HR: 1340h
AN: H33F-0539    [Abstracts]
TI: Numerical Investigation of Multiple-, Interacting-Scale Variable-Density Ground Water Flow Systems
AU: Cosler, D
EM: HYDRODJC@AOL.COM
AF: The Ohio State University, Deptartment of Geological Sciences, 125 South Oval Mall, Columbus, OH 43210
AU: * Ibaraki, M
EM: ibaraki@geology.ohio-state.edu
AF: The Ohio State University, Deptartment of Geological Sciences, 125 South Oval Mall, Columbus, OH 43210
AB: The goal of our study is to elucidate the nonlinear processes that are important for multiple-, interacting-scale flow and solute transport in subsurface environments. In particular, we are focusing on the influence of small-scale instability development on variable-density ground water flow behavior in large-scale systems. Convective mixing caused by these instabilities may mix the fluids to a greater extent than would be the case with classical, Fickian dispersion. Most current numerical schemes for interpreting field-scale variable-density flow systems do not explicitly account for the complexities caused by small-scale instabilities and treat such processes as "lumped" Fickian dispersive mixing. Such approaches may greatly underestimate the mixing behavior and misrepresent the overall large-scale flow field dynamics. The specific objectives of our study are: (i) to develop an adaptive (spatial and temporal scales) three-dimensional numerical model that is fully capable of simulating field-scale variable-density flow systems with fine resolution (~1 cm); and (ii) to evaluate the importance of scale-dependent process interactions by performing a series of simulations on different problem scales ranging from laboratory experiments to field settings, including an aquifer storage and freshwater recovery (ASR) system similar to those planned for the Florida Everglades and in-situ contaminant remediation systems. We are examining (1) methods to create instabilities in field-scale systems, (2) porous media heterogeneity effects, and (3) the relation between heterogeneity characteristics (e.g., permeability variance and correlation length scales) and the mixing scales that develop for varying degrees of unstable stratification. Applications of our work include the design of new water supply and conservation measures (e.g., ASR systems), assessment of saltwater intrusion problems in coastal aquifers, and the design of in-situ remediation systems for aquifer restoration. We present preliminary model results for high-resolution simulation of variable-density flow and transport in homogeneous and heterogeneous porous media. We explicitly solve the three-dimensional advection equation using mass-conservative, flux-integral techniques and finite-volume formulations that provide unrestricted time-step capabilities similar to those associated with semi-Lagrangian methods. Our implementation of B. P. Leonard's MACHO (Multidimensional Advective-Conservative Hybrid Operator) and COSMIC (Conservative Operator Splitting for Multidimensions with Inherent Constancy) methods is an Nth-order (e.g., 7th-order or higher) advection scheme that significantly reduces numerical dispersion and can be adapted spatially and temporally as the simulation progresses. The ability of these higher-order methods to yield accurate, nonoscillatory concentration profiles is illustrated and compared to traditional implicit solution methods such as central and upwind differencing, and van Leer flux limiters. We also show preliminary results from our implementation of adaptive mesh refinement (AMR) techniques and discuss the interrelationship between AMR and the Nth-order advection schemes.
DE: 1829 Groundwater hydrology
DE: 1831 Groundwater quality
DE: 1832 Groundwater transport
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting