Macrodispersion in stratified aquifers - part one: a numerical model -

In gelaagde watervoerende pakketten treedt een spreiding van opgeloste stoffen op die enkele orden van grootte verschilt met de spreiding in een homogeen pakket. Voor de berekening van beschermingszones rondom waterwingebieden is deze spreiding uitermate belangrijk. Er wordt een methode gepresenteerd om het transport in gelaagde pakketten te berekenen. Het convectief transport wordt berekend door numerieke integratie van de bewegingsvergelijkingen. Snelheidsvariaties ten gevolge van de gelaagdheid worden in rekening gebracht. Het dispersief transport wordt gesimuleerd met een random-walk. De beschreven methode kan worden toegepast in uniforme en niet uniforme stroming. Voor het geval van uniforme stroming zijn de numerieke resultaten in goede overeenstemming met de analytische oplossing van Gelhar. Wanneer het pakket door nuttige neerslag of kwel wordt gevoed ontstaat een drie- dimensionale stroming, die met de Dupuit-Forchheimer benadering kan worden bepaald. Een aantal voorbeelden wordt gegeven voor verschillende stromingsproblemen.Abstract not availableDGMH/BWS-B / WillemsJ

Analysis of dispersion by the random walk method

Civil Engineering and Geoscience

Groundwater mechanics, flow and transport

Civil Engineering and GeosciencesHydraulic Engineerin

Understanding the Non-Gaussian Nature of Linear Reactive Solute Transport in 1D and 2D: From Particle Dynamics to the Partial Differential Equations

In the present study, we examine non-Gaussian spreading of solutes subject to advection, dispersion and kinetic sorption (adsorption/desorption). We start considering the behavior of a single particle and apply a random walk to describe advection/dispersion plus a Markov chain to describe kinetic sorption. We show in a rigorous way that this model leads to a set of differential equations. For this combination of stochastic processes, such a derivation is new. Then, to illustrate the mechanism that leads to non-Gaussian spreading, we analyze this set of equations at first leaving out the Gaussian dispersion term (microdispersion). The set of equations now transforms to the telegrapher’s equation. Characteristic for this system is a longitudinal spreading that becomes Gaussian only in the longtime limit. We refer to this as kinetics-induced spreading. When the microdispersion process is included back again, the characteristics of the telegraph equations are still present. Now, two spreading phenomena are active, the Gaussian microdispersive spreading plus the kinetics-induced non-Gaussian spreading. In the long run, the latter becomes Gaussian as well. Another non-Gaussian feature shows itself in the 2D situation. Here, the lateral spread and the longitudinal displacement are no longer independent, as should be the case for a 2D Gaussian spreading process. In a displacing plume, this interdependence is displayed as a ‘tailing’ effect. We also analyze marginal and conditional moments, which confirm this result. With respect to effective properties (velocity and dispersion), we conclude that effective parameters can be defined properly only for large times (asymptotic times). In the two-dimensional case, it appears that the transverse spreading depends on the longitudinal coordinate. This results in ‘cigar-shaped’ contours.Geoscience & EngineeringCivil Engineering and Geoscience

FLODIN A computer program to predict and describe the transport of hydrophobic organic contamination in the soil

Translated from Flemish (Water 1986 v. 19(16) p. 374-379)SIGLEAvailable from British Library Document Supply Centre- DSC:9022.048(BG-Trans--8565)T / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Practical Implementation of New Particle Tracking Method to the Real Field of Groundwater Flow and Transport

In articles published in 2009 and 2010, Suk and Yeh reported the development of an accurate and efficient particle tracking algorithm for simulating a path line under complicated unsteady flow conditions, using a range of elements within finite elements in multidimensions. Here two examples, an aquifer storage and recovery (ASR) example and a landfill leachate migration example, are examined to enhance the practical implementation of the proposed particle tracking method, known as Suk's method, to a real field of groundwater flow and transport. Results obtained by Suk's method are compared with those obtained by Pollock's method. Suk's method produces superior tracking accuracy, which suggests that Suk's method can describe more accurately various advection-dominated transport problems in a real field than existing popular particle tracking methods, such as Pollock's method. To illustrate the wide and practical applicability of Suk's method to random-walk particle tracking (RWPT), the original RWPT has been modified to incorporate Suk's method. Performance of the modified RWPT using Suk's method is compared with the original RWPT scheme by examining the concentration distributions obtained by the modified RWPT and the original RWPT under complicated transient flow systems