Numerical models have the capability of representing the response of the shoreline to structures
exposed to time-varying forcing. In this study, published empirical formulas for the wave
transmission coefficient were incorporated in the GENESIS shoreline change model to calculate
time-dependent wave transmission and shoreline response. The functional utility of time-dependent
wave transmission was assessed running simulations for a single detached breakwater of varying
crest heights and forced with a range of wave conditions. Results indicate that the time-dependent
Kt enters centrally for all wave climates and plays a major role for submerged and emergent near-
surface structures. The application of a time-dependent wave transmission calculation entered most
significantly for submerged structures, for which shoreline position predictions may change by 80%
or more. The time-dependent calculation appears to be necessary to represent emergent near-surface
structures because application of a constant Kt may over-predict shoreline advance by as much as
30%. These percentages apply to the wave climates and structural configurations tested. Greater
changes may be possible for a given application as illustrated by the Grays Harbor case study.
The functional utility of time-dependent wave transmission was further examined in application
to a submerged spur being studied as a possible sediment-control measure for the north jetty at
Grays Harbor, WA. Predicted shoreline response to a proposed submerged shore-parallel spur on
the north jetty differed considerably between the constant and the time-dependent wave transmission
cases. Sensitivity tests indicated that seasonal directionality and energy of the incident waves,
combined with the variable wave transmission, contributed to a significant difference in predictions.
The combined working of wave direction and wave transmission demonstrates the complex
interaction of forcing parameters that cannot be anticipated by a constant transmission coefficient for
design applications.
Predictive capability of numerical shoreline response models such as GENESIS can be improved
by incorporating a time-dependant wave transmission calculation for detached breakwaters. In the
present study, Kt is represented in a more realistic manner than previously, and results indicate that
the time-dependant nature of wave transmission is a major factor in determining shoreline response
for submerged and emergent near-surface structures. In practice, detached breakwaters are often
submerged to reduce cost, produce moderate shoreline change, and to minimize dangerous