w 2 



(n 0.2- 



0.6 0.9 



TIME (et/W a ) 



Figure 34. Bypassing sand transport rate at the downdrift end 

 of a groin x = W as a function of time 



Shoreline Change at a Detached Breakwater 



74. A detached breakwater reduces the wave height behind it and pro- 

 duces a circular wave pattern at each tip, thus decreasing the longshore sand 

 transport rate. The actual effects are quite complex to describe and involve 

 diffraction and the current field resulting from spatial changes in wave 

 height and direction. However, it is possible to find an analytical solution 

 if the situation is idealized. 



75. It is assumed that the incident breaking wave crests are parallel 

 to the x-axis and to the detached breakwater. When the waves reach the break- 

 water, they are assumed to be diffracted at a constant angle behind the break- 

 water (shadowed region) and remain parallel to the x-axis outside of the 

 breakwater (the illuminated region). The diffraction behind the breakwater is 

 symmetric about the center of the breakwater and, accordingly, only half of 

 the problem domain needs to be considered. In Figure 35, a definition sketch 

 is shown. 



55 



