Sediment Transport under Sheet-Flow Conditions

Experiments on sediment transport under sheet-flow conditions were conducted by tracing individual and grouped light plastic particles. The measurements based on individual particles yielded the vertical and temporal variations of the instantaneous sediment concentration and transport velocity from which the sediment-transport rate per unit width was obtained. In addition, moving areas of painted particle groups were measured to estimate instantaneous sediment transport rates per unit width directly. Measured local sediment-transport rates were the largest at one or two particle diameters above the initial bed surface. Instantaneous sediment-transport rates per unit width exhibited a π/6 phase lead relative to the free-stream velocity. The measured sediment-transport rates averaged over a half-cycle were compared with forcing functions Shields and mobility parameters. The present data as well as most available existing data in terms of the normalized transport rate without the settling velocity were well arranged by the mobility number to the power of 1.5.