In the five years since Hurricane Katrina slammed the U.S. Gulf Coast, breaching levees and flooding New Orleans, one thing hasn't changed: Louisiana is still sinking at a rate that's only going to quicken.
The questions now are, is New Orleans ready for another storm like Katrina? And going forward, what's to be done about a region that's headed back into the sea?
Since the storm, the U.S. Army Corps of Engineers and others have spent millions to rebuild the city and its flood protection system.
"We'll be absolutely ready for it," said Corps communications officer Wade Habshey, who is based in New Orleans. "What we have in place now can withstand a Katrina-level storm."
Beyond the city, though, there are still concerns. As coastal areas erode, residents living near the shore face a greater threat of flooding. This could become worse with global warming.
Colonel Edward Fleming, commander for the New Orleans district of the Army Corps of Engineers, says coastal restoration projects are underway, and that he's in Washington seeking approval for six more this week.
Still, he concedes that the state is losing 27 square miles of land a year.
"There's no doubt that at some point the state and the government are going to move forward and are going to have to make some tough decisions and some tradeoffs," Foley said, including deciding where and what structures to build and identifying where changes to zoning, building prohibitions or possible buyouts of homeowners might be appropriate.
"When you have finite resources, whether it's money or whether it's sediment, you have to figure out where you're going to get the best benefit," he said.
Leonard Bahr, a coastal scientist formerly with the Louisiana governor's office, now maintains an independent blog about the Louisiana coast (lacoastpost.com). "The model of bolstering the protections in New Orleans is inappropriate to be used across the rest of Louisiana," he said. "Once you build levees and start pumping, the rest is history. You're doomed to perpetual pumping."
New Orleans' New Defenses
The key features of New Orleans protection system will be in place by the start of the next hurricane season, in June 2011, Habshey said.
They will include a 1.8-mile barrier across Lake Borgne, to the east of the city, capable of withstanding 26-foot waves; 350 miles of levees and floodwalls; and a protection system to the west of the city that will include the world's biggest drainage pumping station.
Others agree that New Orleans will fare better. "I think it's likely that the situation is better than it was when Katrina hit," said Torbjorn Tornqvist of Tulane University in New Orleans.
He and other experts credit improvements to the coastal defense system like the damming of the city's drainage canals and the closing of the infamous Mississippi River Gulf Outlet Canal, a shipping canal that brought surging waters into the city during Katrina.
"I don't think there's much question that New Orleans is considerably more protected," said Bahr. "New Orleans is a unique place. I think the $15 billion that is being spent very quickly by the Corps of Engineers to bolster the levees and protect the city is justifiable, in general."
Lost Wetlands, Lost Buffers
While New Orleans may be in better shape to face a storm, a bigger issue outside the city is the loss of wetlands. Wetlands provide a buffer against storms, and offer crucial habitat for Gulf fisheries species.
Coastal wetlands are constantly eroded, especially in big events like Katrina. Historically, the erosion was balanced by the deposit of new sediment downriver.
"The sediment is not making it to the wetlands anymore because of the levees along the rivers," Tornqvist said. "We need to, in a controlled way, let the water and sediment get through the levees and into the wetlands again."
According to a paper published in Nature Geoscience last summer, if sediment loads to the delta remain at current levels -- about 50 percent less than on an unobstructed river -- more than 3,900 square miles (2.5 million acres) of land will be lost by 2100.
"What needs to be done is a massive program to redirect the river water below New Orleans, to allow the river to really reach the delta," Bahr said.
Seas Rising, Storms Growing
Sediment loss is only part of the problem facing delta lands, the Nature Geoscience study noted. Even if all of the river's sediment could proceed freely to the delta, sea level rise is outpacing sediment deposition by more than threefold, meaning delta lands are certain to disappear.
As engineers predict how the coastal defenses will hold up, one uncertainty is what they will be defending against years down the line. The federal standard for protection is a so-called 100-year standard, which means that the defenses should withstand a storm with a 1 percent likelihood of occurring in any given year, plus a margin of safety.
"One thing we know for a fact is that the conditions we have in the next century will not be the same," Torqvist said.
In addition to sea level rise, many climate change projections predict more intense hurricanes. "Even if the hurricanes remain the same that they were, if sea level is one foot higher, it's going to make a big difference," Torqvist noted.
According to Fleming, the Corps included sea level rise, subsidence and increasing storm intensity in its models when designing the 100-year protection system.
"That 100-year standard is the national standard established by the government. We're public servants. If Congress tells us we're going to start building to a 500-year event, we will accommodate," Habshey said.