implemented either through an unplanned retreat or a planned retreat. Howard, Pilkey, and 

 Kaufman (1985) discuss several measures for implementing a planned retreat along the open 

 coast. Although North Carolina and other coastal areas have required houses to be moved inland 

 in response to erosion along the open coast— where shore protection is expensive— it may be 

 more difficult to convince people that the need for wetland protection also justifies removal of 

 structures. 



There is also a class of institutional measures that increases the flexibility of future 

 generations to implement a retreat if it becomes necessary, without imposing high costs today. 

 For example, permits for new construction can specify that the property reverts to nature one 

 hundred years hence if sea level rises so many feet. Such a requirement can ensure the 

 continued survival of coastal wetlands, yet is less likely to be opposed by developers than policies 

 that prohibit construction. Moreover, with the government's response to sea level rise decided, 

 real estate markets can incorporate new information on sea level rise into property values. The 

 State of Maine (1987) has adopted this approach, specifying that houses are presumed to be 

 moveable. In the case of hotels and condominiums, the owner must demonstrate that the 

 building would not interfere with natural shorelines in the event of a rise in sea level of up to 

 three feet, or that he or she has a plan for removing the structure if and when such a rise occurs. 



Finally, it might be possible to hold back the sea and maintain wetlands artificially. For small 

 amounts of sea level rise, tidal gates might be installed that open during low tide but close during 

 high tide, thereby preventing saltwater intrusion and lowering average water levels. For a larger 

 rise, levees and pumping systems could be installed to keep wetland water levels below sea level. 

 Although these measures would be expensive, they would also help to protect developed areas 

 from the sea. Terrebonne Parish, Louisiana, is actively considering a tidal protection system and 

 a levee and pumping system to prevent the entire jurisdiction from converting to open water in 

 the next century (Edmonson and Jones 1985). They note, however, that effective measures to 

 enable shrimp and other seafood species to migrate between the protected marshes and the sea 

 have not yet been demonstrated. 



Measures to ensure the continued survival of wetland ecosystems as sea level rises need to be 

 thoroughly assessed. We may be overlooking opportunities where the cost of implementing 

 solutions in the near term would be a small fraction of the costs that would be required later. Only 

 if these measures are identified and investigated will it be possible to formulate strategies in a 

 timely manner. 



CONCLUSIONS 



An increasing body of evidence indicates that increasing concentrations of greenhouse gases 

 could cause sea level to rise one or two meters by the year 2100. If current development and river 

 management practices continue, such a rise would destroy the majority of U.S. coastal wetlands. 

 Yet these losses could be substantially reduced by timely anticipatory measures, including land 

 use planning, river diversion, and research on artificially enhancing coastal wetlands, as well as by 

 a reduction in emissions of greenhouse gases. 



Case studies of South Carolina and New Jersey marshes indicate that a two-meter rise would 

 destroy 80 to 90 percent of the coastal marshes, depending on development practices, while a 

 one-meter rise would destroy 50 percent or less. The large body of research previously conducted 

 in Louisiana suggests that its marshes and swamps would be far more vulnerable. Yet anticipatory 

 measures, if implemented soon, could save a large fraction of these wetlands. 



For the rest of the nation, no site-specific research has been undertaken. Most of these 

 wetlands are also within one or two meters of sea level. Preliminary analysis by Armentano et al. 



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