are related to model reaches in Table 5-2. Table 5-2. Comparison of water accounting reaches with river model reaches Water accounting reach Subcatchment code(s) Description , Downstream Pindari , 41661, , Holdfast , 41624, 41625, 41626, 41636, , , , 41635, , 41647, , 41641, Boggabilla , , Kanowna Mungindi , , , , Roseneath , Bonshaw Weir Not assessed Reason Contributing head water catchment (to reach 1) 4161 Contributing head water catchment (to reach 2) 4162, Contributing head water catchment (to reach 3) , , , , , , Contributing head water catchment (to reach 4) 41633, 41632, 41631, Contributing head water catchment (to reach 6) 4168 Contributing head water catchment (to reach 7) Do not contribute any flow to any reach , , , , Contribute to the Boomi Neeworra which flows to Barwon-Darling 5 Uncertainty in surface water modelling results CSIRO 27 November 27 Water availability in the Border Rivers 75

88 5 Uncertainty in surface water modelling results Figure 5-1. Map showing the subcatchments used in modelling, the reaches for which river water accounts were developed ( accounting reach ) and gauged head water catchments ( contributing catchment ). Shaded areas ( floodplain and wetlands ) were classified as subject to periodic inundation. Black dots and red lines are nodes and links in the river model respectively Wetland and irrigation water use The results of the remote sensing analyses (Chapter 1) are in Figure 5-1. Any classification suffers from erroneous assignment to a certain category, commission errors, and errors of omission. The classification was designed to minimise errors of omission, as these cause a large error in water use estimate. Diversion data were provided by Queensland, mostly as monthly values. For 199/91 only annual data were provided, and these were distributed into the months in the same ratios as the average monthly values for the other years. The New South Wales diversions were provided as annual totals. For each year, these annual irrigation diversion data were distributed proportionally to the fraction of net water use in each month compared to water use for the whole year. Calculation and attribution of apparent ungauged gains and losses Calculation and attribution of apparent ungauged gains and losses were undertaken according to the methods described in Chapter Model uncertainty analysis The river model results and water accounts were used to derive measures of model uncertainty. The different analyses are described below. In the interest of brevity, details on the equations used to calculate the indicators are not provided here but can be found in Van Dijk et al. (27). Calculations were made for each reach separately but summary indicators were compared between reaches. 76 Water availability in the Border Rivers November 27 CSIRO 27

89 Completeness of hydrological observation network Statistics on how well all the estimated river gains and losses were gauged or, where not gauged, could be attributed based on additional observations and modelling were calculated for each reach: The volumes of water measured at gauging stations and off-takes, as a fraction of the grand totals of all estimated inflows or gains, and/or all outflows or losses, respectively. The fraction of month-to-month variation in the above terms. The same calculations as above, but for the sum of gauged terms plus water balance terms that could be attributed using the water accounting methods. The results of this analysis for annual totals are also shown in Appendix C. Comparison of modelled and accounted reach water balance The water balance terms for river reaches, as modelled by the baseline river model (Scenario A) and as accounted, were compared for the period of water accounting. Large divergence is likely to indicate large uncertainty in reach water fluxes and therefore uncertainty in the river model and water accounts. Climate range calibrated If the model calibration period is characterised by climate conditions that are a small subset, or atypical of the range of climate conditions that was historically observed, this probably increases the chance that the model will behave in unexpected ways for climate conditions outside the calibration range. The percentage of the overall climate variability range for the 111-year baseline simulation period that was covered by the extremes in the calibration period was calculated as an indicator. Performance of the river model in explaining historical flow patterns All the indicators used in this analysis are based on the Nash-Sutcliffe model efficiency (NSME; Nash and Sutcliffe, 197). NSME indicates the fraction of observed variability in flow patterns that is accurately reproduced by the model. In addition to NSME values for monthly and annual outflows, values were calculated for log-transformed and ranked flows, and high (highest 1 percent) and low (lowest 1 percent) monthly flows. NSME cannot be calculated for the logtransformed flows where observed monthly flows include zero values or for low flows if more than 1 percent of months have zero flow. NMSE is used to calculate the efficiency of the water accounts in explaining observed outflows. 5 Uncertainty in surface water modelling results This indicates the scope for model improvements to explain more of the observed variability. If NSME is much higher for the water accounts than for the model, it suggests that the model can be improved to reduce uncertainty. If similar, additional hydrological data may be required to support a better model. A visual comparison of streamflow patterns at the end-of-reach gauge with the flows predicted by the baseline river model and the outflows that could be accounted was done for monthly and annual time series and for monthly flow duration curves. Scenario change-uncertainty ratio Streamflow patterns simulated for any of the scenarios can be used as an alternative river model. If these scenario flows explain historically observed flows about as well or better than the baseline model, then it may be concluded that the modelled scenario changes are within model noise, that is, smaller or similar to model uncertainty. Conversely, if the agreement between scenario flows and historically observed flows is low much lower than between the baseline model and observations then the model uncertainty is smaller than the modelled change, and the modelled change can be meaningfully interpreted. The metric used to test this hypothesis is the change-uncertainty ratio. The definition was modified from Bormann (25) and calculated as the ratio of the NSME value for the scenario model to that for the baseline (Scenario A) model. A value of around 1. or less suggests that the projected scenario change is not significant when compared to river model uncertainty. A ratio that is considerably greater than 1. indicates that the future scenario model is less accurate in producing historical observations than the baseline model, suggesting that the scenario leads to significant changes in CSIRO 27 November 27 Water availability in the Border Rivers 77

90 flow. The change-uncertainty ratio is calculated for monthly and annual values, in case the baseline model reproduces annual patterns well but not monthly patterns. The same information was plotted as annual time series, monthly flow duration curves and a graphical comparison made of monthly and annual change-uncertainty ratios for each scenario. 5.3 Results Density of the gauging network 5 Uncertainty in surface water modelling results Figure 5-2 shows the location of streamflow, rainfall, and evaporation gauges in the region, and Table 5-3 provides information on the measurement network. The Border Rivers region has a gauging network with a density that is somewhat higher (1.4 to 1.7 times) than the average for the MDB and is ranked as the seventh most densely gauged region out of 18 regions. Many rainfall gauges are located in the southern uplands of the region, whereas most streamflow gauges are along the main Macintyre, Severn (NSW) and Dumaresq Rivers (Figure 5-2). Table 5-3. Some characteristics of the gauging network of the Border Rivers region (43,633 km 2 ) compared with the entire MDB (1,62,443 km 2 ) Gauging network characteristics Border Rivers MDB Number per 1 km 2 Number per 1 km 2 Rainfall Total stations Stations active since Average years of record Streamflow Total stations Stations active since Average years of record 23 2 Evaporation Total stations Stations active since Average years of record Water availability in the Border Rivers November 27 CSIRO 27

91 Figure 5-2. Map showing the rainfall, stream flow and evaporation observation network, and the subcatchments used in modelling Review of model calibration and evaluation information 5 Uncertainty in surface water modelling results This section reviews and summarises the calibration and verification of the IQQM river modelling in the Border Rivers region. It uses published and unpublished calibration reports prepared by the then NSW Department of Land and Water Conservation (DLWC) and the then Queensland Department of Natural Resources and Mines (DNRM) at the time the river models were run (DLWC 1999a, b, and c). These were provided to CSIRO for independent analysis. Model description Water in the Border Rivers region is managed in three subsystems: Macintyre Brook Subsystem: This is the Macintyre Brook system above Booba Sands, where it joins with the Dumaresq River. It is located in Queensland and includes the reservoir Lake Coolmunda. Irrigated farm enterprises include lucerne cropping. Severn-Macintyre River Subsystem: This covers 2 percent of the overall Border Rivers system catchment area. It is located in New South Wales and joins the Macintyre River ~5 km downstream from the junction of the Dumaresq River and Macintyre Brook. It includes Pindari Dam, and water use within the catchment is mainly for lucerne cropping and cotton. Dumaresq-Macintyre River Subsystem: This is the largest of the three systems and covers 7 percent of the overall Border Rivers catchment. It straddles the Queensland New South Wales border and contains Glenlyon Dam. Cotton farming is the main water use. Its outlet is at Mungindi, where it joins the Barwon River, but it also has five more off-takes that interface with the Barwon-Darling IQQM model. CSIRO 27 November 27 Water availability in the Border Rivers 79

92 DLWC and QDNR gave calibration reports for the three systems separately. For IQQM modelling purposes the latter two systems are incorporated into one model and the first subsystem is modelled separately, giving two models for the region. Data availability 5 Uncertainty in surface water modelling results Rainfall data is required by the IQQM model for soil moisture accounting and for computing the direct contributions to storage volumes and river reaches. For the Severn Macintyre River subsystem (NSW), daily rainfall data from one station at Pindari Dam (5414) and another at Orana (5412) were selected on the basis of record length and completeness and gaps in the data were filled using nearby gauge data where necessary. Daily evaporation data from the same locations as for the rainfall data were used and in addition one more station at Boggabilla (534) was used for evaporation data in the model. The model uses the evaporation data for simulating evaporation losses from river and storages and for estimating potential evapotranspiration of the crops. The stream gauging data that could be used for model calibration and evaluation was constrained by the period of overlapping records, the frequency of gauging, and the stability of rating. The available streamflow data were rated as reasonably good in terms of record length and quality. Table 5-4 provides details of the history and quality rating of the gauging stations used in the modelling. All of the stations, except for the gauging station (Macintyre River at Boonal Gauge), have a total record of more than 2 years. Further data on Pindari Dam area-volume relationships, valve operation procedures, irrigator pump capacity, water release and use, and crop types and areas from two different sources were available. Discrepancies in crop data were found, and additional assumptions were required to reconcile these. For the Dumaresq Macintyre River subsystem, daily rainfall and evaporation data from five stations were selected on the basis of record length and completeness and gaps in the data were filled using nearby gauge data where necessary. Streamflow data used in calibration are listed in Table 5-4. The number and quality of streamflow gauging for the period 1986 to 1991 was considered adequate for strategic level calibration, but of insufficient record length to provide statistical rigour for cap auditing purposes, particularly in the high (flood) flow range. Data on Glenlyon dam area-volume relationships and valve operation procedures were available. Crop types and areas data from regional metering inspectors were compared to those published by Border Rivers Commission. Discrepancies of up to 11 percent in total area were found, and additional investigations and assumptions were required to reconcile these. Data on on-farm storages, some pumping data, and licence conditions were also available. 8 Water availability in the Border Rivers November 27 CSIRO 27

93 Table 5-4. Gauges for which streamflow data were used in model calibration, and rating of data quality Station Location Use in modelling Operation period Data quality rating Severn-Macintyre River Subsystem Severn Pindari Tailwater Reach calibration 1966 Good 4166 Severn Ashford Reach calibration 1933 Good Macintyre Dam site Reach calibration Good Macintyre Holdfast Reach calibration 1951 Good Macintyre Boonal Reach calibration Fair* Severn Strathbogie Inflows 1994 Good Frazers Ashford Inflows Good* 4162 Ottleys Coolatai Inflows 1967 Good 4168 Beardy Haystack Inflows 1934 Poor Fair* Campbells Beebo Inflows 1973 Fair* Croppa Tulloona Bore Inflows Poor* 4161 Macintyre Wallangra Inflows 1937 Good* Dumaresq-Macintyre River Subsystem 4161 Barwon Mungindi Reach calibration Good 41623a Callandoon Claries Weir Reach calibration 1996 Fair /4164 Dumaresq downstream Mauro / Glenarbon Weir Reach calibration 1985 Fair Good* Dumaresq Roseneath Reach calibration 1937 Good 1467 Dumaresq Bonshaw Weir Reach calibration 1934 Fair 4162 Macintyre Boggabilla Reach calibration 1894 Fair Poor 41621a Macintyre Goondiwindi Bridge Reach calibration 1917 Fair Macintyre Terrewah Reach calibration 1988 Fair Macintyre Boomi Weir Reach calibration 1976 Fair* Macintyre Kanowna Reach calibration 1988 Fair 41639b Pike Glenlyon dam tailwater Reach calibration 1973 Good Boomi offtake Breakout flow, reach calibration 1973 Fair Boomi Kanowna Breakout flow Good Brush Beebo Inflows 195 Good Dumaresq Farnbro Inflows 1962 Good Macintyre Booba Sands Inflows 1987 Good Mole Donaldson Inflows 1969 Good Oaky Texas Inflows 1969 Good Glenlyon Dam level Inflows 1976? Reedy Dumaresq Inflows Fair Weir Talwood Inflows 1949 Fair * 41638: High flow errors likely (>1 GL/d); 41621: Staff gauge before 1971; 4162: Most reliable after 1979; 4168: Unreliable low flow record; 41636: Unstable cross section, staff gauge before 1978; 41634: 29 percent data missing, unreliable before 1979; 4161: High flow errors likely (>5 GL/d); 41649/4: Gauge changed in 1996; 41643: Not reliable particularly for high flows (>2.4 GL/d). 5 Uncertainty in surface water modelling results Model calibration and validation procedures Calibration of the IQQM model in 1999 followed a stepped process, for each subsystem, where the following processes were progressively evaluated: streamflow behaviour, storage behaviour, testing of operation and management rules, water diversions, planted crop areas and off-allocation diversions. The primary aim of streamflow calibration is to modify the modules that describe flow routing, transmission loss and residual catchment inflows (analogous to what is termed local inflows in our analysis), to best reproduce flows recorded at the outlet of each reach, given historical data on gauged inflows and extractions. It involved: calibration of three flow routing parameters disaggregation of monthly or quarterly water use records into daily estimates a scheme to estimate residual apparent gains in the reach, by correlation analysis with inflows from nearby gauged catchments CSIRO 27 November 27 Water availability in the Border Rivers 81

94 a scheme to estimate transmission losses to explain the difference between modelled and observed outflows accumulated from the previous steps. No independent validation of the entire model was attempted by DLWC and QDNR, although some components could adequately be tested with independent data for the year 1995/1996 (R. Cooke, NSW DWE, pers. comm.). Model performance during the calibration period was assessed. Details for the three subsystems were as follows: Macintyre Brook: the calibration period was 1987 to 1995 inclusive. This was dictated by the start date for gauging at the subcatchment outlet (Booba Sands) and end date of available data at the time of calibration 5 Uncertainty in surface water modelling results Severn Macintyre River: the calibration period for the overall model was 1986 to 199 inclusive (less than five years), being the only available homogenous period free of major operational changes such as the Pindari Dam enlargement after 199. Although no independent validation of the entire model was attempted, calibration could be performed using data for earlier years as well, and in these cases the later period could be used for some degree of independent validation (see below) Dumaresq Macintyre River: the calibration period was 1986 to The start year was to be consistent with the other two subsystem models, and the end date was dictated by the data availability at the time of model calibration. Model performance Performance over the calibration period was assessed by DLWC and QDNR by comparing modelled and observed averages, temporal patterns and frequency of occurrence of (1) stream flow; (2) storage levels; (3) diversions; and (4) planted area. Performance was classified as good, fair, adequate or inadequate (Table 5-5), with reference to the purpose of model construction, which was defined as management scenario testing. Relative difference between modelled and observed quantities Stream flow Table 5-5. Definition of model performance qualifiers used (NSW DNR) Good Fair Adequate Inadequate Average / total flow <1% 1 5% 5 1% >1% Low, mid and high flow range volumes and percentiles <5% 5 1% 1 25% >25% Daily patterns, expressed as relative bias* and unexplained variance (1-r 2 ) Storage levels <5% 5 1% 1 25% >25% Average volume <1% 1 5% 5 1% >1% Low, middle and high range volumes <5% 5 1% 1 2% >2% Annual patterns (end-of-year levels) <1% 1 2% 2 5% >5% Diversions Average / total volume <1% 1 5% 5 1% >1% Standard deviation in annual volumes <1% 1 25% 25 5% >5% Low, mid and high range diversion volumes <1% 1 2% 2 4% >4% Annual planted area Mean annual area <1% 1 5% 5 1% >1% Standard deviation in annual areas <1% 1 25% 25 5% >5% * Refers to the slope of a linear regression; the intercept (constant bias, or offset) was also considered but is not reported here to avoid complexity. Streamflow Initially, flow simulation was assessed using recorded rather than simulated dam releases and spills and diversions, to test the simulation of within-reach routing, residual inflows, and losses by itself. Performance was assessed for low, middle and high flow ranges of the flow-frequency distribution, and daily flows patterns were also compared. The assessment was also repeated after storage, diversion and planting area models replaced the observations to test the performance of the model as a whole. Results are listed in Table Water availability in the Border Rivers November 27 CSIRO 27

95 Initial calibration of the Macintyre Brook model produced a fair to good match of the various indicators. Inclusion of storage and irrigation models degraded the performance, but most aspects were still in the fair to good range. Degradation of model performance as a result of including the irrigation model can be attributed to the scenario applied in this model, which, for the purpose of planning around a worst case, assumed full use of the allocated water for each year. Consequently model usage may be higher than actual usage. Initial calibration of the reach inflow, routing and loss functions in the Severn Macintyre River was performed for periods starting in 1966 to 1973 for different gauges, and ending in This allowed a more formal independent validation for 1986 onwards. The latter is reported in Table 5-6. Performance assessment for the validation period caused some indicators to improve and others to degrade. Overall performance was less, but still in the fair to good range. Table 5-6. Indicators of model performance in reproducing stream flow patterns. Between brackets performance before the storage and diversion models were included, where this differs from the overall qualification Model reach Description Average/ total flow Low flows Mid flows High flows Time series pattern match Macintyre Brook Subsystem 1a,1b* 2a,2b* Coolmunda Dam inflows reaches Inglewood Weir inflow reaches Good Fair Good Good Adequate Good* Good Adequate (Good) Fair Good Good Fair Good 3* Booba Sands Fair (Good) Inadequate (Good) Fair (Good) Good Adequate Fair (Good) 4* Outlet reach Good Fair Good Good Adequate Good Severn Macintyre River Subsystem 1* Pindari tailwater (41619) 2 Ashford station (4166) 3 Macintyre dam site (41618) 4 Holdfast (41612) 5* Boonal (41638) Good (Adequate#) Dumaresq Macintyre River Subsystem 1* Roseneath (41611) 2 Bonshaw weir (4167) 3* Mauro (41649) 4* Boggabilla (4162) 5* Goondiwindi (41621A) 6,7* Boomi (41643, 41637) 8* Kanowna (41648, 41629) 9 Mungindi (4161) Inadequate Fair (Good) Good Inadequate (Adequate) Fair Fair Good Good Inadequate (Adequate) Fair Good (Fair) Good Fair Adequate Fair Inadequate Good (Fair) Fair (Good) Adequate Good Fair Fair Good Good Inadequate Good Fair Inadequate Fair Adequate Good Good Fair Good Adequate (Good) Adequate (Good) Adequate (Adequate Good) Fair (Inadequate Good) Adequate (Good) Fair (Adequate Good) Adequate (Fair Good) Inadequate Good Fair Good Good Good Good Inadequate Good Good Adequate (Good) Adequate Good Adequate (Good) Fair (Inadequate Good) Fair-Good (Good) Fair Good Inadequate Good Good Inadequate Inadequate Fair Adequate Fair Fair Fair Good Inadequate Adequate Adequate (Fair Good) Inadequate Adequate Adequate Good Fair Good Adequate Good * Overall assessment: Macintyre-Brook Subsystem 1) Excellent considering uncertainty in dam inflow time series 2) Surprisingly good, given the uncertainty in diversions, residual inflows and groundwater inflows 3) Good, but could be improved considering surface water-groundwater interactions. Most affected by diversion model. 4) No validation available, evaluation for assembled reaches. Impacts of added modules unclear. Severn-Macintyre River Subsystem 1) Overestimation of low flows due to inaccuracies in dam release data, residual inflow overestimation, rating problems 5) Could not be evaluated for whole-of-system calibration period due to lack of data Dumaresq-Macintyre River Subsystem 1) Considered adequate for low flows given uncertainty in observations 3,4,5,6,7) Considered adequate for high flow given uncertainty in observations 8) Adequate considering gauging uncertainty 5 Uncertainty in surface water modelling results CSIRO 27 November 27 Water availability in the Border Rivers 83

