Something we're often asked at the Murray-Darling Basin Authority is if we've found a solution to the 'sand slug' impacting the River Murray Barmah Choke.
We haven't found a solution but we're working with the community, seeking expert advice, and finding a way forward.
Earlier this year we shared research that revealed a surprising cause of decreasing capacity in the Barmah Choke was a massive sand slug that experts believe has been mobilised largely by land use and mining change in the 1800s.
The Barmah Choke is the narrowest part of the Murray River, that runs through the Barmah-Millewa Forest.
Over the last year we have continued to collect and analyse data so we can better understand the sand slug, how it is moving, and the impact on the Barmah-Millewa Forest.
We measured the depth of sand on the riverbed between Yarrawonga and Barmah and found that there is more than 20 million cubic metres of coarse sand in this reach - enough to fill the Melbourne Cricket Ground 13 times!
The sand is moving slowly downstream and into the reach of the river where it flows through the Barmah-Millewa Forest.
The Barmah-Millewa reach is quite unusual in that water flows out of it, through creeks and flood runners, instead of into it, like most other river systems. It is a low energy reach, and the land is quite flat.
The sand is coarse and heavy and even in high flows, such as a flood, the sand only moves along the bed of the river. This means that when the water flows out into the forest it leaves the sand behind, gradually filling the river channel.
The accumulation of sand in the river is significant and increases as the river flows through the forest. At the upstream end of the river about an eighth of the river is filled with sand - at the Edward-Kolety offtake this increases to about a third.
The sand is accelerating erosion of the riverbanks, filling the deep pools, covering up snags and reducing the capacity of the river. If we do nothing to manage the sand this damage will continue.
This leads to the core question from communities, First Nations and industry - what can we do about this?
There's been a significant commitment from Basin governments and the MDBA to work with the locals to come up with some options.
We're confident there's no silver bullet solution to this problem. Instead, a multi-pronged approach looks to be the most promising option, including protecting key sections of riverbanks, removing sand in targeted areas, and moving water around the reach to reduce summer and autumn flow rates.
These all need to be investigated further to determine how, when and where each of these options could be applied.
Finding solutions to address the sand slug is part of our broader work program to address potential shortfall and capacity issues including through the Barmah Choke feasibility study.
Community consultation has been a key part of our work. We've spent considerable time this year talking with First Nations, irrigators, local government, state water authorities, National Parks representatives and environmental agencies about the problem and the possible solutions.
These conversations won't stop, and we'll continue to engage with the people who, like us, are fighting to preserve this amazing stretch of river.
Later this year we'll submit findings and options to the Basin governments through the Basin Officials Committee (BOC) and recommend that we progress to an options-development stage.
If this is supported, the work will take about a year to complete and will be presented back to BOC.
*Ben Dyer is the Murray-Darling Basin Authority river management director
