Estimates of flow resistance and eddy viscosity coefficients for 2D modelling on vegetated floodplains

Abstract

Abstract:The problem of quantifying the effects of flexible plants on flow resistance and eddy viscosity by vegetated floodplains is first addressed with a one-dimensional (1D) approximation based upon the so-called lateral distribution method. The estimates so obtained are then tested with two-dimensional (2D) numerical simulations based on the full shallow water equations through the use of the computational code Telemac-2D. Data obtained on a physical model of the Besòs River (Spain), whose floodplains were covered with plastic ornamental plants to mimic the effect of flexible vegetation, is used for the validation of the numerical results. Additionally, the values of flow resistance estimated numerically with the 1D and 2D simulations are compared with values obtained in a rectangular flume under flow conditions (slope, water depth and artificial lining) similar to those used on the reduced model. It is then established that as more physical mechanisms are included in the mathematical model used to study the problem, the ratio between the floodplain and the main channel flow resistance coefficient increases. The approach demonstrates that whenever enough flow data is available, the lateral distribution method delivers values of flow resistance and eddy viscosity which are highly consistent with 2D numerical modelling. This finding could mean considerable savings in the burdensome task of specifying flow resistance and turbulence dissipation values for 2D modelling of large compound channel systems.

A vortex‐based model of velocity and shear stress in a partially vegetated shallow channel

“…Most models have used simplified one-dimensional approaches with an empirical Darcy-Weisbach friction factor or a simple eddy viscosity model for the turbulence structure. Vionnet et al [2004] proposed an eddy viscosity model to describe the momentum exchange between the main channel and the floodplain, and used results from a laboratory model to calibrate it. Helmiö [2004] also used a one-dimensional model, with a calibrated DarcyWeisbach friction factor at the vegetation interface, to describe the flow conveyance of two lowland rivers.…”

Modelo analítico para el cálculo de distribuciones de velocidad laterales en secciones tipo potencial-ley

“…Su resolución fue propuesta inicialmente por Wark et al [25] y por Shiono y Knight [26,27]. En la actualidad, el método propuesto por Shiono y Knight (SKM) está ampliamente extendido, y es la base para el desarrollo de modelos que son capaces de representar condiciones de flujo complejas [36][37][38][39].…”

“…siendo la relación entre velocidades (v i =v a ) (combinando (33) y (40)) Conocidos los parámetros β y m de una sección, y eligiendo k e i, las ecuaciones anteriores permiten el cálculo del calado, caudal y velocidad para cada subdivisión, determinando previamente el coeficiente C corr según la expresión (39).…”

“…Modelo analítico para el cálculo de distribuciones de velocidad laterales en secciones tipo potencial-ley, Ribagua, 5:1,[29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47]…”

Calibrating discharge, bed friction, and datum bias in hydraulic models using water level and surface current observations

“…Typically, the measurements are from water gages at a small number of river positions, and a section uniform discharge is estimated by comparing measured water levels with rating curves. A related 1-D approach [McKay and Fischenich, 2011] combines the friction estimates derived from stage/discharge measurements with empirical parameterizations that depend on grain size [Lumerinos, 1970;Wong and Parker, 2006], bedform size [van Rijn, 1984] or vegetation [Vionnet et al, 2004]. For an extended discussion of friction due to nonuniform channel roughness the reader is referred to Yen [2002] and Knight [2006].…”