breaking wave parameter it equal to 0.78, this wave would break in a depth 

 of water of about 3.8 ft. With the existing beach berm at +2.5 ft mlw and 

 the design storm tide at +6.0 ft mlw, these waves would break directly on the 

 bank toe and cause significant erosion. 



In lieu of reducing the diffracted design wave height by narrowing the 

 breakwater gap width, beach fill placement was selected to provide the desired 

 protection for the bank area. The beach fill plan consisted of raising the 

 height of the existing berm to +6.0 ft mlw for a width of 30 ft from the toe 

 of the existing bank and then sloping 1H on 8V to the existing bottom. 



With the storm berm in place at a height of +6.0 ft mlw, wave heights 

 near the toe of the bank would be depth-limited to less than 1 ft during the 

 50-yr storm analyzed for functional performance (at the sponsor's request). 

 Following its placement, the beach fill would be expected to evolve to a stable 

 planform with salients forming behind each breakwater and embayments 

 opposite each gap. As a result of this process, the mean high water line 

 (mhwl) behind the breakwaters would advance bayward and the mhwl opposite 

 the gaps would recede shoreward. Analysis of the diffracted wave patterns in 

 the area and the performance of numerous other offshore breakwater 

 configurations indicate that recession of the mhwl opposite the gaps would be 

 on the order of 15-20 ft. 



During the evolution of the shoreline, the slope of the beach fill would be 

 expected to evolve to a more natural and milder slope. Analysis of the profiles 

 in the area indicates that this slope should be on the order of IV on 10H to 

 IV on 15H. 



Opposite the gaps, the recession of the mhwl and the slope changes were 

 used to determine the wave heights during the 50-yr storm event. 

 Table A6 indicates the depth-limited wave heights during this 

 event relative to the bayward distance from the toe of the 

 bank. These wave heights assume a worst case situation 

 where the entire profile opposite the gap evolves to the milder 

 slope and the horizontal berm ( at +6.0 ft mlw) is 

 substantially decreased in width. 



Since the protection of the bank toe depends on the 

 performance of the beach berm during design storm events, a 

 profile response model was used to evaluate this performance. 

 This model, developed by Kriebel and Dean (1985), calculates 

 beach profile evolution due to storm events, and includes the 

 effects of both water level rise and waves. The initial profile 

 used in the simulation is the proposed beach fill configuration 

 with the assumed equilibrium beach slope. A worst case 

 scenario was evaluated with the model for the beach and shoreline area 

 opposite the gaps by using the storm wave conditions prior to reduction by the 

 offshore breakwaters. The results of this evaluation indicated that even in the 



Table A6 



Depth-Limited Wave 

 Heights Opposite 

 Gaps 



Bayward 

 Distance From 

 Bank Toe (ft) 



Wave Height 

 (ft) 



O 



< 1.0 



10 



2.0 



20 



2.5 



30 



3.0 



Appendix A Case Design Example of Detached Breakwater 



A11 



