alongshore

Alongshore is a directional term used in geography and coastal science to describe a direction parallel to, or extending along, the coastline. It contrasts with cross-shore or offshore directions, which run perpendicular to the shore. The term applies to physical processes, measurements, and features that run along the coast.

In coastal hydrodynamics, alongshore describes currents, sediment transport, and wave-driven processes that move parallel to the shoreline. When waves break at an angle to the coast, they generate an alongshore or longshore current that transports sediments in a series of near-shore actions known as littoral drift or longshore transport.

Alongshore transport causes beaches to erode at some locations and accrete at others, reshaping shoreline profiles over time. Engineering structures such as groins, jetties, and breakwaters are designed to influence alongshore transport by interrupting or redirecting sediment flow, thereby affecting coastal erosion and deposition patterns.

In planning and mapping, alongshore coordinates are used to model shoreline evolution and to describe features that run parallel to the coast, such as sandbars, dune systems, and beach ridges aligned alongshore. The term provides a framework for describing processes and features without reference to the perpendicular cross-shore dimension.