indicating that the maximum number of cycles of 360° phase-difference 
change possible was five. If the cycle started with the two waves 180° 
out of phase, four in-phase values are possible. 
This hypothesis cannot be proven with the data presented here, 
because neither the foreshore nor the offshore reflection was measured 
separately. 
Near the end of the experiment when the profile appeared to have been 
close to equilibrium, the Kp did not vary significantly, possibly 
verifying the original premise that reflection variability, and thus wave 
height variability, would be eliminated as the profile reached equilibrium. 
The position of the -0.8-foot contour and the reflection coefficient 
versus time for experiment 72C-10 are compared in Figure 27. The move- 
ment of the seawardmost -0.8-foot contour is an indicator of the depth 
at the top of the offshore slope reflecting surface. The shoreward 
Movement of the -0.8-foot contour near the end of the experiment did 
not cause any noticeable reduction in the Kp, which was already low. 
IV. DISCUSSION OF RESULTS 
1. Wave Height Variability. 
Two possible causes of wave height variability in experiment 72C-10 
are (a) wave reflection from the changing profile, and (b) re-reflection 
from the wave generator. This experiment was designed primarily to quan- 
tify the amount of variability due to reflection. 
a. Wave Reflection from the Profile. The Kp varied from 0 to 0.15 
in the movable-bed tank in this experiment, which is generally lower than 
in tests with the 1.90-second wave (see Vols. II, III, and IV). No long- 
term increase or decrease occurred in the Kp, but there was a series of 
short-term fluctuations possibly caused by the change in phase difference 
between the waves reflected from the offshore -and foreshore as the dis- 
tance between the offshore and foreshore zones increased. This kind of 
fluctuation had been mentioned as a possible cause of long-term reflec- 
tion variability in the experiments discussed in Volumes II and III. The 
depth variation at the top of the offshore slope did not cause a vari- 
ation in Kp, as was observed in the experiments with the 1.90-second 
wave (Vols. II, III, and IV), probably because the Ky value was already 
small. 
b. Re-Reflection from the Generator. The reflected wave advanced to 
the generator and was re-reflected. As the height of the reflected wave 
varied, the height of the re-reflected wave varied. As the phase dif- 
ference between the re-reflected wave and the generator motion varied 
with changes in the profile, the height and phase of the incident wave 
varied. The height of the wave incident to the profile, which was meas- 
ured by averaging wave heights along the full tank length, had a range 
54 
