Authorities warn of ‘blue sky’ flooding even as waters rage around NSW

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While the water is starting to recede around parts of NSW, following a mammoth deluge on Friday that caused extensive flooding along the Hawkesbury and Nepean Rivers and other parts of the state, experts warn this particular event is far from over.

As sun bears down on the turbulent brown water gushing down the Hawkesbury river, it’s easy to see how people — either locals or those coming to the impacted region for a gawk — can become complacent.

“It’s not a flood like we have seen in the past,” one local says to another while strolling along the picturesque Windsor River Walk in the Sunday sunshine.

“The blue sky … the sun … it’s hard to picture it getting any worse”.

And those few words are what experts fear could cause locals and visitors alike to take unnecessary risks.

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While the flood waters of 2021 and 2022 in the Hawkesbury region reached a height of 12.9m in March 2021 in March and 13.7m at the same time the following year, the event of 2024 nudged just short of 9.5 metres.

But while the depths may be smaller this time around, the danger the turbulent waters pose remains the same, especially given the Warragamba Dam is still set to overflow for more than a week.

With minimal rainfall since Saturday morning, and clear sky ‘bluebird’ days across the weekend, authorities are worried residents across the state may become complacent and underestimate the dangers of the ongoing flood threat.

Speaking to news.com.au, NSW State Emergency Service spokesperson Stephanie Heard said the Hawkesbury-Nepean’s notorious “bathtub effect” often gets forgotten – especially by those who don’t live in the region.

“The big thing with the Hawkesbury-Nepean is that bathtub effect,” she told news.com.au.

“Considering our basin, yes the rain has stopped but last night the flooding had reached the ‘bath plug concept’.

“While there’s no rain, [the water] gets sucked and levels goes up. That’s why the Hawkesbury-Nepean is the greatest risk to us given the way it floods.”

Ms Heard said that while a ‘blue sky’ event might be unusual compared to previous Hawkesbury-Nepean floods, in the state’s West and Southern parts – some of their floods in late 2022 and early 2023 were the “worst on record, and majority happened during a blue sky flood.”

“A lot of the time when we see these downstream communities, one of the risks is the ‘blue sky’,” Ms Heard explained.

“It’s hot and there’s a risk that people and kids might see flood water and want to get boogie boards out, which is something we normally do see.

“However yesterday, I hadn’t seen any vision of that, which gives me comfort that people know the risks.

‘It [blue sky during flood] is something bizarre…it can be peaceful with the blue sky, but the risk is very much still there.”

A number of emergency warnings remain in place, with 32 alerts still active affecting up to 4000 residents in low lying parts of Freemans Reach, Cattai, Pitt Town, Ebenezer and Pitt Town Bottoms.

Senior meteorologist with the Bureau of Meteorology Sarah Scully told the Today Show an “enormous” amount of water is continuing to make its way downstream.

“We are expecting there to be peaks in the lower catchments throughout this morning,” she said on Sunday.

In 2022, the Forbes region experienced a similar ‘blue-sky’ event — which meant that while the region basked in near perfect weather, water continued to accumulate and move down stream through various catchments. In turn, that flow-on effect under the guise of blue skies created “issues with river rises and renewed flood peaks”.

At around the same time, Victorians were also warned about the threat of ‘blue-sky’ flooding as rivers continued to rise in October 2022.

As with the current situation in NSW, with minimal rainfall and clear skies over the past few days, authorities warned residents not to underestimate the dangers of the ongoing flood threat.

Speaking at the time, Victorian State Emergency Service Chief Operations Officer Tim Wiebusch said Victorians needed to remain vigilant throughout what will feel like a rollercoaster of weather events.

“The scenario we’re going to find ourselves in, on and off for the next few weeks, is we’ll have periods of very heavy and extreme rainfall which mean our rivers will be at moderate to major flooding levels,” Mr Wiebusch said in October 2022.

“Then we’ll see the blue sky, but the rivers will continue to rise and impact communities. “The state will have blue skies as we’re heading into the latter part of the week, and while the rain might come again … we’re going to see – for the next six to eight weeks – potential for these rain events that will come and go in between blue skies,” he added.

Since Friday, when parts of the state copped 250mm of rain, thousands of residents across Sydney’s west and northwest have been evacuated while 146 were saved from flood waters since Saturday morning.

Despite the rain easing and major flooding risks dropping along the Hawkesbury River, multiple evacuation notices remain in place.

Water levels are expected to peak on Sunday before subsiding, with little rain predicted to fall until Tuesday after clouds parted over the weekend.

The NSW government announced the recovery package, jointly funded by the Commonwealth, on Sunday morning. It includes funding for local councils to assist with clean-up costs, emergency accommodation and payments for essential items for affected residents.

Residents will have access to grants to help restore essential household items and to undergo repairs to damaged homes.

Parts of the state were hit with up to 180mm of rain in just one night, with fears the Warragamba Dam is still set to overflow for more than a week.

with Lauren Ferri