Water Availability in the Paroo

Transcription

1 Water Availability in the Paroo A report to the Australian Government from the CSIRO Murray-Darling Basin Sustainable Yields Project November 2007

2 Murray-Darling Basin Sustainable Yields Project acknowledgments The Murray-Darling Basin Sustainable Yields Project is being undertaken by CSIRO under the Australian Government's Raising National Water Standards Program, administered by the National Water Commission. Important aspects of the work were undertaken by Sinclair Knight Merz; Resource & Environmental Management Pty Ltd; Department of Water and Energy (New South Wales); Department of Natural Resources and Water (Queensland); Murray-Darling Basin Commission; Department of Water, Land and Biodiversity Conservation (South Australia); Bureau of Rural Sciences; Salient Solutions Australia Pty Ltd; ewater Cooperative Research Centre; University of Melbourne; Webb, McKeown and Associates Pty Ltd; and several individual sub-contractors. Murray-Darling Basin Sustainable Yields Project disclaimers Derived from or contains data and/or software provided by the Organisations. The Organisations give no warranty in relation to the data and/or software they provided (including accuracy, reliability, completeness, currency or suitability) and accept no liability (including without limitation, liability in negligence) for any loss, damage or costs (including consequential damage) relating to any use or reliance on that data or software including any material derived from that data and software. Data must not be used for direct marketing or be used in breach of the privacy laws. Organisations include: Department of Water, Land and Biodiversity Conservation (South Australia), Department of Sustainability and Environment (Victoria), Department of Water and Energy (New South Wales), Department of Natural Resources and Water (Queensland), Murray-Darling Basin Commission. CSIRO advises that the information contained in this publication comprises general statements based on scientific research. The reader is advised and needs to be aware that such information may be incomplete or unable to be used in any specific situation. No reliance or actions must therefore be made on that information without seeking prior expert professional, scientific and technical advice. To the extent permitted by law, CSIRO (including its employees and consultants) excludes all liability to any person for any consequences, including but not limited to all losses, damages, costs, expenses and any other compensation, arising directly or indirectly from using this publication (in part or in whole) and any information or material contained in it. Data is assumed to be correct as received from the Organisations. Citation CSIRO (2007). Water availability in the Paroo. A report to the Australian Government from the CSIRO Murray-Darling Basin Sustainable Yields Project. CSIRO, Australia. 88 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 X Photo on cover: Claypan depression in Nocolenche Nature Reserve by Richard Kingsford, courtesy of NSW Department of Environment and Climate Change (NSW DECC)

3 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 surfacesubsurface connections. We are complementing this work with detailed surface water accounting across the Basin never before has surface water accounting been done in such detail in Australia, over such a large area, and integrating so many different data sources. To deliver on the project CSIRO is drawing on the scientific leadership and technical expertise of national and state government agencies in Queensland, New South Wales, Victoria, the Australian Capital Territory and South Australia, as well as the Murray-Darling Basin Commission and Australia s leading industry consultants. The project is dependent on the cooperative participation of over 15 government and private sector organisations contributing over 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 By building the capacity and capability required to deliver on this ambitious goal, the Flagship is ideally positioned to accept the challenge presented by this complex integrative project. CSIRO has given the Murray-Darling Basin Sustainable Yields Project its highest priority. It is in that context that I am very pleased and proud to commend this report to the Australian Government. Dr Tom Hatton Director, Water for a Healthy Country National Research Flagships CSIRO

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5 Executive Summary Background The CSIRO Murray-Darling Basin Sustainable Yields Project is providing governments with a robust, basin-wide estimate of water availability on an individual catchment and aquifer basis, taking into account climate change and other risks. It will be the most comprehensive basin-wide assessment of water availability undertaken to date. This report describes the assessment undertaken for the Paroo 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 Paroo region is situated in the far north-west of the Murray-Darling Basin (MDB). Located predominantly in southern Queensland the region represents 3.4 percent of the total area of the MDB. The region is based around the ephemeral Paroo River. The population of the region is less than 700 (Or less than 0.1 percent of the MDB total). Settlements include Wanaaring, Hungerford and Eulo. The predominant land use is broad-acre livestock grazing for beef and wool production. There is no commercial forestry in this part of the MDB, and the relatively few farm dams are primarily for stock watering. Current surface water diversions for irrigation make up less than 0.1 percent of the MDB total, and groundwater use is also less than 0.1 of the MDB total. (This excludes use from the confined aquifers of the Great Artesian Basin, which are the major water sources for the region). There are no major dams and very little irrigation. Executive Summary The numerous wetlands of the Paroo region are amongst the most important in the MDB. Wetlands of national importance include Currawinya Lakes (a Ramsar site), the Paroo River Waterholes and the Paroo Distributary Channels. The Paroo River Wetlands in New South Wales are now listed as a Ramsar site. These wetlands include the Nocoleche Nature Reserve and two of the many lakes of the Paroo Overflow which are about 120 km south of the Nocoleche Nature Reserve. The Paroo Overflow Lakes are outside of the Paroo region as defined for this study, but are considered in this report as they are dependent on floodwaters from the Paroo River. The Lakes are on the floodplain south of Wanaaring in New South Wales where floods typically dissipate without reaching the Darling River. Only the Currawinya Lakes (Numalla and Wyara) and the Paroo Overflow Lakes are assessed in this report. 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 over the entire Paroo region is 311 mm. Modelled average annual runoff is 17 mm, or about 2 percent of the total runoff for the MDB. Most of the rainfall and runoff occurs in summer and early autumn. Runoff and river flows are intermittent with the majority occurring as large infrequent floods. Analysis of the pre-development flows along the Paroo River indicates that it changes from a gaining to a losing stream (point of maximum average annual flow) at the Caiwarro gauge. The pre-development average annual flow over the modelling period is 445 GL/year at this location. Current surface water use is very low at less than 0.1 percent of the available water. The Queensland Water Resource Plan that relates to the Queensland portion of the Paroo region requires that at least 99 percent of the average without development flow into New South Wales is maintained. Consequently, diversions in Queensland should not reduce flow across the border by more than 1 percent of the average without development cross-border flow. This requirement is being met in Queensland under current surface water entitlements. Groundwater is currently the main source of water in the region, with almost three-quarters of the groundwater used extracted from the Great Artesian Basin aquifers. There are no groundwater management units (GMU) in the Queensland portion of the region. CSIRO 2007 November 2007 Water availability in the Paroo

6 There are two GMUs in New South Wales the Great Artesian Basin Cap Rocks and Upper Darling Alluvium GMU which together account for 0.34 GL/year of use. Apart from local interaction with shallower aquifers such as Eulo Springs, the deeper groundwater is largely unconnected to the shallow groundwater systems or the river. Groundwater use in the Paroo has little impact on streamflow, and consequently, the GMU in the Paroo have been assigned a very low priority within the context of the project. The current level of water resource development in the region has had no detectable affect on the frequency or volumes of high flows to the Currawinya Lakes or to the Paroo Overflow Lakes. Recent climate and current development (Scenario B) Executive Summary The average annual rainfall for 1997 to 2006 is 310 mm and the modelled average annual runoff is 16 mm. These are not statistically different to the long-term historical averages. A scenario based on the last ten years was therefore not considered in the river modelling. Future climate and current development (Scenario C) The best estimate (median) 2030 climate scenario would lead to a 2 percent reduction in mean annual runoff across the entire region. The extreme estimates, which come from the high global warming scenario, range from a 16 percent reduction to a 40 percent increase in mean annual runoff. By comparison, the range from the low global warming scenario is much narrower: a 5 percent reduction to a 10 percent increase in mean annual runoff. Under the best estimate (median) 2030 climate scenario there would be a 3 percent or 13 GL/year reduction in average surface water availability. This reduction would not affect the volumes or relative level of surface water use. There is considerable uncertainty in the climate predictions for 2030 (different climate models and different global warming scenarios), meaning reductions in average water availability could range from a 16 percent reduction to a 41 percent increase. As the level of water use is low, even these large changes would not lead to changes in the volumes of water used. The extreme climate scenarios for 2030 also indicate: Under the wet extreme, increases in total inflows (40 percent) and end-of-system flows (53 percent) Under a dry extreme, decreases in total inflows (16 percent) and end-of-system flows (17 percent), and No significant impact on modelled water use under either extreme. The predicted impact of the 2030 climate change scenario on the frequency with which flow ceases at the Wanaaring gauge is relatively small, being an increase of 3 percent under the dry extreme and a reduction of 3 percent for the wet extreme. Under the best estimate 2030 climate scenario there would be only minor changes to the average frequency and total volume of beneficial high flows to Lake Numalla and the Paroo Overflow Lakes. However, while average rainfall would be lower under these climate conditions, increases in the highest rainfall intensities are predicted that would increase the frequency of the larger floods. This would increase the average frequency of inflow events to Lake Wyara from once in every 12 years to once in every 5 6 years, and although individual events would be smaller in volume, the total inflow volume would be nearly 70 percent greater. This level of change would be likely to have ecological consequences for Lake Wyara. Both the wet and dry extremes for a 2030 climate scenario would have considerable implications for the volume and frequency of beneficial high flow events to the Currawinya Lakes and to the Paroo Overflow Lakes, and therefore likely to have noticeable effects on wetland ecology. The dry extreme would be the most detrimental. For this case the average period between inflow events would increase by 31 percent for Lake Numalla, 18 percent for Lake Wyara and 13 percent for the Paroo Overflow Lakes. Total inflow volumes would decline by 11 percent for Lake Numalla and by 15 percent for Lake Wyara and the Paroo Overflow Lakes. These levels of hydrologic change would be likely to have considerable ecological consequences. Water availability in the Paroo November 2007 CSIRO 2007

7 Future climate and future development (Scenario D) There are no commercial forestry plantations in the region and relatively few farm dams. This situation is unlikely to change and therefore commercial forestry and farm dams do not pose a risk to future water availability. Groundwater extraction is not expected to increase markedly into the future and so does not pose a risk to future water availability. A scenario considering future development was therefore not considered in the river or groundwater assessment. Uncertainty The runoff estimates for the Paroo region are relatively poor compared to the eastern and southern parts of the MDB. It is considerably more difficult to model runoff in the western and north-western parts of the MDB because the region is drier, there are far fewer rainfall stations and river flows are intermittent with most of the runoff occurring as infrequent floods. The internal uncertainty of the river model is sufficiently small to enable reasonable estimates of changes in streamflow for the Paroo River above Willara Crossing. For these upper reaches, the flow changes associated with future climate are greater than the model uncertainty. For these reaches the model is suitable for assessing the impacts of climate change. The uncertainty in the river model could not be evaluated for the lower reach (Willara Crossing to Wanaaring) because of lack of recent gauging data. Groundwater was assigned a very low priority ranking for the Paroo region in the context of the overall Project. This ranking considers the level of development, size of the resource and degree of connectivity between rivers and aquifers relative to other groundwater systems across the MDB. Due to this ranking, only very simple groundwater assessments were undertaken for the Paroo. While limited assessments are appropriate for this study, additional work may be required for local management of groundwater resources. Executive Summary The largest sources of uncertainty for Scenario C results are the climate change projections (global warming level) and the modelled implications of global warming on regional rainfall. A wide range of the best available climate modelling was used but there is considerable scope for improvement in those global models at predicting regional rainfall. 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. CSIRO 2007 November 2007 Water availability in the Paroo

8 Table of Contents 1 Introduction Background Project methodological framework Climate and development scenarios Rainfall-runoff modelling River system modelling Monthly water accounts Groundwater modelling Environmental assessment References Overview of the region The region Environmental description Surface water resources Groundwater References Rainfall-runoff modelling Summary Modelling approach Modelling results Discussion of key findings References River system modelling Summary Modelling approach Modelling results Discussion of key findings References Uncertainty in surface water modelling results Summary Approach Results Discussion of key findings References Groundwater assessment Summary Assessment of lower priority GMU References Environment Summary Approach Results Discussion of key findings References...79 Appendix A Rainfall-runoff results for all subcatchments Appendix B River modelling reach mass balances Appendix C River system model uncertainty assessment by reach Water availability in the Paroo November 2007 CSIRO 2007

9 Tables Table 1-1. River system models in the Murray-Darling Basin...7 Table 2-1. Summary of land use in the year 2000 within the Paroo region...15 Table 2-2. Important wetlands within the Paroo region...18 Table 2-3. Summary of surface water sharing arrangements for the Queensland portion of the Paroo region...19 Table 2-4. Categorisation of New South Wales groundwater management units including annual extraction, entitlement and recharge...22 Table 2-5. Summary of groundwater management plans...24 Table 2-6. Number and type of bores in the Queensland portion of the Paroo region...24 Table 2-7. Estimated groundwater extraction sub-divided by use for the Paroo groundwater management units...25 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)...32 Table 3-2. Water balance over the entire region by scenario...34 Table 4-1. Storages in the river system model...40 Table 4-2. Modelled water use configuration...40 Table 4-3. Model setup information...42 Table 4-4. River system model average annual water balance for Scenarios O, A and C...44 Table 4-5. Annual water availability for pre-development Scenario C relative to pre-development Scenario A...45 Table 4-6. Change in total diversions in each model subcatchment relative to Scenario A...46 Table 4-7. Relative level of use under scenarios A and C...47 Table 4-8. Indicators of use during dry periods under scenarios A and C...48 Table 4-9. Daily flow event frequency under scenarios P, A, and C at Caiwarro gauge (424201)...50 Table Percent of time that flow occurs under scenarios P, A and C for Wanaaring gauge (424001)...51 Table Relative level of available water not diverted for use under scenarios A and C...51 Table 5-1. Possible framework for considering implications of assessed uncertainties...54 Table 5-2. Comparison of water accounting reaches with river model reaches (QDNR, unpublished)...55 Table 5-3. Some characteristics of the gauging network of the Paroo region (35,587 km 2 ) compared with the entire MDB (1,062,443 km 2 )...59 Table 5-4. Details of streamflow rating uncertainty, calibration and validation periods, number of years between (112 years) with annual rainfall less than the driest and more than the wettest year in the calibration period, respectively, and prior assessment of the models performance...61 Table 5-5. Reach water balance produced by river model and from water accounting...63 Table 5-6. Change-uncertainty ratios for projected annual and monthly streamflow changes in the Paroo at Willara Crossing...64 Table 6-1. Estimated groundwater extraction from New South Wales GMUs within the Paroo region...69 Table 6 2. Estimated future groundwater extraction for the Paroo region...70 Table 7-1. Definition of environmental indicators...77 Table 7-2. Environmental indicator values under scenarios P and A, and percentage change (from Scenario A) in indicator values under Scenario C...77 CSIRO 2007 November 2007 Water availability in the Paroo

10 Figures Figure 1-1. Region by region map of the Murray-Darling Basin...2 Figure 1-2. Methodological framework for the Murray-Darling Basin Sustainable Yields Project...3 Figure 1-3. Timeline of groundwater use and resultant impact on river...8 Figure annual and monthly rainfall averaged over the region. The curve on the annual graph shows the low frequency variability Figure 2-2. Map of dominant land uses of the Paroo region with inset showing the region s location within the Murray-Darling Basin. The assets shown are only those assessed in the project (see Chapter 7). A full list of key assets associated with the region is in Table Figure 2-3. Generalised east-west cross-section for New South Wales portion of Paroo...21 Figure 2-4. Map of groundwater management units within the Paroo region...23 Figure 3-1. Map of the modelling subcatchments and calibration catchments for the Paroo region...28 Figure 3-2. Modelled and observed monthly runoff and daily flow duration curve for the calibration catchment...29 Figure 3-3. Spatial distribution of mean annual rainfall and modelled runoff averaged over Figure annual rainfall and modelled runoff series averaged over the region. The curve shows the low frequency variability Figure 3-5. Mean monthly rainfall and modelled runoff (averaged over for the region)...31 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...32 Figure 3-7. Mean annual rainfall and modelled runoff under scenarios A, Cdry, Cmid and Cwet...33 Figure 3-8. Mean monthly rainfall and modelled runoff under scenarios A and C averaged over across the region (C range is based on the consideration of each month separately the lower and upper limits in C range are therefore not the same as scenarios Cdry and Cwet)...35 Figure 3-9. Daily flow duration curves under scenarios A and C 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)...35 Figure 4-1. River system map showing major rivers, model subcatchments, reaches, calibration reaches, inflow gauges, nodes and links...41 Figure 4-2. Transect of total river flow under pre-development scenarios A and C...44 Figure 4-3. Pre-development Scenario A annual water availability...45 Figure 4-4. Annual water availability under pre-development Scenario C relative to pre-development Scenario A...45 Figure 4-5. Total average annual diversions under scenarios A and C for each model subcatchments...46 Figure 4-6. Total diversions under (a) Scenario A; and the difference in total diversions from Scenario A under (b) Scenario Cwet; (c) Scenario Cmid; and (d) Scenario Cdry...47 Figure 4-7. Reliability of un-supplemented access water for irrigators under scenarios A and C (a) Queensland; and (b) New South Wales...48 Figure 4-8. Daily flow duration curves under scenarios A, P and C at Caiwarro gauge (424201)...49 Figure 4-9. Seasonal plot under pre-development and scenarios A and C at Caiwarro gauge (424201)...49 Figure Daily flow duration curves under scenarios A, P and C for Wanaaring gauge (424001)...50 Figure Seasonal plot under pre-development, scenarios A and C for Wanaaring gauge (424001)...50 Figure Comparison of diverted and non-diverted shares of water under scenarios P, A and C...51 Figure 5-1. Map showing the subcatchments used in modelling, the reaches for which river water accounts were developed ( accounting reach ) and gauged head water catchments ( contributing catchment ). Shaded areas ( floodplain and wetlands ) were classified as subject to periodic inundation. Black dots and red lines are nodes and links in the river model respectively...56 Figure 5-2. Map showing the rainfall, streamflow and evaporation observation network, along with the subcatchments used in modelling...60 Figure 6-1. Map of groundwater management units in the Paroo region...67 Figure 6-2. North-south generalised cross-section of the hydrogeology of the Paroo region...68 Figure 7-1. Location map of environmental assets...75 Figure 7-2. Satellite image of Currawinya Lakes...76 Figure 7-3. Satellite image of Paroo Overflow Lakes...76 Water availability in the Paroo November 2007 CSIRO 2007

11 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 1 Introduction estimate current and likely future water availability in each catchment and aquifer in the MDB considering: o climate change and other risks; o surface-groundwater interactions; and compare the estimated current and future water availability to that required to meet the current levels of extractive use. The Murray-Darling Basin Sustainable Yields Project is reporting progressively on each of 18 contiguous regions that comprise the entire MDB. These regions are primarily the drainage basins of the Murray and the Darling rivers Australia s longest inland rivers, and their tributaries. The Darling flows southwards from southern Queensland into New South Wales west of the Great Dividing Range into the Murray River in southern New South Wales. At the South Australian border the Murray turns south-westerly eventually winding to the mouth below the Lower Lakes and the Coorong. The regions for which the project assessments are being undertaken and reported are the Paroo, Warrego, Condamine-Balonne, Moonie, Border Rivers, Gwydir, Namoi, Macquarie-Castlereagh, Barwon-Darling, Lachlan, Murrumbidgee, Murray, Ovens, Goulburn-Broken, Campaspe, Loddon-Avoca, Wimmera and Eastern Mount Lofty Ranges (see Figure 1-1). CSIRO 2007 November 2007 Water availability in the Paroo 1

12 1 Introduction Figure 1-1. Region by region map of the Murray-Darling Basin The Murray-Darling Basin Sustainable Yields Project will be the most comprehensive MDB-wide assessment of water availability undertaken to-date. For the first time: daily rainfall-runoff modelling has been undertaken at high spatial resolution for a range of climate change and development scenarios in a consistent manner for the entire MDB, the hydrologic subcatchments required for detailed modelling have been precisely defined across the entire MDB, the hydrologic implications for water users and the environment by 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 surfacegroundwater exchange, and detailed analyses of monthly water balances for the last ten to twenty years have been undertaken using available streamflow and diversion data together with additional modelling including estimates of wetland evapotranspiration and irrigation water use based on remote sensing imagery (to provide an independent crosscheck on the performance of river system models). 2 Water availability in the Paroo November 2007 CSIRO 2007

