As part of the options assessment process, complementary options have also been assessed, including groundwater management.
The Chowilla floodplain has long been recognised as a major contributor of salt to the River Murray. In addition, artificially high saline groundwater levels and increased rate of salt accumulation in the floodplain soils are contributing to the ecological decline of the Chowilla Icon Site. It is therefore considered necessary for the long-term management needs of the Chowilla floodplain to continue to investigate the role and application of groundwater management in dealing holistically with the ecological needs of the floodplain. Groundwater management may provide significant floodplain benefit to areas beyond the influence of surface water management. Much broader floodplain protection may also be possible through groundwater management; particularly during times when proposed new surface water infrastructure will not be in operation.
Saline groundwater disposal investigations are continuing to determine the viability of deep aquifer injection; where water is pumped from a shallow unconfined aquifer (Monomon Sands aquifer) and re-injected into a much deeper confined aquifer (Renmark Group aquifer) 450m underground. Deep aquifer injection would be a preferable form of disposal if proven viable as it minimises the footprint on the landscape, results in less adverse environmental consequences, and may have a construction cost significantly less than surface water disposal basins which involve lengthy pipelines.
A trial well has been drilled to approximately 450m near Werta Wert on the Chowilla floodplain which has provided important information in regards to the soil profile and water chemistry. Water and soil samples have been analysed to determine what chemical, biological and physical reactions may arise upon injection of the intercepted saline groundwater into the deeper aquifer. It is expected, pending favorable results from the trial well, that an injection trial will occur in 2009-10.
Rammers, N. Hill T. Yan W. (2005) Regional Disposal Strategy – Renmark Group Deep Injection: Phase 1 Desktop Study Knowledge and Information Division DWLBC (4.3Mb)
Jolly, I.D. McEwan, K.L. and Holland, K.L. (2008) A review of groundwater–surface water interactions in arid/semi-arid wetlands and the consequences of salinity for wetland ecology. CSIRO Land and Water (524kb)
Overton, I.C. and Jolly, I.D. (2003). Investigation of Floodplain and Groundwater Interactions at Chowilla. CSIRO and DWLBC