2nd March 2012 update: It's funny; I use a hit counter service to track who arrives at my blog and what they've typed into Google to get here. Every time it pours rain, I get a "flood" (pun intended) of traffic of people Googling "flooding", "Hawkesbury", "Nepean", and, amusingly "will my house flood in (insert almost every locality in the Hawkesbury Nepean basin)"
Nothing like a bit of rain to get people worried, is there? And it looks like the spillway will be opened at Warragamba for something like 14 years tonight. Everyone's going to wake up in the morning to the threat of bridges closed and all the inconvenience and danger that entails.
In addition to the below remarks I made a year ago, I feel more strongly than ever that people who live in on a flood plain need to better educate themselves about what has happened before. Certainly, the deluge (there I go again) of traffic shows people are interested.
Permit me to endorse the work of the Hawkesbury Nepean Flood Mitigation Action Committee, a group who have agitated for better long term planning, action and education in this area for many years. Harangue your state members. Speak to your local Councillors. Go to your Council and work out what level your house sits at, and acquaint yourselves with how frequently your area, or areas near you have gone under in the last 220 years.
Also, as a Hawkesbury/Nepean local, you might want to subscribe or favourite the other writings of my blog, as I range over subjects diverse and fascinating. Love to hear your feedback!
|Extent of the 1867 flood in the Hawkesbury (from Hawkesbury Council)|
I hate to say it, but it is inevitable that one day we will have a flood in the Hawkesbury-Nepean as least as serious as the historic one we are currently seeing Queensland, and it won't be until then that we'll get real action on flood mitigation in this area.
Then all the pollies will wail about the loss of property and life, all the residents who've moved into the area and have no idea what it's like to live on a floodplain will ask why they were allowed to build or buy in flood-prone areas, and all the Cassandras will say "we warned you for years, and you ignored us."
The map above shows the extent of the largest historical flood experienced in the Hawkesbury, in 1867. If you live around the Hawkesbury, there are two markers you need to visit. One is a nail in the outside wall of the Macquarie Arms pub at Windsor. A second is in the grounds of Windsor Public School. If you cast your eyes across from either of those points and use your imagination, you may get a sense of the scale of a major flood. The water reached that level in 1867. Now look at that map again. If you live in the Hawkesbury, there's a better than even chance that your home lays in that blue area, since our population is densest around Windsor, South Windsor, Bligh Park, Richmond and so on. And any flood will not have to be of the scale of the 1867 event to be catastrophic. This year marks 50 years since the last big flood in living memory, in 1961. It's a common misconception of statistics to think that a statistically overdue event becomes more likely as time passes, but it underlines that a generation of Hawkesbury and Penrith area residents have little personal experience of a big flood. The terrible things we are seeing on TV today will one day play out in our own back yards. Why should we believe that something that has happened many times before will not happen again?
Warragamba dam is not a flood mitigation dam. It has a capacity of 4 sydney harbours. It will only reduce flooding by the amount of storage it has available when it starts raining, which at the moment is 1 sydharb (It is 73% full) (2nd March 2012 note: It is now over 98% full and has increased by 0.5% in less than a day).
Warragamba's catchment extends from Lithgow to Lake George near Canberra. It could easily fill in 1-2 days. Wivenhoe dam (Brisbane) is a flood mitigation dam, holding 5 Sydharbs, 3 for drinking and 2 for flood mitigation. As you just witnessed this is to reduce frequent little floods. It does little to reduce a major flood event.
The rivers flowing through Rockhampton recently received something like 300+ sydharbs in a month. Talk of flood mitigation in that catchment is just that, talk.
Unfortunately, if the catchment above warragamba received anything like the rainfall recently seen in Qld, or Vic for that matter, the free capacity in warragamba would be of little significance.
So what will we do? What should be being done now?