Shear flow in a mildly sloping riffle-pool sequence

A series of physical experiments, together with Large Eddy Simulations (LES), are performed for an open channel flow over a mildly sloping pool-riffle sequence, a bed morphology typical in many coarse-grained rivers. Five lowangled (7.2°) bedforms were placed in a 0.6m wide rectangular flume with a flow Reynolds number of approximately Re=20,000. Our broad goal is to develop a general model of flow over this simplified macroscale bedform. Specific objectives were to measure changes to the three-dimensional distribution of flow and describe turbulent shear zones that form due to pressure gradients and interactions with the side wall. A new parameter, ?, is introduced to describe the lateral distribution of flow. Flow over the bedforms is characterized by a three-dimensional redistribution of flow and increased generation of turbulence in zones of flow deceleration, particularly near the side walls of the channel. Over repeated bedforms, the distribution of flow and turbulence adjust towards a type of equilibrium characterized by stronger lateral gradients in velocity and Reynolds stress.