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Dam spilling one Sydney Harbour a day


Sydney’s floods show no sign of slowing down – with furious victims now questioning if more could have been done. The days of rain have meant Warragamba Dam, the city’s most significant, continues to overflow. Water NSW, which operates the dam, said yesterday that more than 500 gigalitres of water were released daily. Sydney Harbour holds about 500 gigalitres of water, meaning the barrier discharges the equivalent daily.

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 representing 75 percent of the dam’s storage capacity of 2000 GL,” Water NSW said.

“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, 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 percent of storage capacity before the rain event”, a spokesperson said.


The lowest level Warragamba Dam has ever been was 38.8 percent in 2004. “While Water NSW is not authorized to lower the storage based on weather forecasts, significant prereleases before a flood event could make flooding events more dangerous,” the organization said.

“Downstream tributaries could be inundated in a significant rain event (as they are now), and adding 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 the supply level.

“This was done by 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 as torrential rain continues to buck down. The Bureau of Meteorology said the wild weather was forecast to re-intensify north of Sydney on Monday before easing later in the week.

The dam spill has triggered debate among NSW’s politicians, with some arguing more could have been done. Conditions were “going to be treacherous yet again,” senior climatologist Agata Imielska told AFP. She added that rainfall records were forecast to continue tumbling in the coming days.

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 overflowing; it’s the sustained rainfall in concise periods,” she said.

Emergency Services Minister David Elliott is reportedly “absolutely furious” water levels were not lowered. Mr. Elliott, a member of 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.


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