0.066 



0.064 



WAVE 062 

 STEEPNESS UU ° 



H/L 



0.060 



0.058 t" | 



T = 9 SEC 



H n = 3 FT 



2500 3500 4500 



JETTY SPACING, FT 



5500 



Figure 37. Effect of jetty spacing on wave steepness 

 (H/L = 0.057 for no jetties) 



3 ft (60-ft depth) and the condition of no jetties. The wave height increases 

 with increasing ebb current, as expected. Figure 36 shows the dependence of 

 wave amplification on wave period for a 2,500-ft jetty spacing. The wave 

 amplification increases with increasing wave period, since the longer the wave 

 period the sooner the wave interacts with the bottom and refracts and shoals. 

 Figure 37 shows the effect of jetty spacing on wave steepness for a 9-sec wave 

 with an incident wave height of 3 ft (60-ft depth). As expected, an increase 

 in jetty spacing causes a decrease in the wave steepness since it reduces the 

 ebb velocity. The decrease in wave steepness is not dramatic, however, since 

 the jetty spacing does not change the ebb currents very much, as seen in 

 Figures 38 and 39. 



103. The wave climate at a water depth of 60 ft is in terms of signif- 

 icant wave height. Significant wave height is an average of the one-third 

 highest waves of a given wave group. SAW determined that the controlling 

 factor in vessel operation is the highest wave in a wave group. Thus SAW 

 calculated the highest 1 percent wave for each spectrum represented by a 

 significant wave height. Using the wave propagation model, these waves were 

 then propagated to the ocean entrance channel. 



104. The limiting wave heights for the operation of the two classes of 

 split-hull dredge were determined by SAW based upon information from the 



78 



