alternated with periods of shoreline retreat, and volume maximums alternated 

 with volume minimums . Adjacent lines showed cyclicity with a slight phase 

 change, resulting in what appeared to be the north to south movement of a sand 

 wave. Movement to the south was directly related to the direction anticipated 

 using wave data (Fig. 63). The migration rate of the sand wave averaged 5 feet 

 per day to the south. The time interval from a year of maximum loss (dash line. 

 Fig. 41) to the next maximum yearly loss at the same location was 10 or 11 years 

 near the center of Ludlam Beach. Since only one sequence was monitored it is 

 unknown whether this was a constant period, whether it varied, or whether the 

 sand waves were intermittent features produced by unique events . 



Between locations of maximum yearly loss the alongshore distance between 

 wave crests was 16,500 feet when the midpoint was 10,000 feet south of Corson 

 Inlet, and 13,000 feet when midpoint was centered 18,000 feet south of the inlet. 

 The apparent decrease in wavelength may have been caused by either a slowing 

 of the travel rate of a trough or by an acceleration of the sand-wave crest 

 movement. It may also have been due, in part, to a steady loss of volume as 

 the sand wave progressed south. The average wavelength is about 16,000 feet, 

 about one-half the length of Ludlam Beach. The wavelength apparently decreased 

 about 2.5 percent per 1,000 feet as the sand wave moved in a southerly direction. 



At Corson Inlet the volume difference of the sand wave, from minimum to 

 maximum, was 46 cubic yards per foot, which decreased to an average of 15 cubic 

 yards per foot at profile line 3. From profile line 3 south to the Sea Isle 

 City groins the amplitude remained constant. Farther south the amplitude 

 appeared to be affected by the groins. The total volume under the sand wave, 

 assuming a wavelength of 16,000 feet and a maximum volume of 15 cubic yards per 

 foot, was 240,000 cubic yards above MSL. Assuming the sand wave moves south- 

 ward, and that beach sand moves the same rate as the sand wave, the volume in 

 the sand wave moving alongshore would be as shown in Figure 64. A rapid de- 

 crease in volume occurred away from Corson Inlet then slowly declined to the 

 north of the Sea Isle City groin field where the volume increased 25 percent. 

 Because the coastal orientation changes rapidly near Corson Inlet, some of the 

 loss between profile lines 1 and 2 possibly resulted in permanent losses to 

 the offshore zone. 



This study produced no results to substantiate the assumption that beach 

 sand moves alongshore at the same rate that the sand wave moves. However, if 

 the alongshore movement of the sand wave represented an alongshore movement of 

 sand above MSL, the average net alongshore sand transport rate near the center 

 of the island would be about 40,000 cubic yards per year. In a study similar to 

 the present study. Everts, DeWall, and Czerniak (1974) found the volume of a 

 sand wave moving above MSL along the northern one-half of Absecon Island, about 

 30 miles north of Ludlam Beach, was 30,000 to 34,000 cubic yards per year in 

 1964-65. 



An important problem in predicting this type of sand wave is determining 

 its cause. One possible cause at initiation near Corson Inlet was a large non- 

 cyclic input of sediment to the north end of the beach. Such a catastrophic 

 input could result from sediment movement during a severe storm. Bruun (1966) , 

 for example, noted that the channel at Matanzas Inlet, Florida, moves slowly 

 from north to south in the direction of predominantly littoral drift. When it 

 is in an extreme southern position and a severe northeast storm occurs, the 

 channel breaks through the ebb shoal on the north side of the inlet, the south 



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