SA Water has revealed conceptual plans for its proposed safety upgrades to its Mount Bold Dam, in a major overhaul featuring a more efficient three-stage spillway for better controlling water releases.
The current design features a three-stage spillway along the dam crest – with a primary spillway slot 3m wide by 5.6m high – which will replace a series of gates that currently control the release of water.
An additional $12.7 million of funding was earlier this year secured via Local, State and Federal Governments to include improved flood attenuation in the conceptual design.
Image: The current proposed design for Mount Bold’s dam features a three-stage spillway along the dam crest which will replace a series of gates. Photo: SA Water.
SA Water’s General Manager of Sustainable Infrastructure, Amanda Lewry, said the upgrade of South Australia’s largest dam has been more than ten years in the making.
“Our upgrade of Mount Bold’s dam is the culmination of years of planning and will be one of the largest capital projects in our history once completed,” Ms Lewry said.
“To elevate the dam’s safety, we’ll be constructing significant concrete protection downstream of the dam to reduce the risk of erosion, while strengthening the wall with new concrete to increase its capacity to withstand earthquakes and extreme flood events.
“Our proposed new design for the dam will facilitate self-managed flows to enhance the current gated system, which is a series of eight gates that are remotely controlled to release water.
“This is more efficient, allowing for the retention of water during extreme weather events, due to the dam’s ability to temporarily store more water and release it at a rate that’s three times slower compared to having all the gates open.
“When the reservoir is already full, the dam’s primary spillway will play this role up until around a ‘one in one hundred year’ event, where the other two spillways will be activated to help release water and preserve the dam’s structural integrity.
“Inherently, this will provide the dam with a greater ability to minimise the impact to residents downstream by releasing water more steadily.
“Since 2010, we’ve been methodically working through the site’s nuances, such as the surrounding geology, flood hydrology and topography, to ensure the final design achieves the greatest outcome for dam safety.”
Ms Lewry said the most notable piece of the investigative works took place in 2020 when the 46-billion-litre reservoir was gradually emptied to enable detailed investigations of the intake structure, and an upgrade of equipment used to isolate the dam’s valves and pipework.
“We’re now optimising our concept as part of the detailed design phase, with scope for further refinement to ensure we’re delivering a cost-effective project.”
Constructed in 1938, Mount Bold is South Australia’s largest reservoir and stores water that can be diverted to SA Water’s Happy Valley Reservoir, where it is treated and supplied to around 450,000 customers in Adelaide.
Major construction is expected to start in coming years and will take several years to complete.
Feature Image: Mount Bold is South Australia’s largest reservoir and stores water that can be diverted to SA Water’s Happy Valley Reservoir. Photo: SA Water.