Water Availability in the Barwon-Darling

Transcription

1 Water Availability in the Barwon-Darling Summary of a report to the Australian Government from the CSIRO Murray-Darling Basin Sustainable Yields Project June 2008

2 Project framework Scenarios assessed The project framework begins with definition of sub-catchments for modelling and regions for reporting, and with definition of the climate and development scenarios to be assessed (including generation of the time series of climate data that describe these scenarios). The climate data form inputs to spatio-temporal modelling of the implications of these climate scenarios for catchment runoff and groundwater recharge. The catchment development scenarios (farm dams and forestry) are modifiers of the resulting modelled runoff time series. The runoff implications are then propagated through existing river system models. The recharge implications are propagated through groundwater models for the major groundwater resources or considered in simpler assessments for the minor groundwater resources. The connectivity of surface and groundwater is assessed and the actual volumes of surface-groundwater exchange under current and likely future groundwater extraction are quantified. Monthly water balances for the last 10 to 20 years are analysed using all relevant existing data and remotely-sensed measures of irrigation and floodplain evapotranspiration, and are compared to the river modelling results. The implications of the scenarios for water availability and water use under current water sharing arrangements are then assessed and synthesised. Monthly water accounts Define climate scenarios Rainfall-runoff modelling inflows River system modelling Environmental assessments SW GW exchanges Define reporting regions and sub-catchments Groundwater recharge modelling inflows Groundwater modelling and assessment Reporting The uncertainty in the assessments is considered from the perspective of IF this future (of climate and development) THEN these hydrologic implications. There is uncertainty in both the IF and the THEN. The uncertainty in the IF is typically large, since the degree of future global warming cannot be accurately predicted. Additionally, there is still considerable uncertainty in predictions of rainfall change resulting from global warming. The uncertainty in the THEN stems from the adequacy of hydrologic and meteorologic data and the imperfect predictions of hydrologic response to climate change given current understanding. The implications of the uncertainty assessments are summarised under Limitations (page 5) to advise users of the reliability of the assessments with respect to the terms of reference of the project. The assessments of current and potential future water availability have been undertaken by considering four scenarios of historical, recent and future climate and current and future development. All scenarios are defined by daily time series of climate variables based on different scalings of the climate. The first scenario is for historical climate and current development and is used as a baseline against which other scenarios are compared. The second scenario is for recent climate and current development and is intended as a basis for assessing future water availability should the climate in the future prove to be similar to that of the last ten years. The third scenario is for future climate and current development and evaluates three global warming scenarios using 15 global climate models to provide a spectrum of possible climates for From this spectrum three variants are reported: a median or best estimate, a wet variant and a dry variant. The fourth scenario is for future climate and future development and considers the effects of both a 2030 climate and the expansions in farm dams and commercial plantation forestry expected under current policy, and the changes in groundwater extractions anticipated under existing groundwater plans. All scenarios assume current water sharing arrangements and do not attempt to include possible management responses to changes in climate, water availability or development. >>Barwon River at weir near Brewarrina, NSW (MDBC) Acknowledgments Prepared by CSIRO for the Australian Government under the Raising National Water Standards Program of 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. 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. Photos courtesy of the Murray Darling Basin Commission (MDBC), CSIRO Land and Water (CSIRO), Western Catchment Management Authority (Western CMA), and NSW Department of Primary Industries (DPI). CSIRO 2008 all rights reserved. This work is copyright. Apart from any use as permitted under the Copyright Act 1968, no part may be reproduced by any process without prior written permission from CSIRO. 2 Water Availability in the Barwon-Darling >>> Cover: Darling River near Bourke, NSW (MDBC)

