Federal scientists have some bad news for New Orleans and coastal Louisiana: Hurricanes Katrina and Rita turned at least 100 square miles of wetlands — which are barriers against storm surges — into open water and much of that damage may be permanent.
Katrina alone wiped out the single largest tract of wetlands ever recorded in Louisiana, the scientists told reporters at a press briefing Friday.
On top of that, the area that suffered the most wetlands damage, the Breton Sound area southeast of New Orleans, is critical to protecting the city.
“New Orleans is always going to need protection from Breton Sound to prevent flooding,” said Tom Doyle, a scientist with the U.S. Geological Survey.
The less wetlands available to protect an area, the farther inland a storm surge will push, he said.
New lakes likely
In a statement announcing the loss, the USGS said that while some marsh areas may recover “indications are that much of the loss may be permanent.”
“Some of the new areas of open water will likely become new lakes,” it added.
USGS scientists based their estimates on satellite images and said observations over the next year would determine how much of the loss is permanent.
The 100 square miles were broken down into three areas:
- Breton Sound, located east of the Mississippi River in St. Bernard and Plaquemines parishes. Some 39 square miles of marsh, a third of the area, “were converted to open water,” the USGS said.
- The Pontchartrain, Pearl River, Barataria and Terrebonne basins, where there was 47 square miles of marsh damage. Pontchartrain is a lake basin north of New Orleans. The others are basins along the Gulf Coast.
- The Mississippi Delta, south of New Orleans,where there was 14 square miles of wetlands damage.
Southwest damage less certain
Most of the damage east of the Mississippi River was attributed to Katrina, while Rita’s surge caused “detectable marsh loss” west of the Mississippi to the Texas border, the USGS said. Scientists are still working to quantify that damage.
The marsh damage adds to Louisiana’s already significant wetlands loss: about 1,900 square miles since the 1930s due to levee building, oil and natural gas drilling and natural causes. The USGS had previously estimated the coast would lose 650 square miles of marsh by 2050.
Coastal marshes and forested wetlands cover 11,000 square miles of the state's coast.
“The enormity of the disaster is hard to put in words, especially if you’ve flown over the areas,” Col. Richard Wagenaar, the U.S. Army Corps of Engineers district chief in New Orleans, said at a briefing Wednesday. Wagenaar chairs the committee steering efforts to restore coastal Louisiana.
‘Looks stone-cold dead’
The storms inundated fresh marshes with saltwater and killed marsh grasses, said Ronny Paille, a biologist with the U.S. Fish and Wildlife Service.
“It looks stone-cold dead,” he said of the marshes. It will take another growing season or two to see if the marsh springs back, he said.
Rex Caffey, a wetlands and coastal issues professor at Louisiana State University, echoed the USGS concerns, adding that the hurricanes also hammered another natural storm surge buffer: barrier islands just off the coastline.
The Chandeleur islands, in particular, were “very hard hit,” Caffey said, and essentially were halved in size by Katrina, to several square miles.
Barrier islands can bounce back as they collect more sand, Caffey noted, but the Chandeleurs were struck by five major storms in recent years “so that their resilience is diminishing every single time.”