EM 1110-2-1100 (Part II)
30 Apr 02
(4) The wavelength, ratio of calculated wave height to incident wave height, wave phase, and modified
wave height are given as output data. For further information on the ACES system, the reader is referred to
Leenknecht et al. (1992).
II-7-3. Wave Transmission
a. Definition of transmission.
(1) When waves interact with a structure, a portion of their energy will be dissipated, a portion will be
reflected and, depending on the geometry of the structure, a portion of the energy may be transmitted past
the structure. If the crest of the structure is submerged, the wave will simply transmit over the structure.
However, if the crest of the structure is above the waterline, the wave may generate a flow of water over the
structure which, in turn, regenerates waves in the lee of the structure. Also, if the structure is sufficiently
permeable, wave energy may transmit through the structure. When designing structures to protect the interior
of a harbor from wave attack, as little wave transmission as possible should be allowed, while optimizing the
cost versus performance of the structure.
(2) Transmitted wave height will be less than incident wave height, and wave period will usually not be
identical for transmitted and incident waves. Laboratory experiments conducted with monochromatic waves
typically show that the transmitted wave has much of its energy at the same frequency as the incident wave,
but a portion of the transmitted energy has shifted to the higher harmonic frequencies of the incident wave.
For a given incident wave spectrum, there would be a commensurate shift in the transmitted wave spectrum
to higher frequencies.
(3) The degree of wave transmission that occurs is commonly defined by a wave transmission coefficient
Ct = Ht/Hi where Ht and Hi are the transmitted and incident wave heights, respectively. When employing
irregular waves, the transmission coefficient might be defined as the ratio of the transmitted and incident
significant wave heights or some other indication of the incident and transmitted wave energy levels.
(4) Most quantitative information on wave transmission past various structure types has necessarily been
developed from laboratory wave flume studies. Historically, most of the early studies employed mono-
chromatic waves; but, during the past two decades there has been a significant growth in information based
on studies with irregular waves.
b. Transmission over/through structures.
(1) Rubble-mound structures-subaerial.
(a) Figure II-7-18 is a schematic cross section of a typical rubble-mound structure. The freeboard F is
equal to the structure crest elevation h minus the water depth at the toe of the structure ds (i.e., F = h - ds).
Also shown is the wave runup above the mean water level R that would occur if the structure crest elevation
was sufficient to support the entire runup. When F < R, wave overtopping and transmission will occur. The
parameter F/R is a strong indicator of the amount of wave transmission that will occur. Procedures for
determining wave runup are presented elsewhere in the CEM.
(b) A number of laboratory studies of wave transmission by overtopping of subaerial structures have
been conducted (see Shore Protection Manual (1984)). The most recent and comprehensive of these studies
was conducted by Seelig (1980), who also studied submerged breakwaters.
Harbor Hydrodynamics
II-7-19
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