96 For the Dumaresq Macintyre River model, the overall reproduction of gauged stream flow for the calibration period was considered adequate to good. However comparison for the wetter years only (1986 to 1991) suggested that flow simulations deteriorate further downstream. This was ascribed to an overestimation of transmission losses during wet periods due to the use of average parameters. Inclusion of the storage model improved performance for the lower reaches, whereas subsequent inclusion of the diversion model worsened the tendency to under estimate low flow. Overall model performance in fact improved when propagating modelled main stem flows, rather than recalibrating reach by reach. This suggested systematic modelling errors that compensated each other when running the entire model. Storage level 5 Uncertainty in surface water modelling results The performance of the storage module at simulating storage losses, releases and spills was evaluated, as well as its effects on combined simulation of inflows from gauged and ungauged inflows. Where dam operation follows clear operational rules, a better performance can be expected. Performance was assessed for low, middle and high ranges of the storage volume-frequency distribution, as well as the agreement in storage volume at the end of each year (Table 5-7). The final model for the Coolmunda (Macintyre Brook subsystem) represented a compromise between overestimation and underestimation of storage volumes at different times, with minimal impact on model performance in reproducing streamflow downstream. After all model components were included, model performance in simulating low range storage levels was rated inadequate. The reduction in model performance after diversion and planted area models were included can be attributed to the model being set up to model maximum diversions. Overall there was a good match in storage behaviour in Pindari (Severn Macintyre River subsystem). Major drawdowns were not reproduced well. This was due to variable end-of-system flow requirements, while there were also doubts about the accuracy of dam releases. A slight deterioration in performance occurred after the planted area model component was introduced. There was a fair to good match with storage level behaviour in Glenlyon (Dumaresq Macintyre River subsystem). Two observed drawdowns were not replicated well. This was ascribed to wrong estimates of transmission losses. Table 5-7. Indicators of model performance in reproducing storage behaviour. Between brackets terms are the best performance without including the diversion and planted area models, where these differ from the overall qualification. Description Average Low range Mid range High range Coolmunda Pindari and Glenlyon Adequate (Good) Inadequate (Adequate) Adequate (Good) End-of-year levels Assessment Good Adequate Best compromise between over and underestimation at different times Fair (Good) Fair (Good) Good Good Good Major drawdown events not produced well due to variations in operations Diversions and planted areas The performance of the crop and soil moisture model in IQQM was evaluated against historical diversion records, after the initial rainfall loss parameter, soil moisture storage, crop efficiency and crop factor and crop mix data were calibrated (DLWC, 1998). The sub-model that simulates farmers decisions in response to announced allocations and prior climate conditions was evaluated by comparison to recorded planted areas for the calibration period. In the absence of additional records, the diversion component of the Severn-Macintyre River model was classified as adequate, but inclusion of the planted area model component reduced performance considerably. These problems would probably be reduced after putting the three Border Rivers models together for the period after 199. Due to ample water availability, the farmers risk concept appeared inapplicable. Despite this, considerable annual variation in planted areas occurred, which was attributed to market fluctuations that were not simulated. Adjustments made to reproduce planted areas as best as possible led to degradation in the accuracy of diversion estimates. It was not possible to get an adequate match of allocation diversion volumes. This was assumed to be due to irrigator behaviour being different to than assumed, but the impact of the off allocation model component on other aspects of the model was minimal. 84 Water availability in the Border Rivers November 27 CSIRO 27

97 Overall performance of the diversion component of the Dumaresq Macintyre River model was rated as fair to good. Simulated diversions for the entire valley were adequate on an annual basis, but estimates of monthly diversions were under estimated during months with low demands. Table 5-8. Indicators of model performance in reproducing diversion patterns and planted areas. Between brackets performance before the planting area model was included, where this differs from the overall qualification Description Macintyre Brook Subsystem Severn-Macintyre River Subsystem Dumaresq- Macintyre River Subsystem Average / total volume Adequate (Good) Inadequate (Good) Identified weaknesses Annual variability in diversions Adequate Fair Fair Volume of low range diversions Inadequate (Adequate) Volume of mid range diversions Volume of high range diversions Average area Good Good Fair Fair Inadequate (Fair) Inadequate (Fair) Fair (Good) Good Annual variability in area Good Fair Fair Fair Good Good Fair Good Several possible improvements in model structure, assumptions and parameter values were identified in the 1999 Severn Macintyre River subsystem and Dumaresq Macintyre River subsystem reports. Sources of uncertainty that were identified include: role of groundwater. Surface-groundwater interactions are probably important in the Coolmunda system. Also, conjunctive use after 1993 created uncertainty in extraction modelling discrepancies in diversion data. Diversion volumes varied between annual crop return books and operational databases lack of crop area data created problems in calibration and is likely a source of errors inaccuracies in data on storage operations and releases. This was particularly identified as an issue for Coolmunda and Pindari releases transmission losses. Different apparent losses in wet and dry periods suggested that these may not have been described well by the model off allocation diversions and unregulated users. Knowledge and data of on-farm filling practices and flood plain harvesting were insufficient. Later re-calibration of the model has addressed this (R. Cooke, NSW DWE, pers. comm.) breakout and return flows below Goondiwindi introduced uncertainty in end-of-system flow simulations, and may have some impacts on water use by a large cotton irrigator in this reach. Later re-calibration of the model has addressed this (R. Cooke, NSW DWE, pers. comm.). Lack of data on water holes introduced uncertainty in simulations for low flows and losses during dry periods. 5 Uncertainty in surface water modelling results Model uncertainty analysis Full reach-by-reach results of the model uncertainty analysis and water accounts are given in Appendix C. Completeness of hydrological observation network The estimated fraction of all gains and losses that are gauged is shown for each reach in Figure 5-3. The following conclusions are drawn: Overall, gains are fairly well to well gauged; about 6 percent to 9 percent of inflows into successive reaches appear to be gauged. The last reach is an exception with less than 6 percent of apparent gains gauged. This is associated with an ungauged distributary which joins from the reach above for which estimates of flow are available but were not included in the accounts. CSIRO 27 November 27 Water availability in the Border Rivers 85

98 Most losses are also about 7 percent to 9 percent gauged, but Reach 6 is an exception. Again, this is related to ungauged distributaries which branch off from this reach but from which flows can be estimated. Overall, for each reach about 6 percent to 8 percent of the water balance was gauged. Almost all ungauged gains and losses in the model can be attributed to independent estimates of local runoff, irrigation diversions, floodplain water use and other fluxes. Least attribution of gains and losses was achieved in Reach 3. This reach includes the Pindari Dam which has been enlarged and changed operations during the period of accounts. It has considerable storage effects that are not fully taken into account during this evaluation and therefore impact on the water accounts. This probably accounts for the unattributed gains and losses that seem to occur in this reach. Unattributed flows in Reaches 6 and 7 are a result of the ungauged distributary. Overall, the hydrological system is reasonably well metered and accountable in terms of un-metered processes. 5 Uncertainty in surface water modelling results Fraction gauged (a) inflow s/gains outflow s/losses total flow Accounting reach Fraction attributed (b) Accounting reach Figure 5-3. Patterns of indicators of the fraction of inflows/gains, outflows/losses and the total of water balance components that is (a) gauged or (b) could be attributed in the water accounts Comparison of modelled and accounted reach water balance A summary of the regional water balance simulated by the river model and derived by water accounting is listed in Table 5-9. In both cases, numbers are averages for the period 199 to 26 to allow direct comparison. To aid interpretation: the system starts to lose more water than it gains below Boggabilla, where most of the breakouts, wetlands and irrigation extractions commence and by which most of the inflows have occurred (Appendix C) there was no attempt to estimate groundwater exchanges in water accounting due to the lack of direct data. It was estimated at 2 GL/year by the IQQM baseline model. in the water balances there are several instances where definitions of water balance terms in the water accounts vary from those used in the river models. This creates differences in numbers which cancel each other out. For example, double counting of gains and losses can occur because of ungauged distributary flow. These are explained where they are critical to interpretation of the results. The following conclusions are drawn when comparing modelled and accounted water balance: Modelled and accounted gains are generally similar (Appendix C) for individual reaches, once definitional differences are considered. In the lowest two reaches, local inflows in the model are ungauged distributary channels which in the accounts appear as unattributed gains. In the upper five reaches, there are large differences in local inflows between the model and the accounts. The model tends to use local inflows to fit differences in flow between gauges and to smooth out anomalies between gauged flows. Thus while overall local inflows are approximately equal there are strong reach-to-reach differences. 86 Water availability in the Border Rivers November 27 CSIRO 27

99 Modelled and accounted losses, including diversions, are also similar. In Reach 6, the modelled distributary losses appear as unspecified losses in the accounts. The largest difference is the model underestimate of gauged end-of-system outflows, which occurs largely as a result of the underestimation of outflows in very wet years. The largest difference between model and accounts is in the total gains and losses modelled. The accounts include an additional 484 GL/year or 296 GL/year of water which is mainly accounted for in unattributed gains and matching unattributed losses, respectively. These unattributed gains and losses are summed month by month and reach by reach. They represent the unexplained noise in the reach water balance. These can represent the sum of all gauging errors or additional processes such as floodplain discharges that move water from one reach to another. These unattributed terms are largest in reaches 6 and 7 (Appendix C) on the floodplain where there are inherent uncertainties in gauging main stem flows once water breaks overbank. Taking these factors into account, combined with the fact that the baseline scenario rather than calibrated model is used in this comparison, there is good match between model and accounts. The most significant difference is the models underestimation of end-of-system flows, that is 415 GL/y compared to 34 GL/y gauged flows. Of the apparent 111 GL/y difference, 39 GL/y can be attributed to higher diversions simulated by the scenario model. Table 5-9. Regional water balance modelled and estimated on the basis of water accounting Water balance (Jul 199 Jun 26) Model (A) Accounts Difference Difference GL/y percent Main stem inflows % Tributary inflows % Local inflows % Subtotal gains % Unattributed gains and noise % End of system outflows % Distributary outflows n/a Net diversions % 5 Uncertainty in surface water modelling results River flux to groundwater 2 15 n/a River and floodplain losses % Other losses* % Subtotal losses % Unattributed losses and noise % * includes estimated losses to ungauged distributaries Climate range calibrated The period for which the compound model as a whole was calibrated was the five years from 1986 to 199. The number of years in the entire 112-year record used in modelling that were wetter than those included in this calibration period was 26, whereas seven years were wetter. The region-average rainfall range in the calibration period was 547 mm/year to 888 mm/year, compared to 332 mm/year to 984 mm/year for the 112-year period. The average in these five years was 6 percent higher than the long-term average. By comparison, the historical 112-year rainfall record had eight years that were drier and three years that were wetter than the extremes during the period of water accounting 199 to 26. Overall, the calibration period for the Border Rivers appears to provide a poor representation of long-term climate variability. This was necessitated by the data available at the time of calibration, and some individual components of the model were calibrated for longer periods. However, it is noted that all calibration steps except streamflow calibration have been repeated in more recent re-calibrations using data from , thereby extending the calibration range. CSIRO 27 November 27 Water availability in the Border Rivers 87

100 The water accounting period 199 to 26 provides a reasonable representation of climate variability, and provides a further opportunity to assess model performance outside its calibrated climate range. Performance of the river model in explaining historic patterns The better the baseline model simulates streamflow patterns, the greater the likelihood is that it represents the response of river flows to changed climate, land use and regulation changes. There is a possibility that compensating errors mean that the model is right for the wrong reasons. In Appendix C, indicators are listed reach by reach of the model s performance in reproducing different aspects of the patterns in historically measured monthly and annual flows, and all are variants of Nash-Sutcliffe model efficiency. These are summarised in Figure Uncertainty in surface water modelling results The river model generally reproduced flow patterns very well. Monthly flow patterns were reproduced very well for reaches 1, 2, 4 and 5 (NSME for monthly flows=.89.94) and annual patterns even better (NSME for annual flows.93.97). Reaches 6 and 7 had only slightly lower fit of the model to observed flows. The model was least accurate nad performed poorest at reproducing historical flows in Reach 3 (Pindari to Strathbogie), which includes Pindari Dam. The dam was enlarged and its operating rules were changed half way through the accounting period. The model represents the new size and operations. It is no surprise then that the model does not represent flows under different historical conditions. High flows were replicated very well for reaches 2, 4, 5 and 6 (NSME.89.94) and moderately well for Reach 1 and Reach 7. Low flows were not reproduced well in any of the reaches. 1. monthly - normal.8 monthly - log-norm. Model efficiency.6 monthly - ranked monthly - low flows.4 monthly - high flows.2 annual - normal annual - log-norm.. annual - ranked Accounting reach Figure 5-4. Patterns in different measures of model efficiency (the relative performance of the river model in explaining observed streamflow patterns) along the length of the river Flows at the end-of-system were under estimated by 111 GL/year or 27 percent of observed flows (cf. Reach 7, Appendix C). This occurred in particular in relatively wet years (1995/96 and 1998/99) when flows during peak flow months and total annual flows were under estimated by more than 3 percent and several hundred GL (Appendix C). 88 Water availability in the Border Rivers November 27 CSIRO 27

101 8 Monthly streamflow (GL/mo) gauged model Jan-9 Jan-91 Jan-92 Jan-93 Jan-94 Jan-95 Jan-96 Jan-97 Jan-98 Jan-99 Jan- Jan-1 Jan-2 Jan-3 Jan-4 Jan-5 Figure 5-5. Comparison of modelled (model) and observed (gauged) monthly flows at the end of the Border Rivers system at Mungindi Total diversions for accounted reaches (GL/y) Accounts Model Uncertainty in surface water modelling results Water year (starting July) Figure 5-6. Comparison of modelled (model) and recorded (accounts) diversions in Border Rivers accounting reaches. Note that no data were available for Queensland diversions prior to 1993/4 A comparison between modelled and accounted diversions for the reaches is shown in Figure 5-6. It shows that model diversions are higher than those produced by the accounts, particularly in the years of higher diversions. This is largely because the model applies the current level of development to the whole simulation period and there has been considerable recent development beyond historical diversion levels. The majority of diversions are from Reach 6. Scenario change-uncertainty ratio A high change-uncertainty ratio (CUR) corresponds with a scenario change in flows that is likely to be significant given the uncertainty, or noise, in the model. A value of around 1 means that the modelled change is of similar magnitude as the uncertainty in the model. It is noted that this analysis focuses on the month-to-month and year-to-year patterns in flows, and not the possible significance of a change in average flows. The CUR is shown for each reach for changes in monthly and annual total flows in Figure 5-7 a and b, respectively. The results suggest that: the simulated change from pre-development to current flow patterns is of modest to reasonable significance when compared to model performance (CUR = 1. 25), and is of low significance for the end-of-system at Mungindi (CUR =.8 1.1). The modelling itself does not give much reason to suspect that flow patterns at CSIRO 27 November 27 Water availability in the Border Rivers 89

102 Mungindi would have been very different without development. The high CUR in Reach 6 may be a result of a major change in flow patterns down a distributary that bypasses the gauge at the end of the reach the impact of the climate change scenarios in Reaches 3 to 5 appears only moderately significant (CUR =.8 8.3). The changing patterns under the most significant climate change scenario, for any given reach, varies depending on bias between modelled and observed flows. Where the model over estimates historical flows, a drier climate scenario can reduce this bias and therefore explain historical flow patterns better, reducing the significance of the change. Generally, the projected changes in inter-annual flow patterns can be interpreted with reasonable confidence, except for reach six. This can be related to the previously mentioned underestimations of flows during wet years. Use caution when interpreting projected changes at this gauge. 5 Uncertainty in surface water modelling results Change-uncertainty ratio (a) (b) Accounting reach Change-uncertainty ratio Accounting reach P B Cwet Cmid P B Cwet Cmid Cdry Dwet Dmid Ddry Cdry Dwet Dmid Ddry Figure 5-7. Pattern along the river of the ratio of the projected change over the river model uncertainty under the different scenarios modelled for (a) annual and (b) monthly flows 5.4 Discussion of key findings Completeness of the gauging network The Border Rivers region is relatively well gauged. There are 43 active streamflow gauging stations (Section 5.3.1). Of these, more than 3 were used in river model calibration (Section 5.3.2). The density of rainfall and evaporation gauging stations is similar or better than the MDB average, with 45 active rainfall stations. The quality of gauging is probably least at the end of the system, where ungauged losses occur, although these are inherently difficult to gauge. There were no data on dam levels and releases, but these were available for model calibration (Section 5.3.2). Overall the gauging network is sufficient for river modelling, with the possible exception of the lowest reaches Conceptual understanding of regional surface hydrology The independent water accounts cover the vast majority of hydrological fluxes in the region. Between 6 percent and 9 percent of fluxes in each reach are gauged and between 8 percent and 9 percent of the total flux could be attributed quantitatively by using additional estimates from runoff modelling, diversion data and remote sensing data (5.3.3). The system is gaining above Boggabilla due to runoff inputs. About 8 percent of all diversions in the accounting period occur below Boggabilla. An estimated 765 GL/year of annual flows currently passes the Macintyre River at Boggabilla (199 to 25 average) and is partially controlled by dams, while another 335 GL/year inflow occurs downstream. Of the total inflows, about a third (569 GL/year) appears to be evaporated from floodplain and wetlands, 16 percent (252 GL/year) is diverted, and 26 percent (415 GL/year) finds its way to the gauge at Mungindi. 9 Water availability in the Border Rivers November 27 CSIRO 27

