The five beach response planforms used in this classification scheme are as 

 follows: 



a. PERMANENT TOMBOLOS - Very little wave energy reaches the 

 shore and the beach is stable with little transport along the shore. 



b. PERIODIC TOMBOLOS - One or more of the breakwater segments are 

 periodically backed by tombolos with a periodic trapping of littoral 

 material followed by a release of a "slug" of sediment to the downdrift 

 shoreline. 



c. WELL-DEVELOPED SALIENTS - These planforms occur when some- 

 what higher wave energy reaches the lee of the structures and they are 

 characterized by a balanced sediment budget. Longshore moving 

 material enters and leaves the project at approximately the same rate. 



d. SUBDUED SALIENTS - In this case, the shoreline response is not as 

 pronounced, and the amplitude of the salient is of lower relief. 



e. NO SINUOSITY - High wave energy reaches the beach in this case 

 resulting in little if any shoreline response. 



Ahrens and Cox (1990) developed an empirical expression for a beach 

 response index based on the data from the seven offshore breakwater projects 

 presented in Pope and Dean (1986). This index is based on the ratio of the 

 length of the breakwater L s to the offshore distance of the breakwater X. The 

 values of this index for the five beach response classifications of Pope and 

 Dean (1986) are shown in Table A4. 



For the project area, various combinations of breakwater lengths and 

 offshore distances, along with the corresponding beach response index, were 

 evaluated as shown in Table A5. 



In order to maximize the protection to the project area shoreline and 

 maintain the longshore transport rate along the shoreline, the desired planform 

 ranged from subdued salients to well-developed salients. To achieve this 

 planform, the combination of a breakwater length of 100 ft and offshore 

 distance of 133 ft was selected. 



Breakwater segmentation 



A primary area of concern for the project area was the magnitude of 

 diffracted waves in the lee of the gaps. Waves will enter the breakwater gaps 

 and diffract behind the structures and toward the shoreline. Upon reaching 

 the shoreline, sufficient beach width and berm height are required to dissipate 

 this wave energy prior to its reaching the bank toe. If the existing beach 

 width and height are not sufficient to dissipate the wave energy, the options 

 are to design the breakwaters to further decrease the wave energy propagating 



Appendix A Case Design Example of Detached Breakwater 



A9 



