Australia: Warragamba Dam disaster warning - downpour now could 'devastate' western Sydney

The spill of water over the Warragamba Dam wall on Thursday morning should serve as an urgent warning: much of western Sydney would be devastated by flood if there was another major downpour now, reports the Sydney Morning Herald.

This caution comes from Stuart Khan, associate professor at the school of civil and environmental engineering at the University of NSW, who has been telling the state government for three years that it should never let Warragamba rise to full – because ample space is needed for flood mitigation.

According to the report, the government initiated the Hawkesbury-Nepean Valley Flood Management Review in early 2013 in response to extensive flooding across south-eastern NSW the previous year, when Warragamba Dam spilt for the first time in 14 years. This review is still running but its first stage concluded there was no "simple solution or single infrastructure option that can address all of the flood risk in the Hawkesbury-Nepean Valley floodplain".

The state government's current emergency planning for the basin is based on a repeat of a flood in 1867 that inundated 200 square kilometres of north-western Sydney. As said by State Emergency Service (SES) flood risk expert Steve Opper "At some time in the future, a flood of this magnitude will occur," SES flood risk expert Steve Opper told Fairfax Media in 2013. "It is not a question of if; it is a question of when."

However, Associate Professor Khan says there is a solution: controlled releases of water from the dam, so it never approaches full. Sydney needed to make decisions that served both its water supply security and its flood risk.