That's what I'm taking from this Times-Picayune article. What failed were concrete floodwalls. The investigation into what caused the floodwall failures has only just begun, but "two Louisiana State University scientists who have examined the breaches suggest that a structural flaw in the floodwalls might be to blame".
How much of what we "knew" on September 1 is still true today?
Update 2:05pm: I forgot to finish this thought. The reason I think this is significant is because during the days that followed the storm we heard a lot about the levees; the lack of maintenance money; that they were only capable of handling a category 3 storm; and so on. Yet, if what we have is actually a structural flaw, then it doesn't matter at all what they were designed to do because if they're flawed then they're prone to failure.