c. 1962-72 Changes . Shoreline position changes over this period were 

 obtained from the BEP beach profiles. The shoreline position with time is 

 plotted for each profile line in Appendix C; the cumulative rate of change at 

 a profile line is plotted in Figure 29. 



^ 



-690 — 



Accretion 



1 1 I I i_ 



^-30 -20-10 10 20 30 



Mean Shoreline Position Change (ft/yr) 



Figure 29. Yearly change in shoreline position on Ludlam Beach, obtained from 

 BEP survey data, 1962-72. Note influence of Sea Isle City groins. 



The rates of shoreline changes derived from 1962-72 beach profile surveys 

 (Fig. 29) are comparable to the rates of shoreline changes derived from 1949- 

 74 aerial photos (Fig. 28). As shown, the two sources of data yield similar 

 magnitudes, with the rates of shoreline change ranging between -30 to +20 feet 

 per year. Both data sources indicate erosion at the north and south indenta- 

 tions, but the 1962-72 profile data indicate less general erosion of the north 

 protrusion and accretion at the updrift end of the central protrusion (the Sea 

 Isle City groins) . The accretion is a result of the newer groins constructed 

 in 1967 (Fig. 6). The aerial photos, on the other hand, recorded changes over 

 a longer time interval when the groins were in poorer condition and were not 

 trapping sand as effectively. 



For the 1949-74 aerial photo interval, the yearly mean shoreline retreat 

 rate was 6.5 feet per year (Fig. 28) or 80 percent of the 1962-72 rate (8.2 

 feet per year). Sheridan, Dill, and Kraft (1974), using sediment core evidence, 

 concluded that the position of the Delaware barrier island complex, 50 miles to 

 the south, was 7.4 miles east of its present location 7,500 years ago. Thus, 



41 



