h(ft) 



O 



I- 



Figure 7-49 . 



Influence of structure height on wave transmission for Example 

 Problem 13. 



where 



K„ is the coefficient for wave transmission through the breakwater. 



The wave transmission through the structure, K , is a complex function 

 of the wave conditions; structure width, size, permeability, and location of 

 various layers of material; structure height; and water depth. Very low 

 steepness waves, such as the astronomical tides, may transmit totally through 

 the breakwater (K,^ « 1.0) , while wind waves are effectively damped. 

 Locally generated storm waves with high steepness may be associated with low 

 transmission coefficients (Fig. 7-50), which helps explain the popularity of 

 permeable breakwaters at many coastal sites. 



Note, however, that when transmission by overtopping occurs, the opposite 

 trend is present: the transmission coefficient increases as incident wave 

 height increases, all other factors being fixed. Figure 7-51, for example, 

 shows the case of wave transmission for a breakwater armored with tribars. 

 K initially declines, then rapidly increases as transmission by over- 

 topping begins. The large transmission coefficients for this example are in 

 part due to the high porosity of the tribar armor. 



7-81 



