Latest flooding has experts questioning Warragamba Dam wall raising plan

Flooding in the Hawkesbury after the torrential rain of February 8-9, has some experts again questioning the validity of raising the Warragamba Dam wall by 14 metres.

"People were evacuated, bridges were blocked and the Hawkesbury River rose by over 10 metres, yet none of the flood water came over Warragamba Dam which the government keeps telling us needs to be raised urgently," said Jamie Pittock, a professor and flood management expert at the Australian National University.

"These floods demonstrate the dire need for Australia to apply international best practices in floodplain management. Evacuation roads in western Sydney are urgently needed to ensure people can get out in time, and new suburban development on floodplains needs to stop. Raising the Warragamba Dam is simply not the solution."

His concerns were echoed by Chas Keys, the former deputy director general of the NSW SES in the SMH this week.

"Raising Warragamba might cost something like $700 million - a lot of money to palliate the flood threat without getting remotely near to eliminating it," he said.

"Should a genuinely big flood develop from rain over the Nepean and Grose rivers, there will be a massive price to pay from the points at which the Nepean joins the Warragamba and where the Grose comes in at Yarramundi."

Give a Dam campaigner Harry Burkitt from the Colong Foundation for Wildnerness, said the dam wall raising was dangerous and put people's lives at risk.

"Stuart Ayres' plan to add 134,000 thousand more people onto Western Sydney floodplain has to be one of the most dangerous policy initiatives in the history of Australia. For years the people of western Sydney have been told this dam project is all about public safety, when really its primary purpose is to line the pockets of the development and insurance industries," he said.

Mr Ayres, the Minister for western Sydney, stood by the dam plan.

"Had the dam been above 80 per cent [on February 8] with no flood mitigation wall, the Hawksbury-Nepean would be in a lot of trouble. Without a raised dam wall there would be no opportunity to allow water to recede in the catchment forward of the dam before releasing water. The only outcome in this situation is a more severe flood," he said.

"A combination of good planning decisions that keep growth out of high-risk flood-prone areas, increased flood awareness and a higher flood mitigation wall is the best combination to build a more flood resilient community.

"Raising the dam wall will not allow one single home to be built in an area not already available for development."

Warragamba Dam on Friday was 76.7 per cent full, an increase of 34 per cent in the past week.

The Hawkesbury River at North Richmond peaked at 11.4 metres around 8pm on February 9, with major flooding. At 11pm at Windsor it peaked near 9.2 metres, with moderate flooding. It was the first time in 28 years that water had submerged the decks of the two bridges.

The dam wall raising proposal was announced by then premier Mike Baird in June 2016 as flood mitigation in the Hawkesbury-Nepean Valley. It has been criticised by environmental and Indigenous groups for potentially flooding hundreds of Indigenous sacred sites and inundating parts of the Blue Mountains World Heritage Area.

An Environmental Impact Statement outlining the environmental, social, and economic impacts of the dam wall raising is being developed by the NSW government and is due to go out for public comment in the first half of this year.

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