3 Barwon-Darling region >>Darling River, Wilcannia, NSW (Western CMA) The Barwon-Darling region is in northwestern New South Wales and covers 13 percent of the total area of the Murray Darling Basin (MDB). The region is based around the Barwon and Darling Rivers. The population is 50,000 or 2.5 percent of the MDB total, concentrated in the centres of Collarenebri, Walgett, Brewarrina, Bourke, Cobar and Wilcannia. The major land use is dryland pasture used for beef and sheep grazing. Approximately 63,000 ha of land were irrigated in 2000 including 57,900 ha for cotton production on the western plains. The Talyawalka area is a nationally important wetland located to the south of the region on the Darling Riverine Plains between Wilcannnia and Menindee. The area comprises the wetlands of the Talyawalka Anabranch of the Darling River and its distributary, Teryawynia Creek. It is representative of a semi-arid inland floodplain wetland system fringed by Black Box woodland. The region uses 3 percent of the surface water diverted for irrigation in the MDB and groundwater use is less than 1 percent of the MDB total (excluding the confined aquifers of the Great Artesian Basin (GAB)). There are no major public water storages within the region. 2.8% Broad land use in the year 2000 Land use Area percent ha Dryland crops 5.0% 706,200 Dryland pasture 63.7% 9,030,600 Irrigated crops 0.4% 63,000 Cereals 4.1% 2,600 Cotton 92.0% 57,900 Horticulture 0.3% 200 Orchards 0.3% 200 Pasture and hay 2.7% 1,700 Vine fruits 0.6% 400 Native vegetation 30.2% 4,290,900 Plantation forests <0.1% 2,100 Urban <0.1% 3,500 Water 0.6% 90,000 Total 100.0% 14,186, % 0.6% Share of MDB runoff 0.6% Share of MDB runoff Share of total MDB groundwater use (excluding confined aquifers of the Great Artesian Basin) Source: Bureau of Rural Sciences, Share of total MDB groundwater use (excluding confined aquifers of the Great Artesian Basin) June

4 Key findings Average surface water availability for the Darling Basin (assessed at Bourke) under the historical climate is 3515 GL/year. Average surface water use across the Darling Basin under current development is 39 percent. This is a high level of development. Current average surface water use within the Barwon Darling region is 230 GL/year. Groundwater use within the region is about 10 GL/year or about 4 percent of total withinregion water use. This is a low level of groundwater development. The recent climate (1997 to 2006) was similar to the long-term average climate. The best estimate of climate change by 2030 would reduce average surface water availability by 8 percent but would increase surface water use within the region by 2 percent. Future development of farm dams in the region (a 14 percent growth by 2030) is expected. This would reduce runoff by less then 0.5 percent. Groundwater extraction in the region is expected to grow to 240 GL/year to be over 50 percent of the average total water use in the region. For historical climate and current development The annual rainfall and modelled runoff averaged over the Barwon-Darling region are 328 mm and 6 mm, respectively. The region generates about 2.8 percent of MDB total runoff. Current average surface water availability for the entire Darling Basin (assessed at Bourke) is 3515 GL/year and 99 percent of this water is generated in regions upstream of the Barwon Darling region (including 23 percent from the Namoi, 22 percent from the Macquarie Castlereagh and 20 percent from the Border Rivers). Current average surface water use in the Barwon-Darling region is 230 GL/year. Licences within the region are fully utilised, note however, access rules for Barwon-Darling irrigators were altered in July 2007 to cap use at 173 GL/year. Current total average surface water use across the entire Darling Basin reduces streamflow at Bourke by 1365 GL/year. The relative level of use for the Darling Basin is thus 39 percent. This is a high level of development. Groundwater extraction (10 GL/year) is currently less than 10 percent of rainfall recharge for all groundwater management units (GMUs) in the region. The reduction in streamflow due to current groundwater extraction is estimated to be around 1 GL/year. Water resource development in this and upstream regions has nearly doubled the average and maximum periods between substantial flows to the Talyawalka Anabranch system. The average period is now 4 years and the maximum period is 19 years. Individual events are now larger on average but the total volume is lower because there are far fewer flow events. Water resource development has more than doubled the average period between events that drown out Bourke Weir (thereby allowing fish passage). Individual drown-out events at the weir are slightly larger and last slightly longer. For recent climate and current development The average annual rainfall and runoff within the region over the ten-year period 1997 to 2006 are 3 and 8 percent higher respectively than the longterm (1895 to 2006) average values. Neither these differences, nor those in the contributing upstream regions are statistically significant, so a scenario based on the last ten years was not modelled for the region. For future climate and current development Under the best estimate 2030 climate average annual runoff within the region would be reduced by 2 percent. The extreme estimates (which come from the high global warming scenario) range from a 22 percent reduction to a 50 percent increase in average annual runoff. The range from the low global warming scenario is an 8 percent reduction to a 12 percent increase. However, due to changes in runoff in contributing upstream regions, average surface water availability (assessed at Bourke) would, under the best estimate 2030 climate, be reduced by 8 percent and end-of-system flows would be reduced by 10 percent. Total average surface water use within the region would increase by 2 percent due to increased evaporation from on-farm storages. The relative level of use for the entire Darling Basin would then be a very high 41 percent. Under the wet extreme 2030 climate average surface water availability would increase by 31 percent, surface water use within the region would increase by 3 percent and end-of-system flows would increase by 47 percent. Under the dry extreme 2030 climate average surface water availability would decrease by 27 percent, surface water use within the region would increase by 5 percent and end-of-system flows would decrease by 35 percent. Under the best estimate 2030 climate Talyawalka Anabranch system inflow events would be slightly more frequent but smaller in volume. The average period between inflows and the individual event volume would be reduced by 8 and 18 percent, respectively. The average period between drown-outs at Bourke Weir would be increased by 18 percent. The average event volume at the weir would be unaffected. Under the dry extreme 2030 climate there would be large changes to flows to the Talyawalka Anabranch system. The average period between inflows would increase by over 30 percent and the average volume of these events would be reduced by more than 30 percent. The average period between drown-outs at Bourke Weir would be increased by 66 percent and the average event volume would be reduced by 10 percent. The ecological consequences of these changes would be expected to be severe. Under the wet extreme 2030 climate Talyawalka Anabranch system inflows would be similar to withoutdevelopment conditions. Drown-outs at Bourke Weir would be more frequent but event volumes would be slightly smaller. 4 Water Availability in the Barwon-Darling

