However, the following inferences are drawn from the figure: 



(a) Waves from the north are much more pronounced (averaging more 

 than 70 percent of all waves) on Ludlam Beach submarine bars than on 

 the beaches, suggesting a greater longshore transport on the bars for 

 a given expended wave energy . 



(b) Based on a dominance of waves approaching and breaking on the 

 beach or bars from the south, even when deepwater waves approach from 

 the north, a nodal point appears to be at the north end of the island. 

 At the nodal point, waves approaching from the south dominate north of 

 the point, and waves from the north dominate south of the point. This 

 is probably the result of refraction as waves pass over the ebb shoals 

 seaward of Corson Inlet. On Ludlam Beach in 1974, the nodal point 

 occurred about 1,500 feet south of Corson Inlet. 



(c) In the central and south parts of the island, the relative 

 percentage of each wave approach direction appears similar, and long- 

 shore transport rates do not vary greatly from place to place. 



(d) Most of the aerial photos were taken in the spring when sub- 

 marine bars are most abundant and pronoianced. This is the season when 

 the least amount of sand is in storage on the subaerial beach and the 

 offshore sand volume is the largest. Thus, sediment movement alongshore 

 on the bars rather than on the beach is probably most pronounced in late 

 spring and least in the fall. 



(e) Submarine bars are present about 40 percent of the time in the. 

 spring, and may be near-absent in the fall. Therefore, bar transport 

 in 1 year probably occurs an average 20 percent of the time. 



(f) The height of waves breaking on bars is probably larger than 

 the height of those breaking closer to shore. Also, the wave approach 

 angle, because of less refraction, is greater on the bars, suggesting a 

 greater longshore component of sediment transport on the bars. 



(g) The importance of longshore bar transport versus longshore beach 

 transport is in determining where the material is moving, especially 

 relative to coastal structures, such as groins, weir jetties, and weir 

 basins . 



(h) Submarine bars near inlets, especially on the south end of the 



New Jersey islands, flare seaward and join ebb tidal shoals at the 



inlets. This distance is considerably seaward of the usual position of 

 weir sections in jetties. 



3. Onshore and Offshore Sand Movement . 



Sand movement from the beach to the offshore region, or from offshore onto 

 the beach, involves storm, seasonal, and longer term exchanges of sand which may 

 affect coastal stability and structures. Each type of exchange is difficult to 

 predict analytically. Limited data on the amount and distance of sand movement 

 are available and are discussed below. 



79 



