Dam safety upgrade uncovers hidden underwater structures

In only the second time in its history, the Kangaroo Creek Dam in the Adelaide Hills will soon be temporarily emptied, to enable the next stage of work in a major safety upgrade of the dam.

The $94 million project began in early 2016 and is on track for completion in late 2019.

The upgrade will help SA Water better manage any major floods and increase the dam's ability to withstand earthquakes, aligning it with updated safety guidelines set by the Australian National Committee on Large Dams (ANCOLD).

SA Water's General Manager of Asset Operations and Delivery Mark Gobbie said a mostly-intact bridge, which was used before the dam was built, will soon begin to emerge with the emptying of the dam, and will be able to be seen from the public lookout on nearby Gorge Road.

"There are actually three bridges within the reservoir which are usually underwater, with two others upstream more regularly breaking through the water’s surface when the dam dips below 60 per cent of capacity," Mark said.

"We’ve recently begun to gradually lower the water level, with the aim of getting to zero pent capacity by the end of March this year.

"This temporary measure will be in place for around six weeks, to facilitate work on a 10,500 square metre concrete slab on the upstream face of the embankment.

"The water being released from the dam will either be used to, where possible, support dilution flows into the Torrens Lake to help with the control of blue-green algae, or be fed into the Hope Valley Water Treatment Plant for drinking water supply."

Management of the dam’s water level has been an integral part of the work to date, which at times has been challenging due to unseasonal heavy rainfall and flooding.

"In September 2017, Kangaroo Creek reached 73 per cent of capacity, after 10 gigalitres of inflow during the previous three months – this inflow alone represents half of the dam’s capacity," Mark said.

"We were however able to bring the water level back down again in an acceptable timeframe by diverting it elsewhere in the network. This allowed work on the dam outlet to continue and helped to avoid any major work delays."

The project has recently reached another important milestone, with the blasting removal of 300,000 square metres of rock from the nearby hillside, completing this component of work. This has helped to widen the dam’s spillway by an average 33 metres.

"Remaining work is focused on strengthening the dam structure, including raising the embankment and widening its base by placing rock material – some reused from the blasting activities – on the downstream side. We will also be concrete lining the spillway and reinforcing the spillway walls," Mark said.

"This significant construction work requires around 90 people to be on site at any one time, along with a variety of technology and large machinery, so it’s definitely one of our largest projects, in terms of job creation, delivery time and complexity."

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