103 Reviews of the modelling pointed to uncertainties associated with the accuracy of diversion data, the lack of accurate data on off allocation and flood harvesting and overestimates of cropping area due to external market factors controlling farmer decisions, rather than water availability (Section 5.3.2). The model appeared to over estimate diversions for the period 199/91 to 24/5 by 39 GL/year or 15 percent (Section 5.3.3). Again, this is because the model represents current development which, because of an enlarged Pindari dam and increased farm storage has grown beyond the diversions of 199 to 25. Groundwater interactions are a potential source of uncertainty (Chapter 6). In the lower reaches, groundwater was considered an important source of water after 1993, and its influence on the water balance identified as an important source of uncertainty (Section 5.3.2). Groundwater interactions were also considered important in the Coolmunda system (Section 5.3.2). The indirect loss of river water to groundwater (all in the Holdfast-Boggabilla reach) was estimated at 15 GL/year or 2 percent of Boggabilla flows (Section 5.3.3). The greatest uncertainty in future inflows is caused by uncertainty in climate projections up to 28 percent (Chapter 3), followed by uncertainties in runoff response as a result of indirect consequences of climate on land cover. Uncertainties in farm dam expansion were assessed to be of a small magnitude 4 percent of total long-term inflows. Overall, outside of the uncertainty in climate scenarios, the greatest uncertainty is caused by the lack of knowledge and accurate data on irrigation water use Performance and uncertainty in aspects of the river model Based on a combination of reviewed reports (Section 5.3.2) and our own comparison of the river model water balance for the period 199/91 to 24/5 (Section 5.3.3), it was possible to identify hydrological variables that appear to be reproduced well by the model and a number that do not appear to be reproduced well. The model reproduced well to very well monthly and annual inflows and streamflow patterns at most mainstream gauges. Apparently reproduced less well are: high flows in the lower part of the system below Bonshaw Weir (Table 5-6) low flows at all gauges evaluated Implications for use of the results of this project Overall, the internal model uncertainty was less than the external uncertainty in climate change. As such it is considered suitable for the purpose of this study. However, the assessment suggests that caution should be taken when interpreting indicators of projected change associated with end-of-system flow characteristics at Mungindi, particularly the magnitude of peak flows which flood overbank. 5 Uncertainty in surface water modelling results 5.5 References Bormann H (25) Evaluation of hydrological models for scenario analyses: Signal-to-noise-ratio between scenario effects and model uncertainty. Advances in Geosciences 5, Bredehoeft J (25) The conceptual model problem surprise. Hydrogeology Journal 13, DLWC (New South Wales Department of Land and Water Conservation) and QDNR (Queensland Department of Natural Resources) (1999a). Border Rivers System: IQQM Implementation Volume 1 of 7: Calibration Report: Macintyre Brook Subsystem ( ). Catchment Processes Unit, Centre for Natural Resources, NSW Department of Land and Water Conservation, and Surface Water Assessment Group, Queensland Department of Natural Resources. DLWC (New South Wales Department of Land and Water Conservation) and QDNR (Queensland Department of Natural Resources) (1999b). Border Rivers System: IQQM Implementation Volume 2 of 7: Calibration Report: Dumaresq-Macintyre Rivers Subsystem ( ). Catchment Processes Unit, Centre for Natural Resources, NSW Department of Land and Water Conservation, and Surface Water Assessment Group, Queensland Department of Natural Resources. DLWC (New South Wales Department of Land and Water Conservation) and QDNR (Queensland Department of Natural Resources) (1999c). Border Rivers System: IQQM Implementation Volume 3 of 7: Calibration Report: Severn-Macintyre Rivers Subsystem ( ). Catchment Processes Unit, Centre for Natural Resources, NSW Department of Land and Water Conservation, and Surface Water Assessment Group, Queensland Department of Natural Resources. Funtowicz SO and Ravetz J (199) Uncertainty and Quality in Science for Policy. Kluwer Academic Publishers, Dordrecht. Nash JE and Sutcliffe JV (197) River flow forecasting through conceptual models, 1: a discussion of principles. Journal of Hydrology 1, CSIRO 27 November 27 Water availability in the Border Rivers 91

104 Pappenberger F and Beven KJ (26) Ignorance is bliss: Or seven reasons not to use uncertainty analysis. Water Resources Research 42, W532, doi 1.129/25WR482. Refsgaard JC and Henriksen HJ (24) Modelling guidelines terminology and guiding principles. Advances in Water Resources 27, Refsgaard JC, van der Sluijs JP, Brown J and van der Keur P (26) A Framework for dealing with uncertainty due to model structure error. Advances in Water Resources 29, Van der Sluijs JP, Craye M, Funtowicz S, Kloprogge P, Ravetz J and Risbey J (25) Combining quantitative and qualitative measures of uncertainty in model based environmental assessment: the NUSAP System. Risk Analysis 25, Van Dijk AIJM (26) Climate variability impacts on the already stretched Murray-Darling Basin water system assessment and policy implications. In: Proceedings of the World Water Week, Stockholm, Sweden. Weiss C (23) Expressing scientific uncertainty. Law, Probability and Risk 2, Uncertainty in surface water modelling results 92 Water availability in the Border Rivers November 27 CSIRO 27

105 6 Groundwater assessment This chapter describes the groundwater assessments for the Border Rivers region. It has eight sections: a summary a description of the groundwater management units in the region a summary of the hydrogeological context a description of surface water-groundwater connectivity an outline of the groundwater modelling approach a presentation and description of modelling results an assessment of water balances for lower priority groundwater management units a discussion of key findings. 6.1 Summary Issues and observations There are seven groundwater management units (GMUs) in the Border Rivers region. These cover all of the New South Wales portion of the region but only a small fraction of the Queensland portion. The assessments for the New South Wales and Queensland Border Rivers Alluvium GMUs that are presented here are based on use of an existing numerical groundwater model. Assessments for the remaining GMUs are based on simpler water balance analyses. 6 Groundwater assessment Key messages Total groundwater extraction in the Border Rivers region for 24/5 is estimated to have been 34.3 GL. This represents 2 percent of the groundwater use in the Murray-Darling Basin (MDB) (excluding confined aquifers of the Great Artesian Basin). About 37 percent of this extraction was from the New South Wales and Queensland Border Rivers Alluvium GMUs. Current groundwater extraction in the Miscellaneous Alluvium of the Barwon Region GMU exceeds recharge; this is a very high level of development. Development is low in the other GMUs in the region. For the Border Rivers Alluvium GMUs, groundwater modelling of the areas in the Dumaresq River area indicates that for: Historical climate and extraction at 23/4 levels o o o Extraction in the modelled area (~11.2 GL/year) represents about 75 percent of total groundwater recharge, including rainfall recharge, irrigation leakage and induced river losses. This is a high level of development. The spatial pattern of current groundwater extraction leads to large reductions in groundwater levels. As groundwater levels fall, responses would be expected from both groundwater users and resource managers. The effect of these responses would be to reduce extraction in the areas of falling groundwater levels. Extraction has impacted, and will impact further in the future, on flow in the Dumaresq River. During the groundwater model calibration period (196 to 1999) and across the modelled part of the GMUs, the Dumaresq River gained 4.4 GL/year on average. After prolonged groundwater extraction the rivers are predicted to eventually lose 5.2 GL/year to these GMUs. This means that once equilibrium is reached, there will be a potential double accounting error of around 9.6 GL/year inherent in any separate surface and groundwater assessments. Half of this impact is likely to eventuate by 22. However, it may require more than 1 years for groundwater levels to reach dynamic equilibrium. Future water planning should consider these surface-groundwater exchanges. CSIRO 27 November 27 Water availability in the Border Rivers 93

106 For 23 climate and extraction at 23/4 levels o The impact of climate change on surface-groundwater exchanges is negligible. Under the best estimate (median) 23 climate the flux from the river to groundwater is unchanged at 5.2 GL/year. For 23 climate and projected 23 extraction levels 6 Groundwater assessment o Extraction is 23 GL/year in the modelled area less than the extraction limit of 3 GL/year. o This level of extraction (assuming the current spatial pattern) could not be sustained as large reductions in groundwater levels would occur. This would most likely lead to responses from groundwater users and resource managers that would reduce groundwater extraction in the relevant areas. Without such responses projected future extraction could lead to complete drying of the aquifer, thus forcing a reduction in extraction. o Prolonged extraction at these levels would eventually remove another 8.9 GL/year from the river through induced leakage to groundwater. However, the model is likely to overestimate the real impact. Groundwater extraction in New South Wales outside of the Border River Alluvium GMUs is expected to increase by a factor of 5.7 times overall. The increase in the New England Fold Belt GMU is assessed to be a 27-fold increase. For some GMUs these increases lead to a very high level of extraction. For the Miscellaneous Alluvium of Barwon Region GMU extraction would be even further in excess of rainfall recharge. On average, groundwater extraction represents 8 percent of total annual water diversions in the region under current conditions. This would increase to 28 percent on average under the best estimate (median) 23 climate and projected 23 groundwater extractions. In the driest years, groundwater extraction currently represents 26 percent of total annual water use, while under the best estimate (median) 23 climate and projected 23 groundwater extraction it would represent 67 percent of total annual water use. The total impact of these levels of future extraction on the river network is estimated to be around 3 GL/year. This is three times the ultimate impact of prolonged groundwater extraction at 23/4 levels. The scenarios of future groundwater extraction are not of conditions that will eventuate but of the consequences that might arise if no management changes were made. The results therefore highlight pressure points in the system. This project does not elaborate on what management actions might be taken to address any of these pressure points Uncertainty The current form of the groundwater model of the Border Rivers Alluvium GMUs produces results that have a high level of uncertainty due to its poor conceptualisation and the lack of a suitable calibration. It is considered unsuitable for use as a water allocation tool due to its inability to implement local aquifer use rules. Further model calibration is required once a larger stress is placed on the aquifer via pumping, and the measured aquifer response is incorporated into the model. The model is not expected to be accurately representing the drawdowns in the deeper aquifer once pressure levels drop. Notwithstanding the level of uncertainty surrounding the model, the level of analysis for the Border Rivers Alluvium GMUs is commensurate with the priority ranking of these GMUs given the project objectives. There is considerable uncertainty in the future projections of groundwater development outside of the Border Rivers Alluvium GMUs, but the estimates emphasise the importance of development in these areas. The groundwater projections are considered to generally represent the upper limit of groundwater development as it can be constrained by pumping rules, groundwater quality and land suitability. However, the estimates of development impacts are generally conservative due to the use of entitlements in determining stream impacts and the use of connectivity estimates based on conservative best guesses. 94 Water availability in the Border Rivers November 27 CSIRO 27

107 6.2 Groundwater management units in the region Location For management purposes, the aquifers within the Border Rivers region are divided into a number of GMUs (Table 6-1). These units are three dimensional in nature because of the layered nature of geological formations at different depths. Different GMUs cover all the New South Wales portion of the region but only a small part of the Queensland portion of the region; except for the Great Artesian Basin (GAB) GMU which lies at greater depths under the region (Figure 6-1). There are no data available for the area of sediments lying above the GAB in Queensland that is not covered by a GMU. This area is referred to as an unincorporated area. No information for the GAB GMU in Queensland is included. The degree of development of the groundwater source in each GMU (and in the unincorporated area) varies considerably from areas of intensive extraction for irrigation to areas of broad-acre stock and domestic use Ranking Table 6-1 shows the GMU priority ranking for the project and the assessment ranking for the project. The priority ranking is defined to help focus efforts on those GMUs which affect most the overall groundwater or surface water resource in the MDB. It ranges from very low to very high in the context of the project, and is based on the level of groundwater use, potential for growth in use and the potential for groundwater to impact on streamflow. The groundwater assessments vary for different GMUs, reflecting the availability of data and analysis tools as well as the priority of the GMU. They range from minimal to very thorough. For the GMUs in the Border Rivers region a simple ranking denotes a simple water balance approach while moderate denotes a poorly calibrated and conceptualised numerical groundwater model (for the purposes of this project). For all of the GMUs listed in Table 6-1, the analysis method is consistent with the priority ranking. While these assessments are appropriate given the constraints and terms of reference of this project, additional is probably required for local management of groundwater resources. 6 Groundwater assessment Table 6-1. Groundwater management units of the Border Rivers region and associated data Code Name Priority Assessment 24/5 Current Extraction Groundwater entitlements limit use*** Q73 Border Rivers Alluvium (Qld) low moderate *6.3 * GL/y Maximum likely extraction without plan revision N22 Border Rivers Alluvium (NSW) low moderate **6.22 ** N23 Miscellaneous Alluvium of the Barwon Region (NSW) low simple N63 Great Artesian Basin Alluvial (NSW) low simple N61 Great Artesian Basin In-take Beds (NSW) very low simple ****9.28 N83 Inverell Basalt (NSW) low simple N85 New England Fold Belt (NSW) low simple na Unincorporated Area <15 mg/l na na stock and domestic only na GAB Intake Beds (Qld) na na stock and domestic only Na na na Na na na *Supplied by QNRM ** Supplied by NSW DWE ***Current groundwater extraction for Macro Groundwater Sharing Plan areas is based on metered and estimated data provided by NSW DWE. Data quality is variable depending on the location of bores and the frequency of meter reading. **** Determined from values supplied by NSW DWE from the Draft Water Sharing Plan for the Great Artesian Basin Groundwater sources 26. Future extraction will equal the Long-Term Average Extraction Limit. CSIRO 27 November 27 Water availability in the Border Rivers 95

108 6 Groundwater assessment Figure 6-1. Map of groundwater management units in the Border Rivers region Hydrogeological context The hydrogeological context is outlined in Chapter 2. Some additional detail is provided below. Groundwater occurs in aquifers in the Queensland and New South Wales highlands, the GAB and in alluvial deposits associated with the Dumaresq River in Queensland and the Macintyre River in New South Wales. Groundwater salinity is generally less than 1 mg/l total dissolved salts (TDS) in the eastern and central part of the region but increases in the western area. A number of rock types provide groundwater of variable yield and quality in the New South Wales and Queensland highlands, including porous sandstones, fractured granites, other sedimentary rocks and volcanic rocks. Reliable groundwater supplies are also found in highland alluvial deposits which are generally less than 15 m thick. Groundwater in the highlands is mainly for domestic and stock use. Little is known of the recharge and flow mechanisms in these areas. Unincorporated areas where salinity is considered suitable for irrigation purposes (<15 mg/l TDS) occur along the eastern margin of the region within the Queensland highlands. This zone is composed largely of granites and other fractured rock aquifers. These aquifers possess limited resource potential and are largely restricted to stock and domestic use. There are however local pockets of good quality water such as those drawn from the Ruby Creek Granite and the Stanthorpe Ademalite. In addition, some reliable groundwater supplies are also taken from alluvium associated with the area s streams. Groundwater quality is variable within these alluvial aquifers. Further west, the unincorporated areas have higher salinities and are considered marginal for irrigation purposes. However, very localised pockets of fresh water do exist and may be utilised. 96 Water availability in the Border Rivers November 27 CSIRO 27

109 Multi-layered sandstones and mudstones of the GAB aquifer system occur across much of the region, outcropping in many areas on the western flanks of the highlands. These outcrops allow recharge to the GAB aquifers from rainfall and river flow. Groundwater flow in the region is initially to the west. Water quality decreases further along the flow path with fresh to marginal groundwater occurring in the upper aquifers becoming more saline with depth to the west. The water resources within these aquifers are not considered in this assessment except where in-take beds for the GAB outcrop within the region, since groundwater in these areas has the potential to be connected with surface water systems and shallow groundwater systems. The GAB is represented in the region by the following hydrogeological units: the deep Jurassic sandstone confined aquifers that extend beneath the western part of the reporting region and outcrop in the centre the Cretaceous sandstone confined aquifers and shale confining layers which lie conformably above the Jurassic aquifers. The Cretaceous confining layers separate the deeper confined aquifers from the surficial aquifers the GAB intake beds and GAB Alluvium. The GAB hydrogeological units correspond to GMUs as follows: the deep Jurassic and Cretaceous sandstone confined aquifers, and Cretaceous confining layers which are administered by the Water Sharing Plan for the NSW Great Artesian Basin Groundwater Sources (N61 GAB Surat Zone) the GAB Intake Beds that occur where the Jurassic and Cretaceous sandstone aquifers outcrop. This GMU is also administered by the WSP (N61, Eastern Recharge Zone) the GAB Alluvium is a thick sequence of Cainozoic alluvium covering the GAB sequence in the western portion of the region (N63, GAB Alluvial). The deeper GAB Jurassic and Cretaceous confined sandstone aquifers provide a limited groundwater resource to the region. The groundwater within these aquifers is separated from the surface aquifers by thick confining beds. This means there is little interaction with the overlying surface water or groundwater contained in near surface aquifers. The water resources within these confined aquifers are not considered further in this assessment. 6 Groundwater assessment Where the Jurassic and Cretaceous aquifers outcrop within the region they form the GAB intake beds. These outcrops form a designated GMU in New South Wales but not in Queensland, where they are administered under the Water Resources (Great Artesian Basin) Plan (26). There is no licensed groundwater extraction from the GAB intake beds in the Queensland part of the Border Rivers region. However, groundwater from these units is for stock and domestic use. The Queensland GAB intake beds have been assigned a very low priority ranking in the context of the project, requiring only a minimal level of assessment due to the low level of development, the availability of the resource and the connectivity between rivers and aquifers. The major source of high yielding groundwater in the region is the alluvial deposits associated with the Dumaresq and Macintyre Rivers. These sediments are deposited in a narrow valley which broadens downstream near Keetah. The Gunnedah Formation, also known as Unit B in the region, overlies the highland and GAB aquifers and comprises fluviolacustrine sands, gravels and clays up to 7 m thick. The coarser sediments form a palaeochannel which meanders through the incised valley. Useable groundwater resources are restricted to those areas upstream of Keetah that contain fresh groundwater. Downstream of Keetah the only occurrence of fresh groundwater is associated with raised water levels in the region of the Boggabilla Weir. The Narrabri Formation, also known as Unit C in the region, overlies the Gunnedah Formation and comprises alluvial sands, gravels and silts forming an unconfined aquifer. These sediments are generally 1 m to 3 m thick, and form the ground surface in the valley. Units B and C are separated by 2 m to 15 m of semi-permeable clay that controls leakage between the two aquifers. Aquifer transmissivities and groundwater quality decrease markedly from the east to the west of the region. Groundwater in the Narrabri Formation is mostly recharged by stream losses, although diffuse recharge from rainfall and excess irrigation are also likely to contribute minor amounts. Recharge to the deeper Gunnedah Formation aquifers is by cross-formational flow, upward leakage from underlying aquifers and infiltration of rainfall and runoff. CSIRO 27 November 27 Water availability in the Border Rivers 97

