Check for risk of dam failure

Landholders are encouraged to check their farm dam walls for cracks and other issues as the recent heavy rain has increased the risk of “failure” from leaks and bank collapses.

Agriculture Victoria farm water supply specialist Brad Costin said the risk of dam failure has increased significantly, due to a rapid rise in dam water levels following a long period of drought.

“Landholders need to ensure they inspect, check and monitor their gully dams over the next six to twelve months and keep a close look out for signs of bank subsidence, cracking and / or tunnelling,” Mr Costin said.

“Gully dams are of particular concern as much of the water is stored above ground level, held back by an earthen bank.

“In a good site, more than 60 per cent of the water can be stored in this manner but these earthen banks can fail when there is a rapid rise in water level following a period of drought. This failure can range from a minor leak to catastrophic failure of the entire bank.”

During a period of drought, when dam water levels are low, earthen banks slowly dry out resulting in the formation of cracks.

Mr Costin said if the water level rises too rapidly, it can find its way into these cracks causing the dam to leak.

“The problem is more serious in poorly structured soils where the movement of water dislodges soil particles, creating a small tunnel,” he said.

“Left untreated, these tunnels can enlarge rapidly, which can result in the total loss of water and bank collapse.”

“In some older dam banks, where little compaction occurred during construction, the rapid rise of water can result in further settlement and movement of the dam bank creating new cracks through the bank.”

Mr Costin said it was important to treat cracks and other issues in farm dams as quickly as possible.

Treatment options may include reducing the water level (critical at most at-risk sites), packing cracks with moist clay, and rebuilding part of the dam bank.