Sand Tracer Movement Measured in a Strong Rip Current
ENGINEER RESEARCH AND DEVELOPMENT CENTER VICKSBURG MS COASTAL AND HYDRAULICS LAB
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On August 21, 1980, the author and colleagues performed a trial sand tracer experiment in a strong rip current on Ajigaura Beach, Japan, a sandy beach facing the Pacific Ocean. Synoptic observations were made of the flow and sand-movement patterns associated with the rip current. Significant wave height was about 1 m, and current meters recorded average speeds exceeding 50 cmsec in areas where instruments could be placed. Three colors of sand tracer were injected, and ten fixed stations were sampled at intervals for 180 min. The sand cores were split into segments and tracer grains counted under ultraviolet light. Depth of tracer mixing and tracer movement could then be determined. The greatest depth of disturbance was found at the root of the rip, where the feeder currents turned to flow offshore. Pulsations in tracer movement were observed with 45-60 min interval period, and the measurements indicate that the dominant mode of transport was suspended load. Although not completely successful because of equipment failure, the experiment demonstrates that such measurements are possible.
- Physical and Dynamic Oceanography