Pollutant Transport In Rivers Research Articles

A Numerical Model of the Pollutant Transport in Rivers with Multi-Layer Rigid Vegetation

River water pollution is a key environmental issue to human society. How to effectively simulate the flow velocity and pollution transport in a vegetated river can provide a theoretical basis for solving such problems. Based on previous experimental data, this article uses the lattice Boltzmann method and random displacement method to simulate the velocity distribution and nutrient transport in multi-layer rigid vegetated rivers. The simulation results indicate that incorporating the drag force of the vegetation into the model according to different vegetation layers can effectively simulate the velocity in a multi-layer vegetated river. Incorporating the turbulent diffusion and mechanical diffusion effects of nutrients caused by vegetation into the model can effectively simulate the effects of multi-layer vegetation on nutrient transport. This model can provide effective predictions of the flow velocity and pollution transport in multi-layer vegetation.

Modeling Channel Deformation and Pollutant Transport in Rivers in Permafrost Zone with Local Channel Curvature

The results of laboratory and mathematical modeling of pollutant propagation from thawed sources on bank slopes in curvilinear reaches of rivers in permafrost zone are presented. Particular attention is paid to studying the effect of channel deformations caused by thermal erosion on the speed and character of pollutant spot propagation. The laboratory experiments in the hydraulic flume were primarily focused on determining the difference in the deformation dynamics and solute propagation from thawing sources at different shapes of channel curvature for the farther use of these data as input parameters of mathematical model for its verification. The analysis of a series of numerical calculations at a scale of laboratory experiment and an actual natural object suggested the conclusion regarding the effect of channel morphometric characteristics, the hydrological and thermal parameters of water flow, the characteristics of permafrost channel-forming ground on the dynamics of pollutant propagation in curvilinear reaches of the permafrost zone.

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

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.

Introducing a new method for calculating the spatial and temporal distribution of pollutants in rivers

Using constant coefficients is an inefficient way to explain the details of the problem of pollutant transport. This is due to factors such as nonuniform geometry, discharge changes, flow velocity and dispersion coefficient variations. Previous studies indicate that the ratio of studies on pollutant transport in rivers is lower than those on the porous media. However, the relative complexity of the solution of the pollutant transport equation in rivers (especially in the case of variable coefficients) in comparison with porous media highlights the importance of focusing on the solutions for rivers environment. In this study, the one-dimensional equation of pollutant transport in the river with location-dependent variables (velocity, dispersion coefficient and cross-section area) with arbitrary pattern is solved via the generalized integral transform technique (GITT) in a finite-length domain and general initial and boundary conditions. In this study, the results obtained from the presented analytical solution are compared to those obtained from the existing analytical solutions in previous studies for the two states of constant and variable coefficients. To further test the accuracy of this method, we have compared the results obtained from the presented analytical solution with the results obtained from numerical solution based on finite-difference method by applying the conditions of two real rivers. Comparison of the results of the GITT verification with available analytical solutions as well as numerical solutions shows the high accuracy and the applicability of the proposed solution considering arbitrary patterns of the ADRE coefficients and general initial and boundary conditions.

Simulation of pollutants transport in rivers and its effect on the dynamics of a species by a high order method

In the study of environmental transport phenomena, there is a standard analytic methodology to compute distribution, transport, and the fate of a pollutant in unbounded domains. However, to solve the problem in a nontrivial geometry accurately requires the use of a robust computational tool. This paper shows a derivation and an evaluation of a high order spectral element method to simulate the distribution and transport of a pollutant in surface waters and its effect on the population dynamics of a species. The algorithm implements a continuous Galerkin spectral element method in space and the trapezoid scheme to integrate in time. Finally, to validate the numerical method, this paper presents a time-space convergence study. Then, we simulated the transport of pollution runoff over a channel and its effect on a single species population dynamic.

ANALYTICAL SOLUTION OF A NON - HOMOGENEOUS ONE - DIMENSIONAL ADVECTION DIFFUSION EQUATION WITH TEMPORALLY VARYING COEFFICIENTS .

Advection Diffusion Equation is a partial differential equation that describes the transport of pollutants in rivers. Its coefficients (dispersion and velocity) can be constant, dependent on space or time or both space and time. This study presents an analytical solution of a one dimensional non - homogeneous advection diffusion equation with temporally dependent coefficients, describing one dimensional pollutant transport in a section of a river. Temporal dependence is accounted for by considering a temporally dependent dispersion coefficient along an unsteady flow assuming that dispersion is proportional to the velocity. Transformations are used to convert the time dependent coefficients to constant coefficients and to eliminate the advection term. Analytical solution is obtained using Fourier transform method considering an instantaneous point source. Numerical results are presented. The findings show that concentration monotonically decreases with increasing distance and increasing time.

