Optimization of Design and Costs 



One of the reasons that detached breakwaters have seen limited use in the 

 United States is their relatively high cost of construction. Federal public 

 works agencies in the United States have the constraint for project 

 authorization that the benefits realized by a proposed plan must exceed all life- 

 cycle costs (Smith 1986). This has been further defined to apply to 

 incremental benefits and costs of each major component of a proposed project; 

 therefore, it is critical that a breakwater be designed to provide the optimum 

 ratio between incremental benefits and life-cycle costs. Benefits achieved 

 through a public works project are the sum of the incremental decrease in that 

 level of costs directly attributable to the project's functional performance. For 

 federal participation in a project to be possible, maximum net benefits must 

 exceed the project costs. Figure 59 shows this benefit-cost comparison. 

 Generally, the design level associated with the maximum net benefits is 

 selected for project design. 



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ACTUAL BENEFITS ^ 





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Figure 59. Benefits and cost versus design level (from EM 1 1 10-2-2904) 



Smith (1986) presents guidance on the optimization of rubble-mound 

 breakwaters and provides a step-by-step procedure to identify an optimum 

 breakwater cross section in terms of two criteria: structural integrity and 

 functional performance. Functional performance is described as the 

 structure's effectiveness as a wave barrier, and for detached breakwaters, the 

 ability to develop and maintain the desired beach planform. Structural 



Chapter 5 Other Design Issues 



105 



