The initial elevation of the exposed beach protected it from inundation. The developed 

 areas were assumed to be protected, so that developed lowland and exposed beaches are not 

 inundated. If the option of not protecting developed areas had been chosen, the pattern would 

 have been quite different: part of the barrier island system would have been breached, resulting 

 in erosion of coastal areas that were previously sheltered from the open sea, and in migration of 

 beaches. 



Appendix 4-C describes how to use the program that we used to carry out our simulations. 1 



RESULTS 



In this section the general patterns of the response of wetland regions are summarized for 

 the low and high scenarios. The simulation results are given in detail in Appendices 4-A and 4-B. 

 We show percent change in wetland area from current conditions, rather than absolute area, in 

 order to emphasize that our intent is not to predict expected response at specific locations but to 

 describe one class of response, among several that can be hypothesized, that could develop 

 within a generalized regional coastal environment. Thus, although the text refers to specific map 

 designations, interpretation should be applied only to a general coastal environment similar to 

 the one represented by the designation. 



New England Region 



Under the low scenario, the general pattern of salt marsh response in New England involves 

 expansion onto the limited freshwater areas such as those on Cape Cod, or onto unprotected 

 adjacent undeveloped lowland, dunes, or beach. However, where salt marshes with high capacity 

 for lateral erosion are found adjacent to tidal flats immediately landward of open sea, expansion 

 of the flats onto salt marsh also would occur, thus reducing or eliminating existing marshes. (The 

 model may overestimate this effect because attenuation of wave energy is not considered.) This 

 pattern is revealed even by the year 2050 in New Hampshire. These losses, however, are relatively 

 small and/or partially compensated for by expansion of salt marsh onto adjacent freshwater 

 marsh, so that some salt marsh is preserved. 



Under the high scenario, however, more rapid rise later would outstrip the adjustment 

 capacity of salt marshes; these would become extensively converted to tidal flats and might be 

 totally lost in some locations where conditions resemble our New Hampshire simulation (Figure 

 4-13). Even under sheltered conditions, the rise is sufficient to inundate salt marshes in most 

 places with steep slopes and cliffs typical of New England, such as those in Jonesport, Maine, and 

 in Cape Cod, Massachusetts. Thus, for the relatively low accretion rates typical of New England 

 salt marshes and the distribution of land categories found there, a high rate of sea level rise could 

 profoundly reduce the area! distribution of both salt and fresh marshes under conditions stipu- 

 lated in model simulations. 



Mid- and South-Atlantic Region 



Further south from Connecticut to New Jersey, extensive low-lying coastal areas are 

 characteristic. The low scenario predicts salt-marsh distributions similar to the 1975 condition; 

 wetlands could even increase as the intertidal zone encroached onto undeveloped lowlands. 

 Susceptible developed lowlands also might be converted to salt marsh unless protected by dikes. 

 The expansion of salt marsh at the expense of adjacent lowland would already be evident by the 

 year 2050 or before. 



The SLAMM program operates on IBM personal computers and is available from the authors. 



109 



