The Army Corps of Engineers has spent about $4 billion so far of the $14 billion Congress set aside to repair and upgrade the metropolitan area's hundreds of miles of levees by 2011. Some outside specialists said that the leak could mean that billions more will be needed and that some of the work already completed may need to be redone.
"It is all based on a 30-year-old defunct model of thinking, and it means that when they wake up to this one - really - our cost is going to increase significantly," said Bob Bea, a civil engineer at the University of California at Berkeley.
The Army Corps of Engineers disputed the dire assessment. The agency said it is taking the risk of seepage into account and rebuilding the levees with an adequate margin of safety.
"It's always a potential, so it is a design component for every feature," said Walter Baumy, the chief corps engineer in New Orleans.
The 17th Street Canal floodwall collapsed on the day Katrina sacked New Orleans in August 2005, and the failure severely damaged Lakeview. It was one of the biggest of about 50 levee breaches that contributed to the deaths of about 1,300 people.
Fixing the 17th Street Canal has been one of the most expensive and laborious repair jobs since the storm and has served as something of a test case for scientists and engineers, who plan to apply the lessons learned there to the city's other levees.
Among other things, they repaired the wall by driving interlocking sheets of steel 60 feet into the ground, compared with about 17 feet before the storm. The sheet metal is supposed to prevent canal water from seeping under the levee through the wet toothpaste-like soil that lies beneath the city, which was built on reclaimed swamp and filled-in marsh.
Over the past few months, however, the corps found evidence that canal water is seeping through the joints in the sheet metal and then rising to the surface on the other side of the levee.
Engineers said the boggy ground is a more serious problem than the corps realizes. Bea said there is a roughly 40 percent chance of the 17th Street Canal levee collapsing if water rises higher than 6 feet above sea level. During Katrina, the water reached 7 feet in the canal.
