Civil engineers report on levee failures

The American Society of Civil Engineers has investigated the levee failures in New Orleans. From the executive summary of their report ("Preliminary Report on the Performance of the New Orleans Levee Systems in Hurricane Katrina on August 29, 2005"):

Overtopping was most severe on the east side of the flood protection system, as the waters of Lake Borgne were driven west towards New Orleans, and also farther to the south, along the lower reaches of the Mississippi River. Significant overtopping and erosion produced numerous breaches in these areas. The magnitude of overtopping was less severe along the Inner Harbor Navigation Canal (IHNC) and along the western portion of the Mississippi River Gulf Outlet (MRGO) channel, but this overtopping again produced erosion and caused additional levee failures. Field observations suggest that little or no overtopping occurred along most of the levees fronting Lake Pontchartrain, but evidence of minor overtopping and/or wave splashover was observed at a number of locations. There was a breach in the levee system at the northwest corner of the New Orleans East protected area, near the Lakeside Airport.

Farther to the west, in the Orleans East Bank Canal District, three levee failures occurred along the banks of the 17th Street and London Avenue Canals, and these failures occurred at water levels below the tops of the floodwalls lining these canals. These three levee failures were likely caused by failures in the foundation soils underlying the levees, and a fourth “distressed” levee/floodwall segment on the London Avenue Canal shows signs of having neared the occurrence of a similar failure prior to the water levels having receded.

In Senate testimony, lead ASCE investigator Peter Nicholson said he believed Congress should enact a National Levee Inspection and Safety Program modeled on the successful National Dam Safety Program (link):

The levee program, he said, "should include a national inventory of levees, particularly those that protect large, heavily populated urban areas." He encouraged Congress to establish an independent advisory panel responsible for envisioning the future of the Gulf Coast and proposing ways to begin the rebuilding efforts.