Experimental Measurements of Sediment Pickup Probability at Low Transport Stage

The concept of pickup probability is integral to the study of bed load sediment transport, dating back to Einstein's pioneering work. Despite its significance, there have been few efforts to experimentally measure the pickup probability. The scarcity of experimental data is largely due to difficulties associated with precisely pinpointing the timing of individual grain movements. This study introduces an innovative experimental method for measuring the pickup probability for the case of low sediment transport rates. First, the laser scanning technology was employed to monitor the temporal variations in bed surface elevation, enabling the detection of all instances of grain entrainment and deposition. Subsequently, the grains being entrained were identified and separated from the recorded events by establishing a criterion that defines the minimum bed-level change required for a grain to be fully entrained. This criterion allowed for a reasonable distinction between grains that were in motion and those that remained in place. The pickup probability was finally evaluated by assessing the proportion of the channel width that was occupied by grains being entrained at any given moment. The results obtained from this method were found to be in agreement with the findings from previous research.