15 and 205 hours, and varied from 0.016 foot per hour along the center 

 of the tank to 0.025 foot per hour along the tank walls thereafter (for 

 130 hours) . 



Re-reflection is not the likely explanation for the difference in 

 shoreline recession rates, since there was little difference in average 

 incident wave heights and the slower recession rate was associated with 

 the higher range of re-reflection effect within an experiment. Secondary 

 waves are not a likely cause because there was no difference in profile 

 shape. 



(3) Experiments 72B-06 and 72B-10 (2.35-Second Wave) . In these 

 two experiments the effect of re-reflection on the incident wave height 

 variability was slight. In experiment 72B-06 the range of incident wave 

 heights in the movable-bed tank was only 0.01 foot greater than in the 

 fixed-bed tank; in experiment 72B-10 the range in the movable-bed tank 

 was less than in the fixed-bed tank (Table 13). However, there was a 

 0.07- foot difference in average incident wave height. The average K^. 

 was lower in experiment 72B-06 than in experiment 72B-10, indicating that 

 Hfj and H^ would have been lower in experiment 72B-06. The higher Hj 

 in experiment 72B-06 must then have been the result of the difference in 

 phase difference between Hj and H^> as a result of the 38. 3- foot 

 (11.7 meters) difference in initial test length. Secondary waves were 

 also present. 



The profiles in the two experiments developed different profile 

 shapes. Some of those differences were due to the differences in tank 

 width and the presence of the transverse wave in experiment 72B-10 

 (discussed in the following subsection) . In experiment 72B-06 the off- 

 shore zone had a con cave -upward shape; in experiment 72B-10 the offshore 

 zone had a convex-upward shape (Fig. 27, c). This significant difference 

 could have been caused by either secondary waves or re- reflection effects, 

 as a result of the difference in initial test length. This difference in 

 offshore profile shape may have been a contributing cause to the lack of 

 equilibrium in experiment 72B-10. 



(4) Experiments 72A-06 and 72A-10 . In each of these experiments 

 the effect of re-reflection on the incident wave height variability was 

 different, 0.03 foot in experiment 72A-06 and 0.08 foot in experiment 

 72A-10; the difference in average incident wave height between the two 

 experiments (0.03 foot) was significant (Table 13). Thus, varying re- 

 flectivity within an experiment caused variations in Hj-; and the 38.3- 

 foot difference in initial test length affected the average Hj. 

 Secondary waves were the most pronounced in these experiments. 



The profiles in the two experiments developed different shapes (Fig. 

 31). Some of the differences were due to tank width effects, which are 

 discussed in the following subsection. The differences in the shape of 

 the outer offshore were probably due to re-reflection or secondary wave 

 effects. In experiment 72A-06 the outer offshore had a steep segment 

 between stations 16 and 20 and a bar at station 28. In experiment 72A-10 



78 



