The network that was supposed to protect the below-sea-level city from flooding was built to withstand a Category 3 hurricane, the Army Corps of Engineers said. It was overwhelmed when Katrina's winds and storm surge came ashore a week ago as a Category 4 storm.
That has left some lawmakers wondering why officials only considered the consequences of a moderate storm.
"What that, in essence, says is that you're not going to worry about the biggest disasters that could occur, you're only going to worry about the smaller ones," said Rep. David Obey of Wisconsin, the top Democrat on the House Appropriations Committee.
"How many times do we have to see disaster overwhelm our preparedness before we recognize that we are playing Russian roulette with people's lives, with their livelihoods and with the life of whole communities?"
Louisiana lawmakers have long lamented that Corps of Engineers programs designed to protect New Orleans and surrounding areas were starved for cash.
Corps officials, said, however, that funneling more money into the agency's levee repair programs wouldn't have totally averted disaster. The infrastructure around the city was designed to withstand only a Category 3.
"You see there was not sufficient money or time to do anything about this," Al Naomi, a corps official who manages New Orleans' levees, told 60 Minutes Correspondent Scott Pelley.
"If someone had said, 'O.K. here is a billion dollars, stop this failure from happening for a Category 4,' it couldn't have been done in time. I'd of had to start 20 years ago to where I feel today I would've been safe from a Category 4 storm like Katrina.
"You have to recognize before we had Category 3 protection we didn't have anything," Naomi said.
The infrastructure assumed that a storm bigger than a Category 3 has a very low probability of occurring.
When the project was designed about 30 years ago, the corps believed it was protecting the city from an event that might occur only every 200 or 300 years.