Salinity

Managing salinity is one of the biggest challenges in the Murray–Darling Basin. If it’s not properly managed, salinity degrades water quality, hinders plant growth, reduces biodiversity and agricultural productivity, and means poor quality water is available for human consumption.

On this page:

• Why salinity is a problem
• Salinity and where it comes from
• The impact of salinity
• How salt is removed from the system
• What the MDBA is doing

Why salinity can become problem

Some salt in fresh water and soil is normal, and can be tolerated by the plants and animals in the Basin. But the concentration of salt in the soil and water can change, and long periods of high salinity can harm the natural environment as well as crops and livestock.

For example, during the Millennium drought (from 2001 to 2009), unique environments across the Basin were severely damaged by extreme levels of salt in the water. Water was too saline to be used for drinking or watering animals and crops.

Salinity has improved but needs ongoing management

From the 1960s to 1980s, salinity increasingly affected farmers, wildlife and the environment in the Basin. In 1988, Basin state governments and Australian Government together developed the Salinity and Drainage Strategy to address salinity and its causes.

Since that time, a series of salinity management strategies have been implemented and have been very successful in reducing salinity levels, so it's easy to assume that the salinity problem has been 'solved'. However, salinity requires ongoing management. The Murray–Darling Basin Authority (MDBA), Basin state governments and other water managers, undertake salinity management activities and carefully monitor salinity levels to prevent it from becoming a significant problem again.

Salinity and where it comes from

'Salinity' refers to the concentration of salt in the water or soil. The water in the river systems of the Murray–Darling Basin naturally carries salt from the ground and surface water sources as it flows from southern Queensland and the eastern highlands of New South Wales and Victoria to South Australia. The Basin has a naturally salty landscape, particularly in the southern and western parts, resulting from millions of years of rainfall. Salt has become part of the landscape from wind and dust, the natural breakdown of rocks and ancient ocean sediments. Land in some parts of the southern Basin, was part ocean, meaning salt is locked in groundwater. This salt eventually finds its way into waterways and only very slowly returns to the ocean via the Basin's rivers.

Historically, prior to European style land use, the salt that built up in the rivers would get flushed out the mouth of the River Murray. But now people use far more water, leaving much less to flow out to sea. This can cause salinity to rise to dangerous levels in some parts of the Basin.

Reasons that salinity rises

• Land clearing, irrigation, agriculture, and urban and industrial uses introduce salt into the river.
• Less water flowing out of the Murray mouth means less salt can leave the rivers.
• Drought – during prolonged hot, dry conditions there is even less water to dilute the salt entering the river system, meaning that salinity levels rise even higher.

How salinity is measured

Salinity is measured in EC (electrical conductivity) – the unit of measure used across the Basin is generally microSiemens per centimetre (μS/cm). A salinity level below 800 μS/cm is considered low salinity, however, plant and animal tolerances can range significantly with plant levels generally up to an extreme of 5,800 μS/cm (some plants and animals can cope with higher levels of salinity). By comparison, the salinity of seawater varies although 54,000 μS/cm is an approximate value.

Problems caused by salinity

The Basin is a single, interconnected system of rivers. Given everything is connected, a problem that starts in one area can affect the health of plants, animals and communities elsewhere.

If the levels of salt in the water were allowed to keep rising, the water would soon become too salty. It would start to kill the plants and animals that inhabit the rivers and their surroundings and permanently damage the environment. Farmers would be unable to water their crops, and the water would become unsuitable for human and animal consumption.

We must closely monitor and carefully manage salinity levels in the Basin rivers to ensure that they are suitable for people, plants and animals.

What can be done to manage salinity levels in the Basin

The most effective way to manage salinity is to prevent it from entering the rivers in the first place.

This is done by:

• improving farming and irrigation practices to prevent extra salt from seeping or washing into the rivers
• operating salt interception schemes

Salt interception schemes involve pumps that divert groundwater away from rivers and into evaporating basins. Fourteen of these have been installed at locations in the Basin where water in the soil (groundwater) is particularly high in salt. Commercial operators harvest salt at some of these basins.

Releasing water into the ocean

It is not possible to prevent all salt from entering the Basin river system, but once salt has entered the water, it can leave the river system via the mouth of the River Murray. This is the only way for salt to naturally leave the system, which is why it's so important to keep the Murray Mouth open.

Joint projects to reduce salinity in the Basin

The MDBA and Basin state governments work together to manage salinity in the Basin.

• The Basin salinity management strategies (currently the Basin Salinity Management 2030 strategy) were developed to ensure that salinity levels are appropriate for the protection of economic, environmental, cultural and social values. The current strategy is being implemented together by the Australian Government and Basin state governments. This strategy will remain in place until 2030.
• The Basin Plan Water Quality and Salinity Management Plan was created to improve water quality and manage salinity in the Basin. It builds on existing rules and sets objectives and targets to improve the water in the Basin so water is good enough for environmental, social, economic and cultural uses.
• The MDBA keeps a register of salinity 'credits' and 'debits' to keep track of actions that increase salinity in the river system and how they are offset by actions to decrease river salinity.