13 The successful completion of these outcomes, among many others, relies heavily on a focussed collaborative and teamoriented approach between CSIRO, State government natural resource management agencies, the Murray-Darling Basin Commission, the Bureau of Rural Sciences, and leading consulting firms each bringing their specialist knowledge and expertise on the MDB to the project. 1.2 Project methodological framework The methodological framework for the project is shown in the diagram below (Figure 1-2). This also indicates in which chapters of this report the different aspects of the project assessments and results are presented. 1 Introduction Figure 1-2. Methodological framework for the Murray-Darling Basin Sustainable Yields Project The first steps in the sequence of the project are definition of the reporting regions and their composite subcatchments, and definition of the climate and development scenarios to be assessed (including generation of the time series of climate data that describe these scenarios). The second steps are rainfall-runoff modelling and rainfall-recharge modelling for which the inputs are the climate data for the different scenarios. Catchment development scenarios for farm dams and commercial forestry plantations are modifiers of the modelled runoff time series. Next, the runoff implications are propagated through river system models and the recharge implications propagated through groundwater models for the major groundwater resources or considered in simpler assessments for minor groundwater resources. The connectivity of surface and groundwater is assessed and the actual volumes of surfacegroundwater exchange under current and likely future groundwater extraction are quantified. Uncertainty levels of the river system models are then assessed based on monthly water accounting. The results of scenario outputs from the river system model are used to make limited hydrological assessments of ecological relevance to key environmental assets. Finally, the implications of the scenarios for water availability and water use under current water sharing arrangements are assessed, synthesised and reported. CSIRO 2007 November 2007 Water availability in the Paroo 3

14 1.3 Climate and development scenarios The project is assessing the following four scenarios of historical and future climate and current and future development, all of which are defined by daily time series of climate variables based on different scalings of the climate: historical climate and current development recent climate and current development future climate and current development future climate and future development. These scenarios are described in some detail below with full details provided in Chiew et al. (2007a). 1 Introduction Historical climate and current development Historical climate and current development referred to as Scenario A is the baseline against which other climate and development scenarios are compared. The historical daily rainfall time series data that are used are taken from the SILO Data Drill of the Queensland Department of Natural Resources and Water database which provides data for a 0.05 o x 0.05 o (5 km x 5 km) grid across the continent (Jeffrey et al., 2001; and Areal potential evapotranspiration (PET) data are calculated from the SILO climate surface using Morton s wet environment evapotranspiration algorithms ( 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 license 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 license entitlements. Surface groundwater exchanges in the river and groundwater models represent an equilibrium condition for the above levels of surface and groundwater development Recent climate and current development Recent climate and current development referred to as Scenario B is used for assessing future water availability should the climate in the future prove to be similar to that of the last ten years. Climate data for 1997 to 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 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 Three global warming scenarios are analysed in 15 global climate models (GCM) to provide a spectrum of 45 climate variants for the 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 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 Water availability in the Paroo November 2007 CSIRO 2007

15 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 Future climate and future development Future climate and future development referred to as Scenario D considers the dry, mid and wet climate variants from the future climate and current development Scenario C together with likely expansions in farm dams and commercial forestry plantations and the changes in groundwater extractions anticipated under existing groundwater plans. 1 Introduction Farm dams here refer only to dams with their own water supply catchment, not those that store water diverted from a nearby river, as the latter require licenses and are usually already included within existing river system models. A 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 Victoria DSE, 2004) and current policy controls (Queensland Water Act, 2000; New South Wales Water Management Act, 2000; Victoria Water Act, 1989; South Australia Natural Resources Management Act, 2004). Data on the current extent of farm dams is taken from the 2007 Geosciences Australia Manmade 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, and 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 0.05 o 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 km 2 to 2000 km 2 across the MDB (calibration catchments). Although unregulated, streamflow in these catchments for the calibration period may reflect low levels of water diversion and the effects of historical land use change. The calibration period is a compromise between a shorter period that would better represent current development and a longer period CSIRO 2007 November 2007 Water availability in the Paroo 5

16 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 whole-of-basin modelling run (identical parameters across the entire MDB are chosen to ensure a realistic runoff gradient across the drier parts of the MDB) which best matched observed flows at calibration points. The places these default values are used are therefore all areas of very low runoff. 1 Introduction As the parameter values come from calibration against streamflow from 50 km 2 to 2000 km 2 catchments, the runoff defined here is different, and can be much higher, than streamflow recorded over very large catchments where there can be significant transmission losses (particularly in the western and north-western parts of the MDB). Almost all of the catchments available for model calibration are in the higher runoff areas in the eastern and southern parts of the MDB. Runoff estimates are therefore generally good in the eastern and southern parts of the MDB and are comparatively poor elsewhere. The same model parameter values are used for all the simulations. The future climate Scenario C simulations therefore do not take into account the effect on forest water use of global warming and enhanced atmospheric CO 2 concentrations. There are compensating positive and negative global warming impacts on forest water use, and it is difficult to estimate the net effect because of the complex climate-biosphere-atmosphere interactions and feedbacks. This is discussed in Marcar et al. (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 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 6 Water availability in the Paroo November 2007 CSIRO 2007

17 and the remaining scenarios (Scenarios B, C and D respectively) are used to modify the existing inflows series in the river system models (separately for each season). The Scenarios B, C and D inflow series for the river system modelling therefore have the same daily sequences but different amounts as the Scenario A river system modelling series. Table 1-1. River system models in the Murray-Darling Basin Model Description Rivers modelled IQQM Integrated Quantity-Quality Model: hydrologic modelling tool developed by the NSW Government for use in planning and evaluating water resource management policies. Paroo, Warrego, Condamine-Balonne (Upper, Mid, Lower), Nebine, Moonie, Border Rivers, Gwydir, Peel, Namoi, Castlereagh, Macquarie, Marthaguy, Bogan, Lachlan, Murrumbidgee, Barwon-Darling REALM Resource Allocation Model: water supply system simulation tool package for modelling water supply systems configured as a network of nodes and carriers representing reservoirs, demand centres, waterways, pipes, etc. MSM-BigMod Murray Simulation Model and the daily forecasting model Murray BigMod: purpose-built by the Murray-Darling Basin Commission to manage the Murray River system. MSM is a monthly model that includes the complex Murray accounting rules. The outputs from MSM form the inputs to BigMod, which is the daily routing engine that simulates the movement of water. Ovens (Upper, Lower), Goulburn, Wimmera, Avoca, ACT water supply. 1 Introduction WaterCRESS Water Community Resource Evaluation and Simulation System: PC-based water management platform incorporating generic and specific hydrological models and functionalities for use in assessing water resources and designing and evaluating water management systems. Eastern Mt Lofty Ranges (six separate catchments) SMHS Snowy Mountains Hydro-electric Scheme model: purpose built by Snowy Hydro Ltd to guide the planning and operation of the SMHS. Snowy Mountains Hydro-electric Scheme A few areas of the MDB have not previously been modelled and hence some new IQQM or REALM models have been implemented. In some cases ancillary models are used to estimate aspects of water demands of use in the river system model. An example is the PRIDE model used to estimate irrigation for Victorian REALM models. River systems that do not receive inflows or transfers from upstream or adjacent river systems are modelled independently. This is the case for most of the river systems in the MDB and for these rivers the modelling steps are: model configuration model warm-up to set initial values for all storages in the model, including public and private dams and tanks, river reaches and soil moisture in irrigation areas using scenario climate and inflow time series, run the river model for all climate and development scenarios where relevant, extract initial estimates of surface-groundwater exchanges and provide this to the groundwater model where relevant, use revised estimates of surface-groundwater exchanges from groundwater models and re-run the river model for all scenarios. For river systems that receive inflows or transfers from upstream or adjacent river systems, model inputs for each scenario were taken from the upstream models. In a few cases several iterations were required between upstream and downstream models because of the complexities of the water management arrangements. An example is the connections between the Murray, Murrumbidgee and Goulburn regions and the Snowy Mountains Hydro-electric Scheme. CSIRO 2007 November 2007 Water availability in the Paroo 7

18 1.5.1 Surface-groundwater interactions The project is explicitly considering and quantifying the water exchanges between rivers and groundwater systems. The approaches used are described below. The river models used by State agencies have in turn typically been calibrated by State agencies to achieve mass balance within calibration reaches over relatively short time periods. When the models are run for extended periods the relationships derived during calibration are assumed to hold for the full modelling period. In many cases however, the calibration period is a period of changing groundwater extraction and a period of changing impact of this extraction on the river system. That is, the calibration period is often one of changing hydrologic relationships, a period where the river and groundwater systems have not fully adjusted to the current level of groundwater development. To provide a consistent equilibrium basis for scenario comparisons it is necessary to determine the equilibrium conditions of surface and groundwater systems considering their interactions and the considerable lag times involved in reaching equilibrium. 1 Introduction Figure 1-3 shows an indicative timeline of groundwater use, impact on river, and how this has typically been treated in river model calibration, and what the actual equilibrium impact on the river would be. By running the groundwater models until a dynamic equilibrium is reached, a reasonable estimate of the ultimate impact on the river of current groundwater use is obtained. A similar approach is used to determine the ultimate impact of future groundwater use. Figure 1-3. Timeline of groundwater use and resultant impact on river For some groundwater management units particularly fractured rock aquifers there is significant groundwater extraction but no model available for assessment. In these cases there is the potential for considerable impacts on streamflow. At equilibrium, the volume of water extracted must equal the inflows to the aquifer from diffuse recharge, lateral flows and flows from overlying rivers. The fraction that comes from the overlying rivers is determined using a connectivity factor that is estimated from the difference in levels between the groundwater adjacent to the river and the river itself, the conductance between the groundwater pump and the river, and the hydrogeological setting. Given the errors inherent in this method, significant impacts are deemed to be those about 2 GL/year for a subcatchment, which given typical connectivity factors translates to groundwater extraction rates of around 4 GL/year for a subcatchment. 8 Water availability in the Paroo November 2007 CSIRO 2007

19 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 Introduction Wetland and irrigation water use An important component of the accounting is an estimate of actual water use based on remote sensing observations. Spatial time series of monthly net water use from irrigation areas, rivers and wetlands are estimated using interpolated station observations of rainfall and climate combined with remote sensing observations of surface wetness, greenness and temperature. Net water use of surface water resources is calculated as the difference between monthly rainfall and monthly actual evapotranspiration (AET). AET estimates are based on a combination of two methods. The first method uses surface temperature remotely sensed by the AVHRR series of satellite instruments for the period 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, and LANDSAT satellite imagery for the years 1998 to CSIRO 2007 November 2007 Water availability in the Paroo 9

20 The reach-by-reach estimates of net water use from irrigation areas and from floodplains and wetlands are subject to the following limitations: 1 Introduction Partial validation of the estimates suggested an average accuracy in AET estimation within 15 percent, but probably decreasing with the area over which estimates are averaged. Uncertainty in spatial estimates originates from the interpolated climate and rainfall data as well as from the satellite observations and the method applied. Errors in classification of irrigation and floodplain/wetland areas may have added an unknown uncertainty to the overall estimates, particularly where subcatchment definition is uncertain or wetland and irrigation areas are difficult to discern. Estimated net water use cannot be assumed to have been derived from surface water in all cases as vegetation may also have access to groundwater use, either directly or through groundwater pumping. Estimated net water use can be considered as an estimate of water demand that apparently is met over the long-term. Storage processes, both in irrigation storages and wetlands, need to be simulated to translate these estimates in monthly (net) losses from the river main stem. Therefore, the AET and net water use estimates are used internally to conceptual water balance models of wetland and irrigation water use that include a simulated storage as considered appropriate based on ancillary information Calculation and attribution of apparent ungauged gains and losses In a river reach, ungauged gains or losses are the difference between the sum of gauged main stem and tributary inflows, and the sum of main stem and distributary outflows and diversions. This would be equal to measured main stem outflows and water accounting could occur with absolute certainty. The net sum of all gauged gains and losses provides an estimate of ungauged apparent gains and losses. There may be differences between apparent and real gains and losses for the following reasons: Apparent ungauged gains and losses will also include any error in discharge data that may originate from errors in stage gauging or from the rating curves associated to convert stage height to discharge. Ungauged gains and losses can be compensating and so appear smaller than in reality. This is more likely to occur at longer time scales. For this reason water accounting was done on a monthly time scale. Changes in water storage in the river reach, connected reservoirs, or wetlands, can lead to apparent gains and losses that become more important as the time scale of analysis decreases. A monthly time scale has been chosen to reduce storage change effects, but they can still occur. The monthly pattern of apparent ungauged gains and losses are evaluated for each reach in an attempt to attribute them to real components of water gain or loss. The following techniques are used in sequence: Analysis of normal (parametric) and ranked (non-parametric) correlation between apparent ungauged gains and losses on one hand, and gauged and estimated water balance components on the other hand. Estimated components included SIMHYD estimates of monthly local inflows and remote sensing-based estimates of wetland and irrigation net water use. Visual data exploration: assessment of temporal correlations in apparent ungauged gains and losses to assess trends or storage effects, and comparison of apparent ungauged gains and losses and a comparison with a time series of estimated water balance components. Based on the above information, apparent gains and losses are attributed to the most likely process, and an appropriate method was chosen to estimate the ungauged gain or loss using gauged or estimated data. 10 Water availability in the Paroo November 2007 CSIRO 2007

21 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 1 Introduction Groundwater assessment, including groundwater recharge modelling, is undertaken to assess the implications of the climate and development scenarios on groundwater management units (GMUs) across the MDB. A range of methods are used appropriate to the size and importance of different GMUs. There are over 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 CSIRO 2007 November 2007 Water availability in the Paroo 11

22 are selected for which there exists sufficient publicly available information on hydrological indicators (such as commenceto-fill levels) which relate to ecological responses such as bird breeding events. Information sources include published research papers and reports, accessible unpublished technical reports, or advice from experts currently conducting research on specific environmental assets. In all cases the source of the information on the hydrological indicators used in each assessment is cited. The selection of the assets for assessment and hydrologic indicators was undertaken in consultation with State governments and the Australian Government through direct discussions and through reviews by the formal internal governance and guidance structures of the project. 1 Introduction The Directory of Important Wetlands in Australia (Environment Australia, 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 Basin 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 Available at: Battaglia M and Sands P (1997) Modelling site productivity of Eucalyptus globulus in response to climatic and site factors. Australian Journal of Plant Physiology 24, Brown AE, Podger PM, Davidson AJ, Dowling TI and Zhang L (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, 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, pp DSE (2004) Victoria in Future 2004 Population projections. Department of Sustainability and Environment, Victoria. Available at: Environment Australia (2001) A Directory of Important Wetlands in Australia. Available at: 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, Water availability in the Paroo November 2007 CSIRO 2007

23 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, October Jakarta: UNESCO 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, Nash JE and Sutcliffe JV (1970) River flow forecasting through conceptual models 1: A discussion of principles. Journal of Hydrology 10, 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, New South Wales Government (2000) Water Management Act 2000 No 92. Queensland Government (2000) Water Act South Australia Government (2004) Natural Resources Management Act 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 Melbourne, Australia. pp Van Dijk A et al. (2007) Reach-level water accounting for across the Murray-Darling Basin. A report to the Australian Government from the CSIRO Murray-Darling Basin Sustainable Yields Project. CSIRO, Australia. In prep. Victoria Government (1989) Water Act 1989, Act Number 80/ Introduction CSIRO 2007 November 2007 Water availability in the Paroo 13

24 2 Overview of the region 2 Overview of the region The Paroo region is based around the ephemeral Paroo River and includes the settlements of Wanaaring, Hungerford and Eulo. The region reported here covers less than 4 percent of the Murray-Darling Basin (MDB), is situated predominantly within southern Queensland, and has less than 0.1 percent of the Basin s population. It uses less than 0.1 percent of the surface water diverted within the MDB for irrigation and less than 0.1 percent of the share of the groundwater resource outside of the confined aquifers of the Great Artesian Basin (GAB). There are no significant regulated water storages within the region, surface water diversions are small, and very little irrigation is undertaken in the Paroo region. Groundwater from the GAB confined aquifers is the major water supply for the Paroo region. The major land use is broad acre livestock grazing for beef and wool production. There are no commercial forestry plantations in the region and the relatively few farm dams are primarily constructed for stock watering purposes. The region contains (or floods into) some of the most important and largest wetlands in the MDB including the Currawinya Lakes and the Paroo Overflow Lakes, parts of which are internationally recognised Ramsar wetlands sites. The Paroo River empties onto a floodplain south of Wanaaring in New South Wales, and floods typically dissipate on the floodplain and into associated lakes and wetlands without reaching the Darling River. Most of the river flows occur as floods following large, relatively infrequent rainfall events. 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 Paroo region is in the far north-west of the GAB, is predominantly in Queensland and covers 35,587 km 2 or 3.4 percent of the MDB. The region is predominantly flat with a gentle southwards gradient from the Warrego Range in the north. It is bounded to the north-west by the Lake Eyre Basin, forms the north-western edge of the MDB and is bounded to the west by the internally draining Bulloo catchment. It is bounded to the east by the Warrego region and to the south by the Barwon-Darling region. The Paroo region extends to about 100 km across the Queensland-New South Wales border and terminates at the gauging station at Wanaaring on the Paroo River, 300 km above the junction with the Darling River. The region reported on here is defined around the river system model because of the project s focus on assessing water availability. The southern extreme of the region for the project is Wanaaring, as there is no reliable information on the hydrology of the lower reach. The end-of-system flows reported for Wanaaring give some indication of water availability to users and the environment downstream. Major water resources in the Paroo region include the Paroo River, the GAB, alluvial aquifers, wetlands and on-farm water storages. On-farm storages are predominantly associated with livestock watering. Historically, the development of the stream-based water resources of the Paroo was for stock and domestic use as well as to support relatively small areas of irrigation. That pattern continues. Water is mostly sourced from the confined aquifers of the GAB from which 1200 bores feed over 1400 km of bore drains. The region s population is 685, less than 0.1 percent of the MDB, and Wanaaring is the largest town. Smaller settlements in the region include Hungerford and Eulo. The dominant land use is grazing for beef and wool production. Small-scale cropping provides supplementary feed for stock. There is no commercial plantation forestry in the region and farm dams are primarily constructed for stock watering purposes. The land use area (Table 2-1) is based on the 2000 land use of the MDB grid, derived from 2001 Bureau of Rural Sciences AgCensus data. Irrigation estimates are based on crop areas recorded as irrigated in the census. 14 Water availability in the Paroo November 2007 CSIRO 2007

25 Table 2-1. Summary of land use in the year 2000 within the Paroo region Land use Area percent ha Dryland pasture 93.0% 3,017,300 National Parks and State Forests 6.7% 216,400 Water 0.3% 9,900 Total 100.0% 3,243,600 Source: BRS (2000) Average annual rainfall across the entire region is 314 mm, with two-thirds of the region receiving a mean annual rainfall of less than 300 mm. The rainfall and runoff for the Paroo region are amongst the lowest in the MDB. Most of the rainfall and runoff occurs in summer and early autumn. The region s average annual rainfall has remained relatively consistent over the past 111 years, despite significant annual variability. The mean annual rainfall over 1997 to 2006 of 310 mm is similar to the long-term mean. The Paroo region contributes about 2 percent of the total runoff in the MDB. The average annual modelled runoff over the region for the 111-year period is 17 mm. The average annual runoff over the past ten years (1997 to 2006) is similar to the long-term mean. The region has the most sparse stream gauging network in the MDB. The rainfall gauging network is about three times less dense than the MDB average and the streamflow measurement network about ten times less dense. 2 Overview of the region Annual rainfall (mm) Mean monthly rainfall (mm) J F M A M J J A S O N D Figure annual and monthly rainfall averaged over the region. The curve on the annual graph shows the low frequency variability. CSIRO 2007 November 2007 Water availability in the Paroo 15

26 2 Overview of the region Figure 2-2. Map of dominant land uses of the Paroo region with inset showing the region s location within the Murray-Darling Basin. The assets shown are only those assessed in the project (see Chapter 7). A full list of key assets associated with the region is in Table 2-2. Source: BRS (2000) In 2003, the governments of New South Wales and Queensland signed an Inter-government Agreement for the Paroo River, formally recognising the outstanding ecological and cultural values of the Paroo. The agreement is based around making certain there are no cross-border impacts of any policies or strategies implemented on either side of the state boundary that might adversely affect water quality, quantity and related ecosystems. 16 Water availability in the Paroo November 2007 CSIRO 2007

