b. Initial Test Length . Two possible phenomena are affected by 

 varying tank length, re-reflection and secondary waves. Chesnutt (1975) 

 and Chesnutt and Stafford (1977) discussed these phenomena and the possi- 

 ble effects on the rate of profile development. 



c. Tank Width . Experiments 71Y-06 and 71Y-10 probably serve their 

 greatest purpose by pointing out the effect of tank width. This study 

 (Sec. 111,1) discussed the significant lateral variations in the wider 

 tank, which must have resulted from a minor perturbation in profile de- 

 velopment. Lateral variations in profile shape occur on natural beaches, 

 and variations on a wide laboratory beach would not be unexpected. In 

 the 6-foot tank, the profile was essentially two-dimensional; in the 10- 

 foot tank, the natural lateral variations were most likely distorted by 

 the tank walls. 



V. CONCLUSIONS AND RECOMMENDATIONS 



1. Conclusions . 



(a) In two experiments with a water depth of 2.33 feet (0.71 meter) 

 a wave period of 1.90 seconds, and a generator stroke of 0.39 foot (11.9 

 centimeters), the average incident wave height was 0.38 foot (11.3 centi- 

 meters) in experiment 71Y-06 and 0.36 foot in experiment 71Y-10. Reflec- 

 tion measurements in the control tanks with a fixed-bed profile varied 

 from 0.10 to 0.16 in experiment 71Y-06 and from 0.09 to 0.12 in experi- 

 ment 71Y-10, indicating that the wave generators were operating uniformly 

 and that the error in determining reflection from the changing profile 

 was about ±0,03 for experiment 71Y-06 and ±0.015 in experiment 71Y-10. 

 The lower K^ in the wider tank is probably due to an unknown width 

 effect (Tables 6 and 8). 



(b) Kji varied from 0.08 to 0.30 in experiment 71Y-06 and from 0.03 

 to 0.16 in experiment 71Y-10. The variation in K^ correlates with pro- 

 file changes. K^ was high during the development of the foreshore and 

 decreased as the inshore widened. Later increases in Kj^ occurred when 

 the offshore slope steepened. Large fluctuations in Kj^ occurred at 

 times of large shifts in contour position on the flat inshore zone, sug- 

 gesting that reflection is quite sensitive to small changes in depth at 

 the shoreward edge of the submerged reflecting surface (Figs. 3, 4, 45, 

 and 46) . 



(c) Profiles along given ranges in the two experiments developed in 

 the same sequence, but did not reach equilibrium. In the wider tank, the 

 development of the flat shelf in the inshore zone began along one side of 

 the tank and the development progressed slowly across the tank, causing 

 significant differences in breaker type and depth across the tank and a 

 strong seaward current along one side of the tanko This development 

 suggests that tank width can significantly affect laboratory studies of 

 coastal processes (Figs. 7 to 14). 



99 



