New Orleans hurricane defences rely on swamps as much as levees
Rebuilding wetlands as natural protection is expensive and slow but vital
In New Orleans, you can sometimes forget it's a coastal city. But soaring over it in a float plane, you realize New Orleans is almost an island, practically surrounded by sea, rivers and wetlands.
Alisha Renfro, a staff scientist at the National Wildlife Federation, points through the plane's window. From up here, you can see spaces where houses used to be.
"That's the Lower Ninth Ward that was hit the hardest by the hurricane," Renfro says. "And so after Hurricane Katrina, the federal government invested $14.8 billion to update the levees and then adding other structures around New Orleans."
She points out the long storm surge barrier snaking across the water and the world's largest pumping station, which can drain the equivalent of an Olympic swimming pool in less than five seconds.
But just as important as all this bricks and mortar, she says, is a system that was protecting New Orleans before the first levees were built: the wetlands.
"Coastal wetlands are really important to form that natural storm protection that we were so lacking during Hurricane Katrina," Renfro says.
We're flying over an area that's mostly water, dotted with islands of green marsh. Dicky Toups, our pilot, mentions that 20 years ago, he used to hunt ducks in this area, on foot. That's obviously no longer possible because the marshlands, Renfro says, are disappearing.
"Over the last 80 years we've lost 1,900 square miles of land, and that's due to a variety of reasons" such as storms, oil drilling, and sea level rise, she says.
That's one reason the damage from Katrina was so extensive. Had the marshlands been there, they would have acted as a natural break.
"The storm surge itself interacts with the plants and it causes friction and slowing the storm surge down, decreasing the height of that storm surge," Renfro says.
"So not only can it protect the coastal communities, it can also help protect the infrastructure that we've built around our coastal communities from things like large hurricanes."
With sea levels rising worldwide, Renfro says many coastal cities will one day have to deal with this issue.
"And here in Louisiana we're the testing ground of technologies that we're going to see employed in other places in the future."
PHOTO GALLERY | The still devastated Lower Ninth Ward
Below us are long black tubes that, from afar, look like oil pipelines belonging to the many rigs that dot the landscape. But these tubes carry a slurry of sand and water dredged from the Mississippi River that is being pumped into the water to rebuild the marshland.
Here and there, new sandy-green islands are rising from the water, created by pipes and silt. The goal is that eventually trees will grow back, adding another layer of protection.
"We still have a little ways to go," Renfro says.
"We have to start restoring the wetlands in earnest to build redundancy in the system to give us a little more protection during those events. Katrina was a big storm and while I hope that something like that doesn't happen again, we do have to be prepared."