the generated wave, and all other errors not caused by a changing profile. 
The remainder of the variation (0.03 and 0.09 foot) is likely due to vary- 
ing re-reflection. 
c. Secondary Waves. Along the length of the tank, between the gener- 
ator and the toe of the profile, wave heights on a given recording varied 
as the result of the presence of secondary waves (Galvin, 1972; Hulsbergen, 
1974). Wave height variation due to secondary waves appears to be an order 
of magnitude less than variation due to reflection (see Figs. 1, 7, and 8). 
2. Profile Equilibrium. 
The profile in experiment 72A-10 appeared to be in equilibrium after 
25 hours. As the depths over the inner offshore shelf were fluctuating 
along any one range and varying from one range to the next, the profile 
was nevertheless close to, if not at, equilibrium (see Fig. 42). 
In experiment 72A-06 the profile was still changing, even after 135 
hours (see Fig. 11). Apparently, the circulation of the swash continued 
to erode the foreshore causing the shoreline to retreat. This continual 
change prevented the remainder of the profile from reaching equilibrium. 
3. Other Laboratory Effects. 
The differences in tank width and initial test length provide possi- 
ble explanations for the differences in profile shape between the two 
tanks. 
a. Initial Test Length. Two phenomena are affected by varying tank 
length: re-reflection and secondary waves. 
The difference in initial test length between the two tanks, which 
would have caused the phase difference between primary and secondary 
waves at the toe of the profile to be different and thus caused the 
velocity profile at the toe of the profile to be different, may possibly 
account for some of the difference in the development of the toe of the 
outer offshore profile. In experiment 72A-10 the slope below -1.9 feet 
was essentially unchanged; in experiment 72A-06, significant changes 
occurred in this area. 
The re-reflected wave, which is affected by tank length, may also 
account for some of the difference. The average incident wave height 
in experiment 72A-06 was 0.38 foot (11.6 centimeters) and in experiment 
72A-10 was 0.35 foot (10.7 centimeters) (Table 5). This difference 
(0.03 foot) due to re-reflection may account for some but not all of the 
difference. 
b. Tank Width. The development of the circulation patterns in the 
foreshore and inner offshore zones in the 6-foot tank, which did not 
develop in the wider tank, was a most significant difference. Some 
minor perturbation on the foreshore may have triggered an initial 
i) 
