Bold new plans for Adelaide’s largest dam

A dam south of Adelaide – this is The floodgates opened on Friday for the first time in five years – Remediation has long been debated as the release of water from the 46.4 gigaliter reservoir affects residents downstream.

A concept design unveiled today shows plans to remove the dam’s remotely operated spillway gates and replace them with a single main spillway in the center of the wall.

According to SA Water, the central spillway (3m wide and 5.6m high) will withstand extreme weather events, including withstanding a “once in 100 year” flood if the dam is already full. Allows reservoirs to hold more water.

It will also release water from the reservoir three times slower, minimizing potential flooding impacts on residents downstream, SA Water said.

Once the Bald Mountain project is complete, the dam will be able to safely withstand a “once in five million years” weather event.

State and federal governments, along with the Onkaparinga Council earlier this year, pledged an additional $12.7 million to fund the upgrade.

Indaily We asked SA Water for a full project cost estimate, but the final figure wasConcept optimization was undertaken as part of the detailed design, planning and procurement process. ”

Amanda Lewry, SA Water’s general manager of sustainable infrastructure, said the upgrade, “when complete, will be one of the largest capital projects in our company’s history.”

“To increase the safety of the dam, we will build critical concrete protection downstream of the dam to reduce the risk of erosion, while strengthening the walls with new concrete to increase its ability to withstand earthquakes and extreme floods. ‘ she said.

“Our proposed new design of the dam facilitates self-regulated flow to enhance the current gate system, which is a series of eight remotely controlled gates to release water.

“This is more efficient and allows water to be retained during extreme weather. This is because the water can be discharged at

“Once the reservoir is already full, the dam’s main spillway will play this role until ‘once in a hundred years’, whereupon the other two spillways will come into operation and release the water, causing the structural damage to the dam. maintain integrity.”

Lewry said the project was “the most complex upgrade in our portfolio” and has been planned since 2010.

“We are currently optimizing the concept as part of the detailed design phase, and there is room for further refinement to ensure we deliver a cost-effective project,” she said.

“Once the Bald Mountain project is complete, the dam will be able to safely withstand a ‘once in five million year’ weather event.

“Importantly, ongoing inspections have confirmed that the dam remains safe and the upgrades keep it in line with modern safety standards for the fishing industry. .”

Ongoing spring rains have brought Bald Mountain closer to full capacity after the reservoir’s locks opened for the first time in five years on Friday.

SA Water reported that the reservoir has taken in 30 billion liters of water since August, going from 30% to 94% capacity.

A controlled release caused water to flow down the Onkaparinga River, catching some residents off guard.

Susan Jeans, a Clarendon resident, said local residents living near the waterway downstream of Mount Bald Reservoir had not been warned of the release of water that had sprung past their homes, and that her gardens, local parks, and The outbuilding on the neighbor’s property below was flooded.

She said flood fears have returned, similar to when the gates were opened in 2016 and the property was flooded.

At that time, part of the old town of Noarlunga was flooded, causing insurance premiums for residents to skyrocket. Later, improvements were made to the safety of the reservoir.

Jeanes said the water released last week also flooded a concrete footbridge connecting the town of Clarendon to nearby parking lots, bowling clubs and netball clubs, causing problems at the weekend’s Clarendon Springs fair.

“Our garden is not a big deal, just the fact that all of a sudden, out of the blue, water springs up and pushes down a lot of rubber trees far away from us,” she said. said.

A view of Susan Jean’s garden on Friday.Photo: Susan Jeans/Courtesy

Jeanes said he understood that the current and projected rainfall required some preparation and that it was coming gradually, but that it “caused a bit of confusion”.

Mount Bald Reservoir was built in 1938 and is still the largest reservoir in South Australia.

According to SA Water, the stored water can be sent to Happy Valley Reservoir, which supplies water to approximately 450,000 Adelaide customers.