TSR Wiki > Study Help > Subjects and Revision > Revision Notes > Geography > Waves 1
The Importance of Waves
- They contribute energy to the coast. They're created by the transfer of energy from the wind to the sea, blowing over the surface. The wind blowing over the smooth water surface creates ripples that grow into waves as the frictional drag increases. As the winds energy grows so does the height. The wave height is the difference between the trough and the crest.
- Example - The wind speed is 50km, the time is 30 hours and it's open sea, the waves will be 6m high. Waves resulting from local winds and travelling from local distance will not develop to their full height.
- Example - Dover and France are 40km apart so these waves are Sea Waves. This is an insufficient distance for the wind to develop waves to their full height.
- Waves formed by winds blowing over large distances are called Swell Waves. The length of open sea over which the wind blows to generate waves is the Fetch. This along with velocity and period of time during which the wind has blown determines the waves energy.
Wave Terminology
- Wave Period - time taken for a wave to travel through one wave length it can be timed by counting the number of crests per minute or by timing 11 waves and dividing them by 10.
- Wave Length - is the distance between two crests.
- Wave Velocity - is the speed of movement of a crest in a period of time.
- Wave Steepness - is the ratio of the wave height to the wavelength.
- The Energy - is the energy of the wave in deep water.
Waves in Deep Water
- Deep water is when the depth of the water is greater than half the wavelength. Waves only effect the surface of the water and submarines are unaffected by storm.
- Waves do not cause water to move it's only the shape of the wave passing through the water. The passing of a wave causes floating objects to move in an orbital motion
- Example - A boat will be lifted up and then let down while hardly moving over the sea surface.
- The perfect orbital motion is rare in nature and often there is some forward motion of water particles. This is called Mass Transport.
Waves in Shallow Water
- As Waves approach shallow water, when their depth is less than half the wavelength then friction with the seabed increases. As the base of the wave starts to slow down the circular oscillation becomes elliptical.
Breaking Waves
- As the water depth decreases further the wave length decreases due to the friction making waves catch one another, the wave height increases due to the friction and acceleration of the upper part of the wave, and also the wave steepness increases due to ratio of 1:7.
- As the upper part of the wave accelerated and the lower part of the wave is slowing down due to the friction, eventually the upper part spills over the lower part causing the wave to break. Waves break at the Plunge Line and here is where the depth of the water and the height of the wave are approximately equal.
- The body of water that then reaches up the beach is called the Swash and any water returning down to the sea is called the Backwash.
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