Effect of Bank Deformations on Pollutant Transport in Rivers in Cryolithozone: Laboratory and Mathematical Modeling

The study is focused on pollution transport in rivers flowing in cryolithozone and takes into account possible channel deformations caused by thawing of permafrost rocks in which the channel runs. The methods used are laboratory and mathematical modeling. The mathematical model consists of four blocks: hydrodynamic, thermal, deformation, and pollutant transport. The model was validated and tested against the data of a laboratory experiment. Numerical experiments suggested conclusions regarding the propagation of pollutants entering the flow from sources in thawing bank slopes and on river floodplain.

Improvement on the Existing Equations for Predicting Longitudinal Dispersion Coefficient

Accurate prediction of longitudinal dispersion coefficient (K) is a key element in studying of pollutant transport in rivers when the full cross sectional mixing has occurred. In this regard, several research studies have been carried out and different equations have been proposed. The predicted values of K obtained by different equations showed a great amount of uncertainty due to the complexity of the phenomenon. Therefore, there is still a need to make an improvement on the existing predictive models. In this study, a multi-objective particle swarm optimization (PSO) technique was used to derive new equations for predicting longitudinal dispersion coefficient in natural rivers. To do this, extensive field data, including hydraulic and geometrical characteristics of different rivers were applied. The results of this study were compared with those of the previous studies using the statistical error measures. The comparison revealed that the proposed model is superior to the previous ones. According to this study, PSO algorithm can be applied to improve the performance of the predictive equations by finding optimum values of the coefficients. The proposed model can be successfully applied to estimate the longitudinal dispersion coefficient for a wide range of rivers’ characteristics.

A comprehensive one-dimensional numerical model for solute transport in rivers

Abstract. One of the mechanisms that greatly affect the pollutant transport in rivers, especially in mountain streams, is the effect of transient storage zones. The main effect of these zones is to retain pollutants temporarily and then release them gradually. Transient storage zones indirectly influence all phenomena related to mass transport in rivers. This paper presents the TOASTS (third-order accuracy simulation of transient storage) model to simulate 1-D pollutant transport in rivers with irregular cross-sections under unsteady flow and transient storage zones. The proposed model was verified versus some analytical solutions and a 2-D hydrodynamic model. In addition, in order to demonstrate the model applicability, two hypothetical examples were designed and four sets of well-established frequently cited tracer study data were used. These cases cover different processes governing transport, cross-section types and flow regimes. The results of the TOASTS model, in comparison with two common contaminant transport models, shows better accuracy and numerical stability.

Software for Pollutants Transport in Rivers and for Identification of Excessive Pollution Sources

The program packages of realization of mathematical models of pollutants transport in riversand for identification of river water excessive pollution sources located between two controlled cross sections of the river will be considered and demonstrated The software has been developed by the authors on the basis of mathematical models of pollutant transport in the rivers and statistical hypotheses test shy ing methods The identification al shy go shy rithms were elaborated with the supposition that the pollution sources discharge dif shy fe shy rent compositions of pollutants or at the identical com shy po shy sition different propor shy tions of pollutants into the rivers One two and three dimensional advection diffusion mathematical models of river water quality formation both under classical and new original boundary conditions are realized in the package New finite difference schemes of calculation have been developed and the known ones have been improved for these mathematical models At the same time a number of important problems which provide practical realization high accuracy and short time of obtaining the solution by computer have been solved Classical and new constrained Bayesian methods of hypotheses testing for identification of river water excessive pollution sources are realized in the appropriate software The packages are designed as a up to date convenient reliable tools for specialists of various areas of knowledge such as ecology hydrology building agriculture biology ichthyology and so on They allow us to calculate pollutant concentrations at any point of the river depending on the quan shy shy tity and the conditions of discharging from several pollution sources and to identify river water excessive pollution sources when such necessity arise

Some Numerical Results of Multipoints Bomndary Value Problems Arise in Environmental Protection

Abstract In this paper, we investigate two problems arise in pollutant transport in rivers, and we give some numerical results to approximate this solutions. We determined the approximate solutions using two numerical methods: 1. B-splines combined with Runge-Kutta methods, 2. BVP4C solver of MATLAB and then we compare the run-times.

