WAVES UNDULATIONS OF THE WATER CAUSED BY WINDS BLOWING ACROSS THE SURFACE OF THE SEA. They consist of orbital movements of water molecules which diminishes with depth.... Showing significant forward movement only when it approaches the shore and breaks.

Types of Wave Using wave energy we can recognise TWO types of wave… Surfing Breakers Surging Breakers SURFING = HIGH ENERGY ---steep and with short wave lengths Surging = low energy ---shallow and long wave lengths. WAVES ARE THE MAIN SOURCE OF ENERGY THAT DRIVES THE COASTAL SYSTEM.

ENERGY OF WAVES Based on wind velocity, the length of time the wind is blowing, the Fetch (greater the fetch the bigger the wave), water depth. Fetch is the expanse of water over where the dominant waves develop before reaching the coast ( S. E. of UK to Brazil, Hawaii to Antarctica).

Wave Terminology Trough Wave length Wave height Wave period (one wave length) Wave velocity (speed of the crest over a period of time) Wave steepness (ratio of wave length to wave height) Orbital motion (so submarines not affected by storms..as orbits decrease rapidly with depth…therefore large height change with little lateral movement)

Deep waves = depth of water is greater than ½ wave length Shallow waves =depth of water is less than ½ wave length…here friction increases therefore as base slows down as it is shallower…then rotation becomes disturbed and elliptical. As depth decreases so does the wave length. As depth decreases so does wave height and the steepness increases until wave tumbles over. Where a wave breaks = The Plunge line. So where depth of water and wave height are = Water rushes up the beach = swash Water rushes down the beach = backwash

Why do waves break? Waves are the result of the wind blowing over the sea. As they approach land they break. The bottom of the wave touches the sand and slows down due to increased friction. The top of the wave becomes higher and steeper until it topples over.

Constructive Wave Energy Constructive waves (surging) build up sediment above the LWM. swell produced with a large fetch where wave length is larger than 100m yet wave height is only 1 m. Also has a long wave period (6-8/ min) so flat breakers with low energy so low angle beaches produced as swash soon loses energy due to the distance up the beach and then the backwash is also weak…..so sand and shingle go up the beach and form berms at the crest. Ridges and runnels also cause the wave to rapidly lose energy

Types of waves

Destructive Wave Energy Steep and spilling waves Material moved down the beach depositing below the LWM. Short fetch Steep and high waves Wave length small 20 m between crests, wave height over 1m and 10-14/ min. These waves break away from the shore and have high energy (due to steepness) Occur on beaches with a high angle so energy used on a small area. Material moved down the beach except when storm waves toss material up forming a STORM BEACH Down movement to an off shore bar (long shore Breakpoint Bar..so more gentle in the lower section Eventually can reach equilibrium