TM 5-850-1
(2) Direction of littoral drift. Determine the
elliptical rather than circular. Primary characteristics of
individual waves are shown in figure 5-1. For the normal
direction of littoral drift from these or similar
deepwater wave, the various wave characteristics are
observations: (a) Major accumulations of sediment at
related by the following equations:
existing jetties and groins.
(b) Hindcast wave data refracted into
v = 2.26 L = 5.12T
(5-1)
shallow water.
L = 0.195v2 = 5.12T2
(5-2)
(c) Shore patterns in the vicinity of
T = 0.442 L = 0.195v
(5-3)
headlands.
where
(d) Characteristics of beach and bed
v = velocity of propagation of wave, feet per second
materials.
L = wavelength, feet T = wave period, seconds
(e) Current measurements.
b. Tsunamis and hurricane surge.
(3) Beach material. Select suitable material
(1) Tsunamis are very long-period waves (usually
considering the following factors:
5 to 30 minutes in period) that are caused by a
(a) Use clean sand. Some clay or silt
displacement of the ocean bottom due to seismic activity.
admixtures are permissible; particles will be sorted by
Ports around the entire Pacific Ocean are susceptible to
natural wave action.
tsunami waves; however, the effects at different harbors
(b) Proper gradation is required to
vary considerably due to the local bathymetry from the
produce the desired slope. The gradation should be the
continental slope shoreward and to the direction of
same as that of materials found on nearby beaches
approach by the tsunami. Ports and harbors bordering the
having slopes similar to those desired.
(4) Crest height. Match the existing beach
Atlantic Ocean have practically no problem from tsunamis
due to the lack of active seismic regions around the
crest or that of nearby beaches similarly exposed.
(5) Miscellaneous.
periphery of the Atlantic Basin.
(2) Hurricane surge (or typhoon surge) is more
(a) The rate of supply of artificial
common than tsunami surge and presents a problem on the
nourishment must balance the rate of loss from an
East and Gulf Coasts of North and Central America, the
existing beach.
Eastern and Southeastern Coasts of Asia, and islands in
(b) Locate the stockpile of artificial
that area of the Pacific. The occurrence of hurricanes and
nourishment updrift of the problem area. Do not place
typhoons is fairly well documented (especially in the United
the toe of the stockpile in water depths exceeding 20
States), and the frequency of occurrence of various
feet on seacoasts.
intensity hurricanes and the resulting waves and hurricane
(c) Offshore dumping may be used.
surge can be calculated.
It would be considerably
Deposits have been successfully made up to 0.5 mile
beneficial to the site selection process to catalog all existing
offshore and in water depths up to 38 feet.
d. Sand bypassing system. A sand bypassing
data on hurricanes and typhoons to assess the probability
of port downtime for each year; and the probability of
system consists of a stationary hydraulic-suction dredge
extensive damage from both hurricane surge and winds.
pump, which dredges sand from the updrift side of an
c. Explosion-generated water waves.
Explosion-
inlet and pumps it across the inlet channel, usually
generated water waves exhibit the same characteristics as
through a subaqueous pipe. The pump installation is
any waves produced by a local disturbance in deep water.
usually at the head of the updrift jetty. Floating
A train of waves is generated where the maximum
installations are possible but not desirable except under
amplitude wave always has the same period (regardless of
unusual circumstances. The design details are as
distance of propagation). The amplitude of this wave
follows: (1) Position the discharge pipe so that the
decreases as 1/R (R being the distance propagated from
sweep of the current will distribute the sand along the
the source). If the explosion occurs in shallow water, the
problem area.
first wave is usually the largest, regardless of propagation
(2) Govern the required discharge velocity with
distance, due to a very slow rate of dispersion. The
median grain-size sand.
amplitude and frequency of the largest wave are functions
(3) Provide auxiliary equipment for clearing a
of the explosion yield, height or depth of burst, distance
clogged discharge pipe, such as compressed air jets,
from the explosion, water depth, and bottom topography.
complete with compressors, pumps, and tanks.
5-2. Waves and wave pressures.
An explosion is an inefficient method of generating water
a. Individual wave characteristics.
waves and a relatively large-yield nuclear explosion is
Waves
required to create waves of appreciable height. The area
generated in deep water (generally considered as water
affected
by
having a depth > L/2, where L is the wavelength) are
normally identified as the oscillatory type, in which
particles of water oscillate in a circular pattern about
some mean position. In shallow water, the particle
paths
are
5-2
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