NEW ORLEANS — The Army Corps of Engineers acknowledged Thursday that design defects in the levees protecting New Orleans caused the majority of flooding during Hurricane Katrina and that the disaster would almost certainly trigger reforms in how the federal government protected the American public.
The corps said its 40-year effort to construct a hurricane protection system for southern Louisiana had resulted in a set of piecemeal projects that "was a system in name only," a recognition that a wide range of errors, weak links and incomplete construction was at the heart of the massive damage that occurred Aug. 29.
The corps released a 6,000-page report written in the couched language of government engineers but which delivered a stunning set of findings about errors made in the design of storm walls and earthen levees that failed during Katrina.
The report found that four major breaches of I-walls, a type of concrete storm wall that sits on an earthen levee, caused 65% of the flooding in the New Orleans area.
Although the report's summary never uses the words "design defect," corps officials said they now accepted that their work had shortcomings and errors that were responsible, in large part, for the damage.
"We do take accountability," Lt. Gen. Carl Strock, commander and chief engineer of the corps, said at a news conference, where he was joined by five Army generals, the federal coordinator for Gulf Coast reconstruction and an assistant Army secretary.
The corps, Strock said, "is deeply saddened and enormously troubled" by the disaster.
Strock said the remaining I-walls would eventually have to be replaced because they proved ineffective during Katrina. The primary breaches at the 17th Street, London Avenue and Industrial canals occurred when storm waters were still several feet below the tops of the walls, meaning they failed well below the maximum forces they had been designed to withstand.
The report also puts in the historical record a formal acknowledgment of the scope of the disaster, which killed 1,293 people in the New Orleans area.
"The flooding caused a breakdown in New Orleans' social structure, a loss of cultural heritage and dramatically altered the physical, economic, political, social and psychological character of the area," it said. "These impacts are unprecedented in their social consequence and unparalleled in the modern era of the United States."
Although many of the technical findings had been released in preliminary studies by the corps, the report details significant new information:
* Southern Louisiana is sinking much faster than generally recognized, and levees were at substantially lower elevations relative to sea level than they were designed to be. In some cases, levees were 2 1/2 feet below their designed elevations. Moreover, as other federal agencies recognized the problem in recent years, the corps decided not to reexamine the issue.
* The city's pumping system, the only way to remove water from below sea level, was not designed to operate during a major storm. Because most of the region's pumps were inundated after Katrina, the corps was forced to use portable equipment that took 53 days to pump out the city, allowing the flood waters to saturate and destroy structures.
* Twenty-five percent of all the housing in the region was destroyed. In New Orleans, the proportion is believed to be higher. The destruction of homes accounted for 75% of the losses caused by Katrina, estimated by the corps at more than $20 billion. Outside estimates are much higher, exceeding $100 billion.
* A computer simulation showed that if the levees had not failed, the city still would have flooded because 14 inches of rain fell during a 24-hour period, and storm surges went over the levees. If the levees had held, the flooding would have been about one-third of what occurred.
Strock said the repaired sections of levees were now the strongest parts of the system. The repairs were supposed to be completed by June 1, but they are about two months behind schedule. Among ongoing projects is the installation of new pumps at the mouth of the 17th Street Canal. The enormous undertaking required heavy construction work on 169 miles of damaged or destroyed levees.
The report is full of technical language, including descriptions of design flaws as "overestimation of subsurface strength." Corps officials said the reason for such language was not to reduce the effect of the findings, but rather to set a "nonjudgmental tone."
Although the breaches caused most of the flooding, a significant part of the Katrina damage occurred because the storm was larger than the system was designed to withstand.
Although wind speeds had dropped sharply by the time the hurricane hit New Orleans, its power over the Gulf of Mexico had created the largest ocean surge to ever hit North America, the report said.