Review finds design flaws in New Orleans levees

NEW ORLEANS -- The engineers who designed the flood walls that collapsed during Hurricane Katrina did not fully consider the porousness of Louisiana's soil or make other calculations that would have pointed to the need for levees with deeper pilings and wider bases, researchers said.

At least one key scenario was ignored in the design, said the researchers, who are scheduled to report their findings at a congressional hearing today: the possibility that canal water might seep into the dirt on the dry side of the levees, thereby weakening the embankment holding up the flood walls.

''I'd call it a design omission," said Robert Bea, a civil engineering professor at the University of California at Berkeley who took part in the study for the National Science Foundation.

The research team found other problems in the city's flood-control system, including evidence of poor maintenance and confusion over jurisdiction.

Bea also questioned the margin for error engineers used in their designs, saying the standards -- which call for structures to be 30 percent stronger than the force they are meant to stop -- date to the first half of the 1900s, when most levees were built to protect farmland, not major cities.

''The center of New Orleans is certainly not protection of farmland, so the factor of safety was incredibly low," Bea said. ''We're talking about thousands of families without homes and shutting down a commercial infrastructure that's pretty darn important to the United States."

Surging waters from the Gulf of Mexico flowed up and over levees east of the city, and flooding in central New Orleans and parts of downtown was caused by breaches at barriers along the 17th Street and London Avenue canals, both of which were built in the late 1980s. Flood waters inundated 80 percent of New Orleans and had to be pumped out for weeks because of the city's saucer-like topography.

The university team is one of three independent groups working with the Army Corps of Engineers, the agency responsible for the levees' design and construction, to determine why the barriers failed and to make recommendations to repair them. Corps officials have said the barriers never were intended to withstand a storm as powerful as Katrina.