Model Testing . The physical model, as depicted on Figure 2, was construc- 

 ted at a scale of l-to-75. It reproduces 8,000 ft of the shoreline (110 ft in 

 the model), and covers an area of approximately 2.8 sq mi (14,000 sq ft in the 

 model). The model reproduces the Bolsa Chica bathymetry out to the 30 ft 

 depth contour, and wave conditions are simulated using unidirectional ir- 

 regular waves. The criteria used for allowable wave heights in the interior 

 channels and basins were specified as 1 ft for the 1-year design event, and 

 1.5 ft for the 20-year design event. The first series of tests conducted 

 resulted in design modifications to the navigable entrance system that met the 

 wave penetration criteria. 



Completed results from the physical modeling task were not available at 

 the writing of this paper, but they are given in Bottin and Acuff (in prep.). 



INLET STABILITY ANALYSIS 



An analysis was performed to examine the stability of both the non-navig- 

 able and navigable ocean entrance channel alternatives being proposed for 

 Bolsa Chica. Tidal prisms were calculated from numerical modeling simulations 

 of tidal circulation within the proposed configurations for both alternatives. 

 These values were used to apply the O'Brien (1931) criterion for equilibrium 

 cross -sectional channel area. 



The results indicated that the non-navigable entrance channel, as present- 

 ly designed with training jetties terminating at the high water mark, appears 

 to be larger than necessary to be maintained by the calculated tidal prism, 

 and the entrance would be expected to decrease to a smaller cross-section. 

 This would not represent a problem unless subsequent analysis of the tidal 

 circulation in the bay indicates a reduced entrance throat area somehow 

 degrades the circulation within the bay and decreases the water exchange 

 between the bay and ocean. Greater concern was expressed about the ability of 

 the channel to remain open under the action of littoral processes without the 

 protection of a dual jetty system extending into the surf zone at least beyond 

 the mean lower low water line. The possibility that the presently designed 

 non-navigable entrance may close periodically or may require routine mainten- 

 ance dredging should be a consideration in evaluation of this alternative. 



The proposed navigable ocean entrance system, as designed, cannot be 

 classed as a tidal inlet in equilibrium because the design is not based on 



36 



