Laura's coastal cost assessed with drones, satellite images
NEW ORLEANS — Hurricane Laura was hardly done ripping across Louisiana before scientists started combing through satellite imagery and drone footage and preparing to survey coastal areas to see what damage was caused by the monster storm.
Southwest Louisiana’s gulf coast is a fragile yet vibrant region, home to important fisheries, petrochemical plants and small communities of people who live at the water’s edge. But numerous factors have contributed over the decades to erosion, which can be exacerbated by hurricanes. Some key takeaways of the immediate analysis of Laura’s effects have emerged:
IT WILL TAKE MONTHS TO KNOW EFFECTS:
Scientists say some coastal impact from Hurricane Laura is inevitable. Pounding waves can tear at the marshes that make up most of the coast, and storm surge can inundate wetland areas, depositing sand and sediment in places that didn’t have so much before.
Laura certainly moved things around, but it could take months to figure out if the hurricane caused any significant and permanent land loss.
Bren Haase, who heads the state’s Coastal Protection and Restoration Authority, said the eastern Cameron shoreline “got pounded pretty hard.” But they haven’t been able to measure what has happened yet. In the western parts of Cameron Parish, where the shoreline is more sandy beach, many homes were badly damaged and helping people recover is the top priority, but the beach itself seemed to have fared well, he said.
Kara Doran, an oceanographer with the U.S. Geological Survey, said about 70% of the coastline from from Gilchrist, Texas, to Pecan Island, Louisiana — about 125 miles (200 km) — had overwash. That means sand was transported landward, covering as much as 165 yards (150 meters) of marsh. “There was a tremendous amount of water flowing over that area,” Doran said.
But it will take months to assess whether all that water and sand leads to permanent land loss, said Brady Couvillion, also of USGS. Initial satellite imagery showed extensive flooding, much of which got trapped and hasn’t receded. The question is what lies beneath.
“Once those flood waters recede, that area may have converted to open water or it may go back to a marsh condition and that’s what’s going to take some time to assess,” he said.
SALINITY’S A PROBLEM
Another question is how long storm surge waters sit before eventually draining away. If salty water sits behind natural ridges or man-made structures for a long time, it can damage or kill the plant life.
This was a problem after 2005′s Hurricane Rita, said Natalie Snider, Senior Director of Coastal Resilience with the Environmental Defense Fund.
“The saltwater just shocks the system and it can’t handle it,” she said. “We need rain. We need that fresh water to really flush it out.”
Haase said they are mobilizing equipment, such as an amphibious marsh backhoe, to cut a drainage canal about 300 yards (275 meters) long through a beach that has long prevented the Mermentau River from reaching the sea. They’re also moving in pumps to dry out key areas, helping the residents as well as the marsh.
DID THE WETLANDS PROTECT THE COAST?
One of the benefits of having a vibrant coastal wetlands, scientists argue, is that it provides a natural buffer that can reduce the power of a hurricane’s storm surge before it hits inland areas where more people live. Laura took a slight jog to the East just before making landfall which probably prevented some of the worst storm surge from pushing all the way into Lake Charles.
Naomi Yoder, from Healthy Gulf, which advocates for environmental causes along the coast, believes the wetlands in Cameron and Vermilion parishes also lessened the impact of the storm surge in some areas.
Yoder said it’s important not to minimize the damage in places like Lake Charles where the hurricane’s howling winds badly damaged homes and businesses. But she said it helped people in the area to have large swathes of intact wetlands take the brunt of the storm, in places including the Rockefeller Wildlife Refuge and the Sabine National Wildlife Refuge.
A lot of what CPRA does involves restoring land in coastal Louisiana. Haase said the agency has built close to six square miles of new land in Cameron and Vermilion Parishes over the last few years.
He said initial assessments indicate those marsh creation areas survived the storm. This might be in part because the storm blew through so quickly and the storm surge was so high that it simply rode over the marshes, rather than tearing them up.
Every storm is different — coming in at different angles and different speeds — so it’s hard to measure exactly how much protection wetlands provide. But Hasse said: “If you give me a choice of having that land between the Gulf and my home, I will take it every time.”
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