How the river works

Flows along the River Murray are managed using a series of locks, weirs, barrages and storages to support navigation and irrigation, as well as store water for use. These structures are also used to control flows and water levels to support ecosystems along the river, Lower Lakes, Murray Mouth and Coorong.

The river, wetlands and floodplains

The River Murray is part of the Murray-Darling Basin, which drains about 14 per cent of Australia’s land area. Water from the Murrumbidgee and Darling rivers as well as a vast network of tributaries, creeks and watercourses all flow into the River Murray.

Naturally, flows down the River Murray would vary, with melting snows in the Australian Alps in spring producing high flows compared to summertime when flows would be low. This variation would result in wetlands and floodplains experiencing wet and dry cycles between seasons and years.

River flows have been managed to maintain relatively stable water levels in the river for navigation and irrigation. This has led to serious impacts on the ecosystems that rely on these cycles.

As part of implementing the Basin Plan, work is underway to replicate more natural variation in water levels using weirs, barrages and environmental regulators. The construction of environmental regulators will enable greater control of flows and water levels on the floodplain and in wetlands.

Weir pool manipulations involve raising or lowering the water level in the upstream weir pool to wet or dry the floodplain and wetlands. A number of these manipulations have already been undertaken, with really good environmental outcomes. As a result, these manipulations will become part of normal river operations.

The Murray-Darling Basin Authority has also developed a basin-wide strategy to manage constraints such as bridges or river practices that restrict the amount of water that can be delivered to floodplains, to allow higher flows down the river.

Find out more about environmental projects to improve the river, wetlands and floodplains.

The Lower Lakes

Water quality and levels in Lake Alexandrina and Lake Albert are mainly dependent on flows into the lakes from the River Murray and out through the Goolwa Barrages, with wind playing a large part in transferring water between the lakes.

During low flows, the barrages can create a barrier to prevent seawater from entering the freshwater lakes. However, it is important that enough water flows out through the barrages to flush salt and other pollutants from the lakes.

Before the Millennium drought, the lakes were maintained at a relatively stable water level. Managing the river in a way that creates more variable flows will support a healthier ecosystem in the lakes, with greater resilience to cope with dry times. It will also reduce the risk of exposed acid sulfate soils in future droughts.

A range of environmental projects are underway in the Lower Lakes.

The Murray Mouth

The Murray Mouth is the only site where salt, silt, nutrients and other contaminants can be flushed from the entire Murray-Darling Basin out to sea. The barrages are used to coordinate releases of water to flush pollutants from the system and prevent sea water from entering the freshwater Lower Lakes during times of low river flows.

During dry times, if enough water does not flow out of the Murray Mouth to prevent silt building up, dredging may be needed to keep the mouth open and the river system connected to the ocean.

The Coorong

Flows through the Goolwa Barrages and Murray Mouth are critical for maintaining a healthy Coorong, as they influence salinity levels in the northern and southern lagoons.

When there are high river flows through the barrages, freshwater enters the Northern Lagoon and freshens the Coorong. When there are low flows, sea water enters the Northern Lagoon through the Murray Mouth.

Historically, freshwater from the South-East of South Australia played an important role in maintaining salinity levels in the Southern Lagoon. However, for many decades drainage schemes have redirected this water to the sea so the land could be used for agriculture. This caused salinity in the Southern Lagoon to rise.

Without enough fresh water entering the Coorong via the barrages and South-East, evaporation concentrates the amount of salt in the lagoons and they can become too saline for many plants and animals to survive.

Projects are underway, including restoring flows from the South-East to the Coorong, to improve the health of this precious site.