Ex-tropical cyclone Kirrily puts Warragamba Dam at risk of overflowing

Torrential rain caused by ex-tropical cyclone Kirrily is putting Warragamba Dam close to capacity, with expert opinion divided on whether the dam will overflow.

Opinion is split over whether Warragamba Dam will overflow. Picture: Taras Vyshnya

Torrential rain caused by ex-tropical cyclone Kirrily is putting Warragamba Dam close to capacity, with expert opinion divided on whether the dam will overflow.

The low pressure system, downgraded from tropical cyclone Kirrily, made landfall as a category two system in Queensland before commencing an 11-day journey to cross the NSW border on Monday.

Eastern NSW has felt the effects of the ex-tropical cyclone, as it brought rain and a cool southerly change to much of the state, bringing down hot temperatures.

Sydney recorded its warmest night in three years, while Gosford recorded its warmest pair of nights in four years – the last two nights both staying above 23C.

But as the centre of ex-tropical cyclone Kirrily moved off the coast this morning, it has caused flash flooding in some suburbs with Campbelltown recording 40mm of rain and totals up to 67mm in Holsworthy.

Outback regions also recorded heavy rainfall with some totals near 100mm, including 103mm of rain recorded in White Cliffs, amounting to about four months worth of rain – the town’s heaviest rainfall in 31 years.

Warragamba Dam was at 96.5 per cent of capacity as the rain event moved in, with rainfall reaching 20-70mm across the past two days, the highest recorded in Goulburn at 69mm.

A Spokesperson for WaterNSW has addressed the concerns, reassuring residents that Sydney’s main water storage is not going to overflow.

“The state’s dam manager WaterNSW has confirmed storage levels at Warragamba

Dam are at 97 per cent, following recent rainfall,” the WaterNSW spokesperson said.

“Given conditions across the catchment are quite dry due to the recent heat, much

of the latest rain has absorbed into the soil, rather than run into the dam,” they explained.

“Based on these factors, and WaterNSW’s forecasts and modelling, no spill is anticipated at Warragamba Dam.”

However, Sky News Weather meteorologist Rob Sharpe said ex-tropical cyclone Kirrily is likely to cause Warragamba Dam to spill.

The Warragamba Dam hit capacity and overflowed in March 2022. Picture: NSW SES

“The widespread nature of the rain on the already wet catchment is causing the creeks and rivers throughout the 9000km square catchment to flow at a decent speed and so it seems likely to my thinking that Warragamba will go slightly beyond 100 per cent of its capacity,” Mr Sharpe said.

“This won’t cause any issues downstream in the flood plain of the Hawkesbury Nepean.

“However, it is a reminder for residents to be prepared for any potential flood events as a full Warragamba won’t provide any flood mitigation for the region.”

A proposal to raise Warragamba Dam’s wall was scrapped by NSW Labor government in October last year, citing major costs as well as environmental and heritage concerns.

The project proposed to raise the dam’s wall by 14 metres, allowing it to hold an additional trillion litres, as well as possibly reducing flood damage by up to 75 per cent.

More than $1bn would have been required to modify the dam’s wall and would have affected a portion of the Blue Mountains World Heritage Area situated around the dam’s Lake Burragorang reservoir.

Severe weather events have caused the dam to overflow several times in recent years, most recently in March 2022 following heavy rain across NSW and Queensland, flooding areas downstream.