Figure 6-9.-General characteristics of spilling, plunging, and
surging breakers.
is released Plunging breakers are more commonly
associated with swell waves that approach the beach
with much longer wavelengths. The shortening of the
wavelength as the wave feels bottom causes a great mass
of water to build up in the crest in a short time. Longer
period swell waves may double in height when feeling
bottom.
SURGING BREAKER.— Surging breakers are
normally seen only with a very steep beach slope. This
type of breaker is often described as creating the
appearance that the water level at the beach is suddenly
rising and falling. The entire face of the wave usually
displays churning water and produces foam, but an
actual curl never develops.
Littoral Current
Remember that refraction occurs when a wave train
strikes a beach at an angle, and this action causes a mass
transport of water parallel to the beach in the same
direction as the wave train. This mass transports called
the longshore current or littoral current.
Many of the craft used in amphibious operations are
small and, because they are designed to land upon the
beach are not sea-worthy. Owing to the size of landing
craft, significant breaker height, maximum breaker
height, breaker period, breaker type, the angle of
breakers to the beach, the longshore (littoral) current
speed and the number of lines of surf can have a
dramatic effect on amphibious operations and are of
vital importance.
Definition of Terms
The following are some terms that will be used
extensively in surf discussions and should be
understood by the forecaster:
. Breaker height - the vertical distance in feet
between the crest of the breaker and the level of the
trough ahead of the breaker.
. Breaker wave length - the horizontal distance in
feet between successive breakers.
. Breaker period - the time in seconds between
successive breakers. This is always the same as the
deepwater wave period.
l Depth of breaking - the depth of the water in feet
at the point of breaking.
. Surf zone - the horizontal distance in yards
between the outermost breakers and the limit of wave
uprush on the beach.
l Number of lines of surf - the number of lines of
breakers in the surf zone.
l Deep water wave angle - the angle between the
bottom contours and the deep water swell wave crests.
l Breaker angle - the angle between the beach and
the lines of breakers. It is always less than the deep
water wave angle.
6-14
