At least 1,836 people died in the storms and subsequent floods wrought by Katrina. Total property damage was estimated at $81 billion US, making it the costliest natural disaster in American history.
Within two days of hitting New Orleans, nearly 80 per cent of the city was underwater.
The flooding that Katrina wrought not only exposed the shortcomings of southern Louisiana's levee system but also the weaknesses of the Federal Emergency Management Agency (FEMA) in responding to a disaster situation.
In the aftermath, Katrina prompted a series of congressional and governmental reports on disaster preparedness and spurred on a number of high-profile projects.
The most obvious upgrades were physical. After Katrina, the U.S. Army Corps of Engineers (USACE) launched an $11-billion undertaking called the Hurricane and Storm Damage Risk Reduction System (HSDRRS) for southeast Louisiana.
A focus of its efforts was the Louisiana wetlands, which have long provided a natural buffer to surging waters from the Gulf Coast. USACE has been at work diverting freshwater, nutrients and sediment from the Mississippi River to rebuild the wetlands.
Levee system upgraded
USACE has also been upgrading the levee system, which experienced breaches in about 50 places during Katrina's onslaught.
A large part of the levee system was completed by 2008 — in time to be tested by hurricanes Ike and Gustav.
The system consists of 560 kilometres of levees and floodwalls, and includes New Orleans' Inner Harbor, which went into operation in June 2011. The Inner Harbor system is nearly three kilometres wide and features a storm surge barrier that is eight metres above the water line. (At its height, the storm surge during Katrina went six metres, or 20 feet above the water line.)
"We’ve built a series of floodwalls and improved and strengthened the levees that go completely around the city, so it's kind of like a fortress against hurricanes," says Bob Anderson, spokesperson for the Mississippi Valley Division of USACE.
USACE also built the West Closure Complex, the largest drainage pump station in the world, which will be crucial in removing large volumes of accumulated water in the case of another storm surge.
'Learned a lot of lessons'
When it comes to disaster relief, Laura Howe says everyone involved has "learned a lot of lessons from Katrina."
Howe was the southeastern regional spokeswoman for the American Red Cross when Katrina unleashed its fury. She is now its vice-president of public affairs.
One of those lessons was that both governments and big relief organizations need to rely on partnerships in the community.
"Disasters are bigger than any one organization and in order to improve our services we have to expand our partnerships and we have to reach out to other people who can help us and help knit this together," Howe says.
For its part, the Red Cross has now:
- increased the number of trained disaster volunteers who can be deployed across the U.S.;
- increased the number of shelter locations;
- established a network of warehouses with enough supplies for 350,000 shelter residents;
- put in place backup communications systems, something that would have made a big difference during Katrina;
- and created the "Safe and Well" website, which helps reconnect families during emergencies.
Howe noted that the public also learned lessons from Katrina, so that today there is more individual planning and safety precautions begin sooner.
Stronger social networks
However, despite all the efforts that have been made in fortifying physical structures in the Gulf Coast area, community organizers say that this is not a cure-all for huge storms like Katrina and, possibly, Isaac.
"There have to be multiple lines of defense. You can't rely on large infrastructure-scale projects to protect you fully," says Mary Rowe, a Canadian who was in New Orleans between 2006 and 2010 working with the Blue Moon Fund, a national foundation that supported recovery initiatives and evolved into the New Orleans Institute for Resilience and Innovation.
A key part of the response to any disaster is communicating survival information to the people affected. That includes everything from evacuation routes to the location of medical depots and grocery stores.
Rowe says that in the years since Katrina, community groups have made great strides in building networks to more effectively convey that information, and adds that digital innovation has played a large role in creating these networks.
"Seven years ago, when Katrina hit, we weren't text-messaging, we didn't have the whole elaborate social-media environment that we have now, so it was really a much different scenario," Rowe says.
"Now you can get the info on Twitter; there are any number of devices that will allow you to communicate with a large number of people, so they know exactly what the situation is."
For the Red Cross, social media has been "transformational in the way we respond to disasters and in the way we can respond to people in a very personal way," Howe told CBC News.
The American Red Cross now has a digital operations centre in the middle of its disaster operations centre in Washington.
By monitoring what's happening in social media, they "can see almost in real-time what's happening on the ground and get a sense of how things are beginning to unfold," she says.
She adds that the Red Cross is using social media to communicate directly and individually with people in disaster areas.
Social change and disaster recovery
Rowe says another legacy of the Katrina recovery is the Urban Conservancy, an advocacy group that has helped rebuild many small businesses in New Orleans.
The Urban Conservancy emphasizes the fact that by buying locally — rather than at national chains — more money stays in the local economy, which directly benefits the citizens of the New Orleans area.
In 2010, the state of Louisiana was wrapping up the largest housing program in U.S. history, doling out $10.4 billion to 127,000 homeowners and thousands of dollars more to renters and small landowners.
The U.S. department of education provided nearly $2 billion for schools in the Gulf coast region to help them open immediately after the hurricane and help support displaced children. It recently dispersed another $1.8 billion to replace 87 schools that were damaged.
Nevertheless, Robert Olshansky, a professor at the department of urban and regional planning at the University of Illinois, said New Orleans has a long way to go to ensure its social infrastructure is ready for another such disaster.
"Probably the biggest remaining challenge has to do with poverty, housing and job creation, which was a big problem before Katrina," said Olshansky.
He co-authored a book, Clear as Mud: Planning for the Rebuilding of New Orleans, about the recovery process after Hurricane Katrina. He says that lifting people out of poverty is another critical step the city must undertake to ensure that its population can remain resilient in the face of any future disaster.
"Natural disasters affect people in different ways," Olshansky says. "People who have less money and fewer resources can't evacuate, they can't rebuild as easily, they don't have access to money to put their lives back together.
"People who had jobs lose them. People who were living on the edge are going to be much more dramatically affected when things like this happen," he added.
From the perspective of someone who was there in 2005, Howe notes that although the wounds are still pretty fresh from Katrina, the lessons learned mean that, "fundamentally, it's going to be a much different response effort than what you saw during Katrina."