where the empirical overtopping coefficient 

 relative breakwater crest width B increases; 



C gradually decreases as the 

 i.e. , 



C = 0.51 - 0.11 (^ 



< l< 

 n 



3.2 



(7-18) 



The case of monochromatic waves is shown in Figure 7-39 for selected structure 

 crest width-to-height ratios. 



In the case of irregular waves, runup elevation varies from one wave to 

 the next. Assuming waves and resulting runup have a Rayleigh distribution, 

 equation (7-17) can be integrated, with results shown in Figure 7-40 (note 

 that for random waves R is the significant runup determined from the 

 incident significant wave height H and period of peak energy density Tp ) . 

 It can be seen by comparing Figures 7-39 and 7-40 that monochromatic wave 

 conditions with a given height and period will usually have higher average 

 wave transmission coefficients than irregular waves with the given significant 

 wave height and period of peak energy density. This is because many of the 

 runups in an irregular condition are small. However, high structures 

 experience some transmission by overtopping due to the occasional large runup. 



The distribution of transmitted wave heights for irregular waves is given 

 in Figures 7-41 ( see Fig. 7-42 for correction factor) as a function of the 

 percentage of exceedance, p . The following examples illustrate the use of 

 these curves. 



*************** EXAMPLE PROBLEM 9*************** 



FIND: 



The ratio of the significant transmitted wave height to the incident 



significant wave height for an impermeable breakwater with 



and 



#= 0.1 

 n 



-T— = 0.6 (irregular waves) 

 S 



SOLUTION ; From Figure 7-40, the value is found to be 



V^= 0.13 

 s 

 so the transmitted significant wave height is 13 percent of the incident 

 significant height. 



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



*************** EXAMPLE PROBLEM 10*************** 

 FIND : 



(a) The percentage of time that wave transmission by overtopping occurs for 



7-67 



