When Hurricane Katrina struck the Gulf Coast as a Category 3 storm five years ago, it unleashed a series of events that took nearly 2,000 lives, destroyed an American city and devastated an entire region.
Katrina will never happen again -- the name has literally been removed from the World Meteorological Organization's list of storm names. But a storm with Katrina's size and power will almost certainly hit the Gulf Coast again in the future.
Politicians and government bureaucrats say they've learned from the mistakes of Katrina, but how prepared is Louisiana for the next big storm? What would happen to New Orleans if a major hurricane hit today?
An assessment of where things stand shows that the city is far better prepared to evacuate its citizens, but New Orleans' levee system is not yet fully prepared to protect the city from a big storm, and the natural defenses of coastal Louisiana are weaker than ever before.
Watch "World News with Diane Sawyer" for more coverage of our series, Katrina: Where Things Stand
After Katrina, the federal government made it a priority to rebuild the broken levee system, authorizing $12.8 billion in funding. Today, about $15 billion has been spent on levee reconstruction, but the system still can't protect all of New Orleans in the event of a 100-year storm, a hurricane with a 1 percent chance of occurring in any given year.
The Army Corps of Engineers says the massive project is on track to provide 100-year protection by the start of hurricane season next year. And if a hurricane like Katrina, a 400-year storm, were to hit today, authorities say the city would be in far better shape than it was in 2005. New Orleans would get wet, they say, but the levees would hold.
"The area of metro New Orleans that experienced so much flooding during Hurricane Katrina, we believe that with the systems that are in place right now, we wouldn't experience that same level of flooding," said Michael Park, the deputy director of the Army Corps of Engineers' Task Force Hope. "Certainly, with a storm the size of Katrina and the state of completion of the system ... we would expect to experience overtopping of some of the features around the perimeter."
The system was tested during Gustav, when waters did overtop New Orleans' industrial canal, but the flood walls remained in tact.
"Where the breaches occurred in the outfall canals during Hurricane Katrina, we've put in place interim control structures and pump stations that isolate those canals from storm surges," Park said.
If all goes according to plan, New Orleans levee system will not only provide 100-year protection by next year, but its barriers could handle the brunt of a 500-year storm.
"We're designing a level of resiliency into the system so that even for a storm that has a 0.2 percent annual chance of occurrence, we're building it so that the stillwater component of that storm surge would not overtop the levees or flood walls, it would only be wave overtopping," said Park.
One of the major problems of Katrina was a failed evacuation that left many of New Orleans' poor and elderly residents seeking shelter within city limits as the storm came ashore. Instead of evacuating New Orleans entirely, they remained in the city's shelters of last resort, like the downtown convention center and the Superdome, where conditions quickly devolved into misery.
"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."
The coastline has been shrinking for decades. Twenty-three percent of the land that protected the New Orleans metro area in 1956 has now turned into open water, according to the Greater New Orleans Community Data Center. The coastline has continued to shrink in the past five years, losing about 20 square miles each year, and some land that was once forest is now turning into swamp as the water moves inland. The BP oil spill has hardly helped the sensitive ecosystem, though what its longterm effect will be on wetlands loss is unknown.
"New Orleans and the coastal communities would be at greater risk of receiving surge" today, Davis said.
Congress authorized a coastal restoration program in 2007, but so far, Davis said, not a dollar has been spent to turn that goal into a reality. There are some positive signs, though. Everyone from local leaders to the governor to President Obama have spoken about the importance of the coastal wetlands, and the state and the federal government have come forward with firm policy proposals for coastal restoration.
That couldn't come soon enough, experts say, because while the stronger levees and surge barriers do provide a greater measure of hurricane protection today for the New Orleans metro area, all the engineering in the world won't be enough without working in tandem with Mother Nature.
"The time to act is disappearing. At some point, you have to do more than talk. You have to begin to act at a scale that can make a difference," said Davis. "As the Gulf gets closer, the danger goes up."