ADV measurements of velocity distributions in a gravel‐bed flume

Velocity measurements carried out by an acoustic doppler velocimeter (ADV) in a rectangular laboratory flume having a gravel bed are presented. The velocity profiles are measured in six verticals of the channel cross‐section having an increasing distance (from 4 to 38·5 cm) from the flume wall. The experimental runs are carried out for five different bed arrangements, characterized by different concentrations of coarser elements, and for the two conditions of small‐ and large‐scale roughness. For both hydraulic conditions, the velocity measurements are first used to test the applicability of the Dean profile and of the logarithmic profile corrected by a divergence function proposed in this paper. Then, for each value of the depth sediment ratio h / d 84 , the non‐dimensional friction factor parameter is calculated by integration of the measured velocity distributions in the different verticals of the cross‐section. Finally a semi‐logarithmic flow resistance equation is empirically deduced.