Wednesday, August 27, 2008

New Orleans Island

Three years after Katrina, another hurricane is headed for New Orleans.

Tropical Storm Gustav, which will surely be a hurricane again tomorrow night or the next day, is expected to pass the western tip of Cuba Saturday night. It isn’t really possible to predict the movements of a hurricane any farther in advance than that, but the most likely track would have it narrowly miss New Orleans Monday night, following in the footsteps of Katrina.

Every time a hurricane approaches the Gulf of Mexico, people in New Orleans are losing sleep. The city closest to the center of the gulf, it is especially vulnerable to hurricanes. It is just a matter of time before it gets hit again.

And we don’t know how many more hits it can take. The same geological forces that dropped the city itself below sea level are taking away the delta land that protects it from the waves. Every hour the sea takes the roots out from under a tree somewhere in the delta, in an area where the water is too deep for a new tree to grow. When a hurricane hits, a million trees can go down at once. For political reasons, the maps aren’t being redrawn very quickly, but if you compare the pre-Katrina and post-Rita satellite images of the Louisiana coast, you can see that those two events took away vast areas of land.

The city at the mouth of the Mississippi is turning into an island.

One estimate among geologists (famously broadcast on 60 Minutes in 2005, but not news to scientists who have been following this issue) is that around 2100 what remains of the delta will be submerged and the sea will reach New Orleans. Experts disagree about the current rate of subsidence, but there is no debate that most of the city is several meters lower than it was 500 years ago, and whether the ground is sinking at 1 millimeter a year, or 2, it is a problem.

Most of New Orleans could be submerged too — its current sea walls and levees aren’t built to stand up to the waves of the sea. They can handle a Category 1 hurricane only because they don’t face the open sea. Engineers disagree about whether they are fit to stand against a Category 2 hurricane. If Gustav keeps to its forecast, they may get to find out.

Massive sea walls could be built around the city to keep the waves out. Engineers from The Netherlands say it could be done, but it could cost so much, it would be hard to justify in terms of real estate value.

The walls, if they were built, would separate the city from the Mississippi River. So it really wouldn’t be the same city.

On the other hand, there are those who do not want to see New Orleans rebuilt. Such a battle against nature, they say, can only be costly, risky, and futile. And some argue that New Orleans is not “American enough” to justify a national effort to save it.

In my opinion, though, the distinctive character of New Orleans is precisely the reason we cannot afford to lose it. For it to succeed, though, it may have to succeed as an island — which means moving it above sea level. The widely offered suggestion of raising much of the city about two meters above sea level makes sense to me. Doing that across the whole city would cost a fortune, of course — $10 to 40 billion just to deliver the fill, and besides, there aren’t enough highways to carry all the trucks it would take. But compare that to the cost of responding and rebuilding after just one disaster, and the relative cost doesn’t seem disproportionate.

And we’re not talking about blanketing the whole city with a layer of fill all at once. Some neighborhoods, of course, are well above sea level, weren’t flooded, and don’t need to be raised. Many blocks are too historic to be torn down or buried. But there are also areas that will work much better if they are lifted up.

It could make a big difference someday to have hospitals, the electric power supply, and major through streets above sea level. I would also want to build up the sides of the canals with level land a city block wide — then I wouldn’t worry so much about the canal walls.

I am only guessing here, but the point is that some places are more important than others and that you can get a lot of the benefit from being above sea level even if it’s just a fraction of the city, and it’s something that can be done bit by bit. Lots of the homes being rebuilt are on stilts. That’s a move in the right direction. It protects the individual home from flooding, and it’s a necessary step if the street may be raised in a few years. It’s worth thinking big if that’s going to keep New Orleans going into the next century.