Imaging-based measurement of pickup probability for sediment entrainment

We present a novel, high-speed imaging method for measuring the pickup probability for sediment entrainment under flowing water. The pickup probability is defined as the proportion of sediment particles entrained from a given bed region during a turbulent bursting period, so the measurement necessitates a least sampling frequency corresponding to the intermediate range of sediment motion. Moving particles are identified by examining the gray difference between two successive images, and the probability for sediment motion is determined by counting the number of particles in motion. The pickup probability equals the probability for sediment motion times the interval between two consecutive images divided by the intermediate temporal range. The method has been successfully applied to the measurement of bed-load transport in closed channel flows. Preliminary results show that the measured pickup probability for sediment entrainment at critical conditions remains at 2.27％, similar to previous results in the literature.