PART V: DESIGN PROCEDURES 



66. This part recommends a procedure for designing detached breakwaters 

 for shore protection and beach stabilization. There are three major steps in 

 the procedure. The first step is the initial desk-top design, which uses the 

 material presented in Part IV in conjunction with experience with the local 

 coast and general scientific judgment. The second step is to refine the de- 

 sign using either physical or numerical model tests, or both. Finally, field 

 tests may be performed to verify and adjust the design. The scope and scale 

 of the project will influence the degree to which each of these steps is 

 utilized. 



Initial Design 



67. The first step in designing a detached breakwater project is to 

 select the proper design conditions. The average range of wave-climate and 

 sediment-transport conditions at the project site, as well as the extreme con- 

 ditions, will control the eventual stable beach planform. The breakwater 

 configuration must be based on a number of design conditions, including 



(a) extreme storms, (b) average seasonal patterns, (c) periods of unusual 

 quiescence, and (d) the factors controlling the bulk of sediment transport. 

 Selection of design conditions is perhaps the most difficult and critical task 

 in designing structures for beach erosion control. Although a number of years 

 of directional wave data are needed to properly select the design conditions, 

 such data are rarely available. Usually the design conditions must be assumed 

 based on hindcast climatology, LEO, and the historic shoreline response. A 

 coastal geology study of the historic nearshore condition can reveal much 

 about the seasonality, extremes, and long-term evolution of the project site. 

 Aerial photography, historic maps, surveys and sediment sampling programs, and 

 subsurface data may be used to provide information on bar formation and migra- 

 tion, seasonal and storm profiles, shoreline response to existing structures, 

 and variations in littoral transport. Most of the following design conditions 

 discussed will be those associated with the average sediment transport 

 climate. 

 Project length 



68. Determine the length of shoreline to be protected. Neighboring 



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