Spending up to $1 billion raising Warragamba Dam wall is the best way to protect thousands of Sydney homes from being destroyed by flood, a major state government review has found.
But environmentalists say the mammoth project, which has divided opinion for decades, would be too expensive and damage a huge swathe of sensitive rivers and bush, including the Blue Mountains World Heritage Area.
Debate over the role Warragamba Dam should play during floods intensified after the devastating Queensland floods and controversy over the operation of Brisbane’s Wivenhoe Dam.
The probe into flood management in the Hawkesbury Nepean Valley, one of Australia’s most densely developed flood plains, found raising the wall was the best infrastructure option for reducing the flood risk. But the work would cost up to $1 billion and have ”significant potential environmental costs”, the review warned.
It said during a worst possible flood, 73,000 people would need evacuating and more than 20,000 homes would be at risk.
The review considered raising the wall by either 15 or 23 metres. The latter option was proposed in 1995 but did not proceed, despite evidence that floods larger than any yet recorded could occur in the valley.
Primary Industries Minister Katrina Hodgkinson has announced a taskforce to lead the next stage of the review, including an assessment of the engineering, economic, environmental and social impact of raising the dam.
Last year, then Prime Minister Julia Gillard pledged $50 million towards raising the wall by 23 metres. Premier Barry O’Farrell did not support the idea at the time, saying the review had begun. He declined to comment on the findings.
Colong Foundation for Wilderness director Keith Muir said raising the dam wall would badly affect the Blue Mountains World Heritage area.
”You are moving the flood from downstream to upstream … that will put the most protected natural area in Australia under water,” he said.
Water consultant and former senior hydrologist with Sydney Catchment Authority, Amir Deen, said raising the wall was an obvious response to the flood risk but would be a complex task.
”You’d have to strengthen the current dam quite considerably or you’d have to drown it with a new dam either upstream or downstream,” he said.
Greens MP John Kaye said raising the wall would be ”risk management gone crazy” and there were cheaper options that did not damage the environment, such as reclaiming homes in flood-prone areas.