Step 9. Maintenance Cost : Assume all revetments annual 



maintenance cost at 1 percent of initial cost (Table 6) . 



Table 6. Comparative cost estimates. 



Revetment 



Capital 



recovery 



Maintenance 



Cost 



Type 



Factor 



Annual 



Annual 



Construction 



Annual 



Riprap 



0.08718 



$1,962 



$ 230 



$22,500 



$2,192 



Gabion mats 



0.08718 



1,186 



140 



13,600 



1,326 



Lok-Gard blocks 



0.08718 



1,752 



200 



20,100 



1,952 



Tire mats 



0.08718 



$1,090 



$ 130 



$12,500 



$1,220 



Step 10. Annual Cost (for 100 lineal feet) : Cost given in Table 6. 

 Assume 6 percent interest n = 20 (20-year design life). 



Capital recovery factor = 0.08718. 



With all the necessary information for the revetment 

 analysis computed, the completed matrix shows that the 

 car tire mat has the lowest annual cost and therefore, 

 would be recommended (Table 7) . 



Table 7. Analysis matrix for example problem. 



To reduce the length and enhance the clarity of the example problem, 

 the revetment type was selected as the only independent variable. How- 

 ever, in an actual design problem all independent variables could be 

 considered to evaluate their effect on the annual cost. Consideration 

 of all independent variables could make a matrix of 50 or 100 elements 

 which would be warranted if the initial revetment cost was substantial. 



19 



