Australian dam safety officials on alert for possible dam failure in New South Wales

Residents near Jerrara Dam in rural Illawarra, New South Wales, Australia on the NSW South Coast have been ordered to evacuate their homes amidst fear the dam will fail as more than a foot of rain had fallen in the area by 3 p.m. on Aug. 25.

Jerrara Dam is an earth-fill, non-hydroelectric structure that impounds 430 acre-feet of water from Jerrara Creek. It was built in 1955 to supply water to the township of Kiama, which is 75 miles south of Sydney.

In 2013, the Kiama Municipal Council voted to decommission the dam for an estimated US$700,000 after safety concerns were raised about the dam’s structural safety. Contractors began decommissioning work more than a month ago on July 16.

The NSW State Emergency Service (SES) issued the flowing statement this afternoon:

“Jerrara Dam (near Jamberoo, west of Kiama), which is in the process of being decommissioned, has shown signs of the wall failing due to heavy rainfall in the area. NSW SES advises residents living downstream of the dam need to take action to protect themselves and their properties and evacuate immediately.

“The Dam Failure Warning System for Jerrara Dam has issued a Red Alert, for areas downstream of the dam. This alert means dam failure is imminent. Failure of the dam will result in extremely dangerous flooding of the following areas: Mount Brandon Road, Jerrara Road and Jamberoo Road.”

There are concerns that if the dam wall bursts, water it impounds from Jerrara Creek would surge downstream into the Minnamurra River and flood parts of Minnamurra, including a nearby public school.

According to published reports, Kiama Councilor Brian Petschler disagrees with reports Jerrara Dam will fail. He said the dam was in fact nearly empty and posed no risk to downstream residents or students.

He said, in contrast to the Jerrara Dam Red Alert that sounded an imminent failure warning on Aug. 25 at 9:30 a.m., the water level was 26 ft below the top of the dam. Water seen in photographs taken from a helicopter overflying the dam shows water that normally flows over the spillway. The aerial image taken by the crew of a Westpac Life Saver Rescue Helicopter showed a large volume of water flowing over the top of the dam wall on Tuesday morning.

Despite this SES authorities evacuated local residents — people in about six homes in the rural area — due to water rushing through a hole cut in the dam wall by contractors decommissioning the structure.
 

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Gregory B. Poindexter formerly was an associate editor for HydroWorld.com.

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