(4.6 to 13.1 centimeters) in experiment 7QX-1Q. Ignoring the first group 

 o£ 10 waves, the wave heights differed witMn the first 10 minutes by as 

 much as 0.07 foot (2.1 centimeters) in experiment 70X-06 and 0.10 foot 

 (3.0 centimeters) in experiment 70X-10. This difference suggests that the 

 reflection from the movable-bed profile was varying significantly during 

 the initial run. As expected, the wave heights varied less in the fixed- 

 bed tanks, varying 0.04 foot (1.2 centimeters) in experiment 70X-06 and 

 0.05 foot (1.5 centimeters) in experiment 70X-10. 



The average wave height for each record was determined by averaging 

 the average of the last 10 waves in the last 20-second interval for each 

 10 minutes. In experiment 70X-06, the average wave height was 0.32 foot 

 (9.8 centimeters); in experiment 70X-10 the height was 0.38 foot. Neither 

 of these values can be compared to the nominal generated wave height 0.36 

 foot (11 centimeters) as indicated in Volume I, because the position of 

 the gage between nodes and antinodes of the reflected wave envelope is 

 unknown. Since the waves were recorded at the same distance from the 

 reflector, the difference in the wave heights is likely due to the differ- 

 ence in the initial test length as the result of secondary waves or re- 

 reflection from the wave generator. There was little difference in the 

 average wave heights between the movable- and fixed-bed tanks for either 

 experiment. 



The average incident wave heights from the two experiments are shown 

 in Table 5. These heights were determined by averaging all the wave 

 heights on a given envelope as part of the automated method for determin- 

 ing the K/^ (see Vol. I). The values determined in the fixed-bed tanks 

 indicate that the generator operation variation and measurement errors in 

 both movable- and fixed-bed tanks were ±0.005 foot (±0.15 centimeter) in 

 experiment 70X-06 and ±0.015 foot (±0.45 centimeter) in experiment 70X-10. 



The wave height in the movable-bed tank in experiment 70X-06 varied 

 from 0.32 to 0.38 foot and in experiment 70X-10 from 0.34 to 0.39 foot 

 (10.4 to 11.9 centimeters). The variation not attributable to generator 

 variation and measurement error is likely due to re-reflection from the 

 wave generator superposing with the generated wave creating a different 

 incident wave. 



b. Reflection from the Movable-Bed Profile . In measuring the reflec- 

 tion coefficient from a wave envelope recorded by a slowly moving gage 

 (see Vol. I), it is assumed that the reflection coefficient does not change 

 during the 5 to 7 minutes required to make the recording. 



Table 6 gives the reflection coefficient versus time data for experi- 

 ments 70X-06 and 70X-10 as determined by the manual method. 



(1) Experiment 70X-06 . Figure 2 shows the reflection coefficient, 

 K^, versus time data for experiment 70X-06 for all time and for the first 

 10 hours at a larger horizontal scale. During the first 10 hours, the 

 K^ varied between 0.20 and 0.08. At 10 to 25 hours, K^ remained fairly 

 constant (0.14 to 0.16) and then dropped to 0.08 at 31 hours. From 33 to 



