A controversial plan to raise the wall of NSW's Warragamba Dam will not stop the "inevitable" deaths of people living in the valley below, according to the former deputy director-general of the NSW State Emergency Service.
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The Berejiklian government wants to raise the wall at least 14 metres to help prevent the risk of flooding in the Hawkesbury-Nepean Valley.
Dr Chas Keys told a state upper house inquiry on Monday that the best way to save lives at risk from flooding in the valley was to "stop putting people in harm's way".
He argued that raising the dam wall would not stop major floods, which are increasingly more likely due to climate change.
"I'm very strongly of the view that in extreme events - which by definition are rare - we will drown heroic numbers of people in this valley probably with or without the raising of this dam," he said.
"We could have our own New Orleans, Hurricane Katrina, which killed 1600 people in 2005, we could have the Black Saturday fires where 173 people died. It seems to me that they are inevitable."
Dr Keys said measures such as raising the dam wall and building levees created a "psychology of immunity" which would result in increased development on the floodplain.
He said while he was in favour of flood mitigation people shouldn't make matters worse by encouraging such development.
Representatives from the four local councils threatened by the risk of flooding in the valley also gave evidence to the select committee on Monday.
The mayor of Hawkesbury City Council Barry Calvert said the people living in his region had become complacent to the threat of flooding.
"The problem is there hasn't been a major flood in such a long time ... if you talk to people they don't actually believe they live in a flood area," he said.
Cr Calvert said raising the dam wall was a "very simplistic answer to a very complicated question", which needed a complex resolution.
"I'm personally concerned that raising the dam wall will mean we shut the debate down on the issue and we relax ... and that would be very dangerous," he said.
Director of development and regulatory services at Penrith City Council Wayne Mitchell said his council would - among other possible solutions - like to see new road infrastructure.
As it stands, he said, the more than 90,000 people who would need to evacuate in the event of a flood would not be able to do so on the congested roads available.
"We also know from the SES that there will be insufficient warning times to evacuate that number of people so many of our residents in Penrith would be at significant risk," he said.
"That's also compounded by the fact that many people from the Hawkesbury and to the north of Penrith have to evacuate these areas through heavily congested roads, to the Penrith area."
Australian National University flood management expert Professor Jamie Pittock also gave evidence to the select committee on Monday.
He is "disappointed" the government is relying on a once-a-century flood for its planning standard.
"No dam will save us in this valley, any dam we build will be insufficient at some point, any dam will eventually fill and spill," he said.
Earlier this year, UNESCO's World Heritage Committee found the proposal - which will inundate parts of the heritage-listed Blue Mountains upstream, including Aboriginal cultural sites - was incompatible with the areas' World Heritage status.
Australian Associated Press
