WAVES page 3
(8) - Life Cycle of a Wave:
a - Generating area - Sea [size of wave f (fetch, duration, velocity)]
b - Transmission area - Swell
c - Shoaling area - Surf and Swash
(9) Shoaling transformations:
when the wave enters "shallow" water, these changes occur:
(in a section perpendicular to the beach)
|
decrease
|
constant
|
increase
|
|
L
|
T |
H |
|
C
|
T
|
U |
so what happens to
wave steepness?
Make sketch
below:
In words:
the wave slows down because of friction at the bottom, so its celerity decreases and - since the period remains constant - the wavelength also decreases.
But although some energy is lost by friction, a lot is preserved and the conservation of energy principle
causes the wave height to increase, and thus the orbital velocity also increases, (since the period remains constant).
At some time and depth, the wave essentially "topples" and breaks because of three or more reasons:
(1) Wave steepness exceeds the "magic" ratio of 1/7
(2) Orbital velocity "exceeds" celerity
(3) Backrush of water "tackles" the forward motion
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