Three-dimensional numerical simulation of solute transport in a meandering self-formed river channel

Abstract

A three-dimensional (3-D) numerical model with standard k–ε turbulence closure has been applied to model the transport and mixing of solute in a large-scale laboratory channel. The channel is meandering with self-formed cross-sectional shape. Simulation accuracy was evaluated through comparison of computed and measured temporal concentration curves downstream of a pulse injection from a transverse line source. This study shows that the transport and mixing of solute in a meandering channel with a physically realistic bathymetry can be simulated accurately with a 3-D numerical model using k–ε turbulence closure. The prediction accuracy of the temporal concentration curves using different time steps, numerical schemes and Schmidt numbers are presented. The performance was evaluated in terms of a goodness of fit, computed peak concentration and gradients of the rising and falling limbs. The second order upwind scheme for the advective term in the solution of the advection-diffusion equation was found to give a considerably better prediction of the temporal concentration curve than the power law scheme. A value of unity for the turbulent Schmidt number results in a slightly early arrival time of the peak in tracer concentration, reducing the value of Schmidt number to 0.5 was found to result in a more accurate prediction.