Salt - a natural feature of the river scene

The Murray-Darling Basin is a naturally saline environment. The salts come from the weathering of the rocks, from groundwater and from salt deposited over many thousands of years by precipitation (cyclic salt).

There is also a clear relationship betwenn river flow and salinity levels, the lower the flow the higher the level of slainty. Flows are affected by natural conditions, but river regulation can influence the number of perios of very low flows and hence of very high salinty levels.

When the explorer Charles Sturt discovered the Darling River in the dry season of 1829, he found the water too salty to drink.

The most comprehensive information available on river water salinity is for the River Murray. Quite apart from variations over time that are related to river flow, there is a very marked downstream increase in salinity levels.

There are a number of reasons for this, both natural and as a result of human activities. Evaporation from the generally slow-moving river is one factor. Downstream of Euston, there are relatively steady inflows of saline groundwater. Such inflows are particularly significant in the South Autsralian section of the river. These natural processes have been exacerbated by drainage flows from irrigation areas and rising groundwater levels due to irrigation.

More recently, problems have emerged in the much more extensive areas of dryland farming, with rising watertables bringing saline groundwater both close to and to the surface, resulting in land salinisation. Especially at times of low or base flows, shallow saline watertables can contribute most of the water in some tributary streams.