Journal
JOURNAL OF CONTAMINANT HYDROLOGY
Volume 157, Issue -, Pages 47-58Publisher
ELSEVIER
DOI: 10.1016/j.jconhyd.2013.11.002
Keywords
Anomalous dispersion; Transient dispersion; Variable-index model; Numerical solutions; Contaminant transport
Funding
- National Natural Science Foundation of China [11202066]
- R&D Special Fund for Public Welfare Industry [201101014]
- National Basic Research Program of China [2010CB832702]
- National Science Funds for Distinguished Young Scholars [11125208]
- 111 project (China) [B12032]
- National Science Foundation [DMS-1025417]
- Direct For Mathematical & Physical Scien
- Division Of Mathematical Sciences [1025417] Funding Source: National Science Foundation
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Field and numerical experiments of solute transport through heterogeneous porous and fractured media show that the growth of contaminant plumes may not exhibit constant scaling, and may instead transition between diffusive states (i.e., superdiffusion, subdiffusion, and Fickian diffusion) at various transport scales. These transitions are likely attributed to physical properties of the medium, such as spatial variations in medium heterogeneity. We refer to this transitory dispersive behavior as transient dispersion, and propose a variable-index fractional-derivative model (FDM) to describe the underlying transport dynamics. The new model generalizes the standard constant-index FDM which is limited to stationary heterogeneous media. Numerical methods including an implicit Eulerian method (for spatiotemporal transient dispersion) and a Lagrangian solver (for multiscaling dispersion) are utilized to produce variable-index FDM solutions. The variable-index FDM is then applied to describe transient dispersion observed at two field tracer tests and a set of numerical experiments. Results show that 1) uranine transport at the small-scale Grimsel test site transitions from strong subdispersion to Fickian dispersion, 2) transport of tritium at the regional-scale Macrodispersion Experimental (MADE) site transitions from near-Fickian dispersion to strong superdispersion, and 3) the conservative particle transport through regional-scale discrete fracture network transitions from superdispersion to Fickian dispersion. The variable-index model can efficiently quantify these transitions, with the scale index varying linearly in time or space. (C) 2013 Elsevier B.V. All rights reserved.
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