A.M. Goode and B.G. Barnett

Transcription

1 Southern Riverine Plains Groundwater Model Calibration Report A report to the Australian Government from the CSIRO Murray-Darling Basin Sustainable Yields Project A.M. Goode and B.G. Barnett September 2008

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 Goode AM and Barnett BG (2008) Southern Riverine Plains Groundwater Model Calibration Report. A report to the Australian Government from the CSIRO Murray-Darling Basin Sustainable Yields Project. CSIRO, Australia. 138pp. Publication Details Published by CSIRO 2008 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

3 Preface This is a report to the Australian Government from CSIRO. It is an output of the Murray-Darling Basin Sustainable Yields Project which assessed current and potential future water availability in 18 regions across the Murray-Darling Basin (MDB) considering climate change and other risks to water resources. The project was commissioned following the Murray-Darling Basin Water Summit convened by the Prime Minister of Australia in November 2006 to report progressively during the latter half of The reports for each of the 18 regions and for the entire MDB are supported by a series of technical reports detailing the modelling and assessment methods used in the project. This report is one of the supporting technical reports of the project. Project reports can be accessed at Project findings are expected to inform the establishment of a new sustainable diversion limit for surface and groundwater in the MDB one of the responsibilities of a new Murray-Darling Basin Authority in formulating a new Murray-Darling Basin Plan, as required under the Commonwealth Water Act These reforms are a component of the Australian Government s new national water plan Water for our Future. Amongst other objectives, the national water plan seeks to (i) address over-allocation in the MDB, helping to put it back on a sustainable track, significantly improving the health of rivers and wetlands of the MDB and bringing substantial benefits to irrigators and the community; and (ii) facilitate the modernisation of Australian irrigation, helping to put it on a more sustainable footing against the background of declining water resources. Executive summary Background The Southern Riverine groundwater model has been developed for the Murray-Darling Basin Sustainable Yields Project. Groundwater extraction across the Southern Riverine Plains of the Murray-Darling Basin (Figure A1 and Figure A2) plus the neighbouring Murrumbidgee represents about 40% of the groundwater extraction within the Murray-Darling Basin. While models existed for parts of this area, the nature of the groundwater system means that it is no longer appropriate for these areas to be modelled independently. The area contains two significant environmental assets within the Living Murray (Barmah-Millewa and Gunbower-Pericoota-Koontra), which may be dependent on groundwater. There is also sufficient field evidence to suggest that extraction in the plain will have an impact on the streams in the region, including the River Murray. The Southern Riverine Plains is an area which has seen development of the groundwater resource since the early 1980s, with extractions peaking in 2002/03 at slightly over 400 GL (currently averaging approximately 250 GL/year).The development in the groundwater resource has seen it become an increasingly important component of water resource management in the Murray-Darling Basin. The groundwater model, described in this report, is designed to meet the objectives of the Murray-Darling Basin Sustainable Yields Project. It is not the aim of this model to be able to determine the extraction limit of the area or any sub-region thereof. However, the model is designed to assess the relative impacts of various climate scenarios and groundwater pumping on the state of the groundwater resources. The Southern Riverine groundwater model combines a number of existing groundwater models within the area: the New South Wales Lower Murray model (DLWC, 2001), the Katunga WSPA groundwater model and the Campaspe WSPA groundwater model (the Campaspe model was developed in an earlier phase of this project and later superceded by this model). By combining these models, we attempt to minimise the controlling influence of artificial model boundary conditions and provide an enhanced representation of intermediate and regional scale interference patterns. As previously stated this also provides an ability to advance water accounting capabilities across state and management area boundaries. Model description The groundwater model was constructed within the Visual Modflow modelling framework. It spans approximately 290 km from east to west and 250 km from north to south with a 1 km 2 grid cell resolution. It incorporates the major surface drainage features of the Murray River, Edward River, Wakool River, Neimur Creek, Loddon River, Campaspe River and CSIRO 2008 Southern Riverine Plains Groundwater Model Calibration Report

4 the Goulburn and Broken rivers. Geologically the model is divided into four layers: Upper Shepparton, Lower Shepparton, Calivil Formation and Renmark Group layers. The Calivil and Renmark together form the major aquifer, which hold a significant groundwater resource. These two layers are commonly referred to as the Deep Lead in Victoria, but take the form of a broad sheet of material in New South Wales. The model covers nine individual groundwater management units and four regions, as defined by this project. It also includes possible groundwater-dependent ecosystems such as Gunbower Forest, Koondrook-Perricoota Forest, and the Barmah Forest. The groundwater model calibration was completed at an adequate level that meets the requirements of a moderate complexity regional scale groundwater model as defined in Murray-Darling Basin Commission Groundwater Flow Modelling Guidelines (Middlemis, 2000). Modelling results and key messages Key messages identified from the modelling are discussed below. Water accounting across groundwater management unit (GMU) boundaries The results from the groundwater modelling highlight the significant levels of interaction that occur between neighbouring GMUs and regions. In particular it was found that there are significant fluxes of groundwater beneath the Murray River in the Deep Lead aquifers. For example, there are high levels of groundwater extractions in the Lower Murray GWMA in New South Wales (~80 GL/year). In the model approximately 50% of this volume pumped (40 GL/year) is drawn from groundwater resources to the north (from the Murrumbidgee Catchment) and from south of the Murray River. Similarly pumping in the Katunga and Shepparton WSPAs draws large volumes of water from groundwater resources to the south and causes water to flow out of the Kialla and the Mid-Goulburn GMAs. As a result, the predictive scenarios include a net flux of groundwater out of the Kialla and Mid-Goulburn GMAs. This occurs in spite of increased extractions from within these GMAs. A model constructed for the Kialla GMA or Mid-Goulburn GMA in isolation (i.e. not including the neighbouring WSPAs) would have presented the opposite result. Individual isolated models predict net groundwater influxes in response to increasing groundwater extraction. This finding highlights the importance of modelling the entire aquifer as a whole and not splitting it up into a number of smaller groundwater models based on groundwater management regions. It further highlights the fact that neighbouring groundwater models constructed in the same aquifer will lead to significant accounting errors associated with groundwater fluxes across lateral model boundaries. Surface groundwater interactions Current (2004/05) rates of groundwater extraction in the Southern Riverine model are approximately 250 GL/year. Compared to without-development conditions, it was found that 42% (103 GL/year) of the current groundwater pumping is sourced from surface waters (i.e. from reduced flow in rivers) within the model area. However, due to limitations in modelling the without-development conditions it is believed that this figure is likely to be as high as 60% (150 GL/year). This latter figure is supported by modelling results of future conditions (scenarios C and D) where pumping is increased by a further 50 GL/year to ~300 GL/year. Here it was found that 58% of the additional volume extracted was sourced from loss of river flow. The remainder of the volume extracted was obtained from captured or reduced groundwater evapotranspiration, 37%, with 5% sourced from changes in lateral flow across model boundaries. This small volume sourced from changes in fluxes across model boundaries suggests that the model is correctly accounting for the regional scale impacts of groundwater pumping. These issues are discussed in detail in Section 6.2. The time lag associated with the impacts of groundwater pumping on streamflows varies on a scale from years to several decades, depending on the depth and location of extraction wells. Under Scenario A the full impacts of all groundwater extractions are observed within 25 years. Groundwater evapotranspiration (ET) and groundwater-dependent ecosystems (GDEs) The importance of groundwater ET was first highlighted during the calibration process where it was discovered that groundwater ET from forested areas, such as the Gunbower Forest, had a significant influence on the groundwater levels. From the predictive scenario modelling results ET proved to be the groundwater discharge process that is most sensitive to climate change. Under the dry scenarios, decreases in rainfall recharge were largely matched by decreases in groundwater ET. This is mostly realised by losses in water availability to GDEs. In practical terms, this suggests that unless water allocations are reduced in accordance with the reduced rainfall recharge it is possible that GDEs are likely to suffer from reduced water availability as a result of climate change. Southern Riverine Plains Groundwater Model Calibration Report CSIRO 2008

5 All of the modelled scenarios reached dynamic equilibrium within the 222-year modelling period (111 years of warm-up and 111 years of scenario). This suggests that current rates of groundwater extractions will eventually achieve a balance in groundwater inflows and outflows. However, current groundwater use has already and will continue to cause significant drawdown in groundwater levels across the Riverine Plains. As a result continued groundwater extraction at current rates will draw heavily on surface water resources and is possibly already impacting on GDEs. Figure A1. Map of the Southern Riverine Plains Model within the Murray-Darling Basin Figure A2. Detailed map of the Southern Riverine Plains Model CSIRO 2008 Southern Riverine Plains Groundwater Model Calibration Report

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7 Table of Contents 1 Introduction Hydrogeological conceptualisation Modelling area and physiography Geological setting Regions and groundwater management units Murray (NSW GWMA 016, Katunga WSPA) Loddon-Avoca (Mid-Loddon GMA) Campaspe (Campaspe Deep Lead WSPA, Ellesmere GMA) Goulburn-Broken (Mid-Goulburn GMA, Kialla GMA, Goorambat GMA) Shepparton WSPA Model development Model domain Study area Coordinate system Model layering Model input data Storage parameters Hydrogeological conductivity values Rivers and drains Recharge (dryland and irrigation) Evapotranspiration Boundary conditions Model calibration Calibration method Groundwater extraction Calibration model observation bores Calibration model results Summary of hydrographs by region Murray Loddon-Avoca Campaspe Goulburn-Broken Potentiometric surface maps Shepparton Formation Deep Lead Calibration statistics Calibration model water balance Overview Surface groundwater interaction Groundwater management unit water balances Lower Murray (NSW GWMA 016) Mid-Loddon Campaspe Deep Lead Ellesmere Katunga Kialla Mid-Goulburn Goorambat Shepparton Scenario modelling methodology Model scenarios Alterations to the calibration model Scenario model inputs Recharge Rivers and drains Extractions Evapotranspiration Boundary conditions Key indicator bores Integration into the whole-of-mdb modelling framework Scenario reporting structure Scenario modelling results Groundwater levels Surface groundwater interactions Groundwater balance Overview...66 CSIRO 2008 Southern Riverine Plains Groundwater Model Calibration Report

8 6.3.2 Groundwater extractions Groundwater indicators Results by groundwater management unit Campaspe Deep Lead WSPA Groundwater resource condition indicators Ellesmere GMA Groundwater resource condition indicators Goorambat GMA Groundwater resource condition indicators Katunga WSPA Groundwater resource condition indicators Kialla GMA Groundwater resource condition indicators Lower Murray (NSW GWMA 016) Groundwater resource condition indicators Mid-Goulburn GMA Groundwater resource condition indicators Mid-Loddon GMA Groundwater resource condition indicators Shepparton WSPA Groundwater resource condition indicators Results by region Campaspe Goulburn-Broken Loddon-Avoca Murray Discussion of results Modelling limitations and recommendations References Appendix A River gauges Appendix B Calibration model observation bores Appendix C Calibration model hydrographs New South Wales Gunbower Forest Loddon Campaspe Katunga Goulburn-Broken Appendix D Natural flows scenario results Introduction Model results GMU water balances Regional water balances Southern Riverine Plains Groundwater Model Calibration Report CSIRO 2008

9 Tables Table 3-1. Spatial parameters of the model coordinate system...11 Table 3-2. Storage parameters defined in the model...15 Table 3-3. Southern Riverine modelled recharge zones...23 Table 4-1. Calibration model performance criteria (after Middlemis, 2000)...29 Table 4-2. Estimated groundwater usage in New South Wales (supplied by the New South Wales Department of Natural Resources)...30 Table 4-3. Groundwater usage estimates in Victorian groundwater management units...32 Table 4-4. Groundwater usage estimates for Victorian unincorporated areas (grouped by catchment)...32 Table 4-5. Calibration model statistics...48 Table 4-6. Average annual groundwater inflows and outflows for each groundwater management unit within the model area (January 1990 to December 2005)...52 Table 5-1. Summary of the scenario models...57 Table 5-2. Groundwater extraction data for the Southern Riverine scenario models...58 Table 5-3. Groundwater monitoring sites used in the scenario modelling...59 Table 6-1. Median groundwater changes (m) across the Southern Riverine model under scenarios A, B, C and D...63 Table 6-2. Impacts of groundwater pumping on net river losses...66 Table 6-3. Modelled average annual groundwater balance under scenarios A, B, C and D and under the without-development scenario (second 111 years)...67 Table 6-4. Southern Riverine recharge compared to pumping under all scenarios...69 Table 6-5. Definition of groundwater indicators...69 Table 6-6. Groundwater indicators under scenarios A, B, C and D...70 Table 7-1. Groundwater balance for the Campaspe Deep Lead WSPA...71 Table 7-2. Median groundwater changes (m) in the Campaspe Deep Lead WSPA under scenarios A, B, C and D...73 Table 7-3. Groundwater indicators under scenarios A, B, C and D...73 Table 7-4. Groundwater balance for the Ellesmere GMA...73 Table 7-5. Median groundwater changes (m) in the Ellesmere GMA under scenarios A, B, C and D...74 Table 7-6. Groundwater indicators under scenarios A, B, C and D...74 Table 7-7. Groundwater balance for the Goorambat GMA...75 Table 7-8. Median groundwater changes (m) in the Goorambat GMU under scenarios A, B, C and D...76 Table 7-9. Groundwater indicators under scenarios A, B, C and D...76 Table Groundwater balance for the Katunga WSPA...76 Table Median groundwater changes (m) in the Katunga WSPA under scenarios A, B, C and D...78 Table Groundwater indicators under scenarios A, B, C and D...78 Table Groundwater balance for the Kialla GMA...79 Table Median groundwater changes (m) in the Kialla GMA under scenarios A, B, C and D...80 Table Groundwater indicators under scenarios A, B, C and D...80 Table Groundwater balance for the Lower Murray GWMA 016 Calivil Formation and Renmark Group...81 Table Groundwater balance for the Lower Murray GWMA 016 Shepparton Formation...81 Table Median groundwater changes (m) in the Lower Murray groundwater management unit for baseline, recent and future scenarios...83 Table Groundwater indicators for baseline, recent and future scenarios...83 Table Groundwater balance for the Mid-Goulburn GMA...84 Table Median groundwater changes (m) in the Mid-Goulburn GMA under scenarios A, B, C and D...85 Table Groundwater indicators under scenarios A, B, C and D...85 Table Groundwater balance for the Mid-Loddon GMA...86 Table Median groundwater changes (m) in the Mid-Loddon GMU under scenarios A, B, C and D...87 Table Groundwater indicators under scenarios A, B, C and D...87 Table Groundwater balance for the Shepparton WSPA...88 Table Median groundwater changes (m) in the Shepparton WSPA under scenarios A, B, C and D...89 Table Groundwater indicators under scenarios A, B, C and D...89 Table 8-1. Groundwater balance for the Campaspe region...90 Table 8-2. Comparison of the without-development scenario and Scenario A in the Campaspe region...91 Table 8-3. Groundwater balance for the Goulburn-Broken region...92 Table 8-4. Comparison of the without-development scenario and Scenario A in the Goulburn-Broken region...93 Table 8-5. Groundwater balance for the Loddon-Avoca region...93 Table 8-6. Comparison of the without-development scenario and Scenario A in the Goulburn-Broken region...94 Table 8-7. Groundwater balance for the Murray region...95 CSIRO 2008 Southern Riverine Plains Groundwater Model Calibration Report

10 Table 8-8. Comparison of the without-development scenario and Scenario A in the Murray region...96 Table Groundwater balance results under the natural flows scenario Table Groundwater balance results under the natural flows scenario: Campaspe Deep Lead WSPA Table Groundwater balance results under the natural flows scenario: Ellesmere GMA Table Groundwater balance results under the natural flows scenario: Goorambat GMA Table Groundwater balance results under the natural flows scenario: Katunga WSPA Table Groundwater balance results under the natural flows scenario: Kialla GMA Table Groundwater balance results under the natural flows scenario: Mid-Loddon GMA Table Groundwater balance results under the natural flows scenario: Lower Murray NSW GWMA 016 Deep Lead Table Groundwater balance results under the natural flows scenario: Lower Murray NSW GWMA 016 Shepparton Formation Table Groundwater balance results under the natural flows scenario: Shepparton WSPA Table Groundwater balance results under the natural flows scenario: Campaspe region Table Groundwater balance results under the natural flows scenario: Goulburn-Broken region Table Groundwater balance results under the natural flows scenario: Loddon region Table Groundwater balance results under the natural flows scenario: Murray region Figures Figure 2-1. Major towns and rivers superimposed over satellite imagery of the model area...3 Figure 2-2. Southern Riverine model domain looking toward the Great Dividing Range in the south-east...3 Figure 2-3. Regions within the Southern Riverine groundwater model...5 Figure 2-4. Groundwater management units within the Southern Riverine groundwater model...6 Figure 3-1. Southern Riverine model grid and coordinates in Lambert Conical Conformance projection...10 Figure 3-2. Southern Riverine model domain including groundwater management areas and inactivated areas...11 Figure 3-3. East west cross-section of the Southern Riverine model highlighting the hydrogeological layering structure of the model (vertically exaggerated by 300 times)...12 Figure 3-4. Thickness of the Upper Shepparton Aquifer...12 Figure 3-5. Thickness of the Lower Shepparton Aquifer...13 Figure 3-6. Thickness of the Calivil Formation Aquifer...13 Figure 3-7. Thickness of the Renmark Group Aquifer...14 Figure 3-8. Hydraulic conductivity values in Layer 1 (Upper Shepparton Formation)...16 Figure 3-9. Hydraulic conductivity values in Layer 2 (Lower Shepparton)...17 Figure Hydraulic conductivity values in Layer 3 (Calivil Formation)...18 Figure Hydraulic conductivity values in Layer 4 (Renmark Group)...19 Figure Rivers and drains included in the Southern Riverine model...20 Figure All natural surface water features within the Southern Riverine model domain...21 Figure Rainfall districts as defined by the Bureau of Meteorology (2006)...24 Figure Satellite imagery highlighting irrigation areas incorporated into the Southern Riverine model...24 Figure Rainfall sites (1 to 20) input into the Waves Model to deduce dryland recharge variability across the model...25 Figure Southern Riverine model recharge zones...26 Figure Groundwater evapotranspiration rates set across the Southern Riverine model...27 Figure General head boundaries...28 Figure 4-1. Estimated volumes of groundwater extractions in New South Wales...30 Figure 4-2. Distribution of groundwater pumping throughout a calendar year...31 Figure 4-3. Estimated groundwater usage in the Victorian groundwater management units and unincorporated areas...33 Figure 4-4. Groundwater extraction wells included in the Southern Riverine model...33 Figure 4-5. Observation bores screening the Upper Shepparton...34 Figure 4-6. Observation bores screening the Lower Shepparton...35 Figure 4-7. Observation bores screening the Calivil Formation...35 Figure 4-8. Observation bores screening the Renmark Group...36 Figure 4-9. Example hydrographs from the Murray region near Deniliquin (note: this is not a nested site)...37 Figure Example hydrographs from the Murray region in the east between Corowa and Jerilderie...38 Figure Example hydrographs from the Murray region in the south near Echuca...38 Figure Example hydrographs from the Murray region in Gunbower Forest...39 Figure Example hydrographs from the north of the Loddon catchment in the Murray region...39 Figure Example hydrographs from the north-east of the Loddon catchment in the Murray region...40 Figure Example hydrographs from the Katunga WSPA within the Murray region...40 Southern Riverine Plains Groundwater Model Calibration Report CSIRO 2008

11 Figure Example hydrographs from the Mid-Loddon GMA...41 Figure Example hydrographs from the Mid-Loddon GMA...41 Figure Example hydrographs from the Campaspe region near Echuca...42 Figure Example hydrographs from the Campaspe region...42 Figure Example hydrographs from the Campaspe region...43 Figure Example hydrographs from the Goulburn-Broken region...44 Figure Example hydrographs from the Goulburn-Broken region...44 Figure Example hydrographs from the Goulburn-Broken region...45 Figure Comparison of observed and modelled watertables (Shepparton Formation) based on data from March Figure Comparison of observed and modelled watertables (Shepparton Formation) based on data from May Figure Comparison of observed and modelled potentiometric surfaces (Deep Lead) based on data from March Figure Comparison of observed and modelled potentiometric surfaces (Deep Lead) based on data from May Figure Calibration model normalised RMS (%) over the length of the calibration period...48 Figure Average annual groundwater recharge (GL/year) for the calibration model (January 1990 to December 2005)...49 Figure Average annual groundwater discharge (GL/year) for the calibration model (January 1990 to December 2005)...49 Figure Total groundwater extractions compared to total recharge (rainfall, irrigation, river leakage and lateral groundwater flow in)...50 Figure Time series of river leakage and groundwater discharges to the river...51 Figure Time series of net river losses compared to total pumping...51 Figure Water balance for the Lower Murray GWMA (Calivil Formation and Renmark Group)...53 Figure Water balance for the Lower Murray GWMA (Shepparton Formation)...53 Figure Water balance for the Mid-Loddon GMA...53 Figure Water balance for the Campaspe Deep Lead WSPA...54 Figure Water balance for the Ellesmere GMA...54 Figure Water balance for the Katunga WSPA...54 Figure Water balance for the Kialla GMA...55 Figure Water balance for the Mid-Goulburn WSPA...55 Figure Water balance for the Goorambat GMA...55 Figure Water balance for the Shepparton WSPA...56 Figure 5-1. Locations of key indicator bores used in the Southern Riverine scenario modelling...60 Figure 5-2. Flow diagram summarising surface water model and groundwater model running procedure...61 Figure 5-3. Map of the Murray-Darling Basin Sustainable Yield project integrated modelling framework...61 Figure 6-1. Drawdown in the Shepparton Formation during the first 111-year run under Scenario A...64 Figure 6-2. Drawdown in the Calivil Formation during the first 111-year run under Scenario A...64 Figure 6-3. Net river loss to groundwater under Scenario A...65 Figure 6-4. Comparison of net river loss under Scenario A and the without-development scenario...66 Figure 6-5. Modelled total groundwater recharge exceedance curves...67 Figure 6-6. Modelled groundwater recharge components...68 Figure 6-7. Modelled groundwater discharge components...68 Figure 6-8. Comparison of recharge and groundwater extractions highlighting the increasing stresses on the resource...69 Figure 7-1. Groundwater inflows into the Campaspe Deep Lead WSPA...72 Figure 7-2. Groundwater outflows from the Campaspe Deep Lead WSPA...72 Figure 7-3. Impacts of groundwater pumping in the Campaspe Deep Lead WSPA...72 Figure 7-4. Groundwater inflows into the Ellesmere GMA...74 Figure 7-5. Groundwater outflows from the Ellesmere GMA...74 Figure 7-6. Groundwater inflows into the Goorambat GMA...75 Figure 7-7. Groundwater outflows from the Goorambat GMA...75 Figure 7-8. Groundwater inflows into the Katunga WSPA...77 Figure 7-9. Groundwater outflows from the Katunga WSPA...77 Figure Impacts of groundwater pumping in the Katunga WSPA...77 Figure Groundwater inflows into the Kialla GMA...79 Figure Groundwater outflows from the Kialla GMA...79 Figure Impacts of groundwater pumping in the Kialla GMA...80 Figure Groundwater inflows into the Lower Murray GWMA 016 Calivil Formation and Renmark Group Aquifers...82 Figure Groundwater outflows from the Lower Murray GWMA 016 Calivil Formation and Renmark Group Aquifers...82 Figure Impacts of groundwater pumping in the Lower Murray GWMA 016 Calivil Formation and Renmark Group Aquifers82 Figure Groundwater inflows into the Mid-Goulburn GMA...84 Figure Groundwater outflows from the Mid-Goulburn GMA...84 Figure Impacts of groundwater pumping in the Mid-Goulburn GMA...85 CSIRO 2008 Southern Riverine Plains Groundwater Model Calibration Report

12 Figure Groundwater inflows into the Mid-Loddon GMA...86 Figure Groundwater outflows from the Mid-Loddon GMA...86 Figure Groundwater inflows into the Shepparton WSPA...88 Figure Groundwater outflows from the Shepparton WSPA...88 Figure 8-1. Groundwater inflows into the Campaspe region...90 Figure 8-2. Groundwater outflows from the Campaspe region...91 Figure 8-3. Groundwater inflows into the Goulburn-Broken region...92 Figure 8-4. Groundwater outflows from the Goulburn-Broken region...92 Figure 8-5. Groundwater inflows into the Loddon-Avoca region...94 Figure 8-6. Groundwater outflows from the Loddon-Avoca region...94 Figure 8-7. Groundwater inflows into the Murray region...95 Figure 8-8. Groundwater outflows from the Murray region...96 Figure Time series of net river losses to groundwater under the natural flows scenario and Scenario A (second 111 years) Figure Time series of the Murray River elevation at Wakool Junction for the final 20 years of the model run Southern Riverine Plains Groundwater Model Calibration Report CSIRO 2008

