South Australia to dredge Murray Mouth for first time since devastating floods

Since 2002, dredgers have removed more than 14 million cubic metres of sand from the River Murray mouth. (ABC News: Caroline Horn)

The whirring of dredges and pumping of sand will begin again today at the Murray Mouth as the South Australian government reintroduces the practice for the first time since the far-reaching floods of 2022–23.

Maritime Constructions has been contracted by SA Water to perform the works, at a cost of $30 million, to be reimbursed by the Murray-Darling Basin Authority.

The work involves manually removing built-up sand from the river mouth and adjacent channels to allow a clear passage from the river to the ocean when there is not enough natural flows.

Since 2002 the mouth has been almost permanently dredged but the dredgers were stood down for the first time in six years when floodwaters arrived in 2022.

Lake Albert dairy farmer Sam Dodd, a committee member of SA Murray Irrigators, said it was a shame that the action had to be taken because of a looming drought.

“It’s an unfortunate necessity that we need to go back to, removing sand manually by dredging so quickly after a flood,” he said.

Mr Dodd said a few dry months had accelerated a decline in conditions.

“It actually looked more like pure light water with a grey look about 12 months ago, but now it’s back to an aqua-blue colour because of all the sea water,” he said.

Dredging for a healthier river system

University of Adelaide adjunct associate professor of biological studies David Paton has dedicated much of his work as an ecologist to studying the Coorong.

He said dredging works are a preventative measure to help fish move through the system and prevent localised flooding.

“It’s much more efficient to keep on top of it and not allow too much to build up in those channels and block the mouth off,” Dr Paton said.

However, he said dredging has become critical because water across the basin was over-allocated to irrigators.

“Until this century we barely had to dredge at all,” he said.

“If you’ve got a healthy river, you shouldn’t have to dredge the mouth.

“At the present, we basically run the mouth on empty and then when we get a flood, we have a bigger impact, so we need to get the flow up on those other years to avoid dredging.”

Natural is best

Brenton Carle regularly paddles past the Murray Mouth in his job as a tourism operator for Canoe the Coorong.

He said while he wished natural flows were enough, the mouth should be kept open at any cost.

“Dredging is the lesser of two evils,” Mr Carle said.

“Keeping flows coming through gives a migration path for fish to get upstream and also creates a tidal volume inside the current, which means all the birdlife can feed.

“If the marine mouth does close over, then we have huge environmental issues in the current national park.”

Mr Carle said with thousands of birds flocking to the area after the floods, dredging is critical to retain environmental recovery.

“We’re seeing birds in huge numbers that I haven’t seen in 10 years,” he said.

The dredging announcement comes as the federal government strikes a deal with the Greens on the Murray-Darling Basin plan, which could see more than 700 gigalitres of farming water allocated to the environment through buybacks.

South Australian Minister for Climate, Environment and Water Susan Close said dredging is a medium-term solution to improve the health of the basin.

“It will be one of the indicators that we have been successful with the [Murray-Darling Basin] plan if we could have some months or years where dredging was not operating,” she said.