NSW weather update: Warragamba Dam risks overflow after ‘bomb cyclone’ wreaks havoc across Sydney

There are fears that Australia’s largest urban water supply could overflow, adding to the risk of flooding after a damaging and complex low-pressure system dubbed the “bomb cyclone” caused widespread havoc across New South Wales.

Warragamba Dam in western Sydney is nearly at full capacity and is expected to “moderately spill” on Thursday after days of intense rain and destructive winds, Water NSW said.

“The duration and volume of the spill will ultimately be determined by rainfall received across the catchment,” it said.

Thousands of people are without power, trees have been uprooted, and beaches eroded after the wild weather system battered large parts of Australia’s east coast.

State regulations do not allow water to be released at Warragamba Dam before predicted rainfall or to mitigate floods as it supplies 80 per cent of Sydney’s drinking water.

Spills at the dam are not uncommon, previously occurring in May, and three times in 2024.

Warragamba Dam flows into the Hawkesbury-Nepean river catchment, where the bureau has warned flooding could occur on Thursday.

Other, smaller dams were also spilling after reaching capacity following heavy rains.

The downpours formed part of a “vigorous” east coast low the Bureau of Meteorology predicted would move into the Tasman Sea.

Lord Howe Island residents were warned to prepare for increased winds and elevated seas, with waves up to five metres.

Damaging winds with gusts up to 100km/h were expected to continue through Thursday morning around parts of northern NSW.

More than 3400 incidents were reported to the SES during the weather event, beginning on Monday, with 10 flood rescues.

Additional crews from the ACT were joining the response and recovery efforts late on Wednesday.

About 8000 Endeavour Energy customers were without electricity as crews worked to restore power on Wednesday night, down from a peak of 30,000.

Dozens of properties were under evacuation warnings due to flooding at Burrill Lake and Sanctuary Point near Jervis Bay.

In nearby Sussex Inlet, Fay Brown was stranded when roads approaching the Badgee Bridge flooded.

Without a four-wheel drive, Ms Brown would have used a flood access road, but the local council continued a long-standing practice of blocking the road rather than allowing residential access.

“This happens every time we have heavy days of rain. I’ve lived here 11 years and been stuck on at least five occasions,” she told AAP.

“Once we were stuck there for four days.”

- With AAP