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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 |
Lake Warden Location: South coast of Western Australia, north of Esperance. Area: 1570 km2. Rainfall: 670 mm on the coast decreasing sharply to 350 mm in the north. Land use Cereal cropping, grazing on annual pastures. References: Short et al. (2001) Salinity Lake Warden catchment contains both primary (natural Quaternary salt lakes) and secondary salinisation (dryland salinity as a result of land-use changes). Rising pressures and water levels promote groundwater discharge to topographically low-lying areas, and to the extensive system of palaeodrainage lines and lakes. While discharge from the surface aquifers is not usually very saline, constant evaporative concentration creates a surface salinity problem. Discharging groundwaters from the deeper aquifer are already saline and exacerbate lake and stream salinity. Groundwater systems The Lake Warden system is composed primarily of two aquifers: local-scale flows in unconfined and perched sand and siltstone aquifers at the surface, and intermediate- to regional-scale flows in saline, semi-confined to confined aquifers within weathered basement rocks. The recharge area for the deeper aquifer is along a ridge of outcropping highly weathered and fractured basement rock, while the surface aquifer is recharged directly by rainfall. Prior to clearing, the surficial sediments probably did not function as an aquifer, while the underlying bedrock aquifer may not have been fully integrated because of the highly uneven basement topography. Management Under present land use conditions and current recharge rates, up to 45% of the within Lake Warden land area is at risk of salinisation from the surface aquifer. The topographically lower areas will mainly be affected. A 50% reduction in recharge would not substantially alter the area at risk of shallow water tables, but would slow the rate of groundwater rise and reduce the volume of saline discharge to streams and lakes. A 90% recharge reduction would stabilise water levels and reduce the area at risk to less than 10%. With respect to the deep aquifer, a 50% recharge reduction would substantially reduce the rate of groundwater rise in this system and would halve the area at risk by the year 2100. A 90% reduction would, again, stabilise water levels and reduce the area at risk to around 5%. To achieve a recharge reduction of 50%, up to three-quarters of the entire catchment would need to be converted to either perennial pastures or native vegetation, although the establishment and management of some pastures would be difficult due to harsh growing conditions. The most appropriate land-use options are probably those already in place in Lake Warden, including "living with salt", surface drains, and the introduction of salt-tolerant vegetation where grazing and cropping are inappropriate. |
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| design & production by Talkin' Technical Communications | last updated: April 2002 |