(a) For monochromatic waves, this example has a value of 



tan 9 _ 0^5 _ q 7 



-y/H./L yrT7W(T756*12 ) 



From Figure 7-44 (riprap is used for a conservative example) 



1 



therefore 



and 



R 



= H^ (I) = 1.7 m (1.65) = 2.805 m (9.2 ft) 



I = °:^ = 0.178 

 R 2.805 m 



From equation (7-18) 



C = 0.51 - 0.11 (V\= 0.51 - 0.11(0.57) = 0.447 

 and from equation (7-17) 



so 



K^ = C(l - F/R) = 0.447 (1- 0.178) = 0.37 

 To 



lij, = K^q(H.) = 0.37 (1.7 m) = 0.63 m (2.1 ft) 



(b) For irregular wave conditions: in Figure 7-40 the case with F/R = 

 0.178 and B/h = 0.57 shows Y^^ = 0.25 , which is 32 percent smaller than 

 for the case with monochromatic waves (a). 



(c) Find the influence of structure height on wave transmission. Calcula- 

 tions shown in (a) and (b) above are repeated for a number of structure 

 elevations and results presented in Figure 7-49. This figure shows, for 

 example, that the structue would require the following height to produce a 

 transmitted significant wave height of 0.45 m (1.5 ft): 



Condition Structure Height 



Monochromatic waves 4.2 m (13.8 ft) 



Irregular waves 3.4 m (12.1 ft) 



*************************************** 



d. Wave Transmission for Permeable Breakwaters . Wave transmission for 

 permeable breakwaters can occur due to transmission by overtopping and trans- 

 mission through the structure, where the transmission coefficient, K.^ , is 

 given by 



^T=4 



^\o -^ ^^Tt (^-19> 



7-80 



