Celebrating 40 years: What makes the Googong Dam spillway strong enough to handle floods?

July 30, 2019

 Googong Dam from the air, 2017

As Googong Dam celebrates 40 years of supplying water to Canberra and Queanbeyan, we take a look at what makes it strong enough to withstand the pressure of a large flood. 

Buried deep within Googong Dam’s concrete spillway are 48 huge steel ‘anchors’ that extend 30 metres underground to support the dam. 

The anchors need to stay strong because when there’s a big flood, like there was in 2010, the crest of the spillway is hit by much larger forces as the water flows fast and hard over the top. 

The anchors make the spillway strong enough to withstand these forces and protect the integrity of the dam. This is essential, because when it’s full the dam holds almost 120,000 million litres of water – that’s 43 per cent of Canberra and Queanbeyan water storage capacity.

Googong Dam flood event, December 2010

If you’re thinking they’re like a traditional boat anchor though, think again. Googong Dam’s anchors are long and thin – 30 metres long in fact, and around 40cm wide. They’re made of strands of super grade steel wire that are driven deep into the bedrock under the spillway, supported by 16 tonnes of steel reinforcement.

The anchors need to hold the right amount of tension to work properly – so every five years, Icon Water brings in specialised equipment to test the anchors and make sure they’re up to scratch.

One of 48 super grade steel anchors strengthening Googong Dam

In June 2019, specialists conducted hydraulic pull tests on every anchor over a number of weeks, which showed that all 48 anchors are in good condition and are holding the right amount of tension. You can see a video about the anchor testing here.

Googong Dam is the only one of the region’s four water supply dams that is available for recreation, though there are some restrictions on what you can do on and around the water to protect the quality of this drinking water. Find out more about Googong Dam, or Icon Water’s three other dams.