46
Lesson N °7 :
Shoreline under storm conditions
Storms affect the shore in a variety of ways. First , the water surfaces
rises in response to the low atmospheric pressure of the storm.
Second , strong winds blowing onshore drive water landward and cause
it to be stacked against the shore . The combined effect of these two
processes results in unusually high water levels that flood the land .
These sudden changes of coastal water levels produced by storms are
called storm surges.
They create deep water near the shore and allow waves to break much
farther inlnad than usual. Storm surges are particularly destructive when
they happen to coincide with usually high tides.
Tiny waves and giant waves :
The most common type of water wave undoubtedly is the capillary
wave , a tiny wavelet a few centimeters
in wavelength and few
millimeters in height , and with a period of less than half a second.
Other relatively smaller waves are found in very shallow wtaer . These
are called solitary waves , because each acts independently of others.
The giant waves , described as such because of their height , not because
of their length . Typically , they are encountered in the fetch area where
storm winds are raising seas. Here waves of wide-ranging size are
moving at different speeds , sometimes merging with others and
collectively growing in size by wave construction . Some of these ,
which seem unbelievely tall and are in fact much bigger than wave
theory predicts for the wind conditions , are aptly termed rogue waves .
They are especially dangerous if they become oversteepened
and
collapse , sending a wall of turbulent water with all of its mass and
momentum crashing into a helpless vessel.
Standing waves :
Seas , swell and breakers are progressive waves . Their crests and
troughs travel from one point on the sea surface to another. Standing