The beach planform behind the middle breakwater is asymmetric, being 

 sheltered and sand-deprived on the left side and more open to wave energy on 

 the right side. Shoreline recession is more severe between the left andmiddle 

 breakwaters than between the middle and right breakwaters because diffraction 

 in stronger. For the -10-deg case, where sand tended to move from right to 

 left in the figure, substantial accretion resulted from blockage (groin 

 effect) by the middle salient. (In all examples, a "pinned beach" condition 

 was applied on the lateral boundaries, allowing sand to freely enter and leave 

 the modeled area.) 

 Variable Transmission Breakwater 



Detached breakwaters with variable transmission properties alongshore can 

 be represented by contiguous sections having different transmission coeffi- 

 cients. The configuration shown in Fig. 6 illustrates calculated shoreline 

 change produced by two semi -infinite detached breakwater segments with trans- 

 mission coefficient K T1 connected by a segment with transmission coefficient 

 K T2 . This situation mimics the central area of a very long breakwater which 

 might have experienced damage, altering its transmission properties. The 

 breakwater was located 100 m from the initially straight shoreline, and the 

 offshore wave conditions were H = 1.0 m and T = 6.0 sec, with the wave crests 

 arriving parallel to the breakwaters. The simulation time was 120 hr. 



Figure 6 shows that sand was transported away from the beach behind 

 breakwater sections with greater transmission and deposited behind areas 

 protected by breakwater section(s) with less transmission. The shoreline 

 change was delicately controlled by the opposing sand transporting mechanisms 

 of diffraction and transmission, and became more sinuous with increasing 

 difference in transmission coefficients. A double salient tended to form, 

 which is a possible shoreline response behind detached breakwaters and depends 

 on the ratio of distance between the breakwater and initial shoreline and the 

 ratio of structure length to wavelength. Perlin (1979) obtained double 

 salients in simulations neglecting transmission, and a subaqueous double 

 salient was generated by a detached breakwater in the physical model experi- 

 ment performed by Mimura et al . (1983). 



The example calculations demonstrated that GENESIS produces reasonable 

 trends of shoreline change for general combinations of wave transmission, 



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