by the square of the nominal stone diameter rather than the area in the undamaged armor 

 profile. 



If the eroded area over the entire structure is used to compute S rather than 

 just the active region, the ratio of damage by the eroded volume method to that of the 

 damage index can be computed as per Comett (1995) 



s 



h 



2 sin6 ^ 



D% 





100 D^, 



H<h. 



(3.2) 



where 



ta = 



W, = 



K = 



h, = 



H = 



e = 



armor layer thickness 



crest width 



breakwater crest elevation above bottom 



water depth at toe 



design wave height 



seaside angle of armor slope relative to horizontal 



Equation 3.2 assumes the wave height is less than the depth at the toe. 

 Comett noted that the range of this ratio is 0.6 to 1.25 for typical rubble mounds. For 

 S/D% = 0.8, he notes that the zero-damage criteria of D = 5% corresponds to < 5 < 4. 

 This is quite a broad criterion. The damage index method appears to give a better 



37 