13 1 Introduction The Southern Riverine groundwater model has been developed for the Murray-Darling Basin Sustainable Yields Project. Within the context of the project this model represents only a small portion of the work completed, and spatially only a small proportion of the entire Murray-Darling Basin (MDB). However, within the context of integrated water resource management this model provides a stepping stone toward closing the water balance and enabling whole of water cycle management (with particular emphasis on surface groundwater interactions and water accounting across management area boundaries). This model pertains specifically to a part of the MDB commonly known as the Southern Riverine Plains. The entire MDB extends about 850 km from east to west and 750 km from north to south and covers an area of over 1,000,000 km 2. In the south of the MDB, a major geological feature, the Murray Geological Basin (MGB), can be divided into two subregions on the basis of surface geomorphology and structural features: the Riverine Plain in the eastern part and the Mallee region in the west of the MGB. The model reported here occupies a large part of the southern portions of the Riverine Plains of the MGB (i.e. the Southern Riverine Plains). The Southern Riverine Plains is an area which has seen heavy development of the groundwater resource since the mid- 1990s, with extractions peaking in 2002/03 at slightly over 400 GL (currently averaging approximately 250 GL/year). The strong development in the groundwater resource has seen it become an increasingly important component of water resource management in the MDB. In light of the current drought and surface water supply shortages, understanding of the groundwater resource and its connectivity with surface water resources is a priority of this project, and indeed this model. The groundwater model, described in this report, is designed to meet the objectives of the Murray-Darling Basin Sustainable Yield Project. It is not the aim of this model to be able to determine the extraction limit of the area or any sub-region thereof. However, the model is designed to assess the relative impacts of various climate scenarios and groundwater pumping on the state of the groundwater resources. Under this scope the model has been designed as a moderate complexity model suitable for predicting the impacts of proposed developments or management policies (Murray-Darling Basin Commission Groundwater Modelling Guidelines (Middlemis, 2000)). Importantly, this model aims to capture whole of water cycle processes and in particular to further the understanding of surface groundwater interactions. This has been aided through the model s integration into a whole-of-mdb modelling framework which links both surface water and groundwater models across the MDB. In doing so the combined models are used to break down historical management shortfalls such as the double accounting of water resources. The Southern Riverine groundwater model combines a number of existing groundwater models within the area: the New South Wales Lower Murray model (DLWC, 2001), the Katunga WSPA groundwater model and the Campaspe WSPA groundwater model (the Campaspe model was developed in an earlier phase of this project and later superseded by this model). The combining of these models attempts to minimise the controlling influence of artificial model boundary conditions and provide an enhanced representation of intermediate and regional scale interference patterns. As previously stated this also provides an ability to advance water accounting capabilities across state and management area boundaries. This report forms the major documentation for the model conceptualisation, calibration and scenario modelling conducted as part of the Murray-Darling Basin Sustainable Yield Project. CSIRO 2008 Southern Riverine Plains Groundwater Model Calibration Report 1

14 2 Hydrogeological conceptualisation 2.1 Modelling area and physiography The Southern Riverine groundwater model covers a 292 by 250 km area within the Murray-Darling Basin, spanning either side of the Murray River between Yarrawonga and Swan Hill (Figure 2-1). The model area encompasses the rural townships of Swan Hill, Echuca, Deniliquin, Shepparton, Yarrawonga and Wangaratta. Hydrologically the model covers major parts of the Loddon River, Campaspe River, Goulburn River, Broken River, Wakool River, Edward River and Billabong Creek catchments. Topographically the majority of the area is flat with a general slope toward the west (Figure 2-2). The Great Dividing Range rises in the south of the model area reaching elevations near 1500 m around Mt Buffalo. However, much of the highlands are geologically characterised by outcropping bedrock and are therefore inactivated in the groundwater model. Surface drainage across the model is primarily controlled by the structure of the geological basement elements and the orientation of fracture sets (Brown and Stephenson, 1991). Generally flow is in a northwesterly direction towards the Murray-Wakool Junction. Sub-surface drainage also follows this trend. However at times in the past, the flow direction of the main drainage channel, i.e. the Murray River, has been impeded by uplift of the Cadell Block (near Deniliquin) where the main channel flow was turned in a northerly direction toward the present day Edward River. More recent uplift diverted the main drainage channel to the present day Murray River (Brown and Stephenson, 1991). The down-faulted block to the east of the Cadell Fault subsequently became subject to seasonal flooding creating the area known as Barmah Forest (clearly visible in satellite imagery, Figure 2-1). Numerous lakes and swamps, mostly ephemeral, dot the Southern Riverine landscape. Many of these are associated with both active and inactive meander belts (Brown and Stephenson, 1991). A series of terminal and groundwater discharge lakes also occur near Kerang in the lower reaches of the Loddon catchment. The Murray River (and many of its tributaries) within the model domain is heavily regulated to increase the reliability of water supplies. Vegetation has also been significantly altered throughout the model domain. Large areas in the southern half of the MDB have been cleared for wheat and other grain cultivation. There are major irrigation areas adjacent to the Murray, which have been cleared for orchards, vineyards, rice fields and other cultivation. The irrigation is supported by a vast network of distribution canals, channels and drains, and large areas are irrigated by landholders pumping water directly from the rivers. 2 Southern Riverine Plains Groundwater Model Calibration Report CSIRO 2008

15 Figure 2-1. Major towns and rivers superimposed over satellite imagery of the model area Figure 2-2. Southern Riverine model domain looking toward the Great Dividing Range in the south-east 2.2 Geological setting The Southern Riverine region consists of a Tertiary to Quaternary sedimentary unit directly underlain by Palaeozoic bedrock. Regionally the sedimentary deposits vary in thickness from 200 to 600 m. The sedimentary sequence consists of three main packages of sediments from oldest to youngest: the Renmark Group, the Calivil Formation and the Shepparton Formation (Brown and Stephenson, 1991). CSIRO 2008 Southern Riverine Plains Groundwater Model Calibration Report 3

16 The Eocene Oligocene aged Renmark Group was deposited through the filling of deep channels carved into the old land surface by an ancient river system and subsequent spilling over into broad sediment sheets. It forms the basal depositional sequence of almost the entire Murray-Darling Basin (Brown and Stephenson, 1991). It is a thick (up to 200 m in the north) unit found consistently throughout most of the area directly overlying bedrock. This unit comprises a sedimentary sequence of non-marine sand, silt, clays and brown coal with a flat upper surface. It can be further subdivided into three main parts that are not uniformly present everywhere. The older Lower Renmark section is characterised by thick sandy layers interspersed with layers of clay. The Mid-Renmark is dominated by mid to dark grey clay, carbonaceous clay, thick peat layers and a few sandy layers. The Upper Renmark contains mostly sand, some mid to dark grey clay and peat interspersed with sand and gravel (DLWC, 2001). The Miocene Pliocene aged Calivil Formation overlies the Renmark Group and has a relatively uniform thickness varying from 60 to 80 m. It consists of alluvial fan deposits formed where streams strayed into flat areas created by the earlier Renmark deposits (DLWC, 2001). In the southern part of the model area (predominantly in Victoria) the Calivil Formation has incised into the Renmark Group to form deep valleys of coarser grained materials. The upper limit of the Calivil Formation is relatively flat. The formation consists of fine to coarse sand and gravel layers interbedded with layers of clay and silty clay. The Calivil Formation and Renmark Group together are referred to as the Deep Lead aquifer in Victoria. The youngest and uppermost unit is the Shepparton Formation which varies in thickness from 70 to 100 m. It is a highly heterogeneous unit consisting mainly of brown, red-brown and yellow-brown clay, silty clay and sandy clay, with minor lenses of quartz-rich sand and gravel (DLWC, 2001). The Shepparton Formation is sometimes further divided into the sandy Upper and more clay-rich Lower Shepparton formations. This separation is not consistent and variations occur locally, with the Upper being more clay rich in some areas. 4 Southern Riverine Plains Groundwater Model Calibration Report CSIRO 2008

17 2.3 Regions and groundwater management units Regions and groundwater management units within the model area are shown in Figure 2-3 and Figure 2-4. Figure 2-3. Regions within the Southern Riverine groundwater model CSIRO 2008 Southern Riverine Plains Groundwater Model Calibration Report 5

18 Figure 2-4. Groundwater management units within the Southern Riverine groundwater model Murray (NSW GWMA 016, Katunga WSPA) The following text draws from DLWC (2001). The Murray region refers to a large area that spans a significant length of the Murray River. Within the Southern Riverine model area it includes the New South Wales Lower Murray groundwater management unit (GWMA 016), located between the Murray River and Billabong Creek in New South Wales, and also the Katunga Water Supply Protection Area and a small area to the south of the Murray around Gunbower Forest. GWMA 016 and the Katunga WSPA refer principally to the deeper aquifers of the Calivil Formation and Renmark Group, though GWMA 016 does include the Shepparton Formation sediments. The Calivil Formation has a high hydraulic conductivity, especially near the MDB margins where alluvial fan deposits are thickest. In the west this unit fines and becomes thinner, and consequently the transmissivity decreases. The Calivil Formation outcrops in the east near Jerilderie. The Renmark Group is the dominant aquifer as it is the thickest and most transmissive unit. It is also the deepest and does not outcrop anywhere within the Murray region. Recharge across the plain is conceptualised to take place via the following mechanisms: leakage from the major river systems, dryland rainfall recharge, infiltration from irrigated areas, leakage from supply/drainage works and some runoff from surrounding bedrock areas via small streams. Recharge through the Shepparton Formation to the deeper aquifers is restricted due to the clay-rich nature of the Shepparton Formation. However, recharge via rainfall infiltration where the more permeable Calivil Formation outcrops is considered significant. Within the region, accessions to groundwater resulting from irrigated agriculture contribute to rising watertables and waterlogging. In New South Wales the total irrigated area is estimated at 748,000 ha (MIL, 2006) representing by far the dominant land use within the area. Permanent shallow watertables occur on a regional basis over most of the major irrigation districts in the Murray region. Estimates based on the monitoring undertaken by Murray Irrigation Limited are that the area with shallow watertables (0 to 2 m) reached 110,000 ha in 1997 and declined to 40,000 ha in Previous work in irrigation districts such as Berriquin has shown that the estimated rise in watertables has averaged Southern Riverine Plains Groundwater Model Calibration Report CSIRO 2008

19 m/year in recent years, with total accessions equal to about 20 percent of the water delivered to the area. As in many other semi-arid regions, rises in groundwater levels, caused by irrigation schemes, have created problems of soil salinisation and waterlogging. The New South Wales (GWMA 016) area has used an average of 42,000 ML/year of groundwater during the period 1989 to Since 2000, total extractions from the aquifers have varied greatly between 50,000 and 120,000 ML/year. Extractions from the Shepparton Formation have remained relatively static at about 33,500 ML/year (mostly as part of sub-surface drainage schemes for the purpose of salinity control). The Katunga WSPA has been developed extensively for irrigation and represents a significant proportion of the Victorian usage of the Deep Lead resource. In 2002/03 extractions peaked at just over 40,000 ML but have since reduced to approximately 21,500 ML in 2005/ Loddon-Avoca (Mid-Loddon GMA) The mid-loddon Groundwater Management Area consists of three hydrogeological units: the Shepparton Formation, Newer Volcanics and the Deep Lead aquifers. The sands and gravels of the Shepparton Formation can provide significant quantities of water. However, due to its variable lithology and prevalence of fine-grained sediments it is not considered to be reliable source of good quality groundwater. The majority of groundwater use in the GMA is extracted from the Deep Lead aquifers. The occurrence of Newer Volcanics in the catchment can provide enhanced recharge, particularly where it outcrops. The main source of recharge to the Deep Lead is through leakage from the overlying Shepparton Formation. It is also likely that there is a significant throughflow volume sourced from the smaller tributary leads, particularly at the southern end of the GMA (URS, 2006). In the south there is direct infiltration in areas where the Calivil outcrops. River leakage from waterways such as the Loddon River and its tributaries are considered a less important component of the water balance. However, interaction increases where watercourses intersect basalts between Newbridge and Bridgewater (URS, 2006). Irrigation within the Loddon catchment is focused on the Pyramid-Boort Irrigation Area (PBIA) which covers an area of 166,215 ha. Irrigation in the lower reaches of the Loddon catchment (north of the WSPA) is mostly facilitated by water sourced from the Waranga Western Channel and the Loddon River. It has been irrigated extensively for approximately 80 years and consequently the area has been subject to shallow watertables and associated salinity concerns. In recent times, however, watertables across the Loddon catchment have been in steady decline. Pressures in the Calivil Formation have also been observed to be declining, albeit at a slower rate. These trends are thought to be a result of a combination of increased pumping in the Loddon WSPA and below average rainfall in the catchment. Drawdown levels in the north of the Loddon catchment also suggest the possibility of regional-scale drawdown cones spreading from elsewhere within Southern Riverine Plains area. Salinities within the Calivil Formation range from 900 to 2000 mg/l TDS but can be as high as 9000 mg/l TDS within the discharge zone on the lower Loddon Plain (URS, 2006). Groundwater usage in the Mid-Loddon area has averaged 11,150 ML/year during the period from 1989 to Recently, groundwater usage has remained relatively static at about 15,500 ML/year Campaspe (Campaspe Deep Lead WSPA, Ellesmere GMA) The Campaspe catchment contains three aquifer units: the porous Deep Lead (Calivil Formation and Renmark Group) aquifer, the Shepparton Formation and the fractured Coliban Basalt. The Shepparton Formation is widespread across the area except where bedrock outcrops. Hydraulic conductivities and specific yields for the Shepparton Formation are low and thought to range between 0.5 to 8 m/day and 0.01 to 0.02, respectively. Salinity for the Shepparton is less than 1,000 mg/l TDS near the Campaspe River; 3,000 mg/l TDS near Rochester River; and greater than 13,000 mg/l TDS elsewhere (Hyder, 2006). The main Deep Lead commences near Axedale and becomes progressively deeper to the north. The Deep Lead has higher hydraulic conductivities which also increase towards the north, up to 100 m/day in the south and 185 m/day in the north (Hyder, 2006). Salinity within the Deep Lead aquifer is higher in the north than the south and tends to vary between 600 and 4200 mg/l TDS. The Coliban Basalt occurs in the south approximately from Lake Eppalock to Ellmore following the Campaspe River valley. CSIRO 2008 Southern Riverine Plains Groundwater Model Calibration Report 7

