Analysis Of Solute Transport Research Articles

Numerical analysis of solute transport and longitudinal dispersion coefficients in vegetated flow

Reasonable estimates of longitudinal dispersion coefficients are essential for predicting solute dispersion processes. However, the current knowledge of solute dispersion processes in vegetated waters is limited. In this work, we coupled a refined hydrodynamic model with scalar transport equations to simulate the flow field and dispersion process of solutes in water under the effect of vegetation. First, the proposed numerical model was verified using laboratory experiments, revealing the excellent performance of the coupled model in complex conditions. Eight different cases were subsequently simulated to analyse the effects of the upstream flow rate and vegetation height on the streamwise velocity, solute concentration, and longitudinal dispersion coefficients. The simulation results show that the upstream flow variation exerts a marked effect on the streamwise velocity and flow field within the vegetation zone, with a velocity difference within the shear layer reaching 54.7 % for an upstream flow of 0.018 m3·s-1. The height of the vegetation affects both the velocity profile and solute dispersion. Placing emergent vegetation upstream can enhance solute dispersion in the longitudinal direction. The correlation analysis reveals that the longitudinal dispersion coefficients obtained using the routing producer are close to those determined using the theoretical method, with correlation coefficients reaching 0.75. This work presents the appropriate application range and parameters that must be considered in deriving formulas for longitudinal dispersion coefficients.

Multi-scale analysis of solute transport in hydrodynamic fluid flows through a porous channel with anisotropic permeability and boundary absorption

Multi-scale analysis of solute transport in hydrodynamic fluid flows through a porous channel with anisotropic permeability and boundary absorption

Granular Soils and Contaminant Modeling in Tailing Dams

The granular soils of tailings, encompassing clay, gravel, sand, and silt, play a pivotal role in the behavior and stability of tailings dams. Different types of granular soils significantly influence the tailings material’s strength, compressibility, and permeability. This study highlights the importance of understanding the relationship between soil types and contaminant properties when analyzing solute transport through numerical modeling. Consequently, various soil types were incorporated into the initial tailings dam model to simulate contaminant transport based on solute transport analysis. The findings underscored the essential role of granular soils in contaminant dispersion within tailings dams. Finer particles, such as clay and silt, demonstrated higher adsorption capacities, which slow contaminant movement. In contrast, coarser materials, like sand and gravel, enable faster transport, increasing the potential for rapid dispersion.

Numerical Prediction Uncertainty and Data Worth Analysis of Solute Transport in an Agricultural Clay Till Setting With Preferential Flow

AbstractWith modern agricultural practices, it is essential to quantify flow and solute transport fluxes by numerical models and associated predictions. A major challenge in modeling preferential flow settings is the ability to constrain the often numerous parameters needed to physically represent these systems. Following this, there is a lack of understanding of what parameters and observations carry the most worth for a model to reduce its prediction uncertainty. Here, first‐order second moment (FOSM) analyses were used for a heavily monitored clay till field with preferential flow to investigate which parameters and observation types contribute the most to reducing the uncertainty of bromide predictions at various depths. Using a multi‐objective regularized optimization approach, a 1‐D preferential flow model was calibrated and subjected to FOSM analyses. Key parameters contributing to the prediction uncertainty of bromide concentrations in 0.25–3 m were limited to the lower boundary condition, the mass transfer coefficient, the hydraulic conductivity of the micro‐ and macropore, the macropore porosity, and the water content at wilting point. The data with the largest worth and ability to reduce the pre‐calibration prediction uncertainty were concentration observations closest to the sought prediction depth, drain concentrations, and averaged water table measurements from the entire field. The post‐calibration prediction uncertainty was increased primarily by removing concentration observations closest to the prediction depths. While this study provided new insights into parameter importance and data worth further research is required to understand if these findings apply broadly to clay till settings (or any soil setting) with preferential flow.

