Warragamba Dam wall raising ‘will save thousands’

Raising the Warragamba Dam wall by 14m could help save thousands of lives from future flood risk if potential development is fulfilled on a flood plain in Sydney’s west.

NSW Premier Dominic Perrottet said raising the dam wall was the ‘single biggest piece of work’ his government could undertake to protect lives and property from the risk of flooding. Picture: NCA NewsWire / David Swift

Raising the Warragamba Dam wall by 14m could help save thousands of lives from future flood risk if potential development is fulfilled on a flood plain in Sydney’s west, according to new modelling released by the NSW government.

Part of the Coalition’s response to the independent flood inquiry – expected to become public within the next month – the modelling suggests the number of people unable to evacuate in a one-in-100-year flood risk by 2041 would fall to zero if the dam extension went ahead.

The modelling suggests that under current committed development figures, 1700 people would be unable to evacuate if the dam wall remained at its current height.

That leaps to 8600 people by 2041 once 107,000 extra people are included under development projections.

The prospect of another ­wetter-than-average La Nina weather cycle this summer has raised the spectre of the ­Hawkesbury-Nepean valley – encompassing a swath of ­western and northwestern ­Syd­ney, including the suburbs of Penrith, Windsor and Richmond – being hit by another major flood, the third since 2020.

An appendix contained within Mick Fuller and Mary O’Kane’s independent flood inquiry – written by John Hann – endorsed the raising of the dam wall, concluding the project would have the “single largest impact” on flood mitigation compared with other infrastructure options available.

Under 2041 development pro­jections, the number of ­people unable to evacuate would be reduced by 88 per cent if the dam wall was raised, a product of dam outflows being delayed by almost four days and preventing closure of vital infrastructure, including the Windsor Bridge.

With a quarter of a million residents already living in the Hawkesbury-Nepean valley, the case study noted the sole largest drive of flood risk was development on the flood plain, calling for stronger planning controls to be implemented and arguing the measure was the “most effective” way to mitigate the threats of ­inundation.

Mr Hann recommended establishing new flood planning levels and relocating the most vulnerable residential com­­munities in circumstances where it represented a “sustainable and safe alternative to exposure to ongoing extreme flood risk”.

Under modelling contained in the appendix, 135,000 people in the area would be forced to evacuate if a one-in-100-year flood struck in 2041.

The Perrottet government has written to federal Infrastructure Minister Catherine King seeking a 50-50 contribution funding model with the federal government.

Mr Hann’s case study suggest­ed the dam raising’s capital costs would reach $2bn – $400m more expensive than previously thought.

NSW Premier Dominic Perrottet said raising the dam wall was the “single biggest piece of work” his government could undertake to protect lives and property from the risk of flooding.

“Our primary focus is on saving lives, saving properties and the future-proofing of western Sydney,” Mr Perrottet said.

“Residents of western Sydney deserve strong long-term flood mitigation and that’s what our government will deliver,” he added.