After 70 hours the seaward edge of the shelf (-1.2-foot contour) 
began to move in the shoreward direction. By 100 hours the bar had heen 
mostly eroded and the trough was only 0.1 foot or less below the eleya- 
tion of the rest of the shelf, thus making the inner region a gently 
sloping area rather than a shelf. 
Only slight lateral variations occurred in the movement of the 
-1.2-foot contour (Fig. 28), indicating that the houndary between the 
two regions was normal to the direction of wave propagation. At the 
-1.0- and -1.1-foot elevations there were lateral variations in contour 
position. The -1.0-foot contour movement (Fig. 28) indicates that the 
bar crest near station 15 reached an elevation of -1.0 foot, three times 
along range 1 and once along range 3. The -1.1-foot contour movement 
(Fig. 28) indicates that the depth over the shelf edge permanently 
reached -1.1 feet first along range 1, then range 3, and then range 5. 
(b) Outer Region (Experiment 72A-06). Changes in the outer 
region occurred uniformly across the tank. This is indicated by the 
lack of lateral variation in the position of the -1.3-foot contour in 
Figure 28, but these changes were unusual in that the slope reached a 
maximum and then began to decrease, as shown by the spacing between 
-1.3- to -2.1-foot contours in Figures 25, 26, and 27. 
During the first 15 hours, most of the deposition in this outer 
region occurred at elevations -1.3 to -1.6 feet, where a steep slope 
quickly formed (e.g., Fig. 26). This was representative of changes 
along the other ranges. As more material deposited at the shoreward 
edge of the slope and slid down, other contours began moving seaward, 
the -1.7-foot contour at 15 hours, the -1.8-foot contour at 40 hours, 
and the -1.9-foot contour at 85 hours. At the base of the slope, erosion 
began first at the -2.2-foot contour from the beginning and then at the 
-2.1-foot contour at 10 hours and continued until 100 hours. The eroded 
material deposited on a bar which formed seaward of the profile (between 
stations +26 and +28) at 40 hours. The bar crest elevation reached -2.2 
feet at times which differed across the tank (see Fig. 29). 
The initial offshore slope was 0.10. At 100 hours the offshore 
slope was 0.36; after 100 hours the offshore slope became milder as the 
seaward edge of the shelf eroded shoreward and material was deposited at 
depths below 1.7 feet. At 135 hours, the offshore slope was 0.175. 
The area from station +23.5 to +28.2 had an elevation of -2.2 feet. 
(c) Inner Region (Experiment 72A-10). The -1.1-foot 
contour is the boundary between the inner region (shelf) and the outer 
region (steep slope) in this experiment. 
With the first 10 hours the nearly flat shelf formed, as evidenced 
by the shoreward movement of the -1.0-foot contour in Figures 30 to 34. 
The edge of the shelf (-1.1-foot contour) moved to station +12 at 10 
hours and to station +13 at 15 hours, remaining between those two 
stations for the remainder of the experiment. 
5| 
