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Three years after Hurricanes Katrina and Rita ravaged the U.S. Gulf Coast, the region was hit once again by a pair of large storms: Hurricane Gustav made landfall near Cocodrie, Louisiana, on September 1, 2008, as a strong Category 2 storm; and Hurricane Ike made landfall near Galveston, Texas, on September 13, 2008, also as a strong Category 2 storm. Major metropolitan areas were evacuated in the face of each hurricane: residents were ordered to leave New Orleans as Gustav approached, and Ike triggered evacuations of Houston and Galveston.
Luckily, the 2008 hurricanes were not as deadly as Katrina, but the tolls were high enough: each storm caused more than 100 deaths in the Caribbean and the United States, with many billions of dollars of damage. (For comparison, Hurricane Katrina caused nearly 1,900 deaths and roughly $125 billion in damage.) Three days after Hurricane Ike made landfall, nearly 2 million residents of Texas were still without power, and many thousands were facing weeks in shelters. Meanwhile, the remnants of Ike had moved northeastward across the United States, causing flooding and power outages in the Midwest.
Hurricane Ike's enormous size made it unusually destructive for a Category 2 storm. With tropical-storm-force winds spread more than 500 mi across as it approached the U.S. Gulf Coast, Ike was about 70 percent larger than an average hurricane, and it damaged the coast from Texas to eastern Louisiana. The winds of the large hurricane whipped up an unusually large storm surgethe mound of water pushed ashore by the stormestimated at about 10 to 15 ft above normal tides. Many areas along the Gulf Coast were severely affected by Ike's surge. Particularly hard hit was the Bolivar Peninsula, a barrier island northeast of Galveston. Storm surge and waves covered the island, destroying an estimated 80 percent of the homes. "The Bolivar Peninsula was in or near the eyewall of Hurricane Ike when the storm made landfall," said U.S. Geological Survey (USGS) oceanographer Abby Sallenger, leader of the USGS Hurricanes and Extreme Storms Research Group. "This was the location of the strongest winds and where we observed the greatest impacts to the coast."
The extreme-storms group, which is part of the USGS National Assessment of Coastal Change Hazards Program, was busy before and after each storm. As Hurricanes Gustav and Ike approached, the group prepared maps showing the likelihood of inundation (complete submergence of the beach system) and extreme coastal change for Gulf Coast areas expected to be affected by hurricane landfall. The scientists compared measured elevations of primary dunes and beach berms (the "first line of defense") with modeled elevations of storm surge for Category 1, 2, 3, 4, and 5 hurricanes and plotted the results. The higher the predicted storm surge relative to local beach topography, the greater the likelihood of inundation, which produces the most extreme coastal change.
"These maps describe the potential coastal changes that could occur, threatening communities and critical wildlife habitats," said Sallenger. Hurricane landfall and associated elevated water levels, waves, and currents can lead to severe coastal change through erosion and re-deposition. The combination of a growing population living along the coastline and the cumulative effects of previous storms makes the northern Gulf of Mexico region particularly vulnerable.
After each hurricane, the USGS research group quickly mobilized to investigate coastal changes along the Gulf Coast's sandy beaches. Just 3 days after Gustav made landfall and 2 days after Ike, they began collecting aerial video and still photography of post-storm beach conditions. Approximately 4 days after landfall, airborne lidar (light detection and ranging) surveys of post-storm topography were collected. The aerial photographs, including before-and-after sets, were posted online just a few days after each storm, and data from the lidar surveys were posted a couple of weeks after each storm. (See Hurricane Gustav and Hurricane Ike Web sites.)
Comparisons of the post-storm data with earlier data reveal the characteristics, magnitude, and spatial variability of such coastal changes as beach erosion, overwash deposition, and island breaching. Post-storm data are also being compared with the maps the group prepared as each storm approached, to help them further refine predictive models of coastal impacts from severe stormstools that can benefit coastal-zone managers, emergency planners, and residents. The group worked quickly to make their data available online to local, State, and Federal agencies to aid post-storm disaster recovery and future erosion mitigation.
New York Times science editor Cornelia Dean flew with Sallenger and his extreme-storms group during post-Ike flights and produced an article, "After Hurricane Ike, Finding the Coastline Rearranged, Again," a narrated slide show, and a poster about the gradual disappearance of barrier islands, based on USGS aerial photographs.
Visit the USGS Hurricanes and Extreme Storms Web site to learn more about the extreme-storms group's research and to view their aerial photographs (including before-and-after pairs), inundation maps, and lidar images. Additional information about hurricane research conducted by the USGS is posted on the Natural Hazards - Hurricanes Web site.
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