Bed Features in Nonuniform Sediments

This study explores the formation of bed features in nonuniform sediments. Experiments conducted in a recirculating flume show that the amount of sediments on the bed surface influence the size of the bed features in nonuniform sediments. At low velocities, the availability of fine sediment particles on the bed surface controls the size of the bed features. The finer portion of the bed sediment in transport forms the bed features, while the coarser sediment particles form the armor layer beneath the overpassing bed features. At high velocities, when all grains are mobile, antidunes do not form for a Froude number exceeding unity, because of the presence of a pavement or dynamic armored layer near the surface of the bed. No antidunes were observed in the experiment for geometric standard deviations of the bed sediment exceeding 2.3. The study shows that the preferred bed feature is transition flat bed when the Froude number exceeds unity.