20 Groundwater levels in the Deep Lead typically fluctuate greatly (up to 20 m) in response to seasonal pumping. However, a steady drawdown has been observed since the mid-1990s, in response to increased extractions and below-average rainfall in the region (Hyder, 2006). Typically drawdowns are also observed in the Shepparton Formation. Recharge to the Shepparton Formation is typically via rainfall, irrigation or river leakage. Recharge to groundwater from irrigation has been estimated at over 100 mm/year in intensively developed areas such as the Campaspe Irrigation District and the Rochester Irrigation Area (Hyder, 2006). River leakage is estimated to be highly variable along the length of the Campaspe due to the highly variable nature of the Upper Shepparton. Recharge to the Deep Lead occurs mainly via leakage from the overlying Shepparton Formation. Further recharge may also be sourced from the river where it is underlain by sandier material giving it a good hydraulic connection to the Calivil. An average of 15,557 ML of groundwater from the Deep Lead aquifer is thought to be used each year. Since 2000 the usage has ranged between 23,000 and 30,000 ML/year in the Campaspe Deep Lead WSPA. This usage is typically focused in the south. In Ellesmere GMA, only small volumes are extracted. However, the volumes have increased from around 500 ML/year in the 1990s to 3,200 ML/year in 2005/ Goulburn-Broken (Mid-Goulburn GMA, Kialla GMA, Goorambat GMA) The Goulburn-Broken management unit contains the Shepparton and Deep Lead aquifers (Calivil Formation and Renmark Group). The lower Shepparton Formation aquifers are sandy and have high hydraulic conductivities. This aquifer is thought to be thin, irregular, disconnected and partially confined by silt/clay layers, and to contain high salinity groundwater. The Upper Shepparton Formation is more clay and silt rich and therefore has lower permeability. Aquifers in this area have elevated salinity levels due to evapotranspiration during infiltration and directly from the watertable. Hydraulic conductivities in the Shepparton can be as much as 30 m/day in the sandy units and salinities vary between 1,000 and 20,000 mg/l TDS. The Calivil Formation and Renmark Group are considered together to form the Deep Lead aquifer, which has hydraulic conductivities up to 200 m/day and salinities ranging between 300 and 2,400 mg/l TDS. The upper Deep Lead aquifer has fresh water with low salinity, which suggests that there is little vertical mixing with the more saline Shepparton Formation groundwater. However, the lower Deep Lead aquifer has higher salinity values (1,210 to 2,400 µs/cm) suggesting lateral or downward flow from the Shepparton Formation. The three main processes of recharge to the Shepparton Formation are through rainfall infiltration via the land surface, leakage from waterways crossing through the area, and irrigation. Recharge to the Deep Lead aquifer is dominated by leakage from the overlying Shepparton Formation. There is also considered to be significant recharge via direct rainfall infiltration where the Calivil Formation outcrops along the southern margins of the MDB (SKM, 2006). Large volumes of water are discharged via groundwater flow to the north, and to a lesser extent discharge to rivers and streams in times of low flow. Evapotranspiration from the shallow watertables may also be significant, particularly in the north during wetter climatic periods when shallow watertables are evident (SKM, 2006). A significant number of shallow extraction bores are in operation in the north for salinity control purposes (refer to Shepparton WSPA). Groundwater extractions from the Deep Lead are mainly located in the south around Avenel in the Mid-Goulburn GMA with smaller volumes extracted from within the Kialla and Goorambat GMAs. In 2004/05 and 2005/06 approximately 3,500 ML/year was extracted from the Mid-Goulburn GMA. In the Kialla and Goorambat GMAs approximately 850 ML/year and 550 ML/year were extracted respectively Shepparton WSPA The Shepparton WSPA spans the Murray, Campaspe and Goulburn-Broken regions and refers specifically to the Shepparton Formation aquifer. In the Shepparton WSPA the sands and gravels of the Shepparton Formation are capable of supplying large quantities of water. However, due to its irregular salinity it has not, in the past, been considered a reliable source of water for irrigation. This situation has changed in recent drought years as many irrigators are mixing the brackish groundwater with fresh surface water supplies to enhance irrigation water supplies. The area is intensively irrigated and is serviced by an extensive network of surface water supply channels. As a consequence of the intensive irrigation the area is also prone to shallow watertables and salinity problems (GMW, 2006). To control the rising watertables, large volumes of mostly saline water are pumped from shallow spearpoint bores into drainage channels. Shallow salinity control pumping represents a significant volume of total extractions from the Shepparton WSPA. Groundwater usage in the Shepparton WSPA between 1989 and 2006 is estimated to have 8 Southern Riverine Plains Groundwater Model Calibration Report CSIRO 2008

21 averaged approximately 78,500 ML/year. Since 2000 groundwater extractions have varied between an estimated 62,000 and 187,000 ML/year. CSIRO 2008 Southern Riverine Plains Groundwater Model Calibration Report 9

22 3 Model development 3.1 Model domain Study area The model domain covers an area of 292 by 250 km and utilises a 1 km 2 grid cell resolution (Figure 3-1). In the south, outcropping bedrock forms the boundary of the active model domain and the northern boundary is defined by Billabong Creek (Figure 3-2). This northern boundary is inherited from the existing Lower Murray groundwater model. The aquifers represented in the Lower Murray model are also active in the Lower Murrumbidgee groundwater management unit located immediately to the north of this boundary. Consequently any model fluxes across this northern boundary will potentially impact on or interact with the groundwater model to the north. The western boundary is defined by the Murray River north of its confluence with the Loddon River. South of this point, the western boundary is defined by a bedrock high that runs approximately north south between the Loddon and Avoca rivers. Active model cell extents in each of the modelled aquifers can also be seen in Figure 3-4 through Figure 3-7. Figure 3-1. Southern Riverine model grid and coordinates in Lambert Conical Conformance projection 10 Southern Riverine Plains Groundwater Model Calibration Report CSIRO 2008

23 Figure 3-2. Southern Riverine model domain including groundwater management areas and inactivated areas Coordinate system The model utilises the Lambert Conical Conformance coordinate system (LCC). Spatial parameters are defined in Table 3-1 (see also Figure 3-1). Table 3-1. Spatial parameters of the model coordinate system Projection Datum Zunits Units Spheroid South-west model boundary North-east model boundary LAMBERT GDA94 NO METERS GRS E, N E, N Model layering The groundwater model is divided into four active layers based on the hydrogeological conceptualisation of the area ( Figure 3-3): Upper Shepparton Formation Lower Shepparton Formation Calivil Formation Renmark Group. Leakage between aquifer layers is modelled through the use of vertical hydraulic conductivities. These conductivities are adjusted during the model calibration to achieve the observed hydraulic gradients. The distinction between the Upper and Lower Shepparton is somewhat arbitrary as the formation is considered to be extremely variable in character. Inclusion of two model layers to represent the Shepparton Formation allows additional flexibility in modelling vertical fluxes from the surface to the Deep Lead aquifers and enables the inclusion of aquitards if necessary above the Calivil Formation. Maps of layer thickness for each of the model layers are presented in Figure 3-4 through Figure 3-7. CSIRO 2008 Southern Riverine Plains Groundwater Model Calibration Report 11

24 Figure 3-3. East west cross-section of the Southern Riverine model highlighting the hydrogeological layering structure of the model (vertically exaggerated by 300 times) Figure 3-4. Thickness of the Upper Shepparton Aquifer 12 Southern Riverine Plains Groundwater Model Calibration Report CSIRO 2008

25 Figure 3-5. Thickness of the Lower Shepparton Aquifer Figure 3-6. Thickness of the Calivil Formation Aquifer CSIRO 2008 Southern Riverine Plains Groundwater Model Calibration Report 13

26 Figure 3-7. Thickness of the Renmark Group Aquifer 14 Southern Riverine Plains Groundwater Model Calibration Report CSIRO 2008

27 3.2 Model input data Storage parameters Table 3-2 defines the storage parameters (specific yield and specific storage) utilised in the model. The confined storage parameter, specific storage, is defined per meter of aquifer thickness and hence the effective storage coefficient can be obtained by multiplying the specific storage by the aquifer thickness. These values were derived through the calibration process through which it was found that extremely small storage parameters were required to achieve the observed levels of pumping-related drawdown in New South Wales. The issues related to matching the observed levels of drawdown are further discussed in Section 4.2. Table 3-2. Storage parameters defined in the model Aquifer Aquifer type Storage parameter New South Wales Victoria Upper Shepparton Unconfined Specific yield (Sy) Lower Shepparton Confined Specific storage (Ss) 1 x x 10-6 Calivil Confined Specific storage (Ss) 1 x x 10-6 Renmark Confined Specific storage (Ss) 1 x x Hydrogeological conductivity values Hydraulic conductivity values are shown in Figure 3-8 through Figure The Shepparton Formation is characterised by variable hydraulic conductivity and this is reflected in the model parameters. Typically horizontal conductivities range between 0.5 and 5 m/day. However, they have been modelled as high as 75 m/day in a small pocket in the upper reaches of the Goulburn-Broken catchment. In the north of the model area there is very little difference in vertical hydraulic conductivities between the upper and lower Shepparton Formation. Consequently modelled layers 1 and 2 behave as one aquifer. Further south the Upper Shepparton often becomes more hydraulically conductive and the Lower Shepparton acts as a confining layer. The Calivil Formation and Renmark Group are both comprised of highly hydraulically conductive material. Model horizontal hydraulic conductivities in these aquifers are typically between 50 and 100 m/day. The exception to this is in the north-east near Jerilderie where hydraulic conductivities reduce to as low as 5 m/day. CSIRO 2008 Southern Riverine Plains Groundwater Model Calibration Report 15

28 Figure 3-8. Hydraulic conductivity values in Layer 1 (Upper Shepparton Formation) 16 Southern Riverine Plains Groundwater Model Calibration Report CSIRO 2008

29 Figure 3-9. Hydraulic conductivity values in Layer 2 (Lower Shepparton) CSIRO 2008 Southern Riverine Plains Groundwater Model Calibration Report 17

30 Figure Hydraulic conductivity values in Layer 3 (Calivil Formation) 18 Southern Riverine Plains Groundwater Model Calibration Report CSIRO 2008

31 Figure Hydraulic conductivity values in Layer 4 (Renmark Group) CSIRO 2008 Southern Riverine Plains Groundwater Model Calibration Report 19

32 3.2.3 Rivers and drains A large amount of river gauge data exists for all of the major rivers included within the Southern Riverine model area. River level data was sourced from Thiess Environmental Ltd. for all Victorian gauges and Department of Water and Energy for all New South Wales river gauges. A list of the river gauges is provided in Appendix A. Where data gaps were present in the time series, a linear interpolation was applied from the nearest available gauge. Where previous groundwater models were available (namely Campaspe and Lower Murray), river gauge data was sourced from these models. The rivers included in the model are represented by the bold dark blue cells in Figure Only the main stems of major rivers are included in the model. As Figure 3-13 shows, this represents only a minor percentage of all natural surface water features and an even smaller percentage when man-made drainage features are considered. To account for tributaries and drainage channels that cannot be explicitly modelled, a number of drainage areas were included in the model. These are represented by the shaded grey areas in Figure Drainage cells have only been placed in areas that are prone to shallow watertables and are designed to mimic natural or man-made drainage features that would act to intercept rising watertables. These are particularly common in the irrigated areas of New South Wales. In Modflow, drain cells may act only as groundwater discharge points, as opposed to river cells which can act as both recharge and discharge sites. The majority of surface drains (both natural and man-made) are directly hydraulically connected to the rivers. Therefore it is recommended that when using this model to assess stream aquifer interactions, model-predicted discharges to drains should contribute to the total. Figure Rivers and drains included in the Southern Riverine model 20 Southern Riverine Plains Groundwater Model Calibration Report CSIRO 2008

33 Figure All natural surface water features within the Southern Riverine model domain Recharge (dryland and irrigation) Dryland rainfall recharge and irrigation recharge are both incorporated into the model. Of the three previous models within the model domain, only the Campaspe model had readily replicable recharge inputs. The Katunga model utilised constant heads across layer 1 to provide a recharge flux into the top of the model. The Lower Murray model utilised a pilot point calibration process to define a spatially variable recharge pattern across the model. Such an approach was deemed to be inappropriate for the current model in light of the size and resolution of the model. Given the size of the model a methodology was developed that would provide consistency across the model domain whilst providing a recharge input data set that could be manipulated easily in both the calibration and scenario modelling processes. The methodology used to create the recharge data set is summarised below: The model domain was divided into rainfall districts as defined by the Bureau of Meteorology (2006). These rainfall districts define zones of similar rainfall on a resolution deemed appropriate given the model extent (Figure 3-14). Areas of irrigation were identified from satellite imagery (Figure 2-1). These areas include both surface water and groundwater derived irrigation (Figure 3-15) The rainfall districts and irrigation districts were superimposed onto each other creating a set of recharge zones. Twenty locations (rainfall sites) were identified across the model area where rainfall data was to be collated (Figure 3-16). The rainfall sites were assigned to 24 separate recharge zones in Visual Modflow (Figure 3-17). Rainfall for each rainfall site was extracted from the SILO database. Rainfall was scaled to calculate dryland rainfall recharge. Irrigation, where applicable, was added as a constant recharge volume between the months of November and April inclusive. Irrigation was applied in addition to the appropriate rainfall recharge. CSIRO 2008 Southern Riverine Plains Groundwater Model Calibration Report 21

