only to the central reach, since bars and shoals develop near the inlets and 

 beach nourishment operations greatly complicate the wave and transport regime 

 along those reaches and invalidate the uniformity assumed along the central 

 part of the island. Regression analysis indicates that the MSL shoreline is 

 advancing seaward at slightly greater than 1 meter per year while the above 

 MSL volume is decreasing by nearly 0.5 cubic meter per meter per year. A 

 more thorough sand budget than can be developed from these data would be re- 

 quired to confirm whether the MSL position is growing at the expense of the 

 volume or by addition of sand from a source external from the island. If 

 the former is the case, however, the beach may be getting flatter, a condition 

 that has implications for coastal flooding. 



The changes in above MSL volume and in the MSL intercept for each survey 

 period are averaged by reach in Tables 4 and 5. The standard deviation about 

 the mean is also shown to identify periods when erosion or accretion was 

 ubiquitous. The averaging process eliminates the variability between adja- 

 cent profile lines which may be caused by measuring across a migrating coastal 

 feature such as a cijsp, rip channel, or sandbar. The presence of these can 

 be determined by spacing profile lines more closely than the length scale of 

 the feature itself. The changes in shoreline position and volume were deter- 

 mined on an annual basis by summing the changes for each year. The result is 

 the same as subtracting the shoreline position or volume from its value the 

 previous year. The beginning date of 14 December 19 70 and ending date of 

 3 December 1974 allowed computation of 4 complete years with comparable (within 

 several days) annual intervals. This method yields annual rates of change of 

 +0.15 meter per year and -4.81 cubic meters per meter per year for MSL inter- 

 cept and volume, respectively. The slope of the first temporal eigenf unction 

 (mean retained) provides another method of determining whether the measured 

 beach profile is gaining or losing volume (Aubrey, 1979) . There was no measure 

 able slope in this parameter for any of the profile lines along the central 

 reach indicating that the trend, if any, is not significant over the study 

 period. 



The annual spatial variation in the position of the MSL intercept is shown 

 relative to the 4-year mean MSL intercept for that profile line in Figure 

 15. The horizontal line represents the long-term (Nov. 19 70-Dec. 19 74) 

 mean position of the MSL intercept measured from the reference monument. 

 The circles are the annual mean, MSL position for each profile line for 

 the year indicated (Januaty to December) , and the vertical bar represents 

 one standard deviation in the annual fluctuation. The diagram is arranged 

 from the perspective of an observer at sea looking shoreward. Lockwoods 

 Folly Inlet and profile line 1 are, therefore, to the right. Increases 

 in distance to the MSL shoreline (over the long-term mean) are indicated 

 in the usual sense by the mark above the line. Only the central reach was 

 analyzed in this way because of the extreme variability of the inlet 

 reaches. The sum of the annual means does not exactly equal zero because 

 the long-term mean included profile line measurements taken in November 

 and December 1970. The horizontal line provides a useful reference to 

 compare the annual movement in MSL position. Profile line measurements 

 were evenly distributed during each of the years so no single year biased 

 the long-term mean. 



Most of the annual means fall within one standard deviation of the long- 

 term mean. The only exceptions are profile lines 13 (1972) and 4 (1974), 



32 