27 A Regional Natural Resource Management (NRM) Plan 2004 (QMDC and SWNRM, 2004) has been prepared for all the catchments in the MDB region of southern Queensland. The South West Natural Resource Management Group Inc. (SWNRM) is the designated regional body responsible for development and the implementation of the NRM Plan in the Paroo. The NRM Plan is a framework to guide coordinated and holistic planning and on-ground action to improve the management and condition of the natural resources in the region, and identifies resource condition targets and prioritises innovative management strategies to improve catchment health and protect regional assets. The aspirational resource condition and management action targets in the NRM Plan for water have been primarily based on the principles in the water resource plans for the major river systems. The aspirational targets for water are: water to be efficiently used by 2035 groundwater to be sustainably managed for long term environmental, production and social values by 2035 surface water to be sustainably managed for long term environmental, production and social values by The statutory responsibility for the development of water resource plans in the Queensland section of the Paroo sits with the Queensland Department of Natural Resources and Water. In developing the Water Resource Plan for the region which includes the Paroo, the Department engaged a range of stakeholders in the plan area including the South West NRM Group. The resource condition targets seek to incorporate the objectives from the Strategic Management Plan for the Great Artesian Basin (GABCC, 2000) and the objectives from the Water Resource Plan (QDNR, 2003). Cross-border coordination and identification of common issues has been initiated as part of the NRM Plan for the western intersecting streams including the Paroo River (QMDC and SWNRM, 2004). 2.2 Environmental description 2 Overview of the region The Paroo region lies within the Mulga Lands bioregion, one of 17 bioregions found within New South Wales (NPWS, 2004). This bioregion is dominated by horizontal Cretaceous sandstones and claystones deposited in an inland sea about 100 million years ago. Alluvial fans of the Paroo River have deposited sands and clays between the plateau areas of sandstone. The plateau and tablelands typically have shallow, stony, red-brown loams. These merge down-slope, often through patterns of contour banding into brown texture contrast soils. Grey and brown cracking clays dominate the alluvial sequences with limited areas of sand deposition often reworked into source bordering sand sheets or low dunes. The Paroo region supports mulga, Western Bloodwood (Eucalyptus terminalis) and Poplar Box (Eucalyptus populnea), with Mallee (Eucalyptus sp.), White Cypress Pine (Callitris glaucophylla), Silver-leaf Ironbark (Eucalyptus melanophloia), Beefwood (Grevillea striata), Leopardwood (Flindersia maculosa) and Bluebush (Maireana sp.). Spinifex (Triodia sp.) is found on the Block Range ridges. Few trees grow on the western stony plateaus. Dense areas of woody shrubs extend across the sand plains. A review of fauna information in 1997 showed that 256 bird, 56 mammal, 94 reptile and 23 amphibian species have been recorded for the Mulga Lands bioregion (National Land and Water Resources Audit). The eucalypt woodlands associated with riparian areas show the highest species richness (Sattler and Williams, 1999). Significant flora species include the Spiny Sedge (Cyperus gymnocaulos), Bore-drain Sedge (C. laevigatus, found only between Milparinka and Wanaaring), Smooth Heliotrope (Heliotropium curassavicum) and Ellangowan Poison-bush (Myoporum deserti) towards the east of the bioregion (Cunningham et al., 1981; Morton et al., 1995). The Paroo River is considered to be the last free flowing river within the MDB. Its floodplain extends over 800,000 ha and provides feeding and breeding habitat to many thousands of plants and animals. The region contains some of the most important and largest wetlands in the MDB (Table 2-2). The wetlands have been classified as significant refuges for biological diversity (Morton et al., 1995). For example, 63 species of waterbirds have been recorded (see Kingsford and Porter, 1999). The Paroo supports a richer fish assemblage than other rivers in the MDB (Gehrke et al., 1995) and the population of golden perch (Macquaria ambigua) is genetically distinct, and is a separate breeding population from this species in the rest of the MDB (Watts, 1999). CSIRO 2007 November 2007 Water availability in the Paroo 17

28 The types of wetlands are extremely varied based on vegetation, hydrology, geomorphology and water quality particularly salinity (Kingsford and Porter, 1999; Timms, 1999). The Currawinya Lakes National Park in Queensland and Nocoleche Nature Reserve in New South Wales have been reserved for conservation purposes. The Currawinya Lakes (including the Lake Numalla Aggregation referred to here as Lake Numalla and Lake Wyara) are collectively listed under the Ramsar Convention for wetlands of international importance. The lakes in combination are considered to be amongst the most important wetlands in Australia and can support up to 250,000 waterbirds (Kingsford and Porter, 1999). The highest concentration of Freckled Duck (Strictonetta naevosa) ever observed in Australia has been recorded here (Kingsford and Porter, 1999). The Lake Numalla Aggregation covers some 10,700 ha and includes important aboriginal sites with some dating back 1400 years. Lake Wyara is a terminal, saline water body that covers some 6000 ha immediately to the west of Lake Numalla. 2 Overview of the region Table 2-2. Important wetlands within the Paroo region Directory of Important Wetlands in Australia SITE CODE Name Area* Paroo River Wetlands** NSW017 Paroo River Distributary Channels 720,000 Y NSW096 Blue Lake 237 NSW097 Gilpoko Lake 436 NSW100 Mullawoolka Basin 2026 NSW101 Peery Lake (Peri Lake) 5026 Y NSW102 Poloko Lake (Olepoloko Lake) 3722 Y NSW103 Tongo Lake 524 NSW104 Yantabangee Lake 1427 NSW146 Calbocaro Billabong 66 Y NSW159 Tenannia Waterhole 624 ha RAMSAR sites Currawinya Lakes*** QLD123 Lake Numalla Aggregation 10,724 Y QLD124 Lake Wyara 6020 Y QLD125 Lakes Bindegolly and Toomaroo 9677 QLD175 Lake Wombah-Kungie Lake Group 20,000 ha spread over some 250,000 ha QLD176 Paroo River Waterholes ('Caiwarro' Area) 25 Y QLD177 Eulo Artesian Springs Supergroup 30 ha spread over some 100,000 ha * Wetland areas have been extracted from the Australian Wetlands database and are assumed to be correct as provided from State and Territory agencies ** Paroo River Wetlands Ramsar site, area 138,304 ha *** Currawinya Lakes (Currawinya National Park) Ramsar site, area 151,300 ha The Paroo River wetlands in New South Wales have recently been listed as wetlands of international importance under the Ramsar Convention. The Ramsar-listed site consists of two main parts, the Nocoleche Nature Reserve and the Peery component including lakes Peery and Poloko. The Nocoleche Nature Reserve encompasses the Paroo River Distributary Channels. Peery Lake also contains mound springs, which are the natural outlet for artesian water. The more extensive Paroo Overflow Lakes include various shallow swamps and lakes such as Tongo Lake, Mullawoolka Basin, Yanatbangee Lake and Gilpoko Lake (Table 2-2). Most of the lakes hold water for several years after flooding. The wetlands provide breeding habitat and drought refuge for around 100,000 individual birds and approximately 60 species of water birds. The Paroo River Wetlands have been recognised as a significant refuge for biological diversity, as they contain unique genetic, species and ecosystem diversity. The wetlands are important in terms of richness as well as the large numbers of waterbirds that visit and breed in the area. A number of bird species found within these wetlands are associated with the Japanese Australia Migratory Bird Agreement (JAMBA) and the China Australia Migratory Bird Agreement (CAMBA). 18 Water availability in the Paroo November 2007 CSIRO 2007

29 A number of the fauna and flora species recorded in the region are listed under Queensland and Australian government legislation. 2.3 Surface water resources Rivers and storages The major river, the Paroo, flows roughly southward from its headwaters in the Warrego Ranges east of Adavale. The Paroo River rarely discharges into the Darling River and hence is essentially an internal drainage basin, terminating in swamps and wetlands of the Paroo Overflow Lakes below Wanaaring in New South Wales (Richardson, 1997). River flows are intermittent, with most of the runoff coming from infrequent flood events. In exceptionally wet years, such as 1974 and 1990, floods push down to discharge into the Darling River about 20 km upstream from Wilcannia (King et al., 1995) and approximately 386 km below Caiwarro. This occurred only three times over the period 1900 to 1999 (Power et al., 2007). Exceptional floods of around 980 GL are required to fill the Paroo Overflow Lakes below Wanaaring (Maher cited in King et al., 1995). The lower Paroo also receives flows from the Warrego River system via Cuttaburra Creek during periods of high runoff. There are no significant regulated water storages on the Paroo River or within the Paroo region (Webb, McKeown & Associates Pty Ltd, 2007). There are a number of natural waterholes and wetlands that hold water for extended periods Surface water management institutional arrangements Water resources within Queensland are managed under the Water Act The two-tier planning regime involves development of a Water Resource Plan, which sets the strategic rules for water management in a catchment and a Resource Operations Plan, which sets the operational rules. The statutory responsibility for the development of water resource plans in the Queensland section of the Paroo sits with the Queensland Department of Natural Resources and Water. In developing the Water Resource Plan for the region, which includes the Paroo, the Department engaged a range of stakeholders in the plan area including the South West Natural Resource Management Group. 2 Overview of the region The Water Resource (Warrego, Paroo, Bulloo and Nebine) Plan 2003 (QDNR, 2003) covers the entirety of the Queensland portion of the Warrego region. This Water Resource Plan includes objectives for environmental flow and water allocation security. The environmental flow objective includes a provision that the flows of the Paroo and its distributary streams that cross the border from Queensland into New South Wales be at least 99 percent of the pre-development end-of-system flow pattern assessed over a specified period using a river system model. Table 2-3. Summary of surface water sharing arrangements for the Queensland portion of the Paroo region Water products Priority of access Allocated entitlement ML/y Total licensed (long-term) extraction limit 50 Annual volumetric extraction limit 70 Supplemented access High 0 Supplemented access Medium 0 - Local water utilities Medium 0 - Agricultural use Medium 0 Domestic and stock *0 Unallocated 100 Unsupplemented access Low 50 Environmental provisions ** * Domestic and Stock allocations have been converted to nominal allocations ** Environmental Provisions are taken into consideration when setting the conditions of extraction on the entitlement to ensure there is a volume of water available for the environment. Source: QDNRM (2006) CSIRO 2007 November 2007 Water availability in the Paroo 19

30 Future allocation decisions affecting water allocation groups are limited to include: the annual volume probability for a water allocation group be not less than the annual volume probability for the group immediately before the decision is made the 45 percent annual volume probability for a water allocation group be not less than the 45 percent annual volume probability for the group immediately before the decision is made. The Warrego, Paroo, Bulloo and Nebine Resource Operations Plan 2006 (QDNRM, 2006) is designed to implement the objectives and outcomes specified in the Water Resource (Warrego, Paroo, Bulloo and Nebine) Plan The intent of these plans is to provide enhanced certainty and security for water users and the environment. 2 Overview of the region There is no equivalent Water Sharing Plan for the New South Wales portion of the Paroo River. The Unregulated Flow Management Plan for the Northwest (DNR, 2007) covers the Paroo River. It seeks to ensure minimum flows for the protection of basic river health as well as protecting high flows for algal suppression and fish migration. A moratorium on diversions and licences has been put in place Water products and use Water allocated for the Paroo region is detailed in Table 2-3. There is 50 ML of unsupplemented water allocation available from unregulated water harvesting. An upper volumetric limit of 70 ML of unsupplemented water may be accessed by licence holders in any one year. An additional volume of 100 ML/year has been reserved as unallocated water for future town water supply needs. A small area of irrigation has been established near Eulo. Unsupplemented water may be available in times of high flow. Extraction-rate limits govern water use. The provisions under which water may be accessed are detailed on the individual water allocation and include an annual volumetric limit, and a maximum daily rate of take and commence-to-pump conditions. In addition to unsupplemented water, landholders may capture overland flows in accordance with conditions detailed within the Resource Operations Plan The Water Resource Plan requires that those landholders who had existing overland flow works which are not wholly for stock and domestic purposes notify the details of those works to the Queensland Government. One landholding is reported to have constructed a storage dam with capacity for 11 GL of water (S. Moles MDB Community Advisory Committee, pers. comm.). There was 9 GL of surface water used within the Warrego and Paroo regions in 2000/01 (MDBC, 2007) or less than 0.1 percent of the surface water diverted within the MDB. The total licensed extraction limit for the Queensland portion of the Paroo region is 50 GL (Table 2-3). Queensland Water Resource Plans do not establish specific environmental water allocations; rather, environmental water is protected via the water access rules. 2.4 Groundwater Groundwater management units the hydrogeology and connectivity There are no groundwater management units (GMUs) in the Queensland portion of the Paroo and no groundwater model has been developed. The combined Warrego-Paroo-Nebine region of western Queensland MDB is allocated only 1 percent of the total Queensland MDB groundwater allocation. Roughly 74 percent of the allocation is to GAB bores, 23 percent is to shallower sandstone aquifers and 3 percent to the alluvial systems. The Paroo region is underlain by GAB aquifers, which provide the bulk of groundwater supply. The two GMUs in the New South Wales portion of the Paroo region have been assessed as very low priority in the context of the overall project on the basis of the size of the aquifers, the level of development, and the assumed degree of connectivity with the surface water system. A generalised east-west cross-section of the hydrogeology of the New South Wales portion of the region is shown in Figure 2-3 (modified from Evans et al. (1994)). The location of GMUs is provided in Figure Water availability in the Paroo November 2007 CSIRO 2007

31 It is important to clarify the scope of this assessment in relation to the aquifers of the GAB. The GAB consists of the following two primary hydrogeological units: the deep Jurassic sandstone confined aquifers the Cretaceous sandstone confined aquifers and shale confining layers which lie conformably above the Jurassic aquifers. The Cretaceous confining layers separate the deeper confined aquifers from the surficial aquifers. Through the New South Wales water management process there are three other hydrogeological units associated with the GAB (GAB In-take Beds, GAB Alluvium and GAB Cap Rocks). 2 Overview of the region Figure 2-3. Generalised east-west cross-section for New South Wales portion of Paroo Through a combination of hydrogeological characterisation and consideration of the current groundwater management approach it is possible to conceptualise the GAB according to the following four management units: 1. The deep Jurassic and Cretaceous sandstone confined aquifers, and Cretaceous confining layers which are administered by the Water Sharing Plan for the New South Wales Great Artesian Basin Groundwater Sources (N601 GAB Central Zone and N601 GAB Warrego Zone) and in Queensland by the Water Resource (Great Artesian Basin) Plan GAB In-take Beds that occur where the Jurassic and Cretaceous sandstone aquifers outcrop (for the Paroo system, this is outside of the reporting region, to the north-east). 3. GAB alluvium is a thick sequence of Cainozoic alluvium covering the GAB sequence with no corresponding GMU in the Paroo. CSIRO 2007 November 2007 Water availability in the Paroo 21

32 4. GAB Cap Rock aquifers occur across the reporting region where the GAB is not associated with another GMU. This unit can include the weathered and fractured Cretaceous rock aquifers, and Cainozoic alluvium (up to a depth of 60 m; N620 GAB Cap Rock in the New South Wales portion of the catchment). The primary source of groundwater resources in this region is the deeper GAB Jurassic and Cretaceous confined sandstone aquifers. The groundwater within these aquifers is separated from aquifers at the surface by thick confining beds, which means there is little interaction with the overlying surface water or groundwater contained in near surface aquifers. The water resources within these confined aquifers are not considered further in this assessment as the intake beds for the GAB do not outcrop within the catchment area, and there is little for these systems to be connected with surface water systems. The New South Wales portion of the GAB sediments is being assessed because they are part of the macro planning regime that has been rolled out across New South Wales. 2 Overview of the region The Eulo Artesian Springs group in the lower Paroo, located south-west of Eulo, cause mixing and discharge of GAB and shallow aquifer waters, though flow rates are now low and declining. There has been suggestion that the lower reaches may be gaining from these discharges (Jolly, 1989) but this has not been assessed. Water quality in the streams, however, is good (<100 mg/l total dissolved salts (TDS)) suggesting interaction is minimal. Along the Paroo River, local groundwater flow systems occur in deposits of recent Quaternary alluvium gravel, sand, silt and clay of fluviatile origin up to 100 m in depth. Quarantotto (1986) comments that water quality is good to very good in these sediments and has salinities of less than 1000 mg/l TDS. Groundwater is of the bicarbonate or chloride type or mixtures of the two. Recharge of these aquifers is either from rainfall infiltration or from streams. Sandy areas along the rivers, low stream gradients and low flow velocities promote aquifer recharge in these ephemeral streams. Older Quaternary deposits of undifferentiated alluvium comprising sand, gravel, silcrete, sandy red earth and limestone deposited under fluviatile, sheet-wash and aeolian conditions, extend over the flatter areas of the catchment. Depth of alluvium is up to 20 m (Quarantotto, 1986). The sparse groundwater database records suggest that where shallow unconfined aquifers exist in this alluvium, groundwater salinity is variable with the majority of values ranging from 500 mg/l to 4000 mg/l TDS (DNR, 2000) but exceeding 7000 mg/l TDS in some bores (Jolly, 1989). The low rainfall, extent of remnant vegetation and high evaporation in the Paroo region indicate that recharge to these aquifers would be low and infrequent. Local groundwater flow systems also occur in the Tertiary Glendower Formation, comprising quartzose sandstone, conglomerate, siltstone and silcrete plateaux and rises. Outcrops of the Glendower Formation are generally less than 15 m thick, but may be as thick as 70 m, with aquifers occurring in the porous sandstones. The Glendower Formation contains unconfined, semi-confined and confined aquifers. Salinity is highly variable ranging from 557 mg/l to 10,035 mg/l TDS. Groundwater is mainly of the sodium chloride type (Quarantotto, 1986). Surface water-groundwater connectivity within the Paroo region has not been mapped within this project. Jolly (1989) suggests that the Paroo River may be gaining in some reaches from upward leakage from confined aquifers. Leakage from the Hooray Sandstone into Yowrah Creek supports that observation but the impact of spring water on stream flows and salinity has not been assessed. Water quality in the Paroo River suggests that springs have minimal impact on water quality because mean salinity is approximately 100 µs/cm, being much less than the salinity of spring water. Table 2-4. Categorisation of New South Wales groundwater management units including annual extraction, entitlement and recharge Code Name Priority Total entitlement Current extraction* 2004/05 GL Long term average extraction limit GL/y Recharge** N620 GAB Cap Rocks (NSW) very low N46 Upper Darling Alluvium very low *Current groundwater extraction for Macro Groundwater Sharing Plan areas is based on metered and estimated data provided by NSW DWE. Metered usage is for all access and urban entitlement holders. Data quality is variable depending on the location of bores and the frequency of meter reading. Estimated usage is for basic rights entitlement holders. ** This value represents only rainfall recharge in Macro Groundwater Sharing Plan areas. The volume of recharge does not include recharge to national park areas, which has generally been allocated to environmental purposes and is not available for consumptive use. 22 Water availability in the Paroo November 2007 CSIRO 2007

33 2 Overview of the region Figure 2-4. Map of groundwater management units within the Paroo region Water management institutional arrangements The water resources within the Queensland GAB aquifers are administered by the Water Resource (Great Artesian Basin) Plan This plan provides a framework for sustainably allocating and managing water in the GAB. A Resource Operations Plan details the arrangements for implementing the water resource plan. The water resources within the New South Wales GAB aquifers are controlled by the Water Sharing Plan for the New South Wales Great Artesian Basin Groundwater Resources The vision for this plan is to achieve equitable, viable and sustainable management of the GAB in New South Wales for the benefit of the community and the biodiversity of the region. Excluding areas of the GAB covered by the Water Sharing Plan for the New South Wales GAB, groundwater extraction in the New South Wales portion of the Paroo region is controlled by the New South Wales Macro Groundwater Sharing Plans. This plan is prepared under the New South Wales Water Management Act 2000 and provides an extraction limit CSIRO 2007 November 2007 Water availability in the Paroo 23

34 and environmental provisions for the groundwater system. Extraction records for the macro plan regions are generally poor. The annual extraction limit is set as a proportion of rainfall recharge to the system. The macro planning process does not discount the extraction limit for salinity. As such the limits reflect availability in volumetric terms only. The environmental provisions range up to 50 percent of the rainfall recharge. Table 2-5. Summary of groundwater management plans Name of plan Macro groundwater sharing plan Year of plan * Basic rights Domestic and stock rights GL/y 2 Overview of the region Native title Access licences Urban Planned share Announced allocation Environmental provisions None 0 GL/y 0.45 GL/y None Planned share 50% of rainfall recharge for N46 and 5% of rainfall for N620 Supplementary provisions Adaptive provisions None None * NSW DWE advise that the Macro Water Sharing Plans are proposed to commence in Water products and use Bore water from the confined aquifers of the GAB is the main water supply for stock and domestic use in the Paroo region. Generally this artesian water is too sodic for irrigation. Sub-artesian and artesian water of varying quality (500 mg/l to 10,000 mg/l total dissolved salts) is pumped from the Cretaceous Winton Formation. Sub-artesian bores and troughs predominate in the upper catchment, whereas artesian bores and bore drains are the main stock water supply in the lower Paroo where the flat country and free flowing bores provide for the construction of bore drains. The majority of bore drains are located to the east of the Paroo River. The free flowing artesian bores and bore drains are being capped and piped under the Great Artesian Basin Sustainability Initiative. There is no functioning observation or shallow monitoring bores within the region and no groundwater modelling has been undertaken. Groundwater bores are relatively widely spaced across the region. Table 2-6. Number and type of bores in the Queensland portion of the Paroo region Type Number Artesian 258 Sub-artesian 145 Total 403 Abandoned 76 Monitoring (functional) 0 There is some water use from shallow alluvial aquifers, which can be up to 100 m in thickness, and the shallow tertiary sandstones and siltstones, but this is sporadic due to variable water quality, and there has been little information generated on the shallow hydrogeology of the catchment (Cottingham, 1999; Quarantotto, 1986). 24 Water availability in the Paroo November 2007 CSIRO 2007

