They are designed to trap sand that is moving along the shore due to the long shore current. A groin usually extends to the end of the surf zone while a jetty extends further into an inlet to stabilize a navigation channel. The construction of both groins and jetties severely affects the flow of sand moved by the long shore currents, depriving down stream beaches of the sand needed for replenishment. In order to maintain sufficient depth of water for shipping traffic to freely pass through the harbor, dredging must be done. Dredging removes sediments from the harbor floor and moves them to another location.
Waves lose energy when they come closer to shore, hit the ocean bottom and then reach the beach.
Currents move bodies of water from one location to another, like a river flowing within the ocean. An example of a current is the Gulf Stream which brings water from Florida, along the east coast of the United States, and then off the Cape Hatteras coast en route to Europe. Tides are the daily cyclic movement of water towards and away from the coast caused by gravitational forces exerted by the sun and moon. This includes factors such as rock type, geologic history, and topology of the area. These factors influence the rate of weathering and the effectiveness of erosional factors such as moving water and winds.