The confining effect of the tank walls on flow in the longshore di- 

 rection is complicated by other tank width effects. There are critical 

 wavelengths for each tank width which can generate tank oscillations or 

 unique circulation patterns (see Sec. II) . Cross waves were observed 

 over a limited segment of the profile for a short period of time in ex- 

 periment 72B-06 (Vol. VII), but neither the cross waves nor their effect 

 on the profile were measured. Transverse waves were observed and meas- 

 ured throughout experiment 72B-10 (Vol. VII) and their effect on the 

 profile determined. Circulation currents between the antinodes of the 

 standing wave, along with their effects, were measured in experiment 

 72A-06 (Vol. VI). These three special cases of tank width effects are 

 assumed to produce special effects on the sand beds. Tank width effects 

 in all 10 experiments from lowest to highest wave period tested are 

 discussed below. 



a. 1.50-Second Wave (L/W = 1.03, Experiment 72C-10) . The foreshore 

 and inshore zones had significant lateral variations. The shoreline sta- 

 tion along the five ranges varied as much as 2.5 feet (0.76 meter) at any- 

 given time (Fig. 35). Specific instances of this variation are illustra- 

 ted by the two photos in Figure 36. At 50 hours (Fig. 36, a) the shore- 

 line and scarp on the near side (ranges 1 and 3) are farther landward 

 than the shoreline along the far side (ranges 7 and 9) . At this time 

 the backshore, was apparently eroding along ranges 1 and 3, and the sand 

 moved alongshore to range 7 where it caused the shoreline to protrude 

 into the inshore zone. At 85 hours (Fig. 36, b) the scarp was uniform in 

 position across the tank, but the position of the shoreline was seaward- 

 most on the near side (range 1) and landwardmost in the middle (range 5) . 

 At this time the backshore was apparently eroding in the middle of the 

 tank, and the sand moved alongshore to range 1 where it moved out into . 

 the inshore zone. At other times the erosion of the backshore occurred 

 only along ranges 7 and 9 and the sand was transported alongshore to 

 range 1 before moving into the inshore. 



Considerable lateral variation also occurred in the inshore zone of 

 this experiment (Fig. 37 compares movements of the -0.3-, -0.4-, -0.5-, 

 -0.7-, and -0.8-foot (-9.1, -12.2, -15.2, -21.3, and -24.4 centimeters) 

 contours) . The lateral variations were particularly great just below the 

 foreshore (elevation -0.3 foot) and the amount of variation decreased 

 moving in the seaward direction. No lateral variation occurred in the 

 offshore zone (Fig. 38 compares movements of the -0.9-, -1.4-, and 

 -1.9- foot (-27.4, -42.7, and -57.9 centimeters) contours). Erosion of 

 a trough near station 10 started first along the tank walls and pro- 

 gressed toward the center (discussed in Vol. V). 



The three dimensionality of the profile shape is shown in Figure 39, 

 which is a contour map of the sand bed at the end of the experiment. 

 The foreshore and offshore topographies are skewed in the same direction 

 and the inshore topography is approximately symmetric about the tank 

 centerlines. The symmetric development of the inshore is illustrated by 

 the depressions along the tank walls near stations 3 and 13. The tank 

 walls obviously constrained the shape that did develop, but that shape 

 does have a significant variation in the third (longshore) dimension. 



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