The prevailing direction of longshore drift in the following picture is
West to East
What is longshore drift?
Longshore drift is the movement of sediments (such as sand and pebbles) along the coastline. It is driven by the movement of waves hitting the shore at an angle.
The method depicted is likely: Swash and Backwash:
Here, as waves reach the shore, the swash (water rushing up the beach) carries sediment onto the beach. The backwash (water flowing back to the sea) then carries some of this sediment back down the beach.