TABLE 2-4 



SHORE-PROTECTION SCENARIOS 



Area 



Without Anticipating 

 Sea Level Rise 



With Anticipating 

 Sea Level Rise 



Note: In West Ashley/James Island, less protection is necessary if sea level rise is anticipated, 

 because more of the low-lying areas are subject to an orderly abandonment. 

 Source: Gibbs 1984. (Note that Gibbs called our high scenario "medium. ") 



For our modeling, we used the composite habitat elevations we derived from the twelve 

 transects (see Figure 24). The cutoff elevation for highland around Charleston was assumed to 

 be an elevation of 200 cm (6.5 ft). In general, land above this elevation around Charleston is free 

 of yearly flooding and is dominated by terrestrial (freshwater) vegetation. Although terrestrial 

 vegetation occurs at lower elevations that are impounded between dikes or ridges, this 

 information is less relevant for sea level rise modeling. The zone of concern is the area bordering 

 tidal waterways, where slopes are assumed to rise continuously without intermediate depressions. 



The transition zone is defined as a salt-tolerant area between predominant, high-marsh 

 species and terrestrial vegetation. This area is above the limit of fortnightly (spring) tides but is 

 generally subject to flooding several times each year. If storm frequency remains constant, it is 

 reasonable to assume that storm tides will shift upward by the amount of sea level rise (Titus et al. 

 1984). However, most climatologists expect the greenhouse warming to alter storm patterns 

 significantly. Nevertheless, because no predictions are available, we assumed that storm patterns 

 will remain the same. 



High marsh is defined here by a narrow elevation range of 90 to 120 cm (3 to 4 ft), and low 

 marsh ranges from 45 to 90 cm (1.5 to 3.0 ft). This delineation follows the results of surveyed 

 transects and species zonation described earlier. The lower limit of the marsh was estimated from 

 the typical transition to mud flats. Sheltered tidal flats actually occur between mean low water 

 and mean high water but were found to be more common in Charleston in the elevation range of 

 046 cm (0-1.5 ft). This somewhat arbitrary division was also based on the contours available on 

 USGS maps, which enabled estimates of zone areas within the case study region. 



Scenario Results 



Based on the shore-protection alternatives for the five suburbs around Charleston, we 

 computed area distributions under the baseline, low, and high scenarios. Figure 2-5 illustrates 

 shore-protection scenarios and their effects on the wetland transect. Our basic assumption was 

 that the wetland habitats' advance toward land ends at 200 cm NGVD (185 cm above mean sea 



48 



