After 75 hours at station 2 the erosion of the bar along ranges 7 and 9 
was completed and the flat area along ranges 1 and 3 began eroding. 
Between 90 and 100 hours a bar formed at station 5, first along range 5, 
then along range 3, and finally along range 1. The sand eroded from the 
foreshore and inshore zones was deposited seaward of the -1.8-foot contour 
along ranges 1 and 3 and in the flat area near station 10. The area near 
station 10, when formed, was lower along the range 1 side and the area 
remained tilted as sand was then deposited apparently equally across the 
tank. 
After 100 hours the foreshore began eroding and the flat area near 
station 2 continued eroding. Most of the sand was deposited on the flat 
area around station 10; none was deposited seaward of the -1.8-foot con- 
tour. Near the end of the experiment, lateral variations again occurred 
in the position of the receding shoreline. 
The movement of the shoreline and change in water temperature for 
this experiment are also compared in Figure 42. The drop in temperature 
at 10 hours did not appear to affect the foreshore erosion, but the drop 
at 100 hours coincided with the initiation of shoreline recession. 
c. Comparison of the Two Experiments. Although the general profile 
shapes in the two tanks were similar, there were significant differences 
in all profile zones. 
(1) Foreshore Zone. In experiment 72B-06 the foreshore developed 
an equilibrium shape and position (normal to the tank walls) during the 
first 10 hours; in experiment 72B-10 an initially stable foreshore shape 
developed (shoreline not normal to the tank walls) and then later, the 
foreshore began eroding. 
(2) Inshore Zone. In both experiments a longshore bar formed 
during the first 10 minutes by the plunging breaker. However, in experi- 
ment 72B-06 the bar remained stable except for some variation in the crest 
elevation; in experiment 72B-10 the bar near station 2 eroded, starting 
first along the range 1 side of the tank and progressing across the tank 
to range 9. The second bar (near station 5) formed first along the range 
9 side and moved in the opposite direction across the tank to range 1. 
(3) Offshore Zone. In both experiments a steep slope at the 
upper edge of the offshore zone was formed by erosion at the -0.7- to 
-1.0-foot elevations during the first 10 hours. However, differences in 
the shape of the lower offshore zone developed. In experiment 72B-06, 
the profile became concave upward. Sand was eroded at -1.1 to -1.7 
feet along all ranges and deposited at -2.1 and -2.2 feet, and later at 
-2.0 feet along all ranges forming a flat area between stations 20 and 
25 (elevation -2.0 feet). In experiment 72B-10 the profile became con- 
vex upward. Sand was deposited at elevations -0.9 to -1.7 feet along 
all ranges and at elevations -1.9 to -2.2 feet along ranges 1 and 3, 
forming flat areas near stations 10 (elevations -0.8 to -1.1 feet) and 
16 (elevations -1.5 to -1.8 feet). 
Co 
