33. Much of the material transported by inlet-associated tidal currents 

 is derived from erosion of updrift coastal areas and is carried to the inlet 

 by littoral drift processes. Inlet shoals are thus a sediment sink and inlets 

 often contribute to sand starvation and consequent erosion of downdrift 

 beaches. Where sand starvation of a downdrift project beach is the major 

 problem, the remedial action may be a sand bypass operation that transfers 

 sand across the inlet rather than a conventional beach fill operation. 



34. Because sand accumulated in inlet shoals usually comes from updrift 

 beaches it is often of a character suitable for beach fill. However, dredging 

 of inlet shoals may affect the hydrodynamic conditions of the inlet complex 

 and altered bathymetry of ebb tidal shoals may cause changes in waves and 

 wave -generated currents that adversely affect nearby shore areas. Dredging of 

 shoals at active inlets requires detailed study of the possible indirect 

 effects on nearby areas. 



35. Relict tidal shoals that are no longer active because of inlet clo- 

 sure or migration may be more practical as borrow sources than active shoals; 

 however, ebb tidal shoals may be eroded and removed when the tidal currents 

 that maintained them no longer exist. Relict flood tidal shoals create fewer 

 problems, and their situation near the shore and in the lee of the barrier 

 make them economically and operationally attractive borrow sources. However, 

 back-barrier areas including the flood tidal complexes are important elements 

 in the ecology of many coastal and migratory organisms and are sensitive to 

 disturbance of natural conditions. As a result, use of relict tidal shoals 

 creates undesirable environmental effects. 



Linear Shoals 



36. Linear shoals are elongated, ridgelike features occurring on the 

 continental shelf (Figure 3) . They are prominent and abundant in the mid- 

 Atlantic region of the United States (Swift, Duane , and McKinney 1973) and 

 occur in lesser numbers on the south Atlantic coast and parts of the Gulf 

 coast. Similar features have been observed in South American and European 

 waters (Swift et al . 1978). Linear shoals may be tens of kilometers long, 

 more than a kilometer wide, and have a relief of up to 10 m. On the Atlantic 

 shelf, most linear shoals are oriented with the long axis in a N-S to NE-SW 

 direction (Duane et al . 1972). 



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