MDBA ponders fix for sand build-up blocking flow

Dredging has been considered one option to fix a sand build-up or "sand slug" in the Murray River. It is estimated to be bigger than a dozen Melbourne Cricket Grounds.

Dredging has been considered one option to fix a sand build-up or “sand slug” in the Murray River. It is estimated to be bigger than a dozen Melbourne Cricket Grounds.

The Murray Darling Basin Authority (MDBA) has released a preliminary scoping report outlining six ways to address the accumulation of sand at the Barmah Choke on the New South Wales–Victorian border.

The choke is a narrow section of the river where more than 2,000 megalitres per day have reduced water capacity since the 1980s.

The MDBA’s executive director of river management Andrew Reynolds said the sand was from land clearing and mining activities.

He said that over the years, the sand had washed into the river, moved downstream and built up at the choke.

“With that reduction in capacity, the river runs full for longer each year. As a result, we see the erosion of river banks,” Reynolds said.

It meant less water could pass through the river, which Reynolds said has impacted downstream communities.

Dredging a possible solution for sand build-up

Removing sand from the narrow section of the river was one option on the table.

An estimated 20 million cubic metres of sand has settled on the riverbed between the Yarrawonga Weir and Picnic Point. It would fill the Melbourne Cricket Ground (MCG) 13 times.

The Murray River’s Barmah Choke

“Removing it all is certainly not possible. However, removing it at key locations that might impact the flow capacity of the river could help.”

The MDBA was also considering a plan to stabilise the river banks to prevent erosion and the release of water to the Murray River via the Murrumbidgee River through the Snowy Hydro scheme.

Reynolds said the options would be taken to state and federal governments at the end of the year.

“We think the solution is likely to be a combination of those,” he said.

No easy fix for sand build-up

Nick Bond, the director of the Centre for Freshwater Ecosystems at La Trobe University, has researched sand slugs.

He said they were a widespread issue that often occurred in places with a history of mining or major land-use change.

“The volumes of sand involved are often huge. It means the most obvious options like removing the sand can often be quite impractical,” said Bond.

Bond said the sand slug at the Barmah Choke would “almost certainly” need to be addressed using several options.

He said dredging could result in unintended consequences.

“The options being considered are obviously not to try to remove the sand slug in total necessarily, but to simply try and increase the current channel capacity,” Bond said.

“When you remove sediment from a river channel, it can exacerbate local erosion.

“When you start to dredge, those holes that are created can fill in quite quickly, but as that happens effectively, the hole that’s been created can move upstream.”

Bond said the complexities of the Murray River and the sheer volume of water that passed through it increased the difficulty of addressing the issue.

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