recent years has it been possible to quantify this property. Quantification 

 of energy dissipation by a reef is the property that justified consideration 

 of rubble-mound construction since both wave reflection and transmission are 

 usually undesirable. The basic conservation of energy relation for rubble 

 structures can be written as follows: 



K^ + K 2 + dissipation = 1.0 

 t r r 



(15) 



where dissipation in Equation 15 refers to the fraction of the incident wave 

 energy dissipated by the structure. 



39. The following regression equation will provide an accurate estimate 

 of wave reflection from a reef breakwater: 



K = exp 



V,L / + 4^ + S^V C a(t 



VI _£ \ c/ \ mo 



(16) 



where 



C = -6.774 

 C 2 = -0.293 

 C = -0.0860 



C. = +0.0833 



4 



Equation 16 explains about 99 percent of the variance in K for the 204 

 tests considered. The dependent variables and the signs of their coefficients 

 are consistent with current understanding of wave reflection. All the depen- 

 dent variables in Equation 16 affect reflection in a monotonic manner such 



that, other factors being equal, K increases as d /L decreases, h /d 

 j r sp cs 



increases, A /h decreases, and F/H increases. However, some care 

 t c mo 



should be exercised in using Equation 16; for example, reflection will in- 

 crease with increasing crest height only until the crest height approaches the 



limit of wave runup which for a reef would be F/H > 1.5 . Since all terms 



mo ~ 



in Equation 16 are negative for submerged reefs, the equation approaches the 

 correct limiting value of K = for decreasing structure height. On the 

 other hand, Equation 16 was fit to a data set where reflection was strongly 

 correlated to height of the reef which suggests that the equation might not be 

 satisfactory for reefs with crest heights above the limit of runup. This 



38 