35 Entitlements for the New South Wales groundwater management units within the Paroo region area separated into three classes as defined by the New South Wales Water Management Act 2000: Basic Rights, Town Water and General Purpose. The Basic Right entitlements were set for areas controlled via New South Wales Macro Groundwater Sharing Plans on the basis of 1.5 ML/year for each stock and domestic bore. Table 2-7. Estimated groundwater extraction sub-divided by use for the Paroo groundwater management units Code GMU Basic rights Town water General purpose GL/y N620 GAB Cap Rocks (NSW) N46 Upper Darling Alluvium Total References BRS (2000) Land use data. Available at: Cottingham P (1999) Scientific Forum on River Condition and Flow management of the Moonie, Warrego, Paroo, Bullo and Nebine River basins. Department of Natural Resources, Queensland and CRC Freshwater Ecology. Cunningham GE, Mulham WE, Milthorpe PL and Leigh JH (1981) Plants of Western NSW. NSW Government Printing Office in conjunction with the Soil Conservation Service of NSW, Sydney. DNR (2000) Queensland Murray-Darling Salinity Assessment Summary Report. Water Assessment and Planning, Department of Natural Resources, Brisbane. DNR (2007) Unregulated Flow Management Plan for the Northwest. Evans WR, Hillier J and Woolley DR (1994) Hydrogeology of the Darling River Drainage Basin (1:1,000,000 scale map). Australian Geological Survey Organisation, Canberra. GABCC (2000) Strategic Management Plan for the Great Artesian Basin. Great Artesian Basin Consultative Council. GABCC (2006) Great Artesian Basin Resource Operations Plan Great Artesian Basin Consultative Council. Gehrke PC, Brown P, Schiller CB, Moffatt DB and Bruce AM (1995) River regulation and fish communities in the Murray-Darling River system, Australia. Regulated Rivers: Research and Management 11, Jolly ID (1989) Investigation into the potential for increased stream salinisation in the Darling Basin. Centre for Research in Groundwater Processes Report No 10. In: Power RE, Biggs, AJW and Burton, DWG (2007) Salinity Audit Warrego and Paroo Catchments, Queensland Murray-Darling Basin. Department of Natural Resources and Water, Queensland. King AM, Green DL and Brady AT (1995) Wetlands of the Paroo River and Cuttaburra Creek. Technical Services Division, NSW Department of Land and Water Conservation, Sydney. Kingsford RT and Porter J (1999) Wetlands and waterbirds of the Paroo and Warrego Rivers. In: Kingsford RT (Ed.) a free flowing river the ecology of the Paroo River. NSW National Parks and Wildlife Service, Hurstville. Moles S (2007) Comments provided as part of Technical Reference Panel for MDB Sustainable Yields project, CSIRO. Morton SR, Short J and Barker RD with an Appendix by Griffin GF and Pearce G (1995) Refugia for biological diversity in Arid and Semi arid Australia. A report to the Biodiversity Unit of the Department of Environment, Sport and Territories. CSIRO Australia. NPWS (2004) Mulga Lands Bioregion. Available at: Power RE, Biggs AJW and Burton DWG (2007) Salinity Audit Warrego and Paroo Catchments, Queensland Murray-Darling Basin. Department of Natural Resources and Water, Queensland. Quarantotto P (1986) Hydrogeology of the southeastern Eromanga Basin, Queensland. BMR Record 1986/38. QDNR (2003) Water Resource (Warrego, Paroo, Bulloo and Nebine) Plan Queensland Department of Natural Resources. QDNRM (2006) Warrego, Paroo, Bulloo and Nebine Resource Operations Plan Queensland Department of Natural Resources and Mines. QMDC and SWNRM (2004) Regional Natural Resource Management Plan 2004 (NRM), Queensland Murray Darling Committee Inc. and South West Natural Resource Management Group Inc. Richardson K (1997) Environmental issues and values of the Paroo wetlands, DLWC Border Rivers Commission. Sattler P and Williams R (1999) The Conservation Status of Queensland's Bioregional Ecosystems. Queensland Environment Protection Agency, Brisbane. Timms BV (1999) Local runoff, Paroo floods and water extraction impacts on wetlands of Currawinya National Park. In: Kingsford RT (Ed.) a free flowing river the ecology of the Paroo River. NSW National Parks and Wildlife Service, Hurstville. Water Resource (Great Artesian Basin) Plan Water Sharing Plan for the New South Wales Great Artesian Basin Groundwater Resources Watts RJ (1999) Biodiversity in the Paroo River and its wetlands. In: Kingsford RT (Ed.) a free flowing river the ecology of the Paroo River. NSW National Parks and Wildlife Service, Hurstville. Webb, McKeown and Associates (2007) State of the Darling. Interim Hydrology Report to the Murray-Darling Basin Commission. ISBN Overview of the region CSIRO 2007 November 2007 Water availability in the Paroo 25

36 3 Rainfall-runoff modelling This chapter includes information on the climate and rainfall-runoff modelling for the Paroo region. It has four sections: a summary an overview of the regional modelling approach a presentation and description of results a discussion of key findings. 3.1 Summary 3 Rainfall-runoff modelling Issues and observations The methods used for climate scenario and rainfall-runoff modelling across the Murray-Darling Basin (MDB) are described in Chapter 1. There are no significant differences in the methods used to model the Paroo region Key messages The mean annual rainfall and modelled runoff averaged over the Paroo region are 311 mm and 17 mm respectively. Most of the rainfall and runoff occurs in summer and early autumn. River flows are intermittent, with most of the runoff coming from infrequent flood events. The Paroo region covers about 3.3 percent of the MDB and contributes about 2 percent of the total runoff in the MDB. The mean annual rainfall and runoff over the past ten years ( ) are 310 mm and 16 mm respectively, and they are not statistically significantly different from the long-term historical means. The best estimate (median) from climate change impact modelling is a 2 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 16 percent reduction to a 40 percent increase in mean annual runoff. There are no commercial forestry plantations in the region and relatively few farm dams. This situation is unlikely to change and therefore commercial forestry and farm dams are unlikely to significantly impact future runoff Uncertainty Scenario A - historical climate and current development The runoff estimates in the Paroo region (and the western and north-western parts of the MDB) are relatively poor compared to the eastern and southern parts of the MDB. It is considerably more difficult to model runoff in the western and north-western parts of the MDB because the region is drier, there are far fewer rainfall stations, and river flows are intermittent with most of the runoff occurring as infrequent floods. Although there is large uncertainty in the runoff estimates for the Paroo region, the modelling results for Scenario C relative to Scenario A can be used to realistically assess the impact on climate change on runoff. 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. 26 Water availability in the Paroo November 2007 CSIRO 2007

37 3.2 Modelling approach 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 0.05 o 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 ( km 2 ). In the model calibration, the six parameters of SIMHYD are optimised to maximise an objective function that incorporates the Nash-Sutcliffe efficiency of monthly runoff and daily flow duration curve, together with a constraint to ensure that the total modelled runoff over the calibration period is within 5 percent of the total recorded runoff. The runoff for a 0.05 o grid cell in an ungauged subcatchment is modelled using optimised parameter values for a calibration catchment closest to that subcatchment. The rainfall-runoff model SIMHYD is used because it is simple and has relatively few parameters and, for the purpose of this project, provides a consistent basis (that is automated and reproducible) for modelling historical runoff across the entire MDB and for assessing the potential impacts of climate change and development on future runoff. 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 Rainfall-runoff modelling Rainfall-runoff modelling for the Paroo region The rainfall-runoff modelling is carried out to estimate runoff in 0.05 o grid cells in four subcatchments as defined for the river system modelling in Chapter 4 for the Paroo region (Figure 3-1). Optimised parameter values from a single calibration catchment in the north of the Paroo are used to model runoff in all the four subcatchments. This is the only catchment smaller than 2000 km 2 with a streamflow gauging station around the Paroo and neighbouring regions. Nevertheless, streamflow data from the much larger Subcatchment indicate that the mean annual runoff there is similar to the mean annual runoff in Subcatchment Scenario B modelling is not carried out for the Paroo region because the mean annual rainfall and modelled runoff for 1997 to 2006 are not significantly different (at statistical significance level of α = 0.2 with the Student-t and Rank-Sum tests) from the long-term 1895 to 1996 means (see Section 3.3.1). Scenario D modelling is also not carried out for the Paroo region because commercial forestry plantations and farm dams are unlikely to impact significantly on runoff. This is because there is no commercial plantation forestry in the region and relatively few farm dams and this situation is unlikely to change. CSIRO 2007 November 2007 Water availability in the Paroo 27

38 3 Rainfall-runoff modelling Figure 3-1. Map of the modelling subcatchments and calibration catchments for the Paroo region Model calibration Figure 3-2 compares the modelled and observed monthly runoff and the modelled and observed daily flow duration curves for the two calibration catchments. The results indicate that the SIMHYD calibration can reproduce satisfactorily the observed monthly runoff series (Nash-Sutcliffe E value of 0.82) and the daily flow duration characteristic (Nash 28 Water availability in the Paroo November 2007 CSIRO 2007

39 Sutcliffe E value of 0.86). The volumetric constraint used in the model calibration also ensures that the total modelled runoff is within five 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 the daily flow duration curves, but the disagreement between the modelled and observed daily runoff characteristics only occurs for runoff that is exceeded less than 0.1 or 1.0 percent of the time. This is accentuated in the plot because of the linear scale on the y-axis and the 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. However, despite the satisfactory model calibration, the runoff estimates for the Paroo region are relatively poor (particularly in the southern parts of the region) compared to the runoff estimates for the eastern and southern parts of the MDB. This is because, compared to the eastern and southern parts of the MDB, there are far fewer rainfall stations in the Paroo, there is only one gauging station recording streamflow from 50 km 2 to 2000 km 2 catchments and river flows are intermittent with most of the runoff occurring as infrequent floods. 3 Rainfall-runoff modelling Figure 3-2. Modelled and observed monthly runoff and daily flow duration curve for the calibration catchment 3.3 Modelling results Scenario A historical climate and current development Figure 3-3 shows the spatial distribution of mean annual rainfall and modelled runoff for 1895 to 2006 across the Paroo 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 The long-term mean annual rainfall and modelled runoff averaged over the Paroo region are 311 mm and 17 mm respectively. There is a clear north-south gradient in both rainfall and runoff, with mean annual rainfall ranging from about 400 mm in the north to less than 250 mm in the south and mean annual runoff ranging from about 30 mm in the north to 10 mm in the south (Figure 3-4). Most of the rainfall occurs from late spring to early autumn, and most of the runoff occurs in summer and early autumn (Figure 3-5). The Paroo region covers about 3.3 percent of the MDB and contributes about 2 percent of the total runoff in the MDB. In the rainfall-runoff modelling, about 6 percent of the mean annual rainfall in the Paroo becomes runoff, whilst only 2 percent of the mean annual rainfall in the Warrego becomes runoff. This is supported by several streamflow gauges over large catchments in the northern halves of the Paroo and Warrego (to which the rainfall-runoff model is calibrated against) and the assessments of Young et al. (2006). CSIRO 2007 November 2007 Water availability in the Paroo 29

40 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 Paroo are 0.43 and 1.17 respectively, and they are amongst the highest in the MDB (the tenth percentile, median and ninetieth percentile values across the 18 reporting 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 runoff over the past ten years (1997 to 2006) are 310 mm and 16 mm respectively, and they are not significantly different from the long-term means (at a statistical significance level of α = 0.2 with the Student-t and Rank-Sum tests). Potter et al. (2007) present a more detailed analysis of recent rainfall and runoff across the MDB. 3 Rainfall-runoff modelling Figure 3-3. Spatial distribution of mean annual rainfall and modelled runoff averaged over Annual rainfall (mm) Annual runoff (mm) Figure annual rainfall and modelled runoff series averaged over the region. The curve shows the low frequency variability. 30 Water availability in the Paroo November 2007 CSIRO 2007

41 Mean monthly rainfall (mm) J F M A M J J A S O N D Mean monthly runoff (mm) J F M A M J J A S O N D Figure 3-5. Mean monthly rainfall and modelled runoff (averaged over for the region) Scenario C future climate and current development Figure 3-6 shows the percentage change in the modelled mean annual runoff averaged over the Paroo 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 a description of the GCMs and detailed discussion of the methods used to obtain Scenario C climate series). 3 Rainfall-runoff modelling The plot and table indicate that the potential impact of climate change on runoff can be very significant. However, there is considerable uncertainty in the estimates, with results from about half of the GCMs showing a reduction in mean annual runoff and the other half showing an increase in mean annual runoff. These results are different to the southern parts of the MDB where the majority of GCMs indicate that rainfall would decrease. 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 almost half the GCMs indicates a decrease in mean annual runoff greater than 10 percent, and rainfall-runoff modelling with climate change projections from 40 percent of the GCMs indicates an increase in mean annual runoff greater than 10 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 -16, -2 and +40 percent change in mean annual runoff. By comparison, the range based on the low global warming scenario is -5 to +10 percent change in mean annual runoff. Figure 3-7 shows the mean annual runoff across the Paroo region for Scenario A and for the Cdry, Cmid and Cwet scenarios. CSIRO 2007 November 2007 Water availability in the Paroo 31

42 % change in mean annual runoff High global w arming Medium global w arming Low global w arming 3 Rainfall-runoff modelling -60 ipsl cnrm mpi csiro iap giss_aom mri gfdl inmcm ncar_ccsm cccma_t63 ncar_pcm cccma_t47 miub 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 miroc 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 ipsl ipsl ipsl -3-9 cnrm cnrm mpi -2-5 mpi mpi cnrm -3-5 csiro csiro giss_aom -3-5 iap giss_aom csiro -2-4 giss_aom iap -3-9 iap -1-4 mri mri -5-8 mri -2-4 gfdl -6 0 gfdl -4-2 gfdl -2-1 inmcm -1 3 inmcm -1 2 inmcm 0 1 ncar_ccsm 3 11 ncar_ccsm 2 7 ncar_ccsm 1 3 cccma_t cccma_t cccma_t ncar_pcm 9 21 ncar_pcm 6 13 ncar_pcm 2 6 cccma_t cccma_t cccma_t miub miub 8 25 miub 4 10 miroc miroc miroc Water availability in the Paroo November 2007 CSIRO 2007

43 3 Rainfall-runoff modelling Figure 3-7. Mean annual rainfall and modelled runoff under scenarios A, Cdry, Cmid and Cwet CSIRO 2007 November 2007 Water availability in the Paroo 33

44 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 Paroo region), and the percentage changes in the rainfall, runoff and actual evapotranspiration in Scenario C relative to Scenario A. Figure 3-8 shows the mean monthly rainfall and modelled runoff for scenarios A and C averaged over 1895 to 2006 for the Paroo. Figure 3-9 shows the daily rainfall and flow duration curves for scenarios A and C averaged over the region. The modelling results for the four subcatchments in the Paroo are summarised in Appendix A. 3 Rainfall-runoff modelling It should be noted that the Cmid (or Cdry or Cwet) results are from rainfall-runoff modelling using climate change projections from one GCM. As the Cmid scenario is chosen based on mean annual runoff (see Section 3.3.2), the comparison of monthly and daily results in Scenario Cmid relative to Scenario A in Figure 3-8 and Figure 3-9 should be interpreted cautiously. However, the C range results shown in Figure 3-8 are based on the second driest and second wettest results for each month separately from the high global warming scenario, and the C range results shown in Figure 3-9 are based on the second lowest and second highest daily rainfall and runoff results at each of the rainfall and runoff percentiles from the high global warming scenario. The lower and upper limits of C range are therefore not the same as the Cdry and Cwet scenarios reported elsewhere and used in the river system and groundwater models. Twothirds of the GCMs indicate that, as a result of climate change, extreme rainfall that is exceeded 0.1 percent of the time will be more intense (Figure 3-9). As explained earlier, Scenario B (recent climate and current development) modelling has not been carried out for the Paroo because the mean annual rainfall and modelled runoff for 1997 to 2006 is not statistically significantly different to the long-term means. The Scenario B results would therefore be essentially the same as the Scenario A results. The modelling results indicate a median estimate of -2 percent change in mean annual runoff by ~2030 (Scenario C). However, there is considerable uncertainty in the results with extreme estimates ranging from -16 percent to +40 percent. As explained earlier, Scenario D (future climate and future development) modelling has not been carried out for the Paroo because commercial plantation forestry and farm dams are unlikely to significantly impact future runoff. The Scenario D results would therefore be essentially the same as the Scenario C results. Table 3-2. Water balance over the entire region by scenario Scenario Rainfall Runoff Evapotranspiration mm A percent change from Scenario A B Cdry -11% -16% -11% Cmid -4% -2% -4% Cwet 13% 40% 11% Ddry Dmid Dwet Water availability in the Paroo November 2007 CSIRO 2007

45 Mean monthly rainfall (mm) Scenario C range Scenario A Scenario Cmid J F M A M J J A S O N D Mean monthly runoff (mm) Scenario C range Scenario A Scenario Cmid J F M A M J J A S O N D Figure 3-8. Mean monthly rainfall and modelled runoff under scenarios A and C averaged over across the region (C range is based on the consideration of each month separately the lower and upper limits in C range are therefore not the same as scenarios Cdry and Cwet) 3 Rainfall-runoff modelling Figure 3-9. Daily flow duration curves under scenarios A and C 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 long-term mean annual rainfall for the Paroo is 311 mm and the modelled runoff averaged over the same 112-year period for the region is 17 mm. There is a clear north-south gradient in both rainfall and runoff. Mean annual rainfall ranges from about 400 mm in the north to less than 250 mm in the south, and mean annual runoff ranges from about 30 mm in the north to 10 mm in the south. Most of the rainfall occurs from late spring to early autumn, and most of the runoff occurs in summer and early autumn. The Paroo region covers about 3.3 percent of the MDB and contributes about 2 percent of the total runoff in the MDB. The mean annual rainfall over the ten year period from 1997 to 2006 is 310 mm. Over the same period runoff is 16 mm. Neither annual rainfall nor annual runoff is markedly different in statistical terms from the long-term historical means. However, the runoff estimates in the Paroo region (and the western and north-western parts of the MDB) are less certain compared to the eastern and southern parts of the MDB. It is considerably more difficult to model runoff in the western and north-western parts of the MDB because the region is drier, river flows are intermittent with most of the runoff occurring as infrequent floods, there are far fewer rainfall stations and there are little to no gauging stations recording streamflow over small catchment areas. The median estimate from climate change impact modelling is a 2 percent reduction in mean annual runoff by ~2030 relative to ~1990. There is considerable uncertainty in the modelling results with extreme estimates ranging from -16 percent to +40 percent. The main sources of uncertainty are in the global warming projections and the global climate CSIRO 2007 November 2007 Water availability in the Paroo 35

46 modelling of local rainfall response to the global warming. The uncertainty in the rainfall-runoff modelling of climate change impact on runoff is small compared to the climate change projections. There are no commercial forestry plantations in the Paroo and relatively few farm dams. This situation is unlikely to change and therefore commercial forestry and farm dams are unlikely to impact future runoff. 3.5 References 3 Rainfall-runoff modelling 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 Science Basis. Contributions of Working Group 1 to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press. Potter NJ, Chiew FHS, Frost AJ, Srikanthan R, McMahon TA, Peel MC and Austin JM (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. Young W, Brandis K and Kingsford R (2006) Modelling monthly streamflows in two Australian dryland rivers: Matching complexity to spatial scale and data availability. Journal of Hydrology 331, Water availability in the Paroo November 2007 CSIRO 2007

47 4 River system modelling This chapter includes information on the river system modelling for the Paroo 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. The information in this chapter is derived from the Queensland Department of Natural Resources and Water s (QDNRW) calibrated model, IQQM, for the Paroo river system. 4.1 Summary Issues and observations River system modelling for the Paroo region considers six modelling scenarios: 1. Scenario O Scenario O represents the original river system model configuration that was used for planning purposes in QDNRW and DWE. Scenario O represents the original river system model configuration that was used for planning purposes in QDNRW. It is run over the original 1 January 1889 to 31 December 1999 planning period that QDNRW used for developing the Queensland Resource Operations Plan. 4 River system modelling 2. Scenario A Scenario A is based on Scenario O but is run for the common modelling period 1 June 1895 to 30 June This scenario is used as the baseline that all other scenarios are compared against. 3. Scenario P Scenario P is based on the Scenario A model and is run for the common historic climate period. Current levels of development such as public storages and demand nodes are removed from the model to represent pre-development conditions. Note natural water bodies, fixed diversion structures and existing catchment runoff characteristics are not adjusted. 4. Scenarios Cwet, Cmid and Cdry The C scenarios represent a range of future climate conditions that are derived by adjusting the historical climate and flow inputs used in Scenario A, which is described in Chapter 3. The level of development is the same as Scenario A, i.e. the current level of development. Future development scenarios were not modelled in the Paroo region as there was not significant development of plantation forestry, farm dams or groundwater. Consequently results for future development scenarios would be similar to the C scenarios. These scenarios are not of conditions that will eventuate but are of consequences that might arise if no management changes were made. Consequently results from this assessment highlight pressure points in the system, both now and in the future. This assessment does not elaborate on what management actions might be taken to address any of these pressure points. The Paroo River model: is configured to represent the full utilisation of licences. Consequently the demands generated represent what could be diverted if licences were fully utilised. The observed history of use is considerably smaller than what is reflected in this configuration of the model. CSIRO 2007 November 2007 Water availability in the Paroo 37

