water availability in the wimmera - report

October 2007

Water Availability in the WimmeraA report to the Australian Government from the CSIRO Murray-Darling Basin Sustainable Yields Project

Murray-Darling Basin Sustainable Yields Project acknowledgments

The Murray-Darling Basin Sustainable Yields Project is being undertaken by CSIRO under the Australian Government's Raising National Water Standards Program, administered by the National Water Commission. Important aspects of the work were undertaken by Sinclair Knight Merz; Resource & Environmental Management Pty Ltd; Department of Water and Energy (New South Wales); Department of Natural Resources and Water (Queensland); Murray-Darling Basin Commission; Department of Water, Land and Biodiversity Conservation (South Australia); Bureau of Rural Sciences; Salient Solutions Australia Pty Ltd; eWater Cooperative Research Centre; University of Melbourne; Webb, McKeown and Associates Pty Ltd; and several individual sub-contractors.

Murray-Darling Basin Sustainable Yields Project disclaimers

Derived from or contains data and/or software provided by the Organisations. The Organisations give no warranty in relation to the data and/or software they provided (including accuracy, reliability, completeness, currency or suitability) and accept no liability (including without limitation, liability in negligence) for any loss, damage or costs (including consequential damage) relating to any use or reliance on that data or software including any material derived from that data and software. Data must not be used for direct marketing or be used in breach of the privacy laws. Organisations include: Department of Water, Land and Biodiversity Conservation (South Australia), Department of Sustainability and Environment (Victoria), Department of Water and Energy (New South Wales), Department of Natural Resources and Water (Queensland), Murray-Darling Basin Commission.

CSIRO advises that the information contained in this publication comprises general statements based on scientific research. The reader is advised and needs to be aware that such information may be incomplete or unable to be used in any specific situation. No reliance or actions must therefore be made on that information without seeking prior expert professional, scientific and technical advice. To the extent permitted by law, CSIRO (including its employees and consultants) excludes all liability to any person for any consequences, including but not limited to all losses, damages, costs, expenses and any other compensation, arising directly or indirectly from using this publication (in part or in whole) and any information or material contained in it. Data is assumed to be correct as received from the Organisations.

Citation

CSIRO (2007). Water availability in the Wimmera. A report to the Australian Government from the CSIRO Murray-Darling Basin Sustainable Yields Project. CSIRO, Australia. 108 pp

Publication Details

Published by CSIRO © 2007 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 1835-095X

Cover Photo: Channel, Grampians region courtesy of the Wimmera CMA, Victoria

Director’s Foreword Following the November 2006 Summit on the Southern Murray-Darling Basin, the Prime Minister and Murray-Darling Basin state Premiers commissioned CSIRO to report on sustainable yields of surface and groundwater systems within the Murray-Darling Basin. This report from the CSIRO Murray-Darling Basin Sustainable Yields Project details the assessments for one of 18 regions that encompass the Basin.

The CSIRO Murray-Darling Basin Sustainable Yields Project is providing critical information on current and likely future water availability. This information will help governments, industry and communities consider the environmental, social and economic aspects of the sustainable use and management of the precious water assets of the Murray-Darling Basin.

The project is the first rigorous attempt worldwide to estimate the impacts of catchment development, changing groundwater extraction, climate variability and anticipated climate change, on water resources at a basin-scale, explicitly considering the connectivity of surface and groundwater systems. To do this, we are undertaking the most comprehensive hydrologic modelling ever attempted for the entire Basin, using rainfall-runoff models, groundwater recharge models, river system models and groundwater models, and considering all upstream-downstream and surface-subsurface connections. We are complementing this work with detailed surface water accounting across the Basin – never before has surface water accounting been done in such detail in Australia, over such a large area, and integrating so many different data sources.

To deliver on the project CSIRO is drawing on the scientific leadership and technical expertise of national and state government agencies in Queensland, New South Wales, Victoria, the Australian Capital Territory and South Australia, as well as the Murray-Darling Basin Commission and Australia’s leading industry consultants. The project is dependent on the cooperative participation of over 15 government and private sector organisations contributing over 100 individuals. The project has established a comprehensive but efficient process of internal and external quality assurance on all the work performed and all the results delivered, including advice from senior academic, industry and government experts.

The project is led by the Water for a Healthy Country Flagship, a CSIRO-led research initiative which was set up to deliver the science required for sustainable management of water resources in Australia. The Flagship goal is to achieve a tenfold increase in the social, economic and environmental benefits from water by 2025. By building the capacity and capability required to deliver on this ambitious goal, the Flagship is ideally positioned to accept the challenge presented by this complex integrative project.

CSIRO has given the Murray-Darling Basin Sustainable Yields Project its highest priority. It is in that context that I am very pleased and proud to commend this report to the Australian Government.

Dr Tom Hatton

Director, Water for a Healthy Country

National Research Flagships

CSIRO

© CSIRO 2007 October 2007 Water availability in the Wimmera

Executive

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Executive Summary

Background

The CSIRO Murray-Darling Basin Sustainable Yields Project is providing governments with a robust, Basin-wide estimate of water availability on an individual catchment and aquifer basis, taking into account climate change and other risks. This report describes the assessment undertaken for the Wimmera region. While key aspects of the assessment and modelling methods used in the project are contained in this report, fuller methodological descriptions will be provided in a series of project technical reports.

The Wimmera region is in western Victoria and represents 3 percent of the total area of the Murray-Darling Basin (MDB). The region is based around the terminal Wimmera River, Avon River and Yarriambiack Creek. The population is around 50,000 (or 2.5 percent of the MDB total), concentrated in the major centres of Horsham, Stawell and Ouyen. The dominant land use is broadacre cropping of cereals, pulses and oilseeds in the central and northern areas, and dryland livestock grazing in the south. There are currently 6000 ha of irrigated cropping with the major enterprises being vines, pastures and orchards. The area of commercial plantation forestry in the region is small and farm dams are predominantly used for stock and domestic purposes. Native vegetation covers over 16 percent of the region. The region includes the nationally significant wetlands Lake Hindmarsh and Lake Albacutya.

The region uses 1 percent of the surface water diverted for irrigation and urban use in the MDB and uses less than 0.1 percent of the MDB groundwater resource. There are major water storages at the foothills of the Grampians Ranges. Surface water diversions are primarily for stock and domestic use, but also for urban supply and limited irrigation. There are three groundwater management units (GMUs) in the western part of the region. Groundwater extraction is also primarily for stock and domestic use, as well as some urban supply and limited irrigation.

Key Messages

The key messages relating to climate, surface water resources, groundwater and the environment are presented below for scenarios of current and possible future conditions. The scenarios assessed are defined in Chapter 1.

Historical climate and current development (Scenario A)

The average annual rainfall for the entire Wimmera region is 403 mm and modelled average annual runoff is 16 mm. Rainfall is generally higher in the winter half of the year and most of the runoff occurs in winter and early spring. The region generates about 1.7 percent of the total runoff in the MDB. Average annual groundwater recharge, based on throughflow to confined aquifers, is around 12 GL/year.

The surface water assessments of this project only consider implementation of Stage 1 of the Wimmera-Mallee Pipeline Project. For these conditions average annual surface water availability is 206 GL/year and current water use represents 20 percent of this available water. However, on average, 59 percent of the available water is diverted for use, as losses in the distribution system are high. The maximum allocation for all users (including the environment) under the Wimmera and Glenelg River surface water Bulk Entitlements is 206 GL/year. Currently, allocations are below this maximum in 26 percent of years. Implementation of future stages of the Wimmera-Mallee Pipeline Project would be expected to lead to considerably different results.

Current groundwater use is about 1.84 GL/year. This level of use does not affect the Wimmera River, as extractions are distant from the river. Future development is unlikely to change this, although development in some upland areas may have a significant impact. The three existing GMUs are in the west of the region. Groundwater use for the Balrootan GMU is 41 percent of the estimated recharge from throughflow. There is no extraction from the Nhill and Goroke GMUs. Three-quarters of the current extraction is for stock and domestic use or from unincorporated areas.

The water regimes of Lake Hindmarsh and Lake Albacutya have been dramatically affected by water resource development. The fraction of time that these lakes are full has been reduced from 65 to 15 percent for Lake Hindmarsh and from 24 to 2 percent for Lake Albacutya. Prior to water resource development Lake Hindmarsh was never shallow

Water availability in the Wimmera October 2007 © CSIRO 2007

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for more than three years, now it can experience continual shallow conditions for up to eight years. Similarly, Lake Albacutya never used to remain shallow for more than eight years, now it can remain shallow for periods of up to 33 years. These changes are likely to have caused and may continue to cause considerable ecological change in these ecosystems.

Recent climate and current development (Scenario B)

The mean annual rainfall and runoff over the past ten years (1997 to 2006) were 13 percent and 51 percent lower respectively than the 1895 to 2006 long-term means.

If the climate of the last ten years were to persist, river inflows, water availability, diversions, water use and end-of-system outflows would be about half of the values of the historical climate period. Urban supply would be reduced to a lesser extent. Reliability would be severely degraded, with allocations for all users being less than the current maximum allocation volume in 95 percent of years.

Under these conditions and current sharing arrangements, the impacts would differ between user groups. For example, on average, stock and domestic use would receive an increased share of the reduced surface water resource, while irrigation would receive one-third of the current irrigation share, and the environment would receive two-thirds of the current environmental share. A dry year would see greater effects on sharing. For example, the dry-year irrigation share would fall from 9 percent to zero and the dry-year environmental share would fall from 23 to 4 percent of the available resource.

A long-term continuation of the conditions experienced over the last ten years would also lead to major additional changes in the hydrology of lakes Hindmarsh and Albacutya. Lake Hindmarsh would almost never fill and would experience continually shallow conditions for periods of up to 32 years, four times longer than at present. Lake Albacutya would be unlikely to ever fill; water levels would be expected to nearly always be shallow.

Future climate and current development (Scenario C)

Almost all global climate models considered indicate reductions in rainfall and thus runoff by 2030. The best estimate (median) is a 17 percent reduction in average annual runoff by ~2030 relative to ~1990. The extreme estimates, which assume high global warming, range from a 47 percent reduction to a one percent increase in mean annual runoff. By comparison, the range assuming low global warming is from a 16 percent reduction to no change in mean annual runoff.

Climate change is likely to reduce average water availability and use by 2030. Under the best estimate 2030 climate:

� average river inflows would reduce by 17 percent and water transfers into the region from the Glenelg would reduce by 4 percent, together reducing average surface water availability by 21 percent or 43.3 GL/year

� diversions would reduce by 11 percent and water use by 14 percent; however, urban water supplies from head-works would be largely unaffected

� head-works storages would no longer spill (compared to spills every 5 years on average under the historical climate), and end-of-system flows would be reduced by about 25 percent

� allocations to users would be less than the current maximum allocation volume in 56 percent of years � changes in surface water sharing would be less substantial than under a continuation of the recent climate. Only

in dry years would sharing differ greatly from the current situation. In these conditions, the irrigation share would again reduce to zero and the environmental share would be half of the current dry-year share

� the percentage of time for which outflows from the Wimmera River, Yarriambiack Creek and Avon River to receiving wetlands and floodplains ceases would not change significantly. However, outflow volumes would be significantly lower.

Under a dry extreme 2030 climate surface water availability and use would be broadly equivalent to those if the climate of the last ten years were to persist into the future. Under the wet extreme 2030 climate there would a small impacts on surface water resources, including, for example, a 6 percent reduction in water availability.

Climate change is likely to cause major changes to the water regimes of Lakes Hindmarsh and Albacutya and lead to considerable ecological change. Lake Hindmarsh would be full only 4 percent of the time under best estimate 2030 climate scenario, while Lake Albacutya would be unlikely to ever fill. Even the wet extreme 2030 climate would reduce inflows to these lakes.


Executive

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Future climate and future development (Scenario D)

Existing MDB-wide projections for commercial forestry plantations suggest significant growth in the Wimmera region by 2030 is unlikely. Future growth in farm dams is also expected to be small. Changes in these catchment features are unlikely to affect future runoff.

Total expected growth in groundwater extraction by 2030 for the region is about 20 percent. This would raise the relative level of extraction for the Balrootan GMU from about 40 to 50 percent of the estimated lateral throughflow. This level of use appears to be sustainable.

Uncertainty

The runoff estimates in the southern parts of the Wimmera (where most of the runoff is generated) are reasonably good because there are many calibration catchments from which to estimate the model parameter values. The runoff estimates in the northern parts of the Wimmera are less reliable because there are no calibration catchments.

The river model is well suited to evaluate changes in the characteristics of high flows as a consequence of climate scenarios, and probably adequate to evaluate changes in the long-term water balance. The model is unsuitable to evaluate changes in low flows, which may be a problem for assessing baseflow maintenance for ecological purposes. The high level of regulation, including transfers between basins, reservoirs and a complex system of natural and artificial channels and pipelines, and the transmission losses that may occur in these, cause considerable external uncertainty in projected flow patterns.

There is considerable doubt about the groundwater balances in all three GMUs. The calculated ratios have considerable uncertainty.

The largest source of uncertainty for future climate results are the climate change projections (global warming level) and the modelled implications of global warming on local rainfall. A wide range of the best available climate modelling was used but there is considerable scope for improvement in those global models at predicting regional rainfall. The future scenarios include very large reductions to water availability suggesting that improvements in the ability to predict the hydrological consequences of climate change would have substantial benefits for water management.

There are considerable uncertainties associated with the future development projections. Future development could be very different should governments impose different policy controls on these activities. Future groundwater use has been assessed by considering changes in demand, and hence these are simply best guesses.

The environmental assessments consider only a subset of the important assets for this region and are based on limited hydrology parameters with no direct quantitative relationships for environmental responses. Considerably more detailed investigation is required to provide the necessary information for informed management of the environmental assets of the region.

Water availability in the Wimmera Reissue page, May 2009 CSIRO 2009

Table of Contents 1 Introduction ............................................................................................................................ 1

1.1 Background ......................................................................................................................................................................11.2 Project methodological framework ...................................................................................................................................31.3 Climate and development scenarios ................................................................................................................................41.4 Rainfall-runoff modelling ..................................................................................................................................................51.5 River system modelling ....................................................................................................................................................61.6 Monthly water accounts ...................................................................................................................................................91.7 Groundwater modelling ..................................................................................................................................................111.8 Environmental assessment ............................................................................................................................................111.9 References.....................................................................................................................................................................12

2 Overview of the region........................................................................................................ 142.1 The region ......................................................................................................................................................................142.2 Environmental description..............................................................................................................................................172.3 Surface water resources ................................................................................................................................................192.4 Groundwater ..................................................................................................................................................................212.5 References.....................................................................................................................................................................24

3 Rainfall-runoff modelling ..................................................................................................... 263.1 Summary........................................................................................................................................................................263.2 Modelling approach........................................................................................................................................................273.3 Modelling results ............................................................................................................................................................303.4 Discussion of key findings..............................................................................................................................................363.5 References.....................................................................................................................................................................37

4 River system modelling ....................................................................................................... 384.1 Summary........................................................................................................................................................................384.2 Modelling approach........................................................................................................................................................404.3 Modelling results ............................................................................................................................................................454.4 Discussion of key findings..............................................................................................................................................574.5 References.....................................................................................................................................................................58

5 Uncertainty in surface water modelling results ................................................................. 595.1 Summary........................................................................................................................................................................595.2 Approach........................................................................................................................................................................595.3 Results ...........................................................................................................................................................................645.4 Discussion of key findings..............................................................................................................................................705.5 References.....................................................................................................................................................................71

6 Groundwater assessment.................................................................................................... 726.1 Summary........................................................................................................................................................................726.2 Groundwater management units in the Wimmera..........................................................................................................736.3 Hydrogeology .................................................................................................................................................................736.4 Current and future groundwater extraction versus GMU recharge ................................................................................776.5 References.....................................................................................................................................................................78

7 Environment.......................................................................................................................... 807.1 Summary........................................................................................................................................................................807.2 Approach........................................................................................................................................................................817.3 Results ...........................................................................................................................................................................847.4 Discussion of key findings..............................................................................................................................................847.5 References.....................................................................................................................................................................85

Appendix A Rainfall-runoff results for all subcatchments .......................................................... 87

Appendix B River modelling reach mass balances................................................................... 89

Appendix C River system model uncertainty assessment by reach......................................... 96

Erratum sheet, issued May 2009, inside back


Tables Table 1-1. River system models in the Murray-Darling Basin..............................................................................................................7Table 2-1. Summary of land use in the year 2000 within the Wimmera region .................................................................................17Table 2-2. Ramsar wetlands and wetlands of national significance located within the Wimmera region ..........................................19Table 2-3. Summary of surface water entitlements for the Wimmera region.....................................................................................21Table 2-4. Categorisation of groundwater management units, including annual extraction, entitlement and recharge details** ......22Table 3-1. Summary results from the 45 Scenario C simulations (numbers show percentage change in mean annual rainfall and runoff under Scenario C relative to Scenario A) ................................................................................................................................33Table 3-2. Water balance over the entire region by scenario ............................................................................................................35Table 4-1. Storages in the river model in the Wimmera region .........................................................................................................43Table 4-2. Water use configuration in the Wimmera river model.......................................................................................................43Table 4-3. Water management in the Wimmera river model .............................................................................................................43Table 4-4. Rainfall, evaporation and flow factors for model robustness trials ...................................................................................44Table 4-5. Model setup information ...................................................................................................................................................44Table 4-6. River system model average annual water balance under scenarios O, A, B and C in the Wimmera region..................46Table 4-7. River system model average annual water balance under scenarios O, A, B and C in the upper Glenelg River ............47Table 4-8. Average annual water availability under scenarios B and C relative to Scenario A .........................................................48Table 4-9. Details of storage behaviour in Wimmera region..............................................................................................................49Table 4-10. Change in annual water use in each calibration reach under scenarios B and C relative to Scenario A .......................50Table 4-11. Annual total water use under scenarios A, B and C .......................................................................................................52Table 4-12. Level of use under scenarios A, B and C .......................................................................................................................52Table 4-13. Cease-to-flow in percentage time under scenarios P (Scenario A pre-development), A, B and C ................................54Table 4-14. Average share of the total available water to user groups under each scenario............................................................56Table 4-15. Share of the total available water to user groups under each scenario in a dry (90th percentile) year ...........................56Table 5-1. Possible framework for considering implications of assessed uncertainties ....................................................................61Table 5-2. Comparison of water accounting reaches with river model reaches ................................................................................61Table 5-3. Some characteristics of the gauging network of the Wimmera region (30,640 km2) compared with the entire Murray-Darling Basin (1,062,443 km2) ...........................................................................................................................................................64Table 5-4. Streamflow gauging stations for which data were used in Wimmera-Mallee REALM model calibration..........................66Table 5-5. Details of model performance in reproducing observed flow patterns..............................................................................67Table 5-6. Regional water balance modelled and estimated on the basis of water accounting ........................................................69Table 6-1. Annual extraction, entitlement, PCV and recharge details of Wimmera groundwater management units .......................73Table 6-2. Details of extraction figures used in this report.................................................................................................................77Table 6-3. Extraction to recharge ratios for the groundwater management units of the Wimmera region ........................................78Table 7-1. Definition of environmental indicators...............................................................................................................................84Table 7-2. Environmental indicator values for scenarios P, A, B and C ...........................................................................................84

Water availability in the Wimmera October 2007 © CSIRO 2007

Figures Figure 1-1. Region by region map of the Murray-Darling Basin ..........................................................................................................2Figure 1-2. Methodological framework for the Murray-Darling Basin Sustainable Yields Project........................................................3Figure 1-3. Timeline of groundwater use and resultant impact on river...............................................................................................8Figure 2-1. 1895–2006 annual and monthly rainfall averaged over the region. The curve on the annual graph shows the low frequency variability. ..........................................................................................................................................................................15Figure 2-2. Map of dominant land uses of the Wimmera region with inset showing the region’s location within the MDB. The assets shown are only those assessed in the study (see Chapter 7). A full list of key assets associated with the region is in Table 2-2....16Figure 2-3. Historical surface water diversions within the Wimmera region ......................................................................................21Figure 2-4. Map of groundwater management units in the Wimmera region.....................................................................................23Figure 3-1. Map of the modelling subcatchments and calibration catchments ..................................................................................28Figure 3-2. Modelled and observed monthly runoff and daily flow duration curve for the calibration catchments.............................29Figure 3-3. Spatial distribution of mean annual rainfall and modelled runoff averaged over 1895–2006..........................................31Figure 3-4. 1895–2006 annual rainfall and modelled runoff time series averaged over the region (the curve shows the low frequency variability) ..........................................................................................................................................................................31Figure 3-5. Mean monthly rainfall and modelled runoff averaged over 1895–2006 for the region ....................................................31Figure 3-6. Percentage change in mean annual runoff from the 45 Scenario C simulations (15 GCMs and three global warming scenarios) relative to Scenario A runoff .............................................................................................................................................32Figure 3-7. Mean annual rainfall and modelled runoff under scenarios A, Cdry, Cmid and Cwet .....................................................34Figure 3-8. Mean monthly rainfall and modelled runoff under scenarios A, C and D averaged over 1895–2006 across the region (C range is based on the consideration of each month separately - the lower and upper limits in C range are therefore not the same as scenarios Cdry and Cwet).............................................................................................................................................................36Figure 3-9. Daily flow duration curves for rainfall and runoff under scenarios A, C and D averaged over the region (C range is based on the consideration of each rainfall and runoff percentile separately - the lower and upper limits in C range are therefore not the same as scenarios Cdry and Cwet) .......................................................................................................................................36Figure 4-1. Map showing model sub-catchments, major rivers, calibration reach and inflow gauges, nodes and links, and reaches within the Wimmera region ................................................................................................................................................................42Figure 4-2. Transect of total river flow under pre-development conditions for scenarios A, B and C................................................48Figure 4-3. Scenario A water availability............................................................................................................................................48Figure 4-4. Difference in water availability under scenarios B and C relative to Scenario A .............................................................49Figure 4-5. Total Wimmera headworks storage behaviour over the period of lowest storage content under (a) scenarios A and B, (b) scenarios Cwet, Cmid and Cdry ...................................................................................................................................................50Figure 4-6. Average annual water use under scenarios A, B and C from upstream to downstream.................................................50Figure 4-7. (a) Annual total water use under Scenario A; difference between scenarios A and (b) Cwet (c) Cmid (d) Cdry and (e) B...........................................................................................................................................................................................................51Figure 4-8. Reliability of supply to all water users in the Wimmera and Glenelg River system .........................................................52Figure 4-9. Reliability of supply to individual user groups in the Wimmera and Glenelg River system .............................................53Figure 4-10. Monthly flow duration curves at end-of-system flow locations- (a) Inflow to Lake Hindmarsh; (b) Yarriambiack Ck at Horsham and (c) Inflow to Lake Buloke under scenarios P (Scenario A pre-development), A, B and C ..........................................54Figure 4-11. Seasonal plots at each of the end-of-system flow locations - (a) Inflow to Lake Hindmarsh; (b) Yarriambiack Ck at Horsham and (c) Inflow to Lake Bulokeunder under scenarios P (P represents Scenario A pre-development), A, B and C............55Figure 4-12. Average levels of available water to different user groups under each scenario ..........................................................56Figure 4-13. Available water to user groups under each scenario in a dry (90th percentile) year......................................................57Figure 5-1. Map showing the subcatchments used in modelling, with the reaches for which river water accounts were developed (‘accounting reach’) and contributing head water catchments with gauged inflows (‘contributing catchment’). Black dots and red lines are nodes and links in the river model respectively...................................................................................................................62Figure 5-2. Map showing the rainfall, streamflow and evaporation observation network, along with the subcatchments used in modelling............................................................................................................................................................................................65Figure 5-3. Comparison of observed (gauged) and modelled (model) monthly flows at Horsham, showing overestimation of low flows, particularly after 1997 ..............................................................................................................................................................70Figure 6-1. Map of groundwater management units in the Wimmera region.....................................................................................74Figure 6-2. Balrootan GMU groundwater levels of (a) the Tertiary Confined Sands Aquifer, (b) the Murray Group Limestone Aquifer and (c) the Parilla Sand Aquifer .........................................................................................................................................................75Figure 7-1. Location map of environmental assets............................................................................................................................82Figure 7-2. Satellite image of Lake Albacutya and Lake Hindmarsh .................................................................................................83

© CSIRO 2007 October 2007 Water availability in the Wimmera � 1

1Introduction

1 Introduction

1.1 Background

Australia is the driest inhabited continent on Earth, and in many parts of the country – including the Murray-Darling Basin – water resources water for rural and urban use is comparatively scarce. Into the future, climate change and other risks (including catchment development) are likely to exacerbate this situation and hence improved water resource data, understanding and planning and management are of high priority for Australian communities, industries and governments.

On 7 November, 2006, the Prime Minister of Australia met with the First Ministers of Victoria, New South Wales, South Australia and Queensland at a water summit focussed primarily on the future of the Murray-Darling Basin (MDB). As an outcome of the Summit on the Southern Murray-Darling Basin, a joint communiqué called for “CSIRO to report progressively by the end of 2007 on sustainable yields of surface and groundwater systems within the MDB, including an examination of assumptions about sustainable yield in light of changes in climate and other issues.”

The subsequent Terms of Reference for what became the Murray-Darling Basin Sustainable Yields Project specifically asked CSIRO to:

� estimate current and likely future water availability in each catchment and aquifer in the MDB considering: o climate change and other risks o surface-groundwater interactions

� compare the estimated current and future water availability to that required to meet the current levels of extractive use.

The Murray-Darling Basin Sustainable Yields Project is reporting progressively on each of 18 contiguous regions that comprise the entire MDB. These regions are primarily the drainage basins of the Murray and the Darling rivers - Australia’s longest inland rivers, and their tributaries. The Darling flows southwards from southern Queensland into New South Wales west of the Great Dividing Range into the Murray River in southern New South Wales. At the South Australian border the Murray turns south-westerly eventually winding to the mouth below the Lower Lakes and the Coorong. The regions for which the project assessments are being undertaken and reported are the Paroo, Warrego, Condamine-Balonne, Moonie, Border Rivers, Gwydir, Namoi, Macquarie-Castlereagh, Barwon-Darling, Lachlan, Murrumbidgee, Murray, Ovens, Goulburn-Broken, Campaspe, Loddon-Avoca, Wimmera and Eastern Mount Lofty Ranges (see Figure 1-1).

2 � Water availability in the Wimmera October 2007 © CSIRO 2007

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Figure 1-1. Region by region map of the Murray-Darling Basin

The Murray-Darling Basin Sustainable Yields Project will be the most comprehensive MDB-wide assessment of water availability undertaken to-date. For the first time:

� daily rainfall-runoff modelling has been undertaken at high spatial resolution for a range of climate change and development scenarios in a consistent manner for the entire MDB

� the hydrologic subcatchments required for detailed modelling have been precisely defined across the entire MDB

� the hydrologic implications for water users and the environment by 2030 of the latest Intergovernmental Panel on Climate Change climate projections, the likely increases in farm dams and commercial forestry plantations and the expected increases in groundwater extraction have been assessed in detail (using all existing river system and groundwater models as well new models developed within the project)

� river system modelling has included full consideration of the downstream implications of upstream changes between multiple models and between different States, and quantification of the volumes of surface-groundwater exchange

� detailed analyses of monthly water balances for the last ten to twenty years have been undertaken using available streamflow and diversion data together with additional modelling including estimates of wetland evapotranspiration and irrigation water use based on remote sensing imagery (to provide an independent cross-check on the performance of river system models).


1Introduction

The successful completion of these outcomes, among many others, relies heavily on a focussed collaborative and team-oriented approach between CSIRO, State government natural resource management agencies, the Murray-Darling Basin Commission, the Bureau of Rural Sciences, and leading consulting firms – each bringing their specialist knowledge and expertise on the MDB to the project.

1.2 Project methodological framework

The methodological framework for the project is shown in the diagram below (Figure 1-2). This also indicates in which chapters of this report the different aspects of the project assessments and results are presented.

Figure 1-2. Methodological framework for the Murray-Darling Basin Sustainable Yields Project

The first steps in the sequence of the project are definition of the reporting regions and their composite subcatchments, and definition of the climate and development scenarios to be assessed (including generation of the time series of climate data that describe these scenarios). The second steps are rainfall-runoff modelling and rainfall-recharge modelling for which the inputs are the climate data for the different scenarios. Catchment development scenarios for farm dams and commercial forestry plantations are modifiers of the modelled runoff time series.

Next, the runoff implications are propagated through river system models and the recharge implications propagated through groundwater models – for the major groundwater resources – or considered in simpler assessments for minor groundwater resources. The connectivity of surface and groundwater is assessed and the actual volumes of surface-groundwater exchange under current and likely future groundwater extraction are quantified. Uncertainty levels of the river system models are then assessed based on monthly water accounting.

The results of scenario outputs from the river system model are used to make limited hydrological assessments of ecological relevance to key environmental assets. Finally, the implications of the scenarios for water availability and water use under current water sharing arrangements are assessed, synthesised and reported.


