Journal
WATER RESOURCES RESEARCH
Volume 46, Issue -, Pages -Publisher
AMER GEOPHYSICAL UNION
DOI: 10.1029/2010WR009370
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Funding
- U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences through the Center for Frontiers of Subsurface Energy Security (CFSES) at the University of Texas at Austin
- DOE Energy Frontier Research Center [DE-SC0001114]
- National Natural Science Foundation of China [40528003, 50639090]
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In this paper, we investigate the effects of systematic and local heterogeneity on groundwater flow, transport, and residence time distributions (RTDs) of basins where groundwater flow is topography driven. Systematic heterogeneity is represented by an exponentially depth-decreasing hydraulic conductivity and porosity, and local heterogeneity is represented by the dispersivity. The RTDs for both a simple basin with one flow system and a basin with nested local and regional systems gradually evolve to a power law RTD with more pronounced systematic heterogeneity. Exponential decrease of poromechanical properties enhances shallow circulation and subdues deep and regional flows leading to longer flushing times for the large part of the domain, while the shallower portions flush solutes rapidly. Therefore, deeper basins lead to more persistent and pronounced power law RTDs when the poromechanical properties systematically decrease with depth. Separate contributions to the RTD due to stagnation zones associated with local flow cells and due to deeper immobile zones were identified; each leads to a different tailing behavior. Local heterogeneity slightly enhances the power law RTD by causing the tailing to begin earlier but does not affect the late time portion of the RTD. Systematic depth-dependent heterogeneity is an important factor controlling the circulation and associated RTDs of subsurface fluids. It contributes significantly to generation of power law RTDs.
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