International audienceA new dataset of uniform and steady sheet flow experiments is presented in this paper. An Acoustic Concentration and Velocity Profiler (ACVP) is used to measure time-resolved profiles of collocated 2C velocity (u,w) and sediment concentration and to measure the time evolution of the bed interface position. Ensemble averaging over eleven similar experiment realisations is done to evaluate the mean profiles of streamwise velocity, concentration , sediment flux and Reynolds shear stress. The repeatability, stationarity and uniformity of the flow are carefully checked for a Shields number θ ≈ 0.5 and a suspension number of S = 1.1. The mean profile analysis allows to separate the flow into two distinct layers: a suspension layer dominated by turbulence and a bed layer dominated by granular interactions. The bed layer can be further subdivided into a frictional layer capped by a collisional layer. In the suspension layer, the mixing length profile is linear with a strongly reduced von Karman parameter equal to 0.225. The Schmidt number is found to be constant in this region with a mean value of σ s = 0.44. The present results are then interpreted in terms of existing modelling approaches and the underlying assumptions are discussed. In particular, the well-known Rouse profile is shown to predict the concentration profile adequately in the suspension layer provided that all the required parameters can be evaluated separately. However, the strong intermittency of the flow observed in the bed layer under the impact of turbulent large-scale coherent flow structures suggests the limitations of averaged steady two-phase flow models

[1] A two-phase model having a m(I) rheology for the intergranular stresses and a mixing length approach for the turbulent stresses is proposed to describe the sheet flow regime of sediment transport. In the model, two layers are considered: a dilute suspension layer and a dense sediment bed layer. The concentration profile is obtained from the dilatancy law f(I) in the sediment bed layer and from a Rouse profile in the suspension layer. The comparison of velocity profile, concentration profile, and macroscopic parameters (sediment transport rate, thickness, and roughness) with experimental data shows a good agreement. These comparisons demonstrate that the dense granular rheology is relevant to describe intense bed-load transport in turbulent regime (sheet flow). The transition from the dense static bed to the dilute suspension is well described by the present model. Also, the different regimes of the dense granular rheology seems to be able to capture the transition between collision-dominant and turbulent-fluctuations-dominant sheet flows, depending on the particle's characteristics.Citation: Revil-Baudard, T., and J. Chauchat (2013), A two-phase model for sheet flow regime based on dense granular flow rheology,