project coast, extending from the Anaheim Bay east jetty downcoast to the 

 mouth of the Santa Ana River. This task is termed preliminary because it 

 estimates the range of potential impacts of a new entrance on adjacent beaches 

 using the best wave data available at the time of the study. These prelimi- 

 nary estimates are of sufficient accuracy to determine the general range of 

 impact. The wave hindcasting task was a 20 -year numerical wave hindcast 

 providing directional wave data at the Bolsa Chica project site for use in the 

 comprehensive modeling task. The comprehensive shoreline response modeling 

 task was similar to the preliminary modeling with the exception that hindcast 

 waves were used as input to the shoreline response numerical model. 



Methodology . The shoreline response model used in the Bolsa Chica 

 studies is termed a "one -line" model. It assumes that the long-term planform 

 shape of an open- ocean sandy coast is controlled by the incident waves and the 

 longshore current they produce. Although it is recognized that other types of 

 currents, as well as water level and wind also play a role in shoreline 

 evolution, these processes are presumed to be secondary in the long term. 

 Also, cross -shore transport is neglected under the assumption that the beach 

 profile maintains an equilibrium form. Coastal improvements such as beach 

 fills, jetties, breakwaters, and groins can be simulated in the numerical 

 model. A complete description of this shoreline model is given by Hanson 

 (1987) and Hanson and Kraus (1989). 



The shoreline response numerical model: (a) takes an input specification 

 for wave height, wave period, and wave direction at the seaward boundary; (b) 

 refracts, diffracts, and shoals the waves over specified bathymetry to the 

 break point; (c) calculates local longshore sediment transport rates at each 

 longshore grid point; (d) determines the volume of sediment entering and 

 leaving each shoreline grid cell; (e) updates the shoreline position based on 

 net sand movement in or out of the cell; and (f) repeats the process with a 

 new input wave condition at the boundary. For this study the offshore wave 

 condition was updated at six-hour intervals for period of up to ten years. 



Before the model can be applied to a specific site, it is necessary to 

 supply the model with accurate nearshore bathymetry and to calibrate the model 

 using historical shoreline movement data and representative wave climates for 

 the region. Calibration consists of: (a) starting the model with a known 



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