My sympathies go out to those millions of people affected by the hurricane last week which hit Louisiana last week. However, it was a disaster waiting to happen and a lot of the reasons have to do with human society’s stuborness and short-term interests. This is why:-
Firstly, it’s the Mississippi delta itself. In the last 7000 years the river has switched channels about 7 times, each time building up a sub-delta with sediment and then switching to another channel. Each time this switch happens the old parts of the delta subside as their sediments compact and de-water and the lithosphere depresses under the load until most of it is submerged under the sea. This is the natural course of things. The river needs to replenish the sedment for the delta to stay above sea level.
Then there’s the human interaction. In the 19th century it was seen that the river was about to switch from one channel to another so they “tamed” the river with levees. However, this has two effects: firstly the river height is increased and it will continue to do so until at one point the levees WILL fail and the devistation caused will be far greater than it would have been if the river had not been enslaved. Secondly, because the water flow has been increased and the river is not allowed to flood there is no longer any sediment deposition on the delta. The parts which are economically important are being kept dry using sea defences and the other parts are being lost at an alarming rate.
Here’s an article (google cache) from a Baton Rouge newspaper in 2002 which is a pretty decent summary.
As you can see, the problem has been known about for some time, yet no-one has had the political will to either move people and homes from the most vulnerable areas and let the river do its own thing or abandon New Orleans completely and retrench further inland where the subsidence is less (and hope that the levees which bind the great river don’t fail).
As it was Hurricane Katrina luckily only caused the levees on the man-made lakes to the north to fail. If the Mississippi had breached its levees further up stream, where it’s trying to switch channels, there would have been a great deal more destruction than there was. New Orleans was relatively lucky this time.
In my opinion they should take this opportunity to abandon the old city, except for the tourist “French Quarter” and build a new city on land that’s not liable to flood, especially when the Mississippi finally changes course. It won’t happen though. There are too many bloody minded politicians who have shouted “we will rebuild” and hence have too much at stake not to. When they do finally get the city back in order it will only be a matter of time until its submerged again, this time with even more loss of life.