Experts studying the flooding of New Orleans after Hurricane Katrina say the breach of key floodwalls might have been caused by soft soil under the walls, a problem the Army Corps of Engineers had been warned about.

Engineers from the American Society of Civil Engineers and the University of California at Berkeley said Friday there was no evidence that the floodwaters surged over the tops of the floodwalls at 17th Street or London Avenue Canals, as previously thought.

Instead, they said, soft soil may have given way underneath the walls - a danger a contracting company pointed out to the Army Corps of Engineers in the early 1990s. In one section of the 17th Street canal, a levee embankment had moved more than 10 meters from its original spot.

The experts also said they found at least 10 breaches and possibly more in the walls.