110 6.3 Surface water groundwater connectivity The surface-groundwater connectivity mapping aims to (i) provide a catchment context for groundwater-surface water interactions; (ii) constrain the surface water balance; and (iii) constrain groundwater balances. The main output is a map of the magnitude and direction of groundwater fluxes adjacent to main streams. The approach uses Darcy s Law and hence estimates the hydraulic conductivity and groundwater gradients surrounding the streams. The method is dependent on the availability of appropriate groundwater monitoring data and on reported estimates of hydraulic conductivity. 6 Groundwater assessment River levels and groundwater levels were compared at a single point in time to provide a snapshot of the direction and magnitude of the flow between surface water and groundwater. The date selected for production of the flux map and associated calculations was June 26, as this was the most recent date with both a large quantity of available bore and river elevation data. This was an unusually low flow period, however, as it only the variation in the relative (not absolute) river and groundwater levels that is consider, the fact it was an unusually low flow period does not affect the connectivity analyses. An average aquifer thickness of 2 m was used for all river reaches. The adopted hydraulic conductivity values varied across the region between.1 to 1 m/day. The upper Narrabri Formation in the western parts of the region was assigned hydraulic conductivities generally between.1 to 1 m/day. Hydraulic conductivities in the middle sections around the Dumaresq River were generally around 1 m/day, while hydraulic conductivity generally decreased in the eastern parts of the region with values about 1 m/day common in the upper catchment region. Figure 6-2 shows the surface groundwater connectivity results from the flux assessment. Figure 6-2. Map of surface groundwater connectivity 98 Water availability in the Border Rivers November 27 CSIRO 27

111 The lower reaches of the Macintyre River and the Boomi River are low losing rivers. Low hydraulic conductivity is an important control on river aquifer interactions in this area. The assessment found that: The lower reaches of the Macintyre River downstream of the Terrewah gauge (41647) and the Boomi River behave as a disconnected system. The intermediate reaches of the Macintyre River are more variable ranging from low gaining to medium losing. The Macintyre is a gaining river in its upper reaches. The direction and magnitude of river aquifer interactions are variable along the lower reaches of the Dumaresq River ranging from medium losing to low gaining. The middle reaches of the Dumaresq River are classified as high losing while the upper reaches of the Dumaresq are low gaining. The Macintyre Brook is classified as a medium losing river along its lower reaches and a low gaining river along its uppermost reach. Comparisons between river levels at two gauging stations and adjacent groundwater levels show how these fluxes change with time. Groundwater levels retained the same relative relationship with river stage in most reaches studied indicating that the nature of the surface groundwater connection remained essentially stable over time. This was tempered by observations that gaining conditions could be reversed over short time periods in some river reaches due to flood events, indicating a more episodic influence on connectivity. The relationship between groundwater level and river stage for the highly losing section of the Dumaresq River at Bonshaw is shown in Figure 6-3. Here, the ongoing drawdown from groundwater extraction can be seen increasing the gradient from the stream to the aquifer over time. The hydrograph for the deeper aquifer (416363A) shows greater drawdown than the shallower unconfined aquifer (416362A) that is more subdued. The main extraction occurs from the confined aquifer, and piezometric head differences drive fluxes of water from stream to shallow aquifer and from shallow aquifer to deeper aquifer. This stretch of river has changed from being a gaining stream to being a losing stream over this period of time. 6 Groundwater assessment Water level (mahd) Dumaresq Bonshaw A A Feb-1982 Nov-1984 Aug-1987 May-199 Jan-1993 Oct-1995 Jul-1998 Apr-21 Jan-24 Oct-26 Figure 6-3. Comparison of levels of the Dumaresq River and adjacent groundwater levels CSIRO 27 November 27 Water availability in the Border Rivers 99

112 6.4 Groundwater modelling approach About 37 percent of the current groundwater extraction in the Border Rivers region occurs in the Border Rivers Alluvium GMUs in New South Wales and Queensland. These GMUs were analysed using a numerical groundwater model (Chen, 23) that had been previously developed by the Queensland Department of Natural Resources and Mines jointly with the NSW Department of Land and Water Conservation. While this model does not cover the full spatial extent of these GMUs, it does cover an area encompassing 9 percent of groundwater extraction. The model extends over the Dumaresq River alluvial sediments, along the New South Wales Queensland border for about 1 km from Keetah Bridge east and upstream to the confluence of the Dumaresq River with the Mole River, near Lake Glenlyon Model description 6 Groundwater assessment Within the model area there are two aquifers overlying the hydraulic basement that are separated by an aquitard. This hydrogeological sequence is located within the topographic depressions of the Dumaresq River valley where the parent rock was eroded and riverine sediments deposited. The upper aquifer (Unit C) is broadly consistent with the Narrabri Formation further south, and consists of unconsolidated clay, sand and gravel to about 1 m to 3 m thick. It is unconfined and responds hydraulically to floods. The aquitard consists of clay layers. The lower aquifer (Unit B) is broadly consistent with the Gunnedah Formation further south, and consists of consolidated clay, sandstone and gravel up to about 5 m thick. It extends down to about 5 m to 1 m below ground surface and is semi-confined. The hydraulic basement (Unit A) consists of consolidated quartzose sandstones that become finer in texture towards the top of the Unit. The river acts as both a source and a sink for the groundwater depending on river level relative to the adjacent watertable. Groundwater is recharged by rainfall, its surface ponding and irrigation deep drainage. Groundwater is removed by pumping bores and evapotranspiration from shallow areas of the watertable. Some groundwater exchange with the GAB occurs via the Marburg Sandstone near the Peel Fault around the western end of Brush Creek and northwest of Texas. This is represented by a line of constant head in the model. The lateral extent of the alluvial aquifers is modelled as a no-flow boundary except for the upstream, downstream and GAB interface constant head boundaries. Model developers have observed that the sides of the valley that abut the alluvium are relatively extensive and steep, and that a considerable volume of the side slope runoff may infiltrate into the alluvium rather than reaching the stream channel (M. Williams, pers. comm.). The numerical model uses MODFLOW and is constructed using a variety of specialised software. The semi-confined layer is modelled in MODFLOW as a confined layer and hence could not be desaturated. The model was calibrated over 1 January 196 to 31 December 1999 with one-month stress periods and five time steps per stress period. The assumption of the confining layer, while providing reasonable fits over the calibration period, is expected to provide poor matches once piezometric heads fall below the top of the semi-confined layer. 1 Water availability in the Border Rivers November 27 CSIRO 27

113 Mass In Mass Out 1% 3% 5% 1% 9% 11% 1% 13% 76% Rainfall recharge Irrigation recharge River leakage Lateral inflow 71% Figure 6-4. Mass balance for the calibration model River leakage Pumping, Unit B Pumping, Unit C Evapotranspiration Lateral outflow Discharge to GAB Spatially, the model grid is 44 km x 16 km oriented NW SE, with cell dimensions ranging from 1 m to 4 m. The mass balance from the calibrated model over the period 196 to 1999 is shown in Figure 6-4. Natural recharge is the main inflow and river seepage is the main groundwater outflow. Groundwater pumping from the shallower aquifer is less than 1 percent of the pumping from the deeper aquifer Scenario Implementation 6 Groundwater assessment The objective of the numerical modelling is to assess groundwater and surface water impacts under a range of scenarios of groundwater extraction from the Border Rivers Alluvium GMUs. The groundwater impacts are characterised by resource condition indicators; the surface water impacts are characterised by river losses to groundwater. Groundwater extraction was set at 11.2 GL/year for scenarios A and C and at 23. GL/year for Scenario D. Climate can affect the groundwater balance in a number of ways. It can change dryland recharge, the area of irrigation or river flows. The impact of climate on diffuse dryland recharge is assessed through the application of a recharge scaling factor (RSF). The method used to estimate the RSF is described in the section below. The river and groundwater models are run in a sequence to simulate the effect of climate on surface-groundwater exchange fluxes and both groundwater and surface water balances (Chapter 1). The IQQM river model as implemented for the Water Sharing Plan would implicitly include groundwater surface water exchanges within the unattributed losses and gains. The calibration periods for the groundwater and surface water models broadly coincide and hence the change in groundwater-surface exchange fluxes in the MODFLOW outputs from the calibration period is assumed to be the same as the change in groundwater gains and losses from that included in the unattributed gains and losses. In all cases, extraction rates were assumed to be constant Climate impacts on dryland recharge RSFs are applied in the groundwater modelling described in the previous section and in the simple water balance analyses described later. Values of diffuse dryland recharge are used to calibrate the original implementation of the groundwater model and for management of the other GMUs within the Border Rivers. The RSFs are used to multiply these values to provide estimates of dryland recharge under different climate scenarios to be used in further analyses. For Scenario A the RSF is 1. by definition. For other climate scenarios RSFs would be expected to be close to 1.. The impacts of climate change on recharge are reported as percentage changes from Scenario A (Table 6-3). The RSFs are obtained by dividing the percentage change by 1 and adding to 1.. CSIRO 27 November 27 Water availability in the Border Rivers 11

114 The three variants of Scenario C (Cdry, Cmid and Cwet) represent a range of global climate model (GCM) output, selected based on a ranking of mean annual runoff (Chapter 3). Groundwater recharge is not perfectly correlated with mean annual rainfall or runoff. Apart from mean rainfall, diffuse dryland recharge is sensitive to seasonal rainfall and potential evaporation and to the extreme events or years that lead to episodic recharge. In semi-arid to sub-humid areas extreme events become more important. A number of GCMs show an increase in extreme events, but the scenario variants are selected based on mean annual runoff which is more dependent on average and seasonal rainfall. Recharge also depends on the land use and soils. These can be locally variable and reflect local spatial variation in RSFs. An estimate for a small GMU will be sensitive to these local variations, while in larger areas with a broader range of soils and land uses the estimates will be more robust. RSFs were estimated for all 15 GCMs under Scenario C. In all cases, a one dimensional soil-vegetation-atmosphere water transfer model (WAVES; Zhang and Dawes, 1998) was used for selected points around the MDB for combinations of soils and vegetation. Spatial data on climate, vegetation and soils were then used to interpolate values to regions. 6 Groundwater assessment Figure 6-5 shows the percentage change in the modelled mean annual recharge averaged over the Border Rivers region for Scenario C relative to Scenario A for the 45 scenarios (15 GCMs for each of the high, medium and low global warming scenarios). The percentage change in the mean annual recharge and the percentage change in mean annual rainfall from the corresponding GCMs are tabulated in Table 6-2. The plots show that there is a wide range in results across GCMs and scenarios for the Border Rivers with just over half the scenarios predicting less recharge and the remainder predicting more recharge. The high global warming scenario predicts both the highest and lowest change in recharge for the Border Rivers region. In subsequent modelling and reporting only the dry, mid and wet Scenario C variants are shown. These variants are based on the runoff modelling and are indicated in Table 6-2 in bold type. The choice of GCMs for surface runoff is comparable to those that would be chosen if recharge formed the basis of choice with the second highest, second lowest and median in surface run-off being respectively the second highest, sixth lowest and the median for RSF. The large variability in RSFs is related to the large variability in rainfall produced by the various GCMs. Rainfall and RSFs are correlated, but not perfectly. Some GCMs that indicate reductions in rainfall lead to RSFs greater than 1.. This is due to the more extreme events being more frequent, in spite of a reduction in mean rainfall High global warming Medium global warming Low global warming inmcm cnrm iap giss_aom mri mpi csiro ipsl gfdl ncar_ccsm miub ncar_pcm cccma_t63 cccma_t47 miroc Figure 6-5. Percentage change in mean annual recharge from the 45 Scenario C simulations (15 GCMs and three global warming scenarios) relative to Scenario A recharge 12 Water availability in the Border Rivers November 27 CSIRO 27

115 Table 6-2. Summary results from the 45 Scenario C simulations (numbers show percentage change in mean annual rainfall and recharge under Scenario C relative to Scenario A). Those in bold type were selected for further modelling. High global warming Medium global warming Low global warming GCM Rainfall Recharge GCM Rainfall Recharge GCM Rainfall Recharge inmcm -9% -15% inmcm -5% -1% inmcm -2% -4% cnrm -1% -14% cnrm -6% -9% cnrm -3% -4% iap -3% -9% iap -2% -5% mri -2% -3% giss_aom -1% -6% mri -4% -4% iap -1% -2% mri -7% -5% giss_aom -6% -4% mpi -2% -2% mpi -7% -4% mpi -4% -3% giss_aom -3% -2% csiro -5% -3% csiro -3% -2% ipsl % -1% ipsl -1% -1% ipsl % -1% csiro -1% -1% gfdl -6% 2% gfdl -4% 1% gfdl -2% % ncar_ccsm 2% 4% ncar_ccsm 1% 3% ncar_ccsm % 1% miub 3% 15% miub 2% 9% miub 1% 4% ncar_pcm 6% 15% ncar_pcm 4% 9% ncar_pcm 2% 4% cccma_t63 4% 17% cccma_t63 3% 11% cccma_t63 1% 5% cccma_t47 9% 28% cccma_t47 6% 18% cccma_t47 2% 7% miroc 12% 37% miroc 7% 23% miroc 3% 1% 6 Groundwater assessment Table 6-3. Summary results of the scenarios for modelling mean annual recharge for each groundwater management unit in the Border Rivers region Code GMU Cdry Cmid Cwet N22, Q73 Border Rivers Alluvium (NSW/Qld) -2% 1% 28% N23 Miscellaneous Alluvium of Barwon Region (NSW) -4% -1% 43% N63 GAB Alluvial (NSW) -3% 2% 32% N61 GAB Intake Beds (NSW) -2% -1% 32% N83 Inverell Basalt (NSW) -2% 2% 3% N85 New England Fold Belt (NSW) -3% -6% 32% The Scenario D variants (Ddry, Dmid, Dwet) use the same 23 climate predictions as Scenario C. Additionally, Scenario D introduces changes in water management, such as changes in groundwater extraction and increases in commercial plantation forestry and farm dams. River stage, which is calculated from outputs of the river system model (Chapter 4), may vary from Scenario C because of changes to water management. For this scenario, groundwater extraction was increased to a total of 11 GL/year in the Queensland section of the model and 12 GL/year in New South Wales section of the model. This level of pumping is below the combined extraction limit of 3 GL/year defined for the two states. CSIRO 27 November 27 Water availability in the Border Rivers 13

116 6.5 Modelling results and discussion Time lags following development Groundwater extraction takes a finite amount of time to reach an equilibrium impact on streamflow. Figure 6-6. indicates that there is a period of about 2 years at the start of the scenario run before the water loss from the river reaches half of the final impact, which stabilises at about 5 GL/year. The Dumaresq River is a dominantly losing stream along the modelled reaches. The spikes of about 1 GL/year are artefacts of the parameterisation of the last stress period in the original model, and should not be interpreted as expected GMU behaviour. 6 Groundwater assessment GL/y Time (years) Figure 6-6. Annual net river loss for the Dumaresq River model under Scenario A over the 222-year simulation period Groundwater levels Six observation bores were selected to indicate the water level changes under the scenarios in both aquifers and along the length of the Dumaresq River (Table 6-4). The bores were selected because they are neither close to the river nor close to the edge of the aquifer. Under all scenarios the modelled water level in the deeper aquifer drops further than in the shallower unconfined aquifer. Of the 64 bores in the model, 61 extract groundwater from the deeper aquifer. Groundwater levels in the deeper aquifer are least impacted in the downstream parts of the river and most impacted midway along the river. However, the model does not capture the observed water level fluctuations at the upstream (Observation Bore B) and midway (Observation Bore A/B) locations. The results suggest that groundwater extraction rates have a much greater impact on drawdown than climate. The hydrographs from scenarios A and C, which have the same groundwater use but different climate, are very similar. After about 13 years, when the groundwater level fluctuations reach dynamic equilibrium, groundwater levels in the shallower aquifer have decreased by about 2 m to 8 m and groundwater levels in the deeper aquifer have decreased by about 15 m to 7 m. As the deeper aquifer is modelled as confined only, the model transmissivity, and therefore the model saturated aquifer thickness, does not vary with changes in water level and the model cells are never shown as dry. Consequently, and because of the limited thickness and depth of Unit B, modelled drawdowns much in excess of the aquifer thickness are logically impossible and therefore declines of more than 7 m will not be realised. In these cases the modelled drawdowns show the potential rather than the actual impacts of increased pumping (Chen, 23). In reality, the actual drawdown level will be a function of the unconfined storage coefficient and is not able to be predicted here with any level of certainty. Any falls of more than 2 m are considered to be outside of the model calibration range. 14 Water availability in the Border Rivers November 27 CSIRO 27

117 The hydrographs from scenarios C and D, that have the same climate but different groundwater use, are very different. The groundwater use in Scenario C is less than half that in Scenario D, yet the Scenario D drawdown is more than double the Scenario C drawdown. The model is unlikely to simulate drawdowns well once piezometric levels fall within the bounds of the lower aquifer. After about 2 years, when dynamic equilibrium is reached under Scenario D, groundwater levels in the shallower aquifer have decreased by about 1 m to 25 m, and in the deeper aquifer have decreased to the point where it could be expected that the aquifer would dry out in places, although the way the model is conceptualised leads to predictions of ongoing drawdown. Prior to equilibrium, the upstream observation bore in the shallower aquifer became dry under both Scenario Dmid and Scenario Ddry. Under Scenario D many production bores would also run dry. It is highly unlikely, however, that this level of drawdown would occur in reality as groundwater management rules aimed at avoiding the development of hotspots would limit drawdown to pre-defined levels under a Water Sharing Plan. Many of the New South Wales entitlements are held in property accounts that are yet to be activated and are not assigned to a groundwater works. Under the existing management arrangements for the entitlements to be activated they will be remote from the current usage. As such, the pattern of extraction will change and distribute future extraction more widely and decrease the emphasis on current hotspots. Again, drawdowns of more than 2 m are outside of the calibration range of the model. Table 6-4. Median groundwater level over 111 years under Scenario A and the difference in level from Scenario A for scenarios C and D Bore A Cdry Cmid Cwet Ddry Dmid Dwet m 4644A MF MF MF B MF MF MF AB MF MF MF 6 Groundwater assessment 4653A MF MF MF MF MF MF 41643A MF MF MF Average MF MF MF MF: model is considered to be outside of the calibration range as water tables fall more than 2 m in some areas Groundwater balance Figure 6-7 compares the combined annual recharge in the model for Scenario A to the groundwater pumping flux. In this case, combined recharge includes rainfall and surface ponding, leakage from rivers, irrigation accessions and fluxes into the model across the model boundary. In some years extractions exceed recharge, and during these years water is drawn from storage to meet the demand. Recharge exceeds pumping in 88 of the 111 years of the scenario or about 79 percent of the time. In terms of volumes accumulated over the duration of the model, the combined recharge amounts to 162 GL while the extraction is approximately 124 GL. CSIRO 27 November 27 Water availability in the Border Rivers 15

