VI. EXAMPLE OF ESTIMATING WAVE TRANSMISSION COEFFICIENTS 

 **************** EXAMPLE PROBLEM **************** 

 GIVEN : T = 7.9 seconds 



dg = 3.56 meters 



Breakwater top width, B = 1.53 meters 



Breakwater seaward slope, tan 8 = 0.667 (1 on 1.5) 



FIND: The influence of incident wave height and structure height on the 

 transmission coefficient for the permeable breakwater shown in the upper 

 part of Figure 49 (change the structure height by varying the thickness of 

 horizontal layer 1) . Also, compare the predicted transmitted wave heights 

 to heights for a similar smooth impermeable structure (lower part of Fig. 49). 



SOLUTION : The computer program MADSEN (App . G) is used to predict wave 



transmission coefficients for the permeable structure and the program OVER 

 (App. F) is used to predict coefficients for the smooth impermeable break- 

 water. The transmission coefficient for the permeable structure decreases 

 as wave steepness increases, until overtopping occurs when the transmission 

 coefficient increases with steepness (Fig. 50). The transmission coefficient 

 decreases as structure height increases and the initiation of overtopping 

 occurs at a larger value of the incident wave height as the structure height 

 increases. The similar shaped smooth impermeable breakwater has larger 

 values of the transmission coefficient for the steeper waves examined (Fig. 

 50) because the runup is higher on the smooth structure. However, there is 

 no transmission for the impermeable structure for the small waves where the 

 runup does not reach the breakwater crest. The predicted transmitted wave 

 height as a function of breakwater crest height is given in Figure 51 for 

 two values of the incident wave height. 



Moteriai dsolm) Porosity 



Figure 49. 



Breakwater cross sections used in the example for estimating wave 

 transmission coefficients. 



60 



