Experimental Investigation of Dammed Flow in Open Channels: Backwater Effects on Flow Turbulence and Suspended Sediment

The backwater effect of large hydraulic structures (dams or gates) alters upstream hydrodynamics and sediment transport. However, the turbulent characteristics and sediment transport mechanisms under backwater remain unclear. This study investigates how dam-induced backwater affects open-channel turbulence and suspended sediment transport. Laboratory experiments are conducted to analyze flow velocity distribution, turbulence intensity, and suspended sediment concentration (SSC) under varying backwater conditions for clear and sediment-laden flows. Horizontally, an increased backwater indicator (BI, β) reduces streamwise velocity, and substituting section-averaged velocity for friction velocity yields a logarithmic profile (R2=0.977–0.994). Vertically, backwater induces “vertical-plane” secondary flows and an adverse pressure gradient at relative water depth (y/h) larger than 0.2, producing a velocity peak at y/h≈0.4; these vertical flow components are more sensitive to discharge (25%) than to bed-slope changes (33.4%). In sediment-laden flows, near-bed velocities (y/h<0.2) decrease and sensitivity to BI weakens, indicating two-phase feedback. These results fill gaps in understanding backwater flow dynamics and provide a foundation for refining models and optimizing hydraulic-structure design and operation.