34 During calibration it became apparent that groundwater recharge was decreasing significantly in the model calibration period (i.e. more than was occurring through the natural reduction in rainfall that has been observed throughout the Riverine Plains). This was particularly prevalent in the northern half of the model. Thus an irrigation efficiency scaling factor was introduced. This scaling factor accounts for the improvements in irrigation efficiency that have occurred since the early 1990s. Significantly it is considered that the volume of irrigation water reaching the watertable has been reduced by a number of factors including infrastructure improvements, drainage schemes and climate. As a simple means of implementing this process, irrigation-induced groundwater recharge was assumed to decrease by 8% per year starting in 1994 to a total reduction of 80% by This was invoked over Modflow recharge zones 2 to 7 (across the northern half of the model). Note: The irrigation efficiency factor was invoked in New South Wales in response to the model s inability to match the magnitude of observed drawdown cones, particularly in the area of Deniliquin and west toward Swan Hill. It is acknowledged that reduced irrigation recharge may not be the only explanation for the drawdown, i.e. climate-induced variations and inaccuracies in the metered pumping estimates may also have contributed to this. It is likely that the drawdown is attributable to all three explanations. However, in light of available data the most acceptable calibration scaling tool was deemed to be the irrigation accessions. Table 3-3 displays the recharge zones, land use, irrigation intensity, rainfall scaling factors and average annual recharge for the period 1990 to Southern Riverine Plains Groundwater Model Calibration Report CSIRO 2008

35 Modflow recharge zone Table 3-3. Southern Riverine modelled recharge zones SILO rainfall site Land use Irrigation zone Irrigation Rainfall scaling factor mm/y Average annual recharge Medium irrigation Mulwala Canal Low irrigation Medium irrigation Wakool High irrigation Wakool Dryland Medium irrigation Swan Hill Dryland Dryland Medium irrigation Loddon Medium irrigation Barham Dryland Dryland Dryland High irrigation Campaspe Dryland Dryland High irrigation Shepparton High irrigation Katunga High irrigation Goulburn-Broken Dryland Dryland Very low irrigation mm/y Forest CSIRO 2008 Southern Riverine Plains Groundwater Model Calibration Report 23

36 Figure Rainfall districts as defined by the Bureau of Meteorology (2006) Figure Satellite imagery highlighting irrigation areas incorporated into the Southern Riverine model 24 Southern Riverine Plains Groundwater Model Calibration Report CSIRO 2008

37 Figure Rainfall sites (1 to 20) input into the Waves Model to deduce dryland recharge variability across the model CSIRO 2008 Southern Riverine Plains Groundwater Model Calibration Report 25

38 Figure Southern Riverine model recharge zones Evapotranspiration The Modflow groundwater evapotranspiration (ET) package is used to simulate ET from shallow watertables. An extinction depth (depth below natural surface) is set to identify the watertable depth below which no ET will occur. Consequently large areas of the model are unaffected by ET. ET was set at a maximum rate of 120 mm/year with an extinction depth of 2 m across the majority of the model domain. Under forested areas, in particular Gunbower and Barmah forests, the ET rate and extinction depths were both increased to simulate the high levels of ET believed to occur from these areas. In other areas the ET rate was altered to account for discrepancies between observed watertable elevations and the model DTM (Digital Terrain Model). These discrepancies often occur due to the large grid cell size. The pattern of ET set across the model is displayed in Figure Southern Riverine Plains Groundwater Model Calibration Report CSIRO 2008

39 Figure Groundwater evapotranspiration rates set across the Southern Riverine model Boundary conditions Groundwater flow is typically in a northwesterly direction, approximately following the drainage path of the Murray River. Consequently to allow for movement of groundwater out of the model domain, general head boundaries were included in the north-west corner of the model (Figure 3-19). These boundaries were added to the model in the Lower Shepparton, Calivil and Renmark aquifers (layers 2, 3 and 4 respectively). All other model boundaries were designated as no flow boundaries as the majority of the area is bordered by outcropping bedrock. The one exception was in the north and north-east where despite the lack of a physical barrier to groundwater movement a no flow boundary is still used. The key reasons for this are as follows: Groundwater flow under the northern boundary is typically in a westerly direction (i.e. parallel to the boundary). Consequently it is conceptualised that there is little flow of water across this boundary. The extent of interference effects from the aquifers in the neighbouring Murrumbidgee catchment is unclear. Including a general head boundary in this part of the Southern Riverine model would predispose the model to draw water from the neighbouring aquifer under prolonged pumping. In light of the fact that a similar groundwater model has been developed for the Lower Murrumbidgee aquifer it is considered inappropriate that both models can source water from across the common boundary. Given the uncertainty involved (and the nature of the scenario modelling in this project which aims to run to dynamic equilibrium) it was deemed more appropriate to allocate a no flow boundary. In doing so, groundwater recharge is restricted to real processes such as rainfall and river leakage occurring within the model domain, as opposed to recharge processes that may occur outside the model domain. CSIRO 2008 Southern Riverine Plains Groundwater Model Calibration Report 27

40 Two additional general head boundaries were added to small sections in the Campaspe Deep Lead (not shown) and Mid-Goulburn (shown below). These were used to simulate groundwater movement between the Deep Lead and the bedrock. Figure General head boundaries 28 Southern Riverine Plains Groundwater Model Calibration Report CSIRO 2008

41 4 Model calibration 4.1 Calibration method The model was calibrated in transient mode by matching model-predicted groundwater responses to measured groundwater hydrographs in a series of observation bores spread across the model domain. The calibration model was constructed using monthly stress periods from January 1990 to December 2005 (16 years, 192 months). A relatively short calibration period was selected for the following reasons: Due to the size of the model, run times were a key consideration. Therefore a shorter calibration period was preferred. From the mid-1990s and peaking in 2002/03 there was significant development of the groundwater resources in the model domain which saw usage increase from under 100 GL/year to over 400 GL/year. By including this period the model is calibrated over both low and high groundwater usage conditions. An iterative approach was used to refine model parameters in order to optimise the match to observed water levels. Priorities of the calibration were to achieve the following: reproduction of the long-term trends in observation bore hydrographs (in particular long-term drawdown trends) appropriate representation of vertical hydraulic gradients at nested bore sites accurate representation of river interactions via the matching of seasonal fluctuations in shallow watertable bores located near the major rivers. The calibration model was evaluated based on four criteria as specified in the Murray-Darling Basin Commission Groundwater Flow Modelling Guidelines (Middlemis, 2000). These criteria are summarised in Table 4-1. Table 4-1. Calibration model performance criteria (after Middlemis, 2000) Performance measure Water balance Iteration residual error Qualitative measures Quantitative measures Criteria A value of less than 1% should be obtained for the water balance error term for each stress period and cumulatively for the entire simulation. Iteration convergence criterion should be one to two orders of magnitude smaller than the level of accuracy desired in the model head results. Commonly set in the order of millimetres or centimetres. Subjective assessment of the goodness of fit between modelled and measured groundwater level contour plans and hydrographs of bore water levels and surface flows. Justification for adopted model aquifer properties in relation to measured ranges of values and associated non-uniqueness issues. Residual head statistics criteria (specifically the Normalised Root Mean Squared, RMS). Given the intermediate model complexity a normalised RMS less than 10% is considered acceptable. Consistency between modelled head values (in contour plans and scatter plots) and spot measurements from monitoring bores. Comparison of simulated and measured components of the water budget, notably surface water flows, groundwater abstractions and evapotranspiration estimates Groundwater extraction The following section is reported by state in reference to the differing groundwater data sources. New South Wales groundwater extraction data Historical estimates of groundwater extractions have previously been compiled as part of the existing Lower Murray (GWMA 016) groundwater model. This data covered the period 1985 to Metered groundwater usage data for the period 1999/00 to 2005/06 was provided by the New South Wales Department of Natural Resources to allow the extension of the data to cover the Southern Riverine model calibration period. Metered data has its own limitations in that it may not represent the total volume pumped from the aquifer (i.e. it may not include all extraction sites). In recognition of the limitations with groundwater usage data a methodology was developed to allow for extraction data to be scaled CSIRO 2008 Southern Riverine Plains Groundwater Model Calibration Report 29

42 such that the total annual usage for all extraction bores included in the model corresponds with the best estimates of annual groundwater usage. This methodology is as follows: Total annual pumping at each bore is calculated based on available data from the Lower Murray model and recent metered data. An initial total annual pumping volume is calculated for all bores. Best estimates of actual groundwater usage were provided by the New South Wales Department of Natural Resources (Table 4-2 and Figure 4-1). All groundwater bores are scaled such that the modelled groundwater usage equals the best estimates of actual groundwater usage. The annual total of groundwater usage at every bore was distributed into a monthly time series. This distribution followed that utilised in the Lower Murray Groundwater Model (DLWC, 2001) as shown in Figure 4-2. Table 4-2. Estimated groundwater usage in New South Wales (supplied by the New South Wales Department of Natural Resources) Financial year GWMA016 (Deep Lead) Shepparton ML/y 1989/ / / / / / / / / / / / / / / / / Groundwater Usage (GL/yr) NSW - Deep Lead NSW - Shepparton 1989/ / / / / / / / /06 Figure 4-1. Estimated volumes of groundwater extractions in New South Wales 30 Southern Riverine Plains Groundwater Model Calibration Report CSIRO 2008

43 Percent of Groundwater Pumping Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Figure 4-2. Distribution of groundwater pumping throughout a calendar year Victorian groundwater extraction data Groundwater extraction data for the Victorian half of the model was provided by Goulburn-Murray Water (GMW). A summary of the data provided follows: all available metered groundwater usage data. This includes metered bores from Campaspe Deep Lead WSPA, Katunga WSPA, Shepparton WSPA, Kialla GMA, Mid-Goulburn GMA and Mid-Loddon GMA. Metered data usually covered the period from 1999/00 to 2005/06 a list of all licensed groundwater extraction bores within the GMW area including licensed volumes estimated groundwater usage as a percentage of total licensed volume for each GMA (or WSPA) and for all unincorporated areas lists of active and sleeper licences within each GMA. As per the New South Wales data it was not possible to source accurate groundwater usage for every bore on a monthly time step for the whole calibration period (1990 to 2006). Most records of metered data only began around 1999 and there remains a large number of bores that are not metered, both outside and within GMA boundaries. Consequently a methodology was suggested by GMW to estimate the actual groundwater usage from each bore. This methodology is summarised as follows: Bore construction dates for all licensed extraction bores were extracted from the Victorian Groundwater Management System database. The bore construction date is assumed to be the year in which the groundwater licence is issued and groundwater pumping commenced. The total licensed volume for each GMA, WSPA and the unincorporated areas for each year within the calibration period was calculated. Actual metered groundwater usage data was collated where available. In years, or areas, where metered data was not available, GMW provided estimated groundwater usage as a percentage of total licensed volume. The total licensed volumes for each bore was scaled such that the total modelled volume of usage equalled the total metered volume or the estimated total use. Final groundwater usage estimates are provided in Table 4-3, Table 4-4 and Figure 4-3. A map of all groundwater extraction sites is provided in Figure 4-4. CSIRO 2008 Southern Riverine Plains Groundwater Model Calibration Report 31

44 Area Campaspe Deep Lead Table 4-3. Groundwater usage estimates in Victorian groundwater management units Goorambat Katunga Kialla Mid- Goulburn ML/y Mid-Loddon Ellesmere Shepparton Total (incl NSW) 1989/ ,432 1,281 1,091 8, ,477 96, / ,076 1,281 1,094 8, , , / ,151 1,281 1,094 8, , , /93 3, ,161 1,281 1,094 8, , , /94 11, ,500 1,286 1,188 8, , , /95 15, ,653 1,286 1,689 11, , , /96 13, ,977 1,286 1,338 9, , , /97 19, ,100 1,407 1,490 9, , , /98 18, ,122 1,424 2,304 11, , , /99 14, ,101 1,424 2,150 9, , , /00 22, ,645 1,435 2,192 9, , , /01 15, ,795 1,424 2,192 7, , , /02 26, ,873 1,424 2,923 14, , , /03 31, ,470 1,424 2,482 18,435 1, , , /04 23, , ,120 14,095 2,273 62, , /05 26, , ,596 15,580 2,521 70, , /06 23, , ,491 15,832 3,188 94, ,206 Average 15, ,860 1,266 2,090 11, , ,177 Table 4-4. Groundwater usage estimates for Victorian unincorporated areas (grouped by catchment) Area Avoca Broken Campaspe Goulburn Loddon Ovens Total 1989/ / / , / , / , / , / , / , / , , / , / , , / , , / , , , / , ,249 1,312 5, / ,695 1,039 4, / ,723 1,039 4, / ,724 1,041 5,020 Average , , Southern Riverine Plains Groundwater Model Calibration Report CSIRO 2008

