Basin at crisis point: 2022-23 floods choked the Murray River with sand

Irrigators are facing water rationing after it was revealed the 2022-23 floods washed 14 times more sand into the Barmah choke. See the maps.

The 2022-23 floods cut the Barmah-Millewa chokes capacity to a critical low, as the river eats away at 24 high risk breakout points that have not been repaired.

The 2022-23 floods more than doubled the amount of sand washed into the Murray River’s Barmah-Millewa choke’s narrowest point, cutting its daily flow capacity from 9200 megalitres to just 8300ML and dramatically increasing the risk of summer water rationing for irrigators.

The latest study by the Streamology consultancy of the Murray River between Gulpa and Cutting Creeks found “the total net volume of sand added to the 9km sub-reach, because of the 2022-23 flood year, was almost 14 times the amount for previous three years (2019-22)”.

“The bed level increases over the flood year align with the latest flow gauging which measured a reduction in the flow capacity through the Barmah-Millewa to 8300 ML/day under regulated flow conditions.”

Maps showing the absolute (left) and average (right) sand thickness increase that occurred in the area downstream of Gulpa Creek over the 2022-23 flood period. Red shades denote sand thickness decreases, blue shades denote increases. Source: MDBA commissioned Streamology report.

Previous studies of the choke commissioned by the Murray Darling Basin Authority found during the peak of summer, more than 8300ML/day needed to be pushed through the choke to meet irrigators’ and South Australia’s water needs.

The Alluvium consultancy’s Barmah-Millewa Feasibility Study of December 2022 found that “over the past decade, around 975GL on average has been delivered through the Barmah-Millewa Reach during summer when irrigation demands are highest”.

“Around 83 GL (or 8 per cent) of these flows have historically been delivered at above 8300 ML/day through the reach,” it found.

Alluvium warned “there is an inherent risk that there will be times when there is not enough capacity in the river to deliver water to irrigators in the time required, meaning that water orders may be rationed or not filled”.

The 2022 study also identified 24 sites along the choke’s riverbank that urgently needed reinforcement to prevent the river breaking out into the forest, which a leading consultant to the MDBA said had still not been undertaken.

Alluvium’s report stated that if nothing was done, there was a real chance of a breakout that would lead to a further 500 ML/day reduction in flow rates.

Any shortfall in the midst of summer risks the $2.4 billion annual harvest of almonds, tablegrape and winegrapes, on which the Sunraysia, Riverland and other irrigation communities depend.

But despite numerous reports over the past decade warning the choke needed to be dredged or bypasses upgraded, neither the federal or basin state governments have done anything more than announce more studies.

National Irrigators’ Council chair Jeremy Morton said rather than taking action, federal and Basin state governments just kept kicking the can down the road.

The MDBA responded to questions on the issue by stating: “At the Murray–Darling Basin Ministerial Council in February 2023, ministers agreed to progress a preferred suite of options identified in the Barmah-Millewa Feasibility Study to the next phase of development.

“A total of $2.35 million was committed for the 2023-24 financial year of which $587,500 was contributed from the Commonwealth”.

Meanwhile Federal Water Minister Tanya Plibersek is set to spend at least $613 million on buying another 100GL towards boosting the Basin’s environmental flows in 2024-25, on top of the 2075GL already recovered.

Ms Plibersek will also lift the number of her Departmental staff working on boosting basin flows from the current 337 to 521 in the new financial year.

Opposition Water spokeswoman Perin Davey said “only committing $2.35m across all jurisdictions was offensive, given how much they were spending in other areas”.

It is estimated there is more than 20 million cubic metres of coarse sand on the bed of the river between Yarrawonga to Picnic Point, which is a legacy of erosion from historic mining and land clearing.