Analytical solution for contaminant transport through a GCL-enhanced composite cutoff wall system

The geosynthetic clay liners (GCLs) have been recently shown to be effective in cutoff wall applications. Yet, its influence on contaminant transport through cutoff wall system is rarely reported. This study presents an analytical solution for the transport of organic contaminant through a composite cutoff wall system comprising a soil-bentonite wall, a GCL, and an aquifer. The analytical solution was obtained by variable separation method and verified against an existing analytical solution and a numerical solution. Parametric analysis was conducted to elucidate the effects of GCL, soil-bentonite (SB) wall thickness (Lw), aquifer thickness (La), and contaminant half-life (t1/2) on contaminant transport. The results show that by adding a GCL layer, the contaminant concentration and the maximum flux can be significantly decreased. When the GCL retardation factor increases 1 to 300, the required time to reach the maximum flux is delayed from about 62 years to 1500 years. Larger aquifer thickness sufficiently weakens the contaminant transport process. Under the same breakthrough criteria, the required thickness of SB wall decreases by about 20% when the GCL retardation factor increases from 1 to 50. The proposed analytical solution provides a useful tool for the design of the SB-GCL cutoff wall system.

Analytical solutions for transport of organic solutes in multi-layered porous media

In this study, analytical solutions for one-dimensional transport of organic solutes in multilayered porous media are developed using the methods of matrix transfer and variable separation, where multiple factors such as advection, diffusion, mechanical dispersion, adsorption, degradation, boundary condition type and change in concentration are systematically incorporated for the first time. Compared with the existing analytical solutions solved by the techniques of integral transformation or Laplace transformation, the approaches adopted in this paper are simpler and have a quicker convergence speed. Also, the proposed analytical solutions are more practical with clear expressions and consideration of multiple factors, which can be applied to various engineering cases such as bottom liner systems at landfills, covering systems of contaminated sediments and vertical barrier systems in contaminated sites. Furthermore, the correctness of the derived analytical solutions is effectively validated by comparison with the experimental results, as well as with the existing analytical solution and a numerical method. Following this, the effects of different factors on the transport process of a single organic solute in a five-layered medium are investigated, and some novel and vital laws are obtained. Overall, this research contributes to appropriate evaluation of the transport behaviours in multilayered porous media.

Simulation of Solute Transport under Changing Gradient of Water Table

Solute transport in aquifers is usually controlled by dynamic changes in groundwater tables. The influence mechanism of surface hydrological processes, especially precipitation, on solute transport under different water table conditions has not been studied much. Prior to the direct application of the existing solute transport mechanisms and models to the solute transport process, the following questions need to be addressed: (1) Do surface hydrological conditions (e.g., precipitation) cause changes in the gradient of the water table within a specific region? (2) If the gradient of the water table does change, how does the change influence solute transport and distribution in the aquifer? The objective of this study is to investigate how precipitation impacts the gradient of water table and to analyze how the solute transport is influenced by the change in the gradient of water table. To achieve this, we employed an analytical solute transport model for the time-varying gradient of a water table through continuous multipoint monitoring of the groundwater table data. Further, the model was applied to indoor experiments to simulate solute transport with and without precipitation. Finally, the mechanism of solute transport in the aquifer under the changing gradient of the water table was analyzed using mathematical and physical models, and the modeling results were compared with those from a numerical model to analyze the modeling reliability. The results showed that precipitation changed the previously stable gradient of the water table, which further altered the gradient of the water table and the transport path of the tracer. The tracer transport direction was primarily controlled by the flow direction in the sandy aquifer trough without precipitation. However, the route of the tracer transport was consistent with the direction of the change in the water table gradient due to precipitation. The small discrepancy between the results from the analytical and numerical models indicates that the model employed in this study is reliable.

Analytical solution for transport of degradable contaminant in cut-off wall and aquifer

An analytical solution for contaminant transport through a vertical cut-off wall and aquifer system is developed, which can consider the advection, dispersion and degradation processes. The uniqueness of the solution is that it includes hyperbolic eigenfunctions, considers the degradation process and is suitable for an aquifer with finite thickness due to the existence of a river or lake. The solution is first verified against an existing analytical solution and a numerical model using the Comsol software program. The three important aspects are then investigated and some important conclusions are obtained. In some scenarios, the hyperbolic eigenfunctions must be considered; otherwise, the obtained results are unreasonable. When the aquifer thickness is more than a critical value (approximately ten times the cut-off wall thickness in this study), it is reasonable to regard the aquifer as semi-infinite. Contaminant degradation has significant influence on contaminant transport. A higher degradation intensity leads to a lower contaminant concentration but a larger mass flux in the cut-off wall. Therefore, the present solution is suitable for an aquifer with arbitrary thickness and has better applicability than the existing analytical solutions. It is promising to be used as an applicable tool for the design of vertical slurry cut-off walls.

