Turbulence increases sediment transport

In steady, fully developed flows over erodible beds, the average bed shear stress is generally the dominant factor governing sediment flowrate. However, fluctuations induced by turbulence can play a significant role in altering sediment transport dynamics. This study investigates the effects of such turbulence by conducting flume experiments with flow disturbances created by various cylinder arrays placed in the flow. To measure the turbulent flow field, Laser Doppler Velocimetry (LDV) was employed, while bed shear stress was quantified using a shear plate. The bedload motion was analysed using Particle Tracking Velocimetry (PTV), which allowed for the quantification of key variables such as sediment concentration, velocity, and sediment flowrate. A descriptive model was developed to capture the relationship between these primary variables and both the average and fluctuating components of the flow. Our results show that with increasing turbulent fluctuations, both sediment concentration and velocity rise at a fixed mean shear stress. Notably, turbulence influences concentration more strongly than velocity.