X -- 



Figure 2-64. Definition of wave reflection terms. 



Based on a compilation of measurements from several sources, Seelig and Ahrens 

 (1981) developed the curves in Figure 2-65. These curves can be used to 

 obtain a high estimate of the reflection coefficient for smooth slopes, sand 

 beaches, and rubble-mound breakwaters (curves A, B, and C, respectively). The 

 curves show that the wave reflection coefficient decreases as either the wave 

 steepness increases or as the slope angle 6 decreases. 



*************** EXAMPLE PROBLEM 12*************** 



GIVEN : An incident wave with period T = 10 seconds and a wave height Rj^ = 2 

 meters (6.56 feet) impinges on a slope. 



FIND: 



(a) The height of the wave reflected from an impermeable slope with cot9 = 

 5.0. 



(b) Compare the reflection coefficient obtained in (a) above with that 

 obtained for a beach with cotG =50. 



SOLUTION: Calculate 



(a) 



gT2 9.8(100) 



L = - — = ^^ = 156 m (512 ft) 



o 2iT 2ir 



and from equation (2-86) 



K = 



1.0 



= 1.77 



5.0 V 2/156 



The reflection coefficient from curve A for plane slopes in Figure 2-65 is 

 X = 0.29; therefore, the reflected wave height is H^ = 0.29(2) = 0.58 meter 

 (1.90 feet). 



(b) For a 1 on 50 sloped beach. 



C = 



1.0 



50.0 yfznse 



= 0.18 



2-117 



