# waves

note on what causes waves, key terminology, constructive/ destructive waves, transportation, classifying coastal enviroments, storm surge, tides, and why waves break

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Waves
What are waves?
Waves are the vital energy input, within the system
Waves form from the frictional drag of wind passing over the seas surface.
Within each wave, water particles are involved in a series of circular
motions.
Wave controls
Controlled by 3 main characteristics
Wind speed
Wind persistence- the length of time of a particular strength and direction
of the prevailing wind.
Fetch- the distance over water of which the wind had blown. The longer the
fetch the greater the wave size and strength.
Wave terminology
Crest- the highest point of a wave
Trough- the lowest point of a wave
Wave height (H)- the perpendicular distance between crest and trough
Wave period (I) - the time to complete one wave length.
Wave length (L) ­ distance between2 equal points on a wave L=CT
Wave velocity ­ the speed of movement of a crest in a given time.
Wave steepness - the ratio of height to length or gradient. If it extends
above 1:7 the wave will break. Steepness determines whether a wave will be
constructive or destructive. Most waves have a gradient of between 0.0005
and 0.05.
Energy (E) ­ energy is proportional to LH2. A slight increase in height
means a very large increase in energy. Estimates suggest that the average
power of a wave in winter is 11 tonnes per sq m.
Constructive and destructive waves
Constructive
These help build beaches.
Wave lengths are long and wave heights are less than 1 metre.
Breaking waves have low levels of energy and spill onto beach.
The swash is quickly absorbed by the beach.
Sediment thrown up by breaking waves accumulates in ridges or berms.
Backwash has little power to move sediment back towards the sea, so the

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Swash is stronger than backwash.
Destructive
Result of storm activity
Wave lengths are short and waves high so wave breaks from considerable
height creating large amounts of energy that can't be easily absorbed.
Powerful waves run up beach, the volume of water creating the opportunity
for strong backwash to move sediment back down beach.
Backwash is stronger than swash.…read more

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Experience a less extreme pattern of wind and waves. The waves will have
considerable swell over a long fetch but not combined with strong winds such as in
West Africa.
Storm surges
High onshore winds and tides combine to give unusually high sea levels.
Created by:
High tides
Strong onshore winds creating high levels of wave energy.
Low pressure weather systems allowing the sea to expand.…read more