127. Use of the internal and external wave transformation models is 

 depicted in Figure 9. The internal model is applicable to a sea bottom with 

 approximately straight and parallel contours, and breaker height and angle are 

 calculated at grid points alongshore starting from the reference depth of the 

 offshore wave input (Figure 9a) . If an external wave model is used 



(Figure 9b), it calculates wave transformation over the actual (irregular) 

 bathymetry starting at the offshore reference depth. Resultant values of wave 

 height and direction at depths alongshore for which wave breaking has not yet 

 occurred are placed in a file (by the modeler) for input to the internal wave 

 model. These depths, taken, for example, as the depths in each wave calcula- 

 tion cell immediately outside the 6-m contour, define a "nearshore reference 

 line," from which the internal wave model in GENESIS takes over grid cell by 

 grid cell to bring the waves to the breaking point. If structures that 

 produce diffraction are located in the modeling reach, the internal model will 

 automatically include the effect of diffraction in the process of determining 

 breaking wave characteristics. 



Internal Wave Transformation Model 



Breaking waves 



128. Wave transformation from the deepwater reference depth or the 

 nearshore reference line (depending on whether or not the external wave model 

 is used) is initially done without accounting for diffraction from structures 

 or landmasses located in the model reach. The solution strategy is to obtain 

 a first approximation without including diffraction and then modify the result 

 by accounting for changes to the wave field by each diffraction source. 



129. Omitting diffraction, there are three unknowns in the breaking 

 wave calculation: the wave height, wave angle, and depth at breaking. Three 

 equations are needed to obtain these quantities. These are the equation for 

 the breaking wave height based on reference wave data (Equation 9), a depth- 

 limited breaking criterion (Equation 14), and a wave refraction equation 

 (Equation 16) . 



62 



