Yarrawonga Weir fish lift, Murray River

Yarrawonga weir is one of many structures that regulate the flow of the Murray. It raises the upstream water level to facilitate gravity-fed irrigation of farmland in Victoria and New South Wales. It also helps to mitigate flooding downstream and since 1994 has been used to produce hydroelectric energy with a 9.6 MW power station.

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A unique feature of the weir is its fish lift system.

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The lift operates on a daily cycle and works by attracting fish into a holding chamber using an auxiliary flow.

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The floor of the chamber is then raised, allowing the fish inside to be identified and counted.

A silver perch (Bidyanus bidyanus):

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A golden perch (Macquaria ambigua):

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Once the data has been recorded a gate is opened to allow the fish to move upstream.

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Whilst the pass appears to work for native species, including the Murray cod (Maccullochella peelii), there are doubts about the suitability of this system for passing juvenile and small-bodied fish.

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And, as usual, not all fish find the entrance, leading to delays in migration, increased predation and disease risk, and potentially impacting reproductive fitness.

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Downstream movement over the weir can also be problematic at low flow (<8,000 ml/day).

 

Martin // Adelaide
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