Influence of Weak Bed-Load Transport on Mean Flow Characteristics over Immobile Smooth Bed Surface under Dynamic Equilibrium Flow Conditions

Flow-stream-bed interaction has received substantial interest in the field of fluvial hydraulics since few decades and the present study aims to explore the influenece of weak bed-load transport on near-bed flow characteristics under dynamic equilibrium flow conditions. The experimental conditions were tackled in two folds: (1) flow over immobile bed without bed-load transport and (2) weak bed-load transport over the immobile bed. A layer of well-sorted sand grains was glued on the flume bottom to develop an immobile sand bed surface. Uniformly graded sediments were injected into the flows for sediment motion in the form of weak bed-load transport. Nineteen dynamic equilibrium flow conditions were established and an acoustic Doppler velocimeter was used to measure the instanteneous velocity. The weak bed-load transport induced massive damping in Reynolds shear stress distributions and enhanced streamwise velocity gradients. Most significantly, turbulent kinetic energy flux components showed positive streamwise and negative vertical fluxes in the near-bed flow region corroborating an accelerating effect on the inertia of flowing fluid. The results associated to turbulent parts of kinetic energy components are further illustrated in the light of turbulent kinetic energy budget concept to elucidate the influence of weak bed-load transport on mean flow characteristics.