“We have spent a lot of money and gotten some very good patches, but we’re putting them on this decayed old quilt,” said Robert G. Bea, a professor of engineering at the University of California, Berkeley, who is an author of an independent report on the levee failures. “We’re still with this damned patchwork quilt.”

Image Ora M. Singleton is still working on repairs to her Ninth Ward home. "I was led by the Lord to come back." Credit... Lee Celano for The New York Times

As a result, the city still lacks a system that can stand up to that 1-in-100 storm, let alone one like Hurricane Katrina, which the corps calls a 1-in-396 storm. The work that could build the more robust system — originally estimated at $7 billion, and now at least twice that — will not be completed until 2011 at the earliest, and experts agree that even that level of protection will be less than the city needs.

The corps is working on a two-year, $20 million study to find ways of providing even more protection, but it will not even be released until December.

Without a strong rampart of protection against storms, New Orleans will have a hard time persuading its far-flung residents and businesses to return and rebuild. Matt McBride, an engineer who became an anti-corps gadfly on flood-protection issues, left the city along with his wife after deciding he simply did not trust the new system.

“There’s too many things that can go wrong,” Mr. McBride said.

Maggie Carver, a Gentilly resident now living in Woodstock, N.Y., but hoping to get back, said she thought that all the time and work would have resulted in more progress and a clearer sense of safety than she had seen.

“If I sell my house and put everything into rebuilding and living in New Orleans and it happens again, then where am I?” Ms. Carver asked. “I’m in a boat somewhere with four Jack Russell terriers and my grandson. I won’t have anything.”

Patching the System

The corps has hardly been idle in the two years since the flooding. It quickly mobilized a force that grew to as many as 3,300 workers in the New Orleans area, and its cranes and bulldozers belch exhaust at waterways all over town, installing walls of concrete, massive pumps and mounds of earthwork.