DETERMINING THE MEAN DEPTH OF OVERLAND-FLOW IN FIELD STUDIES OF FLOW HYDRAULICS

In field studies of interrill overland flow conducted on runoff plots, the mean depth of flow is usually obtained by averaging measurements of flow depth at regularly spaced points across the plot, including points where there is no flow. Although this procedure may be appropriate in studies aimed at runoff prediction, it is not in studies concerned with flow hydraulics. In the latter studies, more realistic results can be obtained by excluding those points where the depth is zero and reducing the width of flow in proportion to the number of points excluded. Failure to do this results in the underestimation of the actual mean flow depth, Reynolds number, and friction factor. Where discharges are small or microtopography is large, this underestimation is likely to be significant. Copyright 1990 by the American Geophysical Union.