GenCade:Wave Calculation

Offshore wave information can be obtained from either “numerical” gages, i.e., from a hindcast calculation, or from actual wave gages. Wave data are input to the model at a fixed time interval, typically in the range of 3-24 hr. One submodel in GenCade calculates breaking wave height and wave angle as determined from wave information given at a reference depth offshore, under simplified conditions. This submodel is called the internal wave model (not to be confused by internal waves that propagate along density fronts). If the internal wave model cannot be used, a completely independent, external wave model, may be used to supply nearshore wave information to GenCade. Usage of these internal and external models is shown in Figure 1.

Figure 1a. Internal Wave Model Transformation

Figure 1b. External Wave Model Transformation

The internal wave model is applicable to a sea bottom with approximately straight and parallel contours. The breaker height and wave angle are calculated at grid points starting at the reference depth of the offshore wave input (Figure 1a). If an external wave model is used (Figure 1b), it calculates the wave transformation over the actual (irregular) bathymetry starting at the offshore reference depth. Resultant values of wave height and direction just outside the breaker zone are saved in a file (by the modeler) for input to the internal wave model. The wave conditions just beyond the breaking zone define a “nearshore reference line,” from which the internal wave model in GenCade reads in grid cell by grid cell to bring the waves to the breaking point. If coastal structures are located in the modeling reach that produce diffraction, the internal model will automatically include the effect of diffraction in the process of determining breaking wave characteristics.

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