Revision:Waves 2 - Geography

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Wave Energy

The steepness of waves determines whether they are likely to build up or degrade a beach. There are two extreme forms of waves;

Constructing / Surging / Spilling 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. If there are 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 / Surging / Plunging 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. 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.

Wave Refraction

Where waves approach an irregular coastline they're refracted i.e. they become increasing parallel to the coastline. This is best illustrated where 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.

Beaches

Beaches may be divided into three sections;

1. Backshore
2. Foreshore
3. Near shore.

Based upon the influence of the waves. A beach forms a Buffer Zone between the waves and the coast if it is an effective buffer it will dissipate wave energy without experiencing any net change, because it is composing of loose material and a beach can adapt its shape to wave energy and is therefore in dynamic equilibrium with its environment.

Beach Profiles fall between;

1. Those, which are wide and flat.
2. Those, which are narrow and steep.

The Gradient depends upon the relationship between;

1. Wave Energy - a close relationship between the beach and action of two types of waves constructive/destructive. The effect of wave steepness on beach profiles is complicated by the second variable.
2. Particle Size - its recognised that sand produces a different profile from that of shingle. It is not understood how beach material may modify the gradient.

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