Efficient Method for Coupling Field Data and Numerical Modeling for the Estimation of Transverse Mixing Coefficients in Meandering Rivers

Abstract

A numerical model has been developed employing an orthogonal stream-tube gridding system for the investigation of mixing patterns in meandering rivers. The proposed model couples field data and modeling. It uses a measured velocity field to solve the advection-diffusion equation. This equation provides a practical simulation with greater accuracy and lower computational cost for estimation of mixing in meandering channels with a long, full mixing length. The model has been used to estimate the transverse mixing coefficient in surveyed subreaches of the North Saskatchewan River in Canada. Good agreement was observed between the numerical and measured tracer concentrations using reasonable values for the transverse mixing coefficient. The average dimensionless transverse mixing coefficient from the calibrated numerical model for the surveyed reach was 0.39, which was consistent with values estimated using empirical formulas for transverse mixing coefficients in natural meandering rivers. The estimated transverse mixing coefficient was more than an order of magnitude higher in a subreach with a sharp bend than in other subreaches. For comparison, the transverse mixing coefficient was also calculated analytically from standard and general methods of moments between some sections.