range 9 at 115 hours, advanced across the tank, and began along range 1 

 at 190 hours (shov\m by movement of the several -0.4-£oot contours in 

 Fig. 29) . After the bar eroded, the inner region maintained a fairly 

 steep slope for the duration of the experiment. 



(d) Outer Region (Experiment 71Y-10) . Although some deposi- 

 tion occurred during the first 5 hours which moved the -0.6-, -0.7-, and 

 -0.8-foot contours 2 feet in the seaward direction, the outer region re- 

 mained unchanged until after 100 hours. The development of the flat shelf 

 in the outer region followed erosion of the longshore bar in the inner 

 region, as indicated by the movement of the -0.6-foot contour along the 

 five ranges in Figure 29. The shelf began developing first along range 

 9 at 115 hours and along range 1 at 215 hours. The shelf widened as 

 material was eroded from the foreshore and deposited in the offshore. 

 At different times along the five ranges, the seawardmost -0.7-foot 

 contour made significant shifts, first along ranges 7 and 9 and later 

 along ranges 1, 3, and 5. These shifts correlate with the progressive 

 development of the shelf across the tank from range 9 to range 1 and 

 indicate a net movement of sediment across the inshore zone. 



(3) Offshore Zone . 



(a) Experiment 71Y-06 . The movement of contours in the 

 offshore zone is shown in Figures 7, 8, and 9 for ranges 1, 3, and 5. 

 The offshore zone developed from the initial 0.10 slope to a relatively 

 steep slope as a result of the deposition of material seaward of the 

 breaker. 



During the first 10 hours, more deposition occurred at the higher 

 elevations, but after that time, all the contour movements were parallel 

 in the offshore zone until 200 hours. Between 200 and 250 hours and 

 between 315 and 340 hours, significant deposition occurred again at the 

 higher elevations, increasing the offshore zone slope. 



The movement of contours at the three ranges for elevations of -0.9, 

 -1.2, and -2.1 feet is compared in Figure 30. No lateral variations 

 occurred in the movements of the -1.2- and -2.1-foot contours, and only 

 minor variations in the movement of the -0.9-foot contour. 



(b) Experiment 71Y-10 . Figures 10 to 14 show the contour 

 movements in the offshore zone for the five ranges in experiment 71Y-10. 

 During the first 10 hours sediment was deposited between depths of 0.9 

 and 1.4 feet. After 10 hours the contours along a given range were par- 

 allel (indicating uniform deposition at all depths), but there was vari- 

 ation from one range to the next. Along range 9 the contours moved 

 seaward at an average rate of 0.025 foot per hour. Along range 5 the 

 offshore remained essentially stationary for the next 100 hours (until 

 110 hours) and then began prograding seaward at an average rate of 0.024 

 foot (0.73 centimeter) per hour; along range 1, the offshore remained 

 stable until 170 hours and then prograded seaward at a rate of 0.019 

 foot (0.58 centimeter) per hour. 



62 



