NEW ORLEANS (AP) Government engineers performing sonar tests at the site of a major levee failure confirmed that steel reinforcements barely went more than half as deep as they were supposed to, a U.S. Army Corps of Engineers official said.
“We’ve come up with similar results” to those from earlier tests performed by Louisiana State University engineers, Walter Baumy, the Corps’ chief engineer for the New Orleans District, said.
Baumy said the Corps intends to pull out pieces of the remaining wall along each edge of the breach at the 17th Street Canal to verify the sonar test results. The canal itself is now mostly dry at the breach site, with temporary walls holding back water from each side.
Baumy said the Corps cannot explain the disparity between what its 1993 design documents show was supposed to be there and what they’ve found.
The documents indicated that the steel reinforcements in the levee, known as sheet piling, went to a depth of 17.5 ft. (5.25 m) below sea level. Sonar tests indicated the pilings went only to 10 ft. (3 m) below sea level, meaning the flood wall would have been much weaker than intended.
The LSU team is working on a report for the state that will say there were serious, fundamental design and construction flaws at both the 17th Street and London Avenue canals. Both broke during Hurricane Katrina, flooding much of the city.
The team’s leader, Ivor van Heerden, said that the levee design ensured failure under the type of water pressure exerted by Katrina’s storm surge.
The team’s computer modeling showed that the designs failed to account for loose, porous soils such as sand and peat that were prone to allowing water to seep from the canal through to the dry side of the levee.
Much deeper steel pilings driven well below the canal bottoms likely would have stopped seepage to the dry side, engineers have said. The bottom tip of the pilings, at 10 ft. (3 m) below sea level, did not reach the canal bottoms.
But LSU computer models showed that even if the pilings had gone to 17.5 ft. (5.25 m) below sea level at 17th Street as design documents said they should have, they still would have failed.
Engineering studies prior to construction of the flood wall were performed by Eustis Engineering, Modjeski and Masters Inc. and the Corps. Members of the LSU team have expressed shock that all three could have missed what they characterized as fundamental flaws.
Calls to Eustis and Modjeski and Masters were not returned. Van Heerden said the federal government bears ultimate responsibility.