The authority's major projects executive manager, Tim Shanahan, said both weirs were the last barriers to fish passage along Gunbower Creek, with the fishways to provide passage.
“The fishways will allow fish — including the vulnerable Murray cod, which are breeding in Gunbower Creek — to safely move downstream into the Murray River, and to move upstream and recolonise sections of the upper reaches of the creek,” Mr Shanahan said.
“The Koondrook fishway will provide year-round passage to native fish such as golden perch, Murray cod and threatened silver perch from the river into the creek for the first time in more than a century.”
The Cohuna fishway is fully funded by Goulburn-Murray Water and will comprise of a 23-slot vertical slot fishway attached to the existing Cohuna Weir.
The Koondrook Weir fishway is co-funded by the Victorian Environmental Water Holder and the Victorian Government, and is part-funded from the sale of water for the environment to irrigators.
It will comprise of a double-entrance and double-exit vertical slot fishway, with sheet pile walls to create a stilling pool to dissipate energy.
The undershot gates will be replaced with overshot gates to allow for improved flow conditions and safe downstream fish passage.
In order to complete the works, a large section of Gunbower Creek will be lowered during the irrigation off-season to allow for the construction of fishways at the Cohuna and Koondrook weirs.
Water for the environment and irrigation water won’t flow down the creek until the start of the new irrigation season on August 15.
At the Cohuna Weir pool, the water level will be lowered about one metre below the full supply level.
The town supply will not be impacted by the lowering, and G-MW has communicated with relevant stock and domestic customers.
“Up until 2013-14, Gunbower Creek dropped from May to August as part of the annual irrigation shutdown period,” G-MW infrastructure delivery services general manager Warren Jose said.
“Since then, water for the environment has kept the creek flowing to help native fish such as the Murray cod survive and thrive.
“This is a one-off lowering to allow us to complete a key section of the Cohuna and Koondrook fishway works.
“We are lowering the creek now to ensure we don’t impact irrigation delivery. Once irrigation season begins, the flows will recommence.”
Conditions in the creek will be monitored during the drawdown.
Improvements in public access and fencing for safety will also be completed to further enhance and complement the Gannawarra Shire Council's recent Cohuna CBD waterfront development.
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