to perform the required nearshore wave transformation. In this case, GENESIS 

 retrieves the nearshore wave characteristics (output from RCPWAVE) from a data 

 base and performs local refraction, diffraction, and shoaling calculations to 

 obtain a breaking wave height and angle at intervals alongshore. In either 

 case, once the breaking wave field along the modeled reach is available, 

 longshore sand transport rates are calculated and the shoreline positions 

 updated. 



GENESIS is primarily used to calculate long-term changes in shoreline 

 position caused by the alongshore movement of sand. Offshore transport of 

 sand caused by, for example, intense short-duration storm events, is not 

 modeled. However, estimates of shoreline changes resulting from these events 

 could be superimposed on the shoreline position calculated by GENESIS to 

 obtain a first approximation of the potential variation about the calculated 

 shoreline position. Calculations of short-term storm- induced beach change are 

 given by Kraus and Larson (1989) and Scheffner (1989). 



PRELIMINARY SHORELINE RESPONSE STUDY 



In the preliminary shoreline response study, the numerical model GENESIS 

 was calibrated for the period July 1963 to April 1970 and verified for the 

 period April 1970 to January 1983, for the project coast. The SIO wave gage 

 data set and the shoreline position data described above provided the primary 

 inputs to the model. Simulations of the potential shoreline responses to the 

 proposed inlet entrance system were then performed. This study was prelimi- 

 nary since the wave data were limited (3-years long), and the estimates were 

 of sufficient accuracy to determine only the general magnitude of impacts so 

 that conclusions could be reached regarding the ability to mitigate impacts to 

 a prescribed level. Six design alternatives, and several variations of the 

 general alternatives, were modeled using GENESIS. The intent of the simula- 

 tions was to estimate the shoreline impacts of the proposed Bolsa Chica 

 navigable ocean entrance system. A summary of the six modeled design alterna- 

 tives is given in Table 3. 



GENESIS was configured for application to the project coast. The model 

 reach extends from the east jetty of Anaheim Bay to the north jetty of the 

 Santa Ana River and has 270 200-ft wide alongshore calculation cells. The 

 southern boundary condition at the Santa Ana River was simulated as a short 



70 



