CORRECTION FACTORS IN THE DETERMINATION OF MEAN VELOCITY OF OVERLAND-FLOW

The velocity of overland flow has been conventionally measured using t racers, but it is difficult to measure the mean how velocity directly because the centroid of the tracer plume is not easily identified. Con sequently, previous investigators have measured the velocity of the le ading edge of the plume and multiplied it by a correction factor alpha to obtain an estimate of mean velocity. An alternative method is to m easure the velocity of the peak concentration in the tracer plume and multiply this velocity by another correction factor beta to estimate m ean velocity. To investigate the controls of a and beta and develop pr edictive models for these correction factors, 40 experiments were perf ormed in a flume with a mobile sand bed. Multiple regression analyses reveal that both alpha and beta vary inversely with slope and directly with Reynolds number. The derived regression equations may be used to calculate the mean velocity of other shallow overland flows, at least within the range of slope and Reynolds number for which the equations were developed. In the experiments, slope ranged from 2.7 degrees to 10 degrees and Reynolds number from 1900 to 12 600.