Velocity Profiles in Vegetated Open-Channel Flows: Combined Effects of Multiple Mechanisms

Abstract

Vertical profile of longitudinal velocity in vegetated channels reflects complex mechanics of flow-vegetation interactions and determines the bulk flow velocity and flow rate. Most available models of velocity profiles in vegetated channels are based on a single physical concept that underpins theoretical considerations and data interpretation. However, measured velocity profiles suggest that the use of a single concept is not sufficient to cover all possible scenarios of flow-vegetation interactions. As a result, a number of models in which different concepts are applied to different flow regions have been recently developed. Within this framework, the overall velocity profile is represented with a set of linked segments. Although such segment-based models have improved velocity profile description, there is a need for more robust approaches and better analytical formulations. This paper proposes a new approach where a vertical velocity profile in vegetated channels is modelled as a linear superposition of four concepts: (1) uniform velocity distribution, (2) mixing layer analogy and a hyperbolic tangent profile, (3) boundary layer concept and a logarithmic profile, and (4) wake function concept. In contrast to the segment-based models, the proposed analytical expression combines these concepts simultaneously over the whole flow depth allowing significant overlaps of the momentum transport and turbulence production mechanisms. The model is tested using extensive laboratory experiments.