152. The criteria lead to the following expression for the diffraction 

 coefficient K nT for transmissive breakwaters: 



K.r,T — 



Kj) ( 1 - Rrt ) 



h = o 



h 



(20) 



0n < 



in which R KT is the ratio of the smaller valued transmission coefficient to 

 the larger valued transmission coefficient for two adjacent breakwaters. 



153. Figure 13 shows a hypothetical example of shoreline change behind 

 a transmissive detached breakwater. The breakwater is 200 m long and located 

 250 m offshore. Incident waves with T = 6 sec and H = 1.5 m propagate with 

 the wave crests parallel to the initially straight shoreline, and the simula- 

 tion time is 180 hr. As expected, the seaward extent of the induced large 

 cusp (salient) decreases as wave transmission increases. Also, the salient 

 broadens slightly with increased transmission, and the eroded areas on either 

 side of the salient fill in. 



Shoreline position (m) 



100 200 300 400 



Distance alongshore (m) 



500 



Figure 13. Shoreline change as a function of transmission 



72 