45 Groundwater Usage (GL/yr) Unincorporated Murmungee Ellesmere Mid-Goulburn Kialla Goorambat Mid-Loddon Campaspe Deep Lead Katunga Shepparton / / / / / / / / /06 Figure 4-3. Estimated groundwater usage in the Victorian groundwater management units and unincorporated areas Figure 4-4. Groundwater extraction wells included in the Southern Riverine model Note: Groundwater extraction wells in New South Wales appear to line up in rows and columns. This is an artefact of the import of the wells from the existing Lower Murray groundwater model that was constructed on a 2.5 km grid (DLWC, 2001). CSIRO 2008 Southern Riverine Plains Groundwater Model Calibration Report 33

46 4.1.2 Calibration model observation bores In total 142 monitoring wells were utilised in the calibration of the Southern Riverine model. Many of these are nested water level observation sites where water levels from different aquifer depths are monitored at the one location. Calibration bores cover the entire model domain in all layers (Figure 4-5 to Figure 4-8). A list of all observation bores, including coordinates and aquifer screened, is also included in Appendix B. Figure 4-5. Observation bores screening the Upper Shepparton 34 Southern Riverine Plains Groundwater Model Calibration Report CSIRO 2008

47 Figure 4-6. Observation bores screening the Lower Shepparton Figure 4-7. Observation bores screening the Calivil Formation CSIRO 2008 Southern Riverine Plains Groundwater Model Calibration Report 35

48 Figure 4-8. Observation bores screening the Renmark Group 4.2 Calibration model results All calibration model hydrographs are presented in Appendix C. Potentiometric surface comparisons and calibration statistics are provided in Section Summary of hydrographs by region Murray The calibration in the Murray region attempted to match the magnitude of observed drawdown that occurred during the period from the mid-1990s to approximately 2004/05. This drawdown is considered to be a consequence of belowaverage rainfall in the region combined with large increases in deep lead pumping during the period. Through manipulation of hydraulic parameters alone it proved very difficult to achieve both the depth and breadth of the drawdown cone (centred near Deniliquin). As previously explained in Section 3.2.4, an irrigation efficiency factor was introduced to reduce the net recharge in the Lower Murray region and subsequently induce greater drawdown. This proved effective. However, it is acknowledged that the rate and magnitude of observed drawdown is not completely achieved in the final calibrated model. An example of this is provided in Figure 4-9 where the rate of observed drawdown is greater than the rate of calculated drawdown. This example also depicts the model s preferential calibration to the later time data which provides a closer fit than data from the early 1990s. This outcome is consistent with general queries raised as to the accuracy of the earlier extraction data (M. Williams, DWE, pers. comm.). In the east near Jerilderie, there is a distinctive rising trend in water levels, particularly in the Shepparton Formation. The model reproduces these rising trends with reasonable accuracy as shown in Figure An additional hydrogeological pattern that the model attempted to preserve was a significant shift in the head difference between the Upper Shepparton and the deeper aquifers. This is observed as falling heads in the deep aquifers in 36 Southern Riverine Plains Groundwater Model Calibration Report CSIRO 2008

49 contrast to relatively stable heads in the Upper Shepparton (often restricted by drainage and shallow pumping). This occurs at many locations throughout the Murray region, in particular in the south near Echuca (refer to example in Figure 4-11). In the Gunbower Forest area the calibration process highlighted the importance of forest evapotranspiration. The introduction of an increased rate of evapotranspiration and deeper extinction resulted in a good calibration across most of the forested area (Figure 4-12). In this area observed hydrographs depict relatively stable water levels with a slight downward trend from the mid-1990s. Calculated hydrographs generally represent this pattern well. Where inaccuracies occurred, this was typically in the Shepparton Formation and believed to be a result of steep hydraulic gradients along the river which makes accurate modelling at this scale difficult. In the north of the Loddon catchment, near the Murray River, observed hydrographs depict relatively stable water levels with a slight downward trend from the mid-1990s. This is generally well reproduced in the model. At one nested site (see Figure 4-13) a complex relationship between the formations is observed. This site shows heads in the Lower Shepparton consistently higher than both the Upper Shepparton and the Renmark Group aquifer. This is not observed elsewhere in the Loddon region and may indicate a bore failure. The modelled levels indicate minimal variation in heads between layers. Bore in the north-east of the region (toward Gunbower Forest) displays a trend after 2000 that may suggest the impacts of groundwater pumping from further west and/or north-west. The Katunga WSPA, representing approximately 10% of total usage in the Victorian half of the model, has some of the largest drawdowns (both seasonal and long-term) in the region. Fortunately this area also has a large amount of reliable data available via metering and previous studies (e.g. GMW, 2006a). Consequently a good correlation was achieved between observed and modelled hydrographs, particularly in the Deep Lead. However, the same level of correlation was not obtained in the watertable aquifer (Figure 4-15). This is likely to be a product of the complex variability (in time and space) of irrigation schemes combined with extensive shallow pumping and drainage for salinity control purposes that are difficult to replicate in the regional model Layer 2 (CAL) Layer 2 (OBS) Layer 4 (CAL) Layer 4 (OBS) Layer 3 (CAL) Layer 3 (OBS) 65 Figure 4-9. Example hydrographs from the Murray region near Deniliquin (note: this is not a nested site) CSIRO 2008 Southern Riverine Plains Groundwater Model Calibration Report 37

50 Layer 1 (CAL) Layer 1 (OBS) Layer 1 (CAL) Layer 1 (OBS) Layer 1 (CAL) Layer 1 (OBS) 100 Figure Example hydrographs from the Murray region in the east between Corowa and Jerilderie Layer 3 (CAL) Layer 3 (OBS) Layer 1 (CAL) Layer 1 (OBS) 70 Figure Example hydrographs from the Murray region in the south near Echuca 38 Southern Riverine Plains Groundwater Model Calibration Report CSIRO 2008

51 Layer 4 (CAL) Layer 4 (OBS) Layer 4 (CAL) Layer 4 (OBS) 60 Figure Example hydrographs from the Murray region in Gunbower Forest Layer 1 (CAL) Layer 1 (OBS) Layer 2 (CAL) Layer 2 (OBS) Layer 4 (CAL) Layer 4 (OBS) 60 Figure Example hydrographs from the north of the Loddon catchment in the Murray region CSIRO 2008 Southern Riverine Plains Groundwater Model Calibration Report 39

52 Layer 1 (CAL) Layer 1 (OBS) 70 Figure Example hydrographs from the north-east of the Loddon catchment in the Murray region Layer 3 (CAL) Layer 3 (OBS) Layer 1 (CAL) Layer 1 (OBS) 70 Figure Example hydrographs from the Katunga WSPA within the Murray region Loddon-Avoca With the exception of the northern end of the Mid-Loddon GMA, the Loddon-Avoca region generally has poor spatial coverage of observation bores. This is a result of the lack of groundwater development north of the GMA due to the poor quality groundwater in the region. In the Mid-Loddon GMA the calibration was aimed at matching drawdowns observed since the mid-1990s, a result of climate and increasing extractions (Figure 4-16). This was replicated at all sites except for nested site and (Figure 4-17) which was anomalous in that the observed hydrographs did not show the same level of long-term 40 Southern Riverine Plains Groundwater Model Calibration Report CSIRO 2008

53 drawdown as observed elsewhere in the GMA. It is likely that this is a result of localised conditions (possibly irrigationinduced mounding) that could not be replicated in a regional model Layer 1 (OBS) Layer 1 (CAL) Layer 2 (OBS) Layer 2 (CAL) Figure Example hydrographs from the Mid-Loddon GMA Layer 1 (CAL) Layer 1 (OBS) Layer 3 (CAL) Layer 3 (OBS) 90 Figure Example hydrographs from the Mid-Loddon GMA Campaspe The significant levels of long-term drawdown observed in the Deep Lead aquifer and the relatively static watertable levels were the focus of calibration in the Campaspe region. A good example of this is shown in the hydrographs in Figure 4-18 (near Echuca) where the model replicates this trend well. At a number of sites the model was under estimating the level CSIRO 2008 Southern Riverine Plains Groundwater Model Calibration Report 41

54 of seasonal drawdown however, the long-term drawdown was being reproduced (e.g. Figure 4-19). The inability to reproduce the seasonal drawdown was considered to be of lesser importance to the long-term trend. Accurate calibration became more difficult toward the south, where natural surface elevations and watertables change rapidly (adjacent cells can have elevation differences of 20 m or greater). The Deep Leads in the south are also prone to increasing interference from localised processes that are not represented in a regional model. Nevertheless, long-term trends have generally been preserved despite the model not achieving some of the seasonal drawdown levels observed in some of the hydrographs (e.g. Figure 4-20) Layer 4 (CAL) Layer 4 (OBS) Layer 1 (CAL) Layer 1 (OBS) 70 Figure Example hydrographs from the Campaspe region near Echuca Layer 4 (CAL) Layer 4 (OBS) Layer 1 (CAL) Layer 1 (OBS) 65 Figure Example hydrographs from the Campaspe region 42 Southern Riverine Plains Groundwater Model Calibration Report CSIRO 2008

55 Layer 3 (CAL) Layer 3 (OBS) Layer 2 (CAL) Layer 2 (OBS) 110 Figure Example hydrographs from the Campaspe region Goulburn-Broken The southern extents of the Goulburn-Broken region proved to be the most difficult region to calibrate, largely due to the very steep topographic gradients (and similarly steep groundwater level gradients). The Modflow groundwater modelling package is prone to becoming highly unstable in such terrain and particularly where there is a large groundwater gradient between adjacent cells. In the area near Goulburn Weir this proved to be a particular problem where attempts to force steep gradients often resulted in model convergence failures. An example of this is shown in Figure 4-21 where the steep gradients observed between bores and were not able to be preserved due to model stability issues. Another site particularly prone to this problem was bore which is located next to a bedrock high. Elsewhere in the Goulburn-Broken region, particularly in the flatter areas of the north, a generally good calibration was reached with trends similar to those seen in the Campaspe and Katunga WSPAs (Figure 4-22 and Figure 4-23). CSIRO 2008 Southern Riverine Plains Groundwater Model Calibration Report 43

56 Layer 1 (CAL) Layer 1 (OBS) Layer 3 (CAL) Layer 3 (OBS) Layer 1 (CAL) Layer 1 (OBS) Figure Example hydrographs from the Goulburn-Broken region Layer 3 (CAL) Layer 3 (OBS) Layer 1 (CAL) Layer 1 (OBS) 85 Figure Example hydrographs from the Goulburn-Broken region 44 Southern Riverine Plains Groundwater Model Calibration Report CSIRO 2008

57 Layer 3 (CAL) Layer 3 (OBS) Layer 2 (CAL) Layer 2 (OBS) Layer 3 (CAL) Layer 3 (OBS) 100 Figure Example hydrographs from the Goulburn-Broken region 4.4 Potentiometric surface maps Maps comparing observed versus modelled potentiometric surfaces have been used to ensure the model is adequately representing the intermediate to regional scale flow systems. The maps are presented in Figure 4-24 through to Figure These present potentiometric surfaces from both the Shepparton Formation and the Deep Lead at two separate times during the calibration period: March 1995, five years into the calibration period. This time was selected as it is far enough from the start of the model run such that any model instabilities at initialisation should have decayed. It is also the start of the period when there was significant growth in the use of the groundwater resource across the model domain. May 2003, near the end of the calibration period. This time represents the period in which drawdown is at its greatest during the calibration period. After this time groundwater levels typically started to flatten out (possibly approaching equilibrium). Note: These surfaces were created by contouring data from the model observation bores (Section 4.1.2). Areas with little spatial coverage of observation bores (such as the Loddon catchment) will be less accurate than areas with a good spatial coverage of bores (such as the Campaspe and Katunga WSPAs). Overall the modelled potentiometric surfaces indicate a reasonable match to the observed levels. Importantly the intermediate and regional scale flow processes have been reproduced in both the Shepparton Formation and the Deep Lead aquifer. Typically the highest deviations between the observed and modelled levels occur near the model boundaries. This is due to limitations in modelling boundary conditions, in particular the preference to avoid using nontime varying boundary conditions. CSIRO 2008 Southern Riverine Plains Groundwater Model Calibration Report 45

58 4.4.1 Shepparton Formation Figure Comparison of observed and modelled watertables (Shepparton Formation) based on data from March 1995 Figure Comparison of observed and modelled watertables (Shepparton Formation) based on data from May Southern Riverine Plains Groundwater Model Calibration Report CSIRO 2008

59 4.4.2 Deep Lead Figure Comparison of observed and modelled potentiometric surfaces (Deep Lead) based on data from March 1995 Figure Comparison of observed and modelled potentiometric surfaces (Deep Lead) based on data from May 2003 CSIRO 2008 Southern Riverine Plains Groundwater Model Calibration Report 47

60 4.5 Calibration statistics In large models such as this, calibration statistics are typically considered to be less important than matching hydrographs and potentiometric surfaces. This is because calibration statistics such as correlation co-efficients tend to flatter models with large numbers of observation wells and also large variations in elevation across the model domain. The calibration statistics for the Southern Riverine fall into this category. Therefore, during the calibration process, attention was specifically focused on matching observed hydrographs. Nevertheless, the calibration results presented in Table 4-5 and Figure 4-28 indicate a model that is generally well calibrated even when separated by layer or by region. Figure 4-28 also indicates that there is no significant deviation throughout the model run (i.e. there is no particular period during the calibration run when the model is performing particularly poorly). These statistics are well within the performance criteria specified in Section 4.1. Zone Number of observation wells Table 4-5. Calibration model statistics RMS (m) Normalised RMS (%) Correlation co-efficient All Layer Upper Shepparton Lower Shepparton Calivil Formation Renmark Formation Region New South Wales Loddon Campaspe Goulburn-Broken Katunga Normalised RMS ( % ) Figure Calibration model normalised RMS (%) over the length of the calibration period 4.6 Calibration model water balance Overview The dominant groundwater recharge sources throughout the Southern Riverine Plains are low to high intensity irrigation of large areas across the plains and rainfall infiltration recharge in the southern highlands. There is minimal lateral 48 Southern Riverine Plains Groundwater Model Calibration Report CSIRO 2008

