Abstract
Hydrodynamics of a forced riffle pool in a gravel bed river: 1. Mean velocity and turbulence intensity
Canada Research Chair in Fluvial Dynamics, Département de Géographie, Université de Montréal, Montréal, Québec, Canada
Canada Research Chair in Fluvial Dynamics, Département de Géographie, Université de Montréal, Montréal, Québec, Canada
Riffle pools are fundamental units of many gravel bed rivers. Considerable debate exists as to an appropriate hydrodynamic model for this bed form type. Sampling designs in previous studies have not always anticipated the degree of spatial variability of flow parameters in riffle pools nor considered the effect of the nonuniform boundary on hydrodynamics. The objective of this paper is to detail the distribution of mean velocities and turbulence intensities in a forced riffle pool. While limited by the lack of lateral velocity measurements, the data set is of high quality and includes measurements during a bankfull flood. Key observations include the perturbation of velocity profiles from what is observed in uniform flow, lateral convergence and divergence of flow, and the generation of turbulence away from the channel boundary. In the thalweg of the pool head, velocities are high near the water surface and low near the bed. Turbulence intensities are relatively high near the bed and may be significant for sediment entrainment. Higher mean velocities occur over the side bar and could indicate that sediment is routed around the thalweg. The midpool is characterized by the lateral constriction of flow and a shear zone downstream of the forcing element. The pool tail has very high velocities and turbulence intensities near the bed. A velocity reversal occurs in the pool tail at bankfull flow but does not occur in the pool head. A consideration of deceleration and acceleration as a result of vertical expansion and contraction is shown to explain many of the key observations.
Received 22 June 2006; accepted 14 August 2007; published 5 December 2007.
Citation: (2007), Hydrodynamics of a forced riffle pool in a gravel bed river: 1. Mean velocity and turbulence intensity, Water Resour. Res., 43, W12401, doi:10.1029/2006WR005272.
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