118 Combined recharge Extraction from wells Flux (GL/y) Groundwater assessment Time (years) Figure 6-7. Combined recharge compared to groundwater extraction under Scenario A Table 6-5 lists the average annual total recharge and groundwater pumping for the second 111 years under assessment. Changes in pumping in Scenario D have a greater affect on the groundwater fluxes than the changes in climate. Recharge exceeds pumping by about 25 percent in scenarios A and C, but by less that 1 percent in Scenario D. River leakage increases with the higher groundwater pumping rates in Scenario D. It increases as a proportion of the total recharge from less than 4 percent in scenarios A and C to nearly 6 percent in Scenario D. The inflows and outflows of the groundwater system under scenarios A, C and D are shown in Figure 6-8. Groundwater extractions, river leakage and rainfall recharge dominate the water balances. The mass balances of scenarios A and C are similar. The larger groundwater extraction in Scenario D is accompanied by a larger impact on streamflow, as more river water is drawn into the groundwater system. The increase in lateral inflows in Scenario D can also be attributed to the larger groundwater extractions. The estimated increase in groundwater recharge from irrigation return flows is based on the increase in groundwater use. The model has predicted large drawdowns in the lower aquifer layer. Apart from the issue of whether these drawdown levels are logically possible, the drawdown also impacts on the flux of surface water losses to the groundwater system. The excessive drawdowns in parts of the model generate predictions that overestimate surface water losses. This will impact on consideration of the balance between extraction and recharge. Recharge may not exceed extraction to the same degree once the overestimate of stream flow losses is considered. The levels of groundwater extraction in the model may not be able to be achieved under a different conceptualisation, where the lower aquifer layer has the potential to dry out, or become unconfined. 16 Water availability in the Border Rivers November 27 CSIRO 27

119 GL/y A Cmid Dmid Lateral Groundwater flow Rivers to Groundwater Rainfall recharge Recharge from irrigation Figure 6-8. Groundwater system inflows and outflows under scenarios A, Cmid and Dmid Table 6-5. Annual average combined recharge and net loss of river flow Scenario Total recharge GL/y Lateral River derived recharge Calibration -4.4 groundwater flow Groundwater extraction Evapotranspiration Groundwater to Rivers Time recharge exceeds pumping Percent A % Cdry % 6 Groundwater assessment Cmid % Cwet % Ddry % Dmid % Dwet % Dynamic equilibrium conditions for pumping under Scenario D cause water levels to fall below the base of the Dumaresq River alluvium in places, resulting in the drying of the aquifer and eventual loss of production potential from those parts of the aquifer. Groundwater management intervention and natural loss of productivity as the aquifers are dewatered would prevent the aquifers from drying out completely in practice. A different model conceptualisation may result in a different predicted condition, such that if the lower aquifer layer were allowed to become unconfined, water level decline would not be as dramatic as currently predicted. However, bore yields would be substantially lower. In either event, the end result is that levels of extraction would be reduced. Modelling indicates that dynamic equilibrium or quasi steady state conditions take many decades of continuous pumping to be realised. The areas with the largest drawdowns are the slowest to reach equilibrium. Groundwater extraction has had, and will continue to have, an impact on flows in the Dumaresq River. The interaction with the river is associated with both a reduction in groundwater discharge feeding the rivers, and an increase in induced leakage of river water to the groundwater system. The modelling suggests that river flow will be reduced by 8.9 GL/year as a result of prolonged extraction of 11.8 GL/year over and above the 23/4 level of extraction. This corresponds to an effective connectivity factor of.76. The 23/4 levels of extraction (11.2 GL/year) are predicted to lead to an increase in river losses of 9.6 GL/year. This corresponds to an effective connectivity factor of.85. The connectivity factor under the higher pumping scenario may decrease more quickly with pumping rate than is currently being simulated, because of the way MODFLOW simulates the semi-confined layer. Nonetheless, development until now has changed this stretch of river from a gaining stream to a losing stream. CSIRO 27 November 27 Water availability in the Border Rivers 17

120 All the components of groundwater inflow and outflow are summarised below in Table 6-6. The fluxes between scenarios A and C are similar, as are the fluxes within Scenario D. After groundwater pumping, the greatest variation in flux is in river leakage. As irrigation recharge is directly related to the pumping rate this shows a proportionately large, but smallmagnitude increase. Lateral inflows are also enhanced by the increased groundwater pumping, almost three-fold from Scenario A to Scenario D. Table 6-6. Dumaresq River average annual modelled groundwater balance A Cdry Cmid Cwet Ddry Dmid Dwet GL/y Inflows Recharge (gains) 6 Groundwater assessment Rainfall recharge Irrigation recharge From rivers Lateral flow Sub-total Outflows Extraction To rivers Evapotranspiration Lateral flow Sub-total Change in storage (a) (b) Total recharge (GL/y) Crange Cmid A Total Recharge (GL/y) Drange Dmid A Probability of Exceedence Probability of Exceedence Figure 6-9. Annual total recharge exceedence curves for the second 111 years of scenarios (a) A and C, and (b) A and D The exceedence plots in Figure 6-9 rank the annual total recharge from highest to lowest for the second 111 years under assessment. For scenarios A and C there is at most a 1 percent probability that the total recharge will exceed 2 GL/year. However, for Scenario D, there is a 1 percent probability of the total recharge exceeding 2 GL/year, and half of the time (the median) total recharge will exceed 24 GL/year. This difference is due to the impacts of groundwater extraction on river leakage and illustrates the effects of development on the water balance. The current model conceptualisation may overestimate the river losses under Scenario D. The median total recharge for scenarios A and C is about 13 GL/year. 18 Water availability in the Border Rivers November 27 CSIRO 27

121 6.5.4 Groundwater indicators Groundwater resource condition indicators are described in Table 6-7. The results (Table 6-8) show that groundwater resource security is high under all scenarios, although the security indicator is less than 1 percent some of the time under Scenario D. The difference from the exceedence curves (Figure 6-9) is that here, recharge is averaged over a ten-year period. Under Scenario D the Environmental Indicator increases towards (but does not exceed) the threshold value of 1.. This indicates a reduction of water for environmental purposes. Table 6-7. Definition of groundwater indicators Groundwater Indicators Definition Groundwater Security Indicator Percentage of years in which extraction is less than the average recharge over the previous ten-year period. Values less than 1 indicate increasing risk of sustained long-term groundwater depletion and thus a lower security of the groundwater resource. Environmental Indicator Ratio of average annual extraction to average annual recharge (E/R). Values of more than 1. indicate a long-term depletion of the groundwater resource and consequential long-term environmental impacts. Drought Indicator Difference in groundwater level (in metres) between the lowest level during each 111-year scenario simulation and the mean level under the baseline scenario. This is a relative indicator of the maximum drawdown under each scenario. Scenario D shows drawdowns of over 1 m relative to Scenario A in indicator bores where groundwater extraction is high. As mentioned earlier, these large drawdowns are an artefact of the model conceptualisation. Drawdowns greater than the thickness of the lower aquifer layer are unlikely. Any large drawdown levels are unlikely to be achieved as local groundwater management rules would limit the effects of pumping as hotspots of drawdown are identified. These rules would be enforced via a Water Sharing Plan. Many of the New South Wales entitlements are held in property accounts that are yet to be activated and are not assigned to a groundwater works. Under the existing management arrangements for the entitlements to be activated they will be remote from the current usage. As such the extraction would be more widely distributed than current hotspots. This would decrease the drawdowns from that which would otherwise occur. 6 Groundwater assessment Table 6-8. Groundwater indicators under scenarios A, C and D A Cdry Cmid Cwet Ddry Dmid Dwet Groundwater security indicator 1% 1% 1% 1% 97% 98% 99% Environmental Indicator Drought Indicator metres Average na A B AB A A CSIRO 27 November 27 Water availability in the Border Rivers 19

122 6.6 Water balances for lower priority groundwater management units For the lower ranked GMUs in the Border Rivers region (Table 6-1) simple water balance analyses have been undertaken. Two indicators are reported. The first indicator is the ratio of extraction to rainfall recharge (E/R). The level of development for a GMU is categorised in terms of E/R values as follows: low, for..3; medium, for.3.7; high, for.7 1.; and very high, for >1.. For alluvial aquifers, a significant fraction of recharge may come from streams either directly from channels or during floods. In these cases, extraction may be maintained at E/R values greater than 1, although with impacts on streamflow. E/R is not used as an indicator for confined aquifers. The second indicator is the average volumetric impact of groundwater extraction on streamflow. 6 Groundwater assessment Groundwater extraction Estimated current and future groundwater extraction from low priority GMUs within the Border Rivers region is shown in Table 6-9. For areas controlled by New South Wales macro groundwater plans, the estimates of current use are based on metered data and on an average extraction estimate of 1.5 ML/year for each stock and domestic bore (NSW Department of Water and Energy, pers. comm.). The macro groundwater plan program is a broad scale planning process covering areas of New South Wales not under a water sharing plan. The macro water plans contain a standard set of rules extended across catchments with similar attributes and social, economic and environmental values. Macro groundwater plans, like water sharing plans, reflect the priorities of environment, basic landholder rights, town water and licensed domestic and stock use and other extractive uses including irrigation. Long-term extraction limits are based on the calculation of rainfall recharge to each GMU. Code GMU Table 6-9. Estimated groundwater extraction for the Border Rivers region Current extraction* (24/5) Total entitlement Future extraction N23 Miscellaneous Alluvium of the Barwon Region (NSW) N63 Great Artesian Basin Alluvial (NSW) N61 GAB In-take Beds (NSW) **9.28 N83 Inverell Basalt (NSW) N85 New England Fold Belt (NSW) na Unincorporated areas <15 mg/l stock and domestic only na na na GAB Intake Beds (Qld) stock and domestic only na na Total *Current groundwater extraction for macro groundwater plan areas is based on metered and estimated data provided by NSW DWE. Data quality is variable depending on the location of bores and the frequency of meter reading. ** Determined from values supplied by NSW DWE from the Draft Water Sharing Plan for the Great Artesian Basin Groundwater sources 26. Future extraction will equal the Long-Term Average Extraction Limit. GL/y Groundwater extraction within the Border Rivers region is forecast to grow in the future. Estimates of the likely maximum extraction were provided for each GMU by New South Wales Department of Water and Energy for the New South Wales portion of the region. The rate of growth has not been determined but it is assumed here that full growth will be achieved by 23. Within New South Wales, the Likely Maximum Use is based on the historical development of irrigation, urban and stock and domestic water supply works. The estimated growth rate within a region is based-on the rate of historic growth. It is assumed that all new domestic and stock water supply works will be drilled and constructed on separate properties. An average size for each property was calculated. The total additional stock and domestic requirement was then calculated based on assumed usage rates for domestic bores of 2.25 ML/year and for stock bores of.88 ML/ha/year. 11 Water availability in the Border Rivers November 27 CSIRO 27

123 6.6.2 Estimates of rainfall recharge Rainfall recharge is the largest component of the water balance and is therefore the focus of this assessment. The following data were provided by New South Wales Department of Water and Energy. The effect of different stresses on various components of the hydrologic cycle was analysed using the recharge scaling factors (Section 6.4). The scaling factors were calculated from one-dimensional modelling to produce point estimates of root zone drainage from which scaling factors are calculated to transform recharge figures. Scaling factors for Scenario D are identical to Scenario C with the addition of groundwater management rules applied and future levels of development. Scenario D is designed to estimate the change in recharge assuming the 23 climate change scenario and to model the effects of changes in land and groundwater use. The results of applying the scaling factors are shown in Table 6-1. Table 6-1. Scaled recharge under scenarios A and C Code GMU Recharge* Scaled recharge GL/y A B Cdry Cmid Cwet N23 Miscellaneous Alluvium of the Barwon Region (NSW) N63 Great Artesian Basin Alluvial (NSW) N61 GAB Intake Beds (Qld) N83 Inverell Basalt (NSW) N85 New England Fold Belt (NSW) Total Groundwater assessment Percent change from Scenario A - 13% -3% -3% 32% *This represents only rainfall recharge in Macro Plan areas. The volume of recharge does not include recharge to national park areas, which has generally been allocated to environmental purposes and is not available for consumptive use The ratio of current (24/5) groundwater extraction to recharge is shown in Table The ratio of extraction over recharge can be used as an indicator of potential stress on the aquifer. Where E/R exceeds 1., groundwater is being extracted at a rate greater than the rate of recharge. New South Wales macro groundwater sharing plans allocate 3 percent to 5 percent of rainfall recharge to environmental purposes (E/R of.5.7). The overall trend in the data is that groundwater extraction is most highest in a relative sense in the Miscellaneous Alluvium of the Barwon Region GMU. In this GMU, extraction currently exceeds rainfall recharge and E/R is predicted to increase further because climate change is expected to reduce recharge. Some recharge from streams would be expected, thus extraction rates in excess of rainfall recharge might be able to be maintained. For the Miscellaneous Alluvium of the Barwon Region GMU, recharge is slightly lower under Scenario Cmid than in Cdry, thus the largest changes occur under Scenario Cmid. CSIRO 27 November 27 Water availability in the Border Rivers 111

124 Table Comparison of groundwater extraction with scaled rainfall recharge Code GMU Current extraction E/R Scaled E/R Future extraction Scaled E/R N23 N63 Miscellaneous Alluvium of the Barwon Region (NSW) Great Artesian Basin Alluvial (NSW) GL/y Ratio GL/y Ratio A B Cdry Cmid Cwet Ddry Dmid Dwet N61 GAB Intake Beds (Qld) N83 Inverell Basalt (NSW) N85 New England Fold Belt (NSW) Groundwater assessment The Inverell Basalt, GAB Alluvium and New England Fold Belt GMUs are predicted to experience significant growth in groundwater extraction (Scenario D). The predicted growth leads to an increase in the ratio of extraction to recharge. However, considering the relatively low current level of groundwater extraction, the increases are not considered significant and remain within the environmental guidelines outlined by the New South Wales Government. The GAB Water Sharing Plan for the Great Artesian Basin Groundwater Sources will significantly reduce licensed groundwater extraction from the Eastern Recharge Zone, which is the portion of the GAB outcropping within the region. These reductions will lower the ratio of extraction to rainfall recharge Impact of extraction from lower priority groundwater management units on streamflow The future impact of lower priority GMU extraction on streamflow is assumed to be the difference between the likely maximum use as defined in the macro groundwater plan and the current entitlement multiplied by a connectivity factor. Table 6-12 shows future groundwater use, connectivity factors and impacts of future groundwater use on streamflow. Table Estimation of the impacts of future groundwater extraction on streamflow outside of the Border Rivers Alluvium GMUs Code GMU Future changes in groundwater extraction Connectivity Future impact on streamflow GL/y GL/y N23 Miscellaneous Alluvium of Barwon Region (NSW) N63 GAB Alluvial (NSW) N83 Inverell Basalt (NSW) N85 New England Fold Belt (NSW) Total 3.41 These calculations assume that GAB pumping impacts streamflow in the region. However, it is assumed groundwater pumping into the future will not increase and that pumping has occurred at the current level for long enough to be included in the calibration of river models. The numerical groundwater model described earlier does not include cover the entire area of the Border Rivers Alluvium GMUs (Queensland and New South Wales) but groundwater extraction in the alluvium outside of the modelled area is minor. The calculations also assume there is no pumping in areas connected to streams in the unincorporated areas in Queensland. For the macro groundwater plan areas current use is estimated to be equivalent to the entitlement level. The effect of this assumption is to decrease estimated impacts. In this region, the resulting decrease in estimated impacts is considered to be less than 2 GL/year. The calculations use connectivity data supplied by State agencies and reported in MDBC (27). The effects of current use relative to calibration period for the river model are ignored (scenarios A and C), hence only Scenario D is relevant. Future extractions are the likely 112 Water availability in the Border Rivers November 27 CSIRO 27

125 maximum use without plan revision figures from the macro groundwater plan data supplied by New South Wales Department of Water and Energy. It is assumed that groundwater extracted does not return to aquifers (for example, via irrigation of crops), that the full impacts of extraction on streams will occur within 1 years, and that the impact of current extraction on streams has already occurred. The impacts of groundwater extraction on streamflow (Table 6-12) are distributed to the relevant surface water subcatchments or stretches of river. Streamflow losses of less than 2 GL/year in a subcatchment would be difficult to observe, and thus only in subcatchments where the estimated impact from groundwater extraction exceeds a 2 GL/year reduction in streamflow are considered further (including in river modelling, Chapter 4). This cut-off discounts about 12 GL/year of impacts, reducing the total estimated impact from about 3 GL/year (Table 6-12) to about 18 GL/year. The estimated losses in each subcatchment were used to modify daily flow duration curves (Figure 6-1), and thus modify the Scenario D inflows for the relevant subcatchments in the river model (Chapter 4). Figure 6-1 shows the flow duration curves for the Cmid, Dmid and Dmid modified scenarios. The Dmid scenario is the impact before groundwater extraction is included, while Dmid modified is that including extraction. The difference between Cmid and Dmid can be largely attributed to farm dams. Thus, the effect of groundwater extraction can be compared to that of farm dams by comparing the difference between Dmid and Cmid and Dmid-modified and Dmid respectively. Groundwater extraction leads to the percentage of low flows being decreased by 2 to 3 percent in the affected subcatchments, where as the impact of farm dams is spread more broadly across the flow regime. These reductions in base flow would make flow in these streams even more ephemeral, affecting near-river ecosystems and flow in the main channel. In addition to the adjustments in the river model to reflect the increased groundwater extraction in lower priority GMUs, adjustments were made in river reaches to reflect the impact of groundwater extraction in the modelled Border Rivers Alluvium GMUs. This leads to an increase in river leakage of 9.6 GL/year under Scenario A and 18.5 GL/year under Scenario Dmid. The former is referred to as a double accounting term as it represents the discrepancy between the surface water balance representation of the current river model and that which would be expected once the full impacts of current groundwater extraction are realised. These river impacts are described in Chapter 4. 6 Groundwater assessment CSIRO 27 November 27 Water availability in the Border Rivers 113

126 6 Groundwater assessment Figure 6-1. Daily flow duration curves for gauges (a) 4168, (b) 4161, (c) 41621, (d) and (e) The scenarios shown are Cmid (climate change impacts only), Dmid (climate change and future farm dam impacts) and Dmid-modified (climate change, future farm dams and future groundwater extraction impacts) 114 Water availability in the Border Rivers November 27 CSIRO 27

