Flow Velocity and Turbulence Structure in gravel-bed rivers: experimental investigation in a straight laboratory flume

Gravel-bed flows are characterized by complex fluid/bed interactions. The presence of gravels on the bed determines spatial heterogeneities of flow velocity and turbulence structure. In this paper, experimental data collected in a gravel-bed straight laboratory channel are analyzed in order to evaluate the effect of the bed roughness on the velocity and the turbulence intensity profiles. Results show that gravel inflects the velocity distribution near the bed creating an S-shaped profile. The experimental velocity distributions are positively compared with the hyperbolic tangent profile of a pure mixing layer previously tested in vegetated flows. It has been verified that the averaged turbulence intensity profiles have a maximum at a relative water depth which approximately corresponds to that of the inflection point of the averaged velocity profiles.