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An understanding of the hydrologic interactions among atmosphere, land surface, and subsurface is one of the keys to understanding the water cycling system that supports our life system on earth. Properly modeling such interactions is a difficult task because of theinherent coupled processes and complex feedback structures among subsystems. In this paper, we present a model that simulates the landsurface and subsurface hydrologic response to meteorological forcing. This model combines a state of the art landsurface model, the NCAR Community Land Model version 3 (CLM3), with a variably saturatedgroundwater model, the TOUGH2, through an internal interface that includes flux and state variables shared by the two submodels. Specifically, TOUGH2, in its simulation, uses infiltration, evaporation, and rootuptake rates, calculated by CLM3, as source/sink terms? CLM3, in its simulation, uses saturation and capillary pressure profiles, calculated by TOUGH2, as state variables. This new model, CLMT2, preserves the best aspects of both submodels: the state of the art modeling capability of surface energy and hydrologic processes from CLM3 and the more realistic physical process based modeling capability of subsurface hydrologic processes from TOUGH2. The preliminary simulation results show that the coupled model greatly improves the predictions of the water table, evapotranspiration, surface temperature, and moisture in the top 20 cm of soil at a real watershed, as evaluated from 18 years of observed data. The new model is also ready to be coupled with an atmospheric simulation model, representing one of the first models that are capable to simulate hydraulic processes from top of the atmosphere to deep ground.

Characterizing percolation patterns in unsaturated zones has posed a greater challenge to numerical modeling investigations than comparable saturated zone studies, because of the heterogeneous nature of unsaturated media as well as the great number of variables impacting unsaturated zone flow. This paper presents an integrated modeling methodology for quantitatively characterizing percolation patterns in the unsaturated zone of Yucca Mountain, Nevada, a proposed underground repository site for storing high-level radioactive waste. It takes into account the multiple coupled processes of air, water, heat flow and chemical isotopic transport in Yucca Mountain s highly heterogeneous, unsaturated fractured tuffs. The modeling approach integrates a wide variety of moisture, pneumatic, thermal, and isotopic geochemical field data into a comprehensive three-dimensional numerical model for modeling analyses. Modeling results are examined against different types of field-measured data and then used to evaluate different hydrogeological conceptual models and their results of flow patterns in the unsaturated zone. In particular, this integration model provides a much clearer understanding of percolation patterns and flow behavior through the unsaturated zone, both crucial issues in assessing repository performance. The integrated approach for quantifying Yucca Mountain s flow system is also demonstrated to provide a comprehensive modeling tool for characterizing flow and transport processes in complex subsurface systems.

WINGRIDDER V3.0 is a Windows-based software for designing and generating numerical grids for numerical simulators that are based on the "integral finite difference" or the "control volume" numerical scheme (e.g., TOUGH2, Pruess et al., 1996). The user can design and generate grid that properly represents the stratigraphic features, inclined faults, and repository. WINGRIDDER V3.0 is an upgrade from WINGRIDDER V2.0. This revision includes testable requirements as listed in the Requirements Document (RD), 10024-RD-3.0-00, Section 2. With new features, WINGRIDDER V3.0 adds the ability to generate a multiple-interactive-continuum (MINC) grid.

CLMT2 is designed to simulate the land-surface and subsurface hydrologic response to meteorological forcing. This model combines a state-of-the-art land-surface model, the NCAR Community Land Model version 3 (CLM3), with a variably saturated groundwater model, the TOUGH2, through an internal interface that includes flux and state variables shared by the two submodels. Specifically, TOUGH2, in its simulation, uses infiltration, evaporation, and root-uptake rates, calculated by CLM3, as source/sink terms; CLM3, in its simulation, uses saturation and capillary pressure profiles, calculated by TOUGH2, as state variables. This new model, CLMT2, preserves the best aspects of both submodels: the state-of-the-art modeling capability of surface energy and hydrologic processes from CLM3 (including snow, runoff, freezing/melting, evapotranspiration, radiation, and biophysiological processes) and the more realistic physical-process-based modeling capability of subsurface hydrologic processes from TOUGH2 (including heterogeneity, three-dimensional flow, seamless combining of unsaturated and saturated zone, and water table). The preliminary simulation results show that the coupled model greatly improved the predictions of the water table, evapotranspiration, and surface temperature at a real watershed, as evaluated using 18 years of observed data. The new model is also ready to be coupled with an atmospheric simulation model, representing one of the first models that are capable to simulate hydraulic processes from top of the atmosphere to deep-ground.

Modeling fracture-matrix interaction within a complex multiple phase flow system is a key issue for fractured reservoir simulation. Commonly used mathematical models for dealing with such interactions employ a dual- or multiple-continuum concept, in which fractures and matrix are represented as overlapping, different, but interconnected continua, described by parallel sets of conservation equations. The conventional single-point upstream weighting scheme, in which the fracture relative permeability is used to represent the counterpart at the fracture-matrix interface, is the most common scheme by which to estimate flow mobility for fracture-matrix flow terms. However, such a scheme has a serious flaw, which may lead to unphysical solutions or significant numerical errors. To overcome the limitation of the conventional upstream weighting scheme, this paper presents a physically based modeling approach for estimating physically correct relative permeability in calculating multiphase flow between fractures and the matrix, using continuity of capillary pressure at the fracture-matrix interface. The proposed approach has been implemented into two multiphase reservoir simulators and verified using analytical solutions and laboratory experimental data. The new method is demonstrated to be accurate, numerically efficient, and easy to implement in dual- or multiple-continuum models.