Using global node-based velocity in random walk particle tracking in variably saturated porous media: application to contaminant leaching from road constructions |
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| Authors: | Chan-Hee Park Christof Beyer Sebastian Bauer Olaf Kolditz |
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| Institution: | (1) Department of Environmental Informatics, Helmholtz Centre for Environmental Research, UFZ, Permoserstrasse 15, 04318 Leipzig, Germany;(2) Center for Applied Geoscience, University of Tuebingen, Sigwartstr. 10, 72076 Tübingen, Germany;(3) Geoscience Institute, University of Kiel, Ludewig-Meyn-Str. 10, 24118 Kiel, Germany |
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| Abstract: | Precise and efficient numerical simulation of transport processes in subsurface systems is a prerequisite for many site investigation
or remediation studies. Random walk particle tracking (RWPT) methods have been introduced in the past to overcome numerical
difficulties when simulating propagation processes in porous media such as advection-dominated mass transport. Crucial for
the precision of RWPT methods is the accuracy of the numerically calculated ground water velocity field. In this paper, a
global node-based method for velocity calculation is used, which was originally proposed by Yeh (Water Resour Res 7:1216–1225,
1981). This method is improved in three ways: (1) extension to unstructured grids, (2) significant enhancement of computational
efficiency, and (3) extension to saturated (groundwater) as well as unsaturated systems (soil water). The novel RWPT method
is tested with numerical benchmark examples from the literature and used in two field scale applications of contaminant transport
in saturated and unsaturated ground water. To evaluate advective transport of the model, the accuracy of the velocity field
is demonstrated by comparing several published results of particle pathlines or streamlines. Given the chosen test problem,
the global node-based velocity estimation is found to be as accurate as the CK method (Cordes and Kinzelbach in Water Resour
Res 28(11):2903–2911, 1992) but less accurate than the mixed or mixed-hybrid finite element methods for flow in highly heterogeneous media. To evaluate
advective–diffusive transport, a transport problem studied by Hassan and Mohamed (J Hydrol 275(3–4):242–260, 2003) is investigated here and evaluated using different numbers of particles. The results indicate that the number of particles
required for the given problem is decreased using the proposed method by about two orders of magnitude without losing accuracy
of the concentration contours as compared to the published numbers. |
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| Keywords: | Velocity approximation Particle tracking Random walk Transport in porous media Contaminant leaching from road constructions |
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