Transport of Fine Sands by Currents and Waves. II

The transport process of fine sand with a median diameter of about 100 μm in combined current and wave conditions in a laboratory basin was studied. Irregular waves with a single-topped spectrum and peak period of 2.5 s were generated. The significant wave height was varied from 0.07 m to 0.14 m. The water depth was about 0.4 m in all tests. The depth-mean current velocities were varied from 0.1 m/s to 0.3 m/s. The angles between the wave and current directions were 60°, 90°, and 120°. Instantaneous fluid velocities were measured by an acoustical probe and an electromagnetic probe. The acoustical probe was also used to measure the instantaneous sand concentrations. Time-averaged and bed-averaged concentrations were measured by a pump sampler. Current-related and wave-related transport rates were determined by decomposing, multiplying, and time-averaging instantaneous signals. The current-related transport rate in the main current direction was found to be largest when the waves were propagating normal to the current. High-frequency wave-related transport rates were found to be directed onshore because of the wave asymmetry effect. Low-frequency wave-related transport rates were found to be directed offshore because of the bound long waves.