61 groundwater flow into the model as the area is largely bordered by bedrock. However, river leakage is an important recharge mechanism (Figure 4-29). Across the plains groundwater evapotranspiration becomes an important discharge mechanism, particularly under forested areas such as Gunbower and the Barmah Forest. Groundwater evapotranspiration is also important under zones of shallow watertables which are often induced by intensive irrigation. Significant volumes of groundwater also flow out from the model domain toward the north-west, approximately following the flow direction of the Murray River. Refer to Figure 4-30 for a volumetric summary of groundwater discharge mechanisms. The groundwater resource was significantly developed from the mid-1990s, particularly in relation to the deeper aquifers. Accordingly groundwater extraction from pumping wells became an increasingly important component of the water balance during the calibration period. As highlighted in Figure 4-31 groundwater extractions for the total area more than tripled from the early 1990s to its maximum in 2002/03. Impacts of this trend were compounded by decreases in total groundwater recharge 1 driven mostly by climate (including decreases in high streamflow events such as bankfull and overbank events) but also by improvements in irrigation efficiency. Average Flux (GL/yr) Groundwater Recharge Processes 0 Lateral GW Flow River Leakage Rainfall & Irrigation Recharge Storage In Figure Average annual groundwater recharge (GL/year) for the calibration model (January 1990 to December 2005) Groundwater Discharge Processes Average Flux (GL/yr) Lateral GW Flow Pumping Surface Drainage Discharge to River Evapotranspiration Storage Out Figure Average annual groundwater discharge (GL/year) for the calibration model (January 1990 to December 2005) 1 Total groundwater recharge is the sum of rainfall, irrigation, river leakage and lateral groundwater flow in. CSIRO 2008 Southern Riverine Plains Groundwater Model Calibration Report 49

62 Monthly Flux (GL/month) Total Recharge Pumping Figure Total groundwater extractions compared to total recharge (rainfall, irrigation, river leakage and lateral groundwater flow in) Surface groundwater interaction Figure 4-32 and Figure 4-33 present time series data of the river interactions. One of the immediately apparent features is the significant reduction in high flow events after The high flow events in the early part of the record resulted in significant volumes of water recharging the groundwater systems. Then in the months following the flood peak there is a reversal in the hydraulic gradient and significant volumes of groundwater are discharged to the river systems. This ecologically important process has all but ceased after Whilst the major impacts of climate are obvious, the reduced levels of surface groundwater interaction also coincide with a period of intense groundwater development where extractions increased from approximately 150 GL in 1995/96 to approximately 450 GL in 2002/03. The combined impact of increased pumping and a drier climate has altered the state of stream aquifer interactions across the region. This is observed in the slight downward trend in groundwater discharges to rivers after 1997 and the slight upward trend in river leakage. These results are directly attributable to reduced groundwater levels across the region. These trends are not as severe as observed elsewhere in the Murray-Darling Basin. This is a result of intensive irrigation causing shallow groundwater mounding in many areas within the Riverine Plains. 50 Southern Riverine Plains Groundwater Model Calibration Report CSIRO 2008

63 80 River Leakage Net Flux (GL/month) Discharge to River Figure Time series of river leakage and groundwater discharges to the river 100 Net River Loss (incl. Surface Drainage) Net Flux (GL/month). 75 Net River Loss Pumping Figure Time series of net river losses compared to total pumping CSIRO 2008 Southern Riverine Plains Groundwater Model Calibration Report 51

64 4.7 Groundwater management unit water balances A map locating all the GMUs within the model has previously been provided in Figure 2-4. Table 4-6 presents average annual groundwater fluxes for each groundwater management unit within the model domain. This data is averaged over the entire calibration period from January 1990 to December Charts showing this data for each GMU are presented in Figure 4-34 through to Figure Under all scenarios the difference between total inflows and total outflows is either zero or 0.1 GL/year. This falls well within the model water balance performance criteria. Table 4-6. Average annual groundwater inflows and outflows for each groundwater management unit within the model area Groundwater Inflows Recharge Storage Recharge Rivers Flow across model boundary (January 1990 to December 2005) Flow across GMU boundary GL/y Leakage between aquifers Pumping Drains EVT TOTAL Shepparton WSPA n/a n/a n/a n/a Campaspe Deep Lead n/a n/a n/a 43.9 Mid-Goulburn n/a n/a n/a 8.0 Kialla n/a n/a n/a n/a 17.6 Mid-Loddon n/a 2.5 n/a n/a n/a n/a 43.3 Katunga n/a n/a n/a n/a 40.7 NSW GWMA n/a n/a n/a NSW Shepparton n/a n/a n/a Ellesmere n/a n/a n/a n/a 4.9 Goorambat n/a 0.1 n/a n/a n/a n/a 3.2 Unincorporated areas, Shepparton Unincorporated areas, Deep Lead Groundwater Outflows Discharge n/a n/a n/a n/a n/a n/a n/a n/a Shepparton WSPA 77.8 n/a 26.1 n/a Campaspe Deep Lead 0.5 n/a n/a n/a 43.9 Mid-Goulburn 0.0 n/a n/a n/a 8.0 Kialla 0.2 n/a 0.0 n/a n/a n/a 17.6 Mid-Loddon 6.7 n/a 3.4 n/a 15.3 n/a 8.8 n/a Katunga 1.0 n/a 0.0 n/a n/a n/a 40.8 NSW GWMA n/a n/a n/a NSW Shepparton 84.3 n/a Ellesmere 0.8 n/a n/a 0.0 n/a Goorambat 1.0 n/a 0.2 n/a 0.9 n/a 0.2 n/a Unincorporated areas, Shepparton Unincorporated areas, Deep Lead 33.0 n/a n/a 1.7 n/a n/a n/a 0.3 n/a n/a Southern Riverine Plains Groundwater Model Calibration Report CSIRO 2008

65 4.7.1 Lower Murray (NSW GWMA 016) Average Annual Flux (GL/yr) Storage Recharge Rivers Flow across model boundary Flow across GMU boundary Leakage betw een aquifers Groundwater Inflows (GL/yr) Groundwater Outflows (GL/yr) Pumping Drains EVT Figure Water balance for the Lower Murray GWMA (Calivil Formation and Renmark Group) Average Annual Flux (GL/yr) Storage Recharge Rivers Flow across model boundary Flow across GMU boundary Leakage betw een aquifers Groundwater Inflows (GL/yr) Groundwater Outflows (GL/yr) Pumping Drains EVT Figure Water balance for the Lower Murray GWMA (Shepparton Formation) Mid-Loddon Average Annual Flux (GL/yr) Storage Recharge Rivers Flow across model boundary Flow across GMU boundary Leakage betw een aquifers Groundwater Inflows (GL/yr) Groundwater Outflows (GL/yr) Pumping Drains EVT Figure Water balance for the Mid-Loddon GMA CSIRO 2008 Southern Riverine Plains Groundwater Model Calibration Report 53

66 4.7.3 Campaspe Deep Lead Average Annual Flux (GL/yr) Storage Recharge Rivers Flow across model boundary Flow across GMU boundary Leakage betw een aquifers Groundwater Inflows (GL/yr) Groundwater Outflows (GL/yr) Pumping Drains EVT Figure Water balance for the Campaspe Deep Lead WSPA Ellesmere Average Annual Flux (GL/yr) Storage Recharge Rivers Flow across model boundary Flow across GMU boundary Leakage betw een aquifers Groundwater Inflows (GL/yr) Groundwater Outflows (GL/yr) Pumping Drains EVT Figure Water balance for the Ellesmere GMA Katunga Average Annual Flux (GL/yr) Storage Recharge Rivers Flow across model boundary Flow across GMU boundary Leakage betw een aquifers Groundwater Inflows (GL/yr) Groundwater Outflows (GL/yr) Pumping Drains EVT Figure Water balance for the Katunga WSPA 54 Southern Riverine Plains Groundwater Model Calibration Report CSIRO 2008

67 4.7.6 Kialla Average Annual Flux (GL/yr) Storage Recharge Rivers Flow across model boundary Flow across GMU boundary Leakage betw een aquifers Groundwater Inflows (GL/yr) Groundwater Outflows (GL/yr) Pumping Drains EVT Figure Water balance for the Kialla GMA Mid-Goulburn Average Annual Flux (GL/yr) Storage Recharge Rivers Flow across model boundary Flow across GMU boundary Leakage betw een aquifers Groundwater Inflows (GL/yr) Groundwater Outflows (GL/yr) Pumping Drains EVT Figure Water balance for the Mid-Goulburn WSPA Goorambat Average Annual Flux (GL/yr) Storage Recharge Rivers Flow across model boundary Flow across GMU boundary Leakage betw een aquifers Groundwater Inflows (GL/yr) Groundwater Outflows (GL/yr) Pumping Drains EVT Figure Water balance for the Goorambat GMA CSIRO 2008 Southern Riverine Plains Groundwater Model Calibration Report 55

68 4.7.9 Shepparton Average Annual Flux (GL/yr) Storage Recharge Rivers Flow across model boundary Flow across GMU boundary Leakage betw een aquifers Groundwater Inflows (GL/yr) Groundwater Outflows (GL/yr) Pumping Drains EVT Figure Water balance for the Shepparton WSPA 56 Southern Riverine Plains Groundwater Model Calibration Report CSIRO 2008

69 5 Scenario modelling methodology 5.1 Model scenarios Table 5-1 summarises the scenarios that are run as part of the Murray-Darling Basin Sustainable Yields Project. Within this project each scenario is run for 222 years (two model runs of 111 years each). By running over the extended time period the model approaches a dynamic equilibrium state and hence the long-term impact of stresses can be realised. Table 5-1. Summary of the scenario models Scenario State of water resources Climatic conditions A Models the current state of water resource development in the MDB. This includes current average annual surface water and Historical climate conditions from the period July 1895 to June 2006 (111 years). B groundwater diversions and current rates of irrigation. Climatic conditions of the past ten years. For the Southern Riverine Plain region this represents drought conditions. Cdry Cmid Cwet Ddry Dmid Dwet Without development Models an inferred future state of water resource development. This takes into account existing management plans for future developments in water resources. This scenario attempts to recreate conditions prior to the development of the groundwater resource. A future climate scenario based on climate change predictions resulting in a drier climate compared to historical conditions. A future climate scenario based on best estimate or median levels of climate change. In the Southern Riverine Plains this results in a slightly drier climate. A future climate scenario based on climate change predictions resulting in a wetter climate compared to historical conditions. As per Cdry As per Cmid As per Cwet As per scenario A 5.2 Alterations to the calibration model The only alteration to the calibration model was the extension of all the input time series data. There were no changes made to the model structure, model parameters or boundary conditions. All model input time series were extended from the calibration period of January 1990 to December 2005 (16 years, 192 months) to the scenario modelling period of July 1895 to June 2006 (111 years, 1332 months). 5.3 Scenario model inputs Recharge Rainfall data for the period July 1895 to June 2006 were sourced from the SILO database. Data were extracted for the same sites presented in the calibration model (refer Section 3.2.4). Irrigation was assumed to remain constant at rates and areas included for the calibration model in the 2004/05 irrigation season. Recharge reduction factors were applied to all recharge areas as follows: Scenario A 1.00 Scenario B 0.75 CSIRO 2008 Southern Riverine Plains Groundwater Model Calibration Report 57

70 scenarios Cdry and Ddry 0.66 scenarios Cmid and Dmid 0.97 scenarios Cwet and Dwet 1.14 without-development scenario Rivers and drains River stage heights for the scenario modelling are obtained from two surface water models: MSM-BIGMOD the model of the Murray River and its associated distribution network REALM-GSM model covering the Loddon, Campaspe, Goulburn and Broken rivers and associated distribution networks. The majority of river gauges used in the calibration model were available through the two surface water models. However some required interpolation. Where interpolation was required this was done using the nearest available gauge that provided a good correlation with observed model data. The data source for the scenario model gauges is listed in the complete gauge list provided in Appendix A. River data for the without-development scenario was copied from Scenario A Extractions Annual groundwater extraction rates included in the scenario models are shown in Table 5-2. Table 5-2. Groundwater extraction data for the Southern Riverine scenario models Scenario Victorian GMUs New South Wales GMUs A, B, C 2004/05 levels of extraction (as specified in Section 4.1.1) D Without development Average current use for Katunga WSPA and Campaspe Deep Lead WSPA, 60% of entitlement for all other GMUs and unincorporated areas. Katunga WSPA 23,871 ML/year Campaspe DL 24,367 ML/year Mid-Goulburn 6,346 ML/year Mid-Loddon 16,625 ML/year Shepparton 136,654 ML/year Goorambat 852 ML/year Kialla GMA 854 ML/year Ellesmere 4,000 ML/year Unincorporated Areas 8,518 ML/year No groundwater extractions As specified in the Water Sharing Plan for the Murray and Lower Darling Regulated Rivers Water Sources (DIPNR, 2004) GL/year (Deep Lead) 36.0 GL/year (Shepparton) No change as above No groundwater extractions Evapotranspiration No changes were made to evapotranspiration rates. Refer to calibration model data in Section Boundary conditions No changes were made to model boundary conditions. Refer to calibration model data in Section Southern Riverine Plains Groundwater Model Calibration Report CSIRO 2008

