On local velocity measurement in gravity-driven flows with intense bedload of coarse lightweight particles

A broad dataset of sheet-flow experiments with granular material under steady and uniform conditions is presented in this paper with the focus on measurements of streamwise velocity component. Three different lightweight sediment fractions were used during 128 experimental runs across a wide range of sheet-flow modes which were represented by dimensionless Shields parameter from 0.3 up to 2.3. The local velocity information was obtained using three independent methods: Prandtl probe (PT), Ultrasonic Velocity Profiler (UVP) and Acoustic Doppler Velocity Profiler (ADVP). The measurement methods were compared to each other using results in absolute and dimensionless velocity magnitudes. Limitations of the methods are discussed. The results were consistent for all experimental runs and are further used for a description of the observed flow internal structure. The capability of individual measuring methods is demonstrated here on an identification of a transport layer of a linear velocity distribution and of a basal sublayer at the transition between the stationary bed and the transport layer.