Influence of the shear stress on fine sediment exchanges with the substrate using UVP measurements

The dynamic of fine sediment in rivers is closely related to the interactions between fine particles, the riverbed and the flow conditions. The accumulation of fine sediment in the riverbed reduces vertical water exchanges and can have detrimental effects on the ecosystem of rivers. The conditions needed for the deposition of suspended sediment on the surface or inside the riverbed depend on the local flow conditions and have only been little studied. To explore this aspect, flow velocity measurements were performed using a UVP probe to evaluate the shear stress and asses the accuracy of the measurement in locations with different flow conditions along a flume. The shear velocity was inferred from the velocity profiles using the log-law equation. These results were then compared to the estimation of the shear stress using a simple backwater curve model. Results show that the shear velocity can be well evaluated when the flow conditions are not disturbed by protruding grains, even though gravel induce some variability in the results. The use of UVP to measure the shear stress with small relative water depth in comparison with bed roughness still represents challenges that might be addressed in future work.