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1.3 Climate and development scenarios

The project is assessing the following four scenarios of historical and future climate and current and future development, all of which are defined by daily time series of climate variables based on different scalings of the 1895–2006 climate:

� historical climate and current development � recent climate and current development � future climate and current development � future climate and future development.

These scenarios are described in some detail below with full details provided in Chiew et al. (2007a).

1.3.1 Historical climate and current development

Historical climate and current development – referred to as ‘Scenario A’ – is the baseline against which other climate and development scenarios are compared.

The historical daily rainfall time series data that are used are taken from the SILO Data Drill of the Queensland Department of Natural Resources and Water database which provides data for a 0.05o x 0.05o (5 km x 5 km) grid across the continent (Jeffrey et al., 2001; and www.nrm.qld.gov.au/silo). Areal potential evapotranspiration (PET) data are calculated from the SILO climate surface using Morton’s wet environment evapotranspiration algorithms (www.bom.gov.au/climate/averages; and Chiew and Leahy, 2003).

Current development for the rainfall-runoff modelling is the average of 1975 to 2005 land use and small farm dam conditions. Current development for the river system modelling is the dams, weirs and licence entitlements in the latest State agency models, updated to 2005 levels of large farm dams. Current development for groundwater models is 2004 to 2005 levels of licence entitlements. Surface-groundwater exchanges in the river and groundwater models represent an equilibrium condition for the above levels of surface and groundwater development.

1.3.2 Recent climate and current development

Recent climate and current development – referred to as ‘Scenario B’ – is used for assessing future water availability should the climate in the future prove to be similar to that of the last ten years. Climate data for 1997 to 2006 is used to generate stochastic replicates of 112-year daily climate sequences. The replicate which best produces a mean annual runoff value closest to the mean annual runoff for the period 1997 to 2006 is selected to define this scenario.

Scenario B is only analysed and reported upon where the mean annual runoff for the last ten years is statistically significantly different to the long-term average.

1.3.3 Future climate and current development

Future climate and current development – referred to as ‘Scenario C’ – is used to assess the range of likely climate conditions around the year 2030. Three global warming scenarios are analysed in 15 global climate models (GCM) to provide a spectrum of 45 climate variants for the 2030. The scenario variants are derived from the latest modelling for the fourth assessment report of the Intergovernmental Panel on Climate Change (IPCC, 2007).

Two types of uncertainties in climate change projections are therefore taken into account: uncertainty in global warming mainly due to projections of greenhouse gas emissions and global climate sensitivity to the projections; and uncertainty in GCM modelling of climate over the MDB. Results from each GCM are analysed separately to estimate the change per degree global warming in rainfall and other climate variables required to calculate PET. The change per degree of global warming is then scaled by a high, medium and low global warming by 2030 relative to 1990 to obtain the changes in the climate variables for the high, medium and low global warming scenarios. The future climate and current development Scenario C considerations are therefore for 112-year rainfall and PET series for a greenhouse enhanced climate around 2030 relative to 1990 and not for a forecast climate at 2030.


1Introduction

The method used to obtain the future climate and current development Scenario C climate series also takes into account different changes in each of the four seasons as well as changes in the daily rainfall distribution. The consideration of changes in the daily rainfall distribution is important because many GCMs indicate that extreme rainfall in an enhanced greenhouse climate is likely to be more intense, even in some regions where projections indicate a decrease in mean seasonal or annual rainfall. As the high rainfall events generate large runoff, the use of traditional methods that assumes the entire rainfall distribution to change in the same way will lead to an underestimation of mean annual runoff in regions where there is an increase, and an overestimation of the decrease in mean annual runoff where there is a decrease (Chiew, 2006).

All 45 future climate and current development Scenario C variants are used in rainfall-runoff modelling; however, three variants – a ‘dry’, a ‘mid’ (best estimate – median) and a ‘wet’ variant – are presented in more detail and are used in river and groundwater modelling.

1.3.4 Future climate and future development

Future climate and future development – referred to as ‘Scenario D’ – considers the ‘dry, ‘mid’ and ‘wet’ climate variants from the future climate and current development Scenario C together with likely expansions in farm dams and commercial forestry plantations and the changes in groundwater extractions anticipated under existing groundwater plans.

Farm dams here refer only to dams with their own water supply catchment, not those that store water diverted from a nearby river, as the latter require licenses and are usually already included within existing river system models. A 2030 farm dam development scenario for the MDB has been developed by considering current distribution and policy controls and trends in farm dam expansion. The increase in farm dams in each subcatchment is estimated using simple regression models that consider current farm dam distribution, trends in farm dam (Agrecon, 2005) or population growth (Australian Bureau of Statistics, 2004; and Victorian Department of Sustainability and Enviroment (DSE), 2004) and current policy controls (Queensland Government, 2000; New South Wales Government, 2000; Victoria Government, 1989; South Australia Government, 2004). Data on the current extent of farm dams is taken from the 2007 Geosciences Australia ‘Man-made Hydrology’ GIS coverage and from the 2006 VicMap 1:25,000 topographic GIS coverage. The former covers the eastern region of Queensland MDB and the north-eastern and southern regions of the New South Wales MDB. The latter data covers the entire Victorian MDB.

A 2030 scenario for commercial forestry plantations for the MDB has been developed using regional projections from the Bureau of Rural Sciences which takes into account trends, policies and industry feedbacks. The increase in commercial forestry plantations is then distributed to areas adjacent to existing plantations (which are not natural forest land use) with the highest biomass productivity estimated from the PROMOD model (Battaglia and Sands, 1997).

Growth in groundwater extractions has been considered in the context of existing groundwater planning and sharing arrangements and in consultation with State agencies. For groundwater the following issues have been considered:

� growth in groundwater extraction rates up to full allocation � improvements in water use efficiency due to on-farm changes and lining of channels � water buy-backs.

1.4 Rainfall-runoff modelling

The adopted approach provides a consistent way of modelling historical runoff across the MDB and assessing the potential impacts of climate change and development on future runoff.

The lumped conceptual daily rainfall-runoff model, SIMHYD, with a Muskingum routing method (Chiew et al., 2002; Tan et al., 2005), is used to estimate daily runoff at 0.05o grids (~ 5 km x 5 km) across the entire MDB for the four scenarios.

The model is calibrated against 1975 to 2006 streamflow data from about 200 unregulated catchments of 50 km2 to 2000 km2 across the MDB (calibration catchments). Although unregulated, streamflow in these catchments for the calibration period may reflect low levels of water diversion and the effects of historical land use change. The calibration period is a compromise between a shorter period that would better represent current development and a longer period


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that would better account for climatic variability. In the model calibration, the six parameters in SIMHYD are optimised to maximise an objective function that incorporates the Nash-Sutcliffe efficiency (Nash and Sutcliffe, 1970) of monthly runoff and daily flow duration curve, together with a constraint to ensure that the total modelled runoff over the calibration period is within five percent of the total recorded runoff. The resulting optimised model parameters are therefore identical for all cells within a calibration catchment.

The runoff for non-calibration catchments is modelled using optimised parameter values from the geographically closest calibration catchment, provided there is a calibration catchment point within 250 km. Once again the parameter values for each grid cell within a non-calibration catchment are identical. For catchments more than 250 km from a calibration catchment default point the parameter values are used. The default parameter values are taken from the entire MDB modelling run (identical parameters across the entire MDB are chosen to ensure a realistic runoff gradient across the drier parts of the MDB) which best matched observed flows at calibration points. The places these ‘default’ values are used are therefore all areas of very low runoff.

As the parameter values come from calibration against streamflow from 50 km2 to 2000 km2 catchments, the runoff defined here is different, and can be much higher, than streamflow recorded over very large catchments where there can be significant transmission losses (particularly in the western and north-western parts of the MDB). Almost all of the catchments available for model calibration are in the higher runoff areas in the eastern and southern parts of the MDB. Runoff estimates are therefore generally good in the eastern and southern parts of the MDB and are comparatively poor elsewhere.

The same model parameter values are used for all the simulations. The future climate Scenario C simulations therefore do not take into account the effect on forest water use of global warming and enhanced atmospheric CO2 concentrations. There are compensating positive and negative global warming impacts on forest water use, and it is difficult to estimate the net effect because of the complex climate-biosphere-atmosphere interactions and feedbacks. This is discussed in Marcar et al. (2006) and in Chiew et al. (2007b).

Bushfire frequency is also likely to increase under the future climate Scenario C. In local areas where bushfires occur, runoff would reduce significantly as forests regrow. However, the impact on runoff averaged over an entire reporting region is unlikely to be significant (see Chiew et al., 2007b).

For the Scenario D (future climate and future development scenario) the impact of additional farm dams on runoff is modelled using the CHEAT model (Nathan et al., 2005) which takes into account rainfall, evaporation, demands, inflows and spills. The impact of additional plantations on runoff is modelled using the FCFC model (Forest Cover Flow Change), Brown et al. (2006) and www.toolkit.net.au/fcfc.

The rainfall-runoff model SIMHYD is used because it is simple and has relatively few parameters and, for the purpose of this project, provides a consistent basis (that is automated and reproducible) for modelling historical runoff across the entire MDB and for assessing the potential impacts of climate change and development on future runoff. It is possible that, in data-rich areas, specific calibration of SIMHYD or more complex rainfall-runoff models based on expert judgement and local knowledge as carried out by some state agencies would lead to better model calibration for the specific modelling objectives of the area. Chiew et al. (2007b) provide a more detailed description of the rainfall-runoff modelling, including details of model calibration, cross-verification and regionalisation with both the SIMHYD and Sacramento rainfall-runoff models and simulation of climate change and development impacts on runoff.

1.5 River system modelling

The project is using river system models that encapsulate descriptions of current infrastructure, water demands, and water management and sharing rules to assess the implications of the changes in inflows described above on the reliability of water supply to users. Given the time constraints of the project and the need to link the assessments to State water planning processes, it is necessary to use the river system models currently used by State agencies, the Murray-Darling Basin Commission and Snowy Hydro Ltd. The main models in use are IQQM, REALM, MSM-Bigmod, WaterCRESS and a model of the Snowy Mountains Hydro-electric Scheme.

The modelled runoff series from SIMHYD are not used directly as subcatchment inflows in these river system models because this would violate the calibrations of the river system models already undertaken by State agencies to different runoff series. Instead, the relative differences between the daily flow duration curves of the historical climate Scenario A


1Introduction

and the remaining scenarios (Scenarios B, C and D respectively) are used to modify the existing inflows series in the river system models (separately for each season). The Scenarios B, C and D inflow series for the river system modelling therefore have the same daily sequences – but different amounts – as the Scenario A river system modelling series.

Table 1-1. River system models in the Murray-Darling Basin

Model Description Rivers modelled

IQQM Integrated Quantity-Quality Model: hydrologic modelling tool developed by the NSW Government for use in planning and evaluating water resource management policies.

Paroo, Warrego, Condamine-Balonne (Upper, Mid, Lower), Nebine, Moonie, Border Rivers, Gwydir, Peel, Namoi, Castlereagh, Macquarie, Marthaguy, Bogan, Lachlan, Murrumbidgee, Barwon-Darling

REALM Resource Allocation Model: water supply system simulation tool package for modelling water supply systems configured as a network of nodes and carriers representing reservoirs, demand centres, waterways, pipes, etc.

Ovens (Upper, Lower), Goulburn, Wimmera, Avoca, ACT water supply.

MSM-BigMod Murray Simulation Model and the daily forecasting model BigMod: purpose-built by the Murray-Darling Basin Commission to manage the Murray River system. MSM is a monthly model that includes the complex Murray accounting rules. The outputs from MSM form the inputs to BigMod, which is the daily routing engine that simulates the movement of water.

Murray

WaterCRESS Water Community Resource Evaluation and Simulation System: PC-based water management platform incorporating generic and specific hydrological models and functionalities for use in assessing water resources and designing and evaluating water management systems.

Eastern Mt Lofty Ranges (six separate catchments)

SMHS Snowy Mountains Hydro-electric Scheme model: purpose built by Snowy Hydro Ltd to guide the planning and operation of the SMHS.

Snowy Mountains Hydro-electric Scheme

A few areas of the MDB have not previously been modelled and hence some new IQQM or REALM models have been implemented. In some cases ancillary models are used to estimate aspects of water demands of use in the river system model. An example is the PRIDE model used to estimate irrigation for Victorian REALM models.

River systems that do not receive inflows or transfers from upstream or adjacent river systems are modelled independently. This is the case for most of the river systems in the MDB and for these rivers the modelling steps are:

� model configuration � model warm-up to set initial values for all storages in the model, including public and private dams and tanks,

river reaches and soil moisture in irrigation areas � using scenario climate and inflow time series, run the river model for all climate and development scenarios � where relevant, extract initial estimates of surface-groundwater exchanges and provide this to the groundwater

model � where relevant, use revised estimates of surface-groundwater exchanges from groundwater models and re-run

the river model for all scenarios.

For river systems that receive inflows or transfers from upstream or adjacent river systems, model inputs for each scenario were taken from the upstream models. In a few cases several iterations were required between upstream and downstream models because of the complexities of the water management arrangements. An example is the connections between the Murray, Murrumbidgee and Goulburn regions and the Snowy Mountains Hydro-electric Scheme.


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1.5.1 Surface-groundwater interactions

The project is explicitly considering and quantifying the water exchanges between rivers and groundwater systems. The approaches used are described below.

The river models used by State agencies have in turn typically been calibrated by State agencies to achieve mass balance within calibration reaches over relatively short time periods. When the models are run for extended periods the relationships derived during calibration are assumed to hold for the full modelling period. In many cases however, the calibration period is a period of changing groundwater extraction and a period of changing impact of this extraction on the river system. That is, the calibration period is often one of changing hydrologic relationships, a period where the river and groundwater systems have not fully adjusted to the current level of groundwater development. To provide a consistent equilibrium basis for scenario comparisons it is necessary to determine the equilibrium conditions of surface and groundwater systems considering their interactions and the considerable lag times involved in reaching equilibrium.

Figure 1-3 shows an indicative timeline of groundwater use, impact on river, and how this has typically been treated in river model calibration, and what the actual equilibrium impact on the river would be. By running the groundwater models until a ‘dynamic equilibrium’ is reached, a reasonable estimate of the ultimate impact on the river of current groundwater use is obtained. A similar approach is used to determine the ultimate impact of future groundwater use.

Figure 1-3. Timeline of groundwater use and resultant impact on river

For some groundwater management units – particularly fractured rock aquifers – there is significant groundwater extraction but no model available for assessment. In these cases there is the potential for considerable impacts on streamflow. At equilibrium, the volume of water extracted must equal the inflows to the aquifer from diffuse recharge, lateral flows and flows from overlying rivers. The fraction that comes from the overlying rivers is determined using a ‘connectivity factor’ that is estimated from the difference in levels between the groundwater adjacent to the river and the river itself, the conductance between the groundwater pump and the river, and the hydrogeological setting. Given the errors inherent in this method, significant impacts are deemed to be those about 2 GL/year for a subcatchment, which given typical connectivity factors translates to groundwater extraction rates of around 4 GL/year for a subcatchment.


1Introduction

1.6 Monthly water accounts

Monthly water accounts provide an independent set of the different water balance components by river reach and by month. The water accounting differs from the river modelling in a number of key aspects:

� the period of accounting extends to 2006 where possible, which is typically more recent than the calibration and evaluation periods of the river models assessed. This means that a comparison can produce new insights about the performance and assumptions in the river model, as for example associated with recent water resources development or the recent drought in parts of the MDB

� the accounting is specifically intended to estimate, as best as possible, historical water balance patterns, and used observed rather than modelled data wherever possible (including recorded diversions, dam releases and other operations). This reduces the uncertainty associated with error propagation and assumptions in the river model that were not necessarily intended to reproduce historical patterns (e.g. differences in actual historical and potential future degree of entitlement use)

� the accounting uses independent, additional observations and estimates on water balance components not used before such as actual water use estimates derived from remote sensing observations. This can help to constrain the water balance with greater certainty.

Despite these advantages, it is emphasised that the water accounting methodology invokes models and indirect estimates of water balance components where direct measurements are not available. Because of this, these water accounts are not an absolute point of truth. Rather, they provide an estimate of the degree to which the river water balance is understood and gauged, and a comparison between river model and water account water balances provides one of several lines of evidence to inform our (inevitably partially subjective) assessment of model uncertainty and its implications for the confidence in our findings. The methods for water accounting are based on existing methods and those used by Kirby et al. (2006) and Van Dijk et al. (2007) and are described in detail in Kirby et al. (2007).

1.6.1 Wetland and irrigation water use

An important component of the accounting is an estimate of actual water use based on remote sensing observations. Spatial time series of monthly net water use from irrigation areas, rivers and wetlands are estimated using interpolated station observations of rainfall and climate combined with remote sensing observations of surface wetness, greenness and temperature. Net water use of surface water resources is calculated as the difference between monthly rainfall and monthly actual evapotranspiration (AET).

AET estimates are based on a combination of two methods. The first method uses surface temperature remotely sensed by the AVHRR series of satellite instruments for the period 1990 to 2006 and combines this with spatially interpolated climate variables to estimate AET from the surface energy balance (McVicar and Jupp, 2002). The second method loosely follows the FAO56 ‘crop factor’ approach and scales interpolated potential evaporation (PET) estimates using observations of surface greenness and wetness by the MODIS satellite instrument (Van Dijk et al., 2007). The two methods are constrained using direct on-ground AET measurements at seven study sites and catchment stream flow observations from more than 200 catchments across Australia. Both methods provide AET estimates at 1 km resolution.

The spatial estimates of net water use are aggregated for each reach and separately for all areas classified as either irrigation area or floodplains and wetlands. The following digital data sources were used:

� land use grids for 2000/2001 and 2001/02 from the Bureau of Rural Sciences (adl.brs.gov.au/mapserv/landuse/)

� NSW wetlands maps from the NSW Department of Environment and Conservation, (NSW DEC)

� hydrography maps, including various types of water bodies and periodically inundated areas, from Geoscience Australia (GA maps; Topo250K Series 3)

� long-term rainfall and AET grids derived as outlined above

� LANDSAT satellite imagery for the years 1998 to 2004.


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The reach-by-reach estimates of net water use from irrigation areas and from floodplains and wetlands are subject to the following limitations:

� partial validation of the estimates suggested an average accuracy in AET estimation within 15 percent, but probably decreasing with the area over which estimates are averaged. Uncertainty in spatial estimates originates from the interpolated climate and rainfall data as well as from the satellite observations and the method applied

� errors in classification of irrigation and floodplain/wetland areas may have added an unknown uncertainty to the overall estimates, particularly where subcatchment definition is uncertain or wetland and irrigation areas are difficult to discern

� estimated net water use cannot be assumed to have been derived from surface water in all cases as vegetation may also have access to groundwater use, either directly or through groundwater pumping

� estimated net water use can be considered as an estimate of water demand that apparently is met over the long-term. Storage processes, both in irrigation storages and wetlands, need to be simulated to translate these estimates in monthly (net) losses from the river main stem.

Therefore, the AET and net water use estimates are used internally to conceptual water balance models of wetland and irrigation water use that include a simulated storage as considered appropriate based on ancillary information.

1.6.2 Calculation and attribution of apparent ungauged gains and losses

In a river reach, ungauged gains or losses are the difference between the sum of gauged main stem and tributary inflows, and the sum of main stem and distributary outflows and diversions. This would be equal to measured main stem outflows and water accounting could occur with absolute certainty. The net sum of all gauged gains and losses provides an estimate of ungauged apparent gains and losses. There may be differences between apparent and real gains and losses for the following reasons:

� apparent ungauged gains and losses will also include any error in discharge data that may originate from errors in stage gauging or from the rating curves associated to convert stage height to discharge

� ungauged gains and losses can be compensating and so appear smaller than in reality. This is more likely to occur at longer time scales. For this reason water accounting was done on a monthly time scale

� changes in water storage in the river reach, connected reservoirs, or wetlands, can lead to apparent gains and losses that become more important as the time scale of analysis decreases. A monthly time scale has been chosen to reduce storage change effects, but they can still occur.

The monthly pattern of apparent ungauged gains and losses are evaluated for each reach in an attempt to attribute them to real components of water gain or loss. The following techniques are used in sequence:

� analysis of normal (parametric) and ranked (non-parametric) correlation between apparent ungauged gains and losses on one hand, and gauged and estimated water balance components on the other hand. Estimated components included SIMHYD estimates of monthly local inflows and remote sensing-based estimates of wetland and irrigation net water use

� visual data exploration: assessment of temporal correlations in apparent ungauged gains and losses to assess trends or storage effects, and comparison of apparent ungauged gains and losses and a comparison with a time series of estimated water balance components.

Based on the above information, apparent gains and losses are attributed to the most likely process, and an appropriate method was chosen to estimate the ungauged gain or loss using gauged or estimated data.


1Introduction

The water accounting model includes the following components:

� a conceptual floodplain and wetland running a water balance model that estimates net gains and losses as a function of remote sensing-based estimates of net water use and main stem discharge observations

� a conceptual irrigation area running a water balance model that estimates (net) total diversions as a function of any recorded diversions, remote sensing-based estimates of irrigated area and net crop water use, and estimates of direct evaporation from storages and channels

� a routing model that allows for the effect of temporary water storage in the river system and its associated water bodies and direct open water evaporation

� a local runoff model that transforms SIMHYD estimates of local runoff to match ungauged gains.

These model components are will be described in greater detail in Kirby et al. (2007) and are only used where the data or ancillary information suggests their relevance. Each component has a small number of unconstrained or partially constrained parameters that need to be estimated. A combination of direct estimation as well as step-wise or simultaneous automated optimisation is used, with the goal to attribute the largest possible fraction of apparent ungauged gains and losses. Any large residual losses and gains suggest error in the model or its input data.

1.7 Groundwater modelling

Groundwater assessment, including groundwater recharge modelling, is undertaken to assess the implications of the climate and development scenarios on groundwater management units (GMUs) across the MDB. A range of methods are used appropriate to the size and importance of different GMUs. There are over 100 GMUs in the MDB, and the choice of methods was based on an objective classification of the GMUs as high, medium or low priority.

Rainfall-recharge modelling is undertaken for all GMUs. For dryland areas, daily recharge was assessed using a model that considered plant physiology, water use and soil physics to determine vertical water flow in the unsaturated zone of the soil profile at a single location. This model is run at multiple locations across the MDB in considering the range of soil types and land uses to determine scaling factors for different soil and land use conditions. These scaling factors are used to scale recharge for given changes in rainfall for all GMUs according to local soil types and land uses.

For many of the higher priority GMUs, recharge is largely from irrigation seepage. In New South Wales this recharge has been embedded in the groundwater models as a percentage of the applied water. For irrigation recharge, information was collated for different crop types, irrigation systems and soil types, and has been used for the scenario modelling.

For high priority GMUs numerical groundwater models are being used. In most cases these already exist but often require improvement. In some cases new models are being developed. Although the groundwater models have seen less effort invested in their calibration than the existing river models, the project has invested considerable effort in model calibration and various cross-checks to increase the level of confidence in the groundwater modelling.

For each groundwater model, each scenario is run using river heights as provided from the appropriate river system model. For recent and future climate scenarios, adjusted recharge values are also used, and for future development the 2030 groundwater extractions levels are used. The models are run for two consecutive 111-year periods. The average surface-groundwater flux values for the second 111-year period are passed back to the river models as the equilibrium flux. The model outputs are used to assess indicators of groundwater use and reliability.

For lower priority GMUs no models are available and the assessments are limited to simple estimates of recharge, estimates of current and future extraction, allocation based on State data, and estimates of the current and future impacts of extraction on streamflow where important.

1.8 Environmental assessment

Environmental assessments on a region by region basis consider the environmental assets already identified by State governments or the Australian Government that are listed in the Directory of Important Wetlands in Australia (Environment Australia, 2001) or the updated on-line database of the directory. From this directory, environmental assets


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are selected for which there exists sufficient publicly available information on hydrological indicators (such as commence-to-fill levels) which relate to ecological responses such as bird breeding events.

Information sources include published research papers and reports, accessible unpublished technical reports, or advice from experts currently conducting research on specific environmental assets. In all cases the source of the information on the hydrological indicators used in each assessment is cited. The selection of the assets for assessment and hydrologic indicators was undertaken in consultation with State governments and the Australian Government through direct discussions and through reviews by the formal internal governance and guidance structures of the project.

The Directory of Important Wetlands in Australia (Environment Australia, 2001) lists over 200 wetlands in the MDB. Information on hydrological indicators of ecological response adequate for assessing scenario changes only exists for around one-tenth of these. More comprehensive environmental assessments are beyond the terms of reference for the project. The Australian Department of Environment and Water Resources has separately commissioned a compilation of all available information on the water requirements of wetlands in the MDB that are listed in the Directory of Important Wetlands in Australia.

For regions where the above selection criteria identify no environmental assets, the river channel itself is considered as an asset and ecologically-relevant hydrologic assessments are reported for the channel. The locations for which these assessments are provided are guided by prior studies. In the Victorian regions for example, detailed environmental flow studies have been undertaken which have identified environmental assets at multiple river locations with associated hydrological indicators. In these cases a reduced set of locations and indicators has been selected in direct consultation with the Victorian Department of Sustainability and Environment. In regions where less information is available, hydrological indicators may be limited to those that report on the water sharing targets that are identified in water planning policy or legislation.

Because the environmental assessments are a relatively small component of the project, a minimal set of hydrological indicators are used in assessments. In most cases this minimum set includes change in the average period between events and change in the maximum period between events as defined by the indicator.

A quality assurance process is applied to the results for the indicators obtained from the river system models which includes checking the consistency of the results with other river system model results, comparing the results to other published data and with the asset descriptions, and ensuring that the river system model is providing realistic estimates of the flows required to evaluate the particular indicators.

1.9 References

Agrecon (2005) Agricultural Reconnaissance Technologies Pty Ltd Hillside Farm Dams Investigation. MDBC Project 04/4677DO. Australian Bureau of Statistics (2004) Population projections for Statistical Local Areas 2002 to 2022. Available at: www.abs.gov.au. Battaglia M and Sands P (1997) Modelling site productivity of Eucalyptus globulus in response to climatic and site factors. Australian

Journal of Plant Physiology 24, 831–850. Brown AE, Podger PM, Davidson AJ, Dowling TI and Zhang L (2006) A methodology to predict the impact of changes in forest cover on

flow duration curves. CSIRO Land and Water Science Report 8/06. CSIRO, Canberra. Chiew et al. (2007a) Climate data for hydrologic scenario modelling across the Murray-Darling Basin. A report to the Australian

Government from the CSIRO Murray-Darling Basin Sustainable Yields Project. CSIRO, Australia. In prep. Chiew et al. (2007b) Rainfall-runoff modelling across the Murray-Darling Basin. A report to the Australian Government from the CSIRO

Murray-Darling Basin Sustainable Yields Project. CSIRO, Australia. In prep. Chiew FHS (2006) An overview of methods for estimating climate change impact on runoff. Paper prepared for the 30th Hydrology and

Water Resources Symposium, December 2006, Launceston. Chiew FHS and Leahy C (2003) Comparison of evapotranspiration variables in Evapotranspiration Maps of Australia with commonly

used evapotranspiration variables. Australian Journal of Water Resources 7, 1–11. Chiew FHS, Peel MC and Western AW (2002) Application and testing of the simple rainfall-runoff model SIMHYD. In: Singh VP and

Frevert DK (Ed.s), Mathematical Models of Small Watershed Hydrology and Application. Littleton, Colorado, pp335–367. DSE (2004) Victoria in Future 2004 – Population projections. Department of Sustainability and Environment, Victoria. Available at:

www.dse.vic.gov.au. Environment Australia (2001) A Directory of Important Wetlands in Australia. Available at:

http://www.environment.gov.au/water/publications/environmental/wetlands/pubs/directory.pdf IPCC (2007) Climate Change 2007: The Physical Science Basis. Contributions of Working Group 1 to the Fourth Assessment Report of

the Intergovernmental Panel on Climate Change. Cambridge University Press. Jeffrey SJ, Carter JO, Moodie KB and Beswick AR (2001) Using spatial interpolation to construct a comprehensive archive of Australian

climate data. Environmental Modelling and Software 16, 309–330.


1Introduction

Kirby J, Mainuddin M, Podger G and Zhang L (2006) Basin water use accounting method with application to the Mekong Basin. In: Sethaputra S and Promma K (eds) Proceedings on the International Symposium on Managing Water Supply for Growing Demand, Bangkok, Thailand, 16–20 October 2006. Jakarta: UNESCO. 67–77 .

Kirby J et al. (2007) Uncertainty assessments for scenario modelling. A report to the Australian Government from the CSIRO Murray-Darling Basin Sustainable Yields Project, CSIRO Australia. In prep.

