tends to prevent catastrophic failure, even in the event of underdesign. The 

 design parameters for rubble-mound breakwaters are rather inexact compared to 

 those of most rigid civil engineering structures; thus, conservative overde- 

 sign is quite common. 



4. Rubble-mound breakwaters can have a number of secondary purposes 

 that are related to their primary purpose as a wave barrier. A breakwater 

 protecting a harbor entrance and mooring area from wave attack might serve 

 to divert currents and longshore transport of sediments. Also, it could be 

 designed to provide access by people and equipment to the outer or deeper 

 portions of the harbor. A breakwater protecting port facilities where cargo 

 is being discharged and loaded might have these additional purposes and could 

 even serve as a foundation for the port facilities themselves. This paper 

 concentrates on considerations surrounding the wave barrier function. Fur- 

 thermore, the perspective of the Corps as a public works agency is maintained 

 since, in this case, the owners of the structure and the beneficiaries of its 

 protection are the same (i.e. the taxpayers). The discussion to follow could 

 also easily apply to a rubble-mound breakwater financed by private enterprise 

 for commercial purposes, since tangible public benefits can, in many in- 

 stances, be translated as profits. Many features of the planning and design 

 procedures discussed later in this report can be extrapolated to planning 



and design of facilities other than rubble-mound breakwaters. The emphasis 

 and most computational aspects will apply specifically to rubble-mound 

 breakwaters intended as wave barriers. 



The Need for Optimization 



5. The construction cost for rubble-mound breakwaters is usually on the 

 order of millions of dollars for smaller harbor or shore protection projects 

 and on the order of tens of millions of dollars for larger harbor or port 

 projects. The consequences of a dramatic structural failure include costs for 

 repair of the breakwater which may approach the order of magnitude of the 

 original construction costs due in part to expensive mobilization. Also, such 

 consequences may include costs from property damage and inconvenience to port 

 and harbor operations which occurred during the storm that damaged the break- 

 water. These latter costs would typically be of a lower order of magnitude 

 than the breakwater construction costs. All of these costs of rubble-mound 



