The material is first pulled into the currents by the backwash (the water going out to sea) and is then pushed back up the beach by the swash (the water going onto the beach). Longshore drift always moves in the direction of the main wind. If longshore drift continues for a long time, beaches can be changed quite a bit. The changes depend on the details, and vary from place to place. Longshore drift is the net (average) movement of sand grains across a beach in a zig-zag motion.