Thursday, September 20, 2007

Georgia shoreline vulnerable to rising water

Daily Report (Georgia): … Georgia hasn’t had a direct hurricane hit since before 1900, but [Judith A. Curry, chairwoman of the Georgia Tech School of Earth and Atmospheric Sciences] points out that the annual average number of North Atlantic tropical cyclones during the past decade is almost 50 percent greater than during the 1950s, the prior peak of hurricane activity. She also says the current active storm phase is likely to last another 20 years. In other words, it’s only a matter of time.

…More intense hurricanes, coupled with rising seas, could spell disaster for low-lying areas. The National Environmental Trust, a nonprofit, nonpartisan group, on its Web site proffers a scientifically based simulation of what could happen to Tybee Island in 40 to 90 years if a Category 2 storm hits, and if seas already have risen three feet—a scenario postulated by the United Nations Intergovernmental Panel on Climate Change. In the simulation, Tybee is completely submerged.

Tybee has an average elevation of 10 feet to 12 feet above sea level, and according to the most recent storm surge map, about 25 percent of its land—mostly along the north end, on the beach—is vulnerable even to a Category 1 storm. Phillip M. Webber, director of the Chatham Emergency Management Agency, which handles Tybee’s emergency preparedness, acknowledges that a Category 5 storm—when coupled with wave action and rainfall—could submerge the island, at least for a while. Curry, who has seen the Tybee simulation, calls it a reasonable view of what could happen, but she points out that it is a “100-year issue.”

In the near term, however, Georgia’s coastline and islands already are feeling the effects of rising seas. According to Clark R. Alexander—a sedimentary geologist with the Skidaway Institute of Oceanography in Savannah—the state has an instrumental record of changes in sea level dating back to about 1935, thanks to a tide gate installed at Fort Pulaski on Cockspur Island, which shows that seas are rising about one foot per century.

“There is climate change. It is getting warmer. Sea levels are starting to rise as rapidly as they have during this whole interglacial time period that we’re in right now,” he says. “But to take that and attribute it to man’s efforts is difficult right now because of the short time span.” Alexander does attribute coastal erosion—which is affected by rising seas—to human activity.

Much development on Georgia’s barrier islands is taking place in risky areas, Alexander says. Development and revetments accelerate erosion, and erosion costs money. Erosion means Georgia’s islands must be “renourished”—in other words, sand must be shipped in to build up the shoreline. Tybee is renourished every seven years, says Alexander. Next year’s renourishment is slated to cost $10 million….

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