5 >>Brewarrina Weir, NSW (MDBC) For future climate and future development There are no commercial forestry plantations in the region and none are projected for the future. The total farm dam storage volume is projected to increase by 13,200 ML (14 percent) by The projected increase in farm dams will reduce average annual runoff by less than 0.5 percent. Projected 2030 development (groundwater extraction and additional farm dams in upstream regions) would reduce inflows to the Barwon-Darling region (under the best estimate 2030 climate) by 3 percent or 78 GL/year on average. Additional farm dams and groundwater extraction would be responsible for about equal shares of this impact. Diversions would be reduced by 1 percent compared to current conditions and end-of-system flows would be reduced by 3 percent in addition to best estimate climate change impacts. The relative level of use for the entire Darling Basin would then be 42 percent. Regional groundwater extraction is projected to increased 24-fold to 240 GL/year by 2030, moving groundwater use from 4 percent to over 50 percent of total water use within the region. The Gunnedah Basin, GAB Alluvial, Western Murray Porous Rock and Kanmantoo Fold Belt GMUs would all then be at a medium level of development (extraction exceeding 30 percent of recharge) under the best estimate 2030 climate. Projected groundwater extraction would reduce streamflow by 37 GL/year once equilibrium conditions are reached. Future development would have minor additional effects on the hydrology of the Talyawalka Anabranch system and the frequency and magnitude of Bourke Weir drown-outs. Limitations The largest sources of uncertainty for future climate results are the climate change projections (global warming level) and the modelled implications of global warming on regional rainfall. The results from 15 global climate models were used but there are large differences amongst these models in terms of regional rainfall predictions. There are also considerable uncertainties associated with the future projections of farm dams and commercial forestry plantations in the upstream regions which impact on future flows in the region. Future developments could differ considerably from these projections if governments were to impose different policy controls. The river model generally reproduces observed streamflow patterns well and produces estimates that agree reasonably well with water accounts. The projected changes in flows due to future climate are greater than model uncertainty under the wet extreme future climate scenarios, but are similar to model uncertainty under the dry extreme and best estimate future climate scenarios, partly due to the model bias in some reaches. The model provides strong evidence of changes in >>Paroo Overflow, NSW (Western CMA) flow pattern due to prior development, but the projected changes due to future development are very small. While the model is well suited for the purpose of this project, changes in low flows are not simulated well by the model. A simple water balance approach was used to assess the region s groundwater. This is appropriate given the low priority of the GMUs in the context of the project. However, the approach would not be adequate for addressing local groundwater management issues. The estimated impacts of groundwater extraction on streamflow are assigned a low level of confidence. The estimates are sensitive to the connectivity factor used and may be overestimated given the methodology. The environmental assessments of this project only consider 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. June

