both of which show large increases in MSL distance. There is no obvious 

 reason for these radical departures from the long-term mean. 



The year 1971 shows a general landward migration of the mean, MSL 

 intercept with increases only at profile lines 8 and 18. During 19 72, the 

 mean MSL was more variable, with recession along the eastern half of the 

 island (profile line 9 excepted) and both gains and losses on the western 

 half. The annual mean during 1973 was very near the long-term mean while 

 19 74 shows a marked increase in the MSL shoreline at almost all profile 

 lines. 



b. Seasonal Changes . Beaches on the west coast undergo seasonal cycles 

 in response to changing wave and storm conditions with profile shapes char- 

 acteristic of the summer and winter season. Studies of beach shape have 

 shown that the "winter profile" has almost no berm since steep waves shift 

 the sand offshore to form a series of sandbars parallel to shore. The 

 "summer profile" is characterized by a wide berm and by a smooth offshore 

 profile with no bars except, possibly, in deep water. These seasonal pro- 

 file shapes are more characteristic of storm and recovery cycles on east 

 coast beaches (Komar, 1976). The length of the Holden Beach profile lines 

 is not sufficient to show offshore sandbars. Seasonal cycles in MSL inter- 

 cept and above MSL sand volume have been shown on east coast beaches CGoldsmith, 

 Farrell, and Goldsmith, 1974; Everts and Czerniak, 1977; DeWall, Pritchett, and 

 Galvin, 1977; DeWall, 1979; Everts, DeWall, and Czerniak, 1980). 



The seasonal cycle is evident in the above MSL sand volume change 

 averaged across the central reach (Fig. 16) . The amount of erosion or 

 accretion for each year was obtained by summing the volume change for the 

 dates and years indicated and averaging these seasonal values for profile 

 lines 4 through 18. This analysis shows that sand is removed from the 

 beach, either toward the inlets or to below MSL, during the autumn and win- 

 ter and replaced during spring and summer. The direction and degree of 

 motion, whether longshore or onshore-offshore, were not determined from 

 these data. 



EROSION 

 1 1 1 





ACCRETION 

 1 1 1 





140. C 

 11 Oec 



- 20 Mar 1972 

 ■ 15 Mor.1973 

 - 4 M or 1974 



1 



1 





1 



Sprin, 9Ma,. • 7 J,.n.l97l 

 20 Mot." 9 Jun»l972 



1 



1 



15 Mar -14 Jun.1973 C 





IMat.- 30Mo»l974 



Summ»r 7 Juno - 31 Aug 1971 

 9 Jan. - 29 S.pt, 1972 

 14 Jun« - 9 Ocl. 1973 

 30 May " 30 Sipl.1974 



1 



1 



1 



1 



1 

 31 4u 



g.- 14 0«C. 1971 4ulumr 

 • pi.- II Dec. 1972 

 1.- 5 b«c 1973 . 

 tpl- 3 O.c 1974 



1 



1 





1 8 



1 



30 S 





MSL UNIT VOLUME CHANGE ImVm) 



Figure 16. Seasonal changes in above MSL volume 

 averaged over the central reach. 



36 