127 6.7 Conjunctive water use indicators It has been long recognised that groundwater can provide a more secure water source during drier periods. Where such exchanges are feasible, irrigators may elect to change from surface water to groundwater during years of low flow. Even without this, the lower surface water diversions in low flow years mean that groundwater forms a higher proportion of total diversions in those years. Table 6-13 shows these ratios for year of lowest flow up to a year with average flow. Under current conditions, groundwater extractions are 8 percent of total annual water use in the Border Rivers region on average, and as much as 26 percent in the extreme. Under the best estimate 23 climate the situation is similar. However, under the dry extreme 23 climate groundwater use would be as much as 39 percent of the total annual water use in the extreme, while under the wet extreme 233 climate groundwater use would never exceed 18 percent of the total annual water use. Under Scenario D, there is expected to be an almost five-fold expansion in groundwater extractions mainly for stock and domestic in the fractured rock areas. This leads to a decrease in river flows as described above, but the exchange is not one for one. Some of the water that is extracted would have otherwise been used for plant transpiration or would have perhaps moved to another groundwater system and this is expressed as a connectivity factor of less than one. Under Scenario D therefore, groundwater use would be 28 percent of the total annual water use on average, or 67 percent in the extreme. The most extreme case would occur under the dry extreme 23 climate Scenario D, for which in an extreme year, groundwater use would be 78 percent of the total annual water use in the region. These results show that groundwater forms a minor source of water for the region as a whole under average flow years but is important in drier years. Under the drier future conditions, this significance would increase considerably. Table Ratio of groundwater extraction to total water (surface and groundwater) under different scenarios and for low flow periods 6 Groundwater assessment A Cdry Cmid Cwet Dry Dmid Dwet Lowest 1-year period 26% 39% 28% 18% 78% 67% 52% Lowest 3-year period 17% 29% 16% 14% 67% 48% 43% Lowest 5-year period 13% 21% 13% 1% 58% 43% 36% Average 8% 9% 8% 7% 32% 28% 26% 6.8 Discussion of key findings Border Rivers Alluvium The groundwater modelling for the Border Rivers Alluvium GMUs shows that prior to groundwater development the adjacent stretch of the Dumaresq River was a gaining river. Prolonged extraction at 23/4 levels would lead to large reductions in groundwater levels, and if the system were to equilibrate to groundwater extraction at 23/4 levels the river would be a losing river. The total difference from pre-development to equilibrium conditions would be a streamflow reduction of 9.6 GL/year. About half of this difference is likely to be realised by 22. This change in surface-groundwater flux should be considered in future water resource planning. While there is year-to-year variability in rainfall recharge, averaged across ten years recharge does not change much. This indicates that the system is not episodically recharged. Future climate change impacts appear to be small for the Border Rivers Alluvium GMUs. The projected future levels of extraction (assuming the current spatial pattern of production bores) would not be sustainable in the long-term. It would lead to large reduction in groundwater levels that would be expected to trigger responses from irrigators and resource managers that would reduce the level of extraction in areas of falling watertables. If extraction continued at the projected future rates the aquifer would dewater. These increased rates of extraction could reduce streamflow by another 8.9 GL/year if the river-groundwater connection did not change. CSIRO 27 November 27 Water availability in the Border Rivers 115

128 The reductions in groundwater levels under Scenario D take the model outside its calibration range, meaning predictions are not reliable. In reality, these large drawdowns will not be realised. Local management rules would be activated, as these would most likely lead to decreases in allocation. The impacts of climate change are small compared to those of groundwater extraction. Even though the Dwet scenario leads to large increases in recharge, this is offset by reduced losses from the streams. This, together with the changes to the stream from gaining to losing, shows the importance of recent groundwater development. The connectivity as estimated by the model is ~.75.8; these values are generally larger than previous estimates. Connectivity is sensitive to the vertical hydraulic conductivity of the aquitard between the two aquifers. With large drawdowns, it is possible that the watertable will become disconnected and that further pumping will have less impact on losses from the river. However, the current model conceptualisation does not allow the watertable to become disconnected. 6 Groundwater assessment The model used is yet to be ratified for the purposes of water allocation. There are conceptual difficulties with the model and the results are sensitive to the assumed vertical conductivity of the aquitard between the aquifers. The model conceptualisation of the deeper aquifer is exaggerating the drawdown once piezometric levels fall below the top of the deeper aquifer. Extending the calibration period to include a longer period of groundwater extraction would improve the model. While the model has flaws, there is evidence of large drawdowns occurring, and this supports the model predictions of watertable responses under extraction Other stream impacts Most of the future development in the Border Rivers region is expected to occur away from the main aquifers. Under the New South Wales groundwater sharing plans, a maximum likely groundwater extraction without plan revision is defined. This limit may not be realised for a number of reasons, including groundwater quality, transmissivity, land suitability and pumping regulations. Scenario D is therefore not intended as a prediction of conditions that will eventuate, but as a scenario of consequences that might arise if no management changes were made. Consequently, results highlight pressure points in the system into the future. This assessment does not elaborate on what management actions might be taken to address any of these pressure points. The impact of projected groundwater extraction upon streams is estimated. While the figures used for extraction represent an upper limit, there are a number of offsetting factors, for example, no comparable development in the Queensland portion of the region is considered. Ignoring impacts of less than 2 GL/year in a subcatchment, has meant that at a catchment scale, 4 percent of the potential impact is not considered in the river modelling. Current impacts on streams assume that current use is equal to entitlements and that the full impacts of this are realised. Thus, while the projected development may represent an upper limit, the assessment of this impact on streamflow may well be an underestimate. The total impacts of extraction outside the Border Rivers Alluvium GMUs are estimated to be ~3 GL/year. While this estimate has a large uncertainty, it does show the importance of the development in these parts of the region. The local impact on stream flow can also be important with the number of zero flow days increasing by as much as 3 percent of the total time. The GAB Intake Beds are assigned a zero connectivity rate in New South Wales. This connectivity rate is assumed within the context of the very low recharge rates assigned to the in-take beds (about.5 percent of rainfall). The low recharge rates are derived within the context that "recharge is often rejected back to the surface for stream baseflow" (M. Williams, pers. comm.). The low connectivity may be thought to apply to the Intake Beds only after the recharge is rejected, as this is the more robust estimate of long-term recharge to the GAB confined aquifers. This makes sense when it is considered that the recharge rates referred to above were estimated for management of the regional confined GAB aquifers. These aquifers are not connected to the surface water systems of the MDB. Rejected recharge returns to streams as baseflow, indicating that there are small local groundwater flow systems operating at the top of the intake beds. These local systems are highly connected to the surface water system. If this connectivity is accepted, then any groundwater extraction in the intake beds that disrupts the water balance of the local flow systems will also have an influence on the volume of rejected recharge that is returned to the rivers and streams. That is, any storage deficit that occurs in the aquifer due to groundwater pumping, will draw on water that would have previously been reported as streamflow. It is also likely that the initial recharge rates to the intake beds is much higher than the quoted.5 percent rate allowing for the volume of recharge that is rejected. 116 Water availability in the Border Rivers November 27 CSIRO 27

129 6.8.3 Miscellaneous Alluvium of the Barwon Region The ratio of extraction to rainfall recharge (E/R) indicates that the Miscellaneous Alluvium of the Barwon Region GMUs is very highly developed under nearly all scenarios. It is likely that some recharge occurs directly from the stream. These smaller alluvia are flagged in a number of regions by high E/R values. While this does not mean that development is not sustainable, it does mean that development can only be sustained by other sources of water such as river water or lateral flow from an adjacent GMU. Further work would be required to assess the long-term implications of this extraction. 6.9 References Bouwer H and Maddock T (1997) Making sense of the interactions between groundwater and streamflow: lessons for water masters and adjudicators. Rivers 6(1), Chen D (23) Dumaresq River groundwater model: Border Rivers model development, calibration and use. Queensland Department of Natural Resources and Mines. 17pp. Hutchinson MF and Kesteven JL (1998) Monthly mean climate surfaces for Australia. Centre for Resource and Economic Studies, Australian National University. Unpublished. MDBC (27) Updated summary of estimated impact of groundwater extraction on stream flow in the Murray Darling Basin. Draft Report. Prepared by REM on behalf of MDBC, Canberra. Zhang L and Dawes WE (1998) WAVES An integrated energy and water balance model.csiro Land and Water Technical Report No 31/98. 6 Groundwater assessment CSIRO 27 November 27 Water availability in the Border Rivers 117

130 7 Environment This chapter presents the environmental assessments undertaken for the Border Rivers region. It has four sections: a summary an overview of the approach a presentation and description of results a discussion of key findings. 7.1 Summary 7 Environment Issues and observations Assessment of the environmental implications of changes in water availability is largely beyond the terms of reference of this project (see Chapter 1). The exception is reporting against environmental water allocations or environmental flow rules specified in water sharing plans which can be evaluated against quantifiable ecological responses. Otherwise, environmental assessments form a very small part of the project. The Border Rivers region provides a wide range of aquatic habitats and is ecologically important. The floodplain between Goondiwindi and Mungindi contains large areas of anabranches and billabongs. When flooded these areas are known to provide large amounts of dissolved organic carbon to the riverine ecosystem which is essential to aquatic ecosystem functioning. The environmental assessments undertaken within this project for the Border Rivers region are limited to a partial analysis of potential changes in the hydrologic regime affecting the anabranches and billabongs associated with the Macintyre River. Further contextual information on river-related environmental assets and values, including the important Morella Watercourse/Boobera Lagoon/Pungbougal Lagoon complex, is provided in Chapter Key messages Water resource development has decreased the average frequency of flows that connect the anabranches and billabongs of the Macintyre River floodplain by about 16 percent and has reduced the volume of individual events by about 8 percent on average. These changes are likely to have caused changes in the ecosystems associated with these river features. The best estimate 23 climate scenario would see the average period between inundation events increase by a further 24 percent to be 5 percent greater than pre-development. Further small reductions in the average volumes of individual events would also occur. The dry extreme 23 climate scenario would lead to major additional increases in the period between events and major additional reductions in the average volume of individual events. The wet extreme 23 climate scenario would return the average period and event volumes back close to the pre-development values. The hydrologic changes under best estimate and the dry extreme 23 climate scenario would be likely to affect instream processes due to changes in the availability of dissolved organic carbon, and this in turn would be likely to affect fish and other aquatic animals. Future development of farm dams and increased groundwater extraction would not have much additional affect on the hydrology of these high flows to the anabranches and billabongs of the Macintyre River. 118 Water availability in the Border Rivers November 27 CSIRO 27

131 7.1.3 Uncertainty The main uncertainties involving analysis and reporting include: aquatic and wetland ecosystems are highly complex and many factors in addition to water regime can affect ecological features and processes, such as water quality and land use practices the indicators are based on limited hydrology parameters with no direct quantitative relationships for environmental responses. This study only makes general observations on the potential implications of changed water regimes and some related ecological responses using one generic asset and two indicators to represent overall aquatic ecosystem outcomes is a major simplification. Actual effects on these and other assets or localities are likely to vary uncertainties expressed in chapters 3, 4 and 5 affect the hydrologic information used in the environmental assessments. 7.2 Approach Chapter 2 provides a broader description of the catchment, water resources and important environmental assets. This Chapter focuses on the specific rules which apply to the provision of environmental water in the region and on the assessment of hydrologic indicators defined by prior studies for key environmental assets in the region. 7 Environment Summary of environmental flow rules Queensland Water Resource Plans do not establish specific environmental water allocations; rather environmental water is protected via water access rules such as pumping thresholds. The Water Resource (Border Rivers) Plan 23 (QDNR, 23) establishes the following performance indicators for environmental flow objectives: end-of-system flow, low flow, summer flow, beneficial flooding flow and one in 2-year flood. There is no equivalent Water Sharing Plan for the New South Wales portion of the Border Rivers and no environmental flow provisions are established formally at this time. However, since its enlargement, environmental releases are provided from Pindari Dam. A draft Water Sharing Plan was released in August 27 by the New South Wales Department of Water and Energy for public consultation (DWE, 27). The draft plan proposes environmental flows for the Severn River (NSW) via releases from Pindari Dam to its junction with the Dumaresq River and via restrictions to extractions to supplementary flows. The latter apply to the Severn River (NSW) and the remainder of the New South Wales portion of the Border Rivers. The proposed Pindari Dam rules are: continuous low flows of 1 ML/day translucent releases of 5 ML/day during September to May and 2 ML/day during June to August. Translucent releases are the immediate release of specified inflows to the dam (DWE, 27) a stimulus flow of up to 4 ML total to be released over a seven-day period from 1 st September if an inflow of up to 12 ML/day has occurred during the months April to August. The stimulus flow is intended to provide a river flow that better reflects the natural hydrograph; in additional translucent releases the anticipated benefits of the stimulus flow are (i) provision of cues for fish breeding; and (ii) wetting of riparian areas downstream of Pindari Dam (DWE, 27). The current environmental flow rules at Pindari Dam (N. Foster, pers. comm.) are similar; the main proposed change is an increase in the magnitude of the stimulus flow. The proposed supplementary extraction rules have commence-to-pump and cease-to-pump thresholds for different river reaches. For the reach of the Macintyre River downstream of the Dumaresq River junction, the proposed supplementary extraction rules can be summarised as follows: a trigger flow of greater than 5 ML/day at Holdfast 25 percent of the trigger flow volume is reserved for the environment and the remainder shared equally between New South Wales and Queensland. CSIRO 27 November 27 Water availability in the Border Rivers 119

132 The initial New South Wales share of supplementary flows under the draft Plan is 12, ML per year. The end-of-system flow performance indicators of the Queensland Water Resource Plan are reported in Chapter 4. No published studies were available for low flow or summer flow indicators related to ecological condition. The hydrological indicator defined below provides an assessment of the Queensland beneficial flooding flow and the proposed supplementary water not subject to extraction under the draft New South Wales Border Rivers Water Sharing Plan (DWE, 27) Environmental assets and indicators 7 Environment The Border Rivers system provides a wide range of aquatic habitats and is ecologically important. The floodplain between Goondiwindi and Mungindi contains large areas of anabranches and billabongs. When flooded these areas are known to provide large amounts of dissolved organic carbon to the riverine ecosystem which is essential to aquatic ecosystem functioning. The Morella Watercourse/Boobera Lagoon/Pungbougal Lagoon complex is a wetland of national importance (Environment Australia, 21) and is located on this floodplain. Figure 7-1. Satellite image (22) indicating (within yellow polygons) the anabranches of the lower river floodplain of the Macintyre and Barwon rivers from Goondiwindi to Mungindi. Bright green areas indicate irrigated land. DWE (27) identifies the Morella Watercourse/Boobera Lagoon area as receiving beneficial flooding at much higher flow levels. However, the flooding threshold is ill-defined (between 25, ML/day to 8, ML/day at Goondiwindi) and hence hydrologic assessments are not made for this asset. Reliable information on ecologically relevant hydrologic indicators is however, available for the anabranches and billabongs along the Macintyre River. Thoms et al. (25) provide an analysis of commence-to-fill and connectivity of anabranches and billabongs for a study site of limited area on the Macintyre River floodplain. Inundation and connectivity of these anabranches is considered to be important for the provision of dissolved organic carbon to aquatic systems (Thoms et al., 25). Dissolved organic carbon and other nutrients released on the floodplain by inundation are subsequently carried to the river channel and provide an important energy source for riverine organisms; this is an essential part of floodplain-river ecosystem functioning (Thoms et al., 25). A follow-up study (Reid, 26; M. Reid, pers. comm.) examined the same relationships for the entirety of the floodplain between Goondiwindi and Mungindi and found that 9 percent (or 45 km) of the anabranch and billabong systems are hydrologically connected when Macintyre River flows exceed 2, ML/day at Goondiwindi. This threshold flow of 2, ML/day at Goondiwindi is therefore used in assessments for the Border Rivers lower river floodplain system (Table 7-1). 12 Water availability in the Border Rivers November 27 CSIRO 27

133 Table 7-1. Definitions of environmental indicators Indicator Name Average period between flow events Maximum period between flow events Average flow event volume per year Average flow event volume per event Description Average period between flows in excess of 2, ML/day at Goondiwindi gauge Maximum period between flows in excess of 2, ML/day at Goondiwindi gauge Average annual volume above 2, ML/day at Goondiwindi gauge Average event volume above 2, ML/day at Goondiwindi gauge 7.3 Results The projected changes in the average and maximum period and volumes for the various scenarios, including predevelopment Scenario P, are listed in Table 7-2. These were assessed using scenario outputs for the Goondiwindi gauge from the Border Rivers river system model (Chapter 4). Table 7-2. Environmental indicator values under scenarios P and A, and percentage changes (from Scenario A) in environmental indicators under scenarios C and D Indicators P A Cdry Cmid Cwet Ddry Dmid Dwet months percent change from Scenario A Average period between flow events % 26% -11% 43% 27% -9% Maximum period between flow events % 12% % 27% 12% % GL Average flow event volume per year % -22% 32% -45% -23% 3% Average flow event volume per event % -3% 17% -21% -4% 18% 7 Environment 7.4 Discussion of key findings Events of 2, ML/day occur about twice per year on average under the pre-development scenario. Water resource development has increased the average period by one month or about 16 percent. This translates to an 18 percent reduction in the average frequency of events which is slightly greater than the changes in frequency of inundation of 12 percent to 17 percent between natural and current for a range of Macintyre River anabranch channels in commence-to-flow groups from 2 ML/day to over 56, ML/day reported by Thoms et al. (25). The maximum period between events is not affected by water resource development. The volume of water in these events reduced by about 8 percent, and as these events are now less frequent, their total annual average volume is reduced by 25 percent. The best estimate 23 climate scenario would see the average period between events increase by a further 26 percent, such that the average period would be 5 percent longer than for the pre-development scenario. The maximum period between events would increase by 12 percent. Also the average annual volume of events would reduce by 22 percent mainly due to less events per year. The dry extreme 23 climate scenario would lead to major additional increases in the periods between events and major reductions in the total volumes. The wet extreme 23 climate scenario would return the average period and volumes of 2, ML/day events closer to pre-development values. Anywhere between the best estimate and the dry extreme 23 climate scenario would lead to extended periods without hydrologic connectivity between the lower Macintyre River and its floodplain, and with smaller volumes of water. This would be likely to affect instream processes due to changes in the availability of dissolved organic carbon. Similar to the findings of Thoms et al. (25) for pre-development to current conditions, these changes would be expected to affect food webs for fish and other aquatic animals. Riparian vegetation species composition is unlikely to be greatly affected but its condition is likely to deteriorate over time. CSIRO 27 November 27 Water availability in the Border Rivers 121

134 Future development, as assessed, would have only very minor additional affect on the average period between events and on flow event volumes. 7.5 References DWE (27) Draft Water Sharing Plan. NSW Border Rivers Regulated Water Source Guide August 27. NSW Department of Water and Energy. Environment Australia (21) A Directory of Important Wetlands in Australia. Third Edition. Environment Australia, Canberra. QDNR (23) Queensland Water Resource (Border Rivers) Plan, 23. Brisbane. Reid M (26) The importance of connectivity between patches in riverine landscapes: an example from the lower Macintyre River, Murray-Darling Basin. Oral presentation 45 th Australian Society of Limnology Congress, September 26. Albury-Wodonga. Thoms MC, Southwell M and McGinness HM (25) Floodplain-river ecosystems: Fragmentation and water resources development. Geomorphology 71, Environment 122 Water availability in the Border Rivers November 27 CSIRO 27

