WORRY lines etch the gaunt but gentle face of Tom Marshall. He has spent the last six years building up Horne's marina on the elbow of Cape Cod. Today he and his wife watch as the rising tide creeps up the thin bulkhead that protects their home and business. A week ago the tide spilled over the bulkhead and lapped the edge of their front lawn. Now it stands only an inch from the top. The problem started with the first of several midwinter storms. On January 2, a vicious blizzard raged out of the northeast. It washed over Nauset Beach, the narrow barrier of sand that protects the elbow of Cape Cod. By morning a narrow cut had formed. As the storm receded the currents reversed, scouring out a new inlet into Pleasant Bay. A month later, four more storms had increased the width and depth of the new inlet; now it is half a mile wide and 21 feet deep.
The effects have been rapid and impressive. Tides occur an hour earlier and seem to be six to eight inches higher and lower than they had been before. Twenty fishermen face losing their livelihoods as their shellfish beds are slowly smothered under several hundred tons of sand. Erosion is occurring the length of the 12-mile estuary.
Now local officials must decide which areas are irrevocably lost, which can be saved, and who will pay to save them. The new inlet on Nauset Beach also presents the four towns on the elbow of Cape Cod with a rare but narrow window of opportunity to start making policies and regulations that will mitigate the effect of worldwide sea-level rise before it becomes severe in the next 40 years. Sea-level rise
These communities are not alone. Every coastal community will have to start planning for sea-level rise. Bangladesh and India are expected to be devasted as they lose three miles of their valuable coast to sea-level rise. Egypt may lose land that accounts for up to 20 percent of its economy. The Netherlands already spends a greater percentage of its gross national product on coastal defense than the United States spends on military defense.
In the last few years, several studies have suggested that the sea level is rising because of global warming due to mankind's release of carbon dioxide and trace gases. This is the so-called greenhouse effect.
Dr. Orrin Pilkey, a geologist at Duke University, states that, ``For the last 3,000 to 4,000 years, there has been very little sea-level rise and barrier islands have been able to hold their own. Since the 1930s however, this rise has started to accelerate.''
According to a 1983 report prepared by the Environmental Protection Agency (EPA), the sea level may rise as much as one foot over the next 40 years and three to five feet over the next century. Their worst-case scenario projects as much as a 12-foot rise in sea level along parts of the East Coast by the year 2100. They calculate further that the mainland recedes an average of 100 feet for each one foot rise in sea level.
Cape Cod's new inlet shows that overnight a single storm can force a community to start to deal with a situation that other communities might not face for decades, when it could be too late. Dr. Graham Geise, visiting scientist at the Woods Hole Oceanographic Institution, has demonstrated a 150-year cycle for the development and destruction of Nauset Beach. ``The first few years of the cycle are critical; tidal patterns will affect erosion in Pleasant Bay. After about 20 years, however, the barrier beach south of the inlet will wash away because of lack of renourishment from sand. Then erosion will be most severe for several decades and Chatham must face the full brunt of the Atlantic Ocean without the protection of its barrier beach.'' Coastal Zone Management
Coastal communities have two options to deal with sea-level rise. They can either stabilize their coasts or they can learn to live with the inevitable and stage a strategic retreat from the endangered coast.
Traditionally, coastal communities have fought erosion by constructing sea walls, jetties, and groins, rigid structures that slow the local erosion of the coast. Ultimately, however, these hard stabilization strategies only create worse erosion further down the shore because they interfere with the natural flow of sand that must constantly renourish beaches.
In the case of large coastal cities where millions of dollars of development have already been spent, however, such a strategy might still make sense. Louisiana is building sea walls to maintain its present shoreline because that is the basis for its offshore boundary. Any reduction of its offshore boundary could cause the state to lose income from the sale of offshore oil-drilling rights.
Some communities with large tax bases have chosen to build artificial beaches by pumping offshore sand onto the coast. Miami has chosen this soft stabilization approach. It has several advantages. It allows the city to maintain its natural beach, which is one of its main attractions, and it does not interfere with the natural flow of sand. Although the artificial beach will have to be replaced, the irreplaceable mainland is saved.
During a June 1985 meeting at the Skidaway Institute of Oceanography in Savannah, Ga., coastal geologists prepared a position paper for a new national strategy for beach preservation. In the paper, they called for a strategic retreat from the coastline. Dr. James Titus, manager of the EPA's Sea Level Rise Project described such a retreat. ``In Colombia, I just visited a small coastal community faced with erosion. They simply moved their village back 10 miles and renamed it Pueblo Nuevo.''
Several states have passed regulations that achieve the same goal. North Carolina has passed a law that requires that all single-family houses be built behind the 30-year flood line and that all condominums be built behind the 60-year flood line.
New York is considering a law that would require that all new houses built on the coast be movable, so they can be moved back as the seas rise. Some states and local communities are starting to identify land that will be in jeopardy. Undeveloped land can then be set aside as conservation areas and restrictions can be put into deeds that would require that the land revert to the state in a hundred years if it is threatened by sea-level rise. This allows owners and developers to make an immediate profit from their land while allowing them to plan for future risks.
In Chatham, Dr. Geise has already deployed instruments to measure the effects of the new inlet. They will provide him with data to study the natural evolution of an inlet, a geological process that hasn't been fully studied before. The results of the research will allow coastal managers to decide what course to pursue.
William Sargent is director of the Coastlines Project in Woods Hole, Mass. He is author of ``Shallow Waters, A Year on Cape Cod's Pleasant Bay.'' His second book ``The Year of the Crab,'' published by W.W. Norton Company will appear in April.