Richard Bogren, Caffey, Rex H. | 1/4/2011 1:12:33 AM
News Release Distributed 06/10/10
NEW ORLEANS – Isle Derniere, at an elevation 5 feet, was a barrier island off the coast of Louisiana between Caillou Bay and Terrebonne Bay when what is believed to be a category 3 hurricane ripped into it in 1856. Half the island’s population perished, and what was once a resort community was destroyed and never rebuilt.
By 1978, Isle Derniere had been reduced to a series of smaller islands now called Isles Derniere.
Isle Derniere’s fate has been mirrored in the gradual loss of land in the Chandeleur Islands, Abby Sallenger told a group of scientists and policy makers at a national forum on socioeconomic research in coastal systems here on May 26-28 sponsored by the LSU AgCenter’s Center for Natural Resource Economics and Policy.
The former chief scientist of the U.S. Geological Survey’s Center for Coastal Geology who currently leads the USGS storm impact research group used the two groups of islands in his presentation about how the Gulf Coast changes during extreme weather events.
“A sinking delta induces sea level rise,” Sallenger said, “And hurricanes and sea level rise work together to change the landscape.”
While information about Isle Derniere exists only on old maps and in written accounts of the tragic hurricane, the Chandeleur Islands provide a wealth of information based on scientific observations over the past several years.
Sallenger said the USGS has been using sophisticated optical sensing technology called LIDAR to observe the Chandeleur Islands for years. A chain of uninhabited barrier islands approximately 50 miles long in the Gulf of Mexico, they form the easternmost point of Louisiana.
The islands themselves, Sallenger said, are marshes covered by sand dunes. And because of subsidence – the tendency of delta land to slowly sink under its own weight – the sea level is rising.
When Hurricane Katrina hit in 2005, the storm surge was powerful enough to force water entirely over the islands and begin to wash the sand away, much like what happened to Isle Derniere more nearly 150 years earlier.
“It’s an inundation regime,” Sallenger said. “When a surge gets high enough, the island is under water and no longer behaves like classic land forms.”
He called the loss of about 80 percent of the Chandeleur Islands caused by Katrina a “completely degregational phenomenon.”
The marsh provided a platform on which the sand rests, and no one can find where the sand went after Katrina, Sallenger said. And the marsh itself, which was built by sediment, is sinking because levees and other manmade structures have diverted sediment-laden waters away from replenishing it.
“The topography came from sand dunes on the marsh, and Katrina washed them away,” Sallenger said, showing aerial photographs of the chain of barrier islands before and after Hurricane Katrina. “The surge was high enough to put the entire island under water.”
One surprise, he said, is that later photographs show erosion continues. “You can see the land marching back from the water. When the sand goes away, marsh erodes.”
One of the ramifications now, Sallenger said, is that the islands are so low that oil from the damaged BP oil well in the Gulf could be pushed across the land on a storm surge if a tropical storm or hurricane moves into the area.
The same sort of problems could occur at other Gulf Coast areas, but densely populated barrier islands have incentives to maintain their current state, he added.
Some of the land changes also can be attributed to climate change, said Gunnar Knapp, prominent Alaskan resource economist and a professor of economics at the University of Alaska Anchorage Institute of Social and Economic Research. For the past 29 years, he has studied Alaska’s economy and the management of Alaska’s natural resources, particularly the state’s fisheries.
“We can’t predict accurately how the climate will change or how it will affect us,” Knapp said. “What if place no longer makes sense? Do we help people stay? Help people leave? Do nothing?”
In enumerating some lessons from the Exxon-Valdez oil spill, Knapp said, “We vividly recall powerlessness, sorrow, frustration, rage.”
Knapp said that among the lessons he learned from the Exxon-Valdez incident is that it created challenges and opportunities for scientists.
Regarding the approach to dealing with compensating people who suffered economic losses, he recommended looking at the Exxon-Valdez Oil Spill Trustee Council as a model. The trustee council was formed to oversee the restoration of the injured ecosystem through the use of a $900 million civil settlement. It includes three state and three federal trustees or their designees and is advised by members of the public and by members of the scientific community.
“Try not to spread lots of money in stupid ways,” Knapp said. “Do what gets you the most over the long run.
“Can we minimize the perverse incentives of our legal system?” he asked. “We need reforms to how we deal legally with our environmental disasters.”
Finally, Knapp said, people must “deal with the spill, and then move on. Don’t become permanent victims.”
“There are numerous parallels between the Gulf of Mexico and Alaska,” said Rex Caffey, conference chairman and professor of natural resource economics at Louisiana Sea Grant and the LSU AgCenter. “Both regions have been described as ground-zero for climate change, and they face many of the same economic and political uncertainties associated with the challenge of coastal community sustainability.”