Feature Length Live Virtual Presentation

Ian D Rutherfurd ¹ , James Grove ¹ , Thom Gower ² , Christine Lauchlan Arrowsmith ² , Ben Dyer ³

1. Why did you do it? – The Murray River is a conduit of water for Australia's largest irrigation system. The delivery of water has always been constrained by a particularly narrow section of stream known as the Barmah Choke. The Choke limits the amount of irrigation development possible, and also contributes to environmental challenges in managing the unseasonal flooding of the Barmah-Millewa Forest, the world's largest river red gum forest. OVer the last two decades the flow conveyance through the Barmah Choke has been steadily falling. This study builds on earlier consulting reports and focusses on the geomorphic processes that could be reducing the conveyance of the choke.
2. What did you do? We explored why conveyance through the Choke could be declining.
3. What have you learned? Becuase of tectonics, the Barmah forest is a distributary fluvial system that naturally declines in conveyance downstream. Sediment will always choke these challenges leadign to an avulsion. The most likely explanation for the reduction in conveyance through the Choke is a slug (pulse) of anthropogenic sand that has come from historical river bank erosion and from historical gold mining. Surprisingly flow regulation has reduced the sand transport rate.
4. Why does it matter? Reduced conveyance is inevitable. The pulse of sand will not simply move through the choke section and disappear. Major management responses might be required.

Feature Length Live Virtual Presentation 10th Australian Stream Management Conference 2021