The importance of waves

The power of waves is one of the most important forces that changes the shape of the coast. Waves are created by wind blowing over the surface of the sea.

The size of a wave depends on:

  • length of time the wind has been blowing
  • strength of the wind
  • 'fetch' - how far the wind has travelled

Wave types

Waves can be constructive or destructive.

When a wave breaks, water is washed up the beach. This is called the swash. Then the water runs back down the beach, which is called the backwash. With a constructive wave, the swash is stronger than the backwash. With a destructive wave, the backwash is stronger than the swash.

The table below outlines the key differences between the two types of wave.

CharacteristicConstructiveDestructive
EnergyLowHigh
SwashStrongWeak
BackwashWeakStrong
Wave heightLowHigh
Beach shape caused by this type of waveWide and flatSteep and narrow
FrequencyLow (6-8 per minute)High (10-14 per minute)

If the swash is stronger than the backwash (constructive wave), some of the sediment carried in the wave will be left behind to build up the beach. This means that the beach increases in size.

If the swash is weaker than the backwash (destructive wave), very little sediment is carried up the beach. With a strong backwash, material will be removed and the beach will decrease in size.

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