Googong Dam Spillway Remediation

Icon Water working with ActewAGL and alliance partners GHD, Abigroup and John Holland, completed remediation works for the Googong Dam spillway in December 2010. This involved repairing eroded sections, extending the walls and improving the structural integrity of the spillway since its original construction in 1978. The spillway now meets the Australian National Committee on Large Dams (ANCOLD) requirements to pass extreme floods and is able to safely pass 10,500 cubic meters of water per second. This is approximately four times the normal flow over Niagara Falls and a 1 in a million flood event.

 Before the project started
 Figure 1: Before the project started

Googong Dam spillway December 2010 
Figure 2: Googong Dam spillway, December 2010

What did the project involve?

Since February 2009, remediation involved 50,000m3 of rock excavation, around 22,000m3 of concrete and 1100 tonnes of reinforcing steel and anchors. The new concrete spillway walls are 9.5m to 17m high, with a base width of up to 9m. The spillway itself is 52m tall, including three benches (6, 8 and 14m high). The project was delivered on time and on budget, having exhibited high quality innovations and cost-effective methods.

Record capacity

On 9 December 2010, the spillway managed 550 cubic metres of water per second, the Googong Dam’s highest water level for 20 years and one of the highest daily inflow volumes on record since 1870. The erosion shown in Figure 1 was caused by years of flooding at a lesser magnitude. Completion of the remediation works ensured no further erosion as the upgraded spillway is now fit for purpose.

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Further project measures

Icon Water is committed to protecting the environment as we work to secure a diverse and long term water supply for the region. The Googong Dam spillway remediation was one of the first projects to be completed from Icon Water’s water security program. Considerable work was undertaken to protect the local environmental during construction of this project.

The project also involves a range of rehabilitation work to return the area to its pre-construction condition or better, including natural landscaping and a new carpark area at the Googong Dam lookout. As part of Icon Water’s environmental commitments, over a hundred local trees were planted near the site as biodiversity carbon offsets and to increase habitat connectivity across the landscape. A weed management program is also in place to support regrowth of native grasses and shrubs. The project also involved intersection modifications to the Old Cooma Road/Googong Dam Road intersection to improve the area’s road network.