Water Availability in the Namoi and Gwydir Murray-Darling Basin Sustainable Yields Project. 20 December 2007

Transcription

1 Water Availability in the Namoi and Gwydir Murray-Darling Basin Sustainable Yields Project 20 December 2007

2 Project terms of reference Water Summit: PM and First Ministers, Nov 2006 CSIRO to report progressively through to early 2008 on sustainable yields of surface and groundwater systems within the MDB Estimate current and likely future (~2030) water availability in each catchment/aquifer and for the entire MDB considering: climate change and other risks surface-groundwater interactions Compare the estimated current and future water availability to that required to meet the current levels of extractive use

3 Project Context This Project Assessments of current & future water availability Environmental impacts of alternate allocation regimes Socio-economic impacts of alternate allocation regimes Stakeholder and community consultation Water resource planning, management and investment This project will not, in itself, determine sustainable yields or set a new cap on diversions

4 Overview of methods

5 Scenarios A: Historic climate ( ) & current development B: Recent climate ( ) & current development C: Future climate & current development Autumn MAM D: Future climate & future development Future climate 2030 climate based on 4AR IPCC results 3 global warming levels (low, mid, high) 15 global climate models Future development Commercial forestry plantations Farm dams Groundwater extractions Winter JJA Summer SON Spring DJF

6 Development Commercial forestry plantations projections for MDB regions distribute projections in areas suitable for plantations Farm dams current levels, trend analyses, policy controls Groundwater extractions growth in extraction as per State advice

7 Rainfall-runoff modelling SIMHYD and Sacramento models on 5 x 5 km grids Run for scenarios A and B (single runs) Run for Scenario C (15 GCMs x 3 global warming levels) From C select dry, mid, wet future: modify for Scenario D Scenario D Modify 3 runoff series from C for forest expansion Adjust daily flows using Forest Cover Flow Change model Modify 3 runoff series from C for farm dams Adjust daily flows using a dam water balance model Considers rainfall, evaporation, demands, inflows and spills

8 River system modelling Many different river models in use in Basin Mostly daily time step, link-node models These are being extended to Groundwater exchanges being quantified Models being linked and automated Scenario modelled runoff series transformed as inflows Some new models being developed DNRW IQQMs for Namoi (and Peel) and Gwydir

9 Groundwater recharge Diffuse recharge WAVES: considers plant physiology and soil physics Run at 20 point locations across MDB rain gradient Consider range of land uses and soil types Run scenarios A, B, Cdry, Cmid, Cwet Analyse results to obtain recharge scaling factors Apply across all groundwater management units on 5 km grid Irrigation recharge 1-D modelling for key irrigation areas, plus literature values

10 Groundwater modelling Prioritise groundwater management units (GMUs) Extraction level, development level, potential for stream impact 12 high & medium priority GMUs (~80% of resource) Existing and new numerical groundwater models Run models with scenario recharge series and current SW GW flux for 111 years (to equilibrium) and further 111 years Provide equilibrium flux back to river models Simple assessments for low priority GMUs Connectivity mapping across all regions

11 Water accounts For nearly 600 river reaches across the MDB independently assess: Inflows Outflows Diversions Floodplain losses Direct evaporation Exchanges with groundwater Storages (rivers, lakes, reservoirs) Assess river model performance Warrego Fords Bridge c Upstream gauge Warrego Barringun #2 Reach length (km) 141 Area (km 2 ) 5500 Outflow/inflow ratio 0.33 Net losing reach Land use ha % Dryland 192, Irrigable - area - Open water* - - River and wetlands 357, Open water* - - * averages for 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 normal ranked ranked Main gauge inflows Tributary inflows Main gauge outflows Distributary outflows Recorded Diversions Estimated local runoff Monthly streamflow (GL/mo) Water balance Model (A) Accounts Difference Model efficiency Model (A) Accounts Jul 1990 Jun 2006 Monthly Gains GL/y GL/y Normal < GL/y Main stem inflows Log-normalised - - Tributary inflows Ranked Local inflows Low flows only - - Unattributed gains and noise High flows only <0 <0 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 GL/mo ) : 0.0 Unattributed losses and noise high flows (flows>90% percentile) : 5.0 GL/mo Change-uncertainty ratios DH DM DL P CH CM CL Annual streamflow Monthly streamflow Monthly Change-Uncertainty Ratio 100 P C D + high - low 10 O medium Annual Change-Uncertainty Ratio Annual streamflow (GL/y) Reach gains and losses (GL/y) This is a strongly losing reach. Flows are dominated by inflows from upstream. Most of the inflow is gauged. Estimated local runoff explains most of the ungauged gains but large adjustment of runoff model estimates was required. There are few diversions. Ungauged losses are large and attributed to wetland and floodplain losses. Baseline model performance is modest. Accounting explains observed flows moderately. The projected scenario changes are of similar order to the uncertainty for CH and CM scenarios, and greater than uncertainty for P and CL scenarios. 400 unattributed gains 300 ungauged 200 gains 100 gauged gains 0 unattributed losses -100 ungauged -200 losses gauged -300 losses /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 05/06 gauged 100 accounted 10 model Jun-90 Jun-91 Jun-92 Jun-93 Jun-94 Jun-95 Jun-96 Jun-97 Jun-98 Jun-99 Jun-00 Jun-01 Jun-02 Jun-03 Jun-04 Jun Pecentage of months flow is exceeded gauged 450 A P 300 CH 250 CM 200 CL 150 DH 100 DM 50 DL 0 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 05/06 Monthly streamflow (GL/mo).

