Report Examines Path to Failed New Orleans Levees

Initially, the protection scheme revolved around building massive flood barriers to the east of New Orleans. In concept, these would block the storm surge from entering Lake Pontchartrain and the city. But a lawsuit filed by the environmental group Save Our Wetlands led to a 1977 court injunction against the barrier plan. After years of debate, the Corps decided in 1985 to drop that approach and, instead, focused on raising flood walls and levees around canals and the lake.

During those years of legal delay and high inflation, project costs rose tenfold -- from $80 million to $800 million, Shabman said.

At the same time, new information about hurricane frequency and effects was becoming available -- and indicated that the congressionally authorized scheme would not provide the promised protection.

New hurricane science suggested that the chances of a powerful strike were greater than had been anticipated. The sinking of the city meant that the levees were too low, compared with sea level. New computer modeling suggested that the storm surge would be higher in places than predicted.

Together, these changes meant that the system of levees and flood walls they had been building were several feet too low. Already faced with budget woes, the Corps pressed on without making significant changes to address all the new issues, according to the report.

Many of the constraints and conflicts that characterized the hurricane protection project converged during the design of two key flood walls.

Those flood walls, which were built along city canals flowing into Lake Pontchartrain, were supposed to prevent the storm surge from pushing from the lake down into the canals and then into the city.

The Corps did not want to build the flood walls at all, proposing instead a cheaper set of floodgates between the lake and the canals. The Orleans Levee District board, however, objected and prevailed upon Congress to force the Corps to build several miles of flood walls.

Reeling at the potential expense, the Corps sought ways to save money in building the flood walls.

After performing a test, they changed their own design criteria to allow for shorter pilings to support the flood walls, saving tens of millions of dollars in their construction but probably making the walls less stable.

Whether that change caused the walls to topple is a question that continues to divide engineers, however. "It would be true that the deeper the piling, the more stable," said J. Michael Duncan, a civil engineering professor at Virginia Tech who led the Corps investigation into the wall failure. On the other hand, he said, "no investigation has shown that the failure was due to having the sheet piles at the length they were. . . . It's all hindsight."