Salinity

Managing salinity for a healthy River Murray

Managing salinity in the River Murray is vital for the health and protection of South Australia’s drinking water, irrigated crops and river corridor environment.

Salt is a natural part of the Murray-Darling Basin system and as groundwater discharges to the River Murray, it delivers large amounts of salt to the river channel. While this is a natural process, the movement of salt into the river has accelerated due to the clearance of native vegetation and irrigation.

Drainage below irrigation areas can build up on top of regional groundwater and increases the discharge of salt into the river and floodplains. Drainage is a necessary requirement of irrigated agriculture as it prevents the buildup of salt in the soil profile around the root zone of crops. Groundwater mounds grew significantly in the 1970s to early 1990’s due to excessive drainage under irrigation areas when irrigation technology was not as advanced as it is today. Significantly less water is required to flush salt from the root zone of crops under modern horticultural systems.

The exit point for salt from the Murray-Darling Basin is through the Murray Mouth to the Southern Ocean at Goolwa and regular flushing is important to maintain water quality and ecosystem health.

High salinity can affect aquatic ecosystems in the Murray-Darling Basin which are vulnerable to the impacts of salinity. Many plants and animals have specific thresholds beyond which changes in water quality have a detrimental effect. Salt accumulation in the soil profile of floodplains results in habitat degradation by causing the death of key floodplain species such as mature river red gums and black box. Salinity also reduces the ability of these species to regenerate which worsens the problem.

High salinity can also have economic implications by reducing irrigated crop yields, reducing plant health and ultimately damaging crops. High levels of salt can also make water unfit for consumption by stock, corrode infrastructure and reduce the amount of land available for production. All these impacts negatively affect agricultural industries.

Drinking water supplies can be threatened by high salinity. In an average year, 60 per cent of Adelaide’s water supply is sourced from the River Murray. Regional centres and country towns such as Port Augusta are 100 per cent dependent on the River Murray for water, regardless of climatic situation, as currently there are no suitable alternative sources.

The movement of salt resulting from the clearance of native vegetation and irrigation to the River Murray may take decades to occur. This means that salinity management must consider and plan for the impacts well into the future. South Australia works with the other Basin jurisdictions to manage salinity under the Basin Salinity Management 2030 (BSM 2030) Strategy and the Murray-Darling Basin Agreement.

All Basin states are responsible to ensure that their overall impact on the river is neutral or positive. Actions which increase salt in the River Murray must be offset with actions that decrease salt. The need to achieve this balance is reflected in South Australian Government policies and programs that support irrigated agriculture while also minimising and offsetting additional salt entering the River Murray.

Key elements of salinity management include:

• improvements to irrigation efficiency by South Australian irrigators;
• salt interception schemes which, across the Basin, divert on average, about 400,000 tonnes of salt per year away from the river;
• State policies and programs like the salinity zoning policy; and
• returning additional environmental water to the River under the Basin Plan.

For more information on Basin wide salinity management please visit the MDBA website.