MASSIVE floods will hit the Hawkesbury someday, as they have in the past, experts warn.
The largest flood on record occurred in 1867, when water covered the region from Pitt Town to Kurrajong and the Blue Mountains to Riverstone.
Twenty people died, including 12 from one extended family in Cornwallis, and hundreds more people were made homeless.
‘‘Flooding will occur in the Hawkesbury as it has done for many thousands of years,’’ the State Emergency Service’s (SES) controller for western Sydney, Peter Cinque, said.
‘‘We’re going through a long spell now but floods are random, they don’t work on a schedule.’’
University of Western Sydney’s Associate Professor of Water and Environmental Engineering, Ataur Rahman, said with climate change, major floods had occurred more frequently all over the world.
‘‘The last such flood in Australia was in Brisbane in 2011,’’ Professor Rahman said.
‘‘That sort of flood hasn’t happened in the Hawkesbury since 1867, but that’s a long time ago and we expect these types of floods to happen more frequently.’’
He said such a flood today might be more devastating for the Hawkesbury, because it has a much larger population and more buildings than in 1867.
Warragamba Dam could absorb potential flood waters, but Professor Rahman cautioned it was no guarantee a catastrophe could not happen.
‘‘The dam is efficient in reducing smaller floods, but with a flood the size of Brisbane’s it could actually have a negative effect,’’ he said.
‘‘That’s because the water can’t pass quickly downstream and if the rainfall were constant, the spillway would have to be opened.’’
Hawkesbury state MP Dominic Perrottet said a government’s first duty was to ensure the safety of its citizens.
‘‘That’s why I am urging the state government to consider and factor in the real possibility that the Hawkesbury area could one day be faced with a serious flood issue,’’ Mr Perrottet said.
Mr Cinque said the SES continually updated and revised its emergency evacuation plan, working with Hawkesbury Council and government departments. ‘‘The Bureau of Meteorology can predict well enough to give a flood warning, two or three days in advance,’’ he said.
‘‘Our aim is to then get everyone out of areas likely to be flooded, taking them by road because roads are the best routes available.
‘‘Where people can’t evacuate themselves, we’ll provide buses.’’
He said if people refused to leave their homes or were stranded for other reasons, the SES would use boats or helicopters to get them out.
Mr Cinque said such rescues would probably occur on higher ground, on ‘‘little islands’’ in McGraths Hill, Pitt Town, Bligh Park or Richmond. ‘‘But we want to avoid things coming to that,’’ he said.
‘‘When we say evacuate; evacuate. You can’t stay and defend your home in a flood.’’