Coastal transportation
Every grain of sand on a beach has travelled to get there. Waves pick sediment up, carry it along the shore and eventually drop it. The places where it is dropped become beaches, spits and lagoons, so explaining those landforms starts with understanding how sediment moves.
Coasts move sediment in the same four ways that rivers do, which the lesson on river erosion introduces. Which method operates at any moment depends on the size of the sediment and the amount of energy in the water.
The rolling of large, heavy material such as boulders and pebbles along the sea bed, pushed by the force of the water.
Smaller stones and coarse sand bouncing along the sea bed in a series of short hops.
Fine particles carried within the water without touching the bed.
Minerals dissolved in the water and carried invisibly.
The more energy the water has, the larger the sediment it can move. A calm sea may only carry fine material in suspension, while a powerful sea can roll pebbles along by traction. When energy falls, the largest material is dropped first.
Whether waves build a beach up or strip it away depends on the type of wave, which the lesson on coastal erosion explains.
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