71 5.4 Key indicator bores Key indicator bores were selected within all GMUs included in the model. In addition bores were specifically placed in areas of environmental significance, namely the Gunbower-Koondrook-Perricoota Forest and the Barmah Forest. The selected bores are presented in Table 5-3 and Figure 5-1. At each of the sites indicated an observation well is placed in each active model layer to report groundwater hydrographs under each of the scenarios. Table 5-3. Groundwater monitoring sites used in the scenario modelling Bore ID Region X Y Comments Murray Gunbower Forest Murray Gunbower Forest Murray NSW GWMA Murray NSW GWMA Murray NSW GWMA Murray Katunga WSPA Murray Katunga WSPA Murray Katunga WSPA Campaspe Campaspe Deep Lead Campaspe Campaspe Deep Lead Campaspe Campaspe Deep Lead Campaspe Campaspe Deep Lead Loddon Mid-Loddon GMA Loddon Mid-Loddon GMA Loddon Mid-Loddon GMA Loddon Mid-Loddon GMA Goulburn-Broken Mid-Goulburn GMA Goulburn-Broken Shepparton WSPA Goulburn-Broken Shepparton WSPA Goulburn-Broken Shepparton WSPA Goulburn-Broken Shepparton WSPA Goulburn-Broken Mid-Goulburn GMA Goulburn-Broken Mid-Goulburn GMA Goulburn-Broken Mid-Goulburn GMA Campaspe Ellesmere GMA Campaspe Campaspe Deep Lead Campaspe Campaspe Deep Lead Additional sites (not actual monitoring bores) BMSF-1 Murray Barmah Forest BMSF-2 Murray Barmah Forest BMSF-3 Murray Barmah Forest KPF-1 Murray Koondrook-Perricoota Forest KPF-2 Murray Koondrook-Perricoota Forest KPF-3 Murray Koondrook-Perricoota Forest KPF-4 Murray Koondrook-Perricoota Forest MURM-1 Goulburn-Broken Mid-Goulburn GMA CMP-1 Campaspe Campaspe Deep Lead LOD-1 Loddon Mid-Loddon GMA CSIRO 2008 Southern Riverine Plains Groundwater Model Calibration Report 59

72 Figure 5-1. Locations of key indicator bores used in the Southern Riverine scenario modelling 5.5 Integration into the whole-of-mdb modelling framework The whole-of-mdb modelling framework brings together a number of surface water and groundwater models across the MDB, significantly enhancing the ability to account water resources across model, management zone and state boundaries. The Southern Riverine groundwater model acts as an integral link within the framework. It interacts directly with MSM- BIGMOD, a surface water model that simulates the main stem of the Murray River. It also interacts directly with the REALM-GSM, a surface water hydraulic model that simulates the Loddon, Campaspe, Goulburn and Broken rivers in Victoria. The whole-of-mdb modelling framework has been constructed on an automated platform whereby each model can be run automatically, calling upon the necessary outputs from linked models. The process is depicted in its simplest form in Figure 5-2. In the case of the Southern Riverine model, the automated process means that prior to each model run, the groundwater model calls upon the river level data provided by MSM-BIGMOD and REALM-GSM and uses these as inputs for the model run. The groundwater model is then automatically run twice, using the final heads from the first 111 years as input for the second 111 years. In the final stage of the process the groundwater model river fluxes are automatically extracted and reinserted into MSM-BIGMOD and REALM-GSM prior to their final run. This integrated process provides a means of accounting for the combined impacts of both surface water diversions and groundwater extractions (hence reducing the risks of double accounting of water resources). The framework is depicted in Figure Southern Riverine Plains Groundwater Model Calibration Report CSIRO 2008

73 Surface water models run for 111 years, river level data passed to groundwater model. Groundwater model run for FIRST 111 years. Final heads passed to second model run. Groundwater model run for SECOND 111 years. Surface groundwater interaction data returned to surface water model. Surface water models rerun for 111 years. Figure 5-2. Flow diagram summarising surface water model and groundwater model running procedure Figure 5-3. Map of the Murray-Darling Basin Sustainable Yield project integrated modelling framework CSIRO 2008 Southern Riverine Plains Groundwater Model Calibration Report 61

74 5.6 Scenario reporting structure The following three sections describe the results of the scenario modelling undertaken as part of the Murray-Darling Basin Sustainable Yield Project. This is comprised as follows: Section 6 an overview of the results for the entire model area, including data and discussion on the water balance, surface groundwater interactions and groundwater levels Section 7 a summary of the results for each specific GMU. This focuses on a discussion of the water balance for each GMU. Stream aquifer interaction is not reported on a GMU basis. This is in recognition of the inability to attribute river losses to any particular GMU (this would be particularly problematic where GMUs overlie each other, such as the Shepparton WSPA and Katunga WSPA) Section 8 a summary of results by regions and in particular a breakdown of stream aquifer interaction by regions. 62 Southern Riverine Plains Groundwater Model Calibration Report CSIRO 2008

75 6 Scenario modelling results 6.1 Groundwater levels Drawdown maps were created for the Shepparton and Calivil formations, based on the results of the first 111-year model run under Scenario A. The drawdown was calculated as the final heads (June 2006) minus the initial heads (July 1895). By using the winter months, the heads used are recovered levels and hence the effects of seasonal variability are avoided. Consequently the drawdown levels shown can be considered as estimated levels of long-term decline in groundwater level. Figure 6-1 presents the long-term drawdown of the watertable (i.e. the Shepparton Formation aquifer). From this map it is clear that there is very little regional scale depletion of the shallow water resources. This is due to the high rates of irrigation that occur over significant areas of the Riverine Plain. Some of the areas that suggest watertable drawdown in Figure 6-1 are actually model artefacts resulting from instability in the assigned model initial heads. This is particularly the case in the upper reaches of the Loddon catchment. However, the drawdown shown in the Lower Murray (in the area east of Deniliquin) and Shepparton WSPA are considered to be reasonable estimates of likely long-term drawdown, and are reflective of the large volumes of groundwater extractions in these areas. The drawdown map for the Calivil Formation (Figure 6-2) suggests much broader and greater long-term changes in groundwater level as a result of current levels of extraction. This shows a large drawdown cone, centred to the east of Deniliquin, which stretches as far as Gunbower Forest in the west. It is likely that this drawdown cone would extend further west than this in reality. However, it has been limited here to the confines of the model boundaries. The greatest drawdown occurs to the east of most of the pumping where the aquifer is bounded by a bedrock high. To the east of the bedrock high the groundwater levels are actually slowly rising as a result of irrigation and minimal groundwater development. Pumping from the Katunga WSPA merges with and enhances the drawdown cone originating in New South Wales. As the maps show, there is a large area in the east of the model that is predicted to experience long-term drawdown in excess of 10 m. Although the drawdown shown in the south is skewed by boundary effects, it does indicate that there is a degree of longterm drawdown occurring in the Campaspe WSPA and the Mid-Loddon GMA. Again there are large areas that are predicted to experience drawdown in excess of 10 m. Much of the drawdown occurs in the first few years of the model run suggesting that the aquifers approach equilibrium reasonably quickly (i.e. in the first few decades). Table 6-1 highlights that under the mid and dry future climate scenarios, the drawdown levels discussed above are further increased. Notably, under Scenario Ddry additional drawdowns in the order of 1.3 to 2 m are predicted across the entire model domain. As previously mentioned, due to model boundary conditions it is likely that these levels of drawdown are actually underestimates. Table 6-1. Median groundwater changes (m) across the Southern Riverine model under scenarios A, B, C and D Groundwater balance A B Cdry Cmid Cwet Ddry Dmid Dwet Layer Layer Layer Layer Average CSIRO 2008 Southern Riverine Plains Groundwater Model Calibration Report 63

76 Figure 6-1. Drawdown in the Shepparton Formation during the first 111-year run under Scenario A Figure 6-2. Drawdown in the Calivil Formation during the first 111-year run under Scenario A 64 Southern Riverine Plains Groundwater Model Calibration Report CSIRO 2008

77 6.2 Surface groundwater interactions Overall the rivers included in the Southern Riverine model are net losing rivers based on the groundwater model results. Under Scenario A, the average annual net river loss to groundwater was ~200 GL/year. Figure 6-3 presents the 222-year time series of average annual river losses under Scenario A. This shows a number of peaks where high volumes of surface water runoff have created an enhanced gradient between the rivers and the groundwater system, resulting in high net river losses. Often this is immediately followed by a year of low net river losses as the surface water and groundwater systems re-equilibrate. Net river losses increase ~60 GL/year under Scenario A relative to the without-development scenario as a result of the extractions under Scenario A. As a percentage of total extractions this equates to only 23%. This figure of 23% is considered to be a gross underestimate of the net impact of groundwater extractions on surface water flows. The reasoning behind this is explained below: Firstly, as shown in Table 6-2, if surface drains are included in the calculations then this percentage rises to 42%. The model drains are included to represent the effects of regional drainage systems that are aimed at preventing watertable rise beneath irrigation areas. In reality the water entering these drains will eventually be discharged to rivers and streams and hence will form part of the surface water resource. Given that there is a direct hydraulic connection between the surface drains and modelled rivers it is believed that it is appropriate to include changes in drain flows in calculations of surface water impacts. Secondly, the without-development case is not a true representation of without-development conditions (i.e. it still models high levels of irrigation recharge causing elevated watertables that are outside the limits of the model calibration). Therefore a more appropriate comparison is considered to be between the Cmid and Dmid scenarios (as shown in Table 6-2). This comparison gives an understanding of the impacts of future groundwater development. Under this comparison the percentage of increased groundwater extractions that is accounted for by river losses is 58%. This figure compares well with a previous estimate of groundwater losses induced by pumping of 60% across the Murray-Darling Basin (SKM, 2003). In the model 5% of the additional groundwater pumping is sourced from modelled head-dependent boundaries suggesting that groundwater extraction in the Southern Riverine model area will be depleting water sources in neighbouring aquifers (such as the Murrumbidgee alluvium). This issue is further discussed in the following section. The time lag associated with the impacts of groundwater pumping on streamflows varies on a scale from years to several decades, depending on the depth and location of extraction wells. Under Scenario A the full impacts of all groundwater extractions are observed within 25 years. This result is highlighted in Figure Net River Loss (GL/yr) Figure 6-3. Net river loss to groundwater under Scenario A CSIRO 2008 Southern Riverine Plains Groundwater Model Calibration Report 65

78 Figure 6-4. Comparison of net river loss under Scenario A and the without-development scenario Table 6-2. Impacts of groundwater pumping on net river losses Volumes Rivers only Rivers + drains Without development A Without development GL/y A Cmid Dmid Net river loss Increase in net river loss n/a 56.2 n/a n/a 29.6 Groundwater pumping Increase in pumping n/a n/a n/a 51.2 % Surface water flow loss attributable to pumping n/a 23% n/a 42% n/a 58% 6.3 Groundwater balance Overview Total diffuse recharge, comprising both irrigation and rainfall infiltration, provides the greatest volume of aquifer recharge across the Southern Riverine Plains (Table 6-3 and Figure 6-6). The variation in total model inflows between wet and dry scenarios is relatively minor in terms of percentages (Figure 6-5). However, the net volumes are significant and can cause significant stress on the groundwater resource. Lateral groundwater flow into the model area is a significant volume at approximately 100 to 110 GL/year. A proportion of this groundwater inflow from adjacent aquifers is likely to be a model artefact due to the nature of specified head boundary conditions in groundwater models. The Southern Riverine groundwater model is largely flanked by outcropping bedrock (a natural impediment to groundwater flow). The exception to this is the northern and northwestern boundaries. Based on the current and historical groundwater flow direction (toward the north-west), it is conceptualised that this boundary would have significantly more groundwater flowing out of the model area. However, pumping stresses imposed on the scenario models can create levels of regional drawdown that can reverse hydraulic gradients at the model boundaries (compared to the calibration model), thus creating model inflows across the boundary. Whether or not these inflows will occur in reality depends on hydrogeological conditions prevailing in the neighbouring aquifers. If the neighbouring aquifer is also being stressed by groundwater pumping then such inflows may not be realised in the future. Alternatively, if neighbouring aquifers are not heavily stressed and inflows do occur then groundwater depletion and associated loss of river flow effects will simply be exported from the model to its surroundings. It is conceptualised that the inflows at the model boundaries do not represent a true source term in the overall water balance of the MDB and that such inflows simply represent a surrogate for increased river leakage, and to a lesser extent decreases in groundwater evapotranspiration in the model area or its surroundings. 66 Southern Riverine Plains Groundwater Model Calibration Report CSIRO 2008