NSW floods: Warragamba Dam spills equivalent of one Sydney Harbour a day

The devastating Sydney floods are showing no sign of slowing down. Now, furious victims are questioning if more could have been done.

Warragamba Dam on March 21. Picture: Water NSW

Sydney’s floods are showing no sign of slowing down – with furious victims now questioning if more could have been done.

The days of rain has meant Warragamba Dam, the city’s biggest, continues to overflow.

Water NSW, which operates the dam, said yesterday that more than 500 gigalitres of water was being released daily.

Sydney Harbour holds about 500 gigalitres of water, meaning the dam is discharging the equivalent of that daily.

Even with its current discharge level of approximately 500GL today, Warragamba Dam is doing exactly what it is designed to do, making for some spectacular images.
To learn more about how Warragamba Dam operates during a flood event, visit https://t.co/ZsXJxiJAknpic.twitter.com/5ZFpaxop5j

— WaterNSW (@WaterNSW) March 21, 2021

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Discharging water from Warragamba Dam means it spills into the river systems surrounding Sydney however Water NSW said the dam was not to blame.

“Modelling indicates that approximately 1500 GL of water will flow into the dam in the seven days since the extreme weather event commenced, a figure that represents 75 per cent of the dam’s storage capacity of 2000 GL,” Water NSW said in a statement.

“Flow data up to (the morning of March 21) indicates that half of the floodwaters in the Hawkesbury-Nepean river system downstream of the dam were from tributary flow, not the dam.”

Water NSW explained that, in order for the dam to have had enough capacity to capture all inflows from the rain event, “Warragamba would have needed to be taken down to 25 per cent of storage capacity, prior to the rain event”, a spokesperson said.

Warragamba spilling. Picture: Water NSW

Warragamba Dam yesterday. Picture: Water NSW

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The lowest level Warragamba Dam has ever been was 38.8 per cent in 2004.

“While Water NSW is not authorised to lower the storage based on weather forecasts, significant prereleases prior to a flood event could make flooding events more dangerous,” the organisation said.

“Downstream tributaries could be inundated in a big rain event (as they are now), and the addition of extra water released from the dam could increase downstream impacts.

“Water NSW confirms that 130 GL of water has been released in recent months to hold the storage at around 1m below full supply level.

“This was done in accordance with strict operating protocols and resulted in the need for dam releases during this event being delayed by a full day, allowing greater time for preparedness.”

The flooding has hit levels not seen since 1961.

“It is one of the biggest floods we are likely to see for a very long time,” Bureau of Meteorology flood operations manager Justin Robinson said.

Thousands of people have been evacuated from their homes as torrential rain continues to bucket down.

SES Emergency crews near the Nepean River. Picture: NCA NewsWire/Gaye Gerard

The Bureau of Meteorology said the wild weather was forecast to re-intensify north of Sydney on Monday before easing later in the week.

Conditions were “going to be treacherous yet again,” senior climatologist Agata Imielska told AFP.

Rainfall records were forecast to continue tumbling in the coming days, she added.

The dam spill has triggered debate among NSW’s politicians, with some arguing more could have been done.

Premier Gladys Berejiklian yesterday slapped down suggestions the dam should have been lowered more.

“You have to look beyond the dam; it’s all the rivers that are overflowing, it’s the sustained rainfall in very short periods of time,” she said.

Emergency Services Minister David Elliott is reportedly “absolutely furious” water levels were not lowered.

Mr Elliott, who is the member for Baulkham Hills in Sydney’s west, said yesterday there would be a “full and frank discussion” about managing the dam once the rain event was over.