16 -percent probability of some type of tropical storm striking the South 

 Carolina-Georgia border area in any one year and a 7-percent chance that it 

 will be a hurricane. The probability decreases northward to 8 percent for a 

 tropical storm, with a 5- to 8 -percent chance of a hurricane. The region 

 around the North Carolina- South Carolina border increases again to 13 -percent 

 probability for a tropical storm in any one year and a 6 -percent chance of it 

 being a hurricane. Table 1 is a listing of known major storms affecting the 

 coast of South Carolina. Figure 7 shows tracks of late 19th-century and 

 20th-century hurricanes affecting the study area. 



15. Increased tidal elevation along the coast during both tropical and 

 extratropical storms results from surge that accompanies the storm. Storm 

 surge is due to a combination of low pressure over water allowing the water to 

 bulge upward under the storm and rapid wave advance inshore resulting in wave 

 buildup at the shoreline and limited return flow offshore. Increased water 

 levels of 0.3 to 1 m above MSL can be expected along this coast, and records 

 up to 5.8 m above MSL have been reported for major hurricanes (USACE 1974). 

 Myers (1975) used data from South Carolina hurricanes to determine return 

 intervals of total tidal height (astronomical tide height plus storm surge) at 

 selected locations along the South Carolina coast (Figure 8) . Along coast 

 variation in total tidal height from hurricanes of various return intervals is 

 plotted in Figure 9. These data indicate that a tropical storm with a 10-year 

 return interval could be expected to produce a tide 2.1m above MSL at 

 Charleston and a storm with a 500-year return interval (probability of occur- 

 rence is once in 500 years) would produce a tide 5.3m above MSL at 

 Charleston. 



16. Alongshore variation in tidal height for any given return period 

 (Figure 9) was explained by Myers (1975) as being due in part to a shoaling 

 factor, which is a function of inner continental shelf bathymetry. In gen- 

 eral, shallower water produces higher surge. Other factors that influence 

 maximum surge height are strength of the storm, forward speed, radius of the 

 maximum winds, and track of the storm with its distance from the coast. Surge 

 dynamics vary from alongshore moving storms to inshore moving storms. 

 Long-term sea- level variations 



17. Daily and seasonal water-level fluctuations play an important role 

 in South Carolina coastal geomorphology, but in their examination of long-term 

 trends in shoreline change, the WES researchers must also consider long-term 



19 



