DUCK, N.C. -- America's beaches are in trouble -- under assault by nature and man, and retreating toward an uncertain future.
"The coast is in danger from erosion, pollution and urbanization," warns Stephen P. Leatherman, a geology professor and director of Laboratory for Coastal Research at the University of Maryland and a leading expert on beach erosion.
* Virtually all the nation's beaches are shrinking because of rising sea levels. East Coast beaches have narrowed an average of 2 to 3 feet a year over the past century.
* The number of beaches temporarily closed because of polluted waters has risen steadily in recent years, to 2,619 in 1992, according to the Natural Resources Defense Council.
* Housing and tourism have overpopulated many coasts. About 110 million people now reside within 50 miles of the Atlantic, Pacific or Gulf of Mexico, and millions more visit beaches each year.
The three major problems are intertwined, with erosion and pollution often the worst on highly developed shores.
"The health of America's coasts is on the decline," said Beth Millemann, director of the Coast Alliance, an environmental lobbying group. "The coasts cannot tolerate the onslaught of development that has mushroomed along them."
Erosion heads the list of threats.
"About 90 percent of the U.S. beaches are presently eroding on all three coasts," Dr. Leatherman said. "The biggest problems are on the Atlantic and Gulf coasts."
Over the past decade, the U.S. Army Corps of Engineers has spent $8 billion trying to rebuild the shoreline -- "largely dredging sand off ocean bottom and pumping it onto beaches," Dr. Leatherman said. "We still don't know much about the lifetime of these projects. How long are they going to last?"
To find some of the answers, the Corps of Engineers has set up a sophisticated research facility here on the Outer Banks of North Carolina. Since 1980, its scientists have monitored the complex interactions where the Atlantic meets a barrier island beach.
Sand on the barrier islands that line the Atlantic and Gulf shores has always shifted between dunes, beach and offshore sand bars, but stayed within this system. However, the system is disrupted -- and erosion results -- when the sand bars are dredged out for channels or the dunes are disturbed by development.
As man changes the shore, the sea continues to rise slowly, as it has for thousands of years. In the past century, many scientists believe, global warming has dramatically speeded up the process, producing a 1-foot sea rise. Along the Atlantic seaboard, this has meant an average loss of between 200 and 300 feet of beach.
Over the ages, beaches simply retreated inland as the ocean advanced. Now, this natural movement has run smack up against a coastline crowded with condominiums and hotels.
"We've essentially drawn a line in the sand and said, 'the sea shall not pass.' If it does, it'll hit two trillion dollars worth of real estate," Dr. Leatherman said.
There has been "an explosion of growth" along the coasts, Ms. Milleman said. She said it has been fueled, at least in part, by federal programs such as national flood insurance protection and U.S. Department of Transportation funding of highways and bridges to barrier islands.
About 44 percent of the entire U.S. population resides in ocean coastal counties that compose less than 10 percent of the nation's land, according to the Census Bureau.
Along with the people have come garbage, sewage and chemicals that increasingly make coastal waters unsafe for recreation.
Polluted waters have led to more than 7,700 beach closings in the past five years, according to the Natural Resources Defense Council.
And those numbers tell only part of the story. "There are no national standards for monitoring" water quality off beaches, and state and local monitoring is spotty, said Sarah Chasis, an attorney in the coastal division of the environmental group.
Georgia does not monitor its ocean waters for swimmer safety. Florida and Texas state law do not explicitly require such monitoring, although some resort communities do test their beach waters.
"The real problem is cities on the beach -- Atlantic City, N.J.; Ocean City, Md.; Miami Beach, Galveston, Texas," Dr. Leatherman said.
The chemical-laden runoff from acres of pavement in these cities flows toward the beach. "I always tell people, 'Don't go swimming after the first good rain,' " Dr. Leatherman said.
Environmentalists want the federal government to enact a national beach protection program to set minimum standards for water quality and to ensure regular monitoring. They also want state and local governments to limit and regulate coastal growth.
"The beach is not just the edge of a swimming pool -- although some developers would probably want to pump chlorine into the ocean if they could find a way," Ms. Millemann said. "The strip of sand is not all that matters. The beach is part of a fragile ecosystem that must be protected."