The action of waves

The power of waves is one of the most significant forces of coastal change. Waves are created by wind blowing over the surface of the sea. As the wind blows over the sea, friction is created - producing a swell in the water. The energy of the wind causes water particles to rotate inside the swell. This moves the wave forward.

The size and energy of a wave is influenced by:

• the length of time that the wind has been blowing.
• the strength of the wind.
• how far the wave has travelled (called the fetch).

The activity below shows the length of fetch along the south coast of England:

Waves can be destructive or constructive.

When a wave breaks, water is washed up the beach: this is called the swash. Then the water runs back down the beach: this 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.