non-diffracting jetty. The implication of this boundary condition is that no 

 sand can move into the modeled reach from the north. Two other constraints 

 were imposed inside the modeled reach. These were the Huntington Beach Pier 

 and the sea cliffs located between the proposed ocean entrance at Bolsa Chica 

 and the Huntington Beach Pier. The Huntington Beach Pier was simulated as a 

 permeable groin (Hanson 1988, 1989; Gravens and Kraus 1989). The perme- 

 ability factor was determined during the model calibration. The sea cliffs 

 along the Huntington Mesa were simulated as a seawall. This boundary condi- 

 tion prohibits the shoreline from eroding beyond the present position of the 

 cliffs. 



In all the design alternative simulations, the 1983 surveyed shoreline 

 position was used as the initial shoreline. The design alternative simula- 

 tions were performed for 5- and 10-year prediction periods using the same 3- 

 year-long time history of wave conditions as employed in the calibration, 

 repeated as necessary. Calculations were also performed in which the wave 

 input were varied to establish a range of potential shoreline changes, in 

 recognition of large variability in the incident wave climate (Gravens 1988, 

 Gravens 1990). In the design alternative simulations, sand transport into the 

 proposed entrance channel (between the jetties) was permitted but transport 

 out was not. Thus, the ocean entrance channel was modeled as a sediment sink. 



COMPREHENSIVE SHORELINE RESPONSE 



The comprehensive shoreline response modeling consisted of repeating the 

 analysis of the preliminary shoreline response task, except that input wave 

 conditions were derived from the hindcast wave estimates at stations located 

 near the lateral boundaries of the modeled shoreline reach. This allowed 

 systematic variations in the incident waves (wave height and wave angle 

 variations along the shore) to be accounted for in the wave transformation 

 model RCPWAVE (Gravens 1990). The hindcast wave estimates were transformed 

 from the hindcast stations to the offshore boundary of the RCPWAVE grid as 

 illustrated in Figure 2. This transformation included the shadowing effect of 

 Point Fermin at hindcast Station 14 and the local contour orientations at both 

 of the hindcast Stations. RCPWAVE simulations were then performed, and the 

 calculated wave height and angle gradients were imposed as offshore boundary 

 conditions within the model. 



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