Waves

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

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

• 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

Waves in Deep Water cntd

• 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

• 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

Breaking Waves cntd

• 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

Constructive Waves• These are low in height less than a metre, flat and

gentle, have wavelengths up to a 100m, have a long period 6-8 minutes, gentle waves that are low in energy.

• When situated on a gentle slopping beach they have a long way to travel so the swash looses energy and therefore has a weak backwash.

• These waves move sand and shingle up the beach. This increase the gradient of the beach due to material build up and this forms a Berm at its crest. At 90 degrees + the waves loose energy and therefore have further to travel

Destructive Waves

• Their wave height is greater than 1m and the wave length is in proportion to 20m; the frequency wave period is 10-14 minutes.

• They have a high energy and this results in the presence of storm waves, theses usually occur on steep slopping shingle beaches.

• They have plunging waves that concentrate on a small area of a beach.

• When these waves have restricted percolation the backwash will be as strong as the swash.

Destructive Waves cntd

• They create storm beaches as stones are thrown above the high tide mark, most material is carried down the beach by the backwash this forms a Longshore Bar (breaking point).

• The waves are stronger if the beach is steep and they approach at 90 degrees. As the material is carried back down the beach it becomes gentler in the lower section

Constructive & Destructive waves

Wave Refraction

• Where waves approach an irregular coastline they're refracted i.e. they become increasing parallel to the coastline.

• Best illustrated with a headland separates two bays. A wave approaching a shore looses velocity as the depth of the water decreases. The seabed shelves rapidly off a headland than in a bay due to the waves loosing velocity quicker there

Wave Refraction

Wave Refraction

• Approaching Headland• The water becomes shallower• Becomes affected by friction• Higher , more destructive waves• Dominant process is EROSION• There is High energy as the waves are

concentrated into a smaller area• Headland is usually made up of hard resistant

rock

Wave Refraction

• Approaching bay• Affected by shallow water and breaks later • Low energy waves as they spread out over a

large area• Generally – lower, more constructive waves• Dominant Process is DEPOSITION