Marcar NE, Benyon RG, Polglase PJ, Paul KI, Theiveyanathan S and Zhang L (2006) Predicting the Hydrological Impacts of Bushfire and Climate Change in Forested Catchments of the River Murray Uplands: A Review. CSIRO Water for a Healthy Country.

McVicar TR and Jupp DLB (2002) Using covariates to spatially interpolate moisture availability in the Murray-Darling Basin. Remote Sensing of Environment 79, 199–212.

Nash JE and Sutcliffe JV (1970) River flow forecasting through conceptual models 1: A discussion of principles. Journal of Hydrology 10, 282–290.

Nathan RJ, Jordan PW and Morden R (2005) Assessing the impact of farm dams on streamflows 1: Development of simulation tools. Australian Journal of Water Resources 9, 1–12.

New South Wales Government (2000) Water Management Act 2000 No 92. Queensland Government (2000) Water Act 2000. South Australia Government (2004) Natural Resources Management Act 2004. Tan KS, Chiew FHS, Grayson RB, Scanlon PJ and Siriwardena L (2005) Calibration of a daily rainfall-runoff model to estimate high daily

flows. Paper prepared for the Congress on Modelling and Simulation (MODSIM 2005), December 2005. Melbourne, Australia. pp2960–2966.

Van Dijk A et al. (2007) Reach-level water accounting for 1990–2006 across the Murray-Darling Basin. A report to the Australian Government from the CSIRO Murray-Darling Basin Sustainable Yields Project. CSIRO, Australia. In prep.

Victoria Government (1989) Water Act 1989, Act Number 80/1989.


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2 Overview of the region The Wimmera region is based around the terminal Wimmera River, Avon River and Yarriambiack Creek and includes the major centres of Horsham, Stawell and Ouyen. The region covers 3 percent of the Murray-Darling Basin (MDB) within western Victoria. It has 2.5 percent of the MDB’s population, uses 1 percent of the surface water diverted for irrigation and urban use, and uses less than 0.1 percent of the MDB’s groundwater resource. A number of major water storages at the foothills of the Grampians Ranges store water for irrigation, urban and stock and domestic use. The region includes the nationally significant wetlands Lake Hindmarsh and Lake Albacutya.

The dominant land use is broadacre cropping of cereals, pulses and oilseeds in the central and northern areas and dryland livestock grazing in the south. Over 16 percent of the region is covered with native vegetation. The majority of the region’s surface and groundwater diversion is used for stock and domestic purposes. There is currently 6000 ha of irrigated cropping with the major enterprises being vines, pastures and orchards. Over 95 percent of the irrigation water is sourced from surface water diversions and used within a small irrigation system near Horsham and for vines and orchards in the foothills of the Grampians Ranges. A small volume of groundwater is used for pasture seed, pulse and cereal grain production in the south-west of the region. The area of commercial plantation forestry in the region is small and farm dams are predominantly used for stock and domestic purposes. Under the current Victorian policy there is likely to be a small increase in the storage capacity of stock and domestic farm dams.

The following sections summarise the region’s biophysical features including rainfall, topography, land use and the environmental assets of significance. It outlines the institutional arrangements for the region’s natural resources and presents key features of the surface and groundwater resources of the region including historical water use.

2.1 The region

The Wimmera region is located within western Victoria and covers 30,640 km2 or 3 percent of the MDB. It forms part of the southern edge of the MDB (Figure 2-2) and is bounded to the east by the Loddon-Avoca region and to the west and the north by the Murray region. The region varies from the Grampians Ranges in the south to the wide dune fields of the Little Desert in the north.

Major water resources in the Wimmera region include: the Wimmera River that flows from the Grampians Ranges in the south to Lake Hindmarsh and Lake Albacutya, the Avon River, alluvial aquifers, wetlands and water storages. A number of major water storages at the foothills of the Grampians Ranges store water for irrigation, urban and stock and domestic use. Major diversions into the Wimmera region involve Rocklands Reservoir on the Glenelg River and Lake Toolondo.

The mean annual rainfall is 403 mm, varying from 800 mm in the south to 300 mm in the north. Rainfall varies considerably between years and winter is typically the wettest season. The region’s average annual rainfall is relatively consistent in the past 111 years. The mean annual rainfall over the past ten years (1997 to 2006) is 350 mm or 13 percent lower than the long-term mean.


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0

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Figure 2-1. 1895–2006 annual and monthly rainfall averaged over the region. The curve on the annual graph shows the low frequency variability.

The Wimmera region contributes about 2 percent of the total runoff in the MDB. The mean annual modelled runoff for the 111-year period is 16 mm and most runoff in the Wimmera occurs in winter and early spring. The mean annual modelled runoff over the ten-year period from 1997 to 2006 is 51 percent lower than the long-term mean. The runoff estimates in the southern parts of the Wimmera, where most of the runoff occurs, are reasonably robust as there are many calibration catchments from which model parameter values have been estimated.

The regional population is approximately 50,000 which is 2.5 percent of the MDB population. The major centres are Horsham and Stawell in the southern area and Ouyen in the north. The dominant land use is broad acre cropping of grains, pulses, oilseeds and pasture seed in the central and northern areas and dryland livestock grazing in the south. There is currently 6000 ha of irrigated cropping comprising vine fruits, pastures and orchards (Table 2-1). There is minimal commercial plantation forestry in the region and farm dams are predominantly used for stock and domestic purposes.


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Figure 2-2. Map of dominant land uses of the Wimmera region with inset showing the region’s location within the MDB. The assets shown are only those assessed in the study (see Chapter 7). A full list of key assets associated with the region is in Table 2-2.


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The land use area data in Table 2-1 is land use of the MDB grid in 2000, derived from Bureau of Rural Sciences ‘AgCensus’ data. Irrigation estimates are areas recorded as irrigated in the census.

Table 2-1. Summary of land use in the year 2000 within the Wimmera region

Land use Area Area

percent ha

Dryland crops 40.6% 1,240,600

Dryland pasture 41.1% 1,251,300

Irrigated crops 0.2% 6,000

Cereals 1.6% 100

Horticulture 6.6% 400

Orchards 22.4% 1,400

Pasture and Hay 19.8% 1,200

Vine fruits 47.8% 2,900

Native vegetation 16.2% 493,000

Plantation Forestry 0.1% 2,000

Urban 0.3% 8,100

Water 1.5% 44,200

Total 100.0% 3,045,200

Source: BRS (2000)

The region is predominantly covered by the Wimmera Catchment Management Authority (CMA) however there are some parts of the region in the north covered by the Mallee CMA and in the east by the North Central CMA. The CMAs were established in 1997 under the Water Act 1989 and the Catchment and Land Protection Act 1994 to achieve effective integration and delivery of land and water management programs in the respective catchments. The objectives of the Wimmera CMA include:

� maintain and improve the quality of water and condition of rivers � prevent and, where possible, reverse land degradation (including salinity) � conserve and protect the diversity and extent of natural ecosystems.

The Wimmera Regional Catchment Strategy is an integrated framework for land and water management in the catchment. This strategy identifies the priority issues for a region that are developed in consultation with the regional community and other Government agencies working in natural resource management. It is the over-arching strategy for the development, management and conservation of land and water resources in the region. Implementation is the key focus of the region’s land and water management program for the period 2003 to 2007. The Wimmera CMA is the corporate body responsible for the Strategy coordination and development (WCMA 2007).

As part of the Wimmera Regional Catchment Strategy implementation, the Wimmera CMA is preparing two Water Resource Management Plans (WRMPs), one each for the upper Wimmera and the Mt William Creek subcatchments. It involves creating regional guidelines and parameters so that new irrigation developments are ecologically sustainable, protect the security of supply for existing and future water users, and provide water for the environment.

2.2 Environmental description

Prior to European settlement, the Wimmera region supported a diverse range of vegetation. The upper catchment had dense eucalypt woodland and an understorey of shrubs, perennial grasses and herbs. On the plains, vegetation thinned out to Buloke (Allocasuarina leuhmanii) open woodland, Native Pine (Callitris sp) and mallee communities as well as open grassland.

Currently around 16 percent of the region is covered with native vegetation (Table 2-1) including the Grampians and Little Desert national parks, Black Range, Mt Arapilies-Tooan state parks and numerous flora and fauna, wildlife,


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bushland and forest reserves. There are over 3,000 wetlands across the Wimmera supporting a diverse range of flora and fauna.

The Wimmera River is the largest terminal river in Victoria. The river system flows from Mt Cole and the Pyrenees Ranges in the south-east and the Grampians in the south, to a series of terminal lakes in the north-west including Lake Hindmarsh and Lake Albacutya, two of the largest freshwater lakes in Victoria. Lake Albacutya and beyond into Wyperfield National Park are frequently dry. The Wimmera River between Polkemmet and Wirrengren Plain is proclaimed as a Victorian Heritage River.

The wetlands within the region of national or international importance are detailed in Table 2-2. Wetlands classified as Ramsar sites are internationally significant because they meet criteria agreed under The Ramsar Convention on Wetlands of International Importance. Ramsar sites contain representative, rare or unique wetlands, or wetlands that are important for conserving biological diversity. They can be a wide range of natural or human-made habitats. Wetlands may be nationally or regionally significant depending on more locally specific criteria. All wetlands are important for a variety of ecological reasons or because they bear historical significance or have high cultural value, particularly to Aboriginal people.

Lake Hindmarsh and Lake Albacutya are listed in the Directory of Wetlands of Australia (Environment Australia, 2001) as having national importance. In wet years Lake Hindmarsh overflows into Outlet Creek, which carries water to Lake Albacutya. Lake Albacutya filled in 1974 and received flows in 1996.

Lake Hindmarsh is the largest freshwater lake in Victoria, covering 15,600 ha and holding 630,000 ML when full (Ecological Associates, 2004). It generally takes three or four years of no flows before Lake Hindmarsh becomes dry; the longest dry period was 27 years from 1929 until 1956. When flooded it becomes a major aquatic ecosystem, supporting significant breeding bird and fish populations with extensive aquatic plant communities. The flora is characterised by fringing River Red Gum (Eucalyptus camaldulensis) and Black Box (E. largiflorens) woodland and several threatened plant species are found.

Lake Hindmarsh is a drought refuge for waterbirds. Over 50 species of waterbird are recorded, with some in the thousands. Breeding waterbirds include Pelicans (Pelicanus conspiculatus), Great Cormorants (Phalacorcorax carbo), Pied Cormorant (P. varius), and Pacific Heron (Ardea pacificus). Threatened waterbird species recorded include the Great Egret (Egretta alba), Freckled Duck (Stictonetta naevosa), and Blue-billed Duck (Oxyura australis). When full, it supports large numbers of swans, coots and ducks including large numbers of Freckled Duck (Ecological Associates, 2004; Wimmera CMA, 2005a; Wimmera CMA, 2005b).

Lake Albacutya is a wetland of international importance under the Ramsar Convention. Lake Albacutya receives water much less frequently than Lake Hindmarsh and is dry for long periods (Ecological Associates, 2004). Lake Albacutya only filled four times in the 20th century and last filled in 1974 following two exceptionally wet seasons. When full the Lake has a maximum depth of around 6 m and a total capacity of some 290,000 ML. Flora of the Lake Albacutya and surrounds is a mixture of riverine and mallee vegetation communities. The riverine community is similar to that of Lake Hindmarsh. The mallee community has Native Pine (Callitris sp) and Buloke (Allocasurina leumannii) woodland and heath communities. Green Saltbush (Atriplex australiasica) prevails. These vegetation communities provide a wildlife corridor between the lakes and the nearby Wirrengren Plain.


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Table 2-2. Ramsar wetlands and wetlands of national significance located within the Wimmera region

SITE CODE DIWA* name DIWA area RAMSAR sites

ha

VIC008 Heards Lake 135

VIC011 Lake Albacutya 5700 Y**

VIC012 Lake Hindmarsh 15600

VIC019 Mitre Lake 784

VIC020 Natimuk Lake, Natimuk Creek & Lake Wyn Wyn 1170

VIC021 Pink Lake (Lochiel) 106

VIC024 Saint Marys Lake 113

VIC027 White Lake 620

VIC097 Creswick Swamp 16

VIC122 Bitter Swamp 32

VIC124 Friedman's Salt Lake 55

VIC125 Grass Flat (Telfer's) Swamp 34

VIC126 Hately's Lake (Swamp) 267

VIC127 Lake Buloke Wetlands 8270

VIC128 Oliver's Swamp (Lake) 400

VIC147 Wimmera River 56020 Y*

* Directory of Important Wetlands of Australia ** Lake Albacutya RAMSAR site, total area 5731.3 ha

2.3 Surface water resources

2.3.1 Rivers and storages

The Wimmera River flows from the north side of the Great Dividing Range near Elmhurst and Mt Cole in the Pyrenees Ranges, and from the Grampians Ranges to Lake Hindmarsh, rarely into Lake Albacutya then onto a series of smaller lakes and the Wirrengren Plain in the Mallee. Yarriambiack Creek is a distributary stream of the Wimmera River and flows only when there is a high flow in the Wimmera River. The region’s river system is essentially a series of pools which must fill before water spills downstream. The Avon and Richardson rivers flow into and terminate in Lake Buloke. Yarriambiack Creek flows into the terminal Lake Coorong, near Hopetoun.

A number of major water storages are located within the region, primarily at the foothills of the Grampians Ranges. The on-stream storages include Lake Bellfield, Lake Lonsdale and Lake Wartook and the major off-stream storages include Pine Lake, Taylors Lake, Lake Fyan and Toolondo Reservoir. Major diversions are made from the Glenelg River system that runs south from the Grampians Ranges.

Water stored within the Rocklands and Toolondo reservoirs for use in the Wimmera region is from the Glenelg River system. Annual mean modelled transfers of 43.5 GL are a significant source of imported water for the region.

Storage capacity of stock and domestic small catchment dams in the Wimmera region is estimated to be 34 GL (VicMap, 2006).

There are no major surface water resources generated within the northern areas of the region; however, water is transferred via the Northern Mallee Pipeline, from the Wimmera and Glenelg Basins via the Wimmera-Mallee channel system, and from the Goulburn and Loddon basins via the Waranga Western Channel (DSE, 2006). The Wimmera Mallee Pipeline Project currently being implemented will replace 16,000 km of open channels with 9000 km of pipeline to supply 6000 rural customers and 36 towns between the Grampians and the Murray River with stock and domestic water


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(DSE, 2007a). Grampians Wimmera-Mallee Water (GWMW) is responsible for the implementation of the Wimmera Mallee Pipeline Project.

2.3.2 Surface water management institutional arrangements

Water for consumptive use is from water bodies by entitlement issued by Government and authorised under the Water Act 1989. The Victorian Government retains the overall right to the use, flow and control of all surface water. The Minister for Water is responsible for bulk water allocation by granting bulk entitlements for consumptive use and Environmental Water Reserves. Where appropriate, provision is made for other non-consumptive uses including recreation. Rights are allocated to private consumers for irrigation, households and rural domestic and stock use. Generally, water for consumptive use is allocated by bulk entitlement to water authorities who then distribute the water to their customers, and to individuals through a licence. Many individuals have a right to take water for domestic and stock use without a licence from a water source such as a catchment dam or groundwater bore. Water previously available as irrigation sales water is now an independent low reliability entitlement under the Victorian Sales Water Reform Package.

The surface water resources of the Wimmera catchment are covered by bulk entitlements for water allocation from regulated streams and for all urban water use. In 2005/06, a 206,793 ML bulk entitlement and a 2486 ML licensed private diversion entitlement covered unregulated streams within the Wimmera region. The bulk entitlements included Wimmera and Glenelg Flora and Fauna Environmental Reserve of 40,563 ML held by the Minister for the Environment. A combined bulk entitlement of 166,230 ML includes entitlement held by GWMW, Coliban Water, Central Highlands Water and Wannon Water. No basic rights are quantified in water management plans, but diversions are allowed under the Water Act 1989. In addition there is harvesting of runoff water in farm dams (DSE 2006).

GWMW is a government-owned business responsible for managing urban and rural water supply systems throughout a large proportion of the Wimmera region. It is the licensing authority for groundwater and surface water resources in the Wimmera Basin, owns and operates 15 bulk water supply reservoirs, and manages river diversions. The bulk entitlement includes water entitlements for urban use, rural stock and domestic use and irrigation. Approximately 76 percent of the 165,320 ML bulk entitlement held by GWMW is diverted for rural stock and domestic use, 18 percent is diverted for irrigation and 6 percent for urban use (derived from Table 4-2). A small volume of the urban water entitlements is used outside of the region. Goulburn Murray Water provide a bulk water supply to GWMW via the Waranga Main Channel from the Goulburn River system for domestic and stock use and urban water supply.

Central Highlands Water has an average bulk entitlement of 60 ML, Wannon Water has a bulk entitlement of 465 ML and Coliban Water has a bulk entitlement of 385 ML. This entitlement is used to supply urban water to towns outside of the region. The Wimmera Catchment Management Authority is responsible for waterway management in the Wimmera River catchment, and the North Central Catchment Management Authority is responsible for waterway management in the Avon and Richardson river catchments.

Water allocated for the Wimmera region (including transfers out of the region) is detailed in Table 2-3. Note that these sharing arrangements will change under future stages of the Wimmera-Mallee Pipeline Project due to reduction of losses in the distribution system; for example, environmental Bulk Entitlements are expected to increase due to reduction in losses.


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Table 2-3. Summary of surface water entitlements for the Wimmera region

Water Products Priority of Access Average Entitlement ML/y Basic Rights Stock and domestic rights not stated Native title none Extraction Shares Total surface water entitlements* 168,716 Combined urban and rural Bulk Entitlements** high 166,230 Unregulated river licences*** low 2486 Environmental Provisions Total environmental share not stated Environmental Bulk Entitlements**** high 40,563 *Entitlements from the Wimmera and Glenelg Rivers to Grampians Wimmera Mallee Water and the Minister for the Environment are averages of five-year rolling caps ** Sum of Bulk Entitlements to Coliban Water, Central Highlands Water, Grampians Wimmera Mallee Water and Wannon Water. Value includes the considerable losses in the distributions system and so does not indicate likely actual water use under these entitlements *** Sum of individual licences including farm dams **** Bulk Entitlement for Wimmera and Glenelg Rivers

Source: DSE (2007b)

2.3.3 Water products and use

Most surface water supplied in the Wimmera region is for stock and domestic use and urban use. Over the past ten years annual water diversions have fallen from around 160 GL to less than 50 GL. This reflects the low levels of runoff in the Grampians Ranges over this period. In 2005/06, 69 GL of Bulk Entitlement water was diverted for use (down from 84.5 GL in 2004/05) including 0.82 GL of Environmental Water Reserve. Licensed diversions from unregulated streams were 1.7 GL. An estimated 14.4 GL was used from small farm dams in 2005/06 (DSE, 2007b).

An estimated 10.6 GL or 10 percent of total inflows flowed into terminal lakes. This water comprised consumptive water not used under entitlements and the Environmental Water Reserve (DSE, 2007b).

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Figure 2-3. Historical surface water diversions within the Wimmera region


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2.4 Groundwater

2.4.1 Groundwater management units – the hydrogeology and connectivity

The Wimmera region contains three groundwater management units (GMUs) with other areas being unincorporated. The GMUs not only have a defined spatial extent but also a depth interval related to the layering of geological formations. A list of the Wimmera region GMUs is in Table 2-4. As can be seen in Figure 2-4, they represent a small proportion of the reporting region. The GMUs are rated as low or very low priority within the context of this project, based on the degree of development and the stress on the groundwater resource and the degree of connectivity between groundwater and surface water resources. The rating process helps focus project efforts on major components of MDB groundwater resource and results in a simple assessment of each Wimmera region GMU. This involves a hydrogeological description and water balance to determine the implications of climate change and development scenarios on groundwater and surface water resources. Such an assessment may be inappropriate for local issues management.

Table 2-4. Categorisation of groundwater management units, including annual extraction, entitlement and recharge details**

Code Priority GMU Name Extraction 2004/05

Licensed entitlement

Permissible consumptive volume

Rainfall recharge

GL/y

V47 low Balrootan 0.41 1.52 0.98 NA*

V62 very low Goroke 0 0 2.20 NA*

V61 very low Nhill 0 0 1.20 NA*

Unincorporated area 1.03 1.61 Not available NA*

*Aquifers are confined so there is no direct rainfall recharge. Chapter 6 discusses recharge processes to these GMUs. **Stock and Domestic supplies are not included.

The hydrogeology of the Wimmera region is distinctively different in the highland and lowland areas of the region. Highland areas consist of fractured-rock aquifers within extensive folded and fractured marine sedimentary and contact metamorphic rocks. Groundwater salinities range from 2400 to 3600 mg/L Total Dissolved Salts (TDS) and bore yields are generally 1–2 L/s, but can be as high as 30 L/s. Other hydrogeologic units include weathered granites with highly saline groundwater (10,000 mg/L to 20,000 mg/L TDS), high-relief granites that support colluvial deposits containing fresh groundwater (1000 mg/L TDS), and highland alluvium deposited as valley-fill with groundwater salinites ranging from 1000 mg/L to 10,000 mg/L TDS.

All three GMUs are sited in the lowland areas of the Wimmera region. The lowland areas consist of three main sedimentary aquifers:

� The Renmark Group forms the basal aquifer in lowland areas and consists of fine to coarse sands overlain by silts and clays containing coal and carbonaceous sediments. The Renmark Group is not currently used because good quantities of generally better quality water are available in the overlying Murray Group Limestone (MGL) Aquifer

� The MGL is absent in the east, but is an important groundwater resource in the western part of the Wimmera region. It consists of marine deposited limestone and marl. The MGL receives post-development recharge in the southern area, where the watertable is shallow and the overlying aquitard (Bookpurnong Beds) is absent or very thin. To the north (for example, in the Balrootan GMU), significant recharge to the Murray Group Limestone is expected (via leakage through the Parilla Sand Aquifer and a relatively thin aquitard), although some of the groundwater may be a fossil resource. To the north and north-west of the Wimmera region, groundwater in the Murray Group Limestone is considered to be a fossil resource

� The Parilla Sand overlies the Bookpurnong Beds above the MGL. It is a shallow aquifer of fine to medium marine sands containing groundwater with salinities that vary from fresh (less than 1000 mg/L to 2000 mg/L


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TDS) in the south and west of the Wimmera River, to relatively saline (3000 mg/L to 30,000 mg/L TDS) in the east and north eastern Wimmera region.

Figure 2-4. Map of groundwater management units in the Wimmera region

More detail of GMU hydrogeology is presented in Chapter 6. Broadly, the Balrootan GMU applies to the MGL Aquifer to the west of the reporting area, with depth limits of 60 m to125 m; the Nhill and Goroke GMUs correspond to the groundwater resource of the Renmark Group Aquifer. These are also located to the west of the region considered here. The Balrootan GMU overlies the Nhill and Goroke GMUs. The unincorporated area covers the rest of the region. Available current groundwater extraction figures, entitlements, permissible consumptive volume and recharge for the GMUs and unincorporated areas in the Wimmera region are presented in Table 2-4.


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Groundwater levels in the Renmark Group have shown little fluctuation since 1989. Groundwater levels in the MGL have declined near Lake Hindmarsh. There are no obvious trends in MGL groundwater levels near Nhill. Groundwater levels in the Parilla Sands are strongly correlated with rainfall and have declined since around 2000 (URS, 2006).

The productive MGL Aquifer is disconnected from surface water systems in the Wimmera region, except in the far south-west. The watertable predominantly occurs in the Parilla Sands. The Parilla Sand Aquifer is predominantly saline in the Wimmera River trench, east of the Wimmera River and along the Douglas Depression.

As a result, gaining rivers intersecting the Parilla Sand in the lower catchment, in particular the Wimmera River, are susceptible to salinisation, especially during low flow periods. Shallow ephemeral streams in the south-east of the Wimmera catchment are connected, are slightly losing streams in the highland regions and become gaining streams in lowland areas (SKM, 2003).

A fourth GMU is proposed (SKM, 2005) in the Gymbowen region; about 50 percent of the proposed GMU falls within the Wimmera region. It covers the Parilla Sand and MGL Aquifers, with depth limits from the natural surface to the base of the MGL. The recharge to the proposed Gymbowen GMU is around 10.3 GL/year (SKM, 2005), although current entitlement is around 1 GL/year. This area is nominated as a GMU on the basis of a large number of applications for groundwater licences received by the water authority (GWMW). Potentially, extraction volumes from this area may exceed extraction from the existing GMUs.

2.4.2 Water management institutional arrangements

The Wimmera region groundwater resources are controlled within the Balrootan, Goroke and Nhill GMUs. No water management plan exists for these, but the area is subject to Permissible Consumptive Volume (PCV) limits on groundwater extraction. PCV are declared through Ministerial Order. A groundwater entitlement limit is in place within the Balrootan GMU. Actual extraction is currently below these limits.

State legislation broadly controls groundwater extraction within the remainder of the region and there are provisions that allow for declaration of Water Supply Protection Areas and implementation of groundwater management plans where there is a threat from increasing rates of groundwater extraction. A Water Supply Protection Area can be declared under the Water Act 1989 to protect the area’s groundwater or surface water resources through the development of a management plan which aims for equitable management and long-term sustainability (DSE, 2006).

Goroke GMU and Nhill GMU have no reported licensed entitlements but are PCV defined. The Balrootan GMU has a PCV of 0.98 GL/year and a licensed entitlement of 1.52 GL/year, indicating that the GMU is currently over-allocated.

2.4.3 Water products and use

Groundwater extraction within the GMUs of the Wimmera region accounts for 0.03 percent of total groundwater extraction across the MDB or 0.41 GL excluding stock and domestic extractions. Another 1.03 GL licensed extraction occurs outside of the region. There are less than 40 licensed groundwater users in the region, with groundwater being heavily relied upon for domestic and stock supply, particularly in the west of the region where the MGL is used and in the highland areas where water from fractured rock aquifers is used. The Wimmera-Mallee stock and domestic channel network does not extend to the west Wimmera where the GMUs are defined and hence the groundwater represents the main source of water. The Wimmera GMUs are characterised by the fragility of the resource and its importance as a water supply.

The limited groundwater extracted is used for the Nhill town water supply, irrigation and stock and domestic purposes. Groundwater extraction for urban use is metered, although only 50 percent of extraction for irrigation is metered. There is insufficient extraction data to assess historical patterns of groundwater use. Stock and domestic use is not licensed. This use has been estimated in Chapter 6 to be 0.4 GL/year, but supporting data is poor.


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2.5 References

BRS (2000) Land use data. Available at: http://adl.brs.gov.au/mapserv/landuse/. DSE (2006) State Water Report 2004–2005. A statement of Victorian water resources. Department of Sustainability and Environment

Melbourne. DSE (2007a) Department of Sustainability and Environment, http://www.dse.vic.gov.au. DSE (2007b) State Water Report 2005–2006. A statement of Victorian water resources. Department of Sustainability and Environment

Melbourne. Ecological Associates (2004) The Environmental Water needs of the Wimmera Termimal Lakes: Final Report. Wimmera Catchment

Management Committee. Environment Australia (2001) A Directory of Important Wetlands in Australia. Third Edition, Environment Australia, Canberra. SKM (2003) Projections of Groundwater Extraction Rates and Implications for Future Demand and Competition for Surface Water.

MDBC Publication 04/03. SKM (2005) Gymbowen Permissible Annual Volume Assessment. Grampians Wimmera Mallee Water, August 2005. SKM (2007) Groundwater Management Unit Inventory 2005–2006. Unpublished report. URS (2006) Introducing Groundwater in your Catchment. Draft Report prepared for Murray-Darling Basin Commission, Canberra. VicMap (2006) 1:25,000 topographic GIS coverage. Wimmera CMA (2005a) Lake Hindmarsh Fact sheet. Available at: http://www.wcma.vic.gov.au/. Wimmera CMA (2005b) Lake Albacutya fact sheet. Available at: http://www.wcma.vic.gov.au/. WCMA (2007) Wimmera Regional Catchment Strategy. Available at: http://www.wcma.vic.gov.au/.


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3 Rainfall-runoff modelling This chapter includes information on the climate and rainfall-runoff modelling for the Wimmera region. It has four sections:

� a summary � an overview of the regional modelling approach � a presentation and description of results � a discussion of key findings.

3.1 Summary

3.1.1 Issues and observations

� The methods used for climate scenario and rainfall-runoff modelling across the Murray-Darling Basin (MDB) are described in Chapter One. There are no significant differences in the methods used to model the Wimmera region.

3.1.2 Key messages

� The mean annual rainfall averaged over the Wimmera region is 403 mm and the modelled runoff is 16 mm. Rainfall is generally higher in the winter half of the year and most of the runoff occurs in winter and early spring. The Wimmera region covers 2.9 percent of the MDB and contributes about 1.7 percent of the total runoff in the MDB.

� The mean annual rainfall over the ten year period 1997 to 2006 is 13 percent lower than the 1895 to 2006 long-term mean and runoff is 51 percent lower for the same ten year period compared with the previous 111 years. The 1997 to 2006 rainfall is significantly different to the 1895 to 1996 long-term mean (at a statistical significance level of � = 0.05) and the 1997 to 2006 runoff is very significantly different to the 1895 to 1996 long-term mean (at a significance level of � = 0.01).

