Turbulence intermittency effects on initiation threshold of sediment motion in natural waters

The initiation threshold of sediment motion, a key component in quantifying sediment transport, has potential link to intermittent turbulence bursts. Here, we elaborated in situ experiments on coastal sea bottom covered with cohesive sediments, to extract intermittency parameters. For the first time, waiting time between turbulence bursts was utilized to capture the occurrence of sediment initiation events. A relationship found between waiting time and shear stress reveals the different intermittency feature of sediment flux time series before and after reaching the threshold, which can be used to determine the initiation threshold of sediment motion. Multi-site results demonstrate the limitations of traditional empirical formulae for fine-grained sediments, where cohesiveness becomes more pronounced as grain size decreases and the deviation can reach 600%. The empirical formula was modified using grain size, and the modified calculations were in good agreement with observed values, which will greatly assist in sediment transport and geomorphology model predictions.