longest region of shoreline erosion on the southeast side of the entrance 

 system was predicted. In these simulations, the alongshore width of the 

 erosion zone is on the order of 8400 ft and within this region the shoreline 

 is displaced about 60 ft landward. 



The simulations in which year 2 of the southern swell wave conditions 

 were used (Alternatives 3 and 4, simulation codes, PR01C and PR02C , not shown 

 in this paper; see Gravens (1990) resulted in the longest extent of shoreline 

 erosion on the northwest side of the entrance system. The predicted length of 

 the erosion zone is on the order of 11,000 ft, and the maximum eroded berm 

 width is about 180 ft. 



The simulations in which all of the available southern swell wave 

 conditions (year 1 and year 2) were used (shown in Figure 10), resulted in 

 less overall shoreline erosion. The results of these simulations represent 

 the best estimate of the expected shoreline evolution resulting from the 

 construction of the proposed ocean entrance system at Bolsa Chica Bay. The 

 results of the other simulations not shown in this paper (Gravens 1990) repre- 

 sent possible extremes about the baseline simulation given in Figure 10 and 

 will require that impact mitigation plans (sand bypassing and/or backpassing 

 at the entrance) be flexible. 



The previous model results and analysis were presented to the SLC, which 

 established the following two critera for the impact mitigation simulations: 



a. Only that sand which accumulates within 1500 ft of the 

 entrance jetties may be utilized for sand bypassing and/or 

 sand backpassing. No new sources of sand will be used for 

 impact mitigation sand management. 



b. A successful sand management plan will be one in which 

 shoreline change from the 1983 surveyed shoreline position 

 is accretive, or, if the without-pro ject alternative indi- 

 cates erosion, the sand management plan must indicate equal 

 or less erosion. 



Three different sand management plans were developed for the three 



different input wave data sets (the "A", "B" , and "C" type simulations as 



indicated in the simulation code, see Table 4). In general terms, the sand 



management plans require that infrastructure be put in place which will be 



capable of: 1) backpassing approximately 300,000 cu yd/year of sediment from 



shorelines adjacent to both sides of the entrance system to shorelines on the 



order of 1/2 to 1 mile away from the entrance, and 2) bypassing approximately 



83 



