We need to talk about the sand slug

The slug was named and shamed as the culprit behind the decreasing flow capacity in the choke and its sand — a “coarse sandy sediment” — was deemed to be very different from the surrounding river banks.

“So it’s pretty clear that it’s not caused by local erosion,” MDBA river management executive director Andrew Reynolds said in the February reveal.

“To understand where it came from and how it got here, we engaged independent experts.”

After two studies the MDBA came to the conclusion the slug was mobilised by gold-mining and land clearing done in the 19th and early 20th centuries and took this story to the media.

For many people who live and work along the Murray River, this was a hard hypothesis to swallow.

Koondrook resident and deputy chair of Speak Up 4 Water Lloyd Polkinghorne is one of the many who can’t accept the gold mining origins.

“There were a few concerns when I first read the MDBA report, they failed to mention a lot of things which could have caused the sand,” Mr Polkinghorne said.

“There is definitely sand there, but the gold mining happened the best part of 80 years ago, meanwhile our beaches and banks are being eroded right now.”

The third generation irrigator said he was “staggered” a Federal Government authority had failed to mention the human-driven, unnatural flows of water down the Murray.

“It’s almost like they deliberately skirt around the issues which point the finger at them,” he said.

“If they aren’t going to be honest, how are we ever going to address and fix these issues?”

When Country News told the MDBA about the disbelief among locals the authority said they were as surprised as everyone else to learn one of "the most likely sources" was gold mining.

They did admit de-snagging, land use changes and river regulation leading to channel widening were "possible contributors".

MDBA River Murray system review director Ben Dyer said regardless of where the slug came from, it still needed to be managed.

“Our focus is on managing the issue and we appreciate the insights and useful contributions provided by the community,” Dr Dyer said.

“In recent months we've held 35 presentations where we've discussed the findings with communities along the length of the River Murray.”

Mr Dyer also assured there were no plans to bypass the choke with a pipeline.

Cobram resident Mark Bugge said the situation would be hilarious if it wasn’t so serious.

“It’s hard to imagine that’s the best story they could come up with,” Mr Bugge said.

“We live in Cobram and spend a lot of time on the river and the destruction of the system due to the MDBA’s environmental flows is enormous.”

Mr Bugge is adamant the sand slug has been created by environmental flows put down the Murray by the MDBA.

“If they say the sand is too coarse to be local, well that might be true for the banks but the river beaches are all made from coarse sand,” he said.

“There are sand slugs all around Cobram and it’s from the beaches being washed away.”

When the two studies commissioned by the MDBA are read, neither points to gold mining as the leading cause of the slug — not even the study led by James Grove, an expert in how rivers are changed by mining.

Dr Grove's Barmah Choke study considered everything from water skiing to carp, to the construction of weirs in the 1919-1939 period as possible causes.

In the study’s conclusion the panel simply stated: “this work suggest that the excess sediment is predominantly a result of post-European disturbance”.

When contacted by Country News, Dr Grove said the report remained a draft and data still needed to be collected on the volume, size and chemistry of the bed sediment.

“Despite lots of research it is incredibly difficult to point the finger at a single overall cause, or culprit,” Dr Grove said.

He said current data "certainly suggests" most of the sand came from historical activity, as current rates of sand delivery appear much lower.

The MDBA plans to report back to the community groups they've engaged later this year.