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Transport
Waves sometimes approach the coast at an angle; this is because of the direction of the prevailing wind. This causes the waves to break on the beach at the same angle as the prevailing wind. The swash of the waves carries material up the beach at an angle. The backwash then flows back to the sea in a straight line at 90 degrees due to the influence of gravity. This movement of material is called transportation.
On many coasts the combined effect of continually repeating swash and backwash is to transport material sideways along the coast. This movement of material along coasts is called longshore drift and occurs in a zigzag motion along the shoreline.
Coastal transport
There are four methods by which waves and tidal currents can transport sediment. These processes can then contribute to the movement of sediment by longshore drift.
| Process | Description |
|---|---|
| Solution | Soluble minerals are dissolved in sea water and carried along in solution. The load is not visible. Load can come from coastal cliffs made from chalk or limestone, and calcium carbonate is carried along in solution. |
| Suspension | Small particles are carried along in the water, eg silts and clays. When large amounts of sediment are carried in suspension, it can make the water look cloudy. Currents have the energy to pick up large amounts in suspension during a storm, for example when strong winds generate high energy waves. |
| Saltation | Load is bounced along the sea bed, eg small pieces of shingle or large sand grains. This size of sediment is larger and heavier, therefore the currents cannot keep them afloat for long periods. |
| Traction | Pebbles, and larger sediment, are rolled along the sea bed with the force of the water. |
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