� Rainfall-runoff modelling with climate change projections from global climate models indicates that future runoff in the Wimmera is likely to decrease. Almost all the modelling results with different global climate models show a decrease in runoff. The best (or median) estimate is a 17 percent reduction in mean annual runoff by ~2030 relative to ~1990. The extreme estimates, which come from the high global warming scenario, range from a 47 percent reduction to a 1 percent increase in mean annual runoff. By comparison, the range from the low global warming scenario is a 16 percent reduction to no change in mean annual runoff.

� The little to no projected growth in commercial forestry plantations and the small projected increase in farm dam development has negligible impact on future runoff in the Wimmera.

3.1.3 Uncertainty

� Scenario A – historical climate and current development The runoff estimates in the southern parts of the Wimmera where most of the runoff comes from are reasonably good because there are many calibration catchments from which to estimate the model parameter values. The runoff estimates in the northern parts of the Wimmera are less reliable because there are no calibration catchments in the vicinity. The rainfall-runoff model verification analyses for the MDB indicate that the mean annual runoffs estimated for ungauged catchments using optimised parameter values from a nearby catchment have an error of less than 20 percent in more than half the catchments and less than 50 percent in almost all the catchments.


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� Scenario C – future climate and current development The biggest uncertainty in Scenario C modelling is in the global warming projections and the modelled implications of global warming on local rainfall. The uncertainty in the rainfall-runoff modelling of climate change impact on runoff is small compared to the climate change projections. This project takes into account the current uncertainty in climate change projections explicitly by considering results from 15 global climate models and three global warming scenarios based on the Intergovernmental Panel on Climate Change Fourth Assessment Report (IPCC, 2007). The results are then presented as a median estimate of climate change impact on runoff and as the range of the extreme estimates.

� Scenario D – future climate and future development After the Scenario C climate change projections, the biggest uncertainty in Scenario D modelling is in the projection of future increases in commercial forestry plantations and farm dam development and the impact of these developments on runoff. The impact of commercial forestry plantations on runoff is not modelled because the Bureau of Rural Sciences projections indicate little to no growth in commercial forestry plantations in the Wimmera region. The farm dam projection based on current Victorian policy indicates a small increase in farm dam development with negligible impact on runoff. However, there is uncertainty both as to how landholders will respond to these policies and how governments may change policies in future.

3.2 Modelling approach

3.2.1 Rainfall-runoff modelling – general approach

The general rainfall-runoff modelling approach is described more fully in Chapter One and in detail in Chiew et al. (2007a). A brief summary is given below.

The lumped conceptual daily rainfall-runoff model, SIMHYD, with a Muskingum routing method is used to estimate daily runoff at 0.05o grids (~ 5 km x 5 km) across the entire MDB for the four scenarios. The rainfall-runoff model is calibrated against 1975 to 2006 streamflow from about 180 small and medium size unregulated catchments (50–2000 km2). In the model calibration, the six parameters of SIMHYD are optimised to maximise an objective function that incorporates the Nash-Sutcliffe efficiency of monthly runoff and daily flow duration curve, together with a constraint to ensure that the total modelled runoff over the calibration period is within 5 percent of the total recorded runoff. The runoff for a 0.05o grid cell in an ungauged subcatchment is modelled using optimised parameter values for a calibration catchment closest to that subcatchment.

The rainfall-runoff model SIMHYD is used because it is simple and has relatively few parameters and, for the purpose of this project, provides a consistent basis (that is automated and reproducible) for modelling historical runoff across the entire MDB and for assessing the potential impacts of climate change and development on future runoff. It is possible that in data-rich areas, specific calibration of SIMHYD or more complex rainfall-runoff models based on expert judgement and local knowledge as carried out by some state agencies, would lead to better model calibration for the specific modelling objectives of the area. Chiew et al. (2007a) provide a more detailed description of the rainfall-runoff modelling, including details of model calibration, cross-verification and regionalisation with both the SIMHYD and Sacramento rainfall-runoff models and simulation of climate change and development impacts on runoff.

3.2.2 Rainfall-runoff modelling for the Wimmera region

The rainfall-runoff modelling is carried out to estimate runoff in 0.05o grid cells in 24 subcatchments as defined for the river system modelling in Chapter 4 for the Wimmera region (Figure 3-1). Optimised parameter values from seven calibration catchments, all located in the south-eastern corner of the Wimmera, are used.

The impact of commercial forestry on runoff is not modelled because the Bureau of Rural Sciences projections that take into account industry information indicate little to no growth in commercial forestry in the Wimmera region.

In Victoria, future development of farm dams is mainly limited to only those for stock and domestic purposes (Victorian Government, 1989). The increase in farm dams in each subcatchment in the Wimmera is estimated by multiplying the projected increase in rural population by the current average storage volume of stock and domestic farm dams per head


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of population for the corresponding subcatchment. The projected increases in farm dam storage volume by ~2030 for each subcatchment in the Wimmera are given in Appendix A. The total increase in farm dam storage volume over the entire Wimmera region by ~2030 is 320 ML.

Figure 3-1. Map of the modelling subcatchments and calibration catchments


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Figure 3-2. Modelled and observed monthly runoff and daily flow duration curve for the calibration catchments

3.2.3 Model calibration

Figure 3-2 compares the modelled and observed monthly runoff and the modelled and observed daily flow duration curves for the seven calibration catchments. The results indicate that the SIMHYD calibration can reproduce reasonably satisfactorily the observed monthly runoff series (Nash-Sutcliffe E values generally greater than 0.7) and the daily flow duration characteristic (Nash-Sutcliffe E values generally greater than 0.75). The volumetric constraint used in the model calibration also ensures that the total modelled runoff is within 5 percent of the total observed runoff.

The calibration to optimise Nash-Sutcliffe E means that more importance is placed on the simulation of high runoff, and therefore SIMHYD modelling of the medium and high runoff are considerably better than the simulation of low runoff. Nevertheless, an optimisation to reduce overall error variance will result in some underestimation of high runoff and overestimation of low runoff. This is evident in some of the scatter plots comparing the modelled and observed monthly runoff and clearly seen in the daily flow duration curves. The discernible disagreement between the modelled and observed daily runoff characteristics only occurs for runoff that is exceeded less than 0.1 or 1 percent of the time. This is accentuated in the plots because of the linear scale on the y-axis and normal probability scale on the x-axis. In any case, the volumetric constraint used in the model calibration ensures that the total modelled runoff is always within 5 percent of the total observed runoff.


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Most of the runoff in the Wimmera comes from the southern parts of the region, and the runoff estimates there are reasonably good because there are many calibration catchments from which to estimate the model parameter values. The runoff estimates in the northern parts of the Wimmera are less reliable because there are no calibration catchments in the vicinity. The rainfall-runoff model verification analyses for the MDB with data from about 180 catchments indicate that the mean annual runoffs for ungauged catchments are under or over estimated, when using optimised parameter values from a nearby catchment, by less than 20 percent in more than half the catchments and by less than 50 percent in almost all the catchments (see Chiew et al. (2007a) for more detail).

3.3 Modelling results

3.3.1 Scenario A – historical climate and current development

Figure 3-3 shows the spatial distribution of mean annual rainfall and modelled runoff for 1895 to 2006 across the Wimmera region, Figure 3-4 shows the 1895 to 2006 annual rainfall and modelled runoff series averaged over the region, and Figure 3-5 shows the mean monthly rainfall and runoff averaged over the region for 1895 to 2006.

The mean annual rainfall and modelled runoff averaged over the Wimmera region are 403 mm and 16 mm respectively. The mean annual rainfall varies from about 800 mm in the south to 300 mm in the north. The modelled mean annual runoff varies from more than 60 mm in the south to less than 5 mm in the north (Figure 3-3). Rainfall is generally higher in the winter half of the year and most of the runoff occurs in winter and early spring (Figure 3-5). The runoff in the Wimmera, particularly in the northern parts, is amongst the lowest in the MDB. The Wimmera region covers 2.9 percent of the MDB and contributes about 1.7 percent of the total runoff in the MDB.

Rainfall and runoff can vary considerably from year to year with long periods over several years or decades that are considerably wetter or drier than others (Figure 3-4). The coefficients of variation of annual rainfall and runoff averaged over the Wimmera are 0.24 and 0.71 respectively, close to the median values of the 18 MDB regions (the 10th percentile, median and 90th percentile values across the 18 regions are 0.22, 0.26 and 0.36 respectively for rainfall and 0.54, 0.75 and 1.19 for runoff). The mean annual rainfall and modelled runoff over the past ten years (1997 to 2006) are 13 percent and 51 percent lower respectively than the 1895 to 2006 long-term means. The 1997 to 2006 rainfall is statistically different to the 1895 to 1996 rainfall at a significance level of � = 0.05 (with the Student-t and Rank-Sum tests) and the 1997 to 2006 runoff is very significantly different to the 1895 to 1996 runoff (at significance level of � = 0.01). Because the 1997 to 2006 rainfall and runoff are statistically different to the long-term mean, Scenario B modelling is undertaken. The Scenario B is a stochastic replicate selected such that its long-term mean annual runoff matches the 1997 to 2006 mean annual runoff. Potter et al. (2007) presents a more detailed analysis of recent rainfall and runoff across the MDB.


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Figure 3-3. Spatial distribution of mean annual rainfall and modelled runoff averaged over 1895–2006

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Figure 3-4. 1895–2006 annual rainfall and modelled runoff time series averaged over the region (the curve shows the low frequency variability)

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Figure 3-5. Mean monthly rainfall and modelled runoff averaged over 1895–2006 for the region


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3.3.2 Scenario C – future climate and current development

Figure 3-6 shows the percentage change in the modelled mean annual runoff averaged over the Wimmera region for Scenario C relative to Scenario A for the 45 scenarios (15 GCMs for each of the high, medium and low global warming scenarios). The percentage change in the mean annual runoff and the percentage change in mean annual rainfall from the corresponding GCMs are also tabulated in Table 3-1 (see Chiew et al. (2007b) for description of the GCMs and detailed discussion of method used to obtain Scenario C climate series).

The plot and table indicate that climate change would significantly reduce runoff in the Wimmera with almost all the modelling results showing a decrease in runoff.

Because of the large variation between GCM simulations and the method used to obtain the climate change scenarios, the biggest increase and biggest decrease in runoff come from the high global warming scenario. For the high global warming scenario, rainfall-runoff modelling with climate change projections from 60 percent of the GCMs indicates a decrease in mean annual runoff greater than 10 percent, and none of the modelling results show an increase in mean annual runoff greater than 2 percent.

In subsequent reporting here and in other sections, only results from an extreme ‘dry’, ‘mid’ and extreme ‘wet’ variant are shown (referred to as Cdry, Cmid and Cwet). For the Cdry scenario, results from the second highest reduction in mean annual runoff from the high global warming scenario are used. For the Cwet scenario, results from the second highest increase in mean annual runoff from the high global warming scenario are used. For the Cmid scenario, the median mean annual runoff results from the medium global warming scenario are used. These are shown in bold in Table 3-1, with the Cdry, Cmid and Cwet scenarios indicating a -47, -17 and +1 percent change in mean annual runoff. By comparison, the range based on the low global warming scenario is -16 to 0 percent change in mean annual runoff.

Figure 3-7 shows the mean annual runoff across the Wimmera region for Scenario A and for the Cdry, Cmid and Cwet scenarios.

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Figure 3-6. Percentage change in mean annual runoff from the 45 Scenario C simulations (15 GCMs and three global warming scenarios) relative to Scenario A runoff


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Table 3-1. Summary results from the 45 Scenario C simulations (numbers show percentage change in mean annual rainfall and runoff under Scenario C relative to Scenario A)

High global warming Medium global warming Low global warming

GCM Rainfall Runoff GCM Rainfall Runoff GCM Rainfall Runoff

giss_aom -24 -60 giss_aom -15 -43 giss_aom -7 -21

ipsl -20 -47 ipsl -13 -33 ipsl -6 -16

cnrm -16 -43 cnrm -10 -31 cnrm -4 -15

gfdl -15 -42 gfdl -9 -30 gfdl -4 -15

csiro -11 -32 csiro -7 -22 csiro -3 -11

miroc -5 -27 miroc -3 -19 miroc -1 -9

inmcm -8 -26 inmcm -5 -18 inmcm -2 -9

mri -9 -24 mri -6 -17 mri -3 -8

ncar_ccsm -2 -13 ncar_ccsm -1 -9 ncar_ccsm 0 -4

mpi -5 -8 mpi -4 -7 mpi -2 -3

iap -3 -7 iap -2 -5 iap -1 -2

miub 0 -3 miub 0 -3 miub 0 -1

ncar_pcm 2 -2 ncar_pcm 2 -2 ncar_pcm 1 -1

cccma_t63 2 1 cccma_t63 1 1 cccma_t63 1 0

cccma_t47 -1 2 cccma_t47 0 1 cccma_t47 0 0


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Figure 3-7. Mean annual rainfall and modelled runoff under scenarios A, Cdry, Cmid and Cwet


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3.3.3 Summary results for all modelling scenarios

Table 3-2 shows the mean annual rainfall, modelled runoff and actual evapotranspiration (rainfall minus runoff) for Scenario A (averaged over the Wimmera region), and the percentage changes in the rainfall, runoff and actual evapotranspiration in scenarios B, C and D relative to Scenario A. Figure 3-8 shows the mean monthly rainfall and modelled runoff for scenarios A, C and D averaged over 1895 to 2006 for the region. Figure 3-9 shows the daily rainfall and flow duration curves for scenarios A, C and D averaged over the region. The modelling results for all the subcatchments in the Wimmera region are summarised in Appendix A.

It should be noted that the Cmid results (or Cdry or Cwet) are from rainfall-runoff modelling using climate change projections from one GCM. As the Cmid scenario is chosen based on mean annual runoff (see Section 3.3.2), the comparison of monthly and daily results in Scenario Cmid relative to Scenario A in Figure 3-8 and 3-9 should be interpreted cautiously. However, the Crange results shown in Figure 3-8 are based on the second driest and second wettest results for each month separately from the high global warming scenario, and the Crange results shown in Figure 3-9 are based on the second lowest and second highest daily rainfall and runoff results at each of the rainfall and runoff percentiles from the high global warming scenario. The lower and upper limits of Crange are therefore not the same as the Cdry and Cwet scenarios reported elsewhere and used in the river system and groundwater models.

Figure 3-8 indicates that the GCM projections show a bigger decrease in the winter-half rainfall compared to summer-half rainfall and this translates to an even bigger percent runoff reduction in the winter half when most of the runoff in the Wimmera occurs. Although almost all the GCMs show a reduction in mean annual rainfall, more than two thirds of the GCMs indicate that the extreme rainfall that is exceeded 0.1 percent of the time will be more intense (see also Figure 3-9).

The mean annual runoff over the past ten years (1997 to 2006) is 51 percent lower than the 1895 to 2006 long-term mean. For Scenario B modelling, 100 replicates of 112-year daily climate sequences are generated using the annual rainfall characteristics over 1997 to 2006 (see Chiew et al. (2007b) for more details). The replicate that reproduced the 1997 to 2006 mean annual runoff is used to obtain catchment inflows for the river system modelling described in Chapter Four. Because the replicate is chosen based on mean annual runoff, the change in rainfall has little meaning and is therefore not shown in Table 3-2.

The modelling results indicate a median estimate of -17 percent change in mean annual runoff by ~2030 (Scenario C). However, there is considerable uncertainty in the climate change impact estimate with extreme estimates ranging from -47 percent to +1 percent.

There is little to no projected growth in commercial forestry plantations in the Wimmera region. The total farm dam storage volume over the entire Wimmera region is projected to increase by 320 ML by ~2030. This small increase in farm dam development has negligible impact on the mean annual runoff (Scenario D).

Table 3-2. Water balance over the entire region by scenario

Scenario Rainfall Runoff Evapotranspiration

mm

A 403 16 387

percent change from Scenario A

B - -51% -

Cdry -20% -47% -18%

Cmid -6% -17% -5%

Cwet 2% 1% 2%

Ddry -20% -47% -18%

Dmid -6% -17% -5%

Dwet 2% 1% 2%


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Figure 3-8. Mean monthly rainfall and modelled runoff under scenarios A, C and D averaged over 1895–2006 across the region (C range is based on the consideration of each month separately - the lower and upper limits in C range are therefore not the same as

scenarios Cdry and Cwet)

Figure 3-9. Daily flow duration curves for rainfall and runoff under scenarios A, C and D averaged over the region (C range is based on the consideration of each rainfall and runoff percentile separately - the lower and upper limits in C range are

therefore not the same as scenarios Cdry and Cwet)

3.4 Discussion of key findings

The mean annual rainfall and modelled runoff averaged over the Wimmera region are 403 mm and 16 mm respectively. The mean annual rainfall varies from about 800 mm in the south to 300 mm in the north. The modelled mean annual runoff varies from more than 60 mm in the south to less than 5 mm in the north. Rainfall is generally higher in the winter half of the year and most of the runoff occurs in winter and early spring. The Wimmera region covers 2.9 percent of the MDB and contributes about 1.7 percent of the runoff in the MDB.

The mean annual rainfall and modelled runoff over the past ten years (1997 to 2006) are 13 percent and 51 percent lower respectively than the 1895 to 2006 long-term means. The 1997 to 2006 rainfall is significantly different to the 1895 to 1996 rainfall (at a statistical significance level of � = 0.05) and the 1997 to 2006 runoff is very significantly different to the 1895 to 1996 runoff (at a significance level of � = 0.01).

Although the rainfall over the past ten years (1997 to 2006) is 13 percent lower than the 1895 to 2006 long-term mean, the runoff is 51 percent lower than the long-term mean. The likely reasons for this include: rainfall-runoff is a nonlinear process and the changes in rainfall are amplified more in runoff in a drier climate; subsurface water storage is low after a long dry period and significant amount of rainfall is required to fill the storage before runoff can occur; and changes in the daily and seasonal rainfall distribution and sequencing of rainfall events could amplify the reduction in runoff.

The mean annual runoff over the past ten years is lower than the projected decrease in mean annual runoff in the extreme dry climate change scenario (see below). However, because it is based on a relatively short ten years of data, it


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is not sufficient evidence that the hydroclimate has shifted to a new regime. Nevertheless, if the hydroclimate has shifted to a new regime (like in the extreme dry climate change scenario), the dry conditions over the past ten years will occur more frequently.

Most of the runoff in the Wimmera comes from the southern parts of the region, and the runoff estimates there are reasonably good because there are many calibration catchments from which to estimate the model parameter values. The runoff estimates in the northern parts of the Wimmera are less reliable because there are no calibration catchments in the vicinity.

Rainfall-runoff modelling with climate change projections from global climate models indicates that future runoff in the Wimmera will decrease significantly. Almost all the modelling results with different global climate models show a decrease in runoff. Most of the global climate models show a greater reduction in winter-half rainfall and this translates to an even bigger percent reduction in winter-half runoff, when most of the runoff in the Wimmera occurs. However, although the projections indicate a decrease in mean annual rainfall and runoff, more than two thirds of the results also indicate that the extreme rainfall events will be more intense.

The median estimate is a 17 percent reduction in mean annual runoff by ~2030 relative to ~1990. However, there is considerable uncertainty in the modelling results with the extreme estimates ranging from -47 percent to +1 percent change in mean annual runoff. These extreme estimates come from the high global warming scenario, and for comparison the range from the low global warming scenario is -16 percent to no change in mean annual runoff. The main sources of uncertainty are in the global warming projections and the global climate modelling of local rainfall response to the global warming. The uncertainty in the rainfall-runoff modelling of climate change impact on runoff is small compared to the climate change projections.

The little to no projected growth in commercial forestry plantations and the small projected increase in farm dam development has negligible impact on future runoff in the Wimmera.

3.5 References

Chiew et al. (2007a) Rainfall-runoff modelling across the Murray-Darling Basin. A report to the Australian government from the CSIRO Murray-Darling Basin Sustainable Yields Project. CSIRO, Australia. In prep.

Chiew et al. (2007b) Climate data for hydrologic scenario modelling across the Murray-Darling Basin. A report to the Australian government from the CSIRO Murray-Darling Basin Sustainable Yields Project. CSIRO, Australia. In prep.

IPCC (2007) Climate Change 2007: The Physical Basis. Contributions of Working Group 1 to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press.

Potter et al. (2007) Characterisation of recent rainfall and runoff across the Murray-Darling Basin. A report to the Australian government from the CSIRO Murray-Darling Basin Sustainable Yields Project. CSIRO, Australia. In prep.

Victorian Government (1989) Water Act 1989. Act Number 80/1989.


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4 River system modelling This chapter includes information on river system modelling done for the Wimmera region. It has four sections:

� a summary � an explanation of the regional modelling approach � a presentation and description of results � a discussion of key findings.

The information in this chapter is derived from the calibrated REALM model for the Wimmera river system provided by the Victorian Department of Sustainability and Environment (DSE) and Grampians Wimmera Mallee Water (GWMW).

4.1 Summary


The Wimmera region includes the Wimmera River, its tributaries in the Grampians, and the Avon-Richardson Rivers. The Avon-Richardson Rivers are connected to the Wimmera River through the Wimmera-Mallee channel system.

The operation of channels from Rocklands and Moora Moora Reservoirs link the Wimmera region with the Glenelg and Wannon Rivers in southern Victoria. The Loddon-Avoca reporting region influences it via supply from the Waranga Western Channel to stock and domestic demands in the Mallee.

River system modelling for the Wimmera region includes the following modelling scenarios. Future development (Scenario D) was not modelled, as significant development of commercial plantation forestry, farm dams or groundwater is not expected.

� Scenario O Scenario O represents the original river system model configuration that was used for planning purposes by DSE and GWMW. It is run over the original modelling period (Jan 1903 to June 2004) used by the agencies for planning. For the Wimmera region, Scenario O represents pre-Wimmera Mallee Pipeline conditions, but encompasses Stage 8 of the Northern Mallee Pipeline from the River Murray.

� Scenario A Scenario A is based on the Scenario O model but is run for the common historical climate period used in this study (June 1895 to June 2006) and represents the current level of development. This scenario is the baseline scenario that all other scenario results are compared against. For the Wimmera region, Scenario A represents Stage 1 (Supply System #1) of the Wimmera Mallee Pipeline.

� Scenario B Scenario B represents the climatic conditions of the last ten years applied over the common historical modelling period. The level of development is the same as Scenario A (current level of development including Stage 1 of the Wimmera Mallee Pipeline).

� Scenarios Cwet, Cmid and Cdry Scenario C represents a range of future climate conditions, which are derived by adjusting the historic climate and flow inputs used in Scenario A, as described in Chapter 3. The level of development is the same as Scenario A (current level of development including Stage 1 of the Wimmera Mallee Pipeline).

� Pre-development scenarios (Scenario P) Pre-development scenarios are based on the scenario A, B and C models respectively and run for the common modelling period. Current levels of development such as public storages and demand nodes are removed from the models to represent pre-development conditions. Natural water bodies, fixed diversion structures and existing catchment runoff characteristics are not adjusted.


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For the Wimmera and Glenelg river system modelling:

� the model is configured to represent the full utilisation of entitlements. Consequently the demands generated represent what could be diverted if entitlements were fully utilised. The observed history of use is smaller than what is reflected in this configuration of the model

� modelled crop areas are fixed and do not reflect any change in irrigated area as a function of available water resources

� Stage 1 of the Wimmera Mallee Pipeline Project is assumed for all scenarios B and C. An inclusion of further stages (2–6) would lead to different results.

Analysis of the pre-development flows along the Wimmera River indicates that it changes from a gaining stream to a losing stream at the point of maximum average annual flow around the break of slope with the Grampians.

The bulk entitlements for the Wimmera system are based on results for the original model (Scenario O) that runs over a climatic period different to the common modelling period used in this study. Inflows over the extended model period are around 6 percent lower than during the original model period. This is largely a result of including the federation drought and the last two years of extremely low inflows in the assessment period for this study.

4.1.2 Key messages

� Average annual surface water availability in the Wimmera Region is 206 GL/year including 58 GL/year of water transferred from outside the region, mainly from the Glenelg catchment to the south. Diversions and water use are 120.8 and 41.2 GL/year or 59 and 20 percent of the surface water availability, respectively. Losses from storages due to evaporation and in the distribution system are very high compared with water use. The majority of water use is for stock and domestic purposes; 17 percent is supplied to urban centres and small volumes are used for irrigation.

� The maximum allocation for all users (including the environment) under the Wimmera and Glenelg River Bulk Surface Water Entitlements is 206 GL/year. Currently, allocations are below this maximum in 25 percent of years.

� If the climate of the last ten years persists, the average values for; river inflows, water availability, diversions, water use and end-of-system outflows would be about half of the values for the historical climate period. Urban supply is reduced to a lesser extent.

� Reliability of supply would be severely degraded, with available water for all users being less than the current maximum allocation volume in 95 percent of years.

� Climate change is likely to reduce average water availability by 2030. Under the best estimate or median 2030 climate scenario average values for the following would reduce: water availability (21 percent or 43.3 GL), river inflows (17 percent), diversions (11 percent), water use (14 percent) but urban water users supplied directly from headworks would be largely unaffected and end-of-system outflows reduce by around 25 percent.

� Transfers from outside the region reduce by 4 percent. The Glenelg River downstream of Rocklands Reservoir outside the reporting region would be more severely impacted with a decrease in flow of 39 percent. Spills from the Wimmera headworks storages would not occur under this climate, compared to spills every 5 years on average for the historical climate.

� Available water for all users would be less than the current maximum allocation volume in 56 percent of years. � Reduction in inflows under future climate scenarios results in a smaller share of water by the environment. In a

90th percentile dry year under the median estimate 2030 climate scenario, the environment's share of water decreases to 11 from 23 percent under Scenario A.

� The percentage of time with no outflows from the Wimmera River, Yarriambiack Creek and Avon River to receiving wetlands and floodplains would not be changed significantly under future climate. However flow volumes would be significantly lower.

� The climate extremes for 2030 indicate:

o under a wet extreme, inflows would be lower than historical inflows by around 5 percent. Transfers from other basins to the Wimmera region would be increased by 3 percent. Overall, there would be


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little impact on the reliability of supply. However, river outflows would be reduced by 8 percent, and spills from the Wimmera headworks storages would occur on average once every 31 years

o under a dry extreme, water resources conditions will be broadly equivalent to those if the climate of the last ten years were to persist into the future.

� Future development of commercial plantation forestry, farm dams or groundwater is not expected to be significant and thus not modelled in this study.

4.1.3 Robustness

A trial run of the model using inputs representing extremely dry climate conditions assessed how robustly it would behave. During this trial run, allocations to stock and domestic users were zeroed and headworks storages drawn down to very low levels. The model behaved robustly during this extreme test.

The model’s response to increases and decreases in inflows was reasonable and the change in water use and end-of-systems flows consistent with the change in inflows. Mass balance over the modelling period was maintained within one percent for all scenarios.

4.2 Modelling approach

The following section provides a summary of the generic river modelling approach, a description of the Wimmera and Glenelg river model and how the river model was developed. Refer to Chapter 1 for more context on the overall project methodology.

4.2.1 General

River system models that encapsulate descriptions of current infrastructure, water demands, and water management and sharing rules are used to assess the implications of the changes in inflows described in this chapter on the reliability of water supply to users. Given the time constraints of the project and the need to link the assessments to State water planning processes, it is necessary to use the river system models currently used by State agencies and the Murray-Darling Basin Commission. The main models used are IQQM, REALM, MSM-Bigmod, WaterCress and a model of the Snowy Mountains Hydro-electric Scheme. A few areas of the Murray-Darling Basin (MDB) have not previously been modelled, and hence some new IQQM or REALM models have been implemented. In some cases ancillary models are used to estimate aspects of water demands required by the river system model. An example is the PRIDE model used to estimate irrigation demand for Victorian REALM models.

River systems that do not receive inflows or transfers from upstream or adjacent river systems are modelled independently. This is the case for most of the river systems in the MDB. For these rivers, the modelling steps are:

� configure the model � set up model initial values for all storages including public and private dams and tanks, river reaches and soil

moisture in irrigation areas. This is achieved by running the model through a warm-up period � run river model for all scenarios (historical, recent and future climate as well as future development), using

scenario climate and inflow time series � where relevant, extract initial estimates of surface-groundwater exchanges and provide to groundwater model � where relevant, use revised estimates of surface-groundwater exchanges from groundwater models and re-run

river model for all scenarios.


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For river systems that receive inflows or transfers from upstream or adjacent river systems, model inputs for each scenario are taken from the ‘upstream’ model(s). In a few cases, several iterations are required between upstream and downstream models because of the complexities of the water management arrangements. An example is the connections between the Murray, Murrumbidgee and Goulburn regions and the Snowy Mountains Hydro-electric Scheme.

