Alluvial Resistance in Transition Regime

The resistance of alluvial channels depends upon flow and sediment characteristics. This paper considers the bed features and alluvial resistance that occur at, and close to, the transition zone between the upper and lower flow regimes. New flume and river data are published and the results are analyzed to provide satisfactory predictive techniques covering the lower, transition, and upper regimes for use by river engineers. The bed features that occur in the transition regime are shown to be washed‐out dunes that diminish rapidly in height and steepness with increasing shear stress. The increase in depth with increasing unit discharge is much reduced in the transition regime due to lower hydraulic resistance. In certain circumstances, depths in the transition region can decrease with increasing unit discharge. A criterion for the upper limit of the transition regime corresponding to a moving flat bed is proposed by the writers.