Figure 45 illustrates the maximum horizontal excursion of contours at and 

 above MSL, in both seaward and landward directions, which occurred over the 

 10-year study period. The tick marks show the MSL shoreline intercept at the 

 first survey. The horizontal excursion of the beach below 8 feet was nearly 

 twice as large at profile line 1 as it was elsewhere, except at profile line 

 20. The shape of the excursion curves was similar on most profile lines with 

 the maximum horizontal excursion of 200 to 300 feet at MSL. 



7. Overwash Deposition . 



Overwash, the movement of wave uprush and sediment past the normal extent 

 of the beach, often through a breach in the frontal dune, occurs only during 

 the most severe storms at Ludlam Beach. Overwash results from high water 

 caused by storm surge and high tides. The importance of overwash is that it 

 moves locally derived dune and beach sand landward. Sand moving alongshore 

 from other sources may also be moved landward. Deposits are thin and sheet- 

 like, sometimes extending completely across the island. Although overwash 

 can damage structures such as buildings and roads, the sand it deposits is 

 usually accessible for returning to the beach. Historical data on the fre- 

 quency of occurrence of storms producing significant overwash deposits in 

 southern New Jersey are not available. 



Only one large overwash event has occurred in the Ludlam Beach area since 

 1949. This resulted from the severe extratropical cyclone of 6 to 8 March 1962, 

 Five near-record tides were measured during its destructive 60-hour life. Sea 

 Isle City and the region north to Strathmere suffered near complete destruction 

 because of tidal flooding and overwash. 



The series of air photos obtained at low tide on 8 March were analyzed to 

 determine the areal extent of the overwash deposit (Fig. 46). Assuming a beach 

 width of 260 feet, and a dune width of 100 feet, i.e., where erosion, not depo- 

 sition occurred, the surface area of the overwash deposit on Ludlam Beach was 

 1,150,000 square yards. Further, assuming a deposit depth which averaged 1 

 foot, the total loss from the beach system and gain by the island was 385,000 

 cubic yards. Because the deposit depth is only a guess based on ground photos 

 taken before the sand was removed and because the amount of material deposited 

 in Ludlam Bay is unknown, the loss value could vary by 100 percent. The calcu- 

 lated overwash where it occurred was 14.7 cubic yards per foot. Since the 1962 

 storm was an extreme, the overwash values are also probably an extreme. Over- 

 wash values cannot be predicted so the yearly loss by overwash cannot be esti- 

 mated. 



8. Submarine Bars . 



Submarine bars along the southern New Jersey coast appear to be seasonal 

 features formed in the fall and winter as sand is removed from the subaerial 

 beaches. Subsequently, the bars reduce in volume as the sand moves landward 

 from the offshore region in the late spring and summer, thereby rebuilding 

 the beach. The most pronounced bar presence is probably late winter when the 

 beaches above MSL are most depleted. The least sand volume in bars is probably 

 in early fall when there is maximum sand volume on the beach. 



Beach surveys extended only -1 to -2 feet below MSL, not deep enough to 

 intercept the submarine bars. An analysis of the aerial photos was made to 



58 



