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‘The valley can fill up like a bathtub’: Experts warn of known NSW flood risk

The emergency evacuation of thousands of Western Sydney residents living in flood-prone areas has been 200 years in the making, climate experts say.

The NSW government has failed to prepare these residents – and those of the future – for such events, the experts claim, the government instead hoping to double the area’s population in 30 years.

After days of torrential rain, dozens of communities along the Hawkesbury-Nepean River system are facing the worst flooding since 1961.

About 18,000 people had been evacuated from their homes during the NSW floods disaster as of Monday morning.

On Sunday, NSW Premier Gladys Berejiklian warned this week’s expected rainfall was “beyond anyone’s expectations”, saying up to 4000 people around the Hawkesbury Valley should be on standby to evacuate.

But experts say the crisis has been a long time coming.

‘Extremely dangerous situation’

Professor Jamie Pittock, an environmental policy expert at the Australian National University, said authorities have been recording extreme floods in the Hawkesbury-Nepean Valley for more than 200 years.

However despite this flooding risk, the NSW government is still allowing people to live there.

“It’s an extremely dangerous situation,” Professor Pittock told The New Daily. 

“In this particular valley, the flooding is more dangerous than other parts of Australia because the river channel is constricted downstream by river gorges. The valley can fill up like a bathtub in a really big flood.”

Adding to this risk is the location of regional towns on small hills.

“The danger is people get trapped on these small hills, and in a catastrophic flood these people become submerged under water,” Professor Pittock said.

Andrew Gissing, an emergency management expert with the Bushfires & Natural Hazards CRC, agreed the Hawkesbury-Nepean Valley “has one of the greatest flood risks in Australia”.

“Here, several thousand homes are currently at risk of flooding, many facing flood waters several metres deep,” he said.

“There are fears that many will not evacuate and be trapped by rising flood waters, overwhelming the capacity of emergency services to rescue them.”

But rather than encouraging residents to move to safer ground, Professor Pittock said the NSW government plans to move another 134,000 people into the area by 2050.

“Another government failure is they haven’t invested any money into proper evacuation roads for about 20 years,” he said, adding the main arterial roads go over hills and across creeks that can be easily flooded.

“The engineering solution is to build a bloody great arterial road that’s elevated so people can get out. But that simply hasn’t been done.”

Tensions rising over Warragamba Dam

To help mitigate the flood risk in the Hawkesbury-Nepean region, we should raise the wall of the Warragamba Dam by an extra 14 metres, Western Sydney Minister Stuart Ayres said.

The Warragamba Dam, responsible for holding Sydney’s main water supply, overflowed with rain water during the weekend, causing river levels to surge and flood low-lying areas.

Management over the dam has been a long-running political issue.

In 2017, Infrastructure NSW published a flood strategy report that called for the dam wall to be raised, warning the number of people living in danger zones was expected to double by 2050.

“Up to 134,000 people live and work on the floodplain and could require evacuation,” the report reads.

“This number is forecast to double over the next 30 years.”

But Professor Pittock says raising the dam wall will only encourage more downstream development that will be inundated when “the inevitable big flood exceeds design limits”.

The dam won’t regulate flood waters from downstream tributaries like the Grose River and South Creek, and it will also inundate parts of the Blue Mountains World Heritage Area, he said.

Traditional owners have launched a federal bid to stop plans to raise the dam wall, which they say will destroy ancient sites and songlines sacred to the local Gundungurra people.

The Gundungurra Aboriginal Heritage Association is applying to save the area under Aboriginal and Torres Strait Islander heritage protection legislation.

By Samantha Dick

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