6 Rainfall and runoff The annual rainfall and modelled runoff averaged over the Barwon-Darling region are 328 mm and 6 mm respectively. Rainfall is low throughout the year but highest in summer and runoff is highest in summer and early autumn. The rainfall, runoff and the fraction of rainfall that becomes runoff in the region (particularly in the west) are amongst the lowest in the MDB. The region covers 13.4 percent of the MDB but generates only about 2.8 percent of the total runoff. The average annual rainfall and runoff over the ten-year period 1997 to 2006 are 3 and 8 percent higher respectively than the long-term (1895 to 2006) averages. However, because of the inter-annual variability and the relatively short ten-year period used as the basis for comparison, the 1997 to 2006 rainfall and runoff are not significantly different to the long-term average values. Under the best estimate 2030 climate average annual runoff would be reduced by 2 percent. The extreme estimates from the high global warming scenario range from a 22 percent reduction to a 50 percent increase in average annual runoff. The range from the low global warming scenario is an 8 percent reduction to a 12 percent increase. >>Darling Annabranch at the Silver City Highway crossing, NSW (MDBC) There are no commercial forestry plantations in the region and none are projected for the future. The total farm dam storage volume is projected to increase by 13.2 GL (14 percent) by The projected increase in farm dams will reduce mean annual runoff by less than 0.5 percent. Historical mm Recent Dry Current development Future climate Best estimate Wet Dry Future development Best estimate percent change from Historical Rainfall % -3% 13% -13% -3% 13% Runoff % -2% 50% -23% -2% 49% Evapotranspiration % -3% 12% -13% -3% 12% Wet >>Darling River near Bourke, NSW (MDBC) >>Darling River at Bourke, NSW (Western CMA) 6 Water Availability in the Barwon-Darling

7 Rainfall 800 Annual rainfall (mm) Annual rainfall ( ) spatially averaged across the region (based on SILO data) with low-frequency smoothed line shown to indicate longer-term variations. Mean monthly rainfall (mm) Historical Future climate (best estimate) Future climate range 0 J F M A M J J A S O N D Average ( ) monthly rainfall averaged across the region and range (shaded) of potential changes in mean monthly rainfall due to climate change by Average ( ) annual rainfall (mm) distribution (based on SILO data). Runoff 60 Annual runoff (mm) Annual runoff ( ) spatially averaged across the region (based on daily runoff modelling) with low-frequency smoothed line shown to indicate longer-term variations. Mean monthly runoff (mm) Historical Future climate (best estimate) Future climate & development (best estimate) Future climate range 0.0 J F M A M J J A S O N D Average ( ) monthly runoff averaged across the region and range (shaded) of potential changes in mean monthly runoff due to climate change by Average ( ) annual runoff (mm) distribution (based on daily runoff modelling). June

8 Surface water Current average surface water availability for the entire Darling Basin (assessed at Bourke) is 3515 GL/year and 99 percent of this water is generated in regions upstream of the Barwon-Darling region. Current average surface water use in the Barwon Darling region is 230 GL/year. Licences within the region are fully utilised, note however, access rules for Barwon Darling irrigators were altered in July 2007 to cap use at 173 GL/year. Current total average surface water use across the entire Darling Basin reduces streamflow at Bourke by 1365 GL/year. The relative level of use for the Darling Basin is thus 39 percent. This is a high level of development. Water resource development across the Darling Basin has not significantly altered the seasonality of streamflow in the Barwon-Darling region but has reduced the magnitude of two-year average return interval floods by 41 percent, and the magnitude of five- and ten-year average return interval floods by around 30 percent. These reductions in flood magnitude are considerably greater than the reductions likely under the best estimate 2030 climate. Under the best estimate 2030 climate, average surface water availability (assessed at Bourke) would be reduced by 8 percent and end-of-system flows for the Barwon Darling region would be reduced by 10 percent. Total average surface water use within the region would increase by 2 percent due to increased evaporation from on-farm storages. The impacts of climate change vary between water products: water use under Class A, B and C licences would increase by 11, 2 and less than 1 percent, respectively. Floodplain harvesting would reduce by 2 percent. The relative level of use for the entire Darling Basin would then be a very high 41 percent. Under the wet extreme 2030 climate average surface water availability would increase by 31 percent, surface water use within the region would increase by 3 percent and end-of-system flows would increase by 47 percent. Under the dry extreme 2030 climate average surface water availability would decrease by 27 percent, surface water use within the region would increase by 5 percent and end-of-system flows would decrease by 35 percent. Projected 2030 development (groundwater extraction and additional farm dams in upstream regions) would reduce inflows to the Barwon-Darling region (under the best estimate 2030 climate) by 3 percent or 78 GL/year on average. Additional farm dams and groundwater extraction would be responsible for about equal shares of this impact. Diversions would be reduced by 1 percent compared to current conditions and end-of-system flows would be reduced by 3 percent in addition to best estimate climate change impacts. The relative level of use for the entire Darling Basin would then be 42 percent. Without-development Historical Average annual water (GL) >>Bourke Weir, NSW (Western CMA) Future climate (dry)/ current development Future climate (best estimate)/ current development Future climate (wet)/ current development Future climate (dry)/ future development Future climate (best estimate)/ future development Future climate (wet)/ future development Non-diverted Diverted Historical Current development Future climate Future development Dry Best estimate Wet Dry Best estimate Wet Water availability GL/y percent change from Historical Total inflows -33% -9% 44% -36% -12% 40% Total surface water availability % -8% 31% -27% -8% 31% Total end-of-system flow % -10% 47% -38% -13% 43% Diversions Lowest 1-year period % -3% 48% -58% -12% 44% Lowest 3-year period % 0% 9% -23% -5% 8% Lowest 5-year period % 0% 6% -13% -1% 5% Average % 2% 3% -6% 0% 2% Non-diverted water percent Non-diverted water as a percentage of total available water 61% 55% 59% 68% 54% 58% 67% Non-diverted share relative to historical non-diverted share 100% 65% 90% 145% 64% 88% 143% 8 Water Availability in the Barwon-Darling

