Salinity reduction

Reduction of salinity in rivers and streams has been tackled by two main methods -management of reservoirs and management of flows in, and the inflows to rivers. In the first category, salinity in a reservoir on the Collie River in Western Australia is controlled by releasing through scouring off-takes the more dense saline water flowing beneath less saline water in the reservoir, before vertical mixing occurs. The Menindee Lakes Scheme in New South Wales is managed to minimise evaporation loss and so reduce salinity increase by keeping the surface area of the lakes at a minimum during the periods of high evaporation loss.

In the second category, the largest and most important example of stream management to reduce salinity is in the operation of the River Murray system in three States. The methods used include upstream reservoir releases, the interception of saline drainage waters and the diversion of saline tributaries, with disposal to evaporation basins. The design of interception and diversion works and the associated investigation of possible adverse effects on adjoining land and groundwater are complex and necessitate a comprehensive technological approach through a wide range of disciplines. The subsequent flow management procedures are equally complex.

Groundwater salinity may increase after a period of pumping due to leakage from a hydraulically connected saline aquifer, or the movement of a fresh-salt water interface within the pumped aquifer. Sea-water intrusion has been controlled by artificial recharge, control of pumping and the importation of surface water to supplement or replace local groundwater.

Salinity of surface water and groundwater remains a serious problem in many parts of Australia, and increasing technological effort and innovation will be required to effectively control and reduce it.

Australian Academy of Technological Sciences and Engineering