48 irrigation demands are modelled using a soil moisture accounting model that is configured with large areas and monthly demand patterns that ensure all available water is utilised. Consequently the demands do not reflect the variation in demands due to climatic influences. modelled crop areas are fixed and do not reflect any change in irrigated area as a function of available water resources. includes the 0.1 GL/year of unallocated water identified in the Queensland Resource Operations Plan for the region. represents unsupplemented access as water extracted from the main river and modelled distributaries. The beneficial flooding in the lower part of the system is not explicitly modelled and consequently this is not assessed. 4 River system modelling Analysis of the pre-development flows along the Paroo River indicates that it changes from a gaining to a losing stream (point of maximum average annual flow) at the Caiwarro gauge (424201). The pre-development average annual flow over the modelling period at this location is 445 GL/year. The Queensland Resource Operations Plan is based on results for the original model (Scenario O) that runs over a different climatic period to the common modelling period used in this study. Despite the difference in the modelling period the percentage of long-term average flow to New South Wales is almost identical at 99 percent of the pre-development flow. In all but the wettest years, the Paroo River does not discharge into the Darling River, but dissipates onto the lower floodplain and associated lakes and wetlands Key messages The current level of development (maximum permissible use) in the Paroo is very low: less than 1 percent of the long-term average flow is able to be diverted for use. The best estimate 2030 climate scenario indicates a 2 percent reduction in river inflows leading to a 3 percent reduction in average water availability for the region and no change in end-of-system flows. Because water use is low, even assuming maximum permissible use, this reduction in inflow has no impact on diversions. The climate extremes for 2030 indicate: o o o for a wet extreme 2030 climate there would be a 40 percent increase in total inflows, a 41 percent increase in water availability and a 53 percent increase in end-of-system flows, under a dry extreme 2030 climate the following decreases would occur: total inflows would be down by 16 percent, water availability also down by 16 percent, and end-of-system flows down by 17 percent, and however there is no significant impact on modelled water use under either 2030 climate extreme. The Queensland Water Resource Plan that relates to the Queensland portion of the Paroo region requires that at least 99 percent of the average without development flow into New South Wales is maintained. Consequently diversions in Queensland should not reduce flow across the border by more than 1 percent of the average without development cross-border flow. Given current surface water entitlements in Queensland this requirement is being met. Changes in inflows under future climate would lead to small changes in relative level of water diverted for use, but none of these changes would contravene the requirement of the current Plan. 38 Water availability in the Paroo November 2007 CSIRO 2007

49 4.1.3 Robustness Typically the physical processes in the model such as routing and storage behaviour work through a full range of flow and storage conditions. However management rules in the model are closely tied to the historical data set that was used to develop them. When the historical data set is changed to much drier conditions there is no guarantee that models will behave robustly. The Paroo river system model does not contain any resource assessment and supply storages, consequently it was not necessary to test the model for robust behaviour. For each of the scenarios the model response to increases and decreases in inflow was reasonable with the change in diversions and end-of-systems flows consistent with the change in inflow. Mass balance over the modelling period was maintained within 0.2 percent for all scenarios (Appendix B). 4.2 Modelling approach General The following section provides a summary of the generic river modelling approach, a description of the Paroo river model and how the river model was developed. Refer to Chapter 1 for more details on the overall project methodology. 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 above 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 in use are IQQM, REALM, MSM-Bigmod, WaterCRESS and a model of the Snowy Mountains Hydro-electric Scheme. 4 River system modelling A few areas of the Murray-Darling Basin (MDB) have not previously been modelled, and hence some new IQQM or REALM models have been implemented. In some cases ancillary models are used to estimate aspects of water demands of use in the river system model. A key example is the Pride model used to estimate irrigation for Victorian REALM models. River systems that do not receive inflows or transfers from upstream or adjacent river systems are modelled independently. This is the case for most of the river systems in the Basin, and for these rivers the modelling steps are: 1. model configuration 2. 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 3. using scenario climate and inflow time series, run the river model for all scenarios (historical, recent and future climate as well as future development) 4. where relevant, extract initial estimates of surface-groundwater exchanges and provide to the groundwater model 5. 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 transfer from upstream or adjacent river systems, model inputs for each scenario are taken from the upstream model(s). In a few cases several iterations are required between upstream and downstream models because of the complexities of the water management arrangements. An example is the connections between the Murray, Murrumbidgee and Goulburn regions and the Snowy Mountains Hydro-electric Scheme. CSIRO 2007 November 2007 Water availability in the Paroo 39

50 4.2.2 Model description The Paroo region is described by the Paroo River system model (Figure 4-1). The model is an IQQM V representation of the Paroo River system (DNRM, 2003) from the Yarronvale gauge (424202A) to Wanaaring (424001). The model does extend past the Wanaaring gauge to the Darling River but this is not calibrated or reported herein. The outflows from the Paroo River only reach the Darling River under extremely wet conditions and are not considered in the Darling River system model and consequently are not considered in the Barwon-Darling region report. The model represents the Paroo River system to Wanaaring, with 68 links and 70 nodes arranged into 17 river sections. The natural pools and water bodies along the length of the Paroo River are modelled by 20 storage nodes. 4 River system modelling There are no regulated storages in the model. The water use is modelled by seven demand nodes; three represent Queensland stock and domestic demand, two representing Queensland town water supplies, one Queensland unsupplemented access irrigator and one New South Wales town water supply (Table 4-2). Natural water bodies Table 4-1. Storages in the river system model Active storage GL Average annual Inflow Average annual release Average annual net evaporation Paroo system to Wanaaring N/A N/A N/A N/A GL/y Degree of regulation Table 4-2. Modelled water use configuration Number of nodes Medium security water product Licence Pump Model notes constraints GL/y ML/d Irrigation Soil moisture accounting single store for combined crops Qld unsupplemented Nodes configured with large areas and OFS volumes to consume all available water Sub-total Qld TWS Fixed demand plus potential for 100 ML/yr in model representation Qld stock and domestic NSW unregulated TWS For town water supply Sub-total Water availability in the Paroo November 2007 CSIRO 2007

51 4 River system modelling Figure 4-1. River system map showing major rivers, model subcatchments, reaches, calibration reaches, inflow gauges, nodes and links Model setup The original Paroo River model and associated IQQM V executable code were obtained from QDNRW. This model was run for the original period of 1 January 1889 to 31 December 1999 and validated against previous results. The time series rainfall, evaporation and flow inputs to this model were then extended to 30 June CSIRO 2007 November 2007 Water availability in the Paroo 41

52 A pre-development version of this model was created by removing all irrigators and fixed stock and domestic demands. Natural water storages were not changed as they represent the pre-development physical characteristics of the system. The Paroo river system contains a large amount of storage. The initial state of this storage can influence the results obtained. As the Paroo model starts with a warm up period from 1 June 1895 to 30 June 1895 the initial state of all natural water body storages needs to be determined. To do this the model was started with all of these storages empty and run up to 31 May 1895 and the final storage volumes were recorded. This was repeated with all of the storages initially full. The results of this analysis are presented in Table 4-3 and show that under both cases the storages converged to a similar result. Each storage was subsequently configured with this storage volume. Table 4-3. Model setup information Model setup information Version Start date End date 4 River system modelling Paroo IQQM /01/ /12/1999 Connection Wanaaring Paroo outflows to Darling River Baseline models Warm up period 01/06/ /06/1895 Paroo IQQM /06/ /6/2006 Connection Wanaaring Paroo outflows to Darling River Paroo modifications Data Extend to 30/06/2006 Inflows Groundwater loss nodes No adjustment required None Warm up test results Setting initial storage volumes Storages commence empty Storages commence full GL Difference Percent of full volume Natural water bodies storage volume 31/05/ % Storage volume 30 May ( ) Mean Median Natural water bodies GL 42 Water availability in the Paroo November 2007 CSIRO 2007

53 4.3 Modelling results River system water balance The mass balance table (Table 4-4) shows the net fluxes for the Paroo River system. 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 a river gauge. The indirectly gauged inflows represent the inflows that are derived to achieve mass balance between mainstream gauges. Diversions are listed based on the different water products in the reporting region. End-of-system flows are shown for the Wanaaring end-of-system gauge and net evaporation is displayed for all the natural water storages. 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 the five subcatchments in the model. The mass balance of each of these river reaches and the overall mass balance were checked by taking the difference between total inflows and outflows of the system. In all cases the mass balance error was less than 0.2 percent Inflows and water availability Inflows There are several ways that the total inflows into the river system can be calculated. The obvious way would be to sum all of the inflows in the model. For the Paroo IQQM this is 576 GL/year (Table 4-4). However, a large proportion of the inflow is indirectly gauged and therefore estimated as part of model calibration. The approach used to calibrate these inflows varies considerably between model implementations. In some cases inflows are inflated and subsequently compensated for by loss relationships and, in other cases, the losses are inherent in the inflows. Because of these different approaches to calibration, totalling inflows does not provide a consistent assessment of total river system inflows across different models. 4 River system modelling An alternative to simply totalling modelled inflows is to locate the point of maximum average annual flow in the river system under pre-development conditions. As all river models are calibrated to achieve mass balance at mainstream gauges, the gauge with maximum average annual flow is a common reference across all models irrespective of how mass balance is calibrated. The predevelopment scenario removes the influences of upstream extractions and regulation and gives a reasonable indication of total inflows without the influence of development. This can be repeated for each of the climate scenarios by running the pre-development model with each of the climate scenario inputs. A comparison between scenarios for reaches along the Paroo River are shown in Figure 4-2 which shows that the maximum average annual mainstream flow occurs in subcatchment at the Caiwarro gauge (424201) with a value of 445 GL/year (Table 4-5) for the pre-development Scenario A. CSIRO 2007 November 2007 Water availability in the Paroo 43

54 Table 4-4. River system model average annual water balance for Scenarios O, A and C Model start date 01/01/ /07/1895 Model end date 31/12/ /06/2006 O A Cwet Cmid Cdry GL/y Percent change from Scenario A Storage volume Change over period % -15% 404% Inflows Subcatchments Directly gauged % -4% -14% 4 River system modelling Indirectly gauged % -2% -16% Sub-total % -2% -16% Diversions Licensed private diversions QLD unsupplemented access (volumetric limit 70 ML/y) % 0% 0% Sub-total % 0% 0% Stock and domestic QLD unsupplemented access % 0% 0% Sub-total % 0% 0% Outflows End-of-system flow to Wanaaring % 0% -17% Sub-total % 0% -17% Net evaporation* Natural water bodies % 0% -8% Sub-total % 0% -8% Sub-total % 0% -16% Unattributed fluxes Total % -5% -17% * Evaporation from private licensed storages (GL/y) is not included as it is already accounted in diversions Annual flow (GL) C range Cmid A Figure 4-2. Transect of total river flow under pre-development scenarios A and C 44 Water availability in the Paroo November 2007 CSIRO 2007

55 Water availability Table 4-5 shows the maximum water availability for the pre-development Scenario A in GL/year and the relative change in pre-development water availability for the Scenario C variants, calculated at the location of the maximum average annual mainstream flow as defined in Figure 4-2. Table 4-5. Annual water availability for pre-development Scenario C relative to pre-development Scenario A A Cwet Cmid Cdry GL/y Percent change from Scenario A % -3% -16% A time series of annual water availability under pre-development Scenario A is shown in Figure 4-3. The lowest annual water availability was 38 GL in 2005 while the greatest annual water availability was 1940 GL in Figure 4-4 shows the time series change in annual water availability relative to pre-development Scenario A for pre-development Scenario C. Note as there are no major regulating structures upstream of the Wanaaring gauge the numbers presented in Figure 4-3 and Figure 4-4 are not influenced by regulation. Annual water availability (GL) River system modelling Figure 4-3. Pre-development Scenario A annual water availability 1000 Annual water availablity (GL) C range Cmid Figure 4-4. Annual water availability under pre-development Scenario C relative to pre-development Scenario A CSIRO 2007 November 2007 Water availability in the Paroo 45

56 4.3.3 Storage behaviour There are no significant regulated water storages in the Paroo catchment and consequently there are no regulated storages in the Paroo River model to report Consumptive water use Diversions Table 4-6 shows the total average annual diversions for each reach for Scenario A and the percentage change of all other scenarios compared to Scenario A. Figure 4-5 shows total average annual diversions for all scenarios from upstream to downstream. 4 River system modelling Table 4-6. Change in total diversions in each model subcatchment relative to Scenario A A Cwet Cmid Cdry Reach GL/y Percent change from Scenario A % 0% 0% % 0% 0% % 0% 0% % 0% 0% Total 0.3 0% 0% 0% Annual diversions (GL) C range Cmid A Figure 4-5. Total average annual diversions under scenarios A and C for each model subcatchments Figure 4-6 shows an annual time series of total diversion for Scenario A and the difference from Scenario A for Scenario C. The maximum and minimum diversions for Scenario A are 0.35 GL in 1965 and 0.23 GL in 1964 respectively. 46 Water availability in the Paroo November 2007 CSIRO 2007

57 (a) (b) Annual diversions (GL) Annual difference (GL) (c) Annual difference (GL) Annual difference (GL) (d) River system modelling Figure 4-6. Total diversions under (a) Scenario A; and the difference in total diversions from Scenario A under (b) Scenario Cwet; (c) Scenario Cmid; and (d) Scenario Cdry Level of use The level of use for the region is indicated by the ratio of total net diversions (extraction less any returns) to total inflows. Total net diversions are defined as the net water diverted for the full range of water products. This indicates the share of the available water that is diverted for consumptive use. Once again the most reliable indicator of the total inflow is point of maximum mainstream average annual flow. Net diversions are used to reflect the change in mass balance of the system. They do not take into consideration the difference in water quality that may exist between diversions and returns. Table 4-7 shows the level of use indicators for each of the scenarios. The level of use in the river model is very low compared to the rest of the MDB with less than 1 percent of the water resource being diverted under Scenario A and a 0.02 percent increase under Scenario Cdry. Table 4-7. Relative level of use under scenarios A and C A Cwet Cmid Cdry 0.08% 0.06% 0.08% 0.10% Use during dry periods Table 4-8 shows the average use for all water products, as well as the average annual use for the lowest one, three and five-year periods for Scenario A and the percentage change from Scenario A for each other scenario. These figures indicate the impact on water use during dry periods. CSIRO 2007 November 2007 Water availability in the Paroo 47

58 Table 4-8. Indicators of use during dry periods under scenarios A and C Annual Diversion A Cwet Cmid Cdry GL/y Percent change from Scenario A Lowest 1-year period 0.2 2% 0% -5% Lowest 3-year period 0.3 1% 0% -2% Lowest 5-year period 0.3 0% 0% -1% Average 0.3 0% 0% 0% Reliability 4 River system modelling In the Paroo region the level of diversions is low (less than 1 percent of available flows), such that diversions are relatively constant across the years. In most systems there is a difference between the water that is available for use and the water that is actually diverted for use. These differences are due to under utilisation of licences and water being provided from other sources such as rainfall, surplus flows, on farm storages and groundwater. The difference between available and diverted water will vary considerably across products and time. Note that the Paroo model assumes that licences are fully utilised and consequently demand is equal to availability. Figure 4-7 shows the reliability of unsupplemented access water for Queensland irrigators and unregulated water for New South Wales irrigators for each of the scenarios. (a) (b) Annual diversion (GL) C range Cmid A Annual diversion (GL) C range Cmid A Percent of years equal or exceeded Percent of years equal or exceeded Figure 4-7. Reliability of un-supplemented access water for irrigators under scenarios A and C (a) Queensland; and (b) New South Wales River flow behaviour There are many ways of considering the flow characteristics in river systems. For the Paroo three different indicators are provided: daily flow duration seasonal plot daily event frequency. 48 Water availability in the Paroo November 2007 CSIRO 2007

59 Mid system flow characteristics The flow regime will vary depending on which location in the river that is selected. For this analysis the location of the middle of the system is defined as the position where the river changes from a gaining to a losing stream. For the Paroo River this is the Caiwarro gauge (424201). Figure 4-8 shows the daily flow duration curves for Scenario A and Scenario P and the range of change for Scenario C. For a given flow the flow duration curves show the change in frequency between scenarios for that flow. The vertical difference between flow duration curves shows the change in mass between scenarios although care needs to be taken as the plots use a logarithmic scale that distorts the difference of lower flows. Cease-to-flow is considered to occur when model flows are less than 1 ML/day Daily flow (ML) C range Cmid 10 A P Percent time flow is exceeded Figure 4-8. Daily flow duration curves under scenarios A, P and C at Caiwarro gauge (424201) 4 River system modelling Figure 4-9 shows the mean monthly flow for the pre-development scenario and Scenario A. This shows that the seasonality at the end-of-system has not changed between pre-development and current. It also shows the seasonal uncertainty of climate change impacts with February and March becoming wetter with a large uncertainty, and June to December becoming dry with a large certainty. Monthly flow (GL) Crange Cmid A P J F M A M J J A S O N D Figure 4-9. Seasonal plot under pre-development and scenarios A and C at Caiwarro gauge (424201) Table 4-9 shows the size of daily events with 2-, 5- and 10-year recurrence intervals for scenarios P, A and C. Note this analysis estimates the average peak daily flow and not the peak flow for a day, which is considerably higher in most river systems. The table shows that from pre-development to Scenario A there have been a 14 percent reduction in the size of 2-year events and a 5 percent reduction in the larger 5-year and 10-year return interval events. CSIRO 2007 November 2007 Water availability in the Paroo 49

60 Table 4-9. Daily flow event frequency under scenarios P, A, and C at Caiwarro gauge (424201) Return interval P A Cwet Cmid Cdry Years ML/d Percent change from Scenario A 2 57,577 49,764 32% -13% -30% 5 93,411 88,138 11% -18% -22% , ,670 23% -16% -21% End-of-system flow characteristics 4 River system modelling Figure 4-10 shows the flow duration curves for the end-of-system gauge at Wanaaring (424001). Each of the scenarios is plotted on the same plot. Cease-to-flow is considered to occur when model flows are less than 1 ML/day. The plot shows that there is not much change in cease-to-flow percentiles across all of the scenarios. The change between predevelopment and current conditions is small across all flow ranges. Daily flow (ML) C range Cmid A P Percent time flow is exceeded Figure Daily flow duration curves under scenarios A, P and C for Wanaaring gauge (424001) Figure 4-11 shows the mean monthly flow for the pre-development, A and C scenarios for the Wanaaring gauge. This shows that the seasonality at the end-of-system has not changed between pre-development and current. It also shows the seasonal uncertainty of climate change impacts with February and March becoming wetter with a large uncertainty and June to December becoming dry with a large certainty. Note the results at the end-of-system and mid river are similar. Monthly flow (GL) Crange Cmid A P J F M A M J J A S O N D Figure Seasonal plot under pre-development, scenarios A and C for Wanaaring gauge (424001) The percent of time flow occurs for each of the scenarios is presented in Table Cease-to-flow is considered to occur when model flows are less than 1 ML/day. 50 Water availability in the Paroo November 2007 CSIRO 2007

61 Table Percent of time that flow occurs under scenarios P, A and C for Wanaaring gauge (424001) P A Cwet Cmid Cdry Wanaaring 64% 63% 65% 59% 60% Available resource shares Non-diverted water There are several ways of considering the relative level of impact on non-diverted water and diversions. Table 4-11 presents three indicators for relative impact on non-diverted water: the average annual non-diverted water as a proportion of the maximum mainstream average annual flow as a proportion of the maximum mainstream average annual flow for Scenario A for the Queensland portion of the region, the current Resource Operations Plan (ROP) requires that 99 percent of the long-term average of cross border flows compares against pre-development cross border flows. This is based on the historical pre-development flow, as the ROP defines this limit in terms of flows for an historical period. Table Relative level of available water not diverted for use under scenarios A and C 4 River system modelling A Cwet Cmid Cdry Non-diverted water as a percent of total available water 99.9% 99.9% 99.9% 99.9% Non-diverted share relative to Scenario A non-diverted share 100% 145% 98% 83% Proportion of cross border flow relative to pre-development cross border flows 99.9% 145% 98% 83% Combined water shares Figure 4-12 combines the results from water availability, level of use and non-diverted water into a bar chart. The size of the bars indicates total water availability and the sub-division of the bars indicates the diverted and non-diverted fractions. Annual water (GL) Diverted Non-diverted P A Cw et Cmid Cdry Figure Comparison of diverted and non-diverted shares of water under scenarios P, A and C CSIRO 2007 November 2007 Water availability in the Paroo 51

