washover

Washover is the process by which water from waves overtops a coastal dune or barrier beach, transporting sediment and debris from the foreshore to the landward side. It occurs during storms or high tides when surge and wave run-up exceed the crest height of dunes. The overtopping flow can entrain sand and other materials, depositing a layer on the backshore known as a washover deposit. Overwash may form washover fans and, in some cases, breach the dune to create a direct path between the sea and back-barrier environments.

Washover deposits vary in thickness and structure, from thin laminations to meter-scale sand bodies, and often contain shells, organic matter, and reworked dune grains. Their characteristics record past storm activity and sea-level changes in the stratigraphic record of coastal settings.

Factors influencing washover include dune height and geometry, beach gradient, water level, wind, tidal phase, and sediment supply. Increasing storm intensity and sea-level rise are expected to raise overwash frequency and the likelihood of dune breaching, accelerating barrier island evolution and altering back-barrier hydrology and habitats.

In coastal science and management, washover is a key process in barrier dynamics and hazard assessment. Understanding washover helps explain shoreline change, dune integrity, and ecosystem resilience in the face of climate-driven coastal change. Terminology varies; washover and overwash are sometimes used interchangeably, though some authors distinguish the overtopping process (washover) from its sedimentary products (washover deposits) and breaches.