Upgrade on the way for Myponga’s water release gates

A major upgrade of Myponga Reservoir’s dam spillway gates is set to begin this month, as part of SA Water’s $3.7 million investment ensuring the long-term safety of the structure and securing a reliable water supply for the Fleurieu Peninsula into the future.

Sitting atop a section of the dam wall, Myponga’s three spillway gates facilitate controlled releases of water from the reservoir, based on its capacity and rain inflows from the catchment.

The project includes refurbishing the gates’ arms and bearings, along with replacing the seals, rollers, and sill plates, to ensure the gates operate reliably when water is released from the reservoir.

SA Water’s Senior Manager of Infrastructure Planning and Strategy Dr Daniel Hoefel said the reservoir’s water level will be temporarily lowered to allow crews to safely undertake the upgrade.

“Myponga Reservoir’s arch dam is an impressive engineering feat and 60 years on, the wall remains in sound condition with our routine inspections identifying the dam’s spillway gates require an upgrade to ensure they keep operating reliably,” Dr Daniel said.

"The gates are curved steel plates, reinforced with a series of beams that can be opened at varying heights depending on the amount of water being released, and are critical to our ability to maintain the reservoir’s water level and protect the dam’s structural integrity.

"After more than 60 years of operation, this is the first time the gates will be removed since the dam was built, and in order to safely upgrade them, the water needs to sit below the top of the spillway crest.

“This will involve a controlled release of water from either a valve at the bottom of the dam, or both the valve and gates based on operational requirements at the time, until the reservoir reaches 71 per cent of capacity, which commences this week and taking around two weeks.

“Importantly, we’ve scheduled our work during late summer and autumn when the reservoir is naturally at its lowest level to help limit the amount of water we need to release.

“The release also mimics a summer rain event and provides water to vegetation higher up on the banks of the Myponga River and flushing the system with freshwater, which benefits native aquatic species.”

Completed in 1962 and capable of holding 26,800 gigalitres, Myponga Reservoir is currently sitting at 84 per cent of its capacity and supplies the water treatment plant before its piped to homes and businesses.

Mr Hoefel said major work on the gates is expected to commence late this month and will require temporary changes to access along nearby Reservoir Road.

“To safely accommodate our crews and heavy machinery – including a large crane adjacent to the top of the dam wall – pedestrian and vehicle access to Reservoir Road, between the Myponga Reservoir Lookout and Forktree Road, will be temporarily closed during our work,” Dr Daniel said.

“We’ve established electronic messaging boards to inform the local community and commuters about these changes, along with clearly marked detour routes, which are now in place to enable our crews to mobilise to site and set up the crane.

“Visitors to the beautiful Myponga Reservoir Reserve will be able to continue enjoying the site throughout the upgrade, as our work won’t impact recreational access.”

Work on the spillway gates will be undertaken between 7am and 5pm, Monday to Saturday, and is expected to be completed by mid-2024.

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