Summary The initiation of motion in bimodal sands is investigated using a correlation technique. The method, previously developed for homogeneous sands, is extended to bimodal mixtures through a series of experiments with varying sand and fine gravel mixtures, resulting in median diameter ratios up to 8. Two transport thresholds are identified, initially associated with the median diameters of the two modes. The hiding‐exposure effect is then examined, suggesting that the second threshold is linked to the diameter, rather than the diameter of the coarser mode. Finally, a number‐weighted approach to the hiding‐exposure effect is proposed to better account for grain environments.
Daïch et al. (Sun,) studied this question.