Estimating depth-averaged velocities in rough channels

Profiles of streamwise velocity obtained from North Boulder Creek, Colorado , typically are non-logarithmic in form and exhibit the strong influence of form drag associated with coarse bed roughness. The spatially averaged pro file is consistent with recent theoretical profile forms suggested for roug h channels that are based on a partitioning of the total stress between a f luid part and a part associated with form drag on bed particles. Estimates of local depth-averaged velocity using algorithms that are based on several measurements in the flow column improve with explicit Riemann averaging, v ersus simple averaging, of the measurements. Estimates based on a single-po int measurement at 0.6 of the flow depth, assuming a logarithmic or approxi mately logarithmic velocity profile, are the least reliable. Copyright (C) 2000 John Wiley & Sons, Ltd.