Abstract
AbstractSubmerged aquatic vegetation affects flow, sediment and ecological processes within rivers. Quantifying these effects is key to effective river management. Despite a wealth of research into vegetated flows, the detailed flow characteristics around real plants in natural channels are still poorly understood. Here we present a new methodology for representing vegetation patches within computational fluid dynamics (CFD) models of vegetated channels. Vegetation is represented using a Mass Flux Scaling Algorithm (MFSA) and drag term within the Reynolds‐averaged Navier–Stokes Equations, which account for the mass and momentum effects of the vegetation, respectively. The model is applied using three different grid resolutions (0.2, 0.1 and 0.05 m) using time‐averaged solution methods and compared to field data. The results show that the model reproduces the complex spatial flow heterogeneity within the channel and that increasing the resolution leads to enhanced model accuracy. Future applications of the model to the prediction of channel roughness, sedimentation and key eco‐hydraulic variables are presented, likely to be valuable for informing effective river management. © 2016 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.
Highlights
Submerged aquatic vegetation is abundant in many lowland river systems and exerts a strong influence on the functioning of the fluvial system
The results demonstrate that the vegetation model developed here is able to reproduce both the spatial patterns and magnitudes of the velocity profiles, even reproducing complex wake structures and high velocity threads (Gurnell et al, 2006)
Assessing the impact of these dynamic flow–vegetation interactions on patch-scale hydraulics is a direction for future research. Considering these factors, and the ability of the model to reproduce the shape of the velocity profiles and velocity magnitude at the acoustic Doppler velocimeter (ADV) locations, we suggest that the model presented here provides a promising methodology for predicting the patch-scale effect of vegetation on flow within rivers
Summary
Submerged aquatic vegetation is abundant in many lowland river systems and exerts a strong influence on the functioning of the fluvial system. Vegetation, through the additional flow resistance it generates, influences water depth, mean flow velocities (Jarvela, 2002; Green, 2005a; Nepf et al, 2007) and turbulence (Okamoto and Nezu, 2009; Nikora, 2010), which subsequently affects sediment dynamics (Dawson, 1981; Sand-Jensen et al, 1989; López and García, 1998), water quality (Kadlec and Knight, 1996; Ghisalberti and Nepf, 2006) and habitat diversity (Westlake, 1975; Liu et al, 2008). Flow adjustment around vegetation patches controls the magnitude of form drag exerted on the flow This in turn determines the flow resistance as well as the extent of wake regions that introduce process heterogeneity, promote sedimentation and provide habitat for terrestrial and aquatic wildlife (López and García, 1998; Kemp et al, 2000; Liu and Shen, 2008). The physical processes driving flow–vegetation interactions at the patch-scale need to be fully understood to explain how vegetation affects both spatial and temporal flow dynamics and river morphodynamics, eco-hydraulics and stream biogeochemistry
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