Vegetation may not slow wave erosion

One assumption behind attempts to restore coastal wetlands as natural buffers against storms and floods may be wrong, a study suggests.

Experts believe that wetland vegetation could have helped to resist the coastal erosion caused by Hurricane Katrina in 2005 and other recent disasters, such as the Indian Ocean tsunami of 2004 and Cyclone Nargis, which hit Burma last year.

Rusty Feagin of Texas A&M University in College Station and his team devised some experiments that he expected would demonstrate one way in which wetland plants could do this — by resisting the erosion caused by waves beating at the land's edge. He was surprised to find no such effect. It turned out that soil type is much more important, and that the presence or absence of vegetation doesn't make much difference.

Feagin suggests that the conventional wisdom took hold because of studies that show that plants can build wetlands by trapping sediment that would otherwise flow out to sea. "I think we have taken this idea that wetlands can build themselves and jumped to the conclusion that vegetation can prevent erosion," he says. He adds that vegetation may well have other protective effects, such as calming a storm surge that rolls right over a land edge and heads inland.

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