Keywords: 
• non-uniform bed load /
• motion velocity /
• motion trajectories /
• motion/rest time /
• probability distribution /
• flume experiment

Abstract: The sand in a natural riverbed is usually non-uniform and is considered as the basis for simulating and forecasting the evolution of the natural riverbed, to accurately understand the movement of non-uniform sediment particles. In this study, a flume experiment with non-uniform bed load movement was conducted under uniform flow condition. The particle size range of the bed material was 0.10-20 mm. The motion process of sediment particles over the rough bed was filmed using a high-speed camera mounted on the top of the flume, and basic motion parameters such as motion trajectories, velocity, and motion/rest time of the non-uniform bed load were obtained. The particle size range of the bed load was 0.74-8.19 mm. The results showed the following:the motion direction of bed load is changed by aggregates or large particles on the non-uniform bed surface when compared to results of uniform sediment; the longitudinal velocity decreases and the transverse velocity increases on non-uniform bed load; the longitudinal velocity of bed load follows an exponential distribution, the single velocity meets Γ distribution, the transverse velocity and bed load velocity vector angle meets the normal distribution.