Keywords: 
• bed load /
• movement characteristic /
• image processing /
• streaky structure /
• streamwise vortex

Abstract: Bed load transport is closely connected with the turbulent structures of open-channel flow. Studies on the interaction between the movement of sediment particles and flow turbulence are of essential significance to both fluid mechanics and river dynamics. Flume experiments with low equilibrium transport of uniform sediment at different flow conditions were conducted to study the mechanism of interaction between turbulence and sediment movement. The motion of particles on the whole bed were identified by examining the gray difference between the two successive images. Analysis of the measurements yields the following findings:① Influenced by the transverse distribution of flow intensity, the probability for sediment movement was symmetric transversely, reaching its maximum at the center and decreasing gradually toward the side wall; ② Under the influence of turbulent coherent structure, particles accumulated at the region of low-speed streaky structure and were scoured at the region of high-speed streaky structure. The probability for sediment movement exhibited high-and low-speed streaky regions alternatly in the z direction; ③ The increase of friction Reynolds number led to an increase in the interval of the nearby high sediment transport rate regions, ranging from 0.13 to 0.24 times as the width of flume; ④ Under different flow conditions, the values of D/H remained 2, which corresponded to the conceptual model of streamwise vortex, indicating that the structure of streamwise vortex was an important factor to the formation of the alternating concave and convex sediment structures.