4.2.2 Description of river model for the Wimmera region

A representation of components of the Wimmera and Glenelg river system model within the Wimmera region is shown in Figure 4-1. Components outside of the region are not included.

The model is a REALM (V5.0.2) representation of the Wimmera River from the Upper Wimmera River at Glynwylln (gauge 415206), the Grampians and the upper Avon-Richardson Rivers to terminal lakes at Lake Hindmarsh and Lake Buloke. The surface water of the Wimmera River is not connected to the River Murray and hence has no downstream impact on other reporting regions in the MDB. The Wimmera River is however connected to the Glenelg River and Wannon River in southern Victoria through the operation of the Wimmera-Mallee headworks system in the Grampians. Rocklands Reservoir and Moora Moora Reservoir on the Glenelg River supply water to Taylors Lake and distribution heads respectively for supply to the western part of the Wimmera system. The Wannon River can be used to supply Lake Bellfield. The REALM model used in this study includes the upper Glenelg and Wannon Rivers.

The inflows of the upper Glenelg and Wannon Rivers were adjusted for future climate based on changes made to inflows in the Wimmera region. The Wimmera region is also connected to the Loddon-Avoca region via supply from the Warranga Western Channel to stock and domestic demands in the Mallee. Adjustments to the Avoca River inflows were based on the adjustments applied in the Loddon-Avoca region.

The model represents the Wimmera and Glenelg River system, including the Avon-Richardson Rivers, with over 900 links and over 300 nodes arranged into 19 river sections on the main stream of the Wimmera River, five river sections on the Avon-Richardson Rivers and various supporting water accounting functions. The model includes losses from the river at several locations including the distributary of Yarriambiack Creek. The storages are divided into headworks storages located mainly in the Grampians, service basins and recreational lakes located mainly on the Wimmera plains and terminal lakes located in the lower Wimmera and Avon Rivers. Recreational lakes include Dock Lake, Green Lake and Pine Lake, whilst terminal lakes include Lake Buloke, Lake Batyo Catyo, Lake Hindmarsh, Lake Albacutya, First Lake and Lake Brambruk. The headworks in the Grampians heavily regulate the streamflow (Table 4-1). One of the main headworks storages, Rocklands Reservoir, which is represented in the model but is located outside of the Wimmera region, is reported in this document as an inter-basin transfer to the Wimmera region.

The majority of water supply in the Wimmera and Glenelg River system is for stock and domestic use and one irrigation district near Horsham. There are also a number of towns in the region that are represented in the model, including the largest three towns (Horsham, Stawell and Ararat) which account for around 80 percent of total urban water demand in the model. Water use is modelled by 28 stock and domestic demand nodes, one irrigation demand node and ten urban demand nodes (Table 4-2). Water supply to the environment’s entitlement is delivered in the model by specifying instream demands at particular locations in the river to be supplied from the environment’s entitlement. Losses in the model are significant, with an estimated 15 GL of losses occurring in very dry years when delivering less than 2 GL of supply to mainly stock and domestic users through the channel system. In wetter years, losses in delivering water to the same users are around 50 percent of the volume of water released from the headworks.

Water management in the Wimmera and Glenelg River system is modelled based on a resource sharing arrangement that splits the calculated available water to different user groups according to agreed water distribution for given available water volumes (Table 4-3). This allocation first occurs in November and is updated throughout the year. For this report, results are generally presented for the July to June period unless they specifically relate to the allocation process under the bulk entitlements, in which case results are reported for the end of the accounting year at the end of October. It is anticipated under the bulk entitlement that as more of the region is pipelined, the reporting period will gradually change to an accounting year ending in June.


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Figure 4-1. Map showing model sub-catchments, major rivers, calibration reach and inflow gauges, nodes and links, and reaches within the Wimmera region


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Table 4-1. Storages in the river model in the Wimmera region

Active storage Average annual inflow

Average annual regulated release

Average annual net evaporation

Degree of regulation

GL GL/y Headworks Lake Bellfield 78.6 26.5 16.9 1.5 0.69Lake Lonsdale 65.5 57.7 31.9 16.1 0.83Lake Fyans 18.5 Toolondo Reservoir 92.4 Lake Wartook 29.3 26.3 16.4 9.8 1.00Taylors Lake 33.7 Dairy Creek Reservoir 0.1 0.5 0.2 0.0 0.37Panrock Creek Reservoir 0.1 Mt Cole Reservoir 0.8 4.6 0.8 0.1 0.18Pine Lake 62 Sub-total 319.0 115.4 66.1 27.5 0.81Service Basins 66.9 Terminal Lakes 1117.0 Recreational Lakes 9.8 Region total 1512.7

Table 4-2. Water use configuration in the Wimmera river model

Number of nodes

Bulk entitlement Pump constraints

Model notes

GL/y ML/dStock and domestic and supply by agreement

28 115.9 various Includes significant delivery losses

Irrigation 1 28.0 various Includes significant delivery losses Urban 10 9.0 various Sub-total 39

Table 4-3. Water management in the Wimmera river model

Bypass flow Dairy Creek d/s Halls Gap diversion weir All May to December weir inflows Fyans Creek d/s Lower Fyans Creek weir 1 ML/d or natural Accounting system Water user Percent of total available water at

high allocation Percent of total available water

at low allocation Wimmera-Mallee Water (rural) 72% 57% Grampians Water (urban) 8% 36% Coliban Water (urban) <1% 1% Glenelg Water (urban) <1% <1% Environment 19% 1% Development reserve account (pipeline) 1% 5%

4.2.3 Model setup

The original Wimmera and Glenelg river model and associated REALM V5.0.2 executable code were obtained from DSE. This model was run for the original period of January 1903 to June 2004 and validated against previous results. The time series rainfall, evaporation and flow inputs to this model were extended to cover the period January 1891 to June 2006.

A pre-development version of this model involved removing all headworks storages, recreational lakes and service basins, as well as removing all consumptive demands. Natural water storages were not changed as they represent the pre-development physical characteristics of the system.


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The Wimmera and Glenelg Rivers contain a significant amount of total storage relative to inflows. The initial state of these storages can influence the results obtained. As the Wimmera and Glenelg River model starts with a warm-up period from January 1891 to May 1895, the initial state of all storages needs to be determined. To do this, the model was started with all of the storages empty and run up to May 1895, and the final storage volumes were recorded. This was repeated with all of the storages initially full. The modelling results (Table 4-5) show that the two runs did not converge by May 1895 for all storages. The terminal lakes in particular have long detention times and storage traces for these lakes are sensitive to start storage conditions. Similarly Rocklands Reservoir, which is part of the Wimmera REALM model but outside of the region in the upper Glenelg River, is sensitive to start storage conditions because of its size relative to inflows. Where storage volumes from the two runs did not converge by the end of May 1895, an average of the storage volumes starting from empty and full was adopted.

The model was configured for an extremely dry climate trial run (broadly equivalent to post 1997 climate conditions) by changing rainfall, evaporation and inflows according to the factors in Table 4-4. The ranges of the factors reflect spatial variability. The test model run appeared to be robust overall, although it had more iteration failures when the initial storages were set empty than the original model run.

The results of the model setup are summarised in Table 4-5.

Table 4-4. Rainfall, evaporation and flow factors for model robustness trials

Season Rainfall Evaporation Flow DJF 0.78–1.00 1.06 0.04–0.86MAM 0.78–1.00 1.06 0.04–0.86JJA 0.78–1.00 1.06 0.04–0.86SON 0.78–1.00 1.06 0.04–0.86

Table 4-5. Model setup information

Original model Version Start date End date Wimmera REALM 5.0.2 Jan-1903 Jun-2004 Connection Avon River Outflow to terminal Lake Buloke Yarriambiack Creek Outflow to Mallee plains Wimmera River Outflow to terminal Lakes Hindmarsh and Albacutya Baseline model Warm-up period REALM 5.0.2 Jan-1891 Jun-1895 Modelling period REALM 5.0.2 Jun-1895 Jun-2006 Avon River Outflow to terminal Lake Buloke Yarriambiack Creek Outflow to Mallee plains Wimmera River Outflow to terminal Lakes Hindmarsh and Albacutya Modifications Data Extend to cover Jan-1891 to Jun-2006 Inflows No adjustment required Groundwater loss nodes No adjustment required Initial storage volumes No adjustment required for warm-up run starting in January 1891 Warm-up test results Setting initial storage volumes Storages

commence emptyStorages

commence full Difference Percent of full

volume GL percent Lake Bellfield storage volume 31/05/1895 76.0 76.0 0.0 0.0%Lake Lonsdale storage volume 31/05/1895 33.3 34.1 0.8 1.2%Lake Fyans storage volume 31/05/1895 16.5 16.5 0.0 0.0%Toolondo Reservoir storage volume 31/05/1895 63.7 82.3 18.6 20.1%Lake Wartook storage volume 31/05/1895 18.7 20.1 1.4 4.8%Taylors Lake storage volume 31/05/1895 22.8 22.9 0.1 0.3%


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Warm-up test results Setting initial storage volumes Storages

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volume GL percent Rocklands Reservoir storage volume 31/05/1895 35.0 190.6 155.6 44.7%Pine Lake storage volume 31/05/1895 25.5 30.0 4.5 7.3%Service basins storage volume 31/05/1895 n/a 35.0 n/a n/aTerminal lakes storage volume 31/05/1895 943.7 1236.4 292.7 26.2%Recreational lakes storage volume 31/05/1895 7.1 7.1 0.0 0.0%Original model Storage volume end of May (1895-2006) Mean Median GL Lake Bellfield 55.5 61.4 Lake Lonsdale 7.7 0.0 Lake Fyans 12.7 13.0 Toolondo Reservoir 64.4 79.4 Lake Wartook 15.8 17.2 Taylors Lake 13.6 12.4 Pine Lake 24.5 27.1 Service basins 18.8 19.4 Terminal lakes 329.0 256.9 Recreational lakes 3.3 2.9 Robustness test results Minimum allocation Stock and domestic (%) 4% Minimum storage volume (ML) Total headworks 0.4

4.3 Modelling results

4.3.1 River system water balance

The modelled mass balance for the Wimmera region is given in Table 4-6. Scenario O (the original model scenario) fluxes and Scenario A fluxes are displayed as GL/year, while all other scenarios are presented as a percentage change from Scenario A. Note that the averaging period for Scenario O differs from Scenario A.

The directly gauged inflows represent the inflows into the model that are based on river gauges. The indirectly gauged inflows represent the inflows that are derived to achieve mass balance between mainstream gauges. The water use by channel figures in Table 4-6 include all the consumptive demands supplied except that for the urban centres supplied from headworks, which is listed separately in the table. End-of-system flows are shown for the three main outflow points (downstream of Lake Buloke on the Avon River, Yarriambiack Creek and downstream of Lake Brambruk on the Wimmera River) plus other minor outflows, which consist mostly of Avoca River flows. The change in storage between 30 June 1895 and 30 June 2006 averaged over the 111 year period is also included.

Appendix B contains mass balance tables for designated subcatchments in the model. The mass balance of each of the river reaches and the overall mass balance was checked by taking the difference between total inflows and outflows of the system. In all cases, the mass balance error was less than one percent.

The water balance (Table 4-6) shows that catchment inflows decrease under all future climate scenarios. Under the current water sharing arrangement, transfers from other basins do not change as much as the inflows. Water use in the Wimmera region decrease by around 14 percent under the median 2030 climate scenario, with losses also decreasing because of the reduction of water available to be lost. End-of-system flows decrease under all future scenarios.


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Table 4-6. River system model average annual water balance under scenarios O, A, B and C in the Wimmera region

River system model average annual water balance O A B Cwet Cmid CdryModel start date Jan-1903 Jul-1895 Jul-1895 Jul-1895 Jul-1895 Jul-1895Model end date Jun-2004 Jun-2006 Jun-2006 Jun-2006 Jun-2006 Jun-2006

GL/y Percent change from Scenario A Storage volume Change over period -6.5 -12.5 0% 0% 0% 1%Inflows Subcatchments

Directly gauged 19.7 18.5 -52% -5% -17% -46%Indirectly gauged 264.5 255.1 -52% -5% -20% -52%Transfers from other basins 65.0 58.2 -29% 3% -4% -29%

Sub-total 349.2 331.8 -48% -4% -17% -48%Diversions

Licenced private diversions 40.5 34.0 -57% -3% -16% -61%Urban diversions 8.4 7.2 -16% 2% -1% -16%

Sub-total 48.9 41.2 -50% -2% -14% -53%Outflows End-of-system outflow

D/S Lake Buloke 14.7 13.7 -46% -5% -16% -38%Yarriambiack Creek 6.4 6.7 -71% -12% -36% -74%D/S Lake Brambruk 0.2 0.5 -100% -35% -100% -100%Internal model spills 4.0 3.8 -63% -8% -27% -66%Sub-total 25.3 24.7 -57% -8% -25% -53%

Net evaporation* Headworks storages 39.3 40.2 -46% 1% -12% -42%Lakes 113.7 118.5 -56% -8% -26% -57%Sub-total 153.0 158.6 -54% -6% -22% -53%

Sub-total 178.3 183.3 -54% -6% -23% -53%Unattributed fluxes

River unattributed loss 37.5 39.2 -10% -2% -7% -12%Channel / pipe loss 94.8 79.6 -41% 0% -9% -42%

Sub-total 132.2 118.8 -31% -1% -8% -32%* Evaporation from private licensed storages (GL/y) is not included as it is already accounted in diversions.

The Glenelg River is located outside of the Wimmera region, but its operation is integral to the operation of the Wimmera River. A water balance of the upper Glenelg River, as represented in the model, is shown in Table 4-7. Under the median 2030 climate scenario, inflows in the Upper Glenelg decrease by 21 percent but outflow from Rocklands Reservoir drops by 39 percent.


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Table 4-7. River system model average annual water balance under scenarios O, A, B and C in the upper Glenelg River

O A B Cwet Cmid CdryModel start date Jan-1903 Jul-1895 Jul-1895 Jul-1895 Jul-1895 Jul-1895Model end date Jun-2004 Jun-2006 Jun-2006 Jun-2006 Jun-2006 Jun-2006 GL/y Percent change from Scenario A

Storage volume Change over period -3.5 -1.2 -1% 0% 0% -1%Inflows 112.8 106.5 -53% -5% -21% -54%Sub-total 112.8 106.5 -53% -5% -21% -54%Water use Supply by agreement (Illuka) 4.7 4.6 -56% -4% -13% -60%Pipeline security 2.0 4.8 -24% -3% -5% -26%Sub-total 6.7 9.4 -39% -3% -9% -42%Outflows Transfers to Wimmera basin 51.2 43.5 -33% 4% -4% -32%Glenelg R D/S Rocklands Reservoir

27.4 26.5 -70% -22% -39% -73%

Sub-total 78.6 70.0 -47% -6% -17% -48%Net evaporation* Public storages 23.4 22.0 -82% -7% -42% -82%Sub-total 23.4 22.0 -82% -7% -42% -82%Sub-total 102.1 92.0 -55% -6% -23% -56%Unattributed fluxes Sub-total 7.6 6.3 -32% 6% -2% -32%* Evaporation from private licensed storages (GL/y) is not included as it is already accounted in water use.

4.3.2 Inflows and water availability

Inflows

There are several ways to provide an indication on water availability. The most obvious way is to use the total inflow, which is the sum of all of the inflows in the model. For the Wimmera region, this is 274 GL/year prior to instream losses being taken into account under Scenario A.

An alternative is to locate the point of maximum average annual flow in the river system under pre-development conditions. As all river models are calibrated to achieve mass balance at mainstream gauges, the gauge with maximum average annual flow is a common reference across all models irrespective of how mass balance is calibrated. The pre-development scenarios remove the influences of upstream extractions and regulation and give a reasonable indication of total inflows without the influence of development.

A comparison between scenarios for reaches along the Wimmera River are presented in Figure 4-2. It shows that the maximum average annual mainstream flow occurs at the Mackenzie River confluence with a value of 206 GL/year under Scenario A pre-development. The difference between this value and total system inflow is due to instream losses, distributary flows to Yarriambiack Creek and pre-development flows in the Avon-Richardson catchment.


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Water availability

Table 4-8 shows the average water availability for Scenario A in GL/year and the relative change in water availability for scenarios B and C. This information uses the pre-development annual mainstream flow at the Mackenzie River confluence to define water availability (Figure 4-2).

Table 4-8. Average annual water availability under scenarios B and C relative to Scenario A

A B Cwet Cmid CdryGL/y Percent change from Scenario A

205.7 -53% -6% -21% -54%

A time series of annual water availability under Scenario A is shown in Figure 4-3. Figure 4-4 shows the changes in annual water availability from Scenario A for scenarios B and C.

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Note that the above definition of ‘water availability’ is different from a similarly named term ‘available water’ officially used for the Wimmera and Glenelg River system in the Wimmera and Glenelg River Bulk Entitlements (Minister for Water, 2004). The latter is calculated as the sum of live storage minus water borrowed or carried over from the environment, plus anticipated inflows, plus releases to date and minus anticipated headworks losses. ‘Available water’, as defined here, is used later in the report in relation to reliability and share of available water.

4.3.3 Storage behaviour

The modelled behaviour of major public storages in the Wimmera region gives an indication of the level of regulation of a system as well as how reliable the storages are during extended periods of low or no inflows. Table 4-9 shows the lowest recorded storage volume and the corresponding date for each of the scenarios. The average and maximum years between spills is also provided. A spill event commences when the sum of headworks storages exceed 95 percent of the combined full supply volume and ends when the sum of headworks storages falls below 85 percent of full supply volume. A spill is deemed to occur at 95 percent of full supply level because it is likely that some individual storages will spill at times when total system storage is not at full supply level. The end condition is used to include in a spill event periods when the dam is close to full and oscillates between spilling and just below full. Total Wimmera headworks storage in this section of the report excludes the headworks storages in the Glenelg river basin. The time between spills increases under the wet climate change scenario and spills no longer occur under other climate change scenarios.

Table 4-9. Details of storage behaviour in Wimmera region

Total Wimmera headworks storages A B Cwet Cmid CdryMinimum storage volume (ML) 4476 1101 4032 3363 766Minimum storage date 04/2003 04/1915 03/2006 03/2006 04/1915Average years between spills 5.1 no spills 7.6 no spills no spillsMaximum years between spills 20.8 no spills 30.8 no spills no spills

The time series of total headworks storage behaviour during the most severe drought over the last ten years of the project reporting period show that under the drier future climate scenarios the total system storage is lower at the start of the drought and empties several years earlier and for a longer duration than Scenario A (Figure 4-5).


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Figure 4-5. Total Wimmera headworks storage behaviour over the period of lowest storage content under (a) scenarios A and B, (b) scenarios Cwet, Cmid and Cdry

4.3.4 Consumptive water use

Water use

Table 4-10 shows the average annual water use in different river reaches for Scenario A and the percentage change of all other scenarios compared to Scenario A. Figure 4-6 shows average annual water use under all scenarios in reaches of the Wimmera River from broadly upstream to downstream. Note that the river and water supply system in the Wimmera region is highly nonlinear spatially. Therefore the reach-by-reach presentation of water use (also inflows in Section 4.3.2) is only to provide a very coarse indication of the changes from upstream to downstream.

Table 4-10. Change in annual water use in each calibration reach under scenarios B and C relative to Scenario A

A B Cwet Cmid CdryReach GL/y Percent change from Scenario A Lake Bellfield/Fyans/Lonsdale 2.8 0% 2% 1% -1%Wimmera River upstream of Huddleston’s Weir 7.2 -52% -4% -13% -56%Avon-Richardson Rivers 3.3 -54% -4% -14% -59%Wimmera River from Huddleston’s to Mackenzie River confluence

24.2 -58% -2% -17% -60%

Wartook Reservoir supply 3.6 -31% 3% -2% -30%Waranga Western Channel sole supply areas 0.1 -56% -4% -15% -60%Wimmera River d/s Mackenzie River confluence 0.0 0% 0% 0% 0%Total 41.2 -50% -2% -14% -53%

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Figure 4-6. Average annual water use under scenarios A, B and C from upstream to downstream


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Figure 4-7(a) shows the annual time series of total water use under Scenario A and Figure 4-7(b)–(e) show the difference in annual volumes for the other scenarios relative to Scenario A. The maximum and minimum annual total water use under Scenario A are 53 GL in 1962 and 8 GL in 2005 respectively.

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Table 4-11 shows the annual total water use for the lowest one, three and five-year periods as well as the average annual total water use for Scenario A and the percentage change from Scenario A for each other scenario. These figures indicate the impact of the scenarios on total water use during dry periods and on average.


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Table 4-11. Annual total water use under scenarios A, B and C

A B Cwet Cmid Cdry GL/y Percent change from Scenario A Lowest 1-year period 8.4 -61% -10% -38% -66% Lowest 3-year period 13.1 -65% -15% -28% -66% Lowest 5-year period 14.8 -68% -15% -34% -66% Average 41.2 -50% -2% -14% -53%

Level of use

The level of use is indicated here by both (i) the ratio of total water use to water availability and (ii) the ratio of total diversion to water availability. Total water use here includes only consumptive water use. Total diversion is the sum of total water use and channel and pipe losses. Water availability is as defined as earlier. Table 4-12 shows the level of use for each of the scenarios.

Table 4-12. Level of use under scenarios A, B and C

A B Cwet Cmid Cdry Ratio of water use to water availability 20% 21% 21% 22% 21% Ratio of diversion to water availability 59% 70% 62% 66% 69%

Reliability of supply

An indication of the reliability of supply is given by the percentage of years in which available water is less than a given amount. The reliability of supply for all uses is shown in Figure 4-8, which was extracted from the model under each scenario at the end of October. It gives an indication on the size of the resource pool available for diversion under Schedule 2 of the Bulk Entitlements. It shows that available water is less than the maximum allocation volume of 206 GL under Schedule 2 of the Bulk Entitlement in 56 percent of years under the median climate change scenario (Scenario Cmid), compared with 26 percent of years under Scenario A.

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Figure 4-8. Reliability of supply to all water users in the Wimmera and Glenelg River system

Reliability of supply for individual water users are shown in Figure 4-9. Note that ‘Compensation’, a term used in the bulk entitlement, refers to supply to stock and domestic users on the Glenelg River immediately below Rocklands Reservoir. As an example of interpretation of the graphs, the available water to stock and domestic users supplied by channel is estimated to be less than the maximum allocation in around 55 percent of years under median climate change scenario (Scenario Cmid), compared with 25 percent of years under historical climate (Scenario A).


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4.3.5 River flow behaviour

Figure 4-10 shows the flow duration curves for the three end-of-system locations: Wimmera River inflows to Lake Hindmarsh, Yarriambiack Creek flows at Horsham and Avon River flows to Lake Buloke. Wimmera River inflows to Lake Hindmarsh have been used in these plots instead of outflows from Lake Brambruk because it is a more useful indicator of the changes in the contribution of Wimmera River flows to receiving wetlands, which include Lake Hindmarsh, Lake Albacutya and Lake Brambruk. The cease-to-flow percentiles for these scenarios are presented in Table 4-13. Cease-to-flow is considered to occur when model flows are less than 1 ML/month. Cease-to-flow in Yarriambiack Creek is lower under Scenario A pre-development conditions (denoted as P in Figure 4-5 and Table 4-10), which is possibly because of the influence of the headworks storages on minor flood events.

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Figure 4-10. Monthly flow duration curves at end-of-system flow locations- (a) Inflow to Lake Hindmarsh; (b) Yarriambiack Ck at Horsham and (c) Inflow to Lake Buloke under scenarios P (Scenario A pre-development), A, B and C

Table 4-13. Cease-to-flow in percentage time under scenarios P (Scenario A pre-development), A, B and C

Outflow Name P A B Cwet Cmid Cdry Lake Hindmarsh inflows 71.5% 58.3% 53.9% 57.4% 57.8% 53.3% Yarriambiack Creek 47.0% 27.5% 31.5% 27.3% 27.3% 32.2% Lake Buloke inflows 53.5% 66.4% 54.9% 66.0% 62.4% 56.3%

Figure 4-11 shows the mean monthly flow under scenarios P, A, B and C for the three end-of-system outflow locations. The seasonality at the end-of-system has not changed between pre-development and current level of development and


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is not expected to change markedly under future climate scenarios. The high average monthly flow in February for the inflows to Lake Buloke is due to more natural high flow events occurring in February than surrounding months.

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Figure 4-11. Seasonal plots at each of the end-of-system flow locations - (a) Inflow to Lake Hindmarsh; (b) Yarriambiack Ck at Horsham and (c) Inflow to Lake Bulokeunder under scenarios P (P represents Scenario A pre-development), A, B and C

4.3.6 Share of total available water

The share of the total available water to each user group in the Wimmera system is divided according to bulk entitlements. Total available water changes as the climate conditions change, and this in turn changes the share of water between user groups with different priorities given under the current water share arrangement. Table 4-14, Table 4-15, Figure 4-12 and Figure 4-13 show the modelling results on the share of water between different user groups. For example, the environment’s share of water in the 90th percentile dry year, decreases from 23 percent under Scenario A to 11 percent under the median 2030 climate scenario, with urban and stock and domestic water users being entitled to a larger share of the smaller pool of water under extremely dry conditions.


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Table 4-14. Average share of the total available water to user groups under each scenario

A B Cwet Cmid CdryStock and domestic supplied by channel 52% 61% 53% 55% 62%Supply by agreement from Headworks 3% 2% 3% 3% 2%Irrigation 12% 4% 11% 10% 4%Glenelg compensation 2% 2% 2% 2% 1%Recreation 1% 0% 1% 1% 0%Urban supply from Headworks 5% 10% 5% 6% 10%Environment 22% 15% 22% 21% 15%Pipeline security 3% 5% 3% 3% 6%

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Figure 4-12. Average levels of available water to different user groups under each scenario

Table 4-15. Share of the total available water to user groups under each scenario in a dry (90th percentile) year

A B Cwet Cmid Cdry90th percentile year 1941 1939 1898 1930 1970Stock and domestic supplied by channel 53% 66% 54% 68% 66%Supply by agreement 3% 1% 3% 2% 1%Irrigation 9% 0% 8% 0% 0%Glenelg compensation 2% 0% 2% 4% 0%Recreation 0% 0% 0% 0% 0%Urban 6% 19% 6% 9% 19%Environment 23% 4% 22% 11% 4%Pipeline security 3% 9% 4% 6% 9%


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Figure 4-13. Available water to user groups under each scenario in a dry (90th percentile) year

Wimmera-Mallee pipeline

All of the findings in this report assume Stage 1 (Supply System #1) of the Wimmera Mallee Pipeline Project. Further stages (2–6) of the pipeline are expected to be constructed over the coming years, which will see a redistribution of water from existing channel losses to other water users, including the environment. An inclusion of further stages of the pipeline would lead to results different from those reported in this study.


The Wimmera and Glenelg river system model was most recently updated by DSE and GWMW to cover the January 1903 to December 2004 period. The common reporting period for this project is July 1895 to June 2006. Given the variability of flows in the Wimmera River system and the impact that individual events can have on results, the numbers reported previously as part of bulk entitlement reporting differ from the numbers reported in this study. Table 4-6 shows that the average annual inflow over the previous modelling period is 351 GL/year while for the common modelling period is 332 GL/year. This is largely a result of including the federation drought and the last two years of extremely low inflows in the assessment period for this project.

The Wimmera region has a reasonably high degree of regulation (Table 4-1). Under historical climate conditions (Scenario A), the largest water use in the Wimmera region is from losses, which include 159 GL/year of net evaporation from the headworks storages (40 GL) and lakes (119 GL) and 80 GL/year of channel losses on average. The Wimmera Mallee pipeline and evaporation suppression recently undertaken by GWMW both act to reduce these losses to make more water available for other purposes. Water use by consumers is around 41 GL/year on average. Available water for all the users is less than the maximum allocation volume of 206 GL in 26 percent of years.

The climate change scenario Cwet is slightly drier than historic climate conditions, with a reduction in inflows of around 5 percent. Reduction in water use is 2 percent, and reduction in outflows is 8 percent.

The climate change scenario Cmid is drier again, with a reduction in inflows of 17 percent. This is partly compensated by an increase in the proportion of water sourced from the Glenelg River. Supply to consumptive users drops by around 14 percent, but urban water users supplied directly from headworks are largely unaffected. Available water for all the users is less than the current maximum allocation volume in 56 percent of years. End-of-system outflows and the share of water to the environment are reduced by around 25 percent in the Wimmera region and around 39 percent in the Glenelg River downstream of Rocklands Reservoir (located outside of the region). There is an increase in the time


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between reservoir spills in the total Wimmera headworks storages from 5 years under historical climate to no occurrence of spills over the 111 year assessment period. Losses decrease because less water is available in the supply system.

Scenarios B and Cdry result in a reduction in inflows of around 50 percent, with a reduction in transfers from the Glenelg River of around 30 percent.

