"Many people criticize those for staying that did stay, but many of them were people that were very disadvantaged in mobility," said Chester Wilmot, a professor in the Department of Civil and Environmental Engineering at Louisiana State University, who has advised the New Orleans government. "They were people that were sick, they were people that were infirm. ... There are all kinds of things that keep people where they are. There will always be some people that just won't or can't get out."
City officials say they've learned plenty of lessons from the Katrina evacuation and aftermath. Unlike before the storm, the city now keeps a comprehensive list of residents that need assistance to evacuate, and the government is now prepared to help them. And those shelters of last resort are also a thing of the past. Were a storm like Katrina to strike today, the only people that would remain in the city would be emergency responders.
"We've made the determination for a Category 3 or higher storm, we would order a mandatory evacuation for the city," said New Orleans' deputy mayor for Public Safety, Lt. Col. Jerry Sneed, adding that they even have a plan in place for evacuating pets.
Officials again point to the successes of the evacuation for Gustav as evidence that the city is far better prepared for the next storm. Ninety-seven percent of citizens evacuated on their own, and 21,000 evacuated with the city's assistance during Gustav.
"Our citizens listen to us now, too," Sneed said. "The City of New Orleans had not had a major storm since Betsy in the '60s, so we had gotten a little complacent. But now, Katrina's fresh on our minds, and people actually listen."
Also during Katrina, the city's communications system failed, leaving police officers and firefighters on their own, unable to call for support or supplies. Sneed said that the city's radio system for emergency responders is now the best in the country, allowing officials throughout the entire New Orleans metro area to remain in communication during a crisis.
"We're going to get our citizens out. We're going to get them to areas where they'll be safe, and we're going to get them back to the city just as quickly as we possibly can," Sneed said.
Despite the progress that's been made with the levees and disaster response, one source of hurricane protection for the coastline is now arguably in worse condition than before the storm -- the natural Louisiana coastline.
The state's sensitive barrier islands, marshes and wetlands all provide a natural defense to the battering storm surge from hurricanes. These barriers have never recovered from the Katrina disaster, which wiped out 200 square miles of wetlands.
"What Hurricane Katrina did was exacerbate a problem that was already unfolding, like a stroke happening to a person who has chronic diabetes," said Mark Davis, a senior research fellow and director of the Institute on Water Resources, Law and Policy at Tulane University.
"If Katrina happened again, the wetlands would be overwhelmed," Davis said. "A storm as big as Katrina is not one that swamps and marshes are going to stop, but they can provide a buffer if they're healthy and you have enough of them. We certainly have not added to the buffer. We've lost some of what we've had five years ago."