Modifying Elder’s Longitudinal Dispersion Coefficient for Two-Dimensional Solute Mixing Analysis in Open-Channel Bends

Elder’s equation for the longitudinal dispersion coefficient in two-dimensional solute transport analysis cannot be applied to curved channels because the vertical distribution of the longitudinal velocity does not obey the logarithmic law in the bends of an open channel. In this study, a two-dimensional longitudinal dispersion coefficient based on an equation that can appropriately describe the vertical distribution of flow velocity in open-channel bends is derived theoretically. The proposed equations for the vertical velocity distribution and dispersion coefficient are compared and verified with values measured from two different types of open channels, i.e., a laboratory channel and a natural-like channel. The increase in the longitudinal dispersion coefficient based on the difference in the vertical distribution of the flow velocity is evaluated quantitatively. In terms of the longitudinal dispersion coefficient, no significant difference is observed between the observed dispersion coefficient based on the concentration data and the coefficient value calculated using the equation proposed in this study. The dispersion equation proposed in this study can be easily applied to assign the value of the longitudinal dispersion coefficient for the two-dimensional mixing modelling in bends using basic hydraulic factors.

Analytical solution for solute transport in a triple liner under non-isothermal conditions

Analytical solutions for the transport of contaminant through a 1D triple-layer composite liner system consisting of a geomembrane (GMB), a geosynthetic clay liner (GCL) and a compacted clay liner (CCL) under non-isothermal conditions are derived using the generalized integral transform technique. The proposed analytical solutions account for the combined effects of molecular diffusion, sorption and thermodiffusion as well as the temperature-dependent distribution coefficient and effective diffusion coefficient. The proposed analytical solutions are successfully validated against the experimental results of thermodiffusion tests and verified against an analytical solution available in the literature and a numerical model based on commercial finite element software. Using the verified analytical solutions, simulations are performed with representative geometry and material properties for a GMB/GCL/CCL liner system. The results indicate that neglecting the effect of non-isothermal condition can underestimate the benzene outflow rate by over 30% when the temperature difference between the surface and bottom of the liner system exceeds 10 K. The temperature-dependent CCL effective diffusion coefficient and CCL distribution coefficient have a significant effect on benzene transport through the GMB/GCL/CCL liner system, whereas the liner thermal conductivity and the temperature-dependent GCL effective diffusion coefficient and GCL distribution coefficient have a negligible effect.

Analytical solution for transport of pollutant from time-dependent locations along groundwater

The present work derives analytical solutions of advection–dispersion equation (ADE) with temporal coefficients, and a pollutant’s point source moving linearly along the axis of a one-dimensional semi-infinite domain. The source is considered a varying and a uniform pulse source, respectively. The dispersion of pollutant originating from a varying pulse source may be supposed to occur along groundwater flow domain, and that from a uniform pulse source in an open medium like air or along a river flow. The location of the input concentration that is the pollutant’s concentration emanating from the source in an open medium or that reaching the groundwater domain being infiltrated from its source on the ground, is considered moving linearly along the flow direction. The motion of the source is described through an asymptotically increasing temporal function. The illustration of the analytical solution clearly reflects this feature. It also renders that the concentration pattern of the proposed solution is proximal to that of an existing solution obtained with the stationary source. The pertinent existing solutions may also be derived from the proposed solutions. The proposed solutions are found approximate but it is also found that the error of approximation of one of them is too small to have any effect on the concentration pattern. To get these solutions, firstly, the moving source is reduced into a stationary source at the origin, then the governing equations including the ADE, are made free from the three temporal functions, one occurring in the time-dependent position of the source, and the other two as the coefficients of the ADE. In this process, three new position variables, and a new time variable are introduced using as many coordinate transformations. Then the Laplace Integral Transformation Technique (LITT) is used to get the final solutions. The solution in Laplacian domain with uniform pulse source is obtained as a special case of that with the varying pulse source.

