Waves longshore drift

Bay-head beaches are one of the commonest types of coastal deposits, and they tend to straighten a coastline. Wave refraction causes longshore drift to move from headlands to bays where sediments are deposited. Marine deposition also helps straighten coastlines by building beach plains. 

Littoral (or Longshore) Drift/Transportation Movement of material or sediment (usually sand or shingle) along the coastline, caused by waves and currents. 

Littoral transport the movement of littoral drift in the littoral zone by waves and currents including movement parallel (longshore transport) and perpendicular (on/offshore transport) to the shore. 

When waves move parallel to the coast, they simply move sand and shingle up and down the beach. On the other hand, when they approach the coast at an angle, material is moved up the beach by the swash in the direction normal to that of wave approach, and it is then roiied down the steepest slope of the beach by the backwash. Consequently, material is moved in a zigzag path along the beach. This is known as longshore or littoral drift. Such action can... 

For wave-dominated and mixed-dominance inlets, the semi-circular ebb-tidal shoal can be subdivided as depicted in Fig. 31.8 into the ebb shoal proper, bypassing bars to each side of the ebb shoal proper, and attachment bars connecting the bypassing bars to the shore. The ebb shoal was subdivided because the location and size of the ebb shoal proper is related primarily to the tidal jet. In contrast, the bypassing bars and attachment bars are controlled by sediment transport produced primarily by breaking waves. For Shinnecock Inlet (Fig. 31.1), the strong predominant direction of longshore transport to the west pushes the up-drift attachment bar toward the beach that is fully impounded directly adjacent to the east jetty. The down-drift attachment bar is located about 1 km to the west of the inlet. 

Once an ebb shoal develops, if it is not translated too far offshore by the ebb jet it provides an efficient pathway for sand to bypass around the inlet during times of larger waves that can break on the shoal. Therefore, the volume of an ebb shoal will approach an equilibrium value, after which the sediment transported to the ebb shoal by the wave-and wind-induced longshore current will be bypassed to the down-drift beach or transported to the channel and then to the flood shoal. It was proposed several times, but to the author s knowledge never executed, to artificially build an ebb shoal at the location of a newly cut inlet so as to more quickly reestablish natural sand bypassing. 

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