Long shore drift is the process of deposition and transportation where sediment zig-zags along a coastline. This occurs when the prevailing wind hits the shoreline and an angle, or the waves are deflected. During the swash (waves moving up the beach), sediment is transported up the beach at the same angle as the waves' swash. This is then deposited. The back wash (water moving back into the sea) pulls sediment down the beach perpendicular to the coastline, due to gravity.
This process repeats, resulting in sediment being pushed at an angle up the beach and pulled down the beach perpendicular to the coastline. Resulting in the net movement of sediment along the coast. This results in the build up of sediment up the coastline.