The recommended value of S* = 4 and Figures 5 and A-3 were used to pre- 

 dict nearshore wave heights. Predicted and observed wave heights are similar 

 for most of the profile (Fig. 9), with the observed wave height in the shal- 

 lowest water higher than predicted. 



3.0 



2.0 



(m) 



1.0 - 



(m) 



5.0 - 



H = 1.66 m 

 T s =4.52 s 

 a =50° 



/ 



Predicted 



Observed 



^. 



10.0 



Figure 9, 



Observed and predicted wave height at the 

 FRF, 13 September 1978. 



VI. EXAMPLE PROBLEM (USING NEARSHORE WAVE HEIGHT PREDICTION TECHNIQUES) 



GIVEN : A plane bottom slope of 1 on 100 and the input deepwater wave condi- 

 tions in Figure 10. 



FIND : The nearshore significant wave height for water depths between 0.5 and 

 6.0 meters for waves coming from each of the three deepwater wave directions. 



SOLUTION : Nearshore conditions are estimated assuming S* = 4 and the deep- 

 water wave directions (directions 1, 2, and 3) have absolute wave angles of 

 60°, 0°, and 60° with respect to the shoreline. Table 4 summarizes nearshore 

 wave predictions for waves from deepwater direction 3; Figure 11 gives wave 

 predictions from all directions. 



CONCLUSIONS : Results show that the local significant wave height is primarily 

 controlled by depth-limited breaking in 3.0 meters of water or less. In this 

 example, wave direction, refraction effects, and wave period are relatively 

 unimportant input parameters. The lack of influence of these parameters can 

 be seen by examining the predicted nearshore wave heights for directions 1 

 and 2. The deepwater wave directions differ by 60°, but the deepwater angle 

 has almost no effect on the predicted nearshore wave height in water depths 

 of 6.0 meters or less. 



The above example suggests that knowing the total water depth at the point 

 of interest is crucial when designing for extreme wave conditions. 



25 



