On the Scale-Dependency of Field-Scale Nonequilibrium Flow and Contaminant Transport Processes

December 16, 2014

Time: December 16, 2014
Lecturer: Prof. Martinus Th. van Genuchten
Department of Mechanical Engineering of the Federal University of Rio de Janeiro, Brazil
Venue: Pfaffenwaldring 61, Raum U1.003 (MML), Universität Stuttgart
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Accurate simulation of nonequilibrium water flow and contaminant transportprocesses in naturally heterogeneous subsurface systems remains achallenge. A range of dual-porosity and dual-permeabilityformulations can be used to describe preferential or nonequilibriumflow and transport processes in variably-saturated media. Onesimplified macroscopic approach is to use composite functions for theunsaturated hydraulic conductivity to account for the separateeffects of macropores (fractures) and micropores on flow, and tocombine this formulation with a dual-porosity type formulation forsolute transport. Special focus in this seminar will be on the masstransfer coefficient that is then needed to account for soluteexchange between the fracture (mobile water) and matrix (immobilewater) regions. This coefficient is shown to be strongly dependentupon the scale of the problem. Theoretical considerations andliterature data are presented to confirm its dependency on the soluteresidence time. A similar dependency has long been noted for thelongitudinal dispersivity. An example is given illustrating thescale dependency of the mass transfer coefficient for a field-scaleheavy metal contamination problem.
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