Evaluation of Appropriate Advective Transport Function for One-Dimensional Pollutant Simulation in Rivers

Water quality prediction is a valuable tool for pollutant control in aquatic environments. A river system is selected and one-dimensional flow is assumed for the simulation of pollutant transport in this paper. Advective and diffusive terms of transport equation are considered separately. Different functions of advective transport are proposed and applied for a specified velocity on the discrete cells along the river and compared with each other. Abilities and flexibilities of these proposed functions are investigated and the compatible one is determined for the point source pollutant transport in the channel. Fluctuations (Maximum content of negative concentrations), tolerances (Maximum interval of negative concentrations) and attenuation (Decreasing peak of the pollutant distribution) are selected for this purpose. Quick and the proposed functions including trigonometric, simple exponential, symmetric exponential and quadratic exponential of advective transport are selected for the comparison. Results show that during the simulation period (times up to 100 seconds and times more than 100 seconds), for the estimation of attenuation, the peak of the pollutant distribution and the elimination of fluctuations and the tolerances, the proposed symmetric exponential and quadratic exponential functions of advective transport perform better than other numerical methods and presented functions. Also for all these scales both of quadratic exponential and symmetric exponential functions act similarly, therefore they can be used frequently for the simulation of pollutant transport in rivers without creating negative concentration.Moreover, simple exponential function and quick method identically predict the peak of pollutant chemograph at each downstream point.

Adaptation of a Weighted Regression Approach to Evaluate Water Quality Trends in an Estuary

To improve the description of long-term changes in water quality, a weighted regression approach developed to describe trends in pollutant transport in rivers was adapted to analyze a long-term water quality dataset from Tampa Bay, Florida. The weighted regression approach allows for changes in the relationships between water quality and explanatory variables by using dynamic model parameters and can more clearly resolve the effects of both natural and anthropogenic drivers of ecosystem response. The model resolved changes in chlorophyll-a (chl-a) from 1974 to 2012 at seasonal and multi-annual time scales while considering variation associated with changes in freshwater influence. Separate models were developed for each of the four Bay segments to evaluate spatial differences in patterns of long-term change. Observed trends reflected the known decrease in nitrogen loading to Tampa Bay since the 1970s. Although median chl-a has remained constant in recent decades, model predictions indicated that variation has increased for upper Bay segments and that low biomass events in the lower Bay occur less often. Dynamic relationships between chl-a and freshwater inputs were observed from the model predictions and suggested changes in drivers of primary production across the time series. Results from our analyses have allowed additional insight into water quality changes in Tampa Bay that has not been possible with traditional modeling approaches. The approach could easily be applied to other systems with long-term datasets.

Estimación del coeficiente de dispersión longitudinal en ríos de la región central de Argentina utilizando ADCP

The Longitudinal dispersion coefficient (D) is a fundamental parameter required to predict the transport of pollutants in rivers. The experimental determinations of D by conventional techniques, such as tracers test, require a large investment in planning, staff and subsequent analysis, and the results are only valid for the flow conditions present during the test. Using tracers test to estimate D is very expensive in rivers of central region of Argentina which have a large seasonal variability of flow discharges (with maximum values one or two orders of magnitude larger than the mean values), as tracers test should be performed for a wide range of flow conditions. Thus, water quality modelers use empirical formulas developed by various authors estimating the longitudinal dispersion coefficient based on global hydraulic parameters (mean flow depth and velocity, river width, etc.). However, these formulas show large scatter in the results and only perform properly in rivers with similar characteristics that were calibrated. On that basis, an alternative estimation of the coefficient of longitudinal dispersion is performed in this paper through a detailed experimental hydrodynamic characterization performed in a fluvial system with an Acoustic Doppler Current Profiler (ADCP). The Carcarañá River, flowing through the Cordoba and Santa Fe provinces in Argentina, has been selected as a study system. The results of this paper include the values o longitudinal dispersion coefficients in different streams of the analyzed fluvial system which are the compared with values estimated using empirical formulas and plots developed using data from different river systems around the world.

Modern software for the environmental modeling and statistical data analysis

Abstract There are considered three original software packages developed by authors: the first is for statistical processing of the experimental information; the second is a software package of realization of mathematical models of pollutants transport in rivers and the third is for identification of river water excessive pollution sources located between two controlled cross-sections of the river. They are designated on identical methodological basis and are intended for the users who are not professionals in the field of applied mathematics and computer science. The packages are universal, simple and convenient for understanding and application.

