cases be compared to the user cost through the alternate route, for definition 

 of project benefits. Whatever economic philosophy or administrative policy is 

 applied, an estimate of tangible economic benefits must be made. This esti- 

 mate, either with the "user cost with project" or with the benefits them- 

 selves, can be applied in the manner of Figure 15 to optimize the major fea- 

 tures of the project. 



84. The idealized nature of Figure 15 is useful to illustrate the 

 concept of cost-effective optimization, but it is misleading in its impli- 

 cation that a set of alternatives will follow such a smooth comparison of 

 costs and benefits. A typical set of plans could not, in most cases, be 

 ordered by both increasing benefits and first cost. Neither is it the case 

 that increasing first cost always means reduced maintenance. The two types 

 of design criteria — functional performance and structural integrity--are es- 

 sentially independent of each other, and both have an effect on first cost. 

 Practical applications require that an ensemble of alternatives be compared 

 without reference to the order of their benefits, first cost, and maintenance 

 cost. A systematic approach to criteria development as a means of initially 

 identifying alternatives is important in this respect. An alternative is thus 

 known in the optimization process by its governing design criteria rather than 

 its resultant physical features. 



A Practical Approach 



85. The analytical and practical aspects of rubble-mound breakwater 

 design have now been reviewed. The discussion above concerning the principles 

 governing optimization indicates that the first cost, maintenance cost, and 

 user cost with project must be estimated for each plan in a set of alterna- 

 tives. The total costs with project need to range at close intervals from 

 well below to well above the unknown minimum for reliable identification of 

 the optimum alternative. A procedure is proposed below that accomplishes this 

 optimization exercise using information commonly available and already incor- 

 porated in most coastal engineering planning and design efforts. Potential 

 future refinements are mentioned where appropriate. 



Step 1 — define site conditions 



86. The physical conditions and other constraints affecting the design 

 of a rubble-mound breakwater, such as water level, tidal currents, foundation 



57 



