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Why is erosion occurring in the River Murray and particularly through the Barmah Choke?

Erosion of the riverbank has always been a feature of the River Murray.

In recent times however, increased erosion has been a particular concern in the stretch of river between Albury and Swan Hill, including the narrow section known as the Barmah Choke.

This page explains

  • What causes erosion in the River Murray?
  • Why is erosion becoming worse around the Barmah Choke?
  • Is the Basin Plan to blame for erosion?
  • How is the MDBA managing this situation?

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Erosion in the River Murray

Erosion of the riverbank is a natural process but in a river like the Murray, over time people have adjusted the natural pattern of flow to meet the needs of industries and towns, which can increase erosion and change the river formation.

A range of factors can influence erosion, including:

  • sending large volumes of irrigation water through the river in summer when flows would be naturally lower and riverbanks drier. Making dry riverbanks wet in summer can cause more erosion than when the banks are already wet in winter
  • the increased popularity of power-boating, which can create a wave action that washes against the riverbank
  • keeping the river at a constant level so that concentrated wave action eats into the riverbank
  • the use of land close to river, which compromises the riverbank due to clearing of vegetation, modification or building on the bank and intensive access by livestock
  • the removal of large snags over time, which causes the river to run faster and in turn cause greater erosion.

Questions you might have

“Why is erosion becoming worse around the Barmah Choke?”

Being a naturally narrow section of river, the Barmah Choke restricts the volume of water that can flow through. In the past 20 years the capacity of the Barmah Choke channel has further reduced by 20 per cent. This has required river operators to make greater use of other ways to get water through, such as using the Mulwala Canal.

In 2018 the MDBA did a full survey of the reach and found a large amount of sand on the riverbed, which in some cases is 4 metres deep. We are currently examining how it got there.

The sand is not a result of bank erosion, but it does contribute to bank erosion. The sand has made this part of the river shallower, so flows are eroding the riverbanks to make up this space, which means the Barmah Choke is now wider than it used to be.

The reduction in channel capacity due to the sand means the river runs full for longer through summer to get the same volume of water downstream compared with 30 years ago.

“Is the Basin Plan to blame for erosion in the River Murray?”

No. The Basin Plan is designed to restore some of the natural features to the river system, including getting more water up onto floodplains and wetlands in spring to support plants and animals.

Allowing more water to reach the floodplains and wetlands outside the peak irrigation period in summer does not increase erosion.

Despite many changes in the River Murray over the past 20 years, there has been no additional water through the Barmah Choke over the summer period, in part due to the Barmah Choke trade rule.

If anything, the transfer of some irrigation licences to environmental use in winter and spring has resulted in less pressure on the choke.

“How is the MDBA managing erosion in the River Murray?”

The MDBA and Basin state governments are investigating the causes of erosion where it’s greater than usual, and how we might bring it back to more natural rates.

The badly eroded stretch between Hume Dam and Yarrawonga has slowly improved since the late 1990s thanks to lower flows managed through the river and a program to the revive the riverbanks.

The Australian Government and Basin state governments are investing $500,000 to start a new river works program between Yarrawonga and Torrumbarry, which includes the Barmah Choke, building on the successful Hume to Yarrawonga program.

Works may include placement of timber logs, revegetation and fencing, and will focus on high priority sites upstream from the choke where flow is most likely to break out of the riverbanks.

The MDBA continues to investigate the large amount of sand in the choke to understand how fast it is moving and what further impacts on the choke are likely into the future.

Updated: 30 Nov 2020