Waves Objectives and Outcomes: 1- I will know the different characteristics of Constructive and destructive waves.

The Fetch The size of a wave depends on its fetch. The fetch is the distance a wave travels. The greater the fetch, the larger the wave. Wind also has a significant effect on the size of waves. The stronger the wind the larger the wave.

Wave breaks As a wave approaches a beach it slows. This is the result of friction between the water and the beach. This causes a wave to break.

Why do waves break?

Wave definitions Wave fetch: The distance of open water over which a wave has passed. Maximum fetch is the distance from one coastline to the next landmass, it often coincides with prevailing wind direction. (South West in the UK). Wave crest: Highest point of a wave. Wave trough: Lowest point of a wave. Wave height: Distance between trough and crest. Wave length: Distance between one crest/trough and the next. Swash: Water movement up a beach. Backwash: Water movement down a beach

Constructive waves Constructive waves build beaches. Each wave is low. As the wave breaks it carries material up the beach in its swash. The beach material will then be deposited as the backwash soaks into the sand or slowly drains away. These waves are most common in summer.

2. Constructive Waves have a number of important characteristics:2. Constructive Waves have a number of important characteristics: i) Their swash is much stronger than their backwash, causing the beach to be built up by the deposited material. ii) They are less frequent, reaching shore between 6 and 9 times each minute. iii) They are long waves and so roll onto the beach rather than crashing onto it. iv) 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 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.

1.Destructive Waves have a number of important characteristics:Destructive Waves have a number of important characteristics: i)Their backwash is much stronger than their swash, thus allowing them to remove material from the beach. ii) They are frequent in number, usually between 10 and 15 per minute. iii) They are tall waves, meaning they have a greater distance to fall when they break. This causes them to scour out the beach material. iv) Destructive waves create a steep narrow beach.

Effects of waves

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 move faster towards the bay as they are unaffected by friction.

As waves approach a bay, they diverge and there is a reduction in energy, resulting in deposition. Conversely, at a headland, the waves refract (bend around) the headland and the orthogonals (wave direction) converge resulting in the concentration of energy on the headland and its subsequent erosion. Longshore currents caused by the breaking of waves on the headland will result in movement of the material eroded from the headland into the bays.

Wave Refraction

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