Numerical modelling-based comparison of longitudinal dispersion coefficient formulas for solute transport in rivers

摘要

River water quality models usually apply the Fischer equation to determine the longitudinal dispersion coefficient (D-x) in solving the advection-dispersion equation (ADE). Recently, more accurate formulas have been introduced to determine D-x in rivers, which could strongly affect the accuracy of the ADE results. A numerical modelling-based approach is presented to evaluate the performance of various D-x formulas using the ADE. This approach consists of a finite difference approximation of the ADE, a MATLAB code and a MS Excel interface; it was tested against the analytical ADE solution and demonstrated using eight well-known D-x formulas and tracer study data for the Chattahoochee River (USA), the Severn (UK) and the Athabasca (Canada). The results show that D-x has an important effect on tracer concentrations simulated with the ADE. Comparison between the simulated and measured concentrations confirms the appropriate performance of Zeng and Huai's formula for D-x estimation. Use of the newly proposed equations for D-x estimation could enhance the accuracy of solving the ADE.