date (1982/83). Large spatial variability is evident during all three peri- 

 ods. The magnitude of erosion and accretion appears lowest along Hilton Head 

 Island. In all three periods, large average shoreline movement rates appear 

 to occur most often in the vicinity of inlets. 



79. It is important to note that some localities, such as Pritchards 

 Island, alternate between erosion, accretion, and erosion during the three 

 time intervals represented. This points out that often erosion/accretion pro- 

 cesses are not steady, but rather fluctuate with changes in environmental 

 parameters. Magnitude of erosion and accretion appears to increase from the 

 earliest to last period; however, this is probably due to a decrease in number 

 of years over which data were averaged. Over shorter periods, extreme events 

 have a greater influence on average shoreline movement rates. Aerial distri- 

 bution of accretion also seems to increase slightly toward the most recent 

 period, which may also be an artifact of decreasing length of time between 

 survey dates. These data illustrate increased variability in the shoreline 

 change rates over increasingly smaller intervals of time and underline the 

 need for temporally large data sets when using historical shorelines to 

 predict future shorelines. 



80. Shoreline changes over the entire temporal range of data from each 

 digitized transect were categorized into one of three modes: erosional (erod- 

 ing more than 1 m/year) , stable (less than or equal to 1 m/year of change) , 

 and accretional (accreting more than 1 m/year) . Results were summed for each 

 coastal reach and presented as pie graphs. The summary for coastal reach 1 

 (Figure 26) shows the majority of shoreline is erosional (54.9 percent) or 

 stable (30.5 percent). Only a very small proportion (14.6 percent) of tran- 

 sects measured showed long-term accretion rates in excess of 1 m/year. 

 Coastal reach 2 



81. Average shoreline movement within coastal reach 2 (St. Helena Sound 

 to Charleston Harbor) is similar in character to reach 1. The range is from 



7 m/year accretion to 12 m/year of erosion over the period of record (Fig- 

 ure 27). The northern end of this reach, which lies immediately downdrift of 

 the Charleston Harbor jetties, is strongly erosional. This zone of strong 

 erosion includes all of Morris Island and most of Folly Island. The north end 

 of Kiawah Island is strongly accretional, changing to erosional toward its 

 south end and back to strongly accretional on Seabrook Island. Almost the 

 entire length of Edisto Island is strongly erosional, except for some 



63 



