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Natural desalination: How this South Australian creek became less salty

Across Australia, there’s a problem lurking just beneath the surface that costs the nation about $305 million per year in the Murray-Darling Basin alone: salt.

Dryland salinity, which happens when salt that has built up underground over thousands of years is discharged into surface water, has been recognised as an issue in Australia since the 1920s.  

It generally occurs where deep-rooted native vegetation like gum trees have been cleared and replaced with short-rooted agricultural crops, as this allows more rainfall to get into the groundwater. More rainfall raises the water table, which dissolves the salt found in the rocks and soil above.

This increase in salt can have a devastating effect on both the environment and the economy, making it impossible for farmers to grow crops or use the water to feed livestock.

Now, new research from Flinders University in South Australia has shown it might be possible for salt-affected areas to remediate themselves.

PhD graduate Tom Anderson led the study of Scott Creek, a stream in a deforested Adelaide Hills catchment. He looked at 28 years of flow and salinity data from the creek and found salt exported to the surface decreased by an average of 6.4 tonnes per year.

The creek is in an area with high rainfall, and Anderson said the combination of time and volume of water flow was helping to flush salt from the water table. If the trend continues, the stream could reach a lower salinity level by 2090.

This would be within 300 years of the area being deforested, which is faster than expected.

Anderson said the Scott Creek study was the first to reveal a statistically significant trend showing a stream returning to salt equilibrium.

“Evidence of a catchment returning to the original salinity levels before European settlement is exciting news for farmers, as southern Australia continues to face great hardships from salinity issues,” he said.

“Now it’s time to go into other areas to apply the same testing methodology in areas of lower rainfall and subject to more extreme salinity damage.

“Fortunately for the interest of future studies, many rivers throughout South Australia and around the world contain such data.”