empirical criterion to beaches where grain size, tidal range, and wave conditions differ from those
underlying the criterion. Numerical models are recommended for application in general situations of
arbitrary structure configurations, time-varying water level and waves, and different median grain
Numerical models typically represent wave transmission as a constant Kt specific to each
detached breakwater. However, wave transmission properties vary over different time scales as
controlled by tidal variations and incident wave conditions. The purpose of this study is to improve
predictive modeling capability by incorporating an automated time-dependent calculation of wave
transmission and shoreline response. The functioning of the variable Kt for various structure
configurations is demonstrated by comparing the shoreline response predictions of simulations based
upon time-dependant and constant values of Kt.
Wave transmission properties of a structure can vary significantly depending on structure
configuration and composition. Wave transmission properties also vary over different time scales as
controlled by tidal variations and the changes in incident waves. It is desirable to have the capability
of predicting shoreline response to detached breakwaters for a wide range of engineering conditions.
To achieve this goal, an expression for the wave transmission coefficient must be valid over a broad
range of environmental forcing and breakwater designs. Wamsley and Ahrens (2003) critically
evaluated several empirical predictive formulas for wave transmission at detached breakwaters,
leading to an approach judged most appropriate for shoreline response modeling.
The functioning of the time-dependent Kt is assessed by incorporating the predictive formulas in
the numerical model GENESIS. GENESIS has been applied to model shoreline change both in the
field and in movable-bed physical model experiments based on its capability of representing
Hanson and Kraus 1989, 1990, 1991a, 1991b). In GENESIS, wave transformation from deep water
to the location of the structure may be calculated by selecting either an external 2-D wave
transformation model, e.g., STWAVE (Smith et al. 1999), or the internal wave module within
GENESIS. In these previous works, the transmitted wave was calculated with a constant value of Kt
as discussed, for example, by Hanson et al. (1989) and Hanson and Kraus (1991a). Through an
iterative procedure for calculating wave breaking, Kt also influences the breaking wave height and
direction alongshore, thereby determining the associated shoreline response to the structure (Hanson
and Kraus 1989, 1990, 1991a, 1991b).
In the revised GENESIS model as described here, the user may choose either a constant value of
Kt for each structure or allow the model to calculate values based on time-varying water level and
wave height, and structure characteristics. Based on the input values describing the structure, water
level, and calculated wave properties, a corresponding Kt is calculated at each time step. The
calculated Kt exerts strong influence on the wave field behind and adjacent to the structure because it
contributes to wave transmission and diffraction. If the variable Kt option is selected, water level is
read from an input file at a specified input time interval. For each structure, the user specifies
geometric properties (crest height and width, slopes on seaward and landward sides, and median
rock size) and can select between the calculation methods of Ahrens (2001); Seabrook and Hall
(1998); and d'Angremond et al. (1996). Wamsley and Ahrens (2003) provide guidance on selecting
a calculation method for a given application.
Wamsley et al