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When waves approach shore and "feel the bottom", water piles up and breakers form. This process proves that a shoreline is not static. Primarily these waves, breaking at an angle to the shoreline, are what generate a long shore current that parallels the shore. The long shore current not only moves water in the surf zone, it also moves sediment parallel to the shoreline. Long shore current is a function of the angle of wave approach. For example, if the waves approach the shoreline from the south, long shore current moves from south to north (as shown in the figure below).
Long shore current in the surf zone moves parallel to shoreline. As shown here, the direction of the current can be determined by observing the direction of incoming waves.
Although, long shore current and the resulting transport of sediment is only one of the dynamic processes that constantly alter the shoreline. As waves repeatedly hit the shore, water moves onto the beach and then retreats in a continuous cycle. However, the waves are not all that moves on the shoreline. In fact, the sediment on the shore is also always on the move. Great energy is expended on the beach as waves crash against the shoreline. This energy allows the water to transport sediment. The grains are lifted as the waves in the swash zone move onto the beach, and then the grains are deposited again as the water retreats. As long as the waves hit the shoreline “straight on”, the wave crests are parallel to the shoreline, the sand grains will be picked up and redeposit in the same general area. In this case, no real net movement of sand occurs in the swash zone.
Waves generally do not form parallel to the shoreline, and thus, usually approach the shore at an angle. Consequently, beach sand will have a net movement up or down the beach, depending on the direction of incoming waves. Sand grains are transported as the waves move onto the beach. Therefore, the sand gr...
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