Environmental Engineering Reference
In-Depth Information
Figure 1
Reflected and standing waves (a) and the effect of
shoaling on the orbital path of water particles, leading to breaking
waves (b).
Waves break when the critical ratio of water depth to wave height lies between 0·6 and
1·2, around a mean value of 0·78. In other words, average waves break in water depths a
little less than their own height, and so low waves run farther into shallower water than
high waves before breaking. The shoaling angle is also important. Waves break close
inshore where it is steep and farther out on flat shores, measured by the
breaker
coefficient
, B.
where
H
= wave height,
L
= wavelength and
S
= bed slope. The breaking style
influences the way in which wave kinetic energy is used, and four styles are recognized
(Figure 2). The breaker coefficient falls from spilling to surging styles as bed slope
angles increase. Most waves do not approach the coastline orthogonally, with wave crests
parallel to the shore, but are driven obliquely onshore or meet an indented coastline.
Waves are retarded around headlands but drive on less impeded into bays. Such
refracted waves
alter the pattern of energy flux at the coast, with energy convergence
around headlands and divergence in bays (see Plate 1).
