Coasts - Waves , Tides and Sediment Cells

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Waves , Tides and Sediment Cells

L.O. = to compare and contrast constructive & destructive waves, to understand wave refraction, to understand the difference between spring and neap tides and to identify the UK’s sediment cells.

Wave Characteristics Wavelength = the distance between the crest of two adjacent waves. Wave Amplitude = the distance between sea level and the crest. Wave Crest =the highest point of the wave. Wave Trough = the lowest point of the wave. Wave Height = the distance between the crest and the trough of a wave. Swash – when water from the wave rushes up the beach. Backwash – when the swash washes back to the sea. Fetch – the distance of open water over which wind has blown to create the wave. Wave energy – depends on the velocity of the wind and the size of the fetch. Constructive wave – a wave that deposits sand on a beach. Destructive wave – a wave that erodes sand from a beach.

Using the diagram you stuck into your book last lesson “Compare and contrast the characteristics of constructive and destructive waves referring to their formation, wave form, wave break, beach gain/loss and beach profile”. Most beaches are subject to the actions of constructive and destructive waves. Over time constructive waves build a steeper beach profile. This then encourages more destructive waves which was material back into the sea. This then leads to a gentle beach profile which encourages constructive waves. This negative feedback mechanism should lead to a state of equilibrium, but other factors such as wind strength and direction lead to one type of

Constructive Wave Characteristics ●Their swash is much stronger than their backwash, causing the beach to be built up by the deposited material. ●They are less frequent, reaching shore between 6 and 9 times each minute. ●They are long waves and so roll onto the beach rather than crashing onto it. ●Constructive waves create a wide, gently sloping beach. ●Constructive waves will sometimes not seem to break at all but just run up the beach losing energy as they do so. ●The swash is more powerful than the backwash, so more material is carried up the beach than is pulled back down it. ●This leads to an increase in beach sediments. If there are not many waves each wave will be able to complete both its swash and backwash without interference from the next wave coming up the beach. ●Sediment that has been pushed up the beach by the swash will be deposited up shore, and the backwash will drain away into the sand.

Destructive Wave Characteristics ●Destructive waves destroy beaches. The waves are usually very high and very frequent. The back wash has less time to soak into the sand. As waves continue to hit the beach there is more running water to transport the material out to sea. these waves are most common in winter. ●The swash of the wave tends to push material up the shore and the backwash tends to wash it back again. ●If there are a lot of waves they catch up with each other on the beach and the backwash of one wave will tend to meet the swash of the next wave. ●This will limit the motion of the water up the beach and pull some material back out to sea. Less material will be pushed up the beach. ●The backwash will be the most powerful process and there will be a net loss of material from the beach. Typically between 11 and 15 destructive waves will break every minute. ●They are tall waves, meaning they have a greater distance to fall when they break. This causes ●them to scour out the beach material. ●Destructive waves create a steep narrow beach.

Wave Refraction

Wave Refraction ●Wave refraction occurs as waves approach an irregular coastline (e.g. where there are bays / headlands or other irregularities). ●This is the process by which the waves become increasingly parallel to the coastline. ●As waves approach a headland, they begin to slow due to the shallower water around the headland, however the waves which remain in deeper water, continue to...
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