Lateral Bed Load Experiments in a Flume with Strong Initial Transversal Slope, in Sub- and Supercritical Conditions

The role of lateral slope in the generation of bed load transport and bed evolution is investigated. Because of the substantial lack of detailed laboratory or field data, we designed new tests specifically devoted to acquiring accurate measurements in transient flows where the bed surface gradient has a dominant effect on the direction and magnitude of the bed load. The bed was prepared with well-sorted sand and constant nonzero slopes, both longitudinally and transversally over the flume. The flow in each experiment evolved to steady-uniform conditions characterized by a horizontal bed profile in each section and unchanged longitudinal slope. Both sub- and supercritical conditions were investigated. The bounding edges of the bed profile were surveyed on a selected transversal section. Some detailed kinematic description of the grain motion in the bed load layer has been pursued. A shallow-water model for mobile bed, able to include the most recent theories for the treatment of lateral bed load, was developed and numerically applied to the experimental tests. Comparison between measured and calculated data, and between sub- and supercritical conditions, offers several points of interest.