Longshore drift is the movement of material along the shore by wave action. It happens when waves approach the beach at an angle. The swash (waves moving up the beach) carries material up and along the beach. The backwash carries material back down the beach at right angles. This is the result of gravity. This process slowly moves material along the beach and provides a link between erosion and deposition. Material in one place is eroded, transported then deposited elsewhere.