to the north and, to some extent, by Long Island and the shoals south of Cape 

 Cod. However, the waves generated by northeast winds are the dominant cause of 

 changes on the beach (U.S. Army Engineer District, Philadelphia, 1966). 



There are three scales of bathymetry affecting the wave climate of Ludlam 

 Beach: a relatively flat continental shelf, an offshore shoal area where the 

 Inner Continental Shelf rises to meet the beach, and an inner shoal area vis- 

 isble on aerial photos at low tide. Based on analyses of data from an Atlantic 

 City wave gage 20 miles to the north, a typical wave in this region has a 

 period of 8 seconds. This means that the 30-fathom contour is the approximate 

 limit where such a wave begins to be modified by the bottom (from linear wave 

 theory) . The nearest point of the 30-fathom contour to Ludlam Beach is 60 

 miles offshore, and for most of that 60 miles, the bottom slopes upward to the 

 shore at less than 2 feet per mile (Everts, 1978) . 



Within a few miles of the shore, there is a prominent ridge trending N. 50° 

 E.; i.e., a 20° angle with the trend of Ludlam Beach with the angle opening to 

 the north. This ridge appears to be what was called a linear shoal in Duane, 

 et al . (1972). The landward continuation of the ridge intersects the southern 

 part of Ludlam Beach (Fig. 3) . The ridge is well marked by the -30-foot contour. 



Submarine bars are visible on many aerial photos of the littoral zone along 

 the island (see Fig. 2). These bars make a slight angle with the shore, but the 

 angle usually opens to the south rather than to the north as does the submarine 

 ridge marked by the -30-foot contour. A more detailed discussion of these bars 

 is given later in this report. The same aerial photos show large sand deposits 

 off the mouths of Corson and Townsend Inlets. These deposits affect the bottom 

 out to about the -18-foot contour on hydrographic charts (Fig. 3). 



Bottom features are important in their effect on wave height and direction. 

 Computations suggest that bottom dissipation due to wave travel over the Con- 

 tinental Shelf off Ludlam Beach will have little effect on most waves outside 

 a 7-mile radius of the shore. However, bottom dissipation within these last 

 7 miles can be very large, especially for high storm waves which could lose 

 50 percent or more in height, according to the predictions of Bretschneider 

 and Reid (1953) . 



3. Beach Sediment . 



Ludlam Beach is composed of fine sand, although outcrops of consolidated 

 peat are usually exposed at low tide within profile lines 4 to 9 and occasion- 

 ally after storms in profile lines 16, 17, and 18 (Fig. 5). The outcrops are 

 generally 1- to 2-feet-thick planar horizontal beds lying at about MSL elevation. 

 At profile lines 4, 5, and 6, the peat, often containing small stumps, is ex- 

 posed during much of the fall-winter-spring periods of low sand volume on the 

 beach. 



Sand samples were collected at profile lines 4, 10, and 17 from the backshore 

 to slightly below MSL. An analysis of 102 samples collected from January 1968 to 

 March 1969 indicated an average median diameter of 0.23 millimeter (Ramsey and 

 Galvin, 1977). The coarsest sand (0.25 millimeter) was found between midtide and 

 mean low water (MLW) elevations; the finest sand (0.20 millimeter) was obtained 

 on the berm. Samples collected in October, before the fall storms had cut back 

 the beach, averaged 0.19 millimeter in median diameter across the profile. Jan- 

 uary samples averaged 0.26 millimeter. 



Ludlam Beach sand is composed of approximately 95-percent well-rounded 

 quartz (McMaster, 1954). The remainder of the beach sediment is feldspar, 



t8 



