II. RESULTS 
1. Wave Height Variability. 
a. Incident Wave Heights. Wave height measurements from the contin- 
uous recording of water surface elevation along the center range at station 
+25 in both tanks during the first 10 minutes for experiment 72C-10 are 
-shown in Table 4. The wave heights in both tanks varied from 0.37 to 0.48 
foot (11.3 to 14.6 centimeters) during the first 20 seconds. Ignoring 
the first group of waves, the range was 0.07 foot (2.1 centimeters) in 
the movable-bed tank and 0.12 foot (3.7 centimeters) in the fixed-bed 
tank. 
The average wave height in each tank was determined by averaging the 
average of the 10 waves nearest each full minute. The average wave height 
was 0.38 foot (11.6 centimeters) in the movable-bed tank and 0.43 foot 
(13.1 centimeters) in the fixed-bed tank. The initial height differences 
are assumed to occur primarily because the gages were different distances 
from the profile and thus at different points in the standing wave envelope. 
Table 5 shows the computed average incident wave heights in the two 
tanks during 140 hours of testing. These heights were determined by the 
automated method for determining the reflection coefficient, Kp (see 
Vol. I), which assumes that the incident wave is a single sine wave. The 
range of values for the fixed-bed tank was 0.03 foot (0.9 centimeter). This 
variation is probably caused by generator operation variation, measure- 
ment errors, and all errors not caused by a changing profile. The range 
of values in the movable-bed tank was 0.09 foot (2.7 centimeters). The 
difference between the two tanks indicates that 0.06 foot (1.8 centimeters) 
of the variation in the movable-bed tank was due to the changing protile 
which caused a variation in the reflected and re-reflected wave heights. 
The re-reflected wave superposing with the generated wave created an 
incident wave which varied in time. 
b. Wave Reflection. The reflection coefficient, Kp, data deter- 
mined by the manual and automated methods are given in Table 6. The two 
methods are described in Volume I. A plot of Kp versus time comparing 
the two methods for ranges 1, 5, and 9 in the movable-bed tank (Fig. 1), 
indicates that the manual method gave higher values. A scatter plot of 
Kp values for the manual method versus the automated method (Fig. 2) 
for those wave records reduced by both methods also shows that the 
manual values were higher than the automated values. The generalized 
region in Figure 2 is where equivalent data for the 1.90-second wave 
plotted and is the justification for assuming that the average difference 
between the two methods (0.09 for the 1.50-second wave) is constant. 
All Kg data from the movable-bed tank versus time are plotted in 
Figure 3, with the manual method values reduced by 0.09 to give a single 
curve for each of the three ranges. The three Kp values at each time 
have been averaged to give a single curve. The outside ranges show a 
greater variation in Ky than the center range, but the maximum and 
13 