9 Groundwater Groundwater extraction in the Barwon- Darling region for 2004/05 is estimated at 10 GL per year, being 0.6 percent of the total groundwater use in the MDB (excluding confined aquifers of the GAB). Groundwater development within the region is low; current extraction is less than 10 percent of rainfall recharge and 4 percent of total annual within-region water use on average. Current groundwater extraction reduces streamflow by about 1.3 GL/year. The projected 2030 climate would have little effect on groundwater with extraction remaining at less than 10 percent of rainfall recharge. Groundwater extraction is projected to increase to 240 GL/year by 2030, moving groundwater use to just over 50 percent of the total average annual water use in the region. This would reduce streamflow by 37 GL/year by >>Water bore, tank and trough for cattle near Walgett, NSW (MDBC) Code Name Priority Current extraction (1) (2004/05) Total entitlement Long-term average extraction limit N45 Lower Darling Alluvium very low <0.1 < N46 Upper Darling Alluvium very low GL/y Recharge (2) N63 GAB Alluvial low N601 GAB Intake Beds very low np (4) N604 Gunnedah Basin very low N612 Western Murray Porous Rock very low N620 GAB Cap Rocks low 2.9 (3) (3) N811 Lachlan Fold Belt low N813 Warrambungle Tertiary Basalt very low <0.1 < N817 Kanmantoo Fold Belt very low (1) Current groundwater extraction for Macro Groundwater Sharing Plan areas is based on metered and estimated data provided by New South Wales Department of Water and Energy. Data quality is variable depending on the location of bores and the frequency of meter reading. (2) This value represents only rainfall recharge in the NSW Macro Groundwater Sharing Plan areas. The volume of recharge does not account for recharge in national park areas, which is not available for consumptive use and has been effectively allocated to the environment. (3) The long-term average extraction limit and rainfall recharge assigned to the GAB Cap Rocks is not for the deeper GAB confined aquifers but to the GAB Cap Rocks and any associated minor rocks and alluvium to a depth of not more than 60 m. (4) np not provided. June

10 Environment Water resource development in the Barwon-Darling region and upstream contributing regions has nearly doubled the average and maximum periods between important flows to the Talyawalka Anabranch system. Individual inflow events are larger on average than under without-development conditions, but due to lower frequency of events the total volumes entering the Anabranch system are also lower. Water resource development has more than doubled the average period between events that drown out Bourke Weir (thereby allowing fish passage) compared to without development conditions. Individual drown-out events are slightly larger and last slightly longer. Under the best estimate 2030 climate Talyawalka Anabranch system inflow events would be slightly more frequent but smaller in volume. The average period between inflows and the individual event volume would be reduced by 8 and 18 percent, respectively. The average period between drown-outs at Bourke Weir would increase by 18 percent, however, the duration of drown-out events would be largely unaffected. Under the dry extreme 2030 climate there would be large changes to flows to the Talyawalka Anabranch system. The average period between inflows would increase by over 30 percent and the average volume of these events would be reduced by more than 30 percent. The average period between drown-outs at Bourke Weir would be increased by 66 percent and the average event volume would be reduced by 10 percent indicating shorter drown-out durations. The ecological consequences of such changes could be severe. Under the wet extreme 2030 climate Talyawalka Anabranch system inflows would be similar to without development values. Drown-outs at Bourke Weir would be more frequent, although less than under without-development conditions. Drown-out event volumes would be slightly smaller than under withoutdevelopment conditions indicating slightly shorter drown-out event durations. Future development would have only minor additional effects on the hydrology of the Talyawalka Anabranch system and the frequency and magnitude of Bourke Weir drown-outs. >>Brewarrina fish traps, NSW (Western CMA) >>Brewarrina Weir, NSW (DPI) 10 Water Availability in the Barwon-Darling

