Engineering assessments of two new dams under consideration for the Lower Hunter have classified the potential loss of life that would occur if they failed as 'extreme'.
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Modelling for a potential 160 gigalitre dam at Limeburners Creek shows about 50 people living downstream would die if the dam failed.
An independent feasibility study into the project rated the potential loss of life as 'major'. However when 'itinerants', such as road users, were factored in it recommended the risk category should be moved to 'extreme'.
A similar study done for a potential 230 gigalitre on-river storage upstream of Chichester Dam also gave an 'extreme' rating for the potential loss of life in the event of a structural failure.
Hunter Water, which is considering both dams as part of the Lower Hunter Water Security Plan review, says the 'extreme' ratings reflected the need to ensure the highest standards of engineering and construction were used if the project proceeded.
However, communities opposed to the construction of a new dam in the Hunter argue the ratings show the potential dams represent an unacceptable safety risk.
Healthy Hunter Rivers Group spokesman Ken Edwards said the consequences of a dam failure would be catastrophic for surrounding communities.
"As stated in numerous Hunter Water Corporation reports, the board is very sensitive to risk and has a very low risk appetite for running out of water," Mr Edwards said.
"If this dam on Limeburners Creek goes ahead in the name of 'securing the region's water supply', then obviously the board's risk of running out of water seems to be far more important than the potential risk to the loss of lives of the 50 or more people living in the Limeburners Creek Settlement and surrounds.
"There are much better climate independent water supply options which don't have this life threatening risk or the supply risks of dams.
"I am sure all the governments and water and hydro companies who built these failed dams around the world, said "it will never happen".
A Hunter Water spokesman said the organisation had been actively exploring all water supply and demand options and assessing the feasibility of each as part of the Lower Hunter Water Security Plan review.
"No decision has been made at this point in time on the preferred options," he said.
He said Australian dams were considered 'safe technology'.
"This high-level feasibility assessment report was carried out by an independent expert as a key step to ensure risks are identified and mitigated as part of the option assessment process," he said.
"There are well-established design principles and protocols and a mature regulatory system to ensure that water supply dams do not present an unacceptable risk to the community."
He said Hunter Water considered the potential failure of any large piece of infrastructure to be an unacceptable community safety risk.
"So, Hunter Water has adopted an extreme consequence category for both the Upper Chichester and Limeburners Creek Dam investigation areas," he said.
"This ensures the highest level of engineering standards are employed to provide preliminary costing and design information that will be used in the option selection process."
The two potential dam were identified by the CSIRO as being the most suitable locations for new small water storages in the Lower Hunter.
Dams Safety NSW, an independent regulator, has oversight of Hunter Water's surface water storages to ensure their ongoing compliance, integrity safe operation.
In addition to safety concerns, the Healthy Hunter Rivers Group has also highlighted the potential downstream environmental impacts of a new dam.
These include the loss of flora and fauna species and Lower Hunter wetlands.
The group argues that increased water conservation and recycling should form the basis of the region's future water security strategy.
In addition to dams, Hunter Water is also considering desalination, recycled water schemes, stormwater harvesting, groundwater and increased water conservation as part of the Lower Hunter Water Security Plan Review.
It will release in March the results of community and business feedback gained during the review process.
A draft of the revised plan is due to be released mid-year.
