Beach drift (longshore sediment transport) results from the combined, repeated action of wave swash and backwash (wave motion, WM) and the alongshore-directed longshore current (LC): swash carries grains diagonally up the beach face in the direction of the obliquely approaching waves (wave motion dominant), backwash then returns grains more directly down the beach slope under gravity with a comparable contribution from the longshore current, and repeated cycles of this zig-zag motion produce a net alongshore transport path in which the longshore current's cumulative effect exceeds that of any single wave motion event.