Army Corps of Engineers: Katrina Draft Final Report

Performance Evaluation of the New Orleans and Southeast Louisiana Hurricane Protection System
Draft Final Report of the Interagency Performance Evaluation Task Force
Executive Summary (Acrobat .PDF document):

Overarching Findings

The System did not perform as a system: the hurricane protection in New Orleans and Southeast Louisiana was a system in name only. Flood protection systems are an example of a series system—if a single levee or floodwall fails, the entire area is impacted. It is important that all components have a common capability based on the character of the hazard they face. Such systems also need redundancy, an ability for a second tier of protection to help compensate for the failure of the first tier. Pumping may be the sole example of some form of redundancy; however, the pumping stations are not designed to operate in major hurricane conditions. The system’s performance was compromised by the incompleteness of the system, the inconsistency in levels of protection, and the lack of redundancy. Incomplete sections of the system resulted in sections with lower protective elevations or transitions between types and levels of protection that were weak spots. Inconsistent levels of protection were caused by differences in the quality of materials used in levees, differences in the conservativeness of floodwall designs, and variations in structure protective elevations due to subsidence and construction below the design intent due to error in interpretation of datums. The presence of closure gates such as those for the CSX railroad that must function as a part of the system, but are separately controlled, add to the inherent risk in the system. Redundancy was simply not included. Continuity of pumping could have significantly reduced at least the duration of flooding and in some areas the extent. Armoring the back sides and crests of levees and the protected side of floodwalls would have added significant redundancy and reduced breaching. Surge gates at the mouths of the outfall canals are an excellent example of providing redundancy. The combination of the surge protection for the canals and resilient levee-floodwall systems will dramatically reduce risk in Orleans East Bank.

The storm exceeded design criteria, but the performance was less than the design intent: sections of the hurricane protection system were in many ways overwhelmed by the conditions created by Hurricane Katrina. This is particularly true for the sections of the Gulf Intracoastal Waterway (GIWW) along New Orleans East, and the levees in St. Bernard and Plaquemine Parishes where the combination of record high surge and long period waves exceeded the design conditions and devastated the levees. This devastation, however, was aided by the presence of incomplete protection, lower than authorized structures, and levee sections with erodible materials. While overtopping and extensive flooding from Katrina were inevitable, a complete system at authorized elevations would have reduced the losses incurred. The designs were developed to deal with a specific hazard level, the Standard Project Hurricane as defined in 1965; however, little consideration was given to the performance of the system if the design event or system requirements were exceeded.

(Emphases added) Via New York Times: Army Builders Accept Blame for Flooding, Harry Shearer, and Arianna Huffington (" Huffington Post")

From the full report web site:

The IPET is seeking eyewitness accounts describing the behavior of the hurricane protection system during and immediately after the passage of Hurricane Katrina (29 Aug. 2005). If you have information that you think may be useful, please click here to provide information. You may also contact us at Katrina.Accounts@usace.army.mil or 1-866-502-2570, ext. 5004.

The information you provide will be combined with information from other witnesses in a general summary for our report. We are asking for your name and contact information (phone number or address) to allow us to contact you if we have additional questions about the information you provided and to credit your information to a specific location. If you provide your name and contact information it will be made available to others outside the Corps, with your statement. You do not need to provide a name or contact information to submit nformation.