b. 1.90-Second Wave . 



(1) L/W = 1.43 (Experiments 70X- 10 and 71Y-10) . Although the 

 foreshore had some lateral variations, the inshore zones had greater 

 lateral variations, particularly in the development of the flat shelf in 

 the inshore in experiments 70X-10 and 71Y-10, the experiments with the 

 next highest value of L/W. 



In both experiments with L/W = 1.43, the slope of the foreshore and 

 position of the shoreline varied with range at any one time and with time 

 at any one range. The slope varied from 0.04 to 0.60 in experiment 70X-10 

 and from 0.08 to 0.56 in experiment 71Y-10. The shoreline position at any 

 one time varied up to 1.6 feet (48.8 centimeters) in experiment 70X-10 and 

 2.0 feet in experiment 71Y-10 (Fig. 40) (compared to up to 2.5 feet with 

 L/W = 1.03). The most important profile change in all of the experiments 

 with the 1.90-second wave was the development of the long flat shelf with- 

 in the inshore zone. In experiment 70X-10 the shelf development began at 

 15 hours along range 1 and at 95 hours along range 9, as indicated by the 

 initial upward movements of the -0.6-foot contour positions in Figure 41. 

 In experiment 71Y-10 (Fig. 41) the shelf development began at 210 hours 

 along range 1 and 110 hours along range 9. The 80-hour difference in 

 experiment 70X- 10 and the 100-hour difference in experiment 71Y-10 are 

 significant --that this variation occurred in both experiments in the 

 same tank and that the development started on one side in one experiment 

 and on the other side in the other experiment indicates that the varia- 

 tion was not due to a unique external influence or some misalinement in 

 the tank. 



The three dimensionality of the profile shape at the end of the ex- 

 periments is shown in Figure 42. The offshore zones are skewed seaward 

 along ranges 7 and 9 in both experiments, just as in experiment 72C-10. 



(2) L/W = 2.38 (Experiments 70X-06, 71Y-06, and 72D-06) . In 

 three experiments with a 1.90-second wave conducted in the narrower tank, 

 the profile shape usually had less lateral variation, as would be expected 

 from the higher value of L/W. 



In these experiments, lateral variations in slope and position oc- 

 curred on the foreshore. The foreshore slope varied from 0.10 to 0.36 

 in experiment 70X-06, from 0.08 to 0.52 in experiment 71Y-06, and from 

 0.02 to 0.50 in experiment 72D-06 (the experiment with a 0.05 initial 

 slope). The shoreline position varied as much as 2.0 feet in experiment 

 70X-06, 2.3 feet (70.1 centimeters) in experiment 71Y-06, and 1.9 feet in 

 experiment 72D-06 (Fig. 43). The foreshore variations are not less than 

 those with L/W = 1.43 (compare Fig. 43 with Fig. 40), especially since 

 the tank was narrower. 



The inshore in experiment 70X-06 developed the flat shelf with little 

 lateral variation in time of development, but after the shelf developed 

 lateral variations occurred, as indicated by the -0.6-foot contour move- 

 ments in Figure 44. The same holds for experiment 71Y-06 (Fig. 44). In 



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