a. Wave Effects . The most important factor in developing the geometry 

 of a beach, and in the sand movement from or onto the beach, is the waves 

 which act upon it. At Ludlam Beach there appears to be a direct temporal 

 relationship between the relative volume of sand above MSL and the frequency 

 of waves greater than 4 feet in height (see Fig. 16) . Waves exceeding 4 feet 

 at the Atlantic City gage were often associated with storms. The steepness 

 (wave height/wavelength at the gage) of a 4-foot wave with an 8-second period 

 is 0.022. This steepness value is assumed to designate the cutoff point between 

 waves causing erosion and those causing accretion. However, caution is recom- 

 mended when using this value. Saville and Watts (1969) for example, pointed 

 out although bounding wave steepness values between 0.020 and 0.025 are commonly 

 used, these values are derived mostly from laboratory studies and are of doubt- 

 ful accuracy when applied to a field situation. 



Monthly changes in sand volume are directly related to the monthly wave 

 power reaching the beach, as shown in Figure 65. Beach volume changes are from 

 Figure 33. Five years of wave data (1962-67) and 10 years of survey data 

 (1962-72) were averaged to obtain Figure 65. The figure supports the assumption 

 that waves with an 11 -second period and less than 4 feet high cause beach accre- 

 tion. For the North Sea coast, Schijf (1959) observed a relationship between 

 winter gales and summer swell, and their effect on beaches, which was similar 

 to the accretion-erosion changes observed at Ludlam Beach. 



1-5 



Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec. 

 (Mo) 



Figure 65. Monthly wave power of waves exceeding 4 feet 

 in height reaching the Atlantic City shore, 

 showing the relationship between wave power 

 and beach volume change. 



80 



