Bold vision released for SA’s largest dam

A new concept animation released today by SA Water reveals a proposed design for Mount Bold Dam, as part of the utility’s major upgrade to enhance the dam’s safety.

The current design features a three-stage spillway along the dam crest – with a primary spillway slot three metres wide by 5.6 metres 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 the local council, and the State and Federal Government to include improved flood attenuation in the conceptual design.

SA Water’s General Manager of Sustainable Infrastructure Amanda Lewry said the upgrade of South Australia’s largest dam has been more than 10 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,” Amanda 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.

“The most notable piece of work 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.

Ms Lewry said eight of the utility’s dams have been upgraded since 2002.

“Our considered approach to enhancing dam safety is to address the highest risks first and this has resulted in a major upgrade almost every two years since the program began,” Amanda said.

“Mount Bold has had a lower risk when compared to other dams, and as it’s the most complex upgrade in our portfolio, that has required significant long-term planning.

“Rightly so, the refreshed national safety guidelines – set by the Australian National Committee on Large Dams – are particularly conservative and take into account the most extreme of weather scenarios to ensure we’re covering all bases.

“Once our Mount Bold project is complete, the dam will be able to safely pass up to a ‘one in five million year’ weather event.

“Importantly, our ongoing inspections confirm the dam remains safe, with our upgrade keeping it in step with the water industry’s contemporary safety standards.”

Major construction is expected to start in coming years and take several years to complete.

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