78. The distance L is half the length of the detached breakwater. If 



Equations 81 and 82 are plotted, the following behavior will be noticed. When 



the breakwater is placed in front of the initially straight shoreline at time 



t = , erosion of the shoreline starts at points in line with the corners of 



the breakwater. Simultaneously, the shoreline grows to form a salient about 



the line of symmetry behind the breakwater. Because of the gradient of the 



shoreline outside the shadow of the breakwater, material is transported 



toward the breakwater in order to achieve a state of equilibrium with the 



waves. The shoreline behind the breakwater also approaches an equilibrium 



configuration which is parallel to the wave crests diffracted at the angle 



a , . The final shoreline will be inclined at an angle a , behind the 

 ol ol 



breakwater and be straight outside the breakwater. However, the straight 

 portion of the shoreline will at all times be displaced landward a small 

 distance, controlled by the volume of sand that has accumulated behind the 

 breakwater. Figure 36 illustrates the solution in dimensionless form for 



0.20- 







0.15- 



V 



i 0. 10 

 \ 0.08 

 \\ 0.06 



t . = M 



L 2 



0.10^ 



A\ 0.04 

 \\\ 0.02 





0.05- 







0.00- 







0.05- 



1 — — 1 



1 1 1 1 



-1 -0.5 0.5 1 1.5 2 



ALONGSHORE DISTANCE (x/U 



Figure 36. Initial shoreline evolution in the vicinity of a 

 shore-parallel detached breakwater (6 =0.5 , a, =0.4 rad , 



a o2 = 0) 



short elapsed times, and Figure 37 shows the features of the solution after a 



long elapsed time. The length of the salient behind the breakwater increases 



in time toward a maximum value of 



59 



