While 425 square kilometres of land lie within the probable maximum flood in the Hawkesbury-Nepean valley, it has also long been identified as fertile for property development amid rising house prices and supply shortages.
Documents released through the NSW parliament reveal the Department of Planning projects that, by 2041, 12,000 new homes are expected to be built on flood-prone land in the quickly expanding north-west growth area around the valley. Local councils surrounding the valley currently have plans for several thousand more homes.
Many experts fear that is a conservative estimate, particularly if the government goes ahead with its controversial proposal to raise the Warragamba Dam wall.
The plan to raise the wall, which is contentious, even within the government, is often touted as a solution to flooding in the valley. While it may mitigate some floods, many experts believe it would be of limited value with potentially disastrous environmental effects.
There is also a perverse notion of the “levee paradox”, which means raising the wall could make future floods more dangerous.
“The idea is you build flood control infrastructure like levee banks or you raise a dam and it means politicians say great we can relax and develop more on the flood plain,” Jamie Pittock, a professor in environment and society at the Australian National University, says.