The shadow water minister Chris Minns has called for the government to consider lowering the maximum limit on the Warragamba Dam and supplement it with a desalination plant.
He said this was a better alternative than raising the dam wall by 14 metres and inundating protected areas.
Mr Minns was in the Blue Mountains national park last week upon invitation from Blue Mountains MP Trish Doyle, to view some of the area affected, if the dam wall raising proposal were to go ahead.
“The very least the government should do is look at the viability of lowering the maximum limit on Warragamba and supplement it with the 'moth-balled' desalination plant,” he said.
“After all, Sydneysiders are paying $100 a year in ‘availability charges’ for the desalination plant, and other than for testing it has never been turned on.”
But an Infrastructure NSW spokeswoman said this option and a range of others to mitigate flood risk had been considered including lowering the full supply level of the dam, raising the dam by up to 30 metres to provide airspace, dredging the Hawkesbury River, creating river diversion channels, local levees and major upgrades to evacuation roads.
She said lowering the dam’s full storage by five metres and 12 metres was examined but the five-metre lowering was found to have limited benefits for the larger floods. A 12m lowering would reduce the dam’s capacity by around 40 per cent.
“Lowering the full supply water level by a maximum of 12 metres would not only require the current desalination plant to operate continuously but require additional new supplies of water to be built such as more desalination plants and/or new dams,” the spokeswoman said.
“The costs of securing the lost water supply for Sydney would significantly exceed the cost of the dam raising and would also have significant environmental impacts.”
The $700 million Warragamba proposal was announced by then premier Mike Baird in June 2016 as flood mitigation in the Hawkesbury-Nepean Valley. It “will offer significant extra protection for townships downstream, including Windsor, Richmond and parts of Penrith," Mr Baird said at the time.
An Environmental Impact Statement outlining the environmental, social, and economic impacts of the dam wall raising is currently being developed by the NSW government.
“After the devastating Brisbane floods of 2011 the Queensland government decided to lower the maximum limit on Lake Wivenhoe and instead make use of desalination technology to make up the lost capacity,” Mr Minns said.
Prue Car, the Member for Londonderry, said western Sydney households wouldn’t stand for the expensive proposal.
“Lifting the dam wall is a very expensive proposal; it would be the equivalent of $268 per household. That’s money many families in western Sydney simply don’t have,” she said.
“If there is a cheaper, easier, less environmentally destructive alternative then that should be our first option.”
Ms Doyle said: “The government’s proposal to lift the dam wall will inundate kilometres of pristine world heritage protected Blue Mountains national park all so they can squeeze another 80,000 people into our area and onto a flood plain.”
The Infrastructure NSW spokeswoman said: “The proposed Warragamba Dam wall raising by around 14 metres is designed to reduce flood risk for the current and future population based on development that is currently permissible.
“The impacts of temporary inundation on the upstream environment – and options to manage, mitigate or offset them – will be detailed in the Environmental Impact Statement currently being prepared for public exhibition.”
Ross Coster from the Blue Mountains Conservation Society said inundating world heritage listed national park was unacceptable.
“We’ve opposed this before and we’ll oppose it again, it’s not on,” he said.
