Will draining this dam leave a major city without enough water?
The past two years have seen eastern Australia hit by some of the worst flooding on record. Two consecutive years of the La Nina weather pattern have drenched the country with monsoon-level rainfalls.
Now, a third year of La Nina seems likely. And a group of Sydney residents is pushing for the NSW government to take drastic action – by partially draining the Warragamba Dam before the next rains arrive.
But the state government is instead determined to raise the dam wall higher. The problem with this option is construction of the wall is expected to take 10 years.
Sarah Magnusson, spokesperson for residents group The Hawkesbury Community Alliance, says a decade is too long to wait.
"Our community needs flood mitigation now, not in the distant future. Ten years is too late," she said.
"[Drainage] is the best option for urgent flood mitigation for the community, who are filled with fear and uncertainty about what ... coming weeks might bring."
But University of NSW engineering expert Dr Stuart Khan says while the drainage option would be quicker, it risks leaving the Sydney metropolitan area without enough drinking water.
Warragamba Dam currently supplies around 80 per cent of Sydney's water supply.
"Reducing the current water storage in Warragamba Dam is a realistic alternative to raising the dam wall," he said.
"No solution provides complete protection from flooding, maintaining a lower water storage in Warragamba can significantly mitigate many floods, reducing peak flood heights and enabling additional evacuation time."
Do you think draining the dam is a good idea? Or is it not worth the risk of running out of water?
What we have with the dam wall raising is a group of engineers who support raising the wall and using the additional 17 metres as a mitigation dam, collecting water when heavy rains arrive and draining the top 17 metres gradually to reduce flooding in the Nepean/Hawkesbury system. On the other side are conservationists, most of whom are not affected by the flooding, and eco-warriors who will always find a frog or plant that will hold up any infrastructure to support their BANANA (Build Almost Nothing Anywhere Near Anything) mentality. I side with the qualified engineers.
On the question about whether draining Warragamba Dam to a level which will allow the remaining capacity to act as a mitigation dam, my answer is categorically NO! My reason is that the dam is critical for supplying our biggest city and droughts in the past have tested the existing capacity. By releasing any amount of water, there is no guarantee that rain will fall in the right area to refill the dam or if there will be enough rain. This plan to raise the wall has been kicking around for over 30 years, funds have been available from time to time but vocal minorities have been listened to. The time to commence the works is today.