confirm this expectation. Since wave breaking was not considered, unit wave 

 amplitudes were used in the input to the model REFDIF. For simulating 

 effects of water level conditions during extreme storm events, a tidal datum 

 was specified in the model input. 



In applications where wave breaking is important, the model REFDIF 

 should be used in a nonlinear mode. The wave breaking scheme in REFDIF is 

 based on Kirby and Dalrymple's (1986a,b) dissipation scheme; that is. 



Df- 



KCJl-(yh/H)^) (A4) 



where 



Df = dissipation factor 



Ky = empirical constant determined by Dally et al. (1985) 



H = wave height 



h = water depth 



Wave breaking is initiated using the breaking index; that is, H > 0.78 h. If 

 wave height exceeds 0.78 h, the wave breaking scheme is activated and wave 

 amplitude is reduced based on Equation A4. 



Land boundaries such as coastlines and islands are modeled using the thin 

 film approach. Surface-piercing structures or other similar features may be 

 modeled as shoals with very shallow depth, less than 0.1 m (0.03 ft). Earlier 

 apphcations of REFDIF may be found in Kirby and Dalrymple (1986a,b) and 

 Dalrymple et al. (1984a,b). Recent Corps applications of REFDIF include the 

 Revere Beach, San Juan navigational channel. Kings Bay, Chignik and Sitka 

 Harbors, and Indian River Inlet, and Fire Island projects. 



Note that although REFDIF is a monochromatic wave model (i.e., it is a 

 model based on mass balance and founded on the mild-slope equation), it is 

 possible to consider transformation of spectral waves with this model. This 

 may be done by superposition of individual linear monochromatic waves. This 

 approach requires a large number of model runs to represent many frequency 

 and direction bands. Spectral representation becomes less important when 

 wave frequency and direction spectra are narrow. Coastal waves far from the 

 influence of wave energy growth mechanisms typically exhibit a narrow spec- 

 tral character, an indication that discrete frequency analysis may suffice for 

 engineering estimates. A spectral version of the REFDIF model presently in 

 development was not ready for this study. 



Appendix A Saco Bay Nearshore Wave Estimates 



A15 