12 Namoi region 3.8% of MDB area; 88,000 people (<4.5% of MDB) Cattle and sheep grazing; wheat, cotton & other crops on the floodplains Keepit and Split Rock dams store water for irrigation Highest level of groundwater development in NSW One wetland of national importance Lake Goran

13 Key findings by scenario Current average surface water availability is 965 GL/year and a high proportion (37 percent) of this water is used. Groundwater use is also high representing nearly half of all water use in the region and continued use at current levels will lower watertables and reduce streamflow. 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 5 percent and reduce surface water diversions by 1 percent. Likely future development of farm dams (13 percent growth) and groundwater (77 percent growth) would reduce average river inflows by 3 percent, increase streamflow leakage to groundwater by 14 percent and reduce surface water diversions by 4 percent.

14 Historic climate & current development Mean annual rainfall: 633 mm. Mean annual runoff: 24 mm 3.2% of MDB total Surface water availability: 965 GL/year 37% of this water is used this is a high level of use SW diversions (260 GL/yr); streamflow losses induced by GW use (99 GL/yr) Groundwater use in 2004/05 was 255 GL Similar to average surface water diversion ¾ of use from Upper and Lower Namoi GMUs Extraction from Lower Namoi GMU exceeds LTAEL LTAEL for Lower Namoi exceeds total average recharge Continued extraction at LTAEL will lead to large reductions in groundwater levels and reductions in streamflow LTAEL for Upper Namoi is 95% of total average recharge Miscellaneous Alluvium of the Barwon Region GMU is very highly developed and the Peel River Alluvium GMU is moderately developed Water resource development has increased average period between flooding of Namoi river billabongs and wetlands from 3 to 3.8 months. Annual flood volume reduced by 25%

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16 Achieving Sustainable Groundwater Entitlements Structural adjustment program announced in June 2005: funding reductions in entitlements in the Upper and Lower Namoi, Lower Macquarie, Lower Lachlan, Lower Murray, Lower Gwydir and Lower Murrumbidgee groundwater sources. NSW and Australian governments have jointly invested $135 million. Entitlements for each system will be gradually reduced to the long-term average extraction limit (LTAEL) over the life of each Water Sharing Plan. Original Entitlement (ML) Final Entitlement (ML) Reduction (ML) Reduction To-date (ML) Percent Reduction To-date Lower Namoi 167,796 81,593 86,203 78, Upper Namoi 270,679 85, , , Lower Gwydir 65,885 28,850 37,035 32, Total AG Funds Total NSW Funds Total Funds AG Funds To-date NSW Funds To-date Total Funds To-date Precent Expenditure To-date Lower Namoi $15,101,220 $5,587,380 $20,688,600 $10,388,707 $3,843,773 $14,232, Upper Namoi $30,304,602 $13,171,438 $43,664,700 $21,697,244 $9,803,456 $31,500, Lower Gwydir $9,738,000 $6,492,000 $16,230,000 $4,624,650 $3,083,100 $7,707, Note: data in above tables supplied by NSW Dept. Of Water and Energy

17 Recent climate & current development Average annual rainfall and runoff (1997 to 2006) are not statistically different to the long-term average values A scenario based on the last ten years was therefore not modelled CSIRO. MDB Sustainable Yields Project

18 Future climate & current development Under the best estimate (median) 2030 climate: 5% reduction in water availability, 8% reduction in end-of-system flows, and 1% in surface water diversions Under the wet extreme 2030 climate 38% increase in average water availability, 52% increase in end-of-system flows and 10 percent increase in surface water diversions Under the dry extreme 2030 climate 30% decrease in average water availability, 39% decrease in end-ofsystem flows and 17% decrease in surface water diversions No reduction in Tamworth town water supply or Peel River stock and domestic supply expected Rainfall recharge reductions in Lower Namoi GMU would be offset by increased river recharge Rainfall recharge reductions in the Miscellaneous Alluvium of the Barwon Region GMU would mean extraction would exceed recharge by 30% CSIRO. MDB Sustainable Yields Project

