Flow-Sediment Interaction and Formation Mechanism of Sediment Longitudinal Streaky Structures in Rough Channel Flows

Bed-load streaky structures are typical bed morphological features, yet its formation mechanism remains unclear. To fill this knowledge gap, flume experiments were conducted to quantitatively identify the characteristics of turbulent coherent structures, sediment particle movement, and bed surface structure. An innovative workflow was established that combines the particle tracking velocimetry method with the Kalman filter algorithm, specifically for identifying the trajectories of sediment particles on the bed surface. Feature matching velocity was applied to acquire the flow surface field and structure-from-motion (SFM) was used to reconstruct the three-dimensional bed topography. All the flow velocity, sediment movement, and bedforms show streaky features in the streamwise direction at 0. 068<Θ<0.113, and the streaky structures gradually fade away at Θ>0.113. The instantaneous turbulence properties of turbulent flow and sediment movement in the spanwise direction disappear, and fixed time-averaged streaky structures are formed. The streaky structures have larger characteristic scales (width and spanwise distance) in the middle of the channel than those near the sidewalls. The spanwise distance between adjacent streaky structures remains about twice the whole flow depth. Finally, this study proposes a formation mechanism based on fluid-sediment interactions, offering innovative measurement and analysis methods that can significantly contribute to understanding these interactions.