Supply to consumptive users drops by around 50 percent, and urban water users also become affected with a reduction in supply of around 16 percent. The proportion of years when the available water under the bulk entitlement is less than the maximum allocation volume increases from 26 percent currently to around 95 percent. End-of-system outflows and the share of water to the environment are reduced by around 50 percent and there are no spills from the combined headworks storages over the 111 year period of assessment. The proportion of time with no outflow from the system does not significantly change, but there is a large reduction in average outflow volumes. Losses decrease again because less water is available in the supply system.

Under scenarios B and Cdry, the last ten years of drought substantially worsen. The total headworks storage volume starts at around 60 percent lower than it did historically, which results in the modelled storage trace dropping to dead storage levels around three years earlier than happened historically. The share of water available to the environment reduces under these two scenarios in accordance with the current water sharing arrangements in the Wimmera and Glenelg River bulk entitlements. The environment’s share of water in the 90th percentile dry year decreases from 23 percent under Scenario A to 4 percent under Scenario B, with urban and stock and domestic water users being entitled to a larger share of the smaller pool of water under extremely dry conditions.

All of the findings in this report assume Stage 1 (Supply System #1) of the Wimmera Mallee Pipeline Project. Further Stages (2–6) of the pipeline are expected to be constructed over the coming years, which will see a redistribution of water from existing channel losses to other water users, including the environment. An inclusion of further stages of the pipeline would lead to results different from those reported in this project.

The findings in this report also assume current water sharing and management arrangements. Adaptive management processes required under Victorian legislation include long-term water resource assessments and sustainable water strategies, which assist in ensuring the level of equity desired by the broader community is achieved. Thus, water sharing and management arrangement may adapt over time to future water resources conditions.

4.5 References

Minister for Water (2004) Bulk Entitlement (Wimmera and Glenelg Rivers – Wimmera Mallee Water) Conversion Order 2004.


5 Uncertainty in surface w

ater modelling results

5 Uncertainty in surface water modelling results This chapter describes the assessment of uncertainty in the surface water modelling results. It has four sections:

� a summary � an overview of the approach � a presentation and description of results � a discussion of key findings.

5.1 Summary

The uncertainty that is internal to the river model (as opposed to that associated with the scenarios), and the implications that this has for our confidence in the results and their appropriate use, are assessed using multiple lines of evidence. This involves comparing: (i) the river model to historical gauged main stem flows and diversions, which are its main points of reference to actual conditions, and (ii) ungauged inferred inflows and losses in the model to independent data on inflows and losses to ascertain if they can be attributed to known processes. These two aspects of model performance were then combined with some other measures to assess how well the model might predict future patterns of flow.


� The density of gauging in the Wimmera surface water system is similar to the average across the Murray-Darling Basin (MDB). The southern part of the region is well gauged.

5.1.2 Key messages

� The model is well suited to evaluate changes in the characteristics of high flows as a consequence of climate scenarios, and probably adequate to evaluate changes in the long-term water balance.

� The model is unsuitable to evaluate changes in low flows, which may be a problem for assessing baseflow maintenance for ecological purposes.

� Hydrological understanding appears good apart from flow losses in the Wimmera River between Glenorchy Weir and Horsham, which led to unpredicted very low flows after 1997.

� Uncertainty associated with farm dam development and forestry appears small. Groundwater interactions may be important in explaining unattributed gains or losses from the Wimmera River above Horsham.

� Considerable external uncertainty in projected flow patterns is caused by the high level of regulation, including transfers between basins, reservoirs and a complex system of natural and artificial channels and pipelines, and the transmission losses that may occur in these.

5.2 Approach

5.2.1 General

A river model is used in Chapter 4 to analyse expected changes in water balance, flow patterns and consequent water security under climate and/or development change scenarios. Uncertainty in the analysis can be external or internal:

� External uncertainty is external to the model. It includes uncertainty associated with the forcing data used in the model, determined by processes outside the model such as climate processes, land use and water resources development, and


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� Internal uncertainty relates to predictive uncertainty in the river model that is an imperfect representation of reality. It can include uncertainty associated with the conceptual model, the algorithms and software code it is expressed in, and its specific application to a region (Refsgaard and Henriksen, 2004).

Full measurement of uncertainty is impossible. The analysis focuses on internal uncertainty. When scenarios take the model beyond circumstances that have been observed in the past, measurable uncertainty may only be a small part of total uncertainty (Weiss, 2003; Bredehoeft, 2005). The approach to addressing internal uncertainty involved combining quantitative analysis with qualitative interpretation of the model adequacy (similar to ‘model pedigree’, cf. Funtowicz and Ravetz, 1990; Van der Sluijs et al., 2005) using multiple lines of evidence. The lines of evidence are:

� the quality of the hydrological observation network � the components of total estimated stream flow gains and losses that are directly gauged, or can easily be

attributed using additional observations and knowledge, respectively (through water accounting) � characteristics of model conceptualisation, assumptions and calibration � the confidence with which the water balance can be estimated (through comparison of water balances from the

baseline river model simulations and from water accounting) � measures of the baseline model’s performance in simulating observed stream flow patterns, and � the projected changes in flow pattern under the scenarios compared to the performance of the model in

reproducing historic flow patterns.

None of these lines of evidence are conclusive in their own right. In particular:

� the model may be ‘right for the wrong reasons’. For example, by having compensating errors � there is no absolute ‘reference’ truth, all observations inherently have errors and the water accounts developed

here use models and inference to attribute water balance components that were not directly measured, and � adequate reproduction of historically observed patterns does not guarantee that reliable predictions about the

future are produced. This is particularly so if model boundary conditions are outside historically observed conditions, such as in climate change studies like this.

Qualitative model assessment is preferably done by expert elicitation (Refsgaard et al., 2006). The timing of the project prevented this. Instead a tentative assessment of model performance is reviewed by research area experts within and outside the project as well as stakeholder representatives.

The likelihood that the river model gives realistic estimates of the changes that would occur under the scenarios evaluated is assessed within the above limitations.

Overall river model uncertainty is the sum of internal and external uncertainty. The range of results under different scenarios in this project provides an indication of the external uncertainty. River model improvements will reduce overall uncertainty only where internal uncertainty clearly exceeds the external uncertainty.

The implication of overall uncertainty on the use of the results presented in this study depends on: (i) the magnitude of the assessed change and the level of threat that this implies, and (ii) the acceptable level of risk (Pappenberger and Beven, 2006). This is largely a subjective assessment and no attempt is made to judge. A possible framework for users of the project results to consider the implications of the assessed uncertainties is shown in Table 5-1.




Table 5-1. Possible framework for considering implications of assessed uncertainties

Low threat High threat

Low

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Current water sharing arrangements appear sufficient for ongoing management of water resources.

Current water sharing arrangements are likely to be inadequate for ongoing management of water resources, as they do not adequately consider future threats.

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h un

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Current water sharing arrangements appear sufficient for ongoing management of water resources, but careful monitoring and adaptive management is recommended.

Current water sharing arrangements may be inadequate for ongoing management of water resources. Further work to reduce the major sources of uncertainty can help guide changes to water sharing arrangements.

5.2.2 Information sources

Information on the gauging network was obtained from the Water Resources Station Catalogue (www.bom.gov.au/hydro/wrsc) and the Victorian Water Resources Data Warehouse (www.vicwaterdata.net ). The draft model calibration report for the Wimmera-Mallee REALM model (NRE, unpublished) was provided by the Victorian Department of Natural Resources and Environment, and a report on a recent model update was provided by SKM (2004). Time series of water balance components as modelled under the baseline scenario (Scenario A) and all other scenarios were derived as described in Chapter 4. The data used in water accounting are described in the following section.

5.2.3 Water balance accounting

Purpose

Generic aspects of the water accounting methods are described in Chapter 1. This section includes a description of the basic purpose of the accounts, which is to inform the uncertainty analysis carried out as part of this study using an independent set of the different water balance components by reach and by month. The descriptions in Chapter 1 also cover the aspects of the remote sensing analyses to estimate wetland and irrigation water use, as well as the calculations for attribution of apparent ungauged gains and losses. Aspects of the methods that pertain specifically to the current region are presented below.

Framework

The available streamflow data for this region was adequate for water accounting for the water years 1990/91 to 2005/06. Water accounts could be established for two successive reaches. The associated catchment areas are shown in Figure 5-1 and are related to model reaches in Table 5-2.

Table 5-2. Comparison of water accounting reaches with river model reaches

Water accounting reach

Subcatchment code(s) Description

1 4152001, 4152003, 4152013, 4152270, 4152291, 4156100, 4152230

Glenorchy Weir – Horsham (internal gauges had insufficient flow data)

2 4152461, 4152511, 4152513, 4152280 Horsham – Lochiel Bridge Not assessed

Reason

4152011, 4152273, 4152454, 4152453 Contributing head water catchment (to reach 1) 4152173, 4152210 Do not contribute to any reach 4152200 No data 4152221, 4152223, 4156013 Downstream of the last available gauging station 4152413, 4152513, 4152571 No data, do not contribute to any reach


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Figure 5-1. Map showing the subcatchments used in modelling, with the reaches for which river water accounts were developed (‘accounting reach’) and contributing head water catchments with gauged inflows (‘contributing catchment’). Black dots and red lines are

nodes and links in the river model respectively.




Wetland and irrigation water use

The results of the remote sensing analyses (Chapter 1) are in Figure 5-1. It shows lakes and wetlands as well as irrigated areas. The wetlands and lakes are largely disconnected to the river system, although they probably receive water during high flows. This may have influenced our accounting for the wet year 1992/93. Diversion data for the Wimmera system were provided by Sinclair Knight Merz.

Calculation and attribution of apparent ungauged gains and losses

Calculation and attribution of apparent ungauged gains and losses were undertaken according to the methods described in Chapter 1.

5.2.4 Model uncertainty analysis

The river model results and water accounts were used to derive measures of model uncertainty. The different analyses are described below. In the interest of brevity details on the equations used to calculate the indicators are not provided here but can be found in Van Dijk et al. (2007). Calculations were made for each reach separately but summary indicators were compared between reaches.

Completeness of hydrological observation network

Statistics on how well all the estimated river gains and losses were gauged or, where not gauged, could be attributed based on additional observations and modelling, were calculated for each reach:

� the volumes of water measured at gauging stations and off-takes, as a fraction of the grand totals of all estimated inflows or gains, and/or all outflows or losses, respectively

� the fraction of month-to-month variation in the above terms � the same calculations as above, but for the sum of gauged terms plus water balance terms that could be

attributed using the water accounting methods.

The results of this analysis for annual totals are also shown in Appendix C.

Comparison of modelled and accounted reach water balance

The water balance terms for river reaches, as modelled by the baseline river model (Scenario A) and as accounted, were compared for the period of water accounting. Large divergence is likely to indicate large uncertainty in reach water fluxes and therefore uncertainty in the river model and water accounts.

Climate range calibrated

If the model calibration period is characterised by climate conditions that are a small subset, or atypical of the range of climate conditions that was historically observed, this probably increases the chance that the model will behave in unexpected ways for climate conditions outside the calibration range. The percentage of the overall climate variability range for the 111-year baseline simulation period that was covered by the extremes in the calibration period was calculated as an indicator.

Performance of the river model in explaining historical flow patterns

All the indicators used in this analysis are based on the Nash-Sutcliffe model efficiency (NSME; Nash and Sutcliffe, 1970). NSME indicates the fraction of observed variability in flow patterns that is accurately reproduced by the model. In addition to NSME values for monthly and annual outflows, values were calculated for log-transformed and ranked flows, and high (highest 10 percent) and low (lowest 10 percent) monthly flows. NSME cannot be calculated for the log-transformed flows where observed monthly flows include zero values or for low flows if more than 10 percent of months have zero flow. NMSE is used to calculate the efficiency of the water accounts in explaining observed outflows.


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This indicates the scope for model improvements to explain more of the observed variability. If NSME is much higher for the water accounts than for the model, it suggests that the model can be improved to reduce uncertainty. If similar, additional hydrological data may be required to support a better model.

A visual comparison of streamflow patterns at the end-of-reach gauge with the flows predicted by the baseline river model and the outflows that could be accounted was done for monthly and annual time series and for monthly flow duration curves.

Scenario change-uncertainty ratio

Streamflow patterns simulated for any of the scenarios can be used as an alternative river model. If these scenario flows explain historically observed flows about as well or better than the baseline model, then it may be concluded that the modelled scenario changes are within model ‘noise’, that is, smaller or similar to model uncertainty. Conversely, if the agreement between scenario flows and historically observed flows is poor – much poorer than between the baseline model and observations – then the model uncertainty is smaller than the modelled change, and the modelled change can be meaningfully interpreted.

The metric used to test this hypothesis is the change-uncertainty ratio. The definition was modified from Bormann (2005) and calculated as the ratio of the NSME value for the scenario model to that for the baseline (Scenario A) model. A value of around 1.0 or less suggests that the projected scenario change is not significant when compared to river model uncertainty. A ratio that is considerably greater than 1.0 indicates that the future scenario model is much poorer at producing historic observations than the baseline model, suggesting that the scenario leads to significant changes in flow. The change-uncertainty ratio is calculated for monthly and annual values, in case the baseline model reproduces annual patterns well but not monthly patterns. The same information was plotted as annual time series, monthly flow duration curves and a graphical comparison made of monthly and annual change-uncertainty ratios for each scenario.

5.3 Results

5.3.1 Density of the gauging network

Figure 5-2 shows the location of streamflow, rainfall, and evaporation gauges in the region, and Table 5-3 provides information on the measurement network. The Wimmera region has a gauging network with a density that is similar to the average for the MDB (ranked 7 out of 18 regions), although it is the sparsest network in Victoria, commensurate with volume of water generated within the region. Most streamflow gauges are located in the areas of higher rainfall south of the region, where the vast majority of water is generated, and along the Wimmera River. The flow-gauging network is considered relatively dense in these areas (Figure 5-2).

Table 5-3. Some characteristics of the gauging network of the Wimmera region (30,640 km2) compared with the entire Murray-Darling Basin (1,062,443 km2)

Gauging network characteristics Wimmera Murray-Darling Basin Number per 1000 km2 Number per 1000 km2

Rainfall Total stations 217 7.08 6,232 5.87Stations active since 1990 107 3.49 3,222 3.03Average years of record 58 45 Streamflow Total stations 41 1.34 1,090 1.03Stations active since 1990 36 1.17 881 0.83Average years of record 17 20 Evaporation Total stations 10 0.33 152 0.14Stations active since 1990 6 0.17 104 0.10Average years of record 25 27




Figure 5-2. Map showing the rainfall, streamflow and evaporation observation network, along with the subcatchments used in modelling

5.3.2 Review of model calibration and evaluation information

This section provides a summary of the river model, its calibration and prior assessment of its performance based on information reported in NRE (unpublished draft) and SKM (2004).

Model description

Most of the Wimmera region is covered by the Wimmera-Mallee REALM Model. It is a river planning model that simulates the ‘headworks’, south of the Wimmera, and the ‘channel system’, north of the Wimmera. Headworks include


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the water balance of storage reservoirs, a channel system that allows transfers between storages, streams from which water is diverted, urban demands supplied year-round, and rural demands supplied during summer.

The channel system represents the network of open channels that supplies water to the north of the region and rural and urban demands during winter. The system is described by 16 model nodes (Chapter 4 and Figure 5-1).

Data availability and use

Information on available data is from SKM (2004) and therefore relates to the 2004 model update, which includes the Wimmera between Horsham and Lake Albacutya, as well as the three urban supply systems that are operated by Grampians Wimmera Mallee Water (Ararat, Stawell and Halls Gap). For the Wimmera part of the model, seven rainfall input files were developed based on rainfall measured at 11 stations. Average annual potential evaporation patterns were estimated for 15 separate model units. Streamflow data used in the model was from 17 gauging stations in the Wimmera region, Glenelg catchment south of the region, and Avoca catchment to the east (Table 5-4). Flow data on the main river were available at Horsham for 1975 onwards, and at Glenorchy Weir two years later. It was reported that changes to stage height-flow rating tables made since initial model calibrations did not significantly influence the model performance (SKM, 2004).

Table 5-4. Streamflow gauging stations for which data were used in Wimmera-Mallee REALM model calibration

Station Name Start year

238205 Glenelg River @ Rocklands reservoir 1983

238207 Wannon River @ Jimmy Creek 1975

238700 Rocklands channel @ Rocklands 1987

238702 Moora outlet channel @ Moora 1988

408203 Avoca River @ Quambatook 1967

415200 Wimmera River @ Horsham 1975

415201 Wimmera River @ Glenorchy Weir 1977

415202 Mackenzie River @ Wartook 1976

415203 Mount William Creek @ Lake 1985

415206 Wimmera River @ Glynwylln 1995

415217 Fyans Creek @ Grampians Road 1969

415220 Avon River @ Wimmera Highway 1987

415223 Burnt Creek @ Wonwondah east 1987

415226 Richardson River @ Carrs 1992

415246 Wimmera River @ Lochiel railway 2005

415251 Mackenzie River @ Mckenzie Creek 1988

415704 Wannon diversion pipeline 1992

Model calibration

Calibration was performed component by component and progressively down the system, using flow and storage observations for the seven-year period from January 1993 to June 2000. Calibration of the headworks focused on reproducing the transfer of water from one storage to another, which in reality is operated to minimise storage evaporation and maximise harvesting. Recorded historical releases were progressively replaced by operating rules that produce similar release patterns.

Calibration for the channel system was separate for each of the 16 model reaches. The calibration objective was to fill the notional storages each year whilst matching recorded inflows at each of the simulated gauges. In practice it was




aimed to reproduce annual apparent losses in the system rather than individual monthly values. This was done by adjusting water use from the storages and then adjusting transfer losses in the system.

Demands for the summer channel run and irrigation were set to metered records. No restrictions were modelled (in practice these were not introduced until November 1999). Notional storage capacities were set to estimated total urban and rural dam volumes, and releases, storage target filling curves and losses were described using operational rules.

The model has been updated using data until June 2004 (SKM, 2004). The overall model outputs were compared to previous reports and shown to be satisfactory.

Model performance assessment

No independent validation was attempted by DNR or SKM, but model performance in reproducing observations during the calibration period was evaluated. The information below is derived from DNR (unpublished); it is assumed here that these conclusions still hold after more recent updates (SKM, 2004):

� the total headworks storage behaviour, a measure of the amount of water harvested, was reproduced well. The model reproduced progressive drawdown during a recent drought, which provided a high level of confidence of its ability to cope with extreme conditions

� modelled storage levels in Rocklands, Toolondo, Pine and Taylors reservoirs agreed well with historic patterns, with small deviations because of the simplified operational rules describing transfers between storages. Storage levels for Bellfield, Fyans and Lonsdale reservoirs were also reproduced well, particularly peaks and troughs. Lesser simulation was achieved for storage inflows by the rainfall-runoff model in some instances. Historic streamflow patterns at five gauges were reproduced well to very well by the model, with the exception of Burnt Creek, where performance was deemed acceptable (Table 5-5)

� historic release patterns into the northern channel system, at Taylors Lake Outlet, Rocklands-Lubeck channel and the Main Central Channel, were reproduced quite well. The monthly distribution of flows is marginally different but annual and cumulative release volumes match very well

� modelled flows entering 16 supply node areas compared well with historic data, although there was evidence of compensating errors between areas

� overall, the calibration performance of the individual headworks and channel system components was classified as excellent. However, additional channel losses of 7 to 27 percent of inflows were required to bring the two main model components in agreement.

Table 5-5. Details of model performance in reproducing observed flow patterns

Reach Downstream gauging station code and name

Assessment

415201 Wimmera River d/s Glenorchy weir Good reproduction of flood frequency distribution, less so temporal patterns. Uncertainty due to runoff inflows, daily diversion patterns, operational goal of forcing spill at Glenorchy weir and losses applied along the river.

415223 Burnt Creek @ Wonwondah East Acceptable performance. Overestimation of high flows (>20 ML/d) and underestimation of low flows (<20 ML/d), attributed to local runoff.

415200 Wimmera River @ Horsham Very good fit. Reasonable accuracy at flows <300 ML/d achieved with loss function but underestimation of flood flows.

238205 Glenelg River @ Rocklands reservoir Very good fit 238207 Wannon River @ Jimmy Creek Good fit. Model diverts right amount of water at the right time. Source: DNRE, unpublished

Overall the strong points identified were the good reproduction of historical observations of storage height and releases, streamflow at key locations and the volumes supplied to dams.

The greatest uncertainties were deemed to be associated with:

� channel losses in the distribution system � lumping of urban and rural dams � difficulties in reproducing daily operational rules in a monthly time step model.


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These simplifications were due to: a lack of data at the required resolution and limit model complexity. This limits the use of the model to investigate the system down to a ‘fine level of detail’. Overall the model is suitable for the purpose of bulk entitlement conversion and determining the MDB Cap.

5.3.3 Model uncertainty analysis

Completeness of hydrological observation network

The hydrology of the Wimmera-Mallee system is complex. There are inter-basin transfers and transfers to rural water users north of the river system through numerous open channels. Analysis of streamflow data indicated that flows patterns for 1997 to 2006 were very different from those during 1990 to 1996: flows were an order of magnitude smaller for the latter period (Appendix C). The completeness of gauging and hydrological understanding may be described as follows:

� Reach 1 (Glenorchy Weir – Horsham). This is a slightly losing reach with moderately comprehensive gauging. 50 percent of estimated total gains and 85 percent of losses are gauged. Another 30 percent of gains can be attributed to inflows using adjusted SIMHYD runoff estimates. About 20 percent of the water balance remains unattributed. This could be the result of errors in the two gauges or poor simulation of ungauged inflows in both model and accounts. The unattributed fraction is about the same as the difference between modelled and accounted total gains. A comparison of time series suggests that low flows have reduced significantly since 2000, which could not be attributed using inflow data

� Reach 2 (Horsham – Lochiel Bridge). This is a slightly losing reach with comprehensive gauging: 84 percent of gains, and 92 percent of losses, are gauged. Another 10 percent of ungauged inflows could be attributed based on adjusted SIMHYD estimates. The remaining 7 percent of the water balance could not be attributed.

Overall the hydrology in Reach 2 is reasonably well gauged and understood, but the hydrology above Horsham is only moderately well gauged and understood. In particular, the cause for reduced low flows after 1997 could not be attributed directly.

Comparison of modelled and accounted reach water balance

A summary of the regional water balance simulated by the river model and derived by water accounting is listed in Table 5-6. In both cases, numbers are averages for the period 1990 to 2006 to allow direct comparison. Definitions of gain and loss terms may differ between the model and accounts. For example, ungauged inflows in the model may be a combination of ungauged and unattributed inflows in the accounts and ungauged losses in the model may be identified with unattributed losses in the accounts. Neither the river model nor the water accounts include estimates of groundwater exchanges, because no data were available to constrain such estimates (groundwater discharge is implicit in local inflow flow estimates).

Comparing modelled and accounted water balances:

� the model has total gains and losses that are about 30 GL/year larger than accounted values. Estimates of local runoff are considerably larger than those accounted, even if unattributed gains are included

� the model overestimates average end-of-system outflows at Lochiel Bridge by about 14 GL/year or 24 percent. This is probably a result of overestimating flow at the end of Reach 1 by 19 GL/year, as there are few other gains and losses in Reach 2. Overall, there seems to be high uncertainty in inflows which affected inaccuracy in predicting gauged flows

� the model overestimates all flows below 2 GL/month at both downstream gauging stations.




Table 5-6. Regional water balance modelled and estimated on the basis of water accounting

Water balance (Jul 1990 – Jun 2006) Model (A) Accounts Difference GL/y Total gains 157 139 18Gauged inflows 61 65 -4 Ungauged inflows 96 45 51 Unattributed inflows - 30 -30 Total losses 157 139 17 End-of-system outflows 72 59 14 Other gauged outflows 5 - 5 Diversions 61 56 5 River flux to groundwater - - 0 Other ungauged losses 18 - 18 Unattributed losses - 25 -25

Climate range calibrated

The period for which the model as a whole was calibrated (including updates) was 1993 to 2004. In the 111 years of historical rainfall records up to 2006, seven drier years and 18 wetter years occurred. Overall, the climate calibration range is limited.

The same 111-year period also had seven drier years than the water accounting period (1990 to 2006) but only one wetter year. This is because the relatively wet year 1992 was included. The accounts therefore provide a good opportunity to assess model performance for a wet year, as well as during the persistent drought after 2004.

Performance of the river model in explaining historic flow patterns

The better the baseline model simulates streamflow patterns, the greater the likelihood is that it represents the response of river flows to changed climate, land use and regulation changes – notwithstanding that the model is possibly right for the wrong reasons through compensating errors. Appendix C lists reach by reach indicators of the models performance in reproducing historical patterns in measured monthly and annual flows. All are variants of Nash-Sutcliffe model efficiency. Key observations are:

� model performance in explaining historical variations in flow at Horsham and Lochiel Bridge is very good, for monthly flows as well as annual totals (NSME 0.85 and 0.92 to 0.94 for monthly and annual values, respectively)

� flows in the 20 percent of months with peak flows are also well to very well simulated (NSME 0.78 to 0.81)

� low flows (20 percent of months with lowest flows) are very poorly simulated. Comparison of monthly time series indicates that low flows are much overestimated, particularly after 1997 (Figure 5-3), also leading to a large mismatch in the flow duration curve (Appendix C).


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Figure 5-3. Comparison of observed (gauged) and modelled (model) monthly flows at Horsham, showing overestimation of low flows, particularly after 1997

Scenario change-uncertainty ratio

A high change-uncertainty ratio (CUR) corresponds with a scenario change in flows that is likely to be significant given the uncertainty or noise in the model. A value of around one (1) means that the modelled change is similar to the uncertainty in the model. The changes under all scenarios were moderate to very strong for all scenarios and both gauges (CUR 1.6 to 12.7, Appendix C) compared to the uncertainty in the model. This was true for the increase in flows predicted to occur for the pre-development simulation, particularly for medium to high flows. The changes in all climate scenarios were strong when compared to model performance for all but the wet scenario which had a moderate reduction change.


5.4.1 Completeness of the gauging network and understanding of regional surface hydrology

The density of gauging in the Wimmera surface water system compares with the average across the MDB (Section 5.3.1). The southern part of the region, where the Wimmera River is located, is well gauged. The first gauging year was 1975.

Overall, hydrological understanding appears good, with the possible exception of the nature of apparent unattributed flow gains and losses from the Wimmera River between Glenorchy Weir and Horsham (Reach 1; Section 5.3.3). These poorly understood gains or losses led to very low flows after 2000, less than could be accounted for by inflows from upstream or estimated diversions and evaporative river system losses. Explanations may be losses to groundwater, gauging errors or strong reductions in local inflows.

The system is dominated by relatively intensive regulation and water redistribution. Day-to-day operations cannot be reproduced by the monthly time step model in great detail. Further uncertainty is introduced by the large number of small open distribution channels with associated transmission losses.

5.4.2 Performance and uncertainty in aspects of the river model

Earlier assessment of model performance concluded that:

� the model reproduced storage behaviour and release patterns from the various reservoirs well, both in general and during more extreme periods (Section 5.3.2). The finding was not verified in this analysis.

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� simulation of flows was acceptable to very good (Section 5.3.2). This analysis confirms such for annual flow patterns and medium to high flows at the Wimmera river gauging stations of Horsham and Lochiel Bridge, but shows that low flows are not well reproduced, particularly after 2000. DNRE (unpublished) also point out that there appear to be compensating errors in the model, and that high and low flows at Horsham are not simulated well. Assuming that the inflow gauging was of sufficient quality, low flow issues can be ascribed to channel losses or local inflows that are not well reproduced by the model or water accounting.

� overall, therefore, the greatest uncertainty appears associated with channel losses or ungauged inflows, and the likelihood that the model calibration contains compensating errors that affect confidence in model behaviour outside the calibrated range. Model performance for the post-2000 drier conditions confirm this.

5.4.3 Implications for use of the results of this study

The Wimmera-Mallee surface water model appears to provide a reasonable to good representation of most aspects of regional hydrology. High flows appear to be simulated well and there is less scope for compensating errors. However, the performance of the model in reproducing low flows in the Wimmera River is poor, while the possibility of compensating errors also affect estimates of long-term average fluxes. Overestimates of low flows may mean that low flow maintenance for ecological purposes is more at risk than was previously thought.

Conceptual uncertainty and the likelihood of unexpected system behaviour associated with farm dam development and forestry were small (Chapter 3). Uncertainty associated with groundwater is discussed in Chapter 6. The poorly understood gains and losses above Horsham suggest that groundwater interactions may be important, with the prospect of reduced inflows since 2000. Considerable external uncertainty in projected flow patterns is caused by the high level of regulation, including transfers between basins, reservoirs and a complex system of natural and artificial channels and pipelines.

Overall, the model is well suited to evaluate changes in the characteristics of high flows as a consequence of climate scenarios, probably adequate to evaluate changes in the long-term water balance, but unsuited to evaluate changes in low flows.

