The paper aims to evaluate the dam-break characteristics over the movable beds. In this connection two different bed material including sand and pumice were considered as the bed material. Further, the effect of bed level-difference were scrutinized on the dam-break free surface fluctuations and the bed deformation across the downstream. In this connection the numerical study was carried out through Flow-۳D CFD package. Accordingly, the volume of fluid method was used for tracking the dam-break free surface propagation along with the water-sediment interface evolution. The turbulence flow features stem from water-sediment interaction was predicted using kinematic energy-dissipation model. Moreover, the van Rijn bed load transport formula applied to evaluate the erosion and sediment entrainment throughout the downstream channel. Ultimately the re-sults indicated that first, the dam-break rapid unsteady flow evolution causes the formation of the sequential hydraulic jumps, local scouring and sedimentation across the downstream channel. Second, the dimensions of the first jump and scour hole are greater than the second ones, respectively. Third, the second hy-draulic jump is formed due to remaining dam-break flow power. The depths of the first and second scour holes are diminished through the increment of the downstream bed elevation.

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