Waves differ in shallow water compared to in deep, when in deep water the depth of the water is greater then half the wavelength this causes the drag of the wind over the sea surface to make water move in an orbital motion. As waves are surface features the size of orbiting decreases with depth. As waves approach the shore and the seabed gets closer to the surface of the water the base of the wave begins to slow down due to friction this causes the circular oscillation of the wave to become more elliptical. As the water depth gets shallower the wavelength decreases also. As the friction gets more the height and steepness increases until finally the upper part of the wave spills and plunges over this point is called the plunge line and is caused when the depth of the water and height of the wave are equal. The body of rushing water is known as the swash. The water that returns down when the wave returns is called the backwash.
Waves break as the friction slows down the base of the wave, as the waves get closer to the shore this friction heightens causing more elliptical orbit the crest of the wave raises due to this and the velocity and wave length decreases. From here the wave continues to steepen until the ration of 1:7 (wave height and wave length) is reached. At this point the wave breaks.
B: Explain how and why beach profiles vary from one place to another (25Marks)
Beach profiles vary from one place to another due to more then one factor. The first factor is the type of wave that is hitting the beach. There are two types of waves Constructive and Destructive waves.
Constructive waves: These are also known as surging or spilling breakers, they tend to result from swell waves (distant storms). These types of waves are usually relatively gentle and move material up the beach. They are not very large waves and are usually less the one metre high with along wave period of over 100 metres. The frequency of these waves is also relatively long with a time period of 8-10 seconds. The orbits of these waves are also elliptical and have a large swash and small backwash. The sand and shingle on the beach are moved up causing a steep profiled beach. This causes berms to form (ridges of shingle).
Destructive waves: These are high energy waves that cause a large amount of Erosional waves and are associated with local storms. They are usually much taller then 1 metre with a short wavelength of around 20m between crests, the frequency is also very high. The period of the waves is low and the backwash is usually far stronger then the wash. The steep waves plunge down the beach and the profile becomes gentler. Destructive waves comb material down the beach depositing below the low water mark. These waves cause the beach profile to be gentle.
The particle size on the beach complicates the influence of wave energy on the beach. Shingle beaches have a steeper gradient then their sandy counterparts due to the differences in percolation rates. Water will pass through coarse-grained shingle more rapidly then fine grain sand. Usually the larger the size of the shingle the steeper the gradient of the beach. This is due to most of the energy being lost in the swash as the shingle takes it all away due to there being more friction meaning there is not any energy for the backwash to pull material back down. However due to the strong swash berms will be produced. Usually on shingle beaches where a berm has formed there will also be a storm beach consisting of large boulders and alike that have been thrown their by the biggest waves usually during a spring tide.
For a sandy beach the profile will be different, this is due to the small particle size of sand alowwing it to become very compact when wet. This restricts the rate of percolation and causes these types of beaches to usually be gentle.
