Laboratory Study on Sheetflow Sediment Movement in the Oscillatory Turbulent Boundary Layer Based on Image Analysis

Abstract

Laboratory experiments were conducted under sinusoidal sheetflow conditions. By using image analysis, which overcame the demerits introduced by intrusive measurements, the time-varying as well as maximum erosion depths for different flow conditions were estimated. The temporal variation of suspended sand concentration in the sheetflow layer showed high concentration during the deceleration phase and relatively low concentration during the acceleration phase. Rapid sand deposition was observed around flow reversals. The phase lag between the free stream velocity and the sand concentration increased with elevation. The temporal and the spatial distribution of suspended sand concentration revealed an asymmetry in the suspension process, namely relatively long suspension (erosion) and short sedimentation (deposition) reflecting the asymmetry in turbulence. The instantaneous sand particle velocities were estimated using a PIV technique. The mean particle horizontal velocity was found to decrease at the beginning of the acceleration phase, corresponding to the rapid deposition of sand.