worst case scenario for the 50-yr storm event, the storm berm would remain 

 with a width of on the order of 5 to 10 ft. The actual erosion of the storm 

 berm would be expected to be significantly less due to the reduction in the 

 storm wave energy as a result of wave diffraction through the gaps. 



Based on the preceding analyses, a gap width of 100 ft was selected for the 

 project area. 



Breakwater crest elevation 



In addition to diffracted wave energy through the breakwater gaps, wave 

 energy transmitted over the top of the structures was considered to maximize 

 the protection of the shoreline area. This analysis was conducted using a 

 wave transmission model developed by Ahrens (1987) capable of predicting 

 the amount of wave energy transmitted over and through both submerged and 

 non-submerged reef type breakwaters. Table A7 presents the results of this 

 analysis for various combinations of breakwater crest height and slope for 

 various return interval storms. During the 50-yr design storm, the wave 

 heights immediately behind the breakwaters are reduced to about 60 percent, 

 54 percent, and 46 percent of the incident height with breakwater crest 

 elevations of +4.0, +5.0, and +6.0 ft mlw, respectively. During the 25- 

 year event, these reductions are 55 percent, 46 percent, and 38 percent, 

 respectively. These transmitted waves then propagate shoreward where they 

 are further dissipated by the beach salients formed during the evolution of the 

 beach fill to an equilibrium planform and the storm berm. With the proposed 

 beach fill in place, a breakwater crest elevation of + 4.0 ft mlw was selected 

 to limit the transmitted design wave heights to about 4.0 ft (the same height as 

 the diffracted design wave opposite the gaps) which would then be dissipated 

 by the storm berm. 



Beachfill characteristics 



Seven beach profile lines were identified for sample collection. Four 

 1-1 iter samples of surface sediment were taken at locations along each profile 

 spaced equally between the foot of the bluff and a depth of -1.0 ft, mlw. The 

 four samples were then mixed into a composite sample for sieve analysis. 

 These data indicate that the native beach material ranges from fine to coarse 

 sands with a median grain size of about 0.6 mm. For optimum performance, 

 beachfill sources with similar grain size characteristics should be used. 



A12 



Summary of Breakwater and 

 Beachfill Design Components 



Based on the above analyses and evaluations, the recommended plan to 

 accomplish the objectives of stabilizing the existing beach and providing 



Appendix A Case Design Example of Detached Breakwater 