5.5 References

Bormann H (2005) Evaluation of hydrological models for scenario analyses: Signal-to-noise-ratio between scenario effects and model uncertainty. Advances in Geosciences 5, 43–48.

Bredehoeft J (2005) The conceptual model problem—surprise. Hydrogeology Journal 13, 37–46. Funtowicz SO and Ravetz J (1990) Uncertainty and Quality in Science for Policy. Kluwer Academic Publishers, Dordrecht. Nash JE and Sutcliffe JV (1970) River flow forecasting through conceptual models, 1: a discussion of principles. Journal of Hydrology 10,

282–290. NRE (Victoria Department of Natural Resources and Environment) (unpublished) Model Calibration Report for the Wimmera-Mallee

REALM model. Draft, February 2002. Victoria Department of Natural Resources and Environment. Pappenberger F and Beven KJ (2006) Ignorance is bliss: Or seven reasons not to use uncertainty analysis. Water Resources Research

42, W05302, doi 10.1029/2005WR004820. Refsgaard JC and Henriksen HJ (2004) Modelling guidelines–terminology and guiding principles. Advances in Water Resources 27, 71–

82. Refsgaard JC, van der Sluijs JP, Brown J and van der Keur P (2006) A Framework for dealing with uncertainty due to model structure

error. Advances in Water Resources 29, 1586–1597. SKM (Sinclair Knight Merz) (2004) Wimmera-Mallee Simulation Model. Update of the Wimmera-Mallee model input data to June 2004.

Sinclair Knight Merz, October 2004. Van der Sluijs JP, Craye M, Funtowicz S, Kloprogge P, Ravetz J and Risbey J (2005) Combining quantitative and qualitative measures

of uncertainty in model based environmental assessment: the NUSAP System. Risk Analysis 25, 481–492. Van Dijk AIJM (2007) Climate variability impacts on the already stretched Murray-Darling Basin water system – assessment and policy

implications. In: Proceedings of the World Water Week, Stockholm, Sweden. Weiss C (2003) Expressing scientific uncertainty. Law, Probability and Risk 2, 25–46.


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6 Groundwater assessment This chapter describes the assessment for the Wimmera region. It has four sections:

� a summary � a description of the groundwater management units (GMUs) in the Wimmera � a detailed analysis of the hydrogeology as it applies to the region � an assessment of groundwater extraction versus GMU recharge.

6.1 Summary


� Groundwater resources are limited in the Wimmera region and groundwater use represents less than 0.1 percent of groundwater use in the MDB (excluding the confined GAB aquifers). However, groundwater is the only source of water for areas in the western Wimmera region as the stock and domestic channel network does not extend to that area.

� Groundwater is predominantly sourced from the Murray Group Limestone Aquifer, which is found at reasonably shallow depths (60 to 120 m) and contains good quality water.

� There are three GMUs in the Wimmera region, however, entitlements only exist for the Balrootan GMU. There are also entitlements for unincorporated areas, mainly in the Gymbowen area. The three GMUs are in confined aquifers and are not recharged by local rainfall.

6.1.2 Key messages

� Licensed groundwater extraction from the three GMUs in the Wimmera region in 2004–05 was 0.41 GL/year (excluding use from unincorporated areas and unlicensed stock and domestic use). Most of the current entitlements cover unincorporated areas and licensed extraction from these areas for 2004–05 was 1.03 GL/year. Requests for increases in entitlements in these areas prompted a proposal for a new Gymbowen GMU in the region’s south west. Information on stock and domestic use is poor but this use appears to be comparable to licensed entitlements.

� Level of groundwater use in the Wimmera is indicated by the ratio of extraction to permissible consumptive volume (PCV). Groundwater use from the Balrootan GMU is moderate, at 41 percent of PCV. The PCV estimate in this case is comparable to the estimated through-flow. There is no development for two of the GMUs (Nhill and Goroke) as these cover the deep Renmark Group Aquifer.

� The current level of groundwater use is not regarded as a threat to the Wimmera River, primarily because extractions occur in the far west of the region at a considerable distance from the river.

� Projected growth in groundwater use to 2030 for the Balrootan GMU would increase use to 50 percent of PCV. � Future development is unlikely to affect the Wimmera River, although development in some upland areas may

have significant impact.

6.1.3 Uncertainty

There is considerable doubt about the groundwater balances in all three GMUs. The ratios indicating the level of use therefore have considerable uncertainty.


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6.2 Groundwater management units in the Wimmera

The Wimmera region contains three GMUs (Balrootan, Goroke and Nhill). Details of extraction, entitlements, PCV and recharge are shown in Table 6-1. Balrootan has a low priority level and Nhill and Goroke have very low priority levels in the context of the project, due to the comparatively low level of groundwater use and limited potential for groundwater to impact on streamflow. Due to these priority levels the groundwater assessments for the Wimmera were limited to a simple analysis by providing an overview of the hydrogeological setting including surface-groundwater connectivity and an evaluation of the impact of changing rainfall recharge and extraction under each of the scenarios. While these limited assessments are appropriate within the constraints and for the terms of reference of this project, additional work may be required for local management of groundwater resources.

Table 6-1. Annual extraction, entitlement, PCV and recharge details of Wimmera groundwater management units

Code GMU Extraction 2004–05

Licensed entitlement

Permissible consumptive

volume

Rainfall recharge

Recharge to unit*

Projected 2030 use

GL/y V47 Balrootan GMU 0.41 1.52 0.98 NA 1 0.5V62 Goroke GMU 0 0 2.2 NA 2.2 0V61 Nhill GMU 0 0 1.2 NA 1.2 0 Unincorporated area 1.03 1.61 NA NA 7.5 1.31 Stock and domestic** 0.4 NA NA NA NA 0.4* This is largely based on PCV for GMU and recharge to Gymbowen area. Recharge to unincorporated areas is much larger than estimate in Table but this estimate is relevant to extraction. ** Methodology described below, stock and domestic use is not licensed

6.3 Hydrogeology

Chapter 2 provides a broad overview of the hydrogeology of the Wimmera. This section provides a detailed analysis as it applies to the three existing GMUs and the proposed Gymbowen GMU, all of which lie in the west of the Wimmera region.

There are three main aquifers within the Wimmera Basin: the Tertiary Confined Sands Aquifer (TCSA), also known as the Renmark Group Aquifer, the Murray Group Limestone (MGL) Aquifer and the Parilla Sand Aquifer (PSA), also known as the Pliocene Sands Aquifer.

The TCSA persists across most of the region, except where the basement rises to the surface along the southern border of the region and also at Mount Arapiles. The TCSA varies in thickness up to 60 m and contains groundwater of reasonable quality (500 to 1500 mg/L total dissolved solids (TDS)). However, the aquifer is essentially an untapped supply due to the greater depth of the resource and good quality water in the overlying aquifer.

Calcareous clays (up to 50 m thick) separate the basal TCSA from the overlying MGL. The MGL Aquifer is thickest to the west of the region and occurs only as isolated outliers of limestone surrounded by marls to the east (Lawrence, 1975). To the south, the MGL is thin or nonexistent where it abuts the bedrock of the Padthaway ridge. Near the Balrootan GMU, the MGL has an approximate transmissivity of 65 m2/day and a storage co-efficient of 4 x 10-5 (SKM, 1998). Groundwater quality of the MGL aquifer is generally less than 1500 mg/L TDS (McAuley et al., 1992) except for a few small areas, including one immediately west of Goroke and another west of Lake Hindmarsh, where groundwater quality is generally between 1500 and 3000 mg/L TDS.

The Bookpurnong Beds are a shallow marine deposit, generally less than 10 m thick, and form an aquitard on top of the MGL Aquifer with a vertical hydraulic conductivity between 4.4 x 10-5 and 1 x 10-4 m/day (SKM, 1998). These clays grade upwards to the Parilla Sand. Although the Bookpurnong Beds confine the MGL across most of the region, they are not thought to occur in the south of the region, such that the MGL and the PSA are hydraulically connected (SKM, 2002).


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Figure 6-1. Map of groundwater management units in the Wimmera region

The PSA forms the regional watertable aquifer and occurs everywhere except in the small area of outcropping bedrock at Mt Arapiles. The Parilla Sand has an average thickness of 30 m and thins to the south at the edge of the Murray Basin. Overlying the PSA across most of the area is the Woorinen dune fields, except within the Wimmera River trench where the Shepparton Formation fluvial sediments occur.

Groundwater quality within the PSA is variable within the GMU areas. East of Goroke salinities are generally less than 1500 mg/L TDS. West of Goroke, they range from 1500 to 3000 mg/L TDS (McAuley et al., 1992). Close to the Wimmera River, quality within the watertable aquifer is poor, mainly due to evaporative enrichment of salts in areas with shallow watertables. Saline discharge of groundwater from the regional Parilla Sand Aquifer causes downstream increases in the


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salinity of the Wimmera River. Deep pools of saline (40,000 to 50,000 �S/cm) anoxic water occur downstream of Horsham.

Large outwash fan deposits on the foot-slopes of the Grampians Ranges form colluvial aprons that inter-finger with the alluvial sediments of the adjacent floodplains (WCMA, 2003). The fine-grained sands comprising the colluvium are sourced from the Grampians sandstone. These outwash deposits receive winter rainfall recharge and inflows of groundwater from the Grampians. The colluvial groundwater is of low salinity (around 2000 μS/cm) and thus is a potential resource.

The outcropping pre-Tertiary basement (Grampians Group) at the southern basin margin is a major recharge zone, with water entering the aquifers and flowing north-westerly towards the Murray River. On a local scale the major recharge mechanism for the MGL is leakage from the overlying PSA, via the Bookpurnong Beds or directly where there is no aquitard. The PSA is recharged by rainfall and point sources such as lakes and swamps (SKM, 2005).

The clearance of native vegetation across large areas largely changes the groundwater balance of the western areas of the Murray Basin (Allison et al., 1990). However, there can be a substantial lag time between an increase in the rate of rainfall infiltration through the root zone and recharge to the unconfined aquifer. The lag time can be years to decades depending on a number of factors including the depth to groundwater. Some parts of the groundwater system may not have reached the post-clearing equilibrium with the new recharge rate. This affects estimates of recharge to the unconfined aquifer.

Groundwater levels in the TCSA show little fluctuation (Figure 6-2a); however, MGL groundwater levels are declining near Lake Hindmarsh. There are no obvious trends in groundwater level near Nhill (Figure 6-2b). Groundwater levels in the Parilla Sand (Figure 6-2c) are strongly correlated with rainfall, decreasing since the start of the drought (URS, 2006)

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Figure 6-2. Balrootan GMU groundwater levels of (a) the Tertiary Confined Sands Aquifer, (b) the Murray Group Limestone Aquifer and (c) the Parilla Sand Aquifer


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6.3.1 Balrootan GMU

The Balrootan GMU covers the MGL Aquifer, with depth limits of 60 to 125 m. The MGL is approximately 75 m thick within the GMU and is separated from the PSA by a 5 to 10 m thick aquitard (the Bookpurnong Beds). Groundwater salinity within the MGL ranges from 1000 to 1500 mg/L TDS within the GMU. The Renmark Group Aquifer (not part of this GMU) is separated from the MGL by over 50 m of Ettrick Marl.

SKM (1998) estimated a through-flow to the Balrootan GMU of 0.98 GL/year. The through-flow calculation is based on an aquifer thickness of 75 m, a hydraulic conductivity of 0.87 m/day based on a 24-hour pumping test reported in Lawrence (1967) and the groundwater gradient from the Horsham hydrogeological map sheet (McAuley et al., 1992). The PCV for the Balrootan GMU is equal to this through-flow value.

The Bookpurnong Beds cover the entire GMU and are relatively thin. There is a downward hydraulic gradient from the PSA to the MGL. There are no nested observation bore sites within the Balrootan GMU to help measure hydraulic gradients. However, nearby information (McAuley et al., 1992) indicates downward head differences could be 2 to 4 m. Using a 2 m head difference and the vertical hydraulic conductivities for the Bookpurnong Beds reported in Lawrence (1967), the downward flux from the PSA to the MGL is estimated to be 2.7 to 6.1 GL/year. Groundwater salinity in the overlying PSA is similar to the MGL within the Balrootan GMU and therefore leakage from the PSA is unlikely to salinise the MGL.

Recharge mapping across the Wimmera-Mallee region (SKM, 2002) estimated Balrootan GMU post-development recharge at around 12 mm/year. This results in 5 GL/year recharge to the PSA within the Balrootan GMU. It is unclear if the (presumed increased) recharge wetting front has reached the water table at 40 to 50 m. A large salt store in the unsaturated zone (Leaney and Herczeg, 1999) could constrain future groundwater use, though it may be around 100 years away.

A replenishment rate of 0.98 GL/year is used for Balrootan GMU, which is equal to the PCV. The figure is based on through-flow and does not include downward leakage from the PSA. The figure is probably a low estimate of the volume of groundwater that can be extracted.

6.3.2 Nhill GMU and Goroke GMU

The Nhill and Goroke GMUs cover the groundwater resource of the deep TCSA, otherwise known as the Renmark Group Aquifer. Its main recharge area is where the TCSA either outcrops or is very shallow abutting the bedrock high areas (The Merino High) in the south of the Wimmera region including the Grampians. Within the Wimmera region, the Merino High directs groundwater to the north towards the Murray River and west toward the Southern Ocean.

SKM (1998) calculated groundwater inflow at the eastern boundary of the Border Zone Groundwater Sharing Agreement (South Australia – Victoria) regions, that is, the down-gradient end of the Wimmera region. The Border Zone regions of relevance to the Wimmera region include Zone 5B, Zone 6B, Zone 7B and Zone 8B. Summing the SKM (1998) ‘best guess’ groundwater flow across the eastern boundary of those zones provides a through-flow figure of 19.0 GL/year. This through-flow figure is small compared to total aquifer storage. The results are very sensitive to hydraulic conductivity estimates that are based on sparsely distributed and short-term pumping tests. They are not based on any significant stressing of the aquifer system. The through-flow should allow for groundwater extraction by down-gradient users, as well as extraction within the GMU. The PCV values for Nhill and Goroke GMUs are 1.2 and 2.2 GL/year, respectively. These figures make allowance for down-gradient users and are used as replenishment rates.

6.3.3 Proposed Gymbowen GMU

A fourth GMU was proposed for the Gymbowen region (SKM, 2005). Slightly more than 50 percent of the proposed GMU falls within the Wimmera region. It covers the PSA and MGL Aquifer, with depth limits from the natural surface to the base of the MGL. Rainfall recharge for the entire GMU is approximately 10.3 GL/year (SKM, 2005), although only about 6.5 GL/year occurs within the Wimmera region. Current entitlements are approximately 1 GL/year. Nomination of this region as a GMU is based on a large number of applications for groundwater licences received by the water authority


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(Grampians-Wimmera-Mallee Water). Consequently the GMU has the potential to become more important than existing GMUs.

6.4 Current and future groundwater extraction versus GMU recharge

Table 6-1 shows the current extraction, current entitlements, PCV and future projections of groundwater use. Table 6-2 shows more detail.

Table 6-2. Details of extraction figures used in this report

Entitlements as of 2004/05

Metered use in 2004/05

Estimated un-metered use in

2004/05

Total use in 2004/05 Estimated use in 2030

GL/y UrbanUrban Goroke 0 0 0 0 0Urban Nhill 0 0 0 0 0Urban Balrootan 1.0 0.335 0 0.335 0.335Urban Unincorporated 0.856 0.032 0.52 0.552 0.552Urban Total 1.856 0.367 0.52 .887 0.887Other Other Goroke 0 0 0 0 0Other Nhill 0 0 0 0 0Other Balrootan 0.522 0.035 0.035 0.070 0.165Other Unincorporated 0.754 0 0.482 0.482 0.754Other Total 1.276 0.035 0.517 0.552 0.919Stock & Domestic NA NA 0.400* 0.400 0.400Overall Total 3.132 0.402 1.437 1.839 2.206*200 Stock and Domestic bores @ 2ML/bore/y

The potential impact of future development (Scenario D) was evaluated by calculating the ratios of extraction to recharge (E/R)(Table 6-3). The PCV values are used as recharge rates for the three existing GMUs. While downward leakage from the PSA to the MGL was not included in these estimates, post-development recharge may contain elevated salt concentrations which could increase the salinity of groundwater in the PSA. Extraction from the confined aquifers may lead to entrainment of further water either laterally of vertically, and this water may be of lower quality. While E/R values indicate the level of aquifer stress, it does not account for local scale drawdown or salinity issues that may arise with local extraction.

The recharge rate for the unincorporated areas is estimated as the Gymbowen recharge estimate (6.5 GL/year) plus a nominal 1.0 GL/year for other unincorporated areas. A large proportion of the current entitlements in unincorporated areas are for the Gymbowen region, and much of the projected future growth will be in this area. There is also some growth in the uplands areas associated with weathered granite and shallow colluvial-alluvial aquifer systems. If recharge to the whole of unincorporated areas was included, there would be a much larger value, but this estimate would be largely irrelevant to current and projected extraction. A nominal value of 1 GL/y gives a more sensible value for areas where extraction occurs. Stock and domestic use was included in the unincorporated areas for calculation of the E/R values. The data to support the current estimate of stock and domestic values is poor and is considered as an underestimate. It has been assigned to the unincorporated areas as on a pro rata by area basis – most will occur in these areas.


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Table 6-3. Extraction to recharge ratios for the groundwater management units of the Wimmera region

GMU 2004/05 use Projected 2030 groundwater use

Recharge to unit Scenario A Scenario D

GL/y Extraction to recharge ratio

Nhill 0 0 1.2** 0 0

Goroke 0 0 2.2** 0 0

Balrootan 0.41 0.5 1** 0.41 0.5

Unincorporated areas 1.43* 1.71* 7.5*** 0.24 0.28

* Stock and domestic has been included in unincorporated areas ** Values are equal to PCVs. Note this is not rainfall recharge, but is consistent with through-flow estimates. Estimates are considered conservative for replenishment. *** A value of 6.5 GL/yr for Gymbowen plus another 1 GL/yr nominal extraction for unincorporated areas

For the Nhill and Goroke GMUs E/R values are estimated to be zero. For the unincorporated areas the ratios are 0.24 under current use and 0.28 for projected future use. For the Balrootan GMU the ratios are 0.41 for current use and 0.5 for projected future use. All but Balrootan values represent low levels of use, whereas the E/R value for future use in Balrootan is considered to have a moderate level of development.

There is substantial uncertainty in these estimates. There appears to be uncertainty associated with both lateral and vertical fluxes for Balrootan GMU. The uncertainty in future assessments may be considerable.

6.4.1 Impact of extraction on streamflow

A reduction in groundwater levels due to extraction can affect streamflow. In the case of a gaining river the rate of groundwater discharge to the river decreases. In the case of a losing river a decline in groundwater level will increase leakage from the river into the underlying aquifer to a threshold value. Both processes will reduce flow in the river.

Although a reasonable level of connectivity between groundwater and surface water is thought to exist within the Wimmera region, the portion of groundwater extracted from surface water is considered negligible. This is primarily based upon an understanding of the hydraulic properties of the PSA, the regional groundwater flow direction, the volume of groundwater extracted and the distance of most bores from the main river.

Regional groundwater flow is north-westerly towards the River Murray and westerly towards the Southern Ocean. Hence, flow is directed away from the Wimmera River in the vicinity of much of the current groundwater development – that is, the townships of Nhill, Balrootan, Goroke and Gymbowen. Most of the groundwater development occurs between 30 and 40 km from the Wimmera River.

The effect of groundwater pumping under Scenario A conditions was analysed with an analytical model (Jenkins, 1968) that investigates the portion of streamflow depletion resulting from groundwater pumping. Under the current levels of groundwater extraction, the volume of stream depletion is less than 5 percent of the average annual flow over at least the next 100 years. The reason for the relatively small impact is mainly associated with the distance of groundwater extraction from the Wimmera River.

The projected increase in groundwater extraction (Scenario D) in the areas currently developed, does not increase the effect on the Wimmera River. However, the impact could be more profound if groundwater extraction is concentrated to the south of the region within the alluvium of major tributaries such as the Mackenzie River. Groundwater flow in the southern end of the region will be towards the tributaries of the Wimmera River and hence baseflow processes are likely to be more susceptible to interference by groundwater extraction.

6.5 References

Allison G, Cook P, Barnett S, Walker G, Jolly I and Hughes M (1990) Land clearance and river salinisation in the Western Murray Basin, Australia. Journal of Hydrology 119, 1–20 43.

DSE (2004–2005) State Water Report: A statement of Victorian water resources.


6 Groundw

aterassessment

Jenkins CT (1968) Computation of Rate and volume of stream depletion by wells. USGS techniques of water resources investigations of the US Geological Survey. Hydrologic Analysis and Interpretation, 1968.

Lawrence CR (1975) Geology and Hydrochemistry of the Southern Murray Basin. Memoir 30, Geological Survey of Victoria. Leaney F and Herczeg A (1999) The origin of fresh groundwater in the SW Murray Basin and potential for salinisation. CSIRO Land and

Water Technical Report 7/99. McAuley C, Evans C, Robinson M, Chaplin H and Thorne R (1992) Rural Water Corporation, Vic. Horsham Hydrogeological map

(1:250,000 scale). Murray Basin Hydrogeological Map Series. Australian Geological Survey Organisation, Canberra. Rural Water Commission (1993) Low Flow Atlas for Victorian Streams. Prepared for the Department of Conservation and Natural

Resources – Victoria, 1993. SKM (1998) Permissible Annual Volume Project –The Balrootan GMU. Prepared for the Department of Natural Resources and

Environment, 1998. SKM (2002) Recharge in the Mallee – An estimation of groundwater recharge in the Mallee and Wimmera (South-Western Murray

basin): A Land Systems Approach, Final, February 2002. Undertaken jointly with the MDBC and CSIRO. SKM (2005) Gymbowen Permissible Annual Volume Assessment. Grampians Wimmera Mallee Water, August 2005. URS (2006) Introducing Groundwater in your Catchment. Draft Report prepared for Murray-Darling Basin Commission, Canberra. WCMA (2003) Wimmera Regional Salinity Action Plan 2003. Draft plan – prepared for the Wimmera Catchment Management Authority

by the Virtual Consulting Group August 2003.


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7 Environment This chapter describes the major environmental assets in the Wimmera region. It has four sections:

� a summary � an overview of the approach � a presentation and description of results � a discussion of key findings.

7.1 Summary


� Assessment of the environmental implications of changes in water availability is largely beyond the terms of reference (Chapter 1) of this project. The exception is reporting against environmental water allocations and quantified environmental flow rules specified in water sharing plans. Otherwise, environmental assessments form a very small part of the project.

� The Wimmera region contains the wetland of international importance (Ramsar listed) Lake Albacutya and the nationally important Lake Hindmarsh. Chapter 2 provides a more general description of the environment of the region.

� The environmental assessments undertaken within this project for the Wimmera region are limited to a partial analysis of potential changes in the hydrologic regime affecting the above wetlands.

7.1.2 Key messages

� The water regimes of Lake Hindmarsh and Lake Albacutya are dramatically affected by water resource development. For example, the fraction of time that Lake Hindmarsh is full was 65 percent but now fills 15 percent of the time. Lake Albacutya was full 24 precent of the time but now fills only 2 percent of the time. Lake Hindmarsh was never shallow for more than 3 years before; now it is shallow for up to eight years running. Shallow conditions in Lake Albacutya lasted for up to eight years before development; now it remains shallow for periods of up to 33 years. These changes are likely to have caused and may continue to cause considerable ecological change in these ecosystems.

� A long-term continuation of the conditions experienced over the last ten years would also lead to major additional changes in the hydrology of Lakes Hindmarsh and Albacutya. Lake Hindmarsh would almost never fill and would experience continually shallow conditions for periods of up to 32 years, four times longer than at present. Lake Albacutya would be unlikely to ever fill; water levels would be expected to nearly always be shallow.

� Climate change is likely to cause major changes to the water regimes of Lakes Hindmarsh and Albacutya and lead to considerable ecological change. Lake Hindmarsh is full only 4 percent of the time under the best estimate 2030 climate scenario, while Lake Albacutya is unlikely to ever fill. Even the wet extreme 2030 climate reduces inflows.


7 Environm

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7.1.3 Uncertainty

The main uncertainties involving analysis and reporting include:

� aquatic and wetland ecosystems are highly complex and many factors in addition to water regime can affect ecological features and processes, such as water quality and land use practices

� the indicators are based on limited hydrology parameters with no direct quantitative relationships for environmental responses. This study only makes general observations on the potential implications of changed water regimes and some related ecological responses

� using two assets and two indicators for each to represent overall aquatic ecosystem outcomes is a major simplification. Actual effects on these and other assets or localities are likely to vary

� uncertainties expressed in chapters 3, 4 and 5 affect the hydrologic information used in the environmental assessments.

7.2 Approach

This chapter focuses on the specific rules which apply to the provision of environmental water in the region and on the assessment of hydrologic indicators defined by prior studies for key environmental assets in the region. Chapter 2 provides a broader description of the catchment, water resources and important environmental assets.

7.2.1 Summary of environmental flow rules

The Water Authority is not required to provide passing flows for the environment in the Wimmera until a Stream Management Plan is adopted. An environmental bulk water entitlement of 40,563 ML is available for use.

7.2.2 Environmental assets and indicators

The Wimmera region includes Lake Hindmarsh and Lake Albacutya on the Wimmera River (Figure 7-1 and Figure 7-2). These are wetlands of national (Lake Hindmarsh) and international (Lake Albacutya) significance. The following descriptions of these lakes are taken from Environment Australia (2001) unless otherwise cited.

Lake Hindmarsh

Lake Hindmarsh is the largest freshwater lake in Victoria. It covers some 15,600 ha and has a volume of around 630,000 ML when full. It starts to overflow into Lake Albacutya once its volume reaches about 378,000 ML (Ecological Associates, 2004). It receives inflows from the Wimmera River which is regulated in its headwaters. The lake environment includes geological features of state and regional significance – particularly the eastern sand dunes. The lake is a popular recreational area used for many water based activities, and the lake surrounds are used for grazing and cropping. Land tenure is as a ‘Lake Reserve’.

The flora of the lake is characterised by fringing River Red Gum (Eucalyptus camaldulensis) and Black Box (E.largiflorens) woodland. Several threatened plant species are found at the lake. The lake environment is a drought refuge for waterbirds. Over 50 species of waterbird have been recorded here, some numbering in the thousands. Breeding populations have included Pelicans (Pelicanus conspiculatus), Great Cormorants (Phalacorcorax carbo), Pied Cormorant (P. varius) and Pacific Heron (Ardea pacificus). Threatened waterbird species recorded here include the Great Egret (Egretta alba), Freckled Duck (Stictonetta naevosa) and Blue-billed Duck (Oxyura australis).

Lake Albacutya

Lake Albacutya is just downstream of Lake Hindmarsh and is a wetland of international importance under the Ramsar Convention. It receives water via Outlet Creek after Lake Hindmarsh reaches around 378,000 ML. Consequently, Lake Albacutya receives water much less frequently than Lake Hindmarsh and is dry for long periods (Ecological Associates, 2004). Land tenure of the lake is a Regional Park and part of the Wyperfeld National Park.


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When flooded, Lake Albacutya becomes a major aquatic ecosystem retaining water for several years and supporting significant breeding bird and fish populations with extensive aquatic plant communities. When full the lake has a maximum depth of some 5.2 m and a total volume of around 230,000 ML (Ecological Associates, 2004). The lake filled in 1974 and has been dry since 1983, with the longest dry period being 27 years (DEW, 1999).

The flora of the lake and surrounds is a mixture of riverine and mallee vegetation communities. The riverine community is similar to that of Lake Hindmarsh. The Mallee community has Callitris Pine (Allocasurina leumannii) woodland and heath communities. Green Saltbush (Atriplex australiasica) is also prevalent. These vegetation communities provide a wildlife corridor between the lakes and the nearby Wirrengren Plain. Waterbird species frequenting Lake Albacutya are similar to those of Lake Hindmarsh. Internationally significant populations of some 10,000 Banded Stilt (Cladorhynchus leucocephalus) have been recorded at the lake.

Figure 7-1. Location map of environmental assets


7 Environm

ent

Figure 7-2. Satellite image of Lake Albacutya and Lake Hindmarsh

Ecological Associates (2004) studied the environmental water needs of Lake Hindmarsh and Lake Albacutya, and noted a range of lake-filling thresholds. The ‘lake-full’ thresholds for both lakes are used in assessments herein (Table 7-1). For Lake Hindmarsh, the lake-full threshold (when flow commences to Outlet Creek) is 378,000 ML which corresponds to a lake depth of 3.4 m. Only under very large and rare events does the lake fill to around 630,000 ML with a 2.0 m head surcharge. The lake-full threshold for Lake Albacutya is 230,000 ML which corresponds to a depth of 5.2 m when discharge from the lake commences.