62 4.4 Discussion of key findings Model configuration The Paroo River model is configured to represent the full utilisation of licences. This is achieved by configuring nodes with large irrigation areas and large on-farm storages. This forces the model to take water whenever the opportunity arises. The amount of water that is taken is constrained by the pump capacity at the irrigation node. Pump capacities are set to reflect the sharing of volumetric constraints. There are several modelling implications of this type of configuration: 4 River system modelling the irrigation demands do not reflect the change in demand as a function of climatic conditions as there is always a demand for water crop areas are fixed at a large number and do not change as a function of available water resources irrigation usage is not calibrated and consequently modelled usage may be larger than actual usage. The model only considers unsupplemented access from the main river. Extractions from the floodplain are not explicitly modelled and are considered in the mass balance as part of the unattributed losses. The model is not calibrated downstream of Wanaaring and does not consider the incremental increases in areas of the lower floodplain inundated at different flow levels. Limited inferences can be drawn about changes in beneficial flooding of the lower floodplain areas from a consideration of flows at gauges well upstream of the lower floodplain. Scenarios The Paroo River model was originally set up by the QDNRW for the period of 1 January 1889 to 31 December This modelling period was subsequently used in the development of the Resource Operations Plan. The common reporting period for this study is 1 July 1895 to 30 June Given the variability of flows in the Paroo river system and the impact that individual events can have on results, the numbers reported for the Resource Operations Plan may differ from the numbers reported in this study. Table 4-4 shows that there is a 5 percent decrease in inflows for the common modelling period compared to what was used to develop the various water sharing plans. This difference can be attributed to the extremely wet conditions from 1889 to Consumptive use The Paroo River is unregulated (Table 4-1). The largest diversion is for stock and domestic use, followed by unsupplemented irrigation (Table 4-2). Overall the current level of use (ratio of water use to water availability) is less than 1 percent (Table 4-7). Under the climate change median scenario (Cmid), there is a 2 percent decrease in total inflow (Table 4-5). There are no impacts on irrigation or end-of-system flows. 4.5 References DNRM (2003) Paroo River System Hydrology - Calibration of Daily Flow Simulation Model from Upstream of Yarronvale (Qld AMTD km) to Darling River/Paroo River Confluence (NSW AMTD 0.0 km). Department of Natural Resources and Mines, Brisbane. 52 Water availability in the Paroo November 2007 CSIRO 2007

63 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 Issues and observations The density, accuracy and completeness of the gauging network in the Paroo region are the lowest in the Murray-Darling Basin (MDB). This is commensurate with the very low level of water resource development. The Paroo surface water system is ephemeral and characterised by variable and infrequent high inflows, and major losses downstream associated with flow spreading out onto a low relief floodplain with ephemeral lakes and wetlands. Regulation and diversion levels are very low. Because of the requirement for active upstream and downstream gauges, independent water accounts could only be constructed for one reach on the Paroo River (Caiwarro to Willara Crossing). The uncertainty in the river model could not be evaluated for the lower reach (Willara Crossing to Wanaaring) because of lack of recent gauging data. 5 Uncertainty in surface water modelling results Key messages Based on water accounts and comparisons with gauging data for one reach (Caiwarro to Willara Crossing) for the period 1993 to 2004, the following conclusions can be made with respect to the Paroo river model: The internal uncertainty in the model appears to be small compared to the external uncertainty associated with future climate change. The water balance of the region is relatively well understood and the river model reproduces patterns of flow accurately. Diversions largely rely on flood harvesting and wetland replenishment relies on peak flows. The model is capable of evaluating the response of high flows to rainfall events. The greatest likelihood of effects from processes not described by the river model or SIMHYD are associated with changes in rainfall-runoff response due to changes in vegetation or landscape condition and changed vegetation water use patterns and knowledge of the dynamics of overbank floodflows. The uncertainty in river model predictions associated with the possibility that groundwater unexpectedly influences future surface water processes is low. Effects associated with river regulation, irrigation and development appear unlikely given the very low level of development and the limited flow regulation. CSIRO 2007 November 2007 Water availability in the Paroo 53

64 5.2 Approach General A river model is used in Chapter 4 to analyse expected changes in water balance, flow patterns and consequent water security under climate and/or development change scenarios. Uncertainty in the analysis can be external or internal: 5 Uncertainty in surface water modelling results 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 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 Water availability in the Paroo November 2007 CSIRO 2007

65 Table 5-1. Possible framework for considering implications of assessed uncertainties Low uncertainty Low threat Current water sharing arrangements appear sufficient for ongoing management of water resources. High threat Current water sharing arrangements are likely to be inadequate for ongoing management of water resources, as they do not adequately consider future threats. High uncertainty 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 Information sources Information on the gauging network was obtained from the Water Resources Station Catalogue ( the Pinneena 8 database (provided on CDROM by New South Wales) and the Queensland Department of Natural Resources and Water web site ( ). The model calibration report for the Paroo River system model (QDNRM, unpublished) was provided by the Queensland Department of Natural Resources and Water. Time series of water balance components as modelled under the baseline scenario (Scenario A) and all other scenarios were derived as described in Chapter 4. The data used in water accounting are described in the following section Water balance accounting Purpose Generic aspects of the water accounting methods are described in Chapter 1. This section includes a description of the basic purpose of the accounts, which is to inform the uncertainty analysis carried out as part of this 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. 5 Uncertainty in surface water modelling results Framework The available streamflow data for this region was sufficient for water accounting for the period July 1993 to June Water accounts could only be established for one reach (Caiwarro to Willara Crossing). Table 5-2 relates the water accounting reaches to the modelling reaches and presents reasons why other model reaches are not considered in the water accounting. Water accounting was not attempted for headwater catchments, but SIMHYD estimates and gauge data for these catchments are compared in Chapter 3. In other cases, gauges may have closed before or during the water accounting period, leaving insufficient observations for meaningful water accounting. The associated catchment areas are shown in Figure 5-1. Table 5-2. Comparison of water accounting reaches with river model reaches (QDNR, unpublished) Water accounting reach Subcatchment code From To Corresponding river model reach(es) Caiwarro Willara Crossing 3 Not assessed Headwater catchment Yarronvale 1 Insufficient streamflow data Yarronvale Caiwarro 2 Insufficient streamflow data Willara Crossing Wanaaring 4 CSIRO 2007 November 2007 Water availability in the Paroo 55

66 5 Uncertainty in surface water modelling results Figure 5-1. Map showing the subcatchments used in modelling, the reaches for which river water accounts were developed ( accounting reach ) and gauged head water catchments ( contributing catchment ). Shaded areas ( floodplain and wetlands ) were classified as subject to periodic inundation. Black dots and red lines are nodes and links in the river model respectively. 56 Water availability in the Paroo November 2007 CSIRO 2007

67 Diversion data Information on diversions in the accounted reach was not available. Following QDNRM (unpublished) it was assumed that no diversions occurred during the accounting period. The accounted reach has been estimated to have 439 nonlicensable storages (excavated tanks and gully dams) with a total storage volume of 3.7 GL, but these were assumed to have a minimal effect on calibration (QDNRM, unpublished) and therefore were not considered in water accounting. Wetland and irrigation water use The result of the remote sensing analyses (see Chapter 1 for description of methods) is shown in Figure 5-1. Visual inspection of the LANDSAT imagery showed that the wetlands and floodplains in the New South Wales portion of the region were accurately mapped by the New South Wales wetlands and the GA maps. In Queensland, however, large areas of wetlands and floodplains were omitted. For these, based on comparison with the New South Wales wetlands map, all areas having a mean AET more than 80 mm greater than rainfall for the period 2000 to 2006 were included as flooded areas. No irrigation areas were identified. Calculation and attribution of apparent ungauged gains and losses Calculation and attribution of apparent ungauged gains and losses were undertaken according to the methods described in Chapter Model uncertainty analysis The river model results and water accounts were used to derive measures of model uncertainty. The different analyses are described below. In the interest of brevity details on the equations used to calculate the indicators are not provided here but can be found in Van Dijk et al. (2007). 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: 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. 5 Uncertainty in surface water modelling results 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. CSIRO 2007 November 2007 Water availability in the Paroo 57

68 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 logtransformed 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. 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. 5 Uncertainty in surface water modelling results 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 Density of the gauging network Figure 5-2 shows the location of streamflow, rainfall, and evaporation gauges in the region. Table 5-3 provides information on the measurement network. The Paroo region has the sparsest gauging network of the 18 regions that comprise the MDB. The rainfall gauging network is about twelve times less dense than the MDB average and the streamflow measurement network is about twenty times less dense. This is for a region with very high temporal variability in rainfall and streamflow, but with no or very little water resource development. Given the lack of water resource development additional gauging may not be an investment priority. 58 Water availability in the Paroo November 2007 CSIRO 2007

69 Table 5-3. Some characteristics of the gauging network of the Paroo region (35,587 km 2 ) compared with the entire MDB (1,062,443 km 2 ) Paroo MDB No. No. per 1000 km 2 No. No. per 1000 km 2 Rainfall Total stations Stations active since Average years of record Streamflow Total stations Stations active since Average years of record Evaporation Total stations Stations active since Average years of record Review of model calibration and evaluation information This section provides a summary of available information on the development, calibration and performance of the river model used in the analysis (QDNRM, unpublished). Where possible, only the part of the model within the region is discussed. Model description The Paroo River model was developed in IQQM and covers the Paroo River catchment from upstream of Yarronvale in Queensland to the complex flood plain south of Wanaaring in New South Wales. This extends beyond the Paroo region (Chapter 4). Daily rainfall data was available for the whole of the Paroo River system (greater than the Paroo region) from 84 rainfall stations and generally for a long period (as early as 1880 in some cases). Evaporation data was available from 14 pan evaporation stations, covering different periods starting mostly around 1950 or earlier. Potential evapotranspiration was assumed to be fairly close to pan evaporation, and therefore pan evaporation data were used directly. 5 Uncertainty in surface water modelling results The height data from automatic stage height recorders were assessed as generally fair to good quality. Most stations upstream of Wanaaring lack good high flow measurements and high flow ratings were extrapolated from low to medium flow discharge measurements (Table 5-4). Some gauging stations in the catchment that were not used as records were short or of poor quality. In addition to gauges in Queensland, two gauging stations in New South Wales were considered: Willara Crossing (424002) and Wanaaring (424001) the last gauging station on the Paroo River. There were no data to assess whether groundwater has any significant effect on the surface water in the Paroo system and therefore groundwater was ignored in the river model. After the model was calibrated, assumptions were made to represent stock and domestic usage, unregulated irrigation, non-licensable man-made storages (excavated tanks and gully dams), and waterholes that occur naturally throughout the system. It was assumed that historical impacts of diversions and man-made storages were insignificant and therefore they were not considered in calibration. CSIRO 2007 November 2007 Water availability in the Paroo 59

70 5 Uncertainty in surface water modelling results Figure 5-2. Map showing the rainfall, streamflow and evaporation observation network, along with the subcatchments used in modelling. Model calibration Model calibration was based on stream gauging records from four mainstream gauges on the Paroo River (Table 5-4). Five individual model reaches between stream gauging stations on the Paroo River were set up and four of them calibrated using downstream gauging stations. The following methods and processes were considered: 60 Water availability in the Paroo November 2007 CSIRO 2007

71 Inflows: recorded tributary inflows and calculated local inflows (calculated as outflows minus inflows) were used to calibrate a rainfall-runoff model (Sacramento) that was subsequently used to estimate missing data for the entire period of modelling. Where there was no recorded flow data the rainfall-runoff model was used with parameters from a similar catchment. Diversions: there were minimal data on historical extractions but diversions were known to be small. Therefore no diversions were accounted for in model calibration. Losses: the final step in calibration was simulation of losses, ascribed to floodplain dissipation, evaporation, seepage and tributary breakout that were not accounted for separately. These were empirical functions, calibrated to minimise the mismatch between modelled and recorded flow duration curves at the same location. Table 5-4. Details of streamflow rating uncertainty, calibration and validation periods, number of years between (112 years) with annual rainfall less than the driest and more than the wettest year in the calibration period, respectively, and prior assessment of Reach Downstream gauging station code and name A (Paroo Yarronvale) A (Paroo Caiwarro ) (Paroo Willara Crossing) (Paroo Wanaaring ) Percent of stage height range rated the models performance Calibration period Years out of 112 drier Years out of 112 wetter Validation* period Assessment 5.7% Replicates flows well. Low flows are underestimated. 88.7% Replicates flows well. Low flows are slightly underestimated. n/a Replicates flows well for different time periods. Low flows are slightly underestimated. n/a Checked with reach 2 calibration. Losses to numerous ephemeral lakes. * Only partial validation considering performance for shorter periods within the calibration period. Source: QDNRM, unpublished, with exception of the climate change information Model performance assessment Overall model performance was assessed for different periods for each reach. No independent model validation was performed by QDNRM, but partial validation was performed by considering model performance for shorter periods within the calibration period (Table 5-4). The quality of the data was judged to be satisfactory although some model inadequacies with respect to response to low flow regimes occurred. The model was used to simulate the historical runoff and water use for the period January 1889 to June Statistical comparison generally showed good agreement with observed flows. 5 Uncertainty in surface water modelling results Areas of weaknesses adding to the uncertainty of the model use were identified by QDNRM (2004). These were mainly related to a paucity of data. There exists a complex series of large lakes, floodplains and wetlands within the western side of the Paroo River system, but little data to describe how they act and how much water they take from the system. The modelling of this area has been vastly simplified, and possibly poorly modelled. It was recommended that more data should be collected regarding the river and lake system within the Currawinya National Park to develop a better system model. A sensitivity analysis was also recommended to assess the uncertainty associated to each of the following areas: In-stream storages: the rainfall-runoff models were calibrated without considering the effect of the storages. When the storages where added they reduced the flows reaching the gauges, and compensation inflows were added. For scenarios, this method may introduce some error if different storages are used. Losses on the ungauged break-outs and further reach break-up. Flow passing through unlicensed storages, extractions, and water harvesting operations. CSIRO 2007 November 2007 Water availability in the Paroo 61

72 5.3.3 Model uncertainty analysis The calculated indicators of calibration climate range are listed in Table 5-4. All other indicators and results are listed for the assessed reach in Appendix C. Below follows a summary, noting that all numbers quoted refer to the accounting period unless otherwise stated. Completeness of hydrological observation network The Caiwarro to Willara Crossing reach is a moderately losing reach with total outflows estimated at 72 percent of total inflows. An estimated 69 percent of all gains and 50 percent of all losses during the accounting period were gauged. Most of the total estimated gauged and ungauged gains (91 percent) and losses (90 percent) could be attributed through water accounting. 5 Uncertainty in surface water modelling results About three-quarters of the ungauged gains were explained by SIMHYD estimates of local inflows. The ungauged losses could be attributed to river floodplain and wetland losses, which are inherently hard to gauge. Remote sensing is probably the most practical way of estimating these losses. The magnitude of these losses agreed with remote sensing based estimates, and losses increased towards the lower reaches. This left only a small fraction of unattributed losses. It is concluded that a considerable part of the water balance is ungauged, but there are other observations directly or through models that can be used to show that the model water balance represents real fluxes with a good level of confidence. As such, the hydrology of this reach is well understood. 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 5-5. Numbers are averages for the period 1993 to 2004 to allow direct comparison. To aid interpretation, note that: Classification suggested that the estimated total area of ephemerally inundated floodplains and wetlands in the reach considered for water accounting was 2139 km 2. Due to the classification approach these should be considered maximum estimates. Neither the river model nor the water accounts include streamflow losses to groundwater recharge, because no data were available to constrain such estimates. The following conclusions can be drawn when comparing modelled and accounted water balance: Total modelled inflows were within 14 percent of the total of inflows that could be attributed. Local inflows in accounting were estimated to be ~100 GL/year greater than volumes estimated by the model, but this is compensated by a similar, opposite difference in estimated river and floodplain losses. This difference represents about one-fifth of the water balance, within the error of SIMHYD modelling. It is not possible to tell whether these accounted for gains and losses are real fluxes or not. Average modelled end-of-system flows (defined here as Willara Crossing) are within 14 percent or 39 GL/year of observed flows. 62 Water availability in the Paroo November 2007 CSIRO 2007

73 Table 5-5. Reach water balance produced by river model and from water accounting Water balance (Jul 1990 Jun 2006) Model (A) Accounts Difference GL/y Total gains Gauged inflows Ungauged inflows Unattributed inflows Total Total losses End-of-system outflows Other gauged outflows Diversions River flux to groundwater Other ungauged losses Unattributed losses Total Climate range calibrated The number of years outside the calibrated annual rainfall range was four out of 112 years for all reaches, split equally between drier and wetter years (Table 5-4). By comparison, the historic rainfall record had three years that were drier and five years that were wetter than the extremes during the period of water accounting (1993 to 2004). Overall, both the model calibration period and water accounting periods appear to provide a good representation of historic rainfall conditions (96 percent and 93 percent of historical variability in annual rainfall, respectively). Performance of the river model in explaining historic flow patterns The better the baseline model simulates streamflow patterns, the greater the likelihood that it represents the response of flows to changed climate, land use and regulation, notwithstanding the possibility that the model is right for the wrong reasons through compensating errors. In Appendix C, indicators are listed of the models performance in reproducing different aspects of the patterns in historically measured monthly and annual flows (all are variants of Nash-Sutcliffe model efficiency, NSME). 5 Uncertainty in surface water modelling results The Paroo river model accurately explained observed flow patterns at Willara Crossing. Model efficiency was for monthly and annual flows transformed in different ways (Appendix C). The model explained more of observed monthly flow patterns than the water accounts. This can be ascribed to the fact that the model was calibrated to match local ( residual ) inflows. High flows were also well simulated by the model (NSME=0.91). Comparison of flow patterns and the flow duration curve (Appendix C) suggests that the model also accurately simulates low flows, but this could not be expressed in model efficiency due to the occurrence of zero flows for more than 10 percent of the time. Overall, the river model appears to accurately reproduce flow patterns. Scenario change-uncertainty ratio The ratios of change over uncertainty are shown in Table 5-6. 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, and a value close to 1.0 means that the modelled change is of similar magnitude to the uncertainty in the model. Unsurprisingly, given the lack of diversions, the flows simulated under the pre-development (P) scenario are not different from baseline flows. The modelled changes under the wet climate change scenario are considerably greater than uncertainty. The change due to the median climate change scenario was moderate considering model uncertainty, whereas the dry scenario was similar to model uncertainty. CSIRO 2007 November 2007 Water availability in the Paroo 63

74 Table 5-6. Change-uncertainty ratios for projected annual and monthly streamflow changes in the Paroo at Willara Crossing P Cwet Cmid Cdry Annual streamflow Monthly streamflow Discussion of key findings 5 Uncertainty in surface water modelling results Completeness of the gauging network The hydrology of the Paroo surface water system is very sparsely gauged. The rainfall, evaporation and streamflow gauging network is the sparsest in the MDB. The accuracy of the stream height gauging has been assessed as fair to good quality. The quality of the stage rating curve is unclear but may be rather poor with the exception of one gauge (Paroo River at Caiwarro). Flood flows that go overbank are poorly rated and are inherently hard to measure but can be important flows for the environment and downstream rivers. Of the reach that could be analysed (Caiwarro to Willara Crossing), an estimated 60 percent of the total of river reach gains and losses are directly gauged Conceptual understanding of regional surface hydrology Despite the sparseness of the gauging network, the conceptual understanding of the current hydrology of the Paroo River system is good. The system is ephemeral and characterised by highly variable and infrequent inflows and losses downstream. The losses in the analysed reach could be accounted for using additional remote sensing information. Regulation and diversion levels are both small and negligible. Groundwater development is very limited at present and there was no groundwater model for the region (Chapter 6). As a consequence, neither the river model nor the water accounts included an estimate of surface water-groundwater exchanges. A qualitative estimate of its potential importance in explaining wetland and floodplain losses can be derived for the reach analysed as follows. The total losses from floodplains and wetlands in these four reaches were estimated at 122 GL/year to 230 GL/year from an estimated area of km 2. This suggests streamflow losses equate to between ~57 mm/year and ~107 mm/year averaged over the floodplain area. Groundwater recharge rates would be expected to be in the order of a few millimetres per year, and therefore represent a few percent of total floodplain and wetland losses. Overall, the uncertainty associated with the possibility that groundwater influences future surface water processes in unexpected ways was rated as low. Surprises associated with river regulation, irrigation and development would also appear less likely given the very low level of development, and the limited possibilities for flow regulation. There may be more internal model uncertainty in assumptions about runoff generation that are implicit in the river modelling methodology. River inflows in this region are a very small fraction of rainfall and produced by a small number of events (Chapter 3), and end-of-system outflows in turn are a small fraction of runoff (Chapter 4). Therefore, small changes in rainfall, evapotranspiration and/or floodplain and wetland losses can potentially lead to large relative changes in outflow patterns. Potential changes in hydrology that the river modelling or SIMHYD predictions did not address include changes in rainfall-runoff response due to changes in vegetation or landscape condition, bushfires and changed vegetation water use patterns (Chapter 3) Performance and uncertainty in aspects of the river model Water accounting for the river system between Caiwarro and Willara Crossing left 10 percent of total gains and losses unattributed, split about half-half between gains and losses. The river model accurately reproduced flows observed at Willara Crossing. Prior assessment concluded that the model accurately reproduced flow patterns at different gauges, but that low flows were slightly underestimated (QDNRM, unpublished). However, considering the period 1990 to 2005 and location (Willara Crossing), the model appeared to accurately produce low flow patterns. 64 Water availability in the Paroo November 2007 CSIRO 2007

