Accretion

Accretion is the net build-up of sediment on a shoreline, producing seaward growth of the beach or coast called progradation. It happens where the longshore and cross-shore sediment supply exceeds removal, so sand and shingle accumulate on the foreshore, the berm, and offshore bars. Beaches accrete during long swell-dominated periods that move bars onshore and rebuild the berm, then erode in storms. Net accretion appears in repeated beach-profile surveys as a rising, widening profile and an advancing shoreline position. It is the opposite of coastal erosion and is measured against a fixed datum in a sediment budget.