beach fill is subject to uncertainties: the source of the dredged sand 

 often contains significant but variable quantities of finer materials that 

 are soon lost to the littoral zone; the surveys of both the borrow area 

 and the replenished area are subject to uncertainty because sediment trans- 

 port occurs during the dredging activities; and in practice only limited 

 efforts are made to obtain estimates of the size distribution of fill 

 placed on the beach. Thus, the resulting estimate of the quantity of 

 suitable fill placed on the beach is uncertain. More frequent sampling 

 and surveys could help identify this significant element in many sedi- 

 ment budgets. 



4.73 SINKS FOR LITTORAL MATERIALS 



4.731 Inlets and Lagoons . Barrier islands are interrupted locally by 

 inlets which may be kept open by tidal flow. A part of the sediment moved 

 alongshore by wave action is moved into these inlets by tidal flow. Once 

 inside the inlet, the sediment may deposit where it cannot be moved sea- 

 ward by the ebb flow. (Brown, 1928.) The middleground shoals common to 

 many inlets are such depositional features. Such deposition may be reduced 

 when the ebb currents are stronger than the flood currents. (Johnson, 

 1956.) 



It is evident from aerial photography (e.g., of Drum Inlet, N.C., 

 Fig. 4-45) that inlets do trap significant quantities of sand. Caldwell's 

 (1966) estimate of the sand budget for New Jersey, calculates that 23 

 percent of the local gross longshore transport is trapped by the seven 

 inlets in southern New Jersey, or about 250,000 cubic yards per year for 

 each inlet. In a study of the south shore of Long Island, McCormick (1971) 

 estimated from the growth of the f loodtide delta of Shinnecock Inlet (shown 

 by aerial photos taken in 1955 and 1969) that this inlet trapped 60,000 

 cubic yards per year. This amounts to about 20 percent of the net long- 

 shore transport (Taney, 1961a, p. 46), and probably less than 10 percent 

 of the gross transport. (Shinnecock Inlet is a relatively small inlet.) 

 It appears that the rate at which an inlet traps sediment is higher imme- 

 diately after the inlet opens than it is later in its history. 



4.732 Overwash . On low barrier islands, sand may be removed from the 

 beach and dune area by overwashing during storms. Such rates may average 

 locally up to 1 cubic yard per year per foot. Data presented by Pierce 

 (1969) suggest that for over half of the shoreline between Cape Hatteras 

 and Cape Lookout, North Carolina, the short term loss due to overwash was 

 0.6 cubic yard per year per foot of beach front. Figure 4-46 is an aerial 

 view of overwash in the region studied by Pierce (1969). Overwash does 

 not occur on all barrier islands, but if it does, it may function as a 

 source for the beach on the lagoon side. 



4.733 Backshore and Dune Storage . Sand can be temporarily withdrawn 

 from transport in the littoral zone as backshore deposits and dune areas 

 along the shore. Depending on the frequency of severe storms, such sand 

 may remain in storage for intervals ranging from months to years. Back- 

 shore deposition can occur in hours or days by the action of waves after 



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