Magnitude of deviatoric terms in vertically averaged flow equations

The depth-integrated momentum and kinetic energy equations contain velocity correlation terms that involve products of local deviations in velocity co mponents about depth-averaged values. Based on velocity data obtained from North Boulder Creek, Colorado, a simple scaling analysis suggests that cert ain of these terms, which normally can be neglected in the case of smooth c hannels, can be significant parts of the momentum and energy balances in st eep, rough channels owing to the occurrence of non-logarithmic velocity pro files. A linearized version of the kinetic energy equation suggests that, f or flow accelerations over small-amplitude bed forms, the energy of the mea n motion is spatially partitioned between a form involving the depth-averag ed velocity and a form involving the deviatoric part of the velocity profil e; this partitioning is associated with spatial variations in the uniformit y of the vertical profile of the streamwise velocity. These points are cons istent with published flume measurements involving flow over sand-roughened dunes, and with published field measurements of flow over a gravel bar. Co pyright (C) 2000 John WiIey & Sons, Ltd.