135 Appendix A Rainfall-runoff results for all subcatchments Table A-1. Summary of modelling results for all subcatchments under scenarios A and C Scenario A Scenario Cdry Scenario Cmid Scenario Cwet Modelling catchment Area Rainfall APET Runoff Runoff coefficient Runoff contribution Rainfall Runoff Rainfall Runoff Rainfall Runoff km 2 mm percent percent change from Scenario A % 2% -1% -29% 1% -4% 9% 22% % % -1% -28% % -5% 9% 2% % % -1% -27% % -6% 9% 19% % % -1% -27% % -6% 9% 19% % % -1% -26% % -6% 9% 19% % 3% -9% -26% -6% -22% 1% 3% % 1% -1% -26% % -4% 9% 2% % 2% -1% -27% % -9% 9% 18% % 1% -1% -27% % -8% 9% 18% % 4% -1% -28% % -1% 9% 19% % 8% -1% -28% % -7% 12% 33% % % -1% -27% % -1% 9% 17% % % -1% -27% % -9% 9% 17% % 2% -1% -28% % -7% 9% 18% % 1% -1% -27% % -7% 9% 18% % % -1% -27% % -6% 9% 16% % 2% -1% -27% % -6% 9% 18% % % -1% -26% % -5% 9% 19% % 1% -1% -26% % -6% 9% 2% % 4% -1% -26% % -5% 11% 28% % 1% -1% -27% % -1% 9% 17% % % -1% -29% 1% -4% 9% 21% % 1% -1% -29% % -5% 9% 21% % % -1% -3% 1% -4% 9% 23% % 2% -1% -29% % -7% 9% 21% % % -1% -3% 1% -4% 9% 23% % 1% -1% -28% % -1% 9% 21% % 8% -9% -26% -5% -2% 3% 4% % 2% -1% -28% % -8% 9% 21% % 1% -1% -27% % -6% 9% 18% % 2% -1% -28% % -6% 9% 19% % 9% -1% -29% -1% -12% 11% 3% % 2% -1% -29% % -7% 9% 21% % 1% -1% -29% % -6% 9% 22% % 1% -1% -28% % -6% 9% 19% % 1% -1% -28% % -5% 9% 19% Appendix A Rainfall-runoff results for all subcatchments CSIRO 27 November 27 Water availability in the Border Rivers 123

136 Scenario A Scenario Cdry Scenario Cmid Scenario Cwet Appendix A Rainfall-runoff results for all subcatchments Modelling catchment Area Rainfall APET Runoff Runoff coefficient Runoff contribution Rainfall Runoff Rainfall Runoff Rainfall Runoff km 2 mm percent percent change from Scenario A % 3% -1% -29% % -7% 9% 22% % 1% -1% -28% % -6% 9% 21% % 3% -1% -27% % -5% 9% 19% % 2% -1% -26% 1% -5% 9% 19% % 3% -1% -27% -2% -12% 9% 19% % 2% -1% -26% -2% -1% 9% 2% % 2% -1% -27% -4% -14% 9% 2% % 1% -1% -27% % -5% 9% 19% % 5% -1% -28% -4% -17% 4% 8% % 1% -1% -28% % -6% 9% 19% % 4% -1% -27% % -6% 9% 18% % 1% -1% -26% % -3% 9% 2% % 1% -1% -26% % -5% 9% 18% % 2% -1% -27% % -4% 9% 19% % 1% -1% -26% % -4% 9% 19% % 1% -1% -27% % -5% 9% 19% % 1% -1% -27% % -5% 9% 2% % 1% -1% -28% -1% -9% 9% 2% Modelling catchment Table A-2. Summary of modelling results for all subcatchments under scenarios A and D A runoff Plantations increase Farm dam increase Ddry runoff Dmid runoff Dwet runoff mm ha ML ML/km 2 percent change from Scenario A % -4% 21% % -6% 2% % -7% 17% % -6% 19% % -7% 17% % -23% 2% % -5% 19% % -1% 17% % -8% 18% % -11% 18% % -8% 32% % -11% 16% % -9% 17% % -8% 17% % -8% 16% % -7% 15% % -7% 17% % 5% 18% % -8% 18% 124 Water availability in the Border Rivers November 27 CSIRO 27

137 Modelling catchment A runoff Plantations increase Farm dam increase Ddry runoff Dmid runoff Dwet runoff mm ha ML ML/km 2 percent change from Scenario A % -6% 27% % -11% 17% % -7% 18% % -7% 19% % -6% 21% % -9% 18% % -6% 21% % -1% 2% % -21% 4% % -1% 19% % -7% 17% % -8% 17% % -14% 28% % -9% 18% % -6% 21% % -7% 17% % -5% 19% % -7% 21% % -6% 2% % -6% 19% % -5% 19% % -12% 19% % -1% 19% % -14% 2% % -5% 19% % -18% 7% % -6% 19% % -7% 17% % -3% 2% % -5% 18% % -4% 19% % -4% 19% % -5% 19% % -5% 2% % -1% 19% Appendix A Rainfall-runoff results for all subcatchments CSIRO 27 November 27 Water availability in the Border Rivers 125

138 Appendix B River water modelling reach mass balances Subcatchment Appendix B River water modelling reach mass balances River system model average annual water balance Storage volume A Cwet Cmid Cdry Dwet Dmid Ddry Initial storage Final storage Average annual change Inflows Directly gauged Indirectly gauged Groundwater gains Sub-total Outflows End-of-system outflow Net evaporation River unattributed losses Sub-total Unattributed fluxes Total Mass balance error (%) Subcatchment River system model average annual water balance Inflows GL/y A Cwet Cmid Cdry Dwet Dmid Ddry Directly gauged Indirectly gauged Sub-total Outflows End-of-system outflow Groundwater losses River unattributed losses Sub-total Unattributed fluxes Total Mass balance error (%) GL/y 126 Water availability in the Border Rivers November 27 CSIRO 27

139 Subcatchment River system model average annual water balance Inflows A Cwet Cmid Cdry Dwet Dmid Ddry Directly gauged Indirectly gauged Sub-total Diversions NSW usage General security - on allocation General security - off allocation QLD usage Medium security - on allocation Medium security - off allocation Sub-total Outflows End-of-system outflow River unattributed losses Sub-total Unattributed fluxes Total Mass balance error (%) Subcatchment River system model average annual water balance Inflows GL/y A Cwet Cmid Cdry Dwet Dmid Ddry Directly gauged Indirectly gauged Sub-total Diversions NSW usage General security - on allocation General security - off allocation QLD usage Medium security - on allocation Medium security - off allocation High security - town water supply Sub-total Outflows End-of-system outflow Groundwater losses River unattributed losses Sub-total Unattributed fluxes Total Mass balance error (%) GL/y Appendix B River water modelling reach mass balances CSIRO 27 November 27 Water availability in the Border Rivers 127

140 Subcatchment Appendix B River water modelling reach mass balances River system model average annual water balance Storage volume A Cwet Cmid Cdry Dwet Dmid Ddry Initial storage Final storage Average annual change Inflows Directly gauged Indirectly gauged Sub-total Diversions NSW usage General security - on allocation General security - off allocation Floodplain havesting Unregulated QLD usage Medium security - on allocation Medium security - off allocation Unsupplemented access High security - town water supply Sub-total Outflows End-of-system outflow Net evaporation Effluent losses Groundwater losses River unattributed losses Sub-total Unattributed fluxes Total Mass balance error (%) Subcatchment GL/y River system model average annual water balance Storage volume A Cwet Cmid Cdry Dwet Dmid Ddry Initial storage Final storage Average annual change Inflows Directly gauged Indirectly gauged Sub-total Outflows End-of-system outflow Net evaporation River unattributed losses Sub-total Unattributed fluxes Total Mass balance error (%) GL/y 128 Water availability in the Border Rivers November 27 CSIRO 27

141 Subcatchment River system model average annual water balance Inflows A Cwet Cmid Cdry Dwet Dmid Ddry Directly gauged Indirectly gauged Sub-total Diversions NSW usage High security - town water supply Sub-total Outflows End-of-system outflow River unattributed losses Sub-total Unattributed fluxes Total Mass balance error (%) Subcatchment River system model average annual water balance Inflows GL/y A Cwet Cmid Cdry Dwet Dmid Ddry Directly gauged Indirectly gauged Sub-total Diversions NSW usage General security - on allocation General security - off allocation Sub-total Outflows End-of-system outflow River unattributed losses Sub-total Unattributed fluxes Total Mass balance error (%) GL/y Appendix B River water modelling reach mass balances CSIRO 27 November 27 Water availability in the Border Rivers 129

142 Subcatchment Appendix B River water modelling reach mass balances River system model average annual water balance Inflows A Cwet Cmid Cdry Dwet Dmid Ddry Directly gauged Indirectly gauged Sub-total Outflows End-of-system outflow River unattributed losses Sub-total Unattributed fluxes Total Mass balance error (%) Subcatchment River system model average annual water balance Inflows GL/y A Cwet Cmid Cdry Dwet Dmid Ddry Directly gauged Indirectly gauged Sub-total Diversions NSW usage General security - on allocation General security - off allocation Sub-total Outflows End-of-system outflow River unattributed losses Sub-total Unattributed fluxes Total Mass balance error (%) GL/y 13 Water availability in the Border Rivers November 27 CSIRO 27

143 Subcatchment River system model average annual water balance Inflows A Cwet Cmid Cdry Dwet Dmid Ddry Directly gauged Indirectly gauged Sub-total Diversions NSW usage General security - on allocation General security - off allocation Unregulated High security - town water supply QLD usage Medium security - on allocation Medium security - off allocation Unsupplemented access High security - town water supply Sub-total Outflows End-of-system outflow Net evaporation Effluent losses River unattributed losses Sub-total Unattributed fluxes Total Mass balance error (%) GL/y Appendix B River water modelling reach mass balances CSIRO 27 November 27 Water availability in the Border Rivers 131

144 Subcatchment Appendix B River water modelling reach mass balances River system model average annual water balance Inflows A Cwet Cmid Cdry Dwet Dmid Ddry Directly gauged Indirectly gauged Sub-total Diversions NSW usage General security - on allocation General security - off allocation Unregulated QLD usage Medium security - on allocation Medium security - off allocation Unsupplemented access Sub-total Outflows End-of-system outflow Net evaporation Effluent losses River unattributed losses Sub-total Unattributed fluxes Total Mass balance error (%) Subcatchment River system model average annual water balance Storage volume GL/y A Cwet Cmid Cdry Dwet Dmid Ddry Initial storage Final storage Average annual change Inflows Indirectly gauged Sub-total Diversions QLD usage Unsupplemented access Sub-total Outflows End-of-system outflow Net evaporation Effluent losses River unattributed losses Sub-total Unattributed fluxes Total Mass balance error (%) GL/y 132 Water availability in the Border Rivers November 27 CSIRO 27

145 Subcatchment River system model average annual water balance Inflows A Cwet Cmid Cdry Dwet Dmid Ddry Directly gauged Indirectly gauged Sub-total Diversions NSW usage General security - on allocation General security - off allocation Unregulated High security - town water supply QLD usage Medium security - on allocation Medium security - off allocation Unsupplemented access Sub-total Outflows End-of-system outflow Effluent losses River unattributed losses Sub-total Unattributed fluxes Total Mass balance error (%) Subcatchment River system model average annual water balance Inflows GL/y A Cwet Cmid Cdry Dwet Dmid Ddry Indirectly gauged Sub-total Diversions QLD usage Unsupplemented access Sub-total Outflows End-of-system outflow Sub-total Unattributed fluxes Total Mass balance error (%) GL/y Appendix B River water modelling reach mass balances CSIRO 27 November 27 Water availability in the Border Rivers 133

146 Subcatchment Appendix B River water modelling reach mass balances River system model average annual water balance Inflows A Cwet Cmid Cdry Dwet Dmid Ddry Directly gauged Indirectly gauged Sub-total Outflows End-of-system outflow River unattributed losses Sub-total Unattributed fluxes Total Mass balance error (%) Subcatchment River system model average annual water balance Storage volume GL/y A Cwet Cmid Cdry Dwet Dmid Ddry Initial storage Final storage Average annual change Inflows Directly gauged Indirectly gauged Sub-total Diversions QLD usage Medium security - on allocation High security - town water supply Sub-total Outflows End-of-system outflow Net evaporation River unattributed losses Sub-total Unattributed fluxes Total Mass balance error (%) GL/y 134 Water availability in the Border Rivers November 27 CSIRO 27

147 Subcatchment River system model average annual water balance Storage volume A Cwet Cmid Cdry Dwet Dmid Ddry Initial storage Final storage Average annual change Inflows Directly gauged Indirectly gauged Groundwater gains Sub-total Diversions QLD usage Medium security - on allocation High security - town water supply Sub-total Outflows End-of-system outflow Net evaporation River unattributed losses Sub-total Unattributed fluxes Total Mass balance error (%) Subcatchment River system model average annual water balance Storage volume GL/y A Cwet Cmid Cdry Dwet Dmid Ddry Initial storage Final storage Average annual change Inflows Directly gauged Indirectly gauged Groundwater gains Sub-total Diversions QLD usage Medium security - on allocation Sub-total Outflows End-of-system outflow Net evaporation River unattributed losses Sub-total Unattributed fluxes Total Mass balance error (%) GL/y Appendix B River water modelling reach mass balances CSIRO 27 November 27 Water availability in the Border Rivers 135

148 Appendix C River system model uncertainty assessment by reach This Appendix contains the results of river reach water accounting for this region, as well as an assessment of the magnitude of the project change under each scenario compared to the uncertainty associated with the river model. Each page provides information for a river reach that is bounded by a gauging station on the upstream and downstream side, and for which modelling results are available. Table C-1 provides a brief explanation for each component of the results page. Appendix C River system model uncertainty assessment by reach Table Land use Gauging data Correlation with ungauged gains/losses Water balance Description Table C-1. Explanation of components of the uncertainty assessments Information on the extent of dryland, irrigation and wetland areas. Land use areas are based on remote sensing classification involving BRS land use mapping, water resources infrastructure and remote sensing-based estimates of actual evapotranspiration. Information on how well the river reach water balance is measured or, where not measured, can be inferred from observations and modelling. The volumes of water measured at gauging stations and off-takes is compared to the grand totals of all inflows or gains, and/or all outflows or losses, respectively. The fraction of total refers to calculations performed on average annual flow components over the period of analysis. The fraction of variance refers to the fraction of month-tomonth variation that is measured. Also listed are the same calculations but for the sum of gauged terms plus water balance terms that could be attributed to the components listed in the Water balance table with some degree of confidence. The same terms are also summed to water years and shown in the diagram next to this table. Information on the likely nature of ungauged components of the reach water balance. Listed are the coefficients of correlation between ungauged apparent monthly gains or losses on one hand, and measured components of the water balance on the other hand. Both the normal (parametric) and the ranked (or non-parametric) coefficient of correlation are provided. High coefficients are highlighted. Positive correlations imply that the apparent gain or loss is large when the measured water balance component is large, whereas negative correlation implies that the apparent gain or loss is largest when the measured water balance component is small. In the diagram below this table, the monthly flows measured at the gauge at the end of the reach are compared with the flows predicted by the baseline river model, and the outflows that could be accounted for (i.e., the net result of all measured or estimated water balance components other than main stem outflow which ideally should equal main stem outflows in order to achieve mass balance) Information on how well the modelled and the best estimate river reach water balances agree, and what the nature of any unspecified losses in the river model is likely to be. The river reach water balance terms are provided as modelled by the baseline river model (scenario A) over the period of water accounting. The accounted terms are based on gauging data, diversion records, and (adjusted) estimates derived from SIMHYD rainfall-runoff modelling, remote sensing of water use and simulation of temporary storage effects. Neither should be considered as absolutely correct, but large divergences point to large uncertainty in river modelling. Model efficiency Information on the performance of the river model in explaining historic flow patterns at the reach downstream gauge, and the scope to improve on this performance. All indicators are based on the Nash-Sutcliffe model efficiency (NSME) indicator. In addition to the conventional NSME calculated for monthly and annual outflows, it has also been calculated after log-transformation or ranking of the original data, as well as having been calculated for the 1% of months with highest and lowest observed flows, respectively. Using the same formulas, the model efficiency of the water accounts in explaining observed outflows is calculated. This provides an indication of the scope for improving the model to explain more of the observed flow patterns: if NSME is much higher for the water accounts than for the model, than this suggests that the model can be improved upon and model uncertainty reduced. Conversely, if both are of similar magnitude, then it is less likely that a better model can be derived without additional observation infrastructure. 136 Water availability in the Border Rivers November 27 CSIRO 27

149 Table Changeuncertainty ratios Description Information on the significance of the projected changes under different scenarios, considering the performance of the river model in explaining observed flow patterns at the end of the reach. In this table, the projected change is compared to the river model uncertainty by testing the hypothesis that the scenario model is about as good or better in explaining observed historic flows than the baseline model. The metric to test this hypothesis is the change-uncertainty ratio, which is calculated as the ratio of Nash-Sutcliffe Model Efficiency indicators for the scenario model and for the baseline (scenario A) model, respectively. A value of around one or less suggests that is likely that the projected scenario change is not significant when compared to river model uncertainty. Conversely, a ratio that is considerably greater than one implies that the scenario model is much worse in reproducing historic observations than the baseline model, which provides greater confidence that the scenario indeed leads to a significant change in flow patterns. The change-uncertainty ratio is calculated for monthly as well as annual values, to account for the possibility that the baseline model may reproduce annual patterns well but not monthly. Below this table on the left, the same information is provided in a diagram. Below the table on the right, the observed annual flows at the end of the reach is compared to those simulated by the baseline model and in the various scenarios. To the right of this table, the flow-duration curves are shown for all scenarios. Appendix C River system model uncertainty assessment by reach CSIRO 27 November 27 Water availability in the Border Rivers 137

150 Downstream gauge Dumaresq Roseneath Reach 1 Upstream gauge 4163 Tenterfield Clifton Reach length (km) 48 Area (km 2 ) 842 Outflow/inflow ratio 9.9 Net gaining reach Land use ha % Dryland 83,78 1 Irrigable area - - Open water* - - River and wetlands 41 Open water* - - * averages for This is a strongly gaining reach. Flows are dominated by runoff immediately following rain. Most of the inflows are gauged. Estimated local runoff explains most of the ungauged gains but a small adjustment was required. There are few recorded diversions and ungauged losses are small. Baseline model performance is good Accounting explains observed flows very well. The projected changes are generally similar to river model uncertainty, except for the Cwet and Dwet scenario where changes are greater than model uncertainty. Appendix C River system model uncertainty assessment by reach Gauging data Inflows Outflows Overall and gains and losses Fraction of total Gauged Attributed Fraction of variance Gauged Attributed Correlation with ungauged Gains Losses Linear adjustment normal ranked normal ranked Main gauge inflows Tributary inflows Main gauge outflows Distributary outflows Recorded diversions Estimated local runoff Adjusted -4.6% Monthly streamflow (GL/mo) gauged accounted model.1 Jan-9 Jan-91 Jan-92 Jan-93 Jan-94 Jan-95 Jan-96 Jan-97 Jan-98 Jan-99 Jan- Jan-1 Jan-2 Jan-3 Jan-4 Jan-5 Water balance Model (A) Accounts Difference Model efficiency Model (A) Accounts Jul 199 Jun 26 Monthly Gains GL/y GL/y GL/y Normal Main stem inflows Log-normalised.78 - Tributary inflows Ranked Local inflows Low flows only < < Unattributed gains and noise High flows only Losses GL/y GL/y GL/y Annual Main stem outflows Normal Distributary outflows Log-normalised - - Net diversions Ranked River flux to groundwater - River and floodplain losses Definitions: Unspecified losses low flows (flows<1% percentile ) :.9 GL/mo Unattributed losses and noise high flows (flows>9% percentile) : 46.3 GL/mo... Change-uncertainty ratios P B Cwet Cmid Cdry Dwet Dmid Ddry Annual streamflow Monthly streamflow Reach gains and losses (GL/y) /91 91/92 92/93 93/94 94/95 Monthly streamflow (GL/mo). 95/ /97 97/98 98/99 99/ /1 1/2 2/ /4 4/5 5/6 Pecentage of months flow is exceeded unattributed gains ungauged gains gauged gains unattributed losses ungauged losses gauged losses 1 9 gauged Monthly Change-Uncertainty Ratio C D + wet O mid dry Annual streamflow (GL/y) A Cwet Cmid Cdry Dwet Dmid Ddry.1 Annual Change-Uncertainty Ratio 9/91 91/92 92/93 93/94 94/95 95/96 96/97 97/98 98/99 99/ /1 1/2 2/3 3/4 4/5 5/6 138 Water availability in the Border Rivers November 27 CSIRO 27

