Wednesday, September 21, 2005

When Category 3 Doesn't Actually MEAN Category 3

Jeffrey at Library Chronicles found this post from the Pic blog which makes for interesting reading in light of the questions about how and why the floodwalls failed (see below):

Before the giant storm surge from Katrina, a Category 4 hurricane, washed away some levees and crashed through others, the Army Corps of Engineers had maintained that the levee system surrounding the New Orleans area could protect residents from a fast-moving Category 3 hurricane.

But that estimate is a piece of guesswork based on old data that experts say underestimates the risks in some spots...

...the flaws and differences in flood risk built into the current levee design will likely have to be addressed when the levee system is rebuilt and upgraded to defend against the major storms, something that President Bush promised in his speech in New Orleans last week.

"They really need to re-analyze how to rehabilitate the levees using a current risk-based analysis. That can be easily done, that's what needs to be done. They really have to take all the calculations and weave that into a new design," said Lee Butler, an engineering consultant and former corps computer analyst who found possible deficiencies in the corps' levee designs in a study he did for The Times-Picayune.

For that to happen, though, Congress would have to get involved. Corps project manager Al Naomi said that the current congressional mandate doesn't allow for such variations...

The corps isn't authorized to adjust for variations in the landscape that make severe hurricane flooding a more frequent occurrence in some areas. Building higher levees in those areas would conflict with the corps' legal mandate.

"I can't go above it by law," Naomi said. "That's what I am authorized to do. Anything above that means I have to spend money that Congress specifically authorizes for that purpose. Only then we can go build it. It's not simple."

Another problem for corps officials is accurately predicting the risks. Engineers use a combination of data from past flooding and computer modeling to make estimates. But because powerful storms are rare, it's hard to get accurate projections because there isn't much data.


I hope that last line--the part about powerful storms being "rare," isn't about to undergo an adjustment of its own.

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