Coastal transportation and deposition

Longshore drift

Particles of sand are moved along a coastline by the sea water. The waves are driven by the most common wind direction, which is South West in the UK. This movement is called longshore drift.

Longshore drift Longshore drift

  • A pebble or sand particle moves from point A to B, carried by the swash up the beach, the angle determined by the wave and wind direction.
  • It is then pulled down the beach from B to C, carried by gravity and the wave's backwash.
  • This process is repeated over and over again and the particle moves along the shoreline, this process is called longshore drift.

Features of coastal deposition

Spits

There are different depositional features produced by longshore drift including beaches.

Look at the graphic below to see how a sand spit is formed.

Formation of a sand spitFormation of a sand spit

  • Spits form where the coastline changes direction and longshore drift continues to move material along the beach.
  • Longshore drift will deposit material in the sea after the coastline has changed direction.
  • Over time the level of the sand deposited will build-up until it is above sea level.
  • The spit cannot develop right across the bay as the moving water from a river prevents the build-up of sand.
  • Sand spits often have a curved or hooked end. This is created when secondary wind and wave direction causes a wave to strike from a different direction.
  • The beach appears to extend out into the sea and is known as a spit or sandspit.

The formation of spits