John McQuaid of the Times-Picayune has an interesting piece on why the New Orleans levee system failed in so many places. It’s even worse than you would imagine (the levee system, not the article).
The walls may have had design flaws, particularly in their sheet pile foundations, which engineers say were too short to anchor the walls and prevent storm surge from seeping underneath. After Katrina’s surge rose to 10 or 11 feet in the canals, soft soil beneath walls in two areas moved and the walls failed, according to a preliminary report released Wednesday by engineering teams for the National Science Foundation and the American Society of Civil Engineers.
There were also problems with construction materials:
"We did see what we considered to be inferior materials in some cases. But that may have been allowed within the specifications," said Peter Nicholson, a University of Hawaii geotechnical engineer heading the American Society of Civil Engineers levee team. "The best example of that was using sand and so-called shell fill, highly erodable materials that may have been sufficient had there not been any erosion, but once you start the erosion process they quickly disappear."
Speaking of levee malfeasance (and at risk of appearing to defend Louis Farrakhan — a high-consequence low-probability position for a Right Angle blogger), the rapid erosion under levees led me to reexamine this:
"I heard from a very reliable source who saw a 25 foot deep crater under the levee breach," Farrakhan explained. "It may have been blown up to destroy the black part of town and keep the white part dry."
On second thought, how would the “reliable source” have been able to tell that an under-levee “crater” was 25 feet deep? Wouldn’t it have been – let’s go out on a limb here – filled with water? And why am I even wasting time debunking Farrakhan?