GENERATION
AND GROWTH
When
the wind starts
to blow over a relatively calm stretch of water, the sea surface becomes covered
with tiny ripples.
These
ripples
increase in height and decrease
in frequency value as long as the wind continues to blow or until a maximum of
energy has been imparted to the water for that particular wind speed. These tiny
waves are being formed over the entire length and breadth of the fetch. The
waves formed near the windward edge of the fetch move through the entire fetch
and continue to grow in height and period, so that the waves formed at the
leeward edge of the fetch are superimposed on the waves that have come from the
windward edge and middle of the fetch. This description illustrates that at the
windward edge of the fetch the wave spectrum is small; at the leeward edge of
the fetch the spectrum is large.
These
waves are generated and grow because of the energy transfer from the wind to the
wave. The energy is transferred to the waves by the pushing and dragging forces
of the wind. Since the speed of the generated waves is continually increasing,
these waves will eventually be traveling at nearly the speed of the wind. When
this happens the energy transfer from the wind to the wave ceases, When waves
begin to travel faster than the wind, they meet with resistance and lose energy
because they are then doing work against the wind. This then explains the
limitation of wave height and frequency that a particular wind speed may create.
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