151 Downstream gauge 4167 Dumaresq Bonshaw Weir Reach 2 Upstream gauge Dumaresq Roseneath Reach length (km) 44 Area (km 2 ) 757 Outflow/inflow ratio 1.23 Net gaining reach Land use ha % Dryland 75,67 1 Irrigable area - - Open water* - - River and wetlands - - Open water* - - * averages for This is a gaining reach. Flows are dominated by inflows from upstream. Most of the inflows are gauged. Estimated local runoff explains most of the ungauged gains. There are few recorded diversions and ungauged losses are small. Baseline model performance is very good Accounting explains observed flows very well. The projected changes are similar to river model uncertainty for the C mid and Dmid scenarios, and greater than uncertainty for the dry and wet scenarios. Gauging data Inflows Outflows Overall and gains and losses Fraction of total Gauged Attributed Fraction of variance Gauged Attributed Correlation with ungauged Gains Losses Linear adjustment normal ranked normal ranked Main gauge inflows Tributary inflows Main gauge outflows Distributary outflows Recorded diversions Estimated local runoff Monthly streamflow (GL/mo) gauged accounted model.1 Jan-9 Jan-91 Jan-92 Jan-93 Jan-94 Jan-95 Jan-96 Jan-97 Jan-98 Jan-99 Jan- Jan-1 Jan-2 Jan-3 Jan-4 Jan-5 Water balance Model (A) Accounts Difference Model efficiency Model (A) Accounts Jul 199 Jun 26 Monthly Gains GL/y GL/y GL/y Normal Main stem inflows Log-normalised.79 - Tributary inflows 5-5 Ranked.8.95 Local inflows Low flows only < < Unattributed gains and noise High flows only Losses GL/y GL/y GL/y Annual Main stem outflows Normal Distributary outflows Log-normalised - - Net diversions Ranked River flux to groundwater - River and floodplain losses 2-2 Definitions: Unspecified losses low flows (flows<1% percentile ) : 1.1 GL/mo Unattributed losses and noise high flows (flows>9% percentile) : 59.9 GL/mo Change-uncertainty ratios P B Cwet Cmid Cdry Dwet Dmid Ddry Annual streamflow Monthly streamflow Reach gains and losses (GL/y) /91 91/92 92/93 93/94 94/95 Monthly streamflow (GL/mo). 95/ /97 97/98 98/99 99/ /1 1/2 2/ /4 4/5 5/6 Pecentage of months flow is exceeded unattributed gains ungauged gains gauged gains unattributed losses ungauged losses gauged losses Appendix C River system model uncertainty assessment by reach 1 12 gauged Monthly Change-Uncertainty Ratio P C D + wet O mid dry Annual Change-Uncertainty Ratio Annual streamflow (GL/y) /91 91/92 92/93 93/94 94/95 95/96 96/97 97/98 98/99 99/ /1 1/2 2/3 3/4 4/5 5/6 A P Cwet Cmid Cdry Dwet Dmid Ddry CSIRO 27 November 27 Water availability in the Border Rivers 139

152 Downstream gauge Severn D/S Pindari Reach 3 Upstream gauge Severn Strathbogie Reach length (km) 35 Area (km 2 ) 375 Outflow/inflow ratio 1.19 Net gaining reach Land use ha % Dryland 36,28 97 Irrigable area - - Open water* - - River and wetlands 1,18 3 Open water* - - * averages for This is a gaining reach. Inflows are dominated by runoff and releases from Pindari dam. Outflows are dominated by releases from Copeton Dam Most of the inflows are gauged. Estimated local runoff explains most of the ungauged gains but a moderate adjustment was required. There are no recorded diversions. Baseline model performance is moderate. Accounting does not explain monthly flows, because the dam operation determines outflows. Accounting only explains long term flow totals. The projected changes are generally greater than model uncertainty for annual flows and similar to model uncertainty for monthly flows. Appendix C River system model uncertainty assessment by reach Gauging data Inflows Outflows Overall and gains and losses Fraction of total Gauged Attributed Fraction of variance Gauged Attributed Correlation with ungauged Gains Losses Linear adjustment normal ranked normal ranked Main gauge inflows Tributary inflows Main gauge outflows Distributary outflows Recorded diversions Estimated local runoff Monthly streamflow (GL/mo) gauged accounted model.1 Jan-9 Jan-91 Jan-92 Jan-93 Jan-94 Jan-95 Jan-96 Jan-97 Jan-98 Jan-99 Jan- Jan-1 Jan-2 Jan-3 Jan-4 Jan-5 Water balance Model (A) Accounts Difference Model efficiency Model (A) Accounts Jul 199 Jun 26 Monthly Gains GL/y GL/y GL/y Normal.4.1 Main stem inflows Log-normalised.29 < Tributary inflows Ranked.45 < Local inflows Low flows only < < Unattributed gains and noise High flows only < < Losses GL/y GL/y GL/y Annual Main stem outflows Normal Distributary outflows Log-normalised - - Net diversions Ranked River flux to groundwater - River and floodplain losses Definitions: Unspecified losses low flows (flows<1% percentile ) :.8 GL/mo Unattributed losses and noise high flows (flows>9% percentile) : 28.5 GL/mo Change-uncertainty ratios P B Cwet Cmid Cdry Dwet Dmid Ddry Annual streamflow Monthly streamflow Reach gains and losses (GL/y) /91 91/92 92/93 93/94 94/95 Monthly streamflow (GL/mo). 95/ /97 97/98 98/99 99/ /1 1/2 2/ /4 4/5 5/6 Pecentage of months flow is exceeded unattributed gains ungauged gains gauged gains unattributed losses ungauged losses gauged losses Monthly Change-Uncertainty Ratio P B C D + wet O mid dry Annual streamflow (GL/y) gauged A P B Cwet Cmid Cdry Dwet Dmid.1 Annual Change-Uncertainty Ratio 9/91 91/92 92/93 93/94 94/95 95/96 96/97 97/98 98/99 99/ /1 1/2 2/3 3/4 4/5 5/6 14 Water availability in the Border Rivers November 27 CSIRO 27

153 Downstream gauge Macintyre Holdfast Reach 4 Upstream gauge Severn D/S Pindari Reach length (km) 122 Area (km 2 ) 2696 Outflow/inflow ratio 2.61 Net gaining reach Land use ha % Dryland 269,7 1 Irrigable area - - Open water* - - River and wetlands 52 Open water* - - * averages for This is a strongly gaining reach. Flows are dominated by inflows from upstream. Most of the inflows are gauged. Estimated local runoff explains most of the ungauged gains but a moderate adjustment was required. There are some recorded diversions and ungauged losses are small. Baseline model performance is very good Accounting explains observed flows extremely well. The projected changes are greater than river model uncertainty for annual flows and similar to or greater than model uncertainty for monthly flows. Gauging data Inflows Outflows Overall and gains and losses Fraction of total Gauged Attributed Fraction of variance Gauged Attributed Correlation with ungauged Gains Losses Linear adjustment normal ranked normal ranked Main gauge inflows Tributary inflows Main gauge outflows Distributary outflows Recorded diversions Estimated local runoff Adjusted -24.% Monthly streamflow (GL/mo) gauged accounted model.1 Jan-9 Jan-91 Jan-92 Jan-93 Jan-94 Jan-95 Jan-96 Jan-97 Jan-98 Jan-99 Jan- Jan-1 Jan-2 Jan-3 Jan-4 Jan-5 Water balance Model (A) Accounts Difference Model efficiency Model (A) Accounts Jul 199 Jun 26 Monthly Gains GL/y GL/y GL/y Normal Main stem inflows Log-normalised Tributary inflows Ranked Local inflows Low flows only < < Unattributed gains and noise High flows only Losses GL/y GL/y GL/y Annual Main stem outflows Normal Distributary outflows Log-normalised - - Net diversions Ranked River flux to groundwater - River and floodplain losses Definitions: Unspecified losses low flows (flows<1% percentile ) : 1.5 GL/mo Unattributed losses and noise high flows (flows>9% percentile) : 72. GL/mo Change-uncertainty ratios P B Cwet Cmid Cdry Dwet Dmid Ddry Annual streamflow Monthly streamflow Reach gains and losses (GL/y) /91 91/92 92/93 93/94 94/95 Monthly streamflow (GL/mo). 95/ /97 97/98 98/99 99/ /1 1/2 2/ /4 4/5 5/6 Pecentage of months flow is exceeded unattributed gains ungauged gains gauged gains unattributed losses ungauged losses gauged losses Appendix C River system model uncertainty assessment by reach Monthly Change-Uncertainty Ratio P C D + wet O mid dry Annual streamflow (GL/y) gauged A P Cwet Cmid Cdry Dwet Dmid Ddry.1 Annual Change-Uncertainty Ratio 9/91 91/92 92/93 93/94 94/95 95/96 96/97 97/98 98/99 99/ /1 1/2 2/3 3/4 4/5 5/6 CSIRO 27 November 27 Water availability in the Border Rivers 141

154 Downstream gauge 4162 Macintyre Boggabilla Reach 5 Upstream gauge Macintyre Holdfast Reach length (km) 54.3 Area (km 2 ) 718 Outflow/inflow ratio 2.1 Net gaining reach Land use ha % Dryland 692,81 99 Irrigable area - - Open water* - - River and wetlands 9, 1 Open water* - - * averages for This is a strongly gaining reach. Flows are dominated by inflows from upstream. Most of the inflows are gauged. Estimated local runoff explains most of the ungauged gains. There are large recorded diversions and ungauged losses are small. Baseline model performance is very good. Accounting explains observed flows very well. The projected changes are greater than river model uncertainty for the C and D mid and dry scenarios, and similar to or less tham model uncertainty for the remaining scenarios. Appendix C River system model uncertainty assessment by reach Gauging data Inflows Outflows Overall and gains and losses Fraction of total Gauged Attributed Fraction of variance Gauged Attributed Correlation with ungauged Gains Losses Linear adjustment normal ranked normal ranked Main gauge inflows Tributary inflows Main gauge outflows Distributary outflows Recorded diversions Estimated local runoff Adjusted -35.% Monthly streamflow (GL/mo) Water balance Model (A) Accounts Difference Model efficiency Model (A) Accounts 1 Jul 199 Jun 26 Monthly Gains GL/y GL/y GL/y Normal Main stem inflows Log-normalised.78 - Tributary inflows Ranked Local inflows Low flows only < < 1 Unattributed gains and noise High flows only.9.91 Losses GL/y GL/y GL/y Annual 1 Main stem outflows Normal Distributary outflows Log-normalised - - Net diversions Ranked River flux to groundwater 2-2 River and floodplain losses Definitions:.1 Unspecified losses low flows (flows<1% percentile ) : 2.5 GL/mo Unattributed losses and noise high flows (flows>9% percentile) : GL/mo.1 Change-uncertainty ratios P B Cwet Cmid Cdry Dwet Dmid Ddry Annual streamflow Monthly streamflow Reach gains and losses (GL/y) /91 gauged accounted model 91/92 92/93 93/94 94/95 Monthly streamflow (GL/mo). 95/96 96/97 97/98 98/99 99/ /1 1/2 2/ /4 4/5 5/6 Pecentage of months flow is exceeded unattributed gains ungauged gains gauged gains unattributed losses ungauged losses.1 Jan-9 Jan-91 Jan-92 Jan-93 Jan-94 Jan-95 Jan-96 Jan-97 Jan-98 Jan-99 Jan- Jan-1 Jan-2 Jan-3 Jan-4 Jan-5 gauged losses Monthly Change-Uncertainty Ratio P C D + wet O mid dry Annual streamflow (GL/y) gauged A P Cwet Cmid Cdry Dwet Dmid Ddry Annual Change-Uncertainty Ratio 9/91 91/92 92/93 93/94 94/95 95/96 96/97 97/98 98/99 99/ /1 1/2 2/3 3/4 4/5 5/6 142 Water availability in the Border Rivers November 27 CSIRO 27

155 Downstream gauge Macintyre Kanowna Reach 6 Upstream gauge 4162 Macintyre Boggabilla Reach length (km) Area (km 2 ) 2542 Outflow/inflow ratio.31 Net losing reach Land use ha % Dryland 222,98 88 Irrigable area - - Open water* - - River and wetlands 31,25 12 Open water* - - * averages for This is a losing reach. Flows are dominated by inflows from upstream. Most of the inflows are gauged. Estimated local runoff is very small. There are large recorded diversions and ungauged losses are very large. The ungauged losses are primarily flow down another channel which bypasses the outflow gauge. These losses appear as ungauged gains in the Mungindi reach downstream Baseline model performance is reasonable. Accounting explains observed flows poorly. The projected changes are generally much greater than river model uncertainty. Gauging data Inflows Outflows Overall and gains and losses Fraction of total Gauged Attributed Fraction of variance Gauged Attributed Correlation with ungauged Gains Losses Linear adjustment normal ranked normal ranked Main gauge inflows Tributary inflows Main gauge outflows Distributary outflows Recorded diversions Estimated local runoff Adjusted -1.% Monthly streamflow (GL/mo) gauged accounted model.1 Jan-9 Jan-91 Jan-92 Jan-93 Jan-94 Jan-95 Jan-96 Jan-97 Jan-98 Jan-99 Jan- Jan-1 Jan-2 Jan-3 Jan-4 Jan-5 Water balance Model (A) Accounts Difference Model efficiency Model (A) Accounts Jul 199 Jun 26 Monthly Gains GL/y GL/y GL/y Normal Main stem inflows Log-normalised - - Tributary inflows Ranked.78 < Local inflows Low flows only < < Unattributed gains and noise High flows only.93 < Losses GL/y GL/y GL/y Annual Main stem outflows Normal Distributary outflows Log-normalised - - Net diversions Ranked.92.7 River flux to groundwater - River and floodplain losses Definitions: Unspecified losses low flows (flows<1% percentile ) :.6 GL/mo Unattributed losses and noise high flows (flows>9% percentile) : 48.9 GL/mo Change-uncertainty ratios P B Cwet Cmid Cdry Dwet Dmid Ddry Annual streamflow Monthly streamflow Reach gains and losses (GL/y) /91 91/92 92/93 93/94 94/95 Monthly streamflow (GL/mo). 95/ /97 97/98 98/99 99/ /1 1/2 2/ /4 4/5 5/6 Pecentage of months flow is exceeded unattributed gains ungauged gains gauged gains unattributed losses ungauged losses gauged losses Appendix C River system model uncertainty assessment by reach Monthly Change-Uncertainty Ratio P C D + wet O mid dry Annual streamflow (GL/y) gauged A P Cwet Cmid Cdry Dwet Dmid Ddry.1 Annual Change-Uncertainty Ratio 9/91 91/92 92/93 93/94 94/95 95/96 96/97 97/98 98/99 99/ /1 1/2 2/3 3/4 4/5 5/6 CSIRO 27 November 27 Water availability in the Border Rivers 143

156 Downstream gauge 4161 Barwon Mungindi Reach 7 Upstream gauge Macintyre Kanowna Reach length (km) 38 Area (km 2 ) 1743 Outflow/inflow ratio 1.76 Net gaining reach Land use ha % Dryland 168,68 97 Irrigable area - - Open water* - - River and wetlands 5,6 3 Open water* - - * averages for This is a strongly losing reach. Flows are dominated by ungauged inflows. Few of the inflows are gauged. The ungauged inflows largely come from a channel which bypasses the upstream gauge. There are recorded diversions and ungauged losses are small. Baseline model performance is good. Accounting explains observed flows very well. The projected changes are generally similar to or less than river model uncertainty. Appendix C River system model uncertainty assessment by reach Gauging data Inflows Outflows Overall and gains and losses Fraction of total Gauged Attributed Fraction of variance Gauged Attributed Correlation with ungauged Gains Losses Linear adjustment normal ranked normal ranked Main gauge inflows Tributary inflows Main gauge outflows Distributary outflows Recorded diversions Estimated local runoff Monthly streamflow (GL/mo) Water balance Model (A) Accounts Difference Model efficiency Model (A) Accounts Jul 199 Jun 26 Monthly Gains GL/y GL/y GL/y Normal Main stem inflows Log-normalised - - Tributary inflows Ranked.7.7 Local inflows Low flows only < < Unattributed gains and noise High flows only.62.8 Losses GL/y GL/y GL/y Annual Main stem outflows Normal Distributary outflows Log-normalised - - Net diversions Ranked River flux to groundwater - River and floodplain losses Definitions: Unspecified losses low flows (flows<1% percentile ) :.1 GL/mo Unattributed losses and noise high flows (flows>9% percentile) : 83.6 GL/mo Change-uncertainty ratios P B Cwet Cmid Cdry Dwet Dmid Ddry Annual streamflow Monthly streamflow Reach gains and losses (GL/y) /91 91/92 92/93 93/94 gauged accounted model.1 Jan-9 Jan-91 Jan-92 Jan-93 Jan-94 Jan-95 Jan-96 Jan-97 Jan-98 Jan-99 Jan- Jan-1 Jan-2 Jan-3 Jan-4 Jan-5 94/95 Monthly streamflow (GL/mo). 95/ /97 97/98 98/99 99/ /1 1/2 2/ /4 4/5 5/6 Pecentage of months flow is exceeded unattributed gains ungauged gains gauged gains unattributed losses ungauged losses gauged losses Monthly Change-Uncertainty Ratio P C D + wet O mid dry Annual streamflow (GL/y) gauged A P Cwet Cmid Cdry Dwet Dmid Ddry.1 Annual Change-Uncertainty Ratio 9/91 91/92 92/93 93/94 94/95 95/96 96/97 97/98 98/99 99/ /1 1/2 2/3 3/4 4/5 5/6 144 Water availability in the Border Rivers November 27 CSIRO 27