Explained: How is the Australian government planning to save a submerged Sydney?

Again, thousands of residents in Western Sydney face a life-threatening flood disaster. At the time of writing, evacuation orders spanned southwest and northwest Sydney and residents of the Hawkesbury-Nepean Valley were being warned the crisis was escalating.It’s just over a year since the region’s long-suffering residents lived through one of the largest flood events in recent history. And of course, earlier this year floods devastated the Northern NSW town of Lismore.Right now, attention is rightly focused on helping those immediately affected by the disaster. But as the floodwaters subside, we must urgently act to avert a repeat of this crisis.Obviously, nature is a major culprit here. But there’s plenty humans can do to plan for major flooding and make sure we’re not sitting in the path of disaster.So what’s caused the current the flood problem?The first driver of this disaster is nature and geography.For many months now, much of New South Wales has experienced significant rain and associated flooding.There’s a reason both the Hawkesbury-Nepean and Lismore flood the way they do – geography. Both areas sit in low-lying bowl-like depressions in the landscape.Lismore sits at the confluence of several large rivers that each drain significant catchments – and so can deliver large floods.And in the Hawkesbury-Nepean, huge rivers have to pass through a very tight “pinch point” known as the Sackville Bathtub. This slows the flow, causing water to back up across the floodplain.The NSW government wants to raise the wall of the Warragamba Dam to help alleviate this problem. But as others have argued, this controversial proposal might not work. That’s because raising the wall will control only about half the floodwater, and won’t prevent major floods delivered by other rivers feeding the region.The second factor making the current floods so bad is the exposure of infrastructure and housing. In the Hawkesbury-Nepean region, lots of stuff people care about – such as homes, businesses and schools – is in the path of floodwaters.In an ideal world, nothing would be built on a floodplain. But due to Sydney’s growing population and the housing affordability crisis, local governments in Western Sydney have been under pressure to build more and more homes, despite the known flood risk.In 2018, more than 140,000 people lived or worked on the Hawkesbury-Nepean floodplain. Due to this large population and the region’s geography, the area has the most significant and unmitigated community flood exposure in Australia.What’s worse, the region’s population is expected to double over the next 30 years. At the same time, climate change will change rainfall patterns and make severe flooding more likely.

Being prepared