ranges 1 and 3 at this time. At 85 hours (Fig. 14,b) the scarp was 
fairly uniform in position across the tank, but the position of the 
shoreline was seawardmost on the near side (range 1) and landwardmost in 
the middle (range 5), indicating that the backshore and scarp were prob- 
ably eroding along range 5. The more seaward shoreline positions appeared 
to be areas of deposition. 
The slope of the 0 contours in Figure 13 indicates the shoreline re- 
cession rate. The rate was initially quite high (0.15 foot per hour or 
4.62 centimeters per hour for the first 30 hours) and then decreased 
(0.041 foot per hour or 1.25 centimeters per hour from 30 to 115 hours) 
as the experiment continued. Three of the five 0 contours were horizontal 
during the last few hours, indicating that the foreshore may have been 
approaching an equilibrium position. 
Because the backshore slope was 0.10 and not horizontal, the volume 
rate of erosion was not directly proportional to the shoreline recession 
rate. With the recession rate decreasing, the volume erosion was likely 
close to a constant value. 
(2) Inshore Zone. The movement of all contour intercepts in the in- 
shore zone along the five ranges is shown in Figures 15 to 19; the move- 
ment of selected contours along the five ranges is compared in Figure 20. 
Within the first hour a longshore bar and trough developed in the 
inshore zone, as indicated by the seaward movement of the -0.5- and -0.4- 
foot contours and the many multiple contour intercepts at those elevations 
in Figures 15 to 19. By 15 hours the bar had eroded (shoreward movement 
of the -0.4- and -0.5-foot contours). The inshore developed into two 
fairly flat shelves separated by a gently sloping area. 
The -0.6-foot contour, in the middle of the slope, effectively divides 
the inshore zone into an inner region which expanded in the shoreward 
direction as the foreshore retreated landward, and an outer region which 
expanded in the seaward direction as the offshore prograded seaward. 
(a) Inner Region. After 15 hours the inner region was 
essentially a flat shelf between two slopes.’ The depth over the shelf 
varied across the tank at any one time and generally increased with time. 
The lateral variation is shown in Figure 20 for contours at elevation 
-0.3 and -0.4 foot. At any one time the -0.3- and -0.4-foot contours 
varied several feet in position from one range to the next.. The increas- 
ing depth over the inshore shelf is clearly shown in Figure 6, which com- 
pares profijles at 55 and 140 hours. 
(b) Outer Region. The outer region developed during the first 
50 hours as a flat shelf between the steep offshore slope and the inner 
inshore zone as indicated by the -0.6- and -0.7-foot contours and lack of 
many multiple intercepts for elevations -0.6 to -0.9 foot (see Figs. 15 
to 19). 
34 
