breakwater failure are minimized by the tendency for this type of structure 

 not to fail catastrophically . Catastrophic failure of flood control struc- 

 tures (dams and levees) causes tremendous adverse consequences for the prop- 

 erty and people in their flood plains, often including loss of life. The 

 costs of these consequences can easily exceed the order of magnitude of the 

 construction costs for the flood protection. This comparison illustrates 

 that, in comparison to some other civil engineering works, a certain small 

 risk of failure for rubble-mound breakwaters can be tolerated. 



6. Federal public works agencies in the United States have the statu- 

 tory constraint for project authorization that the tangible benefits realized 

 by the proposed plan must exceed all the life-cycle costs. This constraint 

 has been further defined to apply to the incremental benefits and costs of 

 each major feature of a proposed project. A rubble-mound breakwater built as 

 a part of a federally funded project must "carry its own weight" in terms of 

 its incremental net benefits. Recent administrative policies have provided 

 additional restrictive criteria for federal financing of public works projects 

 by requiring cost sharing with regional or local governments. These policies 

 force planners to carefully consider the f inanceability of a project as well 

 as its overall economic feasibility. Local sponsors of federally funded navi- 

 gation projects commonly have severe limits on what costs they can share. A 

 proposed breakwater project may be theoretically justified by a wide margin, 

 but if it is not affordable it will not be built. Conversely, a sponsor may 

 have the luxury of ample funding sources for cost sharing, but if a breakwater 

 plan does not achieve enough incremental benefits, federal participation will 

 not be possible. It is therefore critical that rubble-mound breakwaters be 

 designed to provide the optimum trade-off between life-cycle costs and incre- 

 mental benefits. This paper will deal with methods of formulating such an op- 

 timum plan without extending planning schedules and budgets beyond reason. A 

 commitment, both in time and money, is necessary, however, to address enough 

 key questions for systematic optimization to be possible. 



Organization of the Report 



7. This introduction will be followed by a review of design principles 

 for structural stability, including some of the many practical considerations 

 involved in rubble-mound breakwater design. Current references offering more 



