The overflowing of Sydney’s largest dam has left the city in ‘uncharted territory’ and could send floodwaters racing towards its outer suburbs, an expert has warned.
The heritage-listed Warragamba Dam about 70km west of central Sydney started spilling at 3pm on Saturday as a wild rainstorm battered the coast of New South Wales.
The volume of water is expected to increase into Sunday as rainfall and flooding continues, Water NSW said.
Premier Gladys Berejiklian said on Saturday afternoon she had been briefed on the dam situation ‘in relation to a potential for a one-in-five-year, one-in-10-year, or one-in-20-year event’.
Western Sydney University water expert Ian Wright said the rapid urbanisation of the area around the dam had left residents in the surrounding area on unsteady ground.
Residents in the Warragamba Dam catchment are on high alert and may have to evacuate as the primary reservoir of water supply for Sydney overflows (pictured)
NSW SES have issued an urgent evacuation order for the suburb of Picton located south of the dam as a result of rising flood waters
‘The urban development adds hard, impervious surfaces, and drainage infrastructure. In heavy rain, this can rapidly generate high-velocity floodwaters,’ he told News.com.au.
He said construction of roads and buildings around the dam since 1990 would stop any spillover from the dam from being absorbed back into the earth.
Ms Berejiklian has warned residents in the catchment area, as well as those in the mid-north coast, the Hunter, central coast and metropolitan Sydney to be on high alert and ready to evacuate.
NSW SES have issued a prepare-to-evacuate warning for the suburb of Picton south of the dam due to the rising flood waters.
‘Residents should monitor the situation and be prepared to evacuate when instructed to do so,’ the NSW SES said.
Flood expert Jamie Pittock is less concerned about the Warragamba Dam spilling as he is about tributary rivers downstream from it, such as the Grose River, overflowing and flooding parts of western Sydney.
‘There are around 5,000 houses (in western Sydney) that lie below the one-in-100-year flood return interval,’ the Australia National University professor said.
Water is pictured spilling over the Warragamba Dam west of Greater Sydney on Saturday
More rain is forecast for the New South Wales coast and other parts of the state, with flood warnings in place across the state
Most housing developments around the world are not allowed to be built in a one-in-100-year area, but successive NSW governments have allowed the irresponsible building of housing in these low-lying locations, Prof Pittock said.
‘It’s always worrying when there’s a flood in western Sydney because it’s one of the most dangerous places in Australia for floods.’
Prof Pittock said he was most concerned about Penrith, Richmond and Windsor, as the dam reached 99.2 per cent capacity on Saturday.
Bureau of Meteorology national flood services manager Justin Robinson said a spill at Warragamba Dam could lead to minor flooding in Sydney’s west, specifically at Penrith and North Richmond later on Saturday.
The suburbs of Penrith, Richmond and Windsor are of most concern for potential flooding as the dam reached 99.2% capacity on Saturday
‘It’s a very dynamic and evolving flood situation and we could see some very deep and rapid responding rivers with very high levels,’ he said on Saturday.
Mr Robinson said major flooding is possible for people in the Greater Sydney area, with the Hawkesbury-Nepean River areas bracing for significant flooding.
Other dams such as Nepean, Cataract, Cordeaux and Avon are also expected to reach capacity and begin spilling on Saturday afternoon, Water NSW said.
The mayor of Wollondilly Shire Council, the local government area in which Warragamba Dam is located, told AAP he was concerned about flooding in lower areas.
Western Sydney University water expert Ian Wright, said the rapid urbanisation of the region around the dam (pictured) has left residents in ‘uncharted territory’
Urgent flood warnings in place as NSW Premier Gladys Berejiklian advising residents to stay home
Robert Khan cannot remember the dam spilling over in his nearly 40 years of living in the area and said businesses on the main street of Picton were currently sandbagging their stores.
‘We’ve had drought, bushfires and floods. I know it’s mother nature but how much can a local business take?’ he said.
The dam spill has occurred amid the NSW government’s controversial plans to raise the dam wall by at least 14 metres to potentially hold back additional water in the Blue Mountains.
Between 1998 and 2002, the dam was upgraded to increase capacity by constructing an auxiliary spillway after the dam’s the last significant spill in August 1990.