Adv measurements of velocity distributions in a gravel-bed flume

摘要

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.