The lakes provide valuable habitat can maintain fish and waterbird populations when they are only partially full. Thus in addition to the lake-full indicators, the ‘shallow’ indicator noted by Ecological Associates (2004) is also used in assessments herein. The ‘shallow’ indicator for Lake Hindmarsh is 80,000 ML which corresponds to a depth of 0.92 m; and for Lake Albacutya the ‘shallow’ indicator is 25,000 ML which corresponds to a depth of 0.75 m (Ecological Associates, 2004).


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Table 7-1. Definition of environmental indicators

Name Description Lake Hindmarsh (VIC012)

Percentage of time above ‘lake-full’ threshold of 378,000 ML (commence-to-spill) Percentage of time above ‘shallow’ threshold of 80,000 ML Longest period (in years) below ‘shallow’ threshold of 80,000 ML

Lake Albacutya (VIC011)

Percentage of time above ‘lake-full’ threshold of 230,000 ML (commence-to-spill) Percentage of time above ‘shallow’ threshold of 25,000 ML Longest period (in years) below ‘shallow’ threshold of 25,000 ML

7.3 Results

The projected changes in the environmental indicators are listed for the various scenarios in Table 7-2. These were assessed using scenario storage volumes from the Wimmera River system model (Chapter 4).

Table 7-2. Environmental indicator values for scenarios P, A, B and C

P A B Cdry Cmid CwetLake Hindmarsh percent Percentage of time above ‘lake-full’ (>378,000 ML) 64% 15% <1% <1% 4% 7%Percentage of time above ‘shallow’ (>80,000 ML) 97% 69% 10% 6% 41% 63% years Longest period below ‘shallow’ 3 8 32 32 10 9Lake Albacutya percent Percentage of time above ‘lake-full’ (230,000 ML) 24% 2% 0% 0% 0% 2%Percentage of time above ‘shallow’ (25,000 ML) 76% 16% 3% 3% 5% 13% years Longest period below ‘shallow’ 8 33 107 108 76 58


7.4.1 Lake Hindmarsh

The pre-development scenario (Scenario P) indicates that under the historical climate without the effects of water resource development, Lake Hindmarsh would be full 64 percent of the time and have a water depth of at least 0.92 m (‘shallow’) 97 percent of the time. With current water resource development these frequencies have been dramatically reduced to 15 percent and 69 percent, respectively. Additionally, current development has increased the single longest period for which the water level would be below ‘shallow’ from three to eight years. This is likely to have affected the viability of a range of faunal populations and vegetation communities that use or reside in the remnant deeper sections of the lake.

A long-term continuation of the climate of the last ten years would lead to major changes in the hydrology of Lake Hindmarsh. The lake would almost never fill and would experience continually shallow conditions for periods of up to 32 years – four times longer than at present. The lake levels would only exceed ‘shallow’ for 10 percent of the time.

Under the best estimate 2030 climate scenario the changes would also be considerable, but less major than for a long-term continuation of the recent climate. The lake would be full only 4 percent of the time, with water levels exceeding ‘shallow’ only 41 percent of the time. The longest period of ‘shallow’ conditions would increase from eight to ten years. Substantial ecological changes would be likely to under such conditions.


7 Environm

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The uncertainty around the 2030 climate scenario is considerable. As a result, the hydrologic conditions for Lake Hindmarsh could range from conditions reasonably similar to historical conditions (though with a reduction in the fraction of time spent full) to conditions very similar to the last ten years.

7.4.2 Lake Albacutya

The pre-development scenario (Scenario P) indicates that under the historical climate without the effects of water resource development Lake Albacutya would be full around 24 percent of the time, and have a water depth of at least 0.75 m (‘shallow’) for 76 percent of the time. As a result of water resource development these frequencies have been dramatically reduced to 2 percent and 16 percent, respectively. Additionally, current development has increased the single longest period for which the water level would be below ‘shallow’ from eight to 33 years. The current level of development has therefore dramatically changed the water regime of Lake Albacutya, and consequently has probably changed aspects of its ecology.

Under a long-term continuation of the recent climate, or under either the best estimate or dry extreme 2030 climate scenarios, Lake Albacutya would be unlikely to ever fill, and water levels would be shallow. Even the wet extreme 2030 climate would mean longer periods of shallow conditions than are currently experienced, and a similar (small) fraction of the time spent full. These hydrological changes would be likely to cause considerable changes in the ecological conditions of the lake, with potential loss of significant vegetation and faunal communities.

7.5 References

Department of the Environment and Water Resources (DEW) (1999) Ramsar Information Sheet 1999. Available at http://www.environment.gov.au.

Ecological Associates (2004) The environmental water needs of the Wimmera terminal lakes. Final Report, Wimmera Catchment Management Committee.

Environment Australia (2001) A Directory of Important Wetlands in Australia. Third Edition. Environment Australia, Canberra.


AppendixA

Rainfall-runoffresults

forallsubcatchments

Appendix A Rainfall-runoff results for all subcatchments

Table A-1. Summary of modelling results for all subcatchments under scenarios A and C

Scenario A Scenario Cdry Scenario Cmid Scenario Cwet

Modelling catchment

Area Rainfall APET Runoff Runoffcoefficient

Runoffcontribution

Rainfall Runoff Rainfall Runoff Rainfall Runoff

km2 mm percent percent change percent change percent change

4152001 846 460 1199 25 5% 4% -19% -45% -6% -15% -1% -4%

4152003 327 610 1168 65 11% 4% -19% -42% -6% -15% -1% -4%

4152011 1994 547 1157 37 7% 14% -19% -54% -6% -22% -1% -6%

4152013 45 542 1183 42 8% 0% -19% -43% -6% -15% -1% -4%

4152173 29 614 1134 33 5% 0% -19% -53% -6% -20% -1% -5%

4152200 533 485 1204 29 6% 3% -19% -45% -6% -16% -1% -4%

4152210 7 614 1134 33 5% 0% -19% -53% -6% -20% -1% -5%

4152221 1278 380 1249 11 3% 3% -20% -50% -6% -17% 2% 5%

4152223 3903 427 1206 19 5% 15% -19% -45% -7% -18% 0% 0%

4152230 95 521 1181 35 7% 1% -19% -44% -6% -15% -1% -4%

4152260 130 459 1192 24 5% 1% -19% -51% -6% -20% -1% -5%

4152270 834 614 1134 33 5% 5% -19% -53% -6% -20% -1% -5%

4152273 1 614 1134 33 5% 0% -19% -53% -6% -20% -1% -5%

4152280 85 788 1159 92 12% 2% -19% -54% -6% -21% -1% -5%

4152291 59 697 1131 55 8% 1% -19% -57% -6% -22% -1% -5%

4152413 15764 352 1281 10 3% 32% -20% -45% -5% -13% 4% 9%

4152453 1 547 1157 37 7% 0% -19% -54% -6% -22% -1% -6%

4152454 5 547 1157 37 7% 0% -19% -54% -6% -22% -1% -6%

4152461 1254 448 1202 21 5% 5% -19% -45% -7% -17% -1% -3%

4152511 85 512 1179 33 6% 1% -19% -44% -6% -15% -1% -4%

4152513 227 645 1160 34 5% 2% -19% -56% -6% -23% -1% -6%

4152571 1117 436 1211 19 4% 4% -19% -50% -6% -19% -1% -5%

4156013 1945 337 1294 7 2% 3% -20% -47% -5% -13% 4% 11%

4156100 78 738 1147 83 11% 1% -18% -53% -6% -20% -1% -5%

30640 403 1245 16 4% 100% -20% -47% -6% -17% 2% 1%


App

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Table A-2. Summary of modelling results for all subcatchments under scenarios A and D

Modelling catchment

A runoff Plantations increase

Farm dam increase Ddry runoff Dmid runoff Dwet runoff

mm ha ML ML/km2 percent change from Scenario A

4152001 25 0 19 0.0 -45% -15% -4%

4152003 65 0 20 0.1 -42% -15% -4%

4152011 37 0 150 0.1 -54% -22% -6%

4152013 42 0 4 0.1 -43% -15% -4%

4152173 55 0 2 0.0 -53% -21% -6%

4152200 29 0 0 0.0 -45% -16% -4%

4152210 55 0 1 0.0 -53% -21% -6%

4152221 11 0 0 0.0 -50% -17% 5%

4152223 19 0 3 0.0 -45% -18% 0%

4152230 35 0 1 0.0 -44% -15% -4%

4152260 24 0 11 0.1 -51% -20% -5%

4152270 33 0 27 0.0 -53% -20% -6%

4152273 33 0 0 0.0 -53% -20% -5%

4152280 92 0 7 0.1 -55% -21% -6%

4152291 55 0 6 0.1 -57% -22% -6%

4152413 10 0 7 0.0 -45% -13% 9%

4152453 37 0 0 0.0 -54% -22% -6%

4152454 37 0 0 0.0 -54% -22% -6%

4152461 21 0 3 0.0 -45% -17% -3%

4152511 33 0 0 0.0 -44% -15% -4%

4152513 34 0 9 0.0 -56% -23% -6%

4152571 19 0 52 0.0 -50% -19% -5%

4156013 7 0 0 0.0 -47% -13% 11%

4156100 83 0 6 0.1 -53% -20% -5%

16 0 325 0.0 -47% -17% 1%


AppendixB

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odellingreach

mass

balances

Appendix B River modelling reach mass balances

Reach 1 - Lake Bellfield/Fyans/Lonsdale to Urbans

River system model average annual water balance A B Cwet Cmid Cdry

Model start date Jul-1895 Jul-1895 Jul-1895 Jul-1895 Jul-1895

Model end date Jun-2006 Jun-2006 Jun-2006 Jun-2006 Jun-2006

GL/y Percent change from Scenario A

Storage volume

Change over period -1.0 -100% -100% -100% -100%

Inflows

Sub-catchments

Directly gauged 0.0 0% 0% 0% 0%

Indirectly gauged 88.5 -53% -5% -21% -54%

Transfers from other Wimmera sub-catchments 0.0 0% 0% 0% 0%

Transfers from other basins 5.7 -40% -2% -11% -39%

Sub-total 94.2 -52% -5% -20% -53%

Diversions

Supplied by channel 0.1 -4% -1% -2% -5%

Urban centres supplied from headworks 2.7 0% 2% 1% -1%

Sub-total 2.8 0% 2% 1% -1%

Outflows

End-of-system outflow

Mt William Creek 13.1 -95% -20% -54% -95%

Out of basin reservoir spills 3.8 -63% -8% -27% -66%

Channel to Glenorchy Weir 53.2 -41% -3% -12% -44%

Piped to Lake Taylor 1.2 -61% -7% -35% -60%

Sub-total 71.3 -52% -6% -21% -55%

Net evaporation*

Public storages 18.6 -54% -2% -19% -51%

Sub-total 18.6 -54% -2% -19% -51%

Sub-total 89.9 -53% -5% -20% -54%

Unattributed fluxes

River unattributed loss 0.2 -87% -6% -27% -86%

Channel / pipe loss 1.4 -42% -4% -17% -46%

Sub-total 1.6 -48% -4% -18% -51%

* Evaporation from private licensed storages (GL/y) is not included as it is already accounted in diversions


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Reach 2 - Wimmera River upstream of Huddleston's Weir





Storage volume


Inflows

Sub-catchments



Transfers from other Wimmera sub-catchments 93.9 -47% -4% -16% -49%

Transfers from other basins 0.0 0% 0% 0% 0%

Sub-total 208.9 -50% -5% -18% -50%

Diversions


Urban centres supplied from headworks 0.0 0% 0% 0% 0%

Sub-total 7.2 -52% -4% -13% -56%

Outflows


Wimmera River 87.1 -68% -11% -34% -69%

Channel to Lake Taylor 57.5 -33% -2% -7% -34%

Channel to Lake Buloke 0.1 -21% -25% 29% -66%

Sub-total 144.7 -54% -7% -23% -55%

Net evaporation*

Public storages 8.3 -29% 4% -1% -26%

Sub-total 8.3 -29% 4% -1% -26%

Sub-total 153.0 -53% -7% -22% -54%

Unattributed fluxes


Channel / pipe loss 42.6 -39% 0% -8% -40%

Sub-total 49.0 -39% 0% -8% -39%



AppendixB

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Reach 3 - Avon-Richardson Rivers





Storage volume


Inflows

Sub-catchments

Directly gauged 18.5 -52% -5% -17% -46%

Indirectly gauged 0.0 0% 0% 0% 0%



Sub-total 41.5 -44% -3% -11% -41%

Diversions



Sub-total 3.3 -54% -4% -14% -59%

Outflows


Lake Buloke spills 13.7 -46% -5% -16% -38%

Channel to northern mallee demands 6.8 -52% -3% -12% -54%

Sub-total 20.4 -48% -4% -15% -43%

Net evaporation*

Public storages 4.0 -29% 1% -1% -25%

Sub-total 4.0 -29% 1% -1% -25%

Sub-total 24.4 -45% -4% -13% -40%

Unattributed fluxes

River unattributed loss 0.0 0% 0% 0% 0%

Channel / pipe loss 13.9 -39% -1% -8% -39%

Sub-total 13.9 -39% -1% -8% -39%



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Reach 4 - Wimmera River from Huddleston's Weir to Mackenzie River confluence





Storage volume


Inflows

Sub-catchments




Transfers from other basins 43.5 -33% 4% -4% -32%

Sub-total 212.0 -51% -5% -20% -52%

Diversions


Urban centres supplied from headworks 1.2 -16% 0% -3% -18%

Sub-total 24.2 -58% -2% -17% -60%

Outflows


Wimmera River 103.9 -57% -9% -29% -58%

Yarrambiack Creek 6.7 -71% -12% -36% -74%

Channel to northern mallee demands 35.6 -33% 0% -4% -34%

Sub-total 146.2 -52% -7% -23% -53%

Net evaporation*

Public storages 13.9 -43% 1% -10% -37%

Sub-total 13.9 -43% 1% -10% -37%

Sub-total 160.2 -51% -6% -22% -51%

Unattributed fluxes



Sub-total 28.9 -41% 0% -9% -42%



AppendixB

Riverm

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mass

balances

Reach 5 - Wartook Reservoir supply





Storage volume


Inflows

Sub-catchments





Sub-total 26.1 -54% -5% -21% -55%

Diversions

Supplied by channel 0.4 -54% 7% -4% -53%

Urban centres supplied from headworks 3.3 -28% 2% -2% -27%

Sub-total 3.6 -31% 3% -2% -30%

Outflows


Mackenzie River 10.2 -80% -17% -46% -82%

Sub-total 10.2 -80% -17% -46% -82%

Net evaporation*

Public storages 10.4 -43% 1% -8% -42%

Sub-total 10.4 -43% 1% -8% -42%

Sub-total 20.6 -62% -8% -27% -62%

Unattributed fluxes

River unattributed loss 1.7 -16% 1% 3% -17%


Sub-total 2.0 -19% 2% 2% -20%



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Reach 6 - Waranga Western Channel sole supply areas





Storage volume

Change over period 0.0 -100% -100% -100% -100%

Inflows

Sub-catchments


Indirectly gauged 8.0 0% 0% 0% 0%


Transfers from other basins 1.0 -63% -2% -10% -53%

Sub-total 9.0 -7% 0% -1% -6%

Diversions



Sub-total 0.1 -56% -4% -15% -60%

Outflows


Channel to northern mallee demands 8.1 -37% -2% -7% -37%

Sub-total 8.1 -37% -2% -7% -37%

Net evaporation*

Public storages 0.1 -30% 0% -1% -24%

Sub-total 0.1 -30% 0% -1% -24%

Sub-total 8.2 -37% -2% -7% -37%

Unattributed fluxes


Channel / pipe loss 0.7 358% 16% 75% 370%

Sub-total 0.7 358% 16% 75% 370%



AppendixB

Riverm

odellingreach

mass

balances

Reach 7 - Wimmera River d/s Mackenzie River confluence





Storage volume


Inflows

Sub-catchments





Sub-total 116.8 -56% -9% -27% -56%

Diversions

Supplied by channel 0.0 0% 0% 0% 0%


Sub-total 0.0 0% 0% 0% 0%

Outflows


D/S Lake Brambruk 0.5 -100% -35% -100% -100%

Sub-total 0.5 -100% -35% -100% -100%

Net evaporation*

Public storages 103.3 -59% -9% -28% -60%

Sub-total 103.3 -59% -9% -28% -60%

Sub-total 103.8 -60% -9% -29% -60%

Unattributed fluxes


Channel / pipe loss 0.0 0% 0% 0% 0%

Sub-total 22.8 -14% -3% -10% -12%



App

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Appendix C River system model uncertainty assessment by reach

This Appendix contains the results of river reach water accounting for this region, as well as an assessment of the magnitude of the projected change under each scenario compared to the uncertainty associated with the river model. Each page provides information for a river reach that is bounded by a gauging station on the upstream and downstream side, and for which modelling results are available. Table C-1 provides a brief explanation for each component of the results page.

Table C-1. Explanation of components of the uncertainty assessments

Table Description Land use Information on the extent of dryland, irrigation and wetland areas.

Land use areas are based on remote sensing classification involving BRS land use mapping, water resources infrastructure and remote sensing-based estimates of actual evapotranspiration.

Gauging data Information on how well the river reach water balance is measured or, where not measured, can be inferred from observations and modelling. The volumes of water measured at gauging stations and off-takes is compared to the grand totals of all inflows or gains, and/or all outflows or losses, respectively. The ‘fraction of total’ refers to calculations performed on average annual flow components over the period of analysis. The ‘fraction of variance’ refers to the fraction of month-to-month variation that is measured. Also listed are the same calculations but for the sum of gauged terms plus water balance terms that could be attributed to the components listed in the ‘Water balance’ table with some degree of confidence. The same terms are also summed to water years and shown in the diagram next to this table.

Correlation with ungauged gains/losses

Information on the likely nature of ungauged components of the reach water balance. Listed are the coefficients of correlation between ungauged apparent monthly gains or losses on one hand, and measured components of the water balance on the other hand. Both the ‘normal’ (parametric) and the ranked (or non-parametric) coefficient of correlation are provided. High coefficients are highlighted. Positive correlations imply that the apparent gain or loss is large when the measured water balance component is large, whereas negative correlation implies that the apparent gain or loss is largest when the measured water balance component is small. In the diagram below this table, the monthly flows measured at the gauge at the end of the reach are compared with the flows predicted by the baseline river model, and the outflows that could be accounted for (i.e., the net result of all measured or estimated water balance components other than main stem outflow – which ideally should equal main stem outflows in order to achieve mass balance)

Water balance Information on how well the modelled and the best estimate river reach water balances agree, and what the nature of any unspecified losses in the river model is likely to be. The river reach water balance terms are provided as modelled by the baseline river model (scenario A) over the period of water accounting. The accounted terms are based on gauging data, diversion records, and (adjusted) estimates derived from SIMHYD rainfall-runoff modelling, remote sensing of water use and simulation of temporary storage effects. Neither should be considered as absolutely correct, but large divergences point to large uncertainty in river modelling.

Model efficiency Information on the performance of the river model in explaining historic flow patterns at the reach downstream gauge, and the scope to improve on this performance. All indicators are based on the Nash-Sutcliffe model efficiency (NSME) indicator. In addition to the conventional NSME calculated for monthly and annual outflows, it has also been calculated after log-transformation or ranking of the original data, as well as having been calculated for the 10% of months with highest and lowest observed flows, respectively. Using the same formulas, the ‘model efficiency’ of the water accounts in explaining observed outflows is calculated. This provides an indication of the scope for improving the model to explain more of the observed flow patterns: if NSME is much higher for the water accounts than for the model, than this suggests that the model can be improved upon and model uncertainty reduced. Conversely, if both are of similar magnitude, then it is less likely that a better model can be derived without additional observation infrastructure.


AppendixC

Riversystem

modeluncertainty assessm

entbyreach

Table Description Change-uncertainty ratios

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


App

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Downstream gauge 415200 Wimmera River @ Horsham Reach 1Upstream gauge 415201 Wimmera River @ Glenorchy Weir

Reach length (km) 64Area (km2) 2189Outflow/inflow ratio 0.83Net losing reach

Land use ha %Dryland 213,130 97 Irrigable area - - Open water* - - River and wetlands 5,720 3 Open water* - - * averages for 1990–2006

Gauging data Inflows Outflows Overalland gains and losses

Fraction of totalGauged 0.74 0.62 0.68Attributed 0.84 0.62 0.73Fraction of varianceGauged 0.28 0.73 0.51Attributed 0.83 0.93 0.88

Correlation with ungauged Gains Losses Linear adjustmentnormal ranked normal ranked

Main gauge inflows -0.62 -0.16 -0.36 -0.77Tributary inflows - - - -Main gauge outflows -0.90 -0.50 -0.03 -0.14Distributary outflows - - - -Recorded diversions - - - -Estimated local runoff -0.49 -0.11 -0.44 -0.54 Adjusted -88.5%

Water balance Model (A) Accounts Difference Model efficiency Model (A) AccountsJul 1990 – Jun 2006 MonthlyGains GL/y GL/y GL/y Normal 0.85 0.72Main stem inflows 61 65 -4 Log-normalised - -Tributary inflows 37 0 37 Ranked <0 <0Local inflows 53 8 45 Low flows only <0 <0Unattributed gains and noise - 14 - High flows only 0.81 0.58Losses GL/y GL/y GL/y AnnualMain stem outflows 73 54 19 Normal 0.92 0.86Distributary outflows 5 0 5 Log-normalised 0.09 0.17Net diversions 61 0 61 Ranked 0.87 0.79River flux to groundwater 0 - -River and floodplain losses 0 0 0 Definitions:Unspecified losses 12 - - - low flows (flows<10% percentile ) : 0.0 GL/moUnattributed losses and noise - 33 - - high flows (flows>90% percentile) : 7.3 GL/mo

Change-uncertainty ratiosP B Cwet Cmid Cdry Dwet Dmid Ddry

Annual streamflow 12.1 8.7 1.6 2.8 9.8Monthly streamflow 4.9 5.0 1.7 2.7 5.3

0.01

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Annual Change-Uncertainty Ratio

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90/9

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91/9

2

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Cmid

Cdry

Dwet

Dmid

Ddry

0.001

0.01

0.1

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0 20 40 60 80 100

Pecentage of months flow is exceeded

Mon

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90/9

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2

92/9

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unattributedgains

ungaugedgains

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unattributedlosses

ungaugedlosses

gaugedlosses

This is a gaining reach. Flows are dominated by inflows from the reach above.

Most of the inflows are gauged. Estimated local runoff explains some of the ungauged gains but a moderate adjustment was required. There are no recorded diversions and ungauged losses are small.

Baseline model performance is good. Accounting explains observed flows very well.

The projected changes are greater than the uncertainty in modelling, except for the Cwet scenario, which has changes similar to the uncertainty.

P B C D+ wetO mid– dry

0.001

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Jun-90 Jun-91 Jun-92 Jun-93 Jun-94 Jun-95 Jun-96 Jun-97 Jun-98 Jun-99 Jun-00 Jun-01 Jun-02 Jun-03 Jun-04 Jun-05

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AppendixC

Riversystem

modeluncertainty assessm

entbyreach

Downstream gauge 415246 Wimmera River @ Lochiel bridge Reach 2Upstream gauge 415200 Wimmera River @ Horsham

Reach length (km) 68Area (km2) 1746Outflow/inflow ratio 1.09Net gaining reach

Land use ha %Dryland 171,490 98 Irrigable area - - Open water* - - River and wetlands 3,080 2 Open water* - - * averages for 1990–2006

Gauging data Inflows Outflows Overalland gains and losses

Fraction of totalGauged 0.84 0.92 0.88Attributed 0.94 0.92 0.93Fraction of varianceGauged 0.95 0.99 0.97Attributed 0.99 1.00 0.99

Correlation with ungauged Gains Losses Linear adjustmentnormal ranked normal ranked

Main gauge inflows -0.82 -0.45 -0.13 -0.33Tributary inflows - - - -Main gauge outflows -0.87 -0.67 -0.07 -0.17Distributary outflows - - - -Recorded diversions - - - -Estimated local runoff -0.69 -0.41 -0.02 -0.14 Adjusted -59.1%

Water balance Model (A) Accounts Difference Model efficiency Model (A) AccountsJul 1990 – Jun 2006 MonthlyGains GL/y GL/y GL/y Normal 0.85 0.99Main stem inflows 73 54 19 Log-normalised - -Tributary inflows 1146 0 1146 Ranked <0 0.45Local inflows 6 6 0 Low flows only - -Unattributed gains and noise - 4 - High flows only 0.76 0.98Losses GL/y GL/y GL/y AnnualMain stem outflows 72 59 14 Normal 0.94 1.00Distributary outflows 0 0 0 Log-normalised - -Net diversions 0 0 0 Ranked 0.88 0.97River flux to groundwater 0 - -River and floodplain losses 0 0 0 Definitions:Unspecified losses 7 - - - low flows (flows<10% percentile ) : 0.0 GL/moUnattributed losses and noise - 6 - - high flows (flows>90% percentile) : 8.3 GL/mo

Change-uncertainty ratiosP B Cwet Cmid Cdry Dwet Dmid Ddry

Annual streamflow 12.0 11.2 1.9 3.6 12.7Monthly streamflow 3.8 4.7 1.7 2.6 5.0

0.01

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Annual Change-Uncertainty Ratio

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90/9

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y)

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P

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Cmid

Cdry

Dwet

Dmid

Ddry

0.001

0.01

0.1

1

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0 20 40 60 80 100

Pecentage of months flow is exceeded

Mon

thly

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w (G

L/m

o) .

-500

-400

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0

100

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90/9

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91/9

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92/9

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Rea

ch g

ains

and

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es (G

L/y)

unattributedgains

ungaugedgains

gaugedgains

unattributedlosses

ungaugedlosses

gaugedlosses

This is a gaining reach. Flows are dominated by inflows from the reach above.

Most of the inflows are gauged. Estimated local runoff explains some of the ungauged gains but a moderate adjustment was required. Ungauged losses are small.

Baseline model performance is unknown at the time of writing. Accounting also explains observed flows very well.

The projected changes are unknown at the time of writing.

P B C D+ wetO mid– dry

0.001

0.01

0.1

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1000

Jun-90 Jun-91 Jun-92 Jun-93 Jun-94 Jun-95 Jun-96 Jun-97 Jun-98 Jun-99 Jun-00 Jun-01 Jun-02 Jun-03 Jun-04 Jun-05

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© CSIRO 2009 May 2009 Erratum: Water availability in the Wimmera � i

Erratum: Wimmera This is an erratum sheet, issued May 2009, for the following report::

CSIRO (2007) Water availability in the Wimmera. A report to the Australian Government from the CSIRO Murray-Darling Basin Sustainable Yields Project. CSIRO, Australia. 108pp

List of erratum

Erratum #

Chapter Section Page Errata

1 4 River system modelling 4.3.1 45 Replacement Table 4-6 – channel / pipe loss moved from unattributed fluxes to diversions

1

Table 4-6. River system model average annual water balance under scenarios O, A, B and C in the Wimmera region

River system model average annual water balance O A B Cwet Cmid CdryModel start date Jan-1903 Jul-1895 Jul-1895 Jul-1895 Jul-1895 Jul-1895Model end date Jun-2004 Jun-2006 Jun-2006 Jun-2006 Jun-2006 Jun-2006 GL/y percent change from Scenario A Storage volume Change over period -6.5 -12.5 0% 0% 0% 1%Inflows Subcatchments

Directly gauged 19.7 18.5 -52% -5% -17% -46%Indirectly gauged 264.5 255.1 -52% -5% -20% -52%Transfers from other basins 65.0 58.2 -29% 3% -4% -29%

Sub-total 349.2 331.8 -48% -4% -17% -48%Diversions

Licenced private diversions 40.5 34.0 -57% -3% -16% -61%Urban diversions 8.4 7.2 -16% 2% -1% -16%

Sub-total 48.9 41.2 -50% -2% -14% -53%Channel / pipe loss 94.8 79.6 -41% 0% -9% -42%

Sub-total 143.7 120.8 -0.9 0.0 -0.2 -0.9Outflows End-of-system outflow

D/S Lake Buloke 14.7 13.7 -46% -5% -16% -38%Yarriambiack Creek 6.4 6.7 -71% -12% -36% -74%D/S Lake Brambruk 0.2 0.5 -100% -35% -100% -100%Internal model spills 4.0 3.8 -63% -8% -27% -66%Sub-total 25.3 24.7 -57% -8% -25% -53%

Net evaporation* Headworks storages 39.3 40.2 -46% 1% -12% -42%Lakes 113.7 118.5 -56% -8% -26% -57%Sub-total 153.0 158.6 -54% -6% -22% -53%

Sub-total 178.3 183.3 -54% -6% -23% -53%Unattributed fluxes

River unattributed loss 37.5 39.2 -10% -2% -7% -12%* Evaporation from private licensed storages (GL/y) is not included as it is already accounted in diversions

Enquiries

More information about the project can be found at www.csiro.au/mdbsy. This information includes the full terms of reference for the project, an overview of the project methods and the project reports that have been released to-date.

water availability in the wimmera - report

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