Unless there are major changes in the regulation of land use along the United States sheltered coasts, many landscapes in the nation s estuaries, bays, lagoons and mudflats will be damaged or destroyed by erosion, an expert panel reported yesterday. Mitigating Shore Erosion Along Sheltered Coasts (National Academies Press)The panel said a rising sea level was accelerating erosion on these coasts, even as more and more people seek to live along them. Seawalls, bulkheads and other engineered barriers can offer short-term protection from erosion, the experts said, but long term they often result in the loss of landscapes vital for birds, fish and shellfish and important for their recreational and aesthetic value.

The panel recommended replacing local regulatory regimes with approaches for larger regions carried out with an eye to long-term effects. And it suggested that property owners and regulators think beyond rock and concrete and consider novel protection methods, like the creation of artificial marshes.

The panel was convened by the National Research Council, the research arm of the National Academy of Sciences. Its report, “Mitigating Shore Erosion Along Sheltered Coasts,” was posted yesterday at www.nationalacademies.org. Scientists who study the coast have known that erosion of ocean beaches is a serious threat and that seawalls and other coastal armor meant to protect against it can do more harm than good. But the new report is the first major assessment of erosion and armor on sheltered coastlines, said S. Jeffress Williams, a coastal scientist at the United States Geological Survey, who reviewed the work for the council.

Dr. Williams said the project was, in part, a response to “welcome concern among planners and managers as to how they are going to deal with sea-level rise,” which is accelerating because of climate change. Because sheltered coasts typically slope very gently, a one-foot rise in sea level might send water 200 or 300 feet inland, Dr. Williams said. Threatened by the resulting land loss, property owners typically try to protect their land with seawalls, bulkheads, revetments or other armor. But rising water eventually reaches the armor, drowning the marsh or mudflat in front of it.

“You have eliminated the intertidal habitat, extremely vulnerable habitat for juvenile fishes and shrimp,” said Denise J. Reed, a coastal scientist at the University of New Orleans who was a member of the expert panel. “On the other side of the bulkhead, you don t have mudflat anymore, you just have water.” Already, the expert panel said, coastal armor has sharply altered habitats in places like Mobile Bay, Ala.; Puget Sound, Wash.; and Raritan Bay, N.J.

As of a few years ago, the report says, 30 percent of the shoreline of Mobile Bay was armored, mostly because of decisions individual property owners made one by one. “It’s really quite disturbing,” Dr. Reed said. “It’s death by a thousand cuts.” Because sheltered coastlines do not typically present long stretches of relatively uniform landscape, the way ocean beaches do, they are more likely to be regulated piecemeal, the report says. While one or two seawalls or bulkheads, installed here and there, may have relatively little effect, it continues, “the construction of many structures in relative close proximity to each other” can destroy or strikingly alter habitats.

Once regulators allow development along a sheltered coastline, they invite future armoring, the report goes on, adding, “Therefore consideration should be given at the local planning level to the consequences of development in highly eroding areas.” Dr. Reed said, “If people realized what the cumulative effects of all these individual actions is on the systems they value, they might think differently.”

For example, she said, people might decide to protect their property not with metal or concrete but by encouraging marsh growth. The authors of the report also confronted one of the thorniest problems for coastal scientists and engineers: determining the dollar value of resources that are destroyed when upland infrastructure — houses or roads or the like — is protected. “The specific value of habitats is itself poorly defined,” the report says, suggesting it would be a fruitful area of research.
(Por Cornelia Dean, The N.Y.Times, 13/10/2006)