Waves

When the wind blows over the sea, it creates waves. The size and energy of the wave depends on certain factors:

  • the fetch - how far the wave has travelled
  • the strength of the wind
  • how long the wind has been blowing for
Long fetch (up to 8,000 km) - South-westerly wind will produce large powerful waves. Short fetch (less than 200 km) - South-easterly wind will produce small waves.

Wave types

There are two different types of wave - constructive and destructive. They can affect the coastline in different ways. When a wave reaches the shore, the water that rushes up the beach is known as the swash. The water that flows back towards the sea is known as the backwash. The energy of the swash and backwash determine the type of wave.

Destructive waves

Constructive waves are high in proportion to their length. They have a weak swash but a strong backwash. A tall breaker is a tall wave which breaks downwards with great force.

The characteristics of a destructive wave are:

  • weak swash and strong backwash
  • the strong backwash removes sediment from the beach
  • the waves are steep and close together

Constructive waves

Destructive waves are low in proportion to their height. They have a strong swash and weak backwash.

The characteristics of a constructive wave are:

  • strong swash and weak backwash
  • the strong swash brings sediments to build up the beach
  • the backwash is not strong enough to remove the sediment
  • the waves are low and further apart