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KulinDudinin Catchment Water Management Plan Modelling Water & Salinity in the Catchment Dr Graeme Cox Principal Engineer – Catchment Modeling DHI Australia Kulin Community Consultation Meeting 6-7 April 2009

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Presentation Overview <ul><li>Model Construction/Inputs </li></ul><ul><li>Model Calibration </li></ul><ul><li>Scenarios </li></ul><ul><ul><li>” Do Nothing” Base Case </li></ul></ul><ul><ul><li>Other Management Options </li></ul></ul><ul><li>Recommendations </li></ul>

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Model of Choice <ul><ul><li>regularly ranked as the worlds best tool for integrated catchment modelling. </li></ul></ul>

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Daily Rainfall and Potential Evaporation 1988 to 2008 Repeated

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Model Extents & Topography

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Soils Valley Sandy Duplex Ironstone Duplex Salt Lakes

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Geological Layers for Groundwater 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 11000 12000 13000 14000 15000 [meter] 270 280 290 300 310 320 330 340 350 360 370 380 [meter] 1000 2000 3000 4000 5000 6000 7000 380 Reduced for Fine Scale Model

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Vegetation Treed Cropping since pre 1950 Cropping – Cleared 1965 No cropping – Post 2007

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Vegetation post2007 Bare Soil post1950 Cereal, Cereal, Pasture Saltland post2007 4 post1965 Cereal, Cereal, Pasture 1950 - 1965 Trees Crop/pasture post1965 3 post1965 Cereal, Cereal, Pasture 1950 - 1965 Cereal, Cereal, Bare Fallow, Cereal, Cereal, Pasture Crop/pasture/fallow post1950 2 Constant Trees 5000mm Trees 1 Rotation Vegetation Code

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Overland Flow - Detention Storage Green Areas: 30mm Detention Storage Before Overland Flow (Ponding)

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Overland Flow - Example Snapshot during Jan 2006 Flood event

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Model Calibration <ul><li>Run model from 1950 to 2008 </li></ul><ul><li>Calibration Steps: </li></ul><ul><li>Adjust soil surface infiltration rate until runoff is roughly 5mm/yr at end of catchment </li></ul><ul><li>Scale rooting depth to get rise observed in two bores with water table depths measured in 1950s </li></ul><ul><li>Adjust inital depth to water table (1950) to get other bores levels to match </li></ul>

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Bore Locations 1950s Bores Someone to point to map

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1950s Bores 0.48m/yr 0.29m/yr observed modelled Wet 1960s

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Other Bores

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Other Bores On foot slope Next cell down slope is spot on

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Other Bores

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Other Bores

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Other Bores Clearing Date & Depth to Bedrock are out Local Dyke??

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Other Bores

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Other Bores Clearing Date & Depth to Bedrock are out

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Other Bores <ul><li>Summary </li></ul><ul><ul><li>Very good model agreement with observed groundwater levels </li></ul></ul><ul><ul><li>Exception in the upland areas where </li></ul></ul><ul><ul><ul><li>Depth to bedrock underestimated </li></ul></ul></ul><ul><ul><ul><li>Tree clearing date maybe too early </li></ul></ul></ul><ul><ul><ul><li>Local features eg dyke? </li></ul></ul></ul><ul><ul><li>Upland areas not critical as water table not near surface </li></ul></ul>Clearing Date & Depth to Bedrock are out

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Calibrated Initial Depth To Watertable (1950)

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Catchment Water Balance (1950-2008) 93% 1% 6% Runoff Rain Groundwater Recharge Evapotranspiration 100% 331.1

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Catchment Water Balance (Natural Vegetation) Groundwater Recharge ~99% 1% ~0% Runoff Rain Evapotranspiration Under Natural Vegetation 100% 331.1

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Groundwater Recharge (1975-2008)

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Groundwater Recharge For Different Vegetation From field leakage studies throughout Australia Source: CSIRO Groundwater Recharge (mm/yr) Annual Rainfall (mm/yr)

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Simulated Depth To Groundwater <ul><li>Animation from 1950 to 2008 </li></ul>

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Simulated Depth To Groundwater 2008 1950

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Simulated Depth To Groundwater (2008) White Hatch is Farmer Perceived Salinity Outbreaks as of 2007

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” Do Nothing” Base Case Simulation Results Local Knowledge 8,000 R. George Estimate 4,200 Landholders estimate Salt Affected 12,800 22% 8,000 14% Less than 2m 8,000 14% 4,100 7% Less than 1m 1600 3% 900 2% Less than 0.5m 2030 Area (ha & %) 2007 Area (ha & %) Depth To Water Table

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Simulated Depth To Groundwater <ul><li>Animation from 2008 to 2030 </li></ul><ul><ul><li>DO NOTHING </li></ul></ul>

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Simulated Depth To Groundwater - 2030

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Simulated Depth To Groundwater 2030 2008

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Areas With Water Table Within 1m 2008 2030

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Groundwater under different vegetation Source: CSIRO

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Groundwater Cross Section

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Groundwater Cross Section <ul><li>Vertical scale exergerated x 80 </li></ul>2007 1950 2030

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Groundwater Long Section

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Groundwater Long Section <ul><li>Vertical scale exergerated x 200 </li></ul>2007 1950 2030

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Simulated Area With Watertable Less Than 1m 2008

