Sunday, September 25, 2005

The real reason behind flooding in New Orleans ?

I just read this interesting article in the New Scientist where a group of scientists question the levee overtopping failure theory in New Orleans. According to this group, preliminary measurements show that the water was not high enough at certain points to cause overtopping. They reason that these levees were actually breached and they blame the cuts in federal spending and QC mechanisms within the Army Corps of Engineers. Apparently, the failure investigation report is due out in 2006. Sure. Ample time for another Cat 4 storm.

A small detour here. A levee is typically an earthern wall designed to confine water in a specific region. Typical levee failures are of two kinds : Overtopping failure or Breach failure. In the former case, the water level behind the levee rises to the top of the levee and then then overtops / flows over the levee. As the water flows over the outer surface, it starts eroding material at the foundation ultimately leading to the failure of the levee. Such failures are usually characterized by the levee wall falling backwards. In the latter case (breach), water flowing through and below the dam creates a 'pipe' which gets enlarged over time. Ultimately, the water punches a hole through the dam. Lo and Presto, failure. See pictures here and here

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