Evaluation of longitudinal / transverse dispersion coefficients and prediction of concentration at river confluence in two-dimensional solute transport analysis

Evaluation of longitudinal / transverse dispersion coefficients and prediction of concentration at river confluence in two-dimensional solute transport analysis

Solute transport modelling to manage groundwater pollution from surface water resources

This article provides an analytical solute transport model to investigate the potential of groundwater contamination by polluted surface water in a two dimensional domain. The clogging of streambed which makes the aquifer partially penetrated by the stream, is considered in the model. The impacts of pumping process, hydraulic conductivity and clogging layer on the quality of water produced from nearby drinking water wells are evaluated. It is found that results are consistent with numerical simulation conducted by MODFLOW software. Moreover, the model is applied using data of contamination occurrence in Malaysia, where high contaminants concentrations are found close to streams. Results show that the pumping activities (rate and time period) are crucial factors when evaluating the risk of groundwater contamination from surface water. Additionally, this study illustrates that the increase in either hydraulic conductivity or leakance coefficient parameters due to the clogging layer will enlarge the area of contamination. The model is able to determine the suitable pumping rate and location of the well so that the contamination plume never reaches the extraction well, which is useful in constructing riverbank filtration sites.

스노우팩 내에서 융설 배출수와 용질 농도 간의 상관관계를 통한 용질의 이동 해석

스노우팩 내에서 융설 배출수와 용질 농도 간의 상관관계를 통한 용질의 이동 해석

Internal hydraulics and wind effect in a surface flow constructed wetland receiving agricultural drainage water

Variations of internal water velocities in surface flow constructed wetlands (SF-CWs) affect the hydraulic efficiency and are responsible for heterogeneous distribution of the biogeochemical processes. Internal obstructions, short circuiting due to the presence of immobile zones, and incomplete mixing are among the main culprits. In this study, a high resolution spatial analysis of solute transport is presented aiming at identifying internal flow preferentiality of the system and the influence of wind effects. Dye (Uranine) and salt (Bromide) tracer tests were performed in a compartment-designed SF-CW constituted of alternated deep and shallow zones. Water samples were collected from the outflow and a number of internal stations located according to a 3-transect system at two different depths. Bromide outflow and internal breakthrough curves (BTCs) were fitted using the tank-in-series (TIS) model. The results showed that the hydraulic efficiencies at internal stations (0.08–1.63) generally decreased with increasing distances from the tracer injection point. Both spline interpolation and dye tracer results showed preferential flow alongside the southern side of the SF-CW. Analysis further showed that the shallow zones and the wind blowing in opposite direction to the flow facilitate water mixing and recirculation. The method is a valuable exploiting tool for already operating SF-CWs.

Spin and valley dependent electronic transport in molybdenum disulfide considering up to the second order k-dependent terms: a more exact solution.

Previous studies of electronic transport in molybdenum disulfide (MoS2) are restricted to the first order approximation of the Hamiltonian. In this paper, to obtain more exact results, we firstly present an analytical solution for the Hamiltonian of MoS2 when terms up to the second order (quadratic k-dependent) of the Hamiltonian are taken into account. Our analytical solution is easily applicable to study the transport properties of any single and multi-junctions of MoS2. Then, we propose a device composed of two ferromagnetic barriers with anti-parallel exchange fields and we show that this device has interesting properties such as spin and valley filtering with perfect spin and valley polarizations. Using this device, we can easily switch both spin and valley polarizations to their opposite polarizations only by using electric voltage, which is of fundamental importance in quantum computation and the next generation of logic devices.

