Experts urge new check of levee system

WASHINGTON — An organization of civil engineers has questioned the soundness of large portions of New Orleans' levee system, warning that the federally designed flood walls were not built to standards stringent enough to protect a large city.

The group Friday faulted the agency responsible for the levees, the U.S. Army Corps of Engineers, for adopting safety standards "too close to the margin" to protect human life. It also called for an urgent re-examination of the entire levee system, saying there were no assurances the miles of concrete "I-walls" in New Orleans would hold up against even a moderate hurricane.

"The ability of any I-wall in New Orleans to withstand ... is unknown," said the American Society of Civil Engineers' External Review Panel, appointed to oversee the investigation by the corps of the levee collapse during Hurricane Katrina.

The civil-engineers group also rejected the explanation given by the corps that the system had failed because Katrina had unleashed "unforeseeable" physical forces that weakened the flood walls.

In a letter to Lt. Gen. Carl Strock, the corps' commander, the group cited three previous corps studies that predicted precisely the chain of events that caused the city's 17th Street Canal flood wall to fail. The breach left much of central and downtown New Orleans under water.

"It appears that this information never triggered an assessment ... neither at the time of the design of the 17th Street Canal flood wall, nor following its construction," the letter said.

Corps officials said they had taken steps to address problems identified in the letter, starting with an effort to replace miles of I-walls with sturdier structures. But agency officials insisted the corps was not solely to blame for weaknesses in the system.

During 40 years of levee building in New Orleans, spokeswoman Susan Jackson said, the agency frequently found its hands tied due to restrictions imposed by budgets, Congress or local governments that often failed to meet financial responsibilities to help build and maintain the levees.

The American Society of Civil Engineers panel is one of three independent teams investigating the failure of the levees; until now, it has been the most cautious in its public criticisms. The other teams quickly endorsed its findings.

Two weeks ago, the corps proposed a new theory for why the 17th Street Canal flood wall collapsed Aug. 29, despite never being overtopped by Katrina's floodwaters.

While previous investigations had pointed to weak soils beneath the flood wall, new data suggested a combination of factors. First, the force of rising floodwaters inside the canal bent the walls outward, creating a gap between the walls and their earthen foundation.

Then, water surged into the gap, pressing the walls further until they broke through a layer of weak soil. In effect, the levee was sliced in half along its ridge.

Corps officials initially said they had never known a levee to fail this way and suggested no one could have predicted it.

But the civil-engineers panel said the failure was foreseen by the corps' own studies, dating to the mid-1980s. It said the agency's failure to anticipate the problem reflected an "overall pattern of engineering judgment inconsistent with that required for critical structures."

The engineers panel is to release a formal report in two weeks, but its members chose to send the letter to Strock separately, citing the "gravity and potential impact" of its findings.