satisfactory. No dynamic calibration was attempted. Nevertheless, infor- 

 mation concerning vertical velocity distributions could be obtained as 

 shown in Figure 9. At the inflow region, a helicoidal component was 

 observed with a clockwise circulation with contours shown in Figure 9(a) 

 for the longshore currents. The pitometer only measured velocities below 

 the wave troughs (solid line) and these are connected (dotted line) to 

 surface float values (MWL) to complete the isovelocity patterns. The max- 

 imum longshore current velocity occurred below low water levels near the 

 midsurf area and was somewhat larger than the surface float values. All 

 longshore vertical velocities were in the same direction at each location 

 in the section. This was also true for the onshore-offshore vertical 

 distribution (Fig. 9, b) , except for a narrow zone near wave breaking. 

 These velocities were offshore dominated by backwash in the upper layers 

 and had onshore components near the bottom. It is obvious that the total 

 velocity pattern is extremely complex at this location (section I) and 

 for the circulation patterns induced by the breakwater. Gourlay's 

 research was performed between 19 71 and 1972 in Australia. 



The results of some recent longshore current profile studies in Japan 

 (Mizuguchi, Oshima, and Horikawa, 1978, in Japanese) have been summarized 

 by Kraus and Sasaki (1979) . A 9-meter-long beach of plain concrete with a 

 1 to 10.4 slope was utilized. A propeller-type current meter measured the 

 current at 15 to 20 points across the surf zone and averages were taken in 

 the vertical direction. Wave period was held constant at 0.8 second, 

 breaker heights were only 3 to 4.5 centimeters, and approach angles ranged 

 from 4° to 15°. Maximum velocity recorded was 22 centimeters per second 

 when the largest breaker angle was present. Kraus and Sasaki (1979) men- 

 tioned that the current velocity profile variation in the alongshore direc- 

 tion was monitored and ". . .no systematic acceleration or other signifi- 

 cant anomaly in the alongshore direction was recorded." These researchers 

 were obviously concerned about basin end-wall effects. It is not stated 

 how nor over what alongshore distance this uniformity was obtained. A non- 

 uniform profile created by basin end walls is not the only difficulty 

 faced by laboratory researchers. 



2. Laboratory Boundary and Scale Effects . 



Dalrymple, Eubanks, and Birkemeier (1977) studied the mean wave-induced 

 circulations in enclosed basins. They organized the previous studies and 

 basins employed into three categories: 



(a) Surf zone openings in both waveguide walls to permit recircula- 

 tion outside the waveguide walls. The recirculation occurs 

 behind and beneath the wave generatoi" or through a pipe beneath 

 the beach (used by Brebner and Kamphuis, 1963) . The updrif t 

 current is enhanced by pumping to increase the length of the 

 usable test section with uniform current profile (Kamphuis, 1977). 



^MIZUGUCHI, M., OSHIMA, Y., and HORIKAWA, K., "Laboratory Experiments of 

 Longshore Currents," Proceedings, 25th Coastal Engineering Conference of 

 Japan, 1978, in Japanese (not in bibliography). 



36 



