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Sediment is moved either up or down the beach by swash/backwash or along by long shore drift.
- Clastic sediment: Comes from weathering of rock and varies from very small clay particles to sand/pebbles/boulders.
- Biogenic sediment: Skeletons and sediments of marine organisms.
- Non-cohesive sediment: Larger particles (for example, sand) moved grain by grain.
- Cohesive sediment: Very small clay and mud particles that bond together.
Sources of sediment (load):
- Rivers entering the sea.
- Wave erosion.
- Mud, sand, shingle.
It has been found that the movement of sediment close to the coast around the UK occurs in 'cells'. The result is that the movement of sediment in one cell does not impact on beaches in another.
The process whereby material is moved along a stretch of coastline. Waves approach the shore at an angle (usually in line with prevailing wind direction) and swash moves material up the beach in this direction. Backwash pulls material straight down the beach.
The result is that material is transported in a zig-zag fashion.
It is important to remember that longshore drift can act on a beach in more than one direction, depending on the approach of waves and wind direction. For example, Newquay in Cornwall has a southwesterly prevailing wind direction and wave approach, but can also receive winds and waves from other directions, such as the North West.