the fixed-bed tanks from the range of heights in the movable-bed tanks. 

 In the 6- foot tank, this effect ranged from 0.01 foot in experiment 

 72B-06 to 0.03 foot in the other four experiments. In the 10- foot tank, 

 this effect ranged from in experiment 72B-10 to 0.08 foot in experiment 

 72A-10. This implies that the wider tank may amplify this re-reflection 

 effect . 



(j) The importance of phase difference between the reflected wave and 

 the generator motion to the incident wave height variability is seen best 

 by comparing experiments 72B-06 and 72B-10. The average K^ in experi- 

 ment 72B-06 was 0.08 and in experiment 72B-10 was 0.17, which means that 

 the reflected wave height was greater in the 10-foot tank. However, the 

 average incident wave height was 0.38 foot in 72B-06 and only 0.31 foot 

 in experiment 72B-10. Since the difference in reflected wave height 

 would not have caused that difference, only the phase-difference effect 

 resulting from the difference in initial test length can account for the 

 difference. 



2. Profile Equilibrium . 



(a) In two experiments with all parameters the same except the 

 initial slope (0.05 and 0.10), the final profiles had quite different 

 slopes, although neither reached equilibrium. This further verifies the 

 conclusion of Collins and Chesnutt (1975, 1976) that the initial profile 

 influences the final stable profile shape. 



(b) In two pairs of experiments with the same wave condition but 

 different tank width and initial test length, one experiment in each 

 pair reached equilibrium; the other experiment in each pair developed a 

 different shape which continued to adjust. Laboratory effects are the 

 apparent causes for the differences. 



(c) Profile equilibrium is not easily attained. Two of four summer 

 profiles and the one winter profile reached equilibrium, but none of the 

 five profiles in the transition category (0.020 < H /L < 0.025) reached 

 equilibrium, indicating that profiles for waves in the transition region 

 are more unstable. 



3. Laboratory Effects . 



(a) The initial profile slope affects the profile development at 

 least partially as a result of differences in the phase of secondary 

 waves at the toe of the profile. 



(b) The initial distance from the generator to the shoreline is an 

 important experimental parameter. Differences in this distance affect 

 the phase difference between the reflected wave and the generator motion 

 and thus affect the incident wave height. The effect of varying incident 

 wave height on profile shape is opposite to intuition; in experiments 

 with the same wave condition and different initial distance to the shore- 

 line developed, the higher erosion rate was associated with the lower 



22 



