METHODOLOGY 



The objectives of the present study were met in a two-step procedure: (1) interpretation of the 

 present distribution of coastal land categories and their attributes pertinent to sea level rise, and 

 (2) development of a computer model to simulate the future response of the coastal land 

 categories to postulated rates of sea level rise. Both are described in detail below. 



Data 



To develop a regional/national analysis of U.S. coastal wetiand responses to sea level rise, 

 stratified sampling of the continuous U.S. coastline was undertaken for nine regions (Figure 4-3). 

 Selected 7.5-minute quadrangles were characterized as to coastal features, elevation, and 

 development. The quadrangles were selected to capture, to the extent possible, the variation in 

 coastal landscapes within each region. In addition, within each region, important lagoonal and 

 deltaic wetlands were analyzed (Table 4-3). The sites interpreted for the present study are shown 

 for each region of the United States in Figures 44 through 4-7. A total of 183 quadrangles were 

 used for the 57 sites depicted. The entire case study data set is presented as Appendix 4-A. 

 Although the sites are representative of the coastal wetlands, they do not constitute a statistical 

 sample from which probabilistic inferences can be made concerning all coastal areas of the 

 contiguous United States. 



The data were collected from each 1 km 2 cell registered on the Universal Transverse 

 Mercator (UTM) grid so that re-inventorying would be routine. Of the sixteen categories of 

 coastal types, each is based on the dominant category within the square-kilometer cell. They are 

 summarized in Table 44. The type of coastline is defined as one of the following: (1) steep slope, 

 (2) low slope, terraced, (3) deltaic, and (4) low slope, unterraced. The height of low coastal 

 terrace is estimated for each site and region from the literature (e.g., Richards 1962); however, it 

 is not used in the current version of the simulation model. The mean elevation is based on the 

 dominant category in the cell. Although this introduces an element of imprecision, if a large 

 enough area is considered, the estimate is not biased. Tidal range for both open sea and 

 sheltered areas is taken from the topographic maps, or if necessary from tide tables. 



The presence of naturally sheltered areas (e.g., bays) is coded, as are major protective 

 structures such as levees. Finally, the extent to which the cell can be classified as residentially or 

 commercially developed is noted. The extent of freshwater and brackish wetiands cannot be 

 determined at the regional level from topographic maps. 



TABLE 4-3 



REGIONAL CLASSIFICATION OF COASTAL WETLANDS 

 AND REPRESENTATIVE SAMPLE SITES 



Region Deltaic Lagoonal 



New England Narragansett Bay (RI) Barnstable Marsh (MA) 



Atlantic Charleston area (SC) Sapelo Island (GA) 



James River/Chesapeake Bay 



Gulf Coast Apalachicola Bay (FL) Fort Walton Beach (FL) 



Mississippi River (LA) Galveston Bay (TX) 



Pacific 



Temperate Yaquina (OR) Coos Bay (OR) 



Dry Mediterranean Santa Ynez River (CA) Cabrillo NM (CA) 



Tropical-Subtropical Florida Bay 



94 



