crossshore

Cross-shore is a term used in coastal geography, geomorphology, and engineering to describe processes and sediment transport that occur in the shore-normal direction, perpendicular to the coastline. It contrasts with longshore processes, which occur parallel to the shore along the coastline. Cross-shore dynamics control how beaches gain or lose material and how the shoreline migrates landward or seaward.

Cross-shore transport is driven by waves, tides, and wind-driven circulation. As waves break and run up the beach, swash moves sediment upslope; backwash pulls material seaward. The balance between onshore and offshore movement, along with the beach gradient and presence of sand bars or dunes, determines net cross-shore sediment exchange. Storms often intensify cross-shore transport, causing shoreline retreat or rapid beach accretion in narrows or during replenishment, while calmer conditions can lead to gradual vertical and horizontal beach profile changes.

Factors influencing cross-shore processes include wave height, period and angle of incidence, tidal range, beach slope, grain size, and coastal structures. Cross-shore dynamics are typically studied through beach profile surveys, shoreline position tracking, and numerical models that simulate runup, inundation, and sediment exchange, such as XBeach and Delft3D.

Applications and implications include coastal protection planning, beach nourishment design, dune rehabilitation, and erosion risk assessment. Understanding cross-shore processes helps predict shoreline response to storms and climate-driven sea-level rise, guiding management strategies that balance erosion control with sediment sustainability.