The River Murray flows for 650 km of its total length of 2,600 km through South Australia, where it meanders in an incised channel across a floodplain 1 to 10 km wide, and is underlain by 500 m of predominantly Tertiary bryozoal limestone and sand of the Murray basin. Natural groundwater in the basin commonly has a salinity of 30,000 mg/l.

Groundwater gradients are relatively flat (0.25 m/km) and flow is generally toward the river and reflects the recharge from the higher country of the basin margins, about 250,000 sq km in area. The Tertiary sediments form aquifers of moderate transmissivity (200 to 500 cu m/day/m). Some inflows of saline groundwater are present naturally through the river bed but most inflows are the result of man-made structures and practices.

The waters of the River Murray are vitally important to South Australia for domestic supplies and for irrigation of citrus orchards along the river banks. This irrigation has resulted in the buildup of groundwater mounds which are relieved by a tile drainage system. Drainage water, now of increased salinity, is pumped to evaporation basins on the floodplain close to the river. The raised water levels in these basins and also in the river weir system have increased inflows of saline groundwater to the river. In drought years these salt accessions can make the water unsuitable for irrigation.

Piezometers have been established to monitor the regional groundwater regime, the irrigation groundwater mounds, and the effect of raised water levels in storage basins. The mechanisms of leakage from these basins have been studied to determine remedial measures necessary to intercept and remove saline-groundwater underflow. Alternative evaporation basins sited

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on impermeable clay have been located away from the river floodplain. Pumping schemes for the transport of drainage water to the basins are proposed.

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