ERDC/CHL CHETN-II-45
March 2002
valid over a broad range of environmental forcing conditions and breakwater designs. To
improve the predictive capability of the GENESIS model, several published empirical formulae
for the wave transmission coefficient were evaluated. Sensitivity tests were performed to
determine the most suitable predictive formula for a given structure configuration and properties,
water level, and wave condition. The selected formulae are incorporated in GENESIS to
calculate time-dependent wave transmission and shoreline response for multiple detached
breakwaters of possible different types.
COMPARISON OF PREDICTIVE EQUATIONS FOR TRANSMISSION:
Wave
transmission at structures has been studied extensively with 2-D physical models, most
concerning narrow-crested, emergent structures with little variation in experiment parameters for
a given study. Less data are available for submerged structures with a broad crest width. The
exception is the work of Tanaka (1976), who performed monochromatic wave tests that included
both submerged and emergent crests as well as a broad range of crest widths. Based on his
results, Tanaka established design curves that give the transmission coefficient (defined as Kt =
Ht/Ho, where Ht = transmitted wave; and Ho = unreflected deepwater wave height) as a function
of the relative submergence (R/Ho, where R = structure freeboard) and the relative crest width
(B/Lo, where B = crest width of the structure; and Lo = deepwater wavelength). Note that this
definition for Kt allows for values greater than unity if waves shoal on a submerged structure.
Notation is shown in Figure 1.
Ho
Ht
(-)R ds
B
α
R
h
hc
D50
Figure 1. Notation for wave transmission predictive formulas
Tanaka's work forms the basis of the Japan Ministry of Construction official guidelines on
breakwater design. Adams and Sonu (1986) examined wave transmission across a submerged
breakwater at Santa Monica, CA, through 3-D model tests using random waves. The tests
corroborated the trends of Tanaka's findings within the range of the test parameters in their
study. Adams and Sonu concluded that the curves based on Tanaka's results could serve as a
design tool, but should be applied with caution as they underpredicted the transmission
coefficients based on the random wave tests for Santa Monica.
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