11 >>Royal Spoonbill (Western CMA) There are many nationally important wetlands and some internationally important Ramsarlisted wetlands in the Barwon-Darling region including parts of the Paroo River Wetlands. Most of these are dependent on flows from the tributaries of the Barwon-Darling River and are thus considered in other reports from this project. Talyawalka Anabranch and Teryawynia Creek are located downstream of the Barwon-Darling region but they are assessed and reported here because they receive water directly from the Darling River. Fish passage over the Bourke Weir along the main stem of the Darling River is also assessed. The Talyawalka Anabranch and Teryawynia Creek system is a distributary flow system that receives water from the Darling River near Wilcannia and returns water via the lower Darling River downstream of Menindee. The system consists of Teryawynia, Dry, White Water, Eucalyptus/Waterloo, Victoria, Brummeys, Dennys, Brennans, Sayers, Gum, Boolabooka, North and Ratcatchers lakes. The main vegetation of the inundation area is Black Box and River Red Gum. Dry Lake supports a large expanse of Lignum and Cane Grass is prevalent along Talyawalka Creek. The lakes provide a large area of habitat for waterbirds when flooded. The Talyawalka wetlands are important for the MDB on the basis of the area carrying more than 10,000 waterbirds during surveys. Past Aboriginal occupation of the lake area is evident. Land tenure is leasehold and the lakes are used for grazing and occasional lakebed cropping. Withoutdevelopment years Historical Current development Future climate Future development Dry Best estimate Wet Dry Best estimate Wet percent change from Historical Talyawalka Anabranch commence-to-flow Average period between events (1) % -8% -39% 32% -8% -36% Maximum period between events (1) % 53% -37% 53% 53% -37% GL Average excess volume per event (2) % -18% -8% -35% -21% -6% Average excess volume per year (2) % -11% 55% -49% -14% 51% Bourke Weir drown-out flow years Average period between events (3) % 18% -24% 70% 22% -22% Maximum period between events (3) % 1% -10% 66% 1% -10% GL Average excess volume per event (4) % 2% 28% -12% 2% 27% Average excess volume per year (4) % -13% 61% -47% -16% 57% (1) Events exceeding 30 GL/day at Wilcannia gauge (2) Volume above 30 GL/day at Wilcannia gauge (3) Events exceeding 10 GL/day at Bourke (4) Volume above 10 GL/day at Bourke June

12 About the project The CSIRO Murray-Darling Basin Sustainable Yields Project resulted from the Summit on the Southern Murray- Darling Basin, convened by the then Prime Minister on 7 November The project is providing governments with a robust estimate of water availability for the entire Murray-Darling Basin (MDB) on an individual catchment and aquifer basis taking into account climate change and other risks. The project will report progressively to mid The project will be the most comprehensive assessment of water availability for the MDB 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 the assessments have employed all existing river system and groundwater models as well as new models developed within the project the modelling has included full consideration of the downstream implications of upstream changes between multiple models and between different states, and quantification of the volumes of surface groundwater exchange detailed analyses of monthly water balances for the last 10 to 20 years are being 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. These analyses provide an independent cross-check on the performance of river system models. The assessments reported here have been reviewed by a Steering Committee and a Technical Reference Panel both with representation from Commonwealth and State governments and the Murray Darling Basin Commission. Information on how these results may be used in the development of a new sustainable diversion limit for the Murray Darling Basincan be found at Enquiries More information about the project can be found at This information includes the full terms of reference for the project, an overview of the project methods and the project reports that have been released to-date, including the full report for this region. Z This publication has been designed by ZOO and printed by New Millennium Print to comply with a very high standard of environmental performance as stipulated in the Good Environment Choice environmental labelling standard GECA 20 Printers and Printed Matter