Transient analytical solution for one-dimensional transport of organic contaminants through GM/GCL/SL composite liner

Analytical solution for transport of organic contaminants through composite liner consisting of a geomembrane (GM), a geosynthetic clay liner (GCL), and a soil liner (SL) with finite thickness is presented. The transient diffusion-advection processes in the whole composite liner and adsorption in GCL and SL can be described by the present method. The method is successfully verified against analytical solution to a coupling transient diffusion-advection problem in double-layer porous media. The rationality of the steady-state transport assumption in GM and GCL and the semi-infinite bottom boundary assumption, which are widely adopted in the existing works, is comprehensively investigated. The overestimated zone, underestimated zone and no difference zone caused by the two assumptions under various conditions are identified. With the increase of elapsed time, the overestimated zone disappears, and the underestimated zone becomes smaller and smaller and finally is overwhelmed by the no difference zone. Moreover, the equivalency between GM/GCL/SL and GM/CCL composite liners is also properly assessed by the present method. GM/GCL/SL composite liner performs better than GM/CCL composite liner under high leachate level condition.

Analysis of Solute Transport from a Source with Finite Leachable Mass.

A general approach is developed for the analysis of solute transport from a source with a finite initial mass. The approach uses an effective retardation factor to assign the initial mass that can be leached from the source. Demonstration analyses are presented to illustrate the approach with the numerical simulator MT3DMS. For cases that are tractable with analytical solutions, comparisons between the numerical and analytical results confirm that the proposed approach yields correct results. The approach is straightforward to apply and can accommodate conditions ranging from pure advection to pure diffusion, effectively extending the capabilities of models to simulate sources with finite leachable masses for complex flow fields, reactions and distributions of sources.

Experimental and analytical studies of solute transport during run‐off over vegetated surfaces

AbstractSolute transport in overland flow is considered as one of the main contributors to water pollution. Although many models of pollutant transport mechanism from soil to run‐off water have been proposed, the characteristics of solute transport accompanying the water run‐off over vegetated surface have not been well studied. In this study, a series of laboratory experiments were conducted to study the solute transport over vegetated surfaces. Based on the experimental results, an idea of the “stationary water layer” in run‐off was proposed. Applying the complete mixing theory in the stationary water layer, an analytical solute transport model was developed with the assumption that the upper run‐off completely mixes with the underlying water in the stationary water layer for each site. The results show that the predictions made by the present model are in good agreement with the measured experimental data. For the vegetated surfaces, the depth of stationary water layer is related to the rainfall intensity, bed slope, and vegetation density. The analytical solution shows that the maximum solute transport occurs at the time of concentration. This study advances our understanding of the mechanisms of solute transport over vegetated areas.

Assessment of Nutrient Leaching in Flooded Paddy Rice Field Experiment Using Hydrus-1D

Solute runoff and leaching are two direct pathways of nutrient pollution from paddy fields into water systems. Due to the dynamic nature of paddy fields, solute transport and transformation processes are complex and difficult to understand. Therefore, in this study, nitrogen (N) transport in flooded paddy rice fields with conventional irrigation (flooding irrigation) in the Tanjung Karang Rice Irrigation Scheme (TAKRIS), Sawah Sempadan, were observed and modelled using the Hydrus-1D numerical model during two consecutive rice growing seasons. Based on solute transport analysis results, it was observed that 50.3% to 48% of percolated N was accumulated in the top 40-cm soil layer, while 49.7% to 52% of leachate N was lost below the 40-cm soil layer (40–100 cm) during the off and main seasons, respectively. About 85% of N leaching loss was in the form of NO3−. NO3− was absorbed by rice roots within 0–40 cm and the denitrified root zone; however, there was still a large quantity of NO3− which remained below the root zone, which was quickly transported downward along with the leachate water. The NH4+ concentration in subsurface water was lower than the NO3− concentration due to various processes that removed NH4+ from the topsoil layer (0–40 cm), such as ammonium volatilisation, nitrification, and plant uptake. The total leaching loss of N was 34.9 and 27.9 kg/ha during the off and main seasons, respectively. The simulated and observed water flow and nutrient leaching were in a good agreement (R2 = 0.98, RMSE = 0.24). The results showed that Hydrus-1D successfully simulated the solute movement under different soil depths during the study period.