Modeling the longitudinal profiles of streamwise velocity in an open channel with a model patch of vegetation
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Modeling the longitudinal profiles of streamwise velocity in an open channel with a model patch of vegetation Chunhao Yan1 · Yuqi Shan1,2 · Wei Sun1 · Chao Liu1 · Xingnian Liu1 Received: 13 October 2019 / Accepted: 19 May 2020 © Springer Nature B.V. 2020
Abstract This paper proposes a model for predicting the longitudinal profiles of streamwise velocities in an open channel with a model patch of vegetation. The governing equation was derived from the momentum equation and flow continuity equation. The model can estimate the longitudinal profiles of velocities both inside and outside a vegetation patch. Laboratory experiments indicate that the longitudinal profiles of velocities inside a patch and in the adjacent bare channel have the same adjustment distance in the longitudinal direction, but the profiles have different trends because the vegetation drag drives the flow from the patch to the adjacent bare channel. The model considers different dimensionless parameters in two flow adjustment regions upstream of and inside the patch. Sixteen sets of experimental data from different sources are used to verify the model. The model is capable of modeling the longitudinal profiles of velocities inside and outside patches of cylinders or cylinder-like plants. Compared to a previous model, the current model improves the modeling accuracy of longitudinal profiles of velocities. Keywords Vegetation patch · Analytical model · Partially vegetated channel
1 Introduction In natural rivers and wetlands, aquatic vegetation often grows in the form of patches with a finite length and width and the size of patches is generally on an order of meters [2, 6, 42–45]. Specifically, the width and length of a patch often ranges between 0.3 and 6 m [8, 22, 37], while the size of a patch is considerably smaller than the size of a natural river, thus forming a partially vegetated channel [50]. Vegetation patches play an important role in trapping sediment and altering the local flow fields in a river system. The interactions among flow, sediment and bed morphology produce different feedbacks inside a vegetation patch and the bare channel (e.g., [8, 37, 41]. Inside a patch, fine * Chao Liu [email protected] 1
State Key Laboratory of Hydraulics and Mountain River Engineering, Sichuan University, Chengdu 610065, China
2
Institute for Disaster Management and Reconstruction, Sichuan University, Chengdu 610065, China
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Environmental Fluid Mechanics
suspended sediment and organic matter preferentially deposits in the fully developed flow region due to the low velocity and turbulence [25, 32, 47]. The deposited fine sediment promotes the growth of plants, thus leading to an increase in plant density, which further reduces the velocity and turbulence and enhances sediment deposition [11]. Outside a patch, the flow deflection near the upstream edge of a patch leads to increased velocity in the bare channel, which may produce bed erosion along the side edge of a patch [1, 13]. Because local velocity is related t
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