No, I’m not referring to New Orleans residents voting to re-elect their idiotic mayor Ray Nagin, despite how badly he screwed up during Hurricane Katrina. I’m talking about the fact that it looks like the city of New Orleans is sinking faster than we previously believed.
Parts of New Orleans are sinking far more rapidly than scientists first thought, more than an inch a year, new research suggests.
That may explain some levee failures during Hurricane Katrina and raises more worries about the future.
The research, being published Thursday in the journal Nature, is based on new satellite radar data for the three years before Katrina struck in 2005. The data show that some areas are sinking  from overdevelopment, drainage and natural seismic shifts  four or five times faster than the rest of the city. And that, experts say, can be deadly.
“My concern is the very low-lying areas,” said lead author Tim Dixon, a University of Miami geophysicist. “I think those areas are death traps. I don’t think those areas should be rebuilt.”
For years, scientists figured New Orleans on average was sinking about one-fifth of an inch a year based on 100 measurements of the region, Dixon said. The new data from 150,000 measurements taken from space finds that about 10 percent to 20 percent of the region had yearly subsidence in the inch-a-year range, he said.
As the grounds in those rapidly sinking areas shift downward, the protection from levees also falls, scientists and engineers said.
For example, the Mississippi River Gulf Outlet, built more than three decades ago, has sunk by more than 3 feet since its construction, Dixon said. That, he added, explained why water poured over the levee and part of it failed.
“The people in St. Bernard got wiped out because the levee was too low,” said co-author Roy Dokka, director of the Louisiana Spatial Center at Louisiana State University. “It’s as simple as that.”
The subsidence “is making the land more vulnerable; it’s also screwed up our ability to figure out where the land is,” Dokka said. And it means some evacuation roads, hospitals and shelters are further below sea level than emergency planners thought, he said.
So when government officials talk of rebuilding levees to pre-Katrina levels, it may really still be several feet below what’s needed, Dokka and others say.
“Levees that are subsiding at a high rate are prone to failure,” Dixon said.
The federal government, especially the Army Corps of Engineers, hasn’t taken the dramatic sinking into account in rebuilding plans, said University of Berkeley engineering professor Bob Bea, part of an independent National Academy of Sciences-Berkeley team that analyzed the levee failures during Katrina.
So what actually accounts for this more rapid sinking? Well, there is some disparity of opinion as far as that’s concerened.
Dixon and his co-author Dokka disagree on the major causes of New Orleans not-so-slow falling into the Gulf of Mexico.
Dixon blames overdevelopment and drainage of marshlands, saying “all the problems are man-made; before people settled there in the 1700s, this area was at sea level.”
But Dokka said much of the sinking is because of natural seismic shifts that have little to do with construction.
So it certainly sounds like new levees will need to be significantly higher than previously thought, and will need to be of a lighter material that will sink less, and can be added on to if needed. Let’s hope that those responsible for building these levees are paying attention.
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