I am curious how the levees split apart...
Mark Schleifstein, the environment writer for the New Orleans Times-Picayune, e-mailed me this morning: "For days in advance of this storm, everyone from the mayor of New Orleans to the governor to Max Mayfield gave a clear message: a Category 4 hurricane will overtop the levees. . . .
"Our series and the latest NWS software used by emergency planners throughout New Orleans indicate that even some Category 2 storms could put water over the levees in eastern New Orleans."
I'm also told by another source that the two levees that failed were first overtopped -- then they eroded from the interior and collapsed. Once water starts spilling over the top of a levee its structural integrity can no longer be guaranteed, apparently -- and the Corps of Engineers was aware of that possibility.