Littoraldrift

Littoral drift, also known as longshore drift or littoral transport, is the coastal sediment transport process driven by longshore currents produced as waves break at an angle to the shoreline. It moves materials such as sand and gravel along the coast in a zigzag pattern, following the path of the longshore current within the surf zone.

Mechanism: When waves arrive obliquely, the swash moves material up the beach at that angle, while the backwash returns perpendicular to the shore. The combination creates a current that runs parallel to the coast, carrying sediment along the shore. Sediment transport occurs through bedload movements, saltation of grains, and suspended load; larger particles tend to move mainly by rolling or sliding, while finer grains may be carried in suspension.

Direction and rate of drift depend on the angle and strength of the incident waves, their period, the coastline’s orientation, beach slope, sediment size, and seabed conditions. The coastline is often described as a series of littoral cells—drainage areas where sediment moves within defined boundaries set by headlands and other obstructions. Drift rates vary widely, from a few meters per year to tens of meters per year, and can be amplified during storms or seasonal wave changes.

Human activity and management: Structures such as groins, jetties, and seawalls can interrupt or redirect littoral drift, causing erosion on one side and accretion on the other. Coastal nourishment, dredging, and quarrying of borrow material alter the sediment budget. Climate change and rising sea level also influence drift patterns and shoreline response.

See also: longshore drift, littoral zone, coastal engineering.