The effect of neglecting spatial variations of the parameters in pollutant transport modeling in rivers

Abstract

For many environmental projects and plans, it is necessary to model pollutant transport in rivers. Pollutant transport modeling is a complex phenomenon with multiple factors affecting it. The basic governing equation describing pollutant transport is advection–dispersion equation. There are two main parameters in this equation, namely, dispersion coefficient and flow velocity. In non-uniform flow regimes, these parameters are both spatially variable, therefore, solution of the advection–dispersion equation usually accomplished using numerical methods. Spatial variability of these parameters makes it hard to determine them, particularly for dispersion coefficient in which determining it for non-uniform flows using the corresponding formulas or calibration is an uncertain and challenging task. In this study, based on non-dimensionalized transport equation and the Monte Carlo simulation technique, a methodology is presented for evaluating the effects of spatial variability of the parameters on concentration distribution in rivers. The results imply that for many practical cases of pollutant transport modeling in rivers, spatial variations of flow velocity and dispersion coefficient can be neglected with a reasonable error. Consequently, for these cases, constant-coefficient pollutant transport equation can be applied instead of the variable-coefficient one, hence, simple analytical solutions can be employed rather than complicated numerical models. The proposed approach was applied for a real case study, successfully. It is emphasized that the results of the study are fairly general and can provide insight and simplification in different stages of pollutant transport modeling in rivers.