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.

对于许多环境项目和计划，有必要对河流中的污染物迁移进行建模。污染物迁移模型是一个复杂的现象，受到多种因素的影响。描述污染物迁移的基本控制方程是对流扩散方程。该方程式有两个主要参数，即弥散系数和流速。在非均匀流动状态下，这些参数在空间上都是可变的，因此，通常使用数值方法完成对流扩散方程的求解。这些参数的空间变异性使其难以确定，尤其是对于弥散系数而言，使用相应的公式或校准来确定非均匀流的弥散系数是一项不确定且具有挑战性的任务。在这项研究中，基于无量纲输运方程和蒙特卡洛模拟技术，提出了一种方法来评估参数的空间变异性对河流浓度分布的影响。结果表明，在许多实际的河流污染物运移建模案例中，可以忽略流速和扩散系数的空间变化，并具有合理的误差。因此，对于这些情况，可以使用恒定系数的污染物迁移方程代替可变系数的方程，因此，可以采用简单的解析解而不是复杂的数值模型。所提出的方法已成功应用于实际案例研究。