during Katrina, and that may have been weakened but did not fail, as it will be important for IPET to provide information regarding levels of protection of the system for the upcoming hurricane season.
The explanation of the failure mechanism for the 17th Street Canal breach, while plausible, is not fully convincing. Alternate failure mechanisms should be more rigorously assessed. The IPET should assess the potential for instability at other locations along the hurricane protection system.
Carefully executed direct-simple-shear (DSS) and field-vane-shear (FVS) tests should be performed at the 17th Street Canal breach site as soon as practicable. Results from these tests should be integrated with previously acquired strength data. The IPET should also consider the results from the study conducted by a team of scientists sponsored by the National Science Foundation.
The IPET should provide a history of hurricanes in the Gulf of Mexico and place the major storms (e.g., Betsy, Camille, Katrina), and the SPH, in the context of its probabilistic analysis.
The IPET should provide a thorough and understandable explanation for the method being used in its assessment of risk and reliability of the hurricane protection system. Evidence should be presented that validates the probabilities that are being assigned the various parts of the system. A clear discussion that identifies the level(s) of uncertainty associated with these results should be part of this explanation.
The IPET should provide two separate but related sets of estimates of hurricane wave levels at various locations. The first is a deterministic set of inundation analyses based on a relatively small set (e.g., ~50) of representative storms that include a worst-case scenario. The second entails joint analyses for probability of occurrence for a given storm along with the probability of occurrence of specific hurricane protection system failure modes.
The IPET should not expect to—nor be expected to—obtain credible estimates of risk by June 1, 2006.