Roughness effect on the correction factor of surface velocity for rill flows

Flow velocity is one of the most important hydrodynamic variables for both channelized (rill and gullies) interrill erosive phenomena. The dye tracer technique to measure surface flow Vs based on measurement travel time a needed cover known distance. measured must be corrected obtain mean V using factor αv = V/Vs which generally empirically deduced. can influenced by method applied dye-tracer vary in different conditions. Experiments were performed fixed bed small flume simulating rill channel two roughness conditions (sieved soil, gravel). comparison between chronometer-based (CB) video-based (VB) was carried out. For each slope-discharge combination, 20 measurements Vs, characterized sample Vm, techniques, frequency distributions Vs/Vm resulted independent slope discharge. given technique, all normally distributed, with equal one, featured low variability. Therefore, Vm considered representative velocity. Regardless roughness, values obtained techniques very close good precision. developed analysis highlighted that it not correlated Reynolds number turbulent regime. Moreover, neither Froude nor slope. However, empirical correction demonstrated effect. (CB, VB)-roughness (soil, gravel) constant statistically even if less accurate estimations compared those yielded slope-specific factor.