Amphibious warfare is the most complex operation
in modern warfare. The safety and success of
amphibious landings are largely dependent upon known
surf conditions, although several other environmental
factors can also have a profound effect. Surf conditions
are reported by various individuals, depending upon the
Their input into surf forecasts
(SURFCSTS) are key to major decisions.
chapter, we will begin by discussing the causes of surf
and surf zone characteristics in general. We will then
focus on the actual surf observation (SUROB) at a
beach, and describe the calculation of the modified surf
index (MSI). Finally, we will discuss in detail how tides
affect amphibious operations.
SURF ZONE CHARACTERISTICS
LEARNING OBJECTIVES: Identify the
manual that provides information on surf zone
terminology and detailed instruction on surf
observation procedures. Identify the causes of
surf. Recognize the effects of hydrography on
surf conditions. Define the terms used in surf
Recognize the effects of
refraction on waves.
On occasion, both Navy and Marine Corps weather
observers may be called upon to support amphibious
operations either in exercise conditions or in an actual
When the beach area is secure (in
friendly hands), you may be tasked with observing and
reporting surf conditions from the beach. Under hostile
conditions, Navy UDT/SEALs or Marine Corps
RECON personnel are normally tasked to conduct an
on-scene, covert beach survey, which includes
observing and reporting surf conditions.
reconnaissance photography and satellite imagery can
also provide a good indication of surf conditions at a
hostile beach-landing area. Analysis of surf conditions
from imagery is done by Navy and Marine Corps
analysts/forecasters and Navy oceanographers working
with photographic analysts.
COMNAVSURFLANT/PAClNST 3840.1, Joint
Surf Manual, contains comprehensive information on
amphibious operations, including surf observation
procedures and a listing of various tables used for surf
index calculations. All Navy and Marine Corps surf
observers should review the Joint Surf Manual.
CAUSES OF SURF
Surf, the way that waves break near a beach, is
caused by either local onshore winds or by swell waves
traveling from a distant fetch area. The term surf zone
describes the area between the shoreline and the
outermost limit of the breakers.
The surf zone
encompasses the region between the first approaching
breakers and the limit of wave uprush.
Surf created by local winds is characterized by
breakers with irregular crests, short wave periods, and
many whitecaps in the surf zone. Breakers produced by
sea waves do not appreciably increase in height before
they break. Surf created by swell waves produces
breakers with a more rounded appearance and with a
more regular, but longer period. Swell waves offshore
appear low and rounded, but just before breaking they
rapidly increase in height and steepness. Although sea
waves and swell waves usually exists simultaneously, it
is the swell that most often presents a problem for
Surf forms as deep-water waves approach shallow
water. Deep-water waves are waves moving over water
that has a depth greater than one-half the average
wavelength. Deep-water waves approaching the beach
will feel bottom when the depth of the water is
approximately one-half the deep-water wavelength.
When a wave feels bottom, wave speed and wavelength
decrease while wave height increases. As this happens,
the face of the wave becomes steeper. The steepness of
a wave refers to the ratio of wave height to wavelength.
Waves become breakers when the wave spills water
down the face of the wave (the wave crest). Once the
steepness of a wave becomes 1/7 of the wavelength, the
wave becomes unstable and begins to break. When
approaching a beach, a wave will normally break when
the water depth is 1.3 times the wave height, but may