Warragamba Dam Expected To Spill Monday

Warragamba Dam is anticipated to spill on Monday following heavy rains that began on Thursday. The dam is currently sitting at 96.3 per cent capacity.

One concern is the collapsed riverbank at Cornwallis Road, which has remained unrepaired for over three years since a drain caved in back in March 2021. Subsequent floods in 2021 and 2022 worsened the situation, turning it into an enormous riverside canyon. This alteration has led to a higher volume of floodwaters entering at much lower levels than before, endangering turf and livestock farms, as well as residents in the vicinity. It’s uncertain whether the large amounts of landfill brought in by two affected property owners will hold up against the impending flood.

Many residents are frustrated with the government’s inaction, both in terms of releasing water from the dam ahead of the recent heavy rains and in developing flood mitigation plans. This issue has persisted across administrations, including the previous Liberal National Party government and the current Chris Minns Labor administration.

Aerial view of Warragamba Dam spilling water during the heavy rain period of March 2022

Local SES teams have been preparing for a major rain event expected in late March or April. NSW SES Commissioner Carlene York has cautioned against unnecessary travel on dangerous roads. “The SES are putting out lots of warnings to be ready to our communities … particularly the metropolitan area and out around Hawkesbury/Nepean area,” she said.

Water NSW chief executive Andrew George announced in a media briefing today that Warragamba Dam, a significant source of Sydney’s drinking water, is forecasted to spill on Monday once the rainfall subsides. With the dam currently at 96.3% capacity, only 90 millimeters of rain are needed to trigger the spill, and the Bureau of Meteorology predicts 100-150 mm of rain in the dam’s catchment area during the ongoing downpour.

“That means the Warragamba will move into a spill, likely Monday morning,” George said. “What’s important about that is that the spill will occur likely when the rainfall event has moved on, so it is very important that the community remain vigilant.”

Premier Chris Minns stated that protocols are in place for a controlled spillage of Warragamba if rainfall surpasses a certain threshold. He emphasised the independent flooding risks posed by rivers and creeks in the Hawkesbury-Nepean catchment area, urging caution during severe weather events.

“Any local in the Hawkesbury-Nepean catchment will tell you that you’ve got [rivers and creeks] … that flood independent to what happens at Warragamba Dam,” he said. “I’ve got to make decisions about what’s in the best interests of those communities. And it’s important to note that those tributaries and rivers will flood in any event when you’ve got moderate to severe weather events like we’re seeing,” Minns said.

Minns highlighted the importance of avoiding unnecessary risks, particularly when it comes to traveling through floodwaters. He also acknowledged previous briefings indicating potential remediation works needed for the dam wall due to geotechnical risks.

“There are other geotechnical risks associated with the dam wall which means that Water NSW and the board of Water NSW may have to take action in relation to remediating the structure from an engineering point of view,” he said.