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Case Studies 1. Kyeamba Creek 2. Liverpool Plains 3. Billabong Creek 4. Wanilla 5. Axe Creek 6. South Loddon Plains 7. Kamarooka 8. Lake Warden 9. Brymaroo Printing help |
Wanilla Location: Eyre Peninsula SA, 40 km northwest of Port Lincoln. Area: 180 km2. Rainfall: 520 mm. Land use Cereal cropping and grazing, 10% native forest reserves. Reference: Stauffacher et al. (2000) Salinity Primary salinity is evident in the region with nearby water features such as Salt Creek and Salt Swamp and large salt lakes to the north. Extensive tree clearing in the early 1950s has led to increased saline land to a current level of 8%. Groundwater systems Both local and intermediate groundwater systems lead to salinity. In the steep eastern part of the catchment, many local flow cells overlie the fractured rock and ultimately discharge into the local stream network. In the flatter western portion of the catchment, the intermediate-scale sand and clay alluvial aquifer has a low permeability and low hydraulic gradient and hence there is little lateral movement of groundwater. This means that the aquifer fills and empties with the seasonal pattern of rainfall and evaporation. The current recharge is estimated to be 20 mm per year on average compared with less than 1 mm per year under pristine native cover. Management Modelling shows that the low aquifer transmissivity can lead to some shallow water tables with only 1 mm of annual recharge. This is the cause of primary salinity in the catchment and shows why any increase in recharge will exacerbate salinity. Modelling of agronomic practices indicates that recharge rates could be reduced by up to 50% through the conversion of crops to lucerne. However, even with this reduction in recharge over the whole catchment, areas of shallow water levels are not predicted to decrease in the next 20 to 50 years. Areas will only decrease with a reduction in recharge of 70-90%, only feasible with substantial areas of afforestation. This suggests that profitable vegetation management will not lead to decreased areas of shallow water tables. Pumping shallow groundwater is also not realistic given the low transmissivity of the aquifer. Living with salinity is already happening at Wanilla, as the alluvial aquifer is effectively full. Any further improvements that can be made, (e.g. construction of drains), will help maintain this situation. |
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| design & production by Talkin' Technical Communications | last updated: April 2002 |