Cause Of Levee Failure?: nola.com reports on why the floodwalls of the 17th Street and London canals failed. While these barriers were not topped, i.e. water didn’t flow over them, they were broken and the soil under these walls has been named as the culprit. It appears that “a soft, spongy layer of swamp peat underneath the 17th Street Canal floodwall was the weak point that caused soil to move and the wall to breach … the same peat layer also runs under the London Avenue Canal breaches and probably was instrumental in those collapses as well.”
Even a cursory examination of an Orleans Parish soil map shows that almost all of the flooded area sits on “poorly-drained swamp land” that consists of “organic … clayey surface underlain by a clay subsoil interspersed with organic strata” and “3 feet of loamy materials over clayey and organic swamp lands.” Again, according to the map, the material directly under the 17th Street Canal is “70% organic … more than several feet thick that is underlain by a slightly-firm gray clay.” In other words, swamp peat. This raises the question: If almost all of the parish sits on this stuff, why did the canals fail right where they did? Why right there?
Blaming levee failure on swamp peat is a lot like saying that someone died of cardiac arrest (technically, everyone dies of cardiac arrest; what brought it on would be the true cause of death). Perhaps it was a combination of factors, including highly-directed water flow, increased force on a particular portion of the floodwall, poor structural integrity on the part of the floodwall itself and underlying swamp peat that caused the failure. Besides, what is the Corps of Engineers going to do — replace the pervasive swamp peat with some other material or, dare I say, dig deeper? This Kansas City Star article barely touches on a multi-headed demon of a problem that faces New Orleans.
That the organic-rich soil caused the floodwalls to give seems too uncomplicated, especially given the lack of money allocated towards building up our admittedly-imperfect levee system prior to Katrina. Funding issues and priorities, anyone?
Case in point – Now that New Orleans is almost entirely dry, the Corps plans to rebuild the levees back to previous condition by June 1, 2006. According to the Washington Post, “For now, there are no plans to rebuild the levees stronger than before. The Corps would have to get Congress’ approval for such work.” Do you think such approval will be in hand before the work is already underway?
*sigh*
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More From The Lower Garden District and Tulane: Reports on cleanup efforts in my neighborhood and the reopening of the school. All of this is great news indeed!
You would not believe the intensity of cleanup efforts going on here now. The house on the corner of Euterpe and Magazine (the one that completely collapsed) is nearly gone now — a crew has been here all day working on it. There is still a lot of trash and debris around the city but there is a very noticable improvement in the past few days. In addition to workers, residents are increasingly visible, cleaning up their property. The Rue on the 3500 block of Magazine is open now as well, as is Surrey’s. We patronized both establishments today! Our roof was inspected on Friday and we have some minor damage, mostly missing and cracked slates, flashing around the chimneys that needs to be replaced, and a few other things. The roofer says the water spots on your ceiling resulted from hurricane force winds blowing water under the slates rather than more generalized leaks.
Tulane will be open in the Spring, with classes slated to begin on January 17. Many of the repairs to the campus have been completed. Meanwhile, J is … now becoming involved in some clinics in N.O.
