Our preliminary analysis identified the failure on the 17th Street canal to be initiated by a deflection of the floodwall that allowed application of full hydrostatic pressure vertically along the floodwall/sheet pile. This force coupled with relatively weak shear strengths in the clay layer under the inboard toe of the levee allowed the lateral translation of the levee from the floodwall back along a failure plane in the clay layer. The peat layer above the clay did not initiate the failure. This failure mechanism was not anticipated by the design criteria used.

This statement by the Corp's Interagency Performance Review Team may be true but the failure mechanism should have been anticipated and the design modified accordingly. The implications are stunning. Essentially the design of any New Orleans area levee with a flood wall should be suspect.

Furthermore you've got to wonder why the Corps used this design. You might think they didn't know that this type failure could occur, but it now appears that they tested for and found exactly this contingency in 1986 when they designed the floodwalls. Furthermore they were concerned enough about the design to recommend closable seawalls at the mouths of the outfall canals in 1992 but did not proceed because they could not satisfactorily address the NO Sewerage and Water Board concerns about rainfall induced flooding that would result from diminished pumping capacity when the canals were closed.