developed, with antinodes near station 5, just shoreward of the base of 
the foreshore, and at station 18, just seaward of the flat shelf over 
the steepest part of the profile. Between the first two antinodes of the 
standing wave, over the flat shelf of the inner offshore, a clockwise 
circulation pattern developed, apparently driven by the counterclockwise 
circulation in the foreshore zone. Apparently, the circulation over the 
inner offshore moved the sand to the edge of the shelf, but the lack of 
current movement through the antinode prevented further transport and 
thus increased the steepness. 
Between 25 and 70 hours, while the profile changed only in the length 
of the shelf between the two reflecting zones (foreshore zone and sub- 
merged offshore slope), the Kp did not increase or decrease significant- 
ly, but fluctuated over a range of 0.05. This variation, which was greater 
than the 0.02 maximum variation in the fixed-bed tank, may have been 
caused by changes in the phase difference of the waves reflected from the 
two slopes as they separated. 
After 70 hours the seaward edge of the shelf began eroding, moving 
landward, even though the foreshore was still retreating and the offshore 
was still prograding. Simultaneously, the clockwise circulation pattern 
over the inner offshore began disintegrating and the Kp began decreasing. 
By 100 hours, the bar had eroded and the trough had almost filled. From 
15 to 100 hours the outer offshore steepened, with deposition at the upper 
elevations and erosion at -2.0- and -2.1-foot elevations. The eroded 
material moved seaward and formed a bar over part of the concrete bottom. 
Between 100 and 135 hours the foreshore continued to retreat, the 
inner offshore became a gently sloping region, the outer offshore slope 
steepness decreased, and the Kp continued to drop. 
The sediment-size distribution did not vary significantly during the 
experiment. While the water temperature gradually increased, the shore- 
line retreated at an average rate of 0.015 foot per hour throughout most 
of the experiment. 
Qi: Experiment 72A-10. 
The major events of the profile development in this experiment are 
summarized in Table 13. Figure 40 compares the shoreline movement with 
water temperature changes for experiment 72A-10; Figure 41 compares the 
-1.2-foot contour with Kp changes. 
During the first 1.5 hours the foreshore developed a steep slope, and 
within the first 10 hours an almost flat shelf developed in the inner 
offshore region. From 1.5 to 25 hours the foreshore prograded 0.5 foot, 
beginning first along the outside ranges. In the first 20 hours, sand 
deposited in the outer offshore at depths from 1.2 to 1.5 feet; from 
20 to 25 hours, sand eroded at depths of 1.6 and 1.7 feet, thus forming 
a Slightly steeper slope on the upper part of the outer offshore. During 
this initial profile development, the Kp rose sharply. 
74 
