Resistance to Flow in Steep Rough Streams

A theory of resistance to flow in steep, rough streams is developed that takes into account the existence of a highly turbulent wake zone near the bed of a very rough boundary. Two zones are identified in the flow field. The first one, close to the top of the bed, contains overlapping wakes generated by protruding roughness elements. In the second zone, located above the first one, the velocity distribution is described in terms of a logarithmic profile. Flume data are used to check the validity of this formulation. The compound velocity profile allows for equations to obtain Darcy‐Weisbach and Chézy factors. The proposed approach is compared with the results of four previous theories using data obtained from several mountain rivers. Although flow in actual mountain rivers is more complicated than the idealized case treated in the study, the formulation provides equations that allow accurate prediction of flow resistance with a mean error of ±15%.