erosion. There was a net gain in sand volume over each of the inlet reaches 

 during these storm periods. 



High water levels and wind-generated waves combine to cause beach 

 erosion. Holden Beach, exposed southward and partially protected from the 

 southeast by Frying Pan Shoals, is not affected by northeast storms as much 

 as the other parts of the coast exposed eastward. However, high water 

 levels and strong winds from the southwest-to-southeast direction can be 

 expected to cause erosion. 



Ten erosion or accretion events were selected from 14 events iden- 

 tified (6 erosion and 8 accretion) for close study in an attempt to dis- 

 tinguish the conditions which cause erosion from those associated with 

 accretion. The criterion for selection was that the standard deviation of 

 the volume change along the central reach was less than the mean during that 

 interval. Two of each event occurred during identified storm periods 

 (Table 7, footnote 3). The events are presented in order of the greatest 

 net volume loss and gain. 



(a) 30 September-3 December 19 74 . The most severe erosion event 

 of the entire study period was recorded during the last survey of the pro- 

 gram. A sand loss was recorded at all profile lines except for profile 



line 3, with a maximum loss at profile line 2 (-42.7 cubic meters per meter). 

 Maximum and minimum losses in the central reach were -21.42 and -8.03 cubic 

 meters per meter calculated at profile lines 14 and 4, respectively. The 

 wind record during the interval (Fig. 18) showed no unusual events to 

 account for such a change, and no visual wave observations or sea level 

 data were available to document conditions during the interval. 



(b) 14 January-8 February 19 71 . Wind conditions and relative 

 water levels recorded at Wilmington are shown in Figure 19; visual wave 

 observations are given in Table 8. This interval had strong winds occur 

 about 27 January offshore with a strong longshore component to the east. 

 The highest water level during the interval occurred just before this date. 

 No unusual conditions were indicated in wave observations, which were avail- 

 able for only about 30 percent of the time early in the interval. Erosion 

 was general along the central reach with a maximum and minimum of -17.83 

 and -5.46 cubic meters per meter at profile lines 7 and 8, respectively. 

 This observation at adjacent profile lines emphasizes the longshore vari- 

 ability in erosion. Observed conditions during this erosion period did 



not appear to be substantially different from those during periods of accre- 

 tion, which suggests that water level and wind conditions measured at 

 Wilmington are not well correlated with changes at Holden Beach. 



(c) 29 September-11 December 1972 . No storms or particular events 

 during this interval appeared solely responsible for the erosion (Fig. 20) . 

 However, several wind events were persistent for several days, and these 

 can be visually correlated with higher water levels. Onshore winds occurred 

 19-22 November and again 25-28 November; such winds may pile water against 

 the coast to produce high water levels and generate local waves which cause 

 erosion. Erosion during this interval resulted in a sand loss ranging 



from -14.2 to -1.8 cubic meters per meter at profile lines 9 and 5, respec- 

 tively. During the same interval, both inlet reaches experienced a net 

 gain in sand volume. 



40 