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Drain Discharge Calibration Drain flow calibration difficult due to model grid resolution – 200m

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Options Definition Saltland Perennial System covering area within 1m at 2007 (4100ha) 7 Surface Water Management - No depression storage/ponding on valley floor 6 Single deep drain parallel to Dudinin Ck linking existing drains 5 2m Deep drains covering area within 1m at 2007 (4100ha) - at a spacing/density required to be totally effective eg 50 to 200m spacing over 4100ha 4 Deep rooted farming system (100% arable) 3 Trees replanted on all upland areas (65% of catchment) 2 Base Case (Do Nothing) 20% less rainfall 1 Base Case (Do Nothing) 0 Scenario Description Scenario Number

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Options Modelling Note: In 2008 4100ha modelled with water table less than 1m -74% -3% -6% -49% -33% -11% -40% 0% -5,900 2,100 Saltland Perennial System covering area within 1m at 2007 (4100ha) 7 -200 7,800 Surface Water Management - No depression storage on valley floor 6 -500 7,500 Single deep drain parallel to Dudinin Ck linking existing drains 5 -3,900 4,100 2m Deep drains covering area within 1m at 2007 (4100ha) 4 -2,600 5,400 Deep rooted farming system (100% arable) 3 -900 7,100 Trees replanted on all upland areas (55% of catchment) 2 -3,200 3,800 Base Case (Do Nothing) 20% less rainfall 1 0 8,000 Base Case (Do Nothing) 0 Change in 2030 Area Compared to 8000ha Base Case (ha & %) Area with water table less than 1m in 2030 (ha) Scenario Description Scenario

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Fine Scale Modelling <ul><li>50m x 50m grid </li></ul><ul><li>Overland flow representation simplified </li></ul><ul><li>Saturate Zone Hydraulic Conductivity reduced </li></ul><ul><ul><li>By calibration to measured drain flows </li></ul></ul><ul><ul><li>Supported by </li></ul></ul><ul><ul><li>soil pits data </li></ul></ul>

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Drain Discharge Calibration

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Fine Scale Model Options Definition Combined Engineering and Vegetation Option (Scenario 9 and 10 treatments combined) 11 Vegetation Option: · Saltland perennials (e.g. saltbush) on areas identified as showing signs of salinity by farmers in 2007 - 4100ha · Areas identified as at risk by 2030 to be treated with a 10% tree (Eg Oil Mallee), 20% perennial plants (E.g. Lucerne), and remainder continuous cropping system. Total 4000ha 10 Engineering Option: Single deep drain parallel to Dudinin Ck linking existing drains and extending down to upstream of Commonwealth Road where a detention basin will be sited. 9 Base Case (Do Nothing) 8 Scenario Description Scenario Number

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Modelling Results At Catchment Outlet mg/L = mS/m * 6.5 18,600 +1,600 Drain 1,180 +25,000 Drain -8,530 (-67.5%) Combination 11 19,100 1,210 -8,375 (-67%) Vegetation 10 38,800 +3,200 Drain 2,200 +25,000 Drain -155 (-1%) Single deep drain linking existing drains 9 39,300 2,200 0 Base Case 8 Mean Salt Load 2025-2030 (t/yr) Mean Salinity Concentration 2025-2030 (mg/L) Change in 2030 Area Compared to Base Case (ha) Scenario Short Description Scenario

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Drains - Zone of Influence Zone of Influence Drain Depth 2m Water table height above drain Original Water table Depth Water table 1m d 1m Zone of 1m to Surface Expected 50m - 200m Financial Break Even: 100m?

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Modelled Runoff and Salinity At Catchment Outlet Base Case F0

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Modelled Salt Load At Catchment Outlet Base Case 10

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Modelled Runoff and Salinity At Catchment Outlet Single Deep Drain Connecting Existing F3b

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Modelled Salt Load At Catchment Outlet Single Deep Drain Connecting Existing 11

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Modelled Runoff and Salinity At Catchment Outlet Combination F6

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Modelled Runoff and Salinity At Catchment Outlet Combination 13

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Recommendations Use to manage freshwater flow and enable better production on valley floors. Surface water management has minimal impact on water tables. Model may under estimate benefit. Don’t put much effort in here from a salinity point of view. Replanting trees higher in the catchment has minor impact to 2030. An adaptive management strategy would be beneficial in terms of when and where actions should be triggered. Future rainfall has a significant affect on the areas with high water table and at risk. Promote and implement deeper rooted crop rotations into farming systems of the whole catchment. Deeper rooted crop rotations have a moderate affect to reduce the rate of water table rise. Plant saltland perennial crops into areas too saline for cropping. (Block on Type 1, Alleys Type 3 & Type 2) Saltland Perennial System have a significant affect on reducing area with high water tables. Model overestimates benefit. Introduce deep drains where permeability and benefit are favourable taking into account disposal issues. Deep Drains at close spacings may have a significant affect on reducing areas with high water tables. Drained water should be separated from surface water and disposal options may be required for dry years with overflow in wet years. Deep Drains adds a lot of salt to the surface waters in dry years but in wet years the salt load from the saltland delivers most of the load. Strategy Modelling Observation

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Unsaturated Zone Root Zone Evaporation Transpiration Leakage/ Recharge Rainfall

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Available Water For Plant Growth