Lateral distributions of streamwise velocity in compound channels with partially vegetated floodplains

Abstract

Natural rivers are commonly characterized by a main channel for primary flow conveyance and a floodplain, often partially covered with vegetation such as shrubs or trees, to carry extra flow during floods. The hydraulic resistance due to vegetation on the floodplain typically causes a further reduction of flow velocity and increases the velocity difference between the main channel and the floodplain. As a consequence a strong lateral shear layer leads to the exchange of mass and momentum between the main channel and floodplain, which in turn affects the overall channel conveyance and certain fluvial processes. The prediction of the lateral velocity distribution is important for many flood alleviation schemes, as well as for studies on sediment transport and dispersion in such channels. The present paper proposes a method for predicting the depth-averaged velocity in compound channels with partially vegetated floodplains, based on an analytical solution to the depth-integrated Reynolds-Averaged Navier-Stokes equation with a term included to account for the effects of vegetation. The vegetation is modelled via an additional term in the momentumequation to account for the additional drag force. The method includes the effects of bed friction, drag force, lateral turbulence and secondary flows, via four coefficients f, C D , λ & Γ respectively. The predicted lateral distributions of depth-averaged velocity agree well with the experimental data. The analytical solutions can also be used to predict the distribution of boundary shear stresses, which adds additional weight to the method proposed. vegetation, compound channel, floodplain, velocity

Can the application of a multi‐objective evolutionary algorithm improve conveyance estimation?

“…An additional term may be added to () to simulate the additional drag forces arising from vegetation, if required, as shown by Rameshwaran & Shiono (2007) and Tang & Knight (2009). An analytical solution to exists [see Shiono & Knight (1991) and Knight & Shiono (1996)], which is given in for a domain of constant depth and for a domain with varying depth.…”

An Improved Analytical Model for Vertical Velocity Distribution of Vegetated Channel Flows

“…As a pre-requisite for the analysis in resistance and pollutant mixing process of flow and so on, the vertical velocity distribution in vegetated channel flow has drawn great attention of researchers (e.g. Tsujimoto & Kitamur, 1990, Shimizu & Tsujimoto, 1994Nepf & Koch, 1999;Ghisalberti & Nepf, 2004;Kubrak, et al, 2008;Tang & Knight, 2009;Tang et al, 2010Tang et al, , 2011Nguyen, 2012;Hao et al, 2014). Many investigators have attempted to predict vertical velocity distribution based on semi-empiricism and/or analytical solution of the momentum equation with closure schemes, in which the modelling of eddy viscosity is to describe the turbulent stresses (Klopstra et al, 1997;Meijer & Van Velzen, 1999;Defina & Bixio, 2005;Baptist et al, 2007;Huai, et al, 2009Huai, et al, , 2014Yang & Choi, 2010;Dimitris & Panayotis, 2011;Nepf, 2012;Nikora et al, 2013;Tang, 2018aTang, , 2019aSingh et al, 2019).…”

Optimal prediction of lateral velocity distribution in compound channels

“…In open channel flow, lateral velocity distribution models have become the subject of analysis and application in recent years (Weber and Menendez, 2004). Lateral velocity distributions are required for solving many hydro-engineering problems such as development of stage-discharge curves and estimation of boundary shear stress distribution (Guan, 2003;Tang and Knight, 2009b), identification of erosion or deposition within a reach section of a river, computation of sediment transport capacities (Hu et al, 2010), selection of proper locations for river intakes, river-bank protection designs, prediction of scour depth at bridge piers and abutments (Kouchakzadeh and Townsend, 2000), and computing of the lateral change of bed form across the river (Seo and Gadarlab, 1999). The lateral velocity distribution can be directly utilized to develop river stage-discharge curves, which are one of the main concerns of researchers in both simple and compound river channels, as they play a very important role in river training and flood control works (Knight et al, 2010).…”