Sunwater: Rookwood Weir no barrier to fish movements

When it becomes operational, Rookwood Weir will bolster Central Queensland’s water security. It will enable Lower Fitzroy landowners to transition to higher value agricultural land use and facilitate new industrial business opportunities.

The landmark $367 million project is currently being built on the Fitzroy River, 66 kilometres south-west of Rockhampton. It is equally funded by the Queensland and Australian governments.

During construction of the weir, every effort is being made to mitigate or offset potential impacts on the natural environment. These are detailed in the project’s Environmental Management Plan (EMP). Actions include plans to establish an environmental offset area adjacent to the Mackenzie River, with a mix of v vegetation to provide a range of fauna habitat, including sand banks for turtle nesting. Importantly, the offset area will also act as a large sediment trap, which will improve water quality in the Fitzroy River. A turtle passage ramp will be built into the weir, enabling the endangered Fitzroy River and white-throated snapping turtles to move upstream and downstream of the weir.

A key environmental feature of Rookwood Weir will be its unique fish lock situated on the right bank that will allow fish to maintain access to their natural habitat. When complete, the fish lock will stand 26 metres (equivalent to a seven-story building) above river level and comprise seven chambers. These chambers will ensure the fish lock remains operational during low river flow events in the dry months and high river flow events in the wet season. The fish lock will also minimise the injury and mortality rate for small and large species. Building the fish lock will require 14,000 m3 of reinforced concrete – the equivalent of six Olympic swimming pools.

Up to 34 species of fish have been identified in the Fitzroy River community, including sleepy cod, eastern rainbow, golden perch, and bony bream.

The fish lock operates in much the same way as a boat lock. An outlet valve creates flow, which naturally attracts fish to enter a chamber. When the chamber is full, the outlet valve is closed, and another outlet is opened to an adjacent chamber. Fish then enter the chamber with the same process repeated until fish exit the chamber on the other side of the weir.

Rookwood Weir Environmental Manager Susan Korecki said the fish lock will be one of the largest in Queensland and the first built in the state for more than a decade.

“The Rookwood Weir fish lock will be one of the most advanced in Queensland as we have been able to apply the learning from other fish locks across the state,” she said.

“These were passed onto our design team, which then worked with fish experts to settle on the current design.

“What makes this fish lock unique is its size. This allows it to accommodate the seven chambers that will ensure the safe passage of small to large fish during a variety of river flow events throughout the year.

“It is also important to note that the fish lock has been constructed in a way to minimise the risk of injury or death to fish as they enter and exit,” Ms Korecki said.

To further improve fish safety, a significant design change was made to the weir spillway on the left bank in 2021. The original design posed a risk for fish when the weir is spilling by plunging over the spill way and potentially landing on concrete. To address this issue, a series of concrete steps were designed to sit on top of the spill way to prevent such as occurrence (see picture below).

Construction on the redesigned spillway will be completed early 2023. Work on the fish lock started in late 2021 and is scheduled for completion by the end of 2022. In-river activities are forecast to resume by May 2022 following an inundation event in November and December 2021.

When the weir is operational, Sunwater will continue to monitor its effectiveness to ensure it functions as designed.

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