

Shoreline Position (m) 























30< 



> 



/ N 



25 













20 





i ' 



\ 



, i 



\ 





Hs 



0.2 





15 





A \ 

 1 \ \ 



' / A 





0.5 



- - 1.0 





10 





' / \ x 

 ' / \ x 









5 





/ / / \ \ \ 













-5 

 C 





• // \\ ^ 









— - ~ ^_^___~~ — ' - 





— *~- - 



i 



i i 



i i 



l 



) 150 300 



450 600 



750 



900 





Dis 



ance Alongshore (m) 







Figure 30. 



Influence of varying wave height on shoreline change behind a detached 

 breakwater (Hanson and Kraus 1 990) 



diffracted waves in the lee increases, thus prograding the salient towards the 

 structure. The salient progresses approximately linearly with the increase in 

 wave height, although the accumulated volume for the larger wave height is 

 approximately an order of magnitude larger than for the smallest wave height. 



Using the same structure as discussed above, the second test examined the 

 effects of increasing wave period on beach response. A 1-m offshore 

 significant wave height was used with a wave period varying from 3 to 5 sec. 

 The salient growth is shown to increase with increasing wave period 

 (Figure 31). The longer period waves have a greater shoaling coefficient, 

 which causes them to break further offshore, in turn resulting in a greater 

 breaker height. As discussed above, increasing the breaking wave height 

 advances the salient towards the structure. 



The third test series examined the effects of wave variability on 

 morphologic response (Figure 32). A 200-m-long breakwater located 200 m 

 offshore in the 2-m depth was used for the simulations. A 1-m wave height, 

 4-sec wave period, approaching the initial shoreline normally (0 deg) was used 

 for one of the wave climates; the other three simulations held two of these 

 parameters constant while the third was normally distributed as a percentage 

 of its mean value (see Figure 32). Results indicate that allowing the wave 

 period and wave height to vary has little effect on the observed shoreline 

 response. Variation of these parameters simply redistributes the wave energy 

 in time, without changing the total longshore wave energy flux. However, 

 increasing variability in the wave direction greatly progrades the 



Chapter 3 Tools for Prediction of Morphologic Response 



55 



