to choose a design wave height yielding the optimum combination of first and 

 maintenance costs. A structure designed to resist waves of a moderate storm, 

 but which may suffer damage without complete destruction during a severe storm 

 may have a lower annual cost than one designed to be completely stable for 

 larger waves. 



H/H 



D=0 



is a function 



Table 7-9 shows the results of damage tests where 

 of the percent damage D for various armor units. H is the wave height 

 corresponding to damage D . Yij^Q is the design wave height corresponding 

 to 0- to 5-percent damage, generally referred to as no-damage condition. 



Table 7-9. ^/Hn_/i as a function of cover-layer damage and type of armor 



unit. 



Breakwater trunk, n = 2, random placed armor units, nonbreaking waves, and minor overtopping 

 conditions. 



2 



Values in italics are interpolated or extrapolated. 



3 



CAUTION : Tests did not include possible effects of unit breakage. Waves exceeding the design wave 



height conditions by more than 10 percent may result in considerably more damage than the values 



tabulated. 



The percent damage is based on the volume of armor units displaced from 

 the breakwater zone of active armor unit removal for a specific wave height. 

 This zone, as defined by Jackson (1968a), extends from the middle of the 

 breakwater crest down the seaward face to a depth equivalent to one zero- 

 damage wave height H^^^ below the still-water level. Once damage occurred, 

 testing was continued for the specified wave condition until slope equilibrium 

 was established or armor unit displacement ceased. Various recent laboratory 

 tests on dolosse have indicated that once design wave conditions (i.e., zero- 

 damage) are exceeded, damage progresses at a much greater rate than indicated 



7-211 



