level). Dikes or bulkheads would be constructed under certain protection scenarios at that 

 elevation on the date in question to prevent further inundation. 



Because the results are fairly detailed for the five separate subareas and four protection 

 scenarios within the Charleston case study area, we have only listed the overall changes in Tables 

 2-5 and 2-6 (complete protection and no protection, see p. 50). Results by subarea for all four 

 protection scenarios, given in Appendix 2-B, illustrate the variability of land, water, and wetland 

 acreage from one subarea to another. For example, the peninsula currently has a much lower 

 percentage of low marsh than all other areas. Tidal flat distribution was also variable, ranging 

 from 3.2 percent of the Mt. Pleasant zone to 8.6 percent of the Sullivans Island zone. The 

 summary percentages given in Table 2-6 are appropriately weighted for the five subareas within 

 the study area. 



Table 2-5 lists the number of acres for each elevation zone in 1980 (existing) and for the 

 baseline, low, and high scenarios with and without structural protection by the year 2075. The 

 percentage of the total study area that a habitat covers is given in parentheses in Table 2-5 and 

 graphically presented in Figure 2-6, below. Table 2-5 indicates losses under all scenarios with no 

 protection for the four upper habitats and gains in area for tidal flats and water areas. For 

 example, without protection, highland would decrease from 46.6 percent of the total area in 1980 

 to 41.7 percent in 2075 under the high scenario. This represents a loss of over 2,200 acres or 10 

 percent of the present highland area. Land that is now terrestrial would be transformed into 

 transition-zone or high-marsh habitats a century from now. Under the 2075 high scenario with 

 no protection, high and low marsh, combined, would decrease from 7,700 acres to 1,535 

 acres— a reduction of almost 80 percent. While highland and marsh areas would decrease under 

 the no-protection scenarios, water areas would increase dramatically— from 27.4 percent to as 

 much as 48.7 percent— under the high scenario of 2075. 



FIGURE 2-6 



SHIFT IN WETLANDS ZONATION ALONG A SHORELINE PROFILE 



< 



o 

 in 



Highland 

 2075 

 46% 



Water 

 2075 

 33% 



2075 MSL 



LOW SCENARIO 



Conceptual model of the shift in wetlands zonation along a shoreline profile if sea level rise 

 exceeds sedimentation by 40 cm. In general, the response will be a landward shift and altered 

 areal distribution of each habitat because of variable slopes at each elevation interval. 



With structural protection implemented at different times for each community (see Table 

 24), highland areas would be maintained at a constant acreage, but transition and high-marsh 

 habitats would be completely eliminated by 2075 under the high scenario (because of the lack of 

 area to accommodate a landward shift). Total marsh acreage would decrease from 7,700 acres to 

 3,925 acres (2075 low scenario), or 750 acres (2075 high scenario), under the assumed 

 mitigation in Table 24. 



49 