Process engineering tools to reduce river in-stream pollution

This paper is focused on new possibilities for in-stream pollution control, such as automated systems for real time pollution counteraction based on advection-dispersion models for pollutant transport in rivers. Important related issues are addressed: steps to undertake for in-stream pollution control; the use of process engineering (PE) tools to fulfil these steps; and development of models for pollutant transport to be further used in control. The paper presents a case study involving a Scottish stream.

Identification of pollution sources in the Romanian Somes River using graphical analysis of concentration profiles

AbstractThe paper describes a method for the identification of pollution sources along a river, based on the analysis of graphical information obtained from long‐term monitoring data. Concentration profiles collected during 2004 at monthly resolution in the Romanian Somes River are employed. The graphical analysis method is based on the comparison of experimental concentration profiles against reference profiles showing concentration evolution along the river after pollutant release. Known nitrate and lead pollution sources along the river were used as reference in order to verify the applicability of the proposed method. Results show that the graphical analysis method enables detection of the majority of sources, and it could be used to investigate the seasonal existence of pollution sources. Moreover, the technique can help guide the definition of the structure of mathematical models for the transport of pollutants in rivers. Copyright © 2010 Curtin University of Technology and John Wiley & Sons, Ltd.

2D finite element pollutant transport model for accidental mass release in rivers

A numerical model to simulate the accidental pollutant transport in rivers was developed using the two-dimensional finite element method. RAM4 is developed as the scalar transport module of the software RAMS (River Analysis and Modeling System) which can provide a graphical user interface for various river topographies and has recently been released as a beta version. The significance of RAM4 is that it is able to treat the pollutant mass itself, which is instantaneously released at a certain point of a river. The development of this ability was motivated by the inadequacy of the previous method, whereby the instantaneous mass release was expressed by defining some initial concentration at a source point. This method is not able to balance the injected mass value in accordance with the numerical time step size and the magnitude of flow velocity at this point. RAM4 was connected with the RAMS graphic user interface so that the source point and the released mass value can be controlled with a user-friendly graphical tool. The hydrodynamic module of RAMS, named RAM2, is currently undergoing beta-testing. Therefore, RAM4 was applied to the real river using the popular hydrodynamic model, RMA2, in TABS-MD. Using the obtained flow field computed by RMA2, the model has been simulated for a number of example scenarios of mass dumping accidents in the Han River of Korea in order to verify the applicability of this method in a real situation.

Software realization problems of mathematical models of pollutants transport in rivers

A software package of realization of mathematical models of pollutants transport in rivers is offered. This package is designed as a up-to-date convenient, reliable tool for specialists of various areas of knowledge such as ecology, hydrology, building, agriculture, biology, ichthyology and so on. It allows us to calculate pollutant concentrations at any point of the river depending on the quantity and the conditions of discharging from several pollution sources. One-, two-, and three-dimensional advection–diffusion mathematical models of river water quality formation both under classical and new, original boundary conditions are realized in the package. New finite-difference schemes of calculation have been developed and the known ones have been improved for these mathematical models. At the same time, a number of important problems which provide practical realization, high accuracy and short time of obtaining the solution by computer have been solved. In particular: (a) the analytical description of plane or spatial region for which the diffusion equations and boundary conditions are investigated, i.e. the analytical description of the bank line and the bottom of the river; (b) the analytical description of dependence of coefficients of the equation on the spatial coordinates; (c) the analytical description of dependence of non-homogeneous parts of the diffusion equation (i.e. the capacities of pollution sources) on the spatial coordinates and on the time; (d) the correct choice of ratios between spatial steps of the grid, and also between them and the step of digitations of time in the difference scheme.

Scaling dispersion model for pollutant transport in rivers

This communication presents a scale-dependent model, called Scaling Dispersion (SD) Model, for simulating solute dispersion and transport in rivers without using a user-specified residence time distribution function. The SD model consists of (1) the advection dispersion equation with a transient storage term which is characterized by a variable residence time, (2) a new method for estimation of the longitudinal Fickian dispersion coefficient involved in the model, and (3) a split-operator method for numerical solution of the equations involved in the model. Comparisons between the SD model and the most widely used transient storage model against tracer test data observed in three US rivers show that the SD model is capable of simulating different types of residence time distributions commonly observed in streams with an accuracy higher than or at least comparable with existing solute transport models, demonstrating the efficacy of the SD model. The SD model unifies the residence time distributions observed in natural rivers within a single modelling framework for the first time. The SD model provides an efficient and cost effective tool for predicting solute dispersion and transport in streams and rivers.