APPENDIX D: COMPUTER PROGRAM BWDAMAGE 



Estimation of Rubble-Mound Breakwater 

 Armor Layer Expected Damages 



Program purposes 



1 . The computer program BWDAMAGE estimates the expected annual damage 

 to a rubble-mound breakwater, both in cost and percentage of the armor layer 

 displaced. It also estimates the interval that repairs of a specified damage 

 level could be scheduled. This information is vital to breakwater optimiza- 

 tion analyses which require an estimate of expected repair costs to fully de- 

 fine the life cycle costs of the structure. 



Program capabilities 



2. The program assumes that the damage to a particular breakwater con- 

 figuration is primarily a function of the type of armor unit that has been 

 placed. The breakwater of interest has been designed to suffer a minimum dis- 

 placement (erosion) of the primary armor during a design event represented by 

 a significant wave height H., . The level of damage acceptable at this level 

 of incident wave energy is in current practice defined by the resolution of 

 scale model tests and is on the order of 1-5 percent. BWDAMAGE assumes that 

 the damage caused by more severe incident events represented by a significant 

 wave height H is predictable by a function of the following form: 



"s\ [2r("/V^^] 



f,D(^ 1= r.D(H^)e" . u ^ (P^^ 



where S is the "reserve stability factor." S^ 'is a relative measure of 

 r •' r 



the rate at which breakwaters built with a particular type of armor unit will 

 suffer damage with increasing wave heights. A higher S^, value implies a 

 higher rate of damage. The program applies the ^D(Hg = H^^) and S^ values 

 presented in Table 3 of the main text. The values in Table 3 were determined 

 with monochromatic scale model tests which made no account of rocking and the 

 probable associated armor unit breakage. The predictions using the above for- 

 mula should not be used in final design decisions without careful verification 

 in laboratory tests with irregular waves and attention to armor unit rocking. 

 The armor units in the program's library include quarrystone (rough, uniform), 

 quadripods, tribars, and dolosse. The program also allows input of an armor 

 unit title, %U{H^) , and S^, for any other type of unit. 



D1 



