The multiple intercepts in Figures 30 to 34 indicate the development 
of a bar and trough on the shelf of the inner region. For example, along 
range 5 (Fig. 32) the bar crest reached an elevation of -1.0 foot between 
30 and 45 hours and at 55 hours, as indicated by the movement of the -1.0- 
foot contour. The trough eroded to a depth of 1.2 feet from 35 hours to 
65 hours and to a depth of 1.3 feet from 65 hours on, as indicated by the 
appearance of multiple intercepts for the elevations at those times. 
The lateral variations in the depth over the shelf are best seen in 
Figure 35. The greatest variation was in the bar crest elevation at 
station +12, which reached -1.0 foot at quite different times across the 
tank when the -0.9- and -1.1-foot contours were relatively stable. 
(d) Outer Region (Experiment 72A-10). In contrast to condi- 
tions in the 6-foot tank, few changes occurred in the outer region of the 
10-foot tank. During the first 15 to 20 hours sand was deposited at 
elevations -1.2 to -1.5 feet and from 20 to 25 hours sand was eroded at 
-1.6 and -1.7 feet (see Fig. 32). After 25 hours, no significant change 
occurred in the outer region, except for a tendency of the -1.8- and -1.9- 
foot contours to diverge with time (Figs. 30 to 34). The slope of the 
offshore zone was approximately 0.15 between -1.1- and-1.7-foot elevations 
and the original 0.10 slope below -1.7 feet. 
No pronounced lateral variation in the shape of this region appeared. 
3. Sediment-Size Distribution. 
The four sand samples collected at the beginning of the two experiments 
and analyzed by the sieve method ‘iad an average median grain size of 0.22 
millimeter (2.19 phi) (see Table A-2 in the App.). This number should 
be used as the reference for comparing the results reported here with 
other experiments. The Visual Accumulation (VA) tube average median size 
for the same four samples was 0.205 millimeter. The difference between 
VA tube and sieving is typical of the results reported in Volume I. 
The results presented in Tables 8, 9, and 10 are the values of all 
samples from these two experiments analyzed by the VA tube method. 
a. Experiment 72A-06. The median grain sizes of samples collected 
at the beginning of the experiment (0 hours) and at 50, 100, and 135 
hours are given in Table 8; the values are summarized in Table 10. The 
average median at 0 hours was 0.20 millimeter. In the foreshore zone, 
the mean of the medians remained at 0.20 millimeter and the range remained 
the same until 135 hours, when the mean increased 0.01 millimeter and the 
range increased. The mean of the medians in the offshore zone remained at 
0.20 millimeter throughout the experiment, but the range of values increas- 
ed at 50 hours and again at 100 hours, and then decreased to the’ 50-hour 
range at 135 hours. There was no significant change in sediment-size 
distribution, compared to the other LEBS experiments. 
b. Experiment 72A-10. The median grain sizes of samples collected 
at the beginning of the experiment (0 hours) and at 50 and 80 hours are 
58 
