20 June 2022

Rain delays replacement of Cooma's ageing weir and fishway

| Claire Fenwicke
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Cooma weir and fishway

The design for replacing the weir at the Murrumbidgee Reserve near Cooma has been released. Photo: Westlake and Punnett Design Engineers.

Heavy rain and a wet winter forecast have delayed the planned construction of the Cooma Weir and Fishway.

Work was meant to begin in May and be finished by October.

A statement from Snowy Monaro Regional Council said the project was revisited during a meeting in April.

“Due to the high rains and river flows, the decision was made to delay the project until 2023,” it said.

“The current conditions make undertaking the project as originally scheduled unsafe.”

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Tenders were also flagged as an issue, with all five submissions coming in over budget.

“Costs returned in the submitted tender applications are significantly higher than previous estimates due to the heightened risk and difficulty completing the project, with rain and river flows continuing to be much higher than normal,” a council statement said.

“NSW Department of Primary Industries [climate outlook] has indicated rainfall will likely remain high over the next three months.”

All tenderers identified they would need significant instream preparation works before work on the actual project could begin.

This presented a risk as it meant the construction would extend beyond the start of the snow melt in October.

Cooma weir

The Cooma Weir was constructed from rock in the 1960s. Photo: SMRC.

The five tenderers would be invited to re-submit their interest once the council’s project management team completed a more detailed pre-construction plan.

It has been recommended council explore an alternative design of temporary river diversion or a bunding system to alleviate environmental risk to both the chosen contractor and the council.

A constructibility assessment would also be undertaken to reduce the risk associated with ‘dewatering’ the site, which would be needed so that work could be carried out safely.

Water NSW described dewatering as a process of removing groundwater which “keeps water from seeping into the site which could affect engineering and protects the ongoing integrity of the structure and surrounding area.”

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The weir site is located adjacent to the Cooma Water Treatment Plant at 820 Mittagang Road. It was constructed from rock in the 1960s and has been used ever since.

In about 1997 a rock fishway was also built into the weir to try and bring the structure up to standard and allow for the freedom of movement for native fish in the area.

The weir and fishway have been severely damaged by major weather events, making it unviable to continue repairing the structures.

Council’s raw water supply came from the weir and the project aimed to deliver a complete replacement of the weir and fishway that would allow the continued supply of raw water for Cooma and the migration of native fish species for the foreseeable future.

In addition to the weir and fishway construction, council has planned improvement works at the site, including installing a walkway along the fishway and upgrading park amenities.

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