2500 LB. TO 4500 LB. 

 ARMOR STONE 



g£gpea3e^Ps 2Q£ =gv*y?=sr^ 



6.0' 



34.5'- 



WOVEN PLASTIC FILTER CLOTH 



12" MIN. THICKNESS OF 

 BEDDING STONE (3" TO 8") 



Figure A3. Typical breakwater section 



area. As discussed in the Shore Protection Manual (1984), the shoreline 

 response resulting from the construction of an offshore breakwater is governed 

 by the resulting changes in the longshore sediment transport and the onshore- 

 offshore sediment transport in the vicinity of the breakwater. For obliquely 

 incident waves, the longshore transport rate in the lee of the structure will 

 initially decrease, causing deposition of some of the longshore drift. A beach 

 salient is formed, which will continue to grow until either the longshore rate 

 past the structure is reestablished or a tombolo (attachment of the salient to the 

 breakwater) is formed. 



For the project area, the objective was to reduce the wave energy reaching 

 the eroding shoreline to a level that would not cause erosion during storm 

 events. This objective was to be accomplished without creating any adverse 

 effects along the adjacent shoreline areas. Of the two shoreline responses, 

 salient formation was preferred so that the breakwaters would not become 

 attached to shore creating a barrier to littoral drift (i.e., tombolo formation). 

 Tombolo formation is prevented by allowing sufficient wave energy to enter 

 the protected region. 



Breakwater length versus distance offshore 



Pope and Dean (1986) investigated seven offshore breakwater projects in 

 the United States and concluded that the beach response in the lee of the 

 breakwaters is a direct result of the amount of wave energy reaching the 

 beach. A classification scheme was developed where the lowest wave energy 

 in the lee of the breakwaters results in tombolo formation and little or no 

 response of the shoreline occurs when high wave energy reaches the shoreline. 



A8 



Appendix A Case Design Example of Detached Breakwater 



