backswash

Backswash refers to the backward movement of water following the breaking of a wave on a shore or beach. It is the part of the wave action that flows back down the beach slope after the main uprush, or swash, has reached its highest point. This backward flow is a crucial component of the sediment transport process along coastlines.

The strength and volume of the backswash are influenced by several factors, including the steepness of the beach, the size and energy of the incoming waves, and the permeability of the beach material. On steep beaches, water tends to run back more quickly and with greater force due to gravity. On gentler slopes, the backswash may be slower and more diffuse.

The interaction between the swash and backswash is a primary mechanism for moving sand and pebbles. The forward swash carries sediment up the beach, and as the backswash retreats, it carries some of that sediment back down towards the sea. The net effect of these movements over time determines whether a beach accumulates or erodes material. Understanding backswash is therefore important for coastal geomorphology, coastal engineering, and the study of beach dynamics.