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These confused seas are really a composite of numerous waves
having different lengths , heights ,and periods that are continually
merging and separating as they move in different directions and at
different speeds through the fetch area. The interaction of several
waves is called wave interference.
Storm waves outside the generating area :
the waves raised by the storm move through the fetch at a celerity
that depends on their length and period . Short –length , short –
period waves move slowly , whereas long-length , long –period
waves move rapidly , combining and separating all the time and
creating chaotic seas in the fetch area. Once the waves are outside
the generating area , no further energy is imparted to them by the
storm winds, so their wavelength , speed and period remain
unchanged. Consequently , waves with longer periods and lengths
will outurn waves with shorter periods and lengths .This effect
imposes order on the seas , as the waves begin to sort themselves
according to speed and , hence , according to length and period . The
process of wave separation is termed dispersion.
Waves in shallow water :
Once waves enter shallow water , the sea bottom exerts a strong
influence on their form and celerity. Three important changes are
brought about by shallow -water conditions : transformation of the
waves’ s properties , wave refraction , and collapse as a shore breaker
.
When waves begin to interact with the bottom , they slow down , and
their speed, which in deep water depended on wavelength and period
, now is regulated directly by water depth. Regardless of their height
or length , the celerity of all shallow-water waves
is governed
entirely by water depth.
One of the most important results of a wave’ s entering shallow
water is refraction , that is , the bending of the wave crest in
response to changes in wave speed.