19 Future climate & future development Growth in commercial forestry plantations is expected to be negligible and total farm dam volume is expected to increase by 19.5 GL by 2030 an increase of 13%. Combined impact: 1.5% reduction in runoff Groundwater extraction by 2030 is expected to be 450 GL/year an increase of about 77% over current levels Groundwater use would then be 66% of total average water use and 94% of total water use in years of minimum surface water diversion Most of the increase would be in the New England Fold Belt, Gunnedah Basin and Oxley Basin GMUs Given current extraction levels, the increases would mean very high levels of development in the Miscellaneous Alluvium of the Barwon Region and Peel River Alluvium GMUs Total eventual impact of GW use at 2030 levels would be an average streamflow reduction of 113 GL/yr. Of this, 76 GL/yr would be due to increases in GW use Combined farm dam and GW use impacts 3% reduction in inflows & 14% increase in streamflow leakage to GW 4% reduction in surface water diversions.

20 Scenario summary water availability and use

21 Gwydir region 2% of MDB area; 26,500 people or 1.4% of MDB total 85,000 ha of irrigated cotton grown in 2000 Gwydir Wetlands are Ramsar-listed: four separate components the first listings in Australia on private land

22 Key findings by scenario Current average surface water availability is 782 GL/year and a very high proportion (41 percent) of this is diverted for use. Groundwater use is 12 percent of average total water use. The recent climate was similar to the long-term average climate. The best estimate of climate change by 2030 would reduce average surface water availability by 10% and reduce surface water diversions by 8%. Likelyfuture development of farm dams (14% growth) and groundwater (175% growth) would reduce annual river inflows by 2% and cause a net river leakage to groundwater resulting to a reduction in surface water diversions by 3%.

23 Historic climate & current development Mean annual rainfall: 644 mm. Mean annual runoff: 41 mm 3.4% of MDB total Surface water availability: 782 GL/yr; 41% diverted for use Groundwater extraction in 2004/05 was about 46 GL 77% extraction from the Lower Gwydir Alluvium GMU Current extraction from the Lower Gwydir Alluvium GMU exceeds LTAEL AGSE is funding reduction in entitlements to LTAEL by Extraction could be sustained at LTAEL Neither irrigation recharge nor extraction will have a large impact on streamflow in the Gwydir River As a result of water resource development there has been an increase of more than 75% in the average period between floods that inundate 20,000 ha (about 20%) of the Gwydir Wetlands 64% increase in the maximum period between events (from 7 to 11.5 years). 42% reduction in the average annual flooding volume into the wetlands

24 Recent climate & current development Average annual rainfall and runoff (1997 to 2006) are not statistically different to the long-term average values A scenario based on the last ten years was therefore not modelled

25 Future climate & current development Best estimate 2030 climate: 10% reduction in average surface water availability; 6% reduction in end-of-system flows; 8% reduction in diversions Wet extreme 2030 climate: 34% increase in average surface water availability, 33% increase in end-of-system flows; 20% increase in diversions Dry extreme 2030 climate: 29% decrease in average water availability; 27% decrease in end-of-system flows; 25% decrease in diversions Best estimate 2030 climate the average and maximum period between the smaller floods inundating the Gwydir Wetlands would not change greatly. However, the average annual flooding volume would fall a further 20% to be 53% lower than pre-development. Likely additional effects on wetland vegetation and wetland use by waterbirds for breeding

26 Future climate & future development Projected growth in commercial forestry plantations in the region is negligible. Total farm dam volume is projected to increase by 15.1 GL by 2030 an increase of 14% over current total farm dam volume. Impact: 1.5% reduction in mean annual runoff A 12-fold increase in groundwater use is expected by 2030 outside the Lower Gwydir Alluvium GMU Leading to high level of extraction in Misc. Alluvium of Barwon Region The total impact of the increases would be a streamflow reduction of about 37 GL/yr 14x the full impact of prolonged use at 2004/05 levels GW use would rise from 12 to 36% of average total water use and from 55 to 85% of total water use in years of minimum surface water use. Minimal change in Lower Gwydir Alluvium GMU: extraction at LTAEL could be sustained Combined average impacts: 24 GL/yr (2%) river inflow loss (farm dams 13 GL/yr; GW use 11 GL/yr) and net streamflow leakage of 2 GL/yr to GW 3% reduction in diversions (to be 11% lower than current 8% total (incl. climate change) reduction in average end-of-system flows limited additional impact on the hydrology of the Gwydir Wetlands

27 Summary by scenario water availability and use

28 Murray-Darling Basin Sustainable Yields Project funded under the Raising National Water Standards Program of the National Water Commission