75 A large range of the annual rainfall variability was included in the river model calibration (Table 5-4). Water accounts could not be developed for the lowest reach (Willara Crossing to Wanaaring) as this gauge was closed in Therefore the uncertainty in simulated changes in end-of-system flows could not be independently assessed. QDNRM (unpublished) state there were important losses to ephemeral water bodies in the lower reach and the quality of gauging at Wanaaring was unknown. For the accounting reach overall, water balance terms generally agreed with the river model and water accounts. At most about one-fifth of the water balance or ~100 GL/year is uncertain, but there is a strong possibility for compensating gains and losses. However, the implications for flows further downstream of Willara Crossing may be small Implications for use of the results of this study For the assessed location on the Paroo River (Willara Crossing) the changes in flow pattern predicted under the wet climate change scenario was substantially greater than uncertainty, but changes were small compared to model uncertainty for the other two climate change scenarios, and there was no change between current and pre-development flow patterns for this station. Any diversions largely rely on flood harvesting and wetland replenishment relies on peak flows. The model appears to accurately evaluate the response of high flows to rainfall events. Overall it was concluded that the model is likely to be adequate for use in the assessment for the system above Willara Crossing. However, model adequacy is unclear for the last reach to Wanaaring. 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, Bredehoeft J (2005) The conceptual model problem surprise. Hydrogeology Journal 13, 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, Pappenberger F and Beven KJ (2006) Ignorance is bliss: Or seven reasons not to use uncertainty analysis. Water Resources Research 42, W05302, doi /2005WR Refsgaard JC and Henriksen HJ (2004) Modelling guidelines terminology and guiding principles. Advances in Water Resources 27, 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, QDNRM (Queensland Department of Natural Resources and Mines) (unpublished). Paroo River System Hydrology, Volume 1. Calibration Of Daily Flow Simulation Model From Upstream Of Yarronvale (Qld AMTD 303/7km) To Darling River/Paroo River (NSW AMTD 0.0 Km). Hydrology Report PR, Surface Water Group, Queensland Department of Natural Resources and Mines. 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, Van Dijk AIJM (2006) 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. Van Dijk AIJM et al. (2007) River model uncertainty assessment. A report to the Australian Government from the CSIRO Murray-Darling Basin Sustainable Yields Project. CSIRO, Australia. In prep. Weiss C (2003) Expressing scientific uncertainty. Law, Probability and Risk 2, Uncertainty in surface water modelling results CSIRO 2007 November 2007 Water availability in the Paroo 65

76 6 Groundwater assessment This chapter includes information on groundwater for the Paroo region. It has two sections: a summary an assessment of lower priority groundwater management units. 6.1 Summary 6 Groundwater assessment The groundwater component for the Paroo region is assigned a very low priority ranking in the context of the overall Murray-Darling Basin Sustainable Yields Project. The priority ranking takes into account level of development, size of the available resource and degree of connectivity between rivers and aquifers relative to other groundwater management units (GMU) across the Murray-Darling Basin (MDB). Only a simple assessment was done, consistent with the very low priority. This includes a background description of the hydrogeology, rainfall recharge and extraction. While these limited assessments are appropriate with the constraints and for the terms of reference of this project, additional work may be required for local management of groundwater resources Issues and observations The groundwater systems in the Paroo include some shallow alluvial and sandstone aquifers and the deeper confined aquifers of the Great Artesian Basin (GAB). Water quality in nearly all aquifers is relatively poor and suitable only for stock and domestic use Key messages Groundwater is the main source of water currently used in the Paroo region. However, almost three-quarters of this comes from the combined GAB aquifers. The confined aquifers of the GAB are generally unconnected to water resources of the MDB. They are considered in this project where groundwater extraction impacts on either shallower aquifers or on streams. Extraction from the GAB aquifers is not expected to increase markedly into the future. There are no MDB GMU in Queensland and extraction in 2004/5 for the two GMU in New South Wales (GAB Cap Rocks, Upper Darling Alluvium) accounts for GL/year. This represents less than 0.1 percent of the current extraction in the MDB (excluding the confined GAB aquifers). While there is evidence of local interaction with shallower aquifers (e.g. Eulo Springs), the deeper groundwater systems are largely unconnected to the shallow systems or the river. Groundwater use in the Paroo has little impact on streamflow relative to total streamflow. Groundwater extraction in New South Wales is likely to grow by 2030, but the total extraction level would still be small. 66 Water availability in the Paroo November 2007 CSIRO 2007

77 6 Groundwater assessment Figure 6-1. Map of groundwater management units in the Paroo region CSIRO 2007 November 2007 Water availability in the Paroo 67

78 6.2 Assessment of lower priority GMU Groundwater extraction A generalised north-south cross-section of the hydrogeology of the region is shown in Figure 6-2 (modified from Ife and Skelt, 2004). The location of the GMU is shown in Figure Groundwater assessment Figure 6-2. North-south generalised cross-section of the hydrogeology of the Paroo region The GAB consists of the following two primary hydrogeological units: The deep Jurassic sandstone confined aquifers, and The Cretaceous sandstone confined aquifers and shale confining layers which lie conformably above the Jurassic aquifers. The Cretaceous confining layers separate the deeper confined aquifers from the surficial aquifers. Through the New South Wales water management process there are three other hydrogeological units associated with the GAB (GAB In-take Beds, GAB Alluvium and GAB Cap Rocks). Through a combination of hydrogeological characterisation and consideration of the current groundwater management approach it is possible to conceptualise the GAB according to the following four management units: The deep Jurassic and Cretaceous sandstone confined aquifers, and Cretaceous confining layers which are administered by the Water Sharing Plan for the NSW Great Artesian Basin Groundwater Sources (N601 GAB Central Zone and N601 GAB Warrego Zone) and in Queensland by the Water Resource (Great Artesian Basin) Plan GAB In-take Beds that occur where the Jurassic and Cretaceous sandstone aquifers outcrop (there is no outcrop within the reporting region). GAB alluvium is a thick sequence of Cainozoic alluvium covering the GAB sequence (no GMU in this region). GAB Cap Rock aquifers occur across the reporting region. This unit can include the weathered and fractured Cretaceous rock aquifers, and Cainozoic alluvium (up to a depth of 60 m; N620 GAB Cap Rock). The primary source of groundwater resources in this region is the deeper GAB Jurassic and Cretaceous confined sandstone aquifers. The groundwater within these aquifers is separated from aquifers at the surface by thick confining beds, which means there is little interaction with the overlying surface water or groundwater contained in near surface aquifers. The water resources within these confined aquifers are not considered further in this assessment. There is some water use from shallow alluvial aquifers, which can be up to 100 m in thickness, and the shallow Tertiary sandstones and siltstones, but this is sporadic due to variable water quality, and there has been little information generated on the shallow hydrogeology of the catchment (Cottingham, 1999; Quarantotto, 1986). 68 Water availability in the Paroo November 2007 CSIRO 2007

79 Within Queensland, sub-artesian (145 registered bores) and artesian (258 registered bores) water of varying quality (500 mg/l to 10,000 mg/l) is pumped from the Cretaceous Winton Formation. There are no functioning shallow monitoring bores and no groundwater modelling of the catchment (Power et al., 2007). These bores come under the Water Resource (Great Artesian Basin) Plan and are, therefore, not considered in this assessment. The combined Warrego-Paroo-Nebine-Bulloo region of western Queensland MDB is allocated only 1 percent of the total Queensland MDB groundwater allocation. Roughly 74 percent of allocation is to GAB bores, 23 percent is to shallower sandstone aquifers and three percent to the alluvial systems. Around 1300 bores draw from the Queensland GAB aquifers and provide the bulk of stock and domestic water, but water quality is generally inadequate for irrigation. There are no MDB GMUs in the Queensland portion of the Paroo and no groundwater model has been developed. The water resources within the Queensland GAB aquifers are administered by the Water Resource (Great Artesian Basin) Plan This plan provides a framework for sustainably allocating and managing water in the GAB. A Resource Operations Plan details the arrangements for implementing the water resource plan. Estimated groundwater extraction from the New South Wales MDB GMUs within the Paroo region is shown in Table 6-1. Table 6-1. Estimated groundwater extraction from New South Wales GMUs within the Paroo region Code GMU Current Extraction* (2004/05) Total Entitlement Extraction Limit Recharge** N620 GAB Cap Rocks (NSW) N46 Upper Darling Alluvium TOTAL GL/y 6 Groundwater assessment *Current groundwater extraction for Macro Groundwater Sharing Plan areas is based on metered and estimated data provided by NSW DWE. Metered usage is for all access and urban entitlement holders. Data quality is variable depending on the location of bores and the frequency of meter reading. Estimated usage is for basic rights entitlement holders. ** This value represents only rainfall recharge in Macro Groundwater Sharing Plan areas. The volume of recharge does not include recharge to national park areas, which has generally been allocated to environmental purposes and is not available for consumptive use Future groundwater extraction The New South Wales Groundwater Macro Plan program is a broad scale planning process covering areas of New South Wales not under a water sharing plan. The Macro Plans contain a standard set of rules extended across catchments with similar attributes and values social, economic and environmental. The Macro Plans reflect the priorities of environment, basic landholder rights, town water and licensed domestic and stock use and other extractive uses including irrigation. Long-term extraction limits have been set based on the calculation of rainfall recharge to each GMU. Groundwater extraction within the Paroo region is forecast to grow in the future. New South Wales DWE has provided estimates of the likely maximum amount of extraction for each GMU. The rate of growth has not been determined and it is assumed for the purpose of this analysis that full growth will be achieved by The likely maximum use has been determined in collaboration with the communities within which the Macro Plan was developed. This figure is based on the historical development of stock and domestic water supply works. The growth rate within a region is estimated based on the rate of historical growth. It is assumed that all new domestic and stock water supply works will be drilled and constructed on separate properties, and an average size for each property is calculated. The total additional stock and domestic requirement is then calculated based on assumed application rates for domestic bores of 2.25 ML/year and for stock bores of ML/ha/year. CSIRO 2007 November 2007 Water availability in the Paroo 69

80 Table 6 2. Estimated future groundwater extraction for the Paroo region Code GMU Total Entitlement Future Extraction GL/y N620 GAB Cap Rocks (NSW) N46 Upper Darling Alluvium Total Estimates of rainfall recharge 6 Groundwater assessment Rainfall recharge to the New South Wales portion of aquifers in the Paroo region was estimated by New South Wales DWE (Table 6-1) Impact of extraction on streamflow The Eulo Artesian Springs group in the lower Paroo (south-west of Eulo) cause mixing and discharge of GAB and shallow aquifer waters, though flow rates are now low and declining. There has been the suggestion that the lower reaches may be gaining from these discharges (Jolly, 1989) but this has not been assessed. Water quality in the streams, however, is good (<100 mg/l) suggesting interaction is minimal. The New South Wales Macro Plan allocates 30 percent to 50 percent of recharge to environmental purposes. For the Paroo region, extraction does not exceed 1 percent of recharge, hence there is minimal to no impact on streamflow. 6.3 References Cottingham P (1999) Scientific Forum on River Condition and Flow management of the Moonie, Warrego, Paroo, Bullo and Nebine River basins. QDNR and CRC Freshwater Ecology. Ife D and Skelt K (2004) Murray-Darling Basin Groundwater Status : Summary Report, Murray-Darling Basin Commission, Canberra Jolly ID (1989) Investigation into the potential for increased stream salinisation in the Darling Basin. Centre for Research in Groundwater Processes Report No. 10. In: Power RE, AJW Biggs, and DWG Burton (2007). Salinity Audit Warrego and Paroo Catchments, Queensland Murray-Darling Basin. Department of Natural Resources and Water, Queensland. Power RE, Biggs AJW and Burton DWG (2007) Salinity Audit Warrego and Paroo Catchments, Queensland Murray-Darling Basin. Department of Natural Resources and Water, Queensland. Quarantotto P (1986) Hydrogeology of the southeastern Eromanga Basin, Queensland. BMR Record 1986/ Water availability in the Paroo November 2007 CSIRO 2007

81 7 Environment This chapter presents the environmental assessments undertaken for the Paroo region. It has four sections: a summary an overview of the approach a presentation and description of the results a discussion of key findings. 7.1 Summary Issues and observations Assessment of the environmental implications of changes in water availability is largely beyond the terms of reference (see Introduction) 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. 7 Environment The Paroo region contains some of the most important wetlands for waterbirds in Australia, including the Ramsar-listed Currawinya Lakes in Queensland. Although outside the Paroo region defined for this project, the Paroo River Wetlands in New South Wales (recently listed as Ramsar wetlands), are largely dependent on flooding from the Paroo River. The low degree of water resource development and extraction means the Paroo is a relatively natural hydrological system and this is likely to be reflected in the health of its wetland and aquatic ecosystems. The environmental assessments undertaken within this project for the Paroo region are limited to a partial analysis of potential changes in the hydrologic regime affecting a small portion of the extensive wetlands of the Paroo system Key messages The current low level of water resource development in the Paroo region has had no detectable affect on frequency or volumes of high flows to the Lake Numalla Aggregation (referred to here as Lake Numalla) and Lake Wyara or to the Paroo Overflow Lakes. For Lake Numalla, the best estimate 2030 climate would not greatly affect either the average period between major inflows or the volume of inflows to the lake. Under the wet or dry extreme 2030 climate the average period between events would decrease or increase respectively by 31 percent. Under the dry extreme 2030 climate average inflow events would be 11 percent larger in volume, but because there would be fewer events there would be 15 percent less inflow overall. Under the wet extreme 2030 climate there would be nearly twice the total inflow volume, expressed as more and larger flood events. These considerable levels of change would be expected to noticeably affect lake ecology. For Lake Wyara, the best estimate 2030 climate would lead to a 55 percent reduction in the average period between inflow, due to increases in extreme rainfall intensity and hence flooding. However, the maximum period between inflow events would increase by 20 percent. Under the best estimate 2030 climate the total volume of inflows would increase by 68 percent. However, individual inflow events (of which there would be more) would be 28 percent smaller on average. Under the dry extreme 2030 climate events would be 6 percent larger in volume on average, but with inflow events being less frequent, there would be 11 percent less inflow overall. Under the wet extreme 2030 climate there would be over four times the total inflow volume, expressed as many more floods that on average would be slightly smaller in volume. Again, these considerable levels of change would be expected to have noticeable effects on lake ecology. CSIRO 2007 November 2007 Water availability in the Paroo 71

82 Under the best estimate 2030 climate the Paroo Overflow Lakes would experience a small increase (4 percent) in the average period between high flow events, but a 25 percent increase in the maximum period between events. The total event volume would remain largely unchanged; however the average volume of flow events would increase by 5 percent because of fewer events. Under the dry extreme 2030 climate there would be an 11 percent decrease in event volume (less events and of smaller volume) and under the 2030 wet climate scenario a 29 percent increase in the average volume of events combined with more events would increase the total event volume by 61 percent. Again, these considerable levels of change would be expected to have noticeable effects on lake ecology Uncertainty The main uncertainties involving analysis and reporting include: 7 Environment 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 considering only a few of the important environmental assets and using a limited number of indicators to represent overall aquatic ecosystem outcomes is a major simplification. Actual effects on these and other assets or localities are likely to vary uncertainties expressed in Chapters 3, 4 and 5 affect the hydrologic information used in the environmental assessments. 7.2 Approach 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. A broader description of the catchment, water resources and important environmental assets are provided in Chapter Summary of environmental flow rules Queensland Water Resource Plans do not establish specific environmental water allocations, rather environmental water is protected via water access rules such as pumping thresholds. The Water Resource (Warrego, Paroo, Bulloo and Nebine) Plan 2003 (QDNR, 2003) establishes the following performance indicators for environmental flow objectives: end-of-system flow low flow summer flow beneficial flooding flow one in two-year flood End-of-system flows both for the region and for the Queensland portion of the region are reported in Chapter 4. The hydrological indicators defined below relate to the categories of beneficial flooding and partially the one in two-year flood. No published studies were available to define ecologically relevant hydrological indicators specifically for the other environmental flow objectives. There is, at this time, no Water Sharing Plan for the New South Wales portion of the Paroo region and no environmental flow provisions have been established in this portion of the region Environmental assets and indicators The Paroo region contains some of the most important and largest wetlands in the Murray-Darling Basin. These wetlands and other assets are more fully described in Chapter Water availability in the Paroo November 2007 CSIRO 2007

83 Two environmental assets were identified two of the Currawinya Lakes (Numalla and Wyara) and the Paroo Overflow Lakes ( the Mullawoolka Basin and Blue, Gilpoko, Pokolo, Peery, Tongo and Yantabangee lakes) with available literature relating flow in the Paroo River to wetland inundation (Figure 7-1, Figure 7-2 and Figure 7-3). The studies of Timms (1999) and Kingsford et al. (2002), as outlined in this section, provide information on these connections. The general distribution pattern of water along the Paroo River to these wetlands is described in Kingsford and Porter (1999). Currawinya Lakes The Currawinya Lakes (including lakes Numalla and Wyara) are wetlands of international importance under the Ramsar Convention. The area has many important Aboriginal sites some dating back 1400 years. The lakes are within the Currawinya National Park although some land is leasehold and used for grazing purposes. The lakes in combination are considered to be among the most important wetlands in Australia and can support up to 250,000 waterbirds. The highest concentration in Australia of Freckled Duck (Strictonetta naevosa) has been recorded here (Kingsford and Porter, 1999). The following descriptions are summarised from Environment Australia (2001) unless as otherwise cited. Lake Numalla, and an aggregation of smaller nearby lakes, covers some 10,700 ha. The lake is about 5 m in depth when full and rarely dries completely. The flora of the lake is dominated by a fringe of open woodland of Black Box (Eucalyptus largiflorens) and River Cooba (Acacia stenophylla). Grasslands of Cane Grass (Eragrostis australiasica) and shrubs of Lignum (Muehlenbeckia florulenta) are found in clay pans around the lake. Some 39 species of waterbirds have been recorded at Lake Numalla, including species protected by international agreements, and many species have been recorded to breed there. 7 Environment Lake Wyara is a terminal, saline water body that covers some 6000 ha immediately to the west of Lake Numalla. Maximum water depth of the lake is some 10 m and it seldom dries out completely. As a saline wetland, Lake Wyara is mostly an open lake with River Red Gum (Eucalyptus camaldulensis) only at the northern margin. Salt tolerant aquatic macrophytes such as Ruppia sp and Chara australis are found within the lake. Over 100,000 waterbirds have been recorded on the lake which provides food supplies for some waterbird species not found at Lake Numalla (Kingsford and Porter, 1999). Water flows into the Currawinya Lakes from the Paroo River with moderate floods of 2.5 m to 3.5 m at the Caiwarro gauge (Timms, 1999). Flows above 3.5 m at Caiwarro are considered to be major and provide significant volumes to Lake Numalla (Timms, 1999). The frequency of events of 3.5 m or greater at the Caiwarro gauge is therefore used as a hydrologic indicator in the assessments of Lake Numalla (Table 7-1). The 3.5 m gauge height is equivalent to about 38,000 ML/day according to the rating curve for the Caiwarro gauge (QNRW). Additionally, the average annual volume and average event volume of flows above this 38,000 ML/day threshold are assessed to indicate relative (not absolute) changes in the total volume of inflow to the lake. Lake Wyara receives inflow at around 4.75 m at the Caiwarro gauge (Timms, 1999). The frequency of flows of 4.75 m or above on the Caiwarro gauge is therefore used as a hydrologic indicator in the assessment for Lake Wyara (Table 7-1). The 4.75 m gauge height is equivalent to about 112,600 ML/day according to the rating curve for the Caiwarro gauge (QNRW). Additionally, the average annual volume and the average event volume of flows above this 112,600 ML/day threshold are assessed to indicate relative (not absolute) changes in the total volume of inflow to the lake. Paroo Overflow Lakes The Paroo Overflow lakes is the term used by Kingsford and Porter (1999) for Mullawoolka Basin and for Blue, Gilpoko, Pokolo, Peery, Tongo and Yantabangee lakes. Individually each site is a wetland of national importance and lakes Peery and Poloko (within the Paroo-Darling National Park) form the Peery component of the recently-listed Paroo River Wetlands Ramsar site. The Peery component of the Ramsar site covers 67,171 ha or about one half of the total area of the Ramsar site. The Paroo Overflow Lakes support a high diversity (63 species) and large populations (over 10,000) of waterbirds (Kingsford and Porter, 1999). The flora of these lakes is similar to that of Lake Numalla (Environment Australia, 2001). The following provides a brief description of each of these sites based on information in Environment Australia (2001) proceeding along the water flow path of the Paroo River from north to south. CSIRO 2007 November 2007 Water availability in the Paroo 73

