APPENDIX B: COMPUTER PROGRAM BWCOMP 

 Comparison of Breakwater Volumes and Costs 



Program purpose 



1 . The program BWCOMP calculates breakwater volumes and costs demon- 

 strating the effect of varying breakwater slopes on wave transmission, the 

 choice of armor size and shape, and overall volume and cost. 



Background 



2. Systematic comparison of the relative cost of rubble-mound break- 

 waters designed with varying combinations of slope is tedious and awkward to 

 present in project reports, yet it must be accomplished to assure that a cost- 

 effective cross section is chosen. Wave transmission by overtopping during a 

 given wave condition is a function of a breakwater's seaward slope, its crest 

 elevation and width, and its surface roughness. A breakwater's stability is a 

 function of its seaward slope, its leeward slope, the size and shape of its 

 armor units, and other factors which affect the overall cost to a lesser de- 

 gree. The cost of armor units varies with size and shape. The problem of 

 cost comparison is further complicated by the interrelation of most of these 

 factors. 



3. The program BWCOMP was designed to make the task of comparing varia- 

 tions of these factors easier to accomplish and present. The following sim- 

 plifying assumptions make the program economical to use: 



a. Wave transmission by permeation through the structure is typi- 

 cally much smaller than transmission by overtopping and can be 

 neglected for this comparative analysis. 



b. The unit price ($ per unit volume or unit weight) and availabil- 

 ity of primary armor units tend to be most critical to the over- 

 all breakwater cost and constructibility, as compared to unit 

 price variations and availability of secondary armor, under- 

 layers, filter material, or core material. A single average 

 unit price can therefore be derived, for the purposes of this 

 comparative analysis, to include all materials except the pri- 

 mary armor. 



c. Most rubble-mound breakwaters intended primarily as wave bar- 

 riers for harbors or ports must be designed for some overtopping 

 during extreme events, with primary armor extending down the 

 leeward slope below the water line. Final designs of rubble- 

 mound breakwaters may have complex features in detail, but the 

 above assumptions allow adoption of a standard parameterized 

 cross section, as shown in Figure 17 of the main text. A 



B1 



