Sources of salt

Processes that mobilise salt into the River Channel (Source: Salinity Horizons Report, Sinclair Knight Merz 2010)

Within parts of the Murray-Darling Basin, saline groundwater naturally flows into rivers. Water flowing through the river system and out to sea through the Murray Mouth is the only natural means by which salt can leave the Murray-Darling Basin. An open Murray Mouth and adequate flows downstream are therefore vital to ensuring management of salt within the River Murray system.

Dryland and irrigated farming practices have increased the movement of salt through:

• The clearance of deep-rooted native vegetation from the landscape, and its replacement with shallow-rooted crops and pastures increasing dryland groundwater recharge.
• Diversion of water from rivers for irrigation in areas adjacent to the river resulting in increased localised groundwater discharge.

 

Pre-European water table contours

This has led to rising groundwater levels bringing salt to the land surface and increasing salt inflows into the catchment through tributaries and the main river system.

2010 water table contours and irrigated areas

Impacts of Salinity

Salinity has a range of economic, environmental and social costs.

From an economic perspective, salinity can adversely affect agricultural industries through reducing irrigated crop yields, reducing plant health and ultimately killing crops. Additionally, high levels of salt can make water unfit for consumption by stock, corrode equipment and infrastructure and reduce the amount of land available for production.

River Murray ecosystems are vulnerable to the impacts of salinity with their associated flora and fauna having specific thresholds to adapt to changes in water quality. Increasing salinity levels along the South Australian River Murray, Lower Lakes and Coorong, are having a negative impact on ecosystem health.

Floodplain ecosystems are particularly vulnerable with salinity becoming concentrated in the soil profile leading to a decline in vegetation condition, reduced recruitment of key habitat species such as River Red Gums and general habitat degradation.

Seepage at Bookpurnong, photo taken December 2003

Salinity in the River Murray is also a threat to water supplies for human consumption. In an average year 60 percent of Greater Adelaide’s water supply is sourced from the River Murray. Regional centres and country towns such as Port Augusta are 100 percent dependent on the River Murray for water regardless of the climate situation as there are no other alternative sources of supply for these areas.

For drinking water purposes salinity needs to remain within a target range of 800-900 EC (consistent with the National Water Quality Management Strategy Australian Drinking Water Guidelines), with levels above 1400 EC likely to trigger augmentation of supply. Increases in salinity also increase costs to domestic users; for example, by increasing corrosion within domestic hot water services necessitating more frequent replacement.

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