84 Tongo Lake (NSW103) is just over 500 ha in size and has dense Lignum (Muehlenbeckia florulenta) vegetation, with River Cooba (Acacia stenophylla) and Black Box (Eucalyptus largiflorens) fringing the lake. The lake receives water directly from the Paroo River and is wet about 20 percent of the time. Land in and around the lake is used for grazing. Mullawoolka Basin (NSW100) is just over 2000 ha in size and is mostly fresh but can become saline when shallow. It receives water directly from the Paroo River via channels which bypass Tongo Lake. Vegetation in and around the lake is similar to that of Tongo Lake. Land in and around the lake is used for grazing. Yantabangee Lake (NSW104) is just over 1400 ha in size and receives water from the Mullawoolka Basin after it has filled. Water can remain for nearly two years. Again vegetation in and around the lake is similar to that of Tongo Lake and Mullawoolka Basin. Land in and around the lake is used for grazing. 7 Environment Blue Lake (NSW096) is about 237 ha in size and receives water via the Mullawoolka Basin which can remain for up to one year. Vegetation around the lake is similar to that for the wetlands above. Land in and around the lake is used for grazing. Gilpoko Lake (NSW097) is some 436 ha in size and receives water via a channel from Yantabangee Lake. Vegetation around the lake is similar to that for the wetlands above. Land in and around the lake is used for grazing. Poloko Lake (NSW102) is over 3700 ha in size and receives water once Yantabangee Lake has filled. Once full, water can remain for nearly two years. Vegetation around the lake is similar to that for the wetlands above. Land in and around the lake is used for grazing. Peery Lake (NSW101) is over 5000 ha in size and receives water from the Paroo River as well as local creeks. Water can remain for up to three years after flooding. The northern part of the lake has mound springs. Vegetation around the lake is similar to that for the wetlands above, but with the addition of some River Red Gums (Eucalyptus camaldulensis) around the mound springs. Land in and around the lake is used for grazing. It is important to note that water contributions to the Paroo Overflow Lakes system arise from the Paroo River and Warrego River catchments, with the latter entering the Paroo system via Cuttaburra Creek (see Warrego region report). The effects of flow contributions from the Warrego on the Overflow Lakes have not been considered. Kingsford et al. (2002) identify a moderate inundation event for this area as 170,000 ML/month as measured at the Caiwarro gauge. To determine an approximate area flooded by these events, this study combined the monthly flow data presented in Kingsford et al. (2002) into discrete annual event volumes. These were compared to the area inundated for the key event of each year presented in Kingsford et al. (2002), and it was identified that events of 170,000 ML would flood approximately 40,000 ha of the Paroo Overflow Lakes. The frequency of flows of 170,000 ML/month at the Caiwarro gauge is therefore used as a hydrologic indicator in the assessment of the Paroo Overflow Lakes (Table 7-1). Additionally, the average annual volume and the average event volume of flows above this 170,000 ML/month threshold are assessed. Larger event volumes would flood the Paroo Overflow Lakes to a greater extent. 74 Water availability in the Paroo November 2007 CSIRO 2007

85 7 Environment Figure 7-1. Location map of environmental assets CSIRO 2007 November 2007 Water availability in the Paroo 75

86 7 Environment Figure 7-2. Satellite image of selected areas of Currawinya Lakes Figure 7-3. Satellite image of Paroo Overflow Lakes 76 Water availability in the Paroo November 2007 CSIRO 2007

87 Table 7-1. Definition of environmental indicators Name Currawinya Lakes Lake Numalla indicators Description Average period (years) between flows in excess of 38,000 ML/day at Caiwarro gauge Maximum period (years) between flows in excess of 38,000 ML/day at Caiwarro gauge Average flow volume above 38,000 ML/day at Caiwarro gauge per year Average flow volume above 38,000 ML/day at Caiwarro gauge per event Lake Wyara indicators Average period (years) between flows in excess of 112,600 ML/day at Caiwarro gauge Maximum period (years) between flows in excess of 112,600 ML/day at Caiwarro gauge Average flow volume above 112,600 ML/day at Caiwarro gauge per year Average flow volume above 112,600 ML/day at Caiwarro gauge per event Paroo Overflow Lakes Paroo Overflow Lakes indicators 7.3 Results Average period (years) between flows in excess of 170,000 ML/month at Caiwarro gauge Maximum period (years) between flows in excess of 170,000 ML/month at Caiwarro gauge Average flow volume above 170,000 ML/month at Caiwarro gauge per year Average flow volume above 170,000 ML/month at Caiwarro gauge per event The projected changes in the chosen environmental indicators are listed for the various scenarios in Table 7-2. These were assessed using scenario outputs for the Caiwarro gauge from the Paroo river system model (see Chapter 4). It is important to note that the Currawinya Lakes frequency indicators are based on daily flow, while the Paroo Overflow Lakes frequency indicators are based on total monthly flow. 7 Environment Table 7-2. Environmental indicator values under scenarios P and A, and percentage change (from Scenario A) in indicator values under Scenario C P A Cdry Cmid Cwet Years Percent change from Scenario A Lake Numalla indicators Average period between inflow events % 4% -31% Maximum period between inflow events % 0% 0% GL Average above-threshold volume per year % 2% 88% Average above-threshold volume per event % 5% 31% Lake Wyara indicators Years Average period between inflow events % -55% -76% Maximum period between inflow events % 20% -49% GL Average above-threshold volume per year % 68% 424% Average above-threshold volume per event % -28% -8% Paroo Overflow indicators Years Average period between inundation events % 4% -21% Maximum period between inundation events % 25% 0% GL Average above-threshold volume per year % 1% 61% Average above-threshold volume per event % 5% 29% 7.4 Discussion of key findings There is no change in the indicator values between the pre-development scenario and the current development baseline scenario for either the Currawinya Lakes or the Paroo Overflow Lakes. This indicates that the current maximum CSIRO 2007 November 2007 Water availability in the Paroo 77

88 permissible water resource development in the Paroo has had no detectable impact on the beneficial high flows to these wetlands Currawinya Lakes Lake Numalla Under the best estimate 2030 climate the average period between major inflows to Lake Numalla would increase slightly (4 percent). This increase is unlikely to have major ecological consequences. Under the wet and dry 2030 climate extremes the average period would decrease or increase by 31 percent respectively. The maximum period between the flooding events does not change because there is a single long dry period that occurs in all scenarios. 7 Environment The change in flood volumes provides a somewhat complex picture. Under the best estimate 2030 climate, the total volume of flood water is similar to baseline, although the average event volume is 5 percent greater due to a slight decrease in the number of events. Under the dry extreme 2030 climate there is 15 percent less flood water overall, however floods are less frequent resulting in an increase in the average flood volume of 11 percent. Under the wet extreme 2030 climate there is nearly twice the total flood volume, which is expressed as more and larger flood events. The ecological implications of these changes would require further investigation. However, they would be expected to at least affect the frequency with which waterbirds use the lake. Lake Wyara Under the best estimate 2030 climate the average period between inflow events to Lake Wyara decreases by 55 percent, although there is a 20 percent increase in the maximum period between events. The reduction in the average period between the larger inundation events is likely to be a result of the increase in the intensity of the highest rainfall (see Figure 3.9). The level of confidence in this result is indicated by the fact that two-thirds of the global climate models indicate an increase in the highest daily rainfall amounts. The changes in both the average and maximum periods for the best estimate 2030 climate would be expected to affect the salinity, habitat and faunal population dynamics of the lake, but would be difficult to predict. The hydrologic changes under the wet extreme 2030 climate indicate major consequences for Lake Wyara. Under the wet 2030 climate extreme the average period between wetting events is reduced by 76 percent and the maximum period between flooding events decreases by 49 percent. Under these conditions the lake would likely be less saline and have a different species composition of waterbirds, vegetation and other aquatic life forms. Under the dry 2030 climate an 18 percent increase is predicted for the average period between flooding events and a 26 percent increase in the maximum period between events. This would potentially lead to the lake being dry for extended periods, increase salinity levels and result in changes in the species composition and abundance of waterbirds, vegetation and other aquatic life forms. The change in flood volumes provides a complex picture. Under the best estimate 2030 climate, the total volume of flood water is 68 percent greater than baseline. However, individual flood events of which there are more than baseline are 28 percent smaller on average. Under the dry extreme 2030 climate there is 11 percent less flood water overall, and floods are less frequent, however an average flood event is 6 percent larger in volume. Under the wet extreme 2030 climate there is over four times the total flood volume, which is expressed as many more floods that are however, slightly smaller in volume on average. The ecological implications of these changes would require further investigation Paroo Overflow Lakes Under the best estimate 2030 climate the Paroo Overflow Lakes would experience a small increase (4 percent) in average period between high flow events. The maximum period between events would increase by 25 percent, which would be likely to reduce waterbird use of the area. Under the dry 2030 climate extreme the average period between floods increase by 13 percent and the maximum period between flood events would increase by 10 percent. These changes would be likely to have an adverse impact on the availability of suitable habitat for waterbirds. 78 Water availability in the Paroo November 2007 CSIRO 2007

89 The wet 2030 climate extreme however, would lead to a 21 percent decrease in the average period between flooding of the Paroo Overflow Lakes which would be primarily of benefit to habitats and the species resident in, or using, these wetlands. No change is predicted for the maximum period between events for this scenario. The change in flood volumes provides a relatively simple picture for the Paroo Overflow Lakes. Under the best estimate 2030 climate the average volume of flow events remains similar to the current scenario, with a slight increase in the average flood size due to a slight decrease in the number of events. Under the dry extreme 2030 climate there is an 11 percent decrease in event volume with fewer events resulting in an average event size simular to the current scenario. Under the 2030 wet climate scenario there would be a 61 percent increase in event volume and more events resulting in a 29 percent increase in the average volume of individual events. The ecological implications of these changes to event size would require further investigation. 7.5 References Environment Australia (2001) A Directory of Important Wetlands in Australia. Third Edition. Environment Australia, Canberra. Available at: Kingsford RT and Porter J (1999) Wetlands and waterbirds of the Paroo and Warrego Rivers. In: Kingsford RT (Ed.) A free flowing river the ecology of the Paroo River. NSW National Parks and Wildlife Service, Hurstville. Kingsford RT, Brandis K, Young WJ and Fryar S (2002) Environmental Flows on the Paroo and Warrego Rivers: Progress Report Year 2. Department of Environment and Heritage, Canberra. Timms BV (1999) Local runoff, Paroo floods and water extraction impacts on wetlands of Currawinya National Park. In: RT Kingsford (Ed.) A free flowing river the ecology of the Paroo River. NSW National Parks and Wildlife Service, Hurstville. 7 Environment CSIRO 2007 November 2007 Water availability in the Paroo 79

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91 Appendix A Rainfall-runoff results for all subcatchments Table A-1. Summary of modelling results for all subcatchments under scenarios A and C Scenario A Scenario Cdry Scenario Cmid Scenario Cwet Modelling catchment Area Rainfall APET Runoff Runoff Runoff coefficient contribution Rainfall Runoff Rainfall Runoff Rainfall Runoff km 2 mm percent percent change from Scenario A % 4% -14% -19% -4% 2% 14% 46% % 23% -13% -18% -4% 2% 13% 44% % 66% -11% -16% -4% -3% 12% 39% % 7% -10% -14% -3% -4% 13% 38% % 100% -11% -16% -4% -2% 13% 40% Appendix A Rainfall-runoff results for all subcatchments CSIRO 2007 November 2007 Water availability in the Paroo 81

92 Appendix B River modelling reach mass balances Subcatchment River system model average annual water balance A Cwet Cmid Cdry GL/y Storage volume Initial storage Final storage Inflows Appendix B River modelling reach mass balances Sub-catchments Directly gauged Indirectly gauged Sub-total Diversions Licensed private diversions QLD Unsupplemented access (volumetric limit 70 ML/y) Sub-total Stock and domestic QLD unsupplemented access NSW unsupplemented access Sub-total Outflows End-of-system outflow Sub total Net evaporation Natural water bodies Sub-total Sub-total Unattributed fluxes Total Mass balance error (%) Net evaporation private storages Water availability in the Paroo November 2007 CSIRO 2007

93 Subcatchment River system model average annual water balance A Cwet Cmid Cdry GL/y Storage volume Initial storage Final storage Inflows Sub-catchments Directly gauged Indirectly gauged Sub-total Diversions Licensed private diversions QLD Unsupplemented access (volumetric limit 70 ML/y) Sub-total Stock and domestic QLD unsupplemented access NSW unsupplemented access Sub-total Outflows End-of-system outflow Sub total Net evaporation Natural water bodies Sub-total Sub-total Unattributed fluxes Total Appendix B River modelling reach mass balances Mass balance error (%) Net evaporation private storages CSIRO 2007 November 2007 Water availability in the Paroo 83

94 Subcatchment River system model average annual water balance A Cwet Cmid Cdry GL/y Storage volume Initial storage Final storage Inflows Sub-catchments Directly gauged Indirectly gauged Appendix B River modelling reach mass balances Sub-total Diversions Licensed private diversions QLD Unsupplemented access (volumetric limit 70 ML/y) Sub-total Stock and domestic QLD unsupplemented access NSW unsupplemented access Sub-total Outflows End-of-system outflow Sub total Net evaporation Natural water bodies Sub-total Sub-total Unattributed fluxes Total Mass balance error (%) Net evaporation private storages Water availability in the Paroo November 2007 CSIRO 2007

95 Subcatchment River system model average annual water balance A Cwet Cmid Cdry GL/y Storage volume Initial storage Final storage Inflows Sub-catchments Directly gauged Indirectly gauged Sub-total Diversions Licensed private diversions QLD Unsupplemented access (volumetric limit 70 ML/y) Sub-total Stock and domestic QLD unsupplemented access NSW unsupplemented access Sub-total Outflows End-of-system outflow Sub total Net evaporation Natural water bodies Sub-total Sub-total Unattributed fluxes Total Appendix B River modelling reach mass balances Mass balance error (%) Net evaporation private storages CSIRO 2007 November 2007 Water availability in the Paroo 85

96 Appendix C River system model uncertainty assessment by reach This Appendix contains the results of river reach water accounting for this region, as well as an assessment of the magnitude of the project change under each scenario compared to the uncertainty associated with the river model. Each page provides information for a river reach that is bounded by a gauging station on the upstream and downstream side, and for which modelling results are available. Table C-1 provides a brief explanation for each component of the results page. Appendix C River system model uncertainty assessment by reach Table Land use Gauging data Correlation with ungauged gains/losses Water balance Model efficiency Description Table C-1. Explanation of components of the uncertainty assessments Information on the extent of dryland, irrigation and wetland areas. Land use areas are based on remote sensing classification involving BRS land use mapping, water resources infrastructure and remote sensing-based estimates of actual evapotranspiration. Information on how well the river reach water balance is measured or, where not measured, can be inferred from observations and modelling. The volumes of water measured at gauging stations and off-takes is compared to the grand totals of all inflows or gains, and/or all outflows or losses, respectively. The fraction of total refers to calculations performed on average annual flow components over the period of analysis. The fraction of variance refers to the fraction of month-tomonth variation that is measured. Also listed are the same calculations but for the sum of gauged terms plus water balance terms that could be attributed to the components listed in the Water balance table with some degree of confidence. The same terms are also summed to water years and shown in the diagram next to this table. Information on the likely nature of ungauged components of the reach water balance. Listed are the coefficients of correlation between ungauged apparent monthly gains or losses on one hand, and measured components of the water balance on the other hand. Both the normal (parametric) and the ranked (or non-parametric) coefficient of correlation are provided. High coefficients are highlighted. Positive correlations imply that the apparent gain or loss is large when the measured water balance component is large, whereas negative correlation implies that the apparent gain or loss is largest when the measured water balance component is small. In the diagram below this table, the monthly flows measured at the gauge at the end of the reach are compared with the flows predicted by the baseline river model, and the outflows that could be accounted for (i.e., the net result of all measured or estimated water balance components other than main stem outflow which ideally should equal main stem outflows in order to achieve mass balance) Information on how well the modelled and the best estimate river reach water balances agree, and what the nature of any unspecified losses in the river model is likely to be. The river reach water balance terms are provided as modelled by the baseline river model (scenario A) over the period of water accounting. The accounted terms are based on gauging data, diversion records, and (adjusted) estimates derived from SIMHYD rainfall-runoff modelling, remote sensing of water use and simulation of temporary storage effects. Neither should be considered as absolutely correct, but large divergences point to large uncertainty in river modelling. 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. 86 Water availability in the Paroo November 2007 CSIRO 2007

97 Table Changeuncertainty ratios Description Information on the significance of the projected changes under different scenarios, considering the performance of the river model in explaining observed flow patterns at the end of the reach. In this table, the projected change is compared to the river model uncertainty by testing the hypothesis that the scenario model is about as good or better in explaining observed historic flows than the baseline model. The metric to test this hypothesis is the change-uncertainty ratio, which is calculated as the ratio of Nash-Sutcliffe Model Efficiency indicators for the scenario model and for the baseline (scenario A) model, respectively. A value of around one or less suggests that is likely that the projected scenario change is not significant when compared to river model uncertainty. Conversely, a ratio that is considerably greater than one implies that the scenario model is much worse in reproducing historic observations than the baseline model, which provides greater confidence that the scenario indeed leads to a significant change in flow patterns. The change-uncertainty ratio is calculated for monthly as well as annual values, to account for the possibility that the baseline model may reproduce annual patterns well but not monthly. Below this table on the left, the same information is provided in a diagram. Below the table on the right, the observed annual flows at the end of the reach is compared to those simulated by the baseline model and in the various scenarios. To the right of this table, the flow-duration curves are shown for all scenarios. Appendix C River system model uncertainty assessment by reach CSIRO 2007 November 2007 Water availability in the Paroo 87

98 Downstream gauge Paroo Willara Crossing Reach 1 Upstream gauge A Paroo Caiwarro Reach length (km) 92 Area (km 2 ) Outflow/inflow ratio 0.72 Net losing reach Land use ha % Dryland 808, Irrigable area Open water* River and wetlands 213, Open water* - - * averages for This is a moderately losing reach. Flows are dominated by the inflows from the reach above. Most of the inflows are gauged. There are no recorded diversions, and considerable river and floodplain losses. Baseline model performance is good. Accounting also explains observed flows very well after adjusting estimated local runoff. Some of the projected scenario changes are greater than river model uncertainty, although the Cdry scenario is close to uncertainty. Appendix C River system model uncertainty assessment by reach Gauging data Inflows Outflows Overall and gains and losses Fraction of total Gauged Attributed Fraction of variance Gauged Attributed Correlation with ungauged Gains Losses Linear adjustment normal ranked normal ranked Main gauge inflows Tributary inflows Main gauge outflows Distributary outflows Recorded diversions Estimated local runoff Adjusted -15.9% Monthly streamflow (GL/mo) gauged accounted model Water balance Model (A) Accounts Difference Model efficiency Model (A) Accounts Jul 1990 Jun 2005 Monthly Gains GL/y GL/y GL/y Normal Main stem inflows Log-normalised - - Tributary inflows Ranked Local inflows Low flows only - - Unattributed gains and noise High flows only Losses GL/y GL/y GL/y Annual Main stem outflows Normal Distributary outflows Log-normalised Net diversions Ranked River flux to groundwater River and floodplain losses Definitions: Unspecified losses low flows (flows<10% percentile ) : 0.0 GL/mo Unattributed losses and noise high flows (flows>90% percentile) : 60.4 GL/mo Change-uncertainty ratios P B Cwet Cmid Cdry Dwet Dmid Ddry Annual streamflow Monthly streamflow Reach gains and losses (GL/y) /91 91/92 92/93 93/94 94/95 Monthly streamflow (GL/mo). 95/ /97 97/98 98/99 99/00 00/01 01/02 02/ /04 04/05 05/06 Pecentage of months flow is exceeded unattributed gains ungauged gains gauged gains unattributed losses ungauged losses Jan-90 Jan-91 Jan-92 Jan-93 Jan-94 Jan-95 Jan-96 Jan-97 Jan-98 Jan-99 Jan-00 Jan-01 Jan-02 Jan-03 Jan-04 Jan-05 gauged losses Monthly Change-Uncertainty Ratio P C + wet O mid dry Annual streamflow (GL/y) gauged A P Cwet Cmid Cdry Annual Change-Uncertainty Ratio 90/91 91/92 92/93 93/94 94/95 95/96 96/97 97/98 98/99 99/00 00/01 01/02 02/03 03/04 04/05 88 Water availability in the Paroo November 2007 CSIRO 2007