Beach Erosion

. Cape Hatteras Lighthouse is the 208-foot tall landmark was just hauled more than a quarter-mile back from its former perch, where it was threatened by the encroaching sea. Coastal erosion chewed away about 1,300 feet of beach, bringing the waves to within 150 feet of the 4,800-ton sentinel. When the light was erected in 1870, it stood about 1,500 feet back from the waves. The lighthouse, on the Outer Banks, North Carolina's long barrier beach, was built to warn ships from waters called "the graveyard of the Atlantic." Ironically, the move should serve as a warning about the growing problem of coastal erosion. Erosion is not just plaguing the Outer Banks. Coastal residents up and down the United States are worrying about undermined cliffs, disappearing beaches, and the occasional dwelling diving into the briny. Beaches are constantly moving, building up here and eroding there, in response to waves, winds, storms and relative sea level rise. Yet when commoners like you and me, and celebs like Steven Spielberg, build along the beach in places like Southampton, N. Y., we don't always consider erosion. After all, real-estate transactions are seldom closed during hurricanes or northeasters, which cause the most dramatic damage to beaches. Yet Southampton, like all the barrier beaches that protect land from the sea, is vulnerable to obliteration by the very factor that makes it so glamorous: the sea. And the problem is increasing because the sea is rising after centuries of relatively slow rise, and scientists anticipate that the rate of rise will continue to increase in the next century. Land, in many places, is also slowly sinking. The result is a loss of sand that places the occasional beachside home inconveniently near -- or in -- the water. Still, erosion cuts in two directions. Without the process of erosion, we would not have the beaches, dunes, barrier beaches, and the highly productive bays and estuaries that owe their very existence to the presence of barrier beaches. Erosion of glacial landforms provides most of the beach sand in Massachusetts. A popular destination The beach-erosion problem has many causes. Among them are: * The ubiquitous desire to live near the sea. * A historically rapid rise in average ocean levels, now estimated to be rising at about 25 to 30 centimeters per century in much of the United States. * The gradual sinking of coastal land (since the height of the land and the sea are both changing, we use "relative sea level rise" to describe the rise of the ocean compared to the height of land in a particular location). * Efforts to reduce erosion that have backfired and instead increased it. * Global warming, which is expected to accelerate the rise in sea level. The upshot is a threat to beaches and coastal communities around the world. At stake is far more than a movie mogul's mansion. New Orleans, now several feet below sea level, would face a greater threat of annihilation. Island nations across the Pacific Ocean could disappear beneath the waves. Millions of Bangladeshis, already exposed to typhoons that drown hundreds of thousands at a time, would have to find new homes in one of the Earth's most crowded nations. The predictions growing out of global warming studies are unsettling. Much of Long Island's extensive barrier beach, including not just the homes of the rich and famous in the Hamptons, but also public treasures like the vastly popular park at Jones Beach, would be submerged if sea levels rise by three feet, according to a projection by the National Environmental Trust, a Washington, DC, advocacy group. A three-foot rise over the next 50 to 100 years is possible, but extremely unlikely, according to current predictions. Coastal erosion is a knotty issue. Slowing global warming -- the ultimate cause for heightened concern about the future -- is proving problematic, to put it charitably. And many localized cures for erosion are worse than the disease. Some are "beggar-thy-neighbor" solutions that steal sand from one location to save another. Others are expensive Band Aids that pump sand from deep waters to the beach, where it immediately begins washing away. . A widespread problem How extensive is the coastal erosion problem? Consider: * During a 1992 storm, the Atlantic Ocean broke through a barrier island near Westhampton, N.Y., destroying about 190 of the 246 homes on the island. The breakthrough was blamed on structures designed to build up beaches that blocked the flow of sand along the shore. These so-called groins build up some beaches while depriving others of their essential sand supply. * Seventy-two percent of coastal towns in Massachusetts are "exhibiting a long-term erosive trend," says O'Connell. * Beaches in Southern California are losing vast amounts of sand, and some are down to bare rock. The beach sand came from river sediment, but damming and water removals have impeded that supply. One drastic solution, the removal of Matilija dam on the Ventura River, is under consideration, with twin goals of restoring trout to the ocean, and sand to the beaches around Santa Barbara. * In Britain, the Observer magazine described, under the headline "Incredible Shrinking Britain," cliffside houses tumbling into the English Channel. * In Galveston, Texas, more than 140 property owners entered legal limbo when beach erosion moved the public beach (defined as bare sand without vegetation) to their property. *

A thin line of protection All geology is about change. Continents, as we know, drift gradually around the globe. The ocean floor is being created at the mid-ocean ridges and recycled beneath the crust at the margins. Mountains rise up and gradually erode back. These changes are slow, inexorable, and usually gradual. The changes on a beach, in contrast, can happen literally overnight, at least during a storm. Even without storms, sand may be lost to longshore drift (the currents that parallel coastlines). Or sand may be pulled to deeper water, essentially lost to the coastal system. On the positive side, sand arrives from eroding uplands, river sediment, and longshore drift. Change -- with a purpose All this change, however, is useful to those who live sheltered by the beach. Aside from providing recreation and wildlife habitat, beaches are protection for whatever lies behind. Like those foam-packed highway barriers that give way on impact, beaches absorb energy from the sea. Beaches are a very significant dissipater of wave energy, the wider, more gently sloping and permeable they are, the more energy will dissipate before it reaches landward development or natural resources. . Simple solutions boomerang Cities like Miami Beach that built right up to the bluffs above the beach soon noticed that the bluffs were eroding, bringing the ocean a bit too close for comfort. The city responded by reinforcing the bluffs with