“The ridges which will be acting to hold the water in could very easily collapse,” he said. “The area is full of landslips already.”

“They just say Tillegra will be built. It’s an absolute insanity.”

“Hunter Water have not openly told their customers what the cost of this dam will be to ratepayers, and it’s about time they did,” she said.

CONTROVERSY over the proposed Tillegra Dam in the NSW Hunter Valley is growing, with a new analysis showing the dam could cost up to $1billion to build and increase water bills for some residents by up to 84per cent.

The massive 450 billion litre dam, one of the only new large dams to be built in Australia for decades, has been roundly condemned by environmentalists and locals since it was announced by the Iemma Government in 2006.

New modelling — done by the Greens and based on Independent Pricing and Regulatory Tribunal data and other government documents — calculated the annual repayments of the cost of building the dam at different cost levels and then averaged it over the number of households on the central coast and the lower Hunter region.

Tribunal chief executive James Cox has called for public submissions on the cost of water in the region, and said the Government’s construction of the Tillegra Dam would have implications for prices.

The analysis, issued yesterday by Greens MP John Kaye, showed that on the lowest of the government estimates, annual household bills would increase by $79 or 25 per cent.

Geotechnical engineer Graham Holt, who opposes the project, said the cost of the dam could blow out to $1billion from the Government’s $300million estimate, because the site was riddled with fault lines.

“The ridges which will be acting to hold the water in could very easily collapse,” he said. “The area is full of landslips already.”

At a cost of $1billion, household water bills on the central coast and in the Hunter would increase by $262 a year, or 84per cent.

Water expert Charles Essery said the dam was a folly, and a blowout in costs was probable.

He said there were examples all around the world of dams built on poor or unsound geology whose prices had blown out to several times their original estimate.

“At meetings I have had with government, they have refused to commit to a specific cost,” Dr Essery said.

“They just say Tillegra will be built. It’s an absolute insanity.”

A spokesman for NSW Water Minister Nathan Rees said there was no justification for the claims. An environmental impact statement on the Tillegra Dam was expected shortly.

Sally Corbet, from the group No Tillegra Dam, said the Government had been secretive about costs.

“Hunter Water have not openly told their customers what the cost of this dam will be to ratepayers, and it’s about time they did,” she said.

Credit: John Stapleton