Saline water disposal options in the Murray Basin

Large volumes of saline water are produced in the Murray Basin, principally from naturally occurring saline groundwater discharge to rivers and lakes and discharge induced by land use change, and subsurface drainage effluent from irrigation areas. Disposal of this saline water is fundamental to salinity and land management strategies. It has traditionally involved either River Murray or non-River Murray options, and should preferably include elements of both. Reuse of saline water is probably the major disposal technique in irrigation regions. Total reuse is limited by eventual soil degradation and groundwater salinisation; maintaining the appropriate salt balance in the root zone is essential for long term viability. River Murray options are either as uncontrolled outflow (mostly non-point saline inflows) or controlled outflow (e.g. from groundwater pumping, flushing of evaporation basins). Controlled outflow is limited by salt load, time of outfall and frequency of floods. Dilution flows to reduce river salinity are generally not economic. Non-River Murray options are evaporation basins (with or without salt harvesting), aquifer disposal, desalinisation and pipelines to the sea.  Use of River Murray lagoons and backwaters to dispose of irrigation drainage waters often leads to severe environmental costs.  Major existing and planned evaporation basins are reviewed. Full engineering, hydrogeological and environmental investigations should be encouraged; poorly sited evaporation basins should be evaluated and their use phased out if unacceptable. Detailed consideration of short and long term effects of leakage is essential. Most shallow disposal bores cause significant adverse effects by displacing highly saline groundwater to the Murray River. This practice should be phased out. The use of deep disposal bores requires detailed investigations, and is unlikely to be extensive. A good understanding of the rate of transmission of pressure and salt in the aquifer is critical in aquifer disposal. Desalination is very expensive, and not economic or practical. Pipelines to the sea have been shown to be highly uneconomic, although further analysis may favour this option in the long term. All disposal options are economically evaluated and contrasted. A key factor in the economics of disposal is salinity of the water. For low-salinity water, reuse and controlled outfall (often with holding basins) via the River Murray are clearly most economic. As salinity increases, evaporation basins become more economic. Most other options (except for well located shallow aquifer injection bores) are much more expensive.  Public perceptions of feasible disposal options are often poor.  Environmental effects can be grouped into those with short term costs to the ecosystem and those with long term hydrogeological consequences. Investigation and evaluation of environmental effects of the major salt disposal options (principally evaporation basins) are now becoming key factors in the choice of the preferred option. An effective saline water disposal strategy for the Murray Basin is one of the highest priorities in salinity management. Economic and environmentally acceptable options exist now, although they may be politically difficult at the local scale. More consideration of how to manage the naturally occurring discharge areas of the Mallee may have significant long term benefits. Best use should be made of all technically and environmentally feasible disposal sites.

Tags: Earth Sciences, GA Publication, Journal, NSW, Published_External, SA, VIC
Organization: Geoscience Australia Data