The thin gray line of concrete floodwalls erected along drainage canals was supposed to protect New Orleans. But when Katrina hit, portions of the walls came tumbling down, flooding the city.
Experts are just now beginning to probe why those floodwalls failed. They want to determine whether the storm surge from Katrina poured over them, or whether the walls collapsed because of a possible flaw.
“This is fairly typical of some of the failures we've seen,” says Professor Ivor van Heerden, a hurricane expert at Louisiana State University who has examined the wreckage. “These walls underwent catastrophic structural failure.”
NBC News has obtained what may be a key clue, hidden in long forgotten legal documents. They reveal that when the floodwall on the 17th Street Canal was built a decade ago, there were major construction problems — problems brought to the attention of the U.S. Army Corps of Engineers.
A 1998 ruling, by an administrative judge for the Corps' Board of Contract Appeals, shows that the contractor, Pittman Construction, told the Corps that the soil and the foundation for the walls were “not of sufficient strength, rigidity and stability” to build on.
“That's incredibly damning evidence,” says van Heerden, “I mean, really, incredibly damning.”
Pittman won the contract in 1993. There already was an earthen levee made of soil. Embedded in that was a thin metal wall called sheet piling. The contractor was hired to pour concrete on top of all that to form the flood wall.
But the 1998 documents — filed as part of a legal dispute over costs — indicate the contractor complained about “weakness” of the soil and “the lack of structural integrity of the existing sheet pile around which the concrete was poured.” The ruling also referenced the “flimsiness” of the sheet piling.
NBC showed the findings to engineering experts.
“That type of issue about the strength of the soils, of course, bears directly on the performance of a floodwall,” says retired LSU oceonography and engineering professor Joe Suhayda.
“I think it is very significant,” adds Robert G. Bea, a former Corps engineer and professor at the University of California, Berkeley, who is part of a National Science Foundation inquiry into the failure of flood controls. “It begins to explain some things that I couldn't explain based on the information that I've had.”
The construction company said as a result of these problems the walls were shifting and “out of tolerance,” meaning they did not meet some design specifications. Nevertheless, the Army Corps of Engineers accepted the work.
“It seems to me that the authorities really should have questioned whether these walls were safe,” says van Heerden.
The judge, in her ruling, blamed the contractor for the construction errors and turned down Pittman's request for more funds.
Pittman Construction is now out of business. (A firm called CR Pittman Construction, also based in New Orleans, is a separate company.)
In a statement, the Corps of Engineers tells NBC:
"The records on the Pittman contract appeal will undoubtedly be part of any thorough investigation to determine the cause of the levee breaches in New Orleans. The Corps is preserving evidence that could be used in the investigation. The exact composition and structure of the team responsible for a potential investigation has not been determined at this time."
Lisa Myers is NBC’s senior investigative correspondent