Grahamstown Dam risk assessment complete
Hunter Water is taking immediate action to reduce the amount of water stored in Grahamstown Dam, in response to a comprehensive risk assessment which identified that Grahamstown Dam could be damaged in the unlikely event of an earthquake being experienced near the dam.
The risk assessment, undertaken with expert consultants and an independent expert panel, was submitted to the regulator Dams Safety NSW in early July. This work forms part of Hunter Water’s commitment as a responsible dam owner to ensure we meet modern engineering and safety standards, and regulatory obligations.
Hunter Water Managing Director, Darren Cleary, said while the review found that Grahamstown Dam continues to operate safely in both normal and flood conditions, it was critical to take decisive action to reduce the identified risk to people and nearby properties, while longer-term solutions for the dam were developed.
“In response to the report findings, we’ll be slowly reducing the amount of water in the dam over the coming weeks to lower its overall storage to around 90 per cent capacity.
“This precautionary step means we reduce the amount of water that could potentially be released in an uncontrolled manner to low-lying areas downstream of the dam’s embankments (walls) if they are damaged in the unlikely event of an earthquake near the dam.
“We’ll maintain this water level, while we proactively work through the report recommendations for additional short-term mitigation measures such as reviewing our emergency response plan, as well as developing longer-term, permanent upgrades to strengthen the dam walls.
“The safety of our community is paramount. I’d like to reassure our community that the dam continues to operate safely under normal conditions,” said Mr Cleary.
The risk assessment has identified the largest risk to the dam walls, or embankments, is an earthquake, or a series of smaller ones close to the dam. The review estimates that the risk of this occurring to the main embankment is 1 in 3,500, or a 0.03% chance, per year.
It also found this risk is not new, and that the risks associated with earthquakes have existed since Grahamstown Dam was constructed 60 years ago. The use of the latest technology in geotechnical engineering, scientific monitoring and computer modelling has allowed Hunter Water and its technical experts to better understand how the dam might respond to a range of rare events.
The dam did not experience noticeable damage during the 1989 Newcastle earthquake. This may have been due to the location of the earthquake in relation to the dam or the short duration of that earthquake.
“A detailed letter is in the mail today to residents and community members who live around Grahamstown Dam to inform them about the report findings and invite them to attend one of the drop-in information sessions we’ll be holding between Tuesday 23 July and Thursday 1 August.
“I encourage community members to attend if they would like to find out more about the report or ask questions of our dam safety experts. We’ve also made available on our website a summary report of the findings, as well as the full version of the risk assessment,” said Mr Cleary.