Uprush and Backwash
Swash consists of two phases: uprush (onshore flow) and backwash (offshore flow). Generally uprush velocities are greater but of shorter duration compared to the backwash. Onshore velocities are at greatest at the start of the uprush and then decrease, whereas offshore velocities increase towards the end of the backwash. The direction of the uprush varies with the prevailing wind, whereas the backwash is always perpendicular to the coastline. This asymmetrical motion of swash can cause longshore drift as well as cross-shore sediment transport.