In any given year, what are the risks of your house burning down, you getting sick, or you crashing your car?
Low, I hope. These events have a low probability, but serious consequences. So we weigh the risk, and take out insurance.
So it is with our floodplain. There have been 124 floods in the Hawkesbury-Nepean since the 1790s. We had one this year (a baby — between 1:5 and 1:10 probability), and worse ones are a statistical inevitability.
The NSW Government 2017 report, Resilient Valley, Resilient Communities says that the damage of a bad flood could be between $5 billion and $7 billion dollars, considering that 134,000 people live and trade on the floodplain.
In a bad flood, 90,000 of those people would need to be evacuated. 12,000 homes would be inundated.
The report also says that this risk could be reduced by 75% if Warragamba Dam is raised by 15 meters, saving lives and slashing $5 billion from the damage bill. A wise investment, I think.
The cost would be that, in those rare rainfall events, a fringe of land around the current high waterline of Lake Burragorang would be subjected to temporary inundation, amounting to 0.04-0.05% of the Greater Blue Mountains World Heritage Area. Crucially, preliminary modelling suggests the most sensitive areas of the catchment, like the Kowmung River and its tributaries, would not be affected at all.
There is a lot of misinformation put about concerning the Warragamba Dam raising project. That it’s a stalking horse for development on the floodplain. That it will ruin a world heritage site. That it’s about increasing Sydney’s water supply.
These claims are not true — even though these issues are important. The project is about protecting life and property. I observe that most people who are opposed to the project don’t live on the floodplain. They live elsewhere, high and dry. They endure no risk to themselves, their families, or property. They are entitled to their views, but have no stake in the outcome.
The attached video is an interview I did recently when I was approached by someone doing some academic research from my alma mater, the University of Sydney. I summarise many of the points I frequently make about the project, and Hawkesbury Council’s attitude towards it.
I’ve written about this subject many times before: