"BWDAMAGE" has been developed which applies Equation 14 and the information 

 of Table 3 to estimate E{7oD/yr} , E{$D/yr} , and the repair interval by both 

 methods discussed above. This program has been documented in a CETN,* and it 

 is presented in Appendix D of this report. Once a repair interval and the as- 

 sociated extent of repairs have been estimated for an alternative, discounted 

 cash flow methods can be used to estimate the equivalent annual amount which 

 can be substituted for E{$D/yr} . The damage functions, as stated in Part 

 III, are currently the least reliable of the analytical tools available for 

 rubble-mound breakwater design and should be used with circumspection. 



Step 9 — tabulate and sum 

 costs for each alternative 



101. This is the final analytical step of the proposed procedure, fol- 

 lowed only by laboratory verification of the analytical predictions. The min- 

 imum sum of the three costs identifies the cost-effective optimum alternative, 

 as indicated in the following equation: 



The first cost must be transformed from a present worth value to an equivalent 

 annual amount E{$1^ /yr} by discounting- prior to the summation. Incremental 

 benefits E{$B/yr} can be estimated by subtracting E{$L'/yr} from 

 E{$L/yr}: 



iL)_ ^(^ 



Net benefits E{$Bj^g|./yr} can in turn be estimated by subtracting E{$1^ /yr} 

 and E{$D/yr} from E{$B/yr} as follows: 



kt - ./Ml Jil^^ 



1 - i^} 



This method of estimating benefits may not be appropriate for some projects, 

 however, as discussed at the beginning of Part V. 



* US Army Engineer Waterways Experiment Station, Coastal Engineering Research 

 Center, in preparation, "Estimation of Rubble-Mound Breakwater Expected 



Damages — Computer Program BWDAMAGE (MACE-18)," Coastal Engineering Technical 

 Note, Vicksburg, Miss. 



66 



