HR: 0800h
AN: H11C-0312    [Abstracts]
TI: Regional Hydraulic Conductivity Field Inferred From Joint Calibrations of 3-D Groundwater Flow and $^{4}$He Transport Models
AU: Castro, M C
EM: mccastro@umich.edu
AF: University of Michigan, Department of Geological Sciences, 2534 C. C. Little Building, 425 East University Avenue, Ann Arbor, MI 48109-1063 United States
AU: * Patriarche, D
EM: delfpat@umich.edu
AF: University of Michigan, Department of Geological Sciences, 2534 C. C. Little Building, 425 East University Avenue, Ann Arbor, MI 48109-1063 United States
AU: Goblet, P
EM: patrick.goblet@ensmp.fr
AF: Ecole des Mines de Paris, Centre d\'{ }Informatique G\'{e}ologique, UMR 7619 SISYPHE, 35 rue Saint Honor\'{e}, Fontainebleau, 77305 France
AB: The conceptual and practical gains achieved by expanding a 2-D finite element model [Castro and Goblet, 2003] to a true 3-D one through an application in the Carrizo aquifer and surrounding formations in southwestern Texas are investigated through a series of groundwater flow and $^{4}$He transport simulations. Such a 3-D model represents 4 formations, covers a surface area of $\sim$7000 km$^{2}$, and comprises more than 5 million elements. 3-D simulations allow for a more detailed and accurate definition of the heterogeneities of the system, by specifically identifying and differentiating processes that directly impact the three-dimensional hydraulic conductivity field. It is shown that while hydraulic conductivity decreases exponentially along the regional groundwater flow direction, such decrease is better described as a function of depth rather than recharge distance. This relationship reflects the combined influences of differential compaction of the media as well as down-dip lithological change. The intrinsic permeability derived from this relationship agrees with field information. In addition, our relationship intrinsic permeability-depth derived from the obtained hydraulic conductivity field in the 3-D model domain for depths $<$ 2 km is in agreement with that one proposed by Saar and Manga [2004] for the Oregon Cascades volcanic setting, as well as that proposed by Manning and Ingebritsen [1999]. These findings suggest that large-scale permeability evolution with depth is, to a large extent, independent of the type of medium. The $^{4}$He external flux value for which calibration of the 3-D transport model was achieved is 1.5$\times$10$^{-15}$ mol m$^{-2}_{rock}$ s$^{-1}$. Calculated hydraulic conductivities vary from 5$\times$10$^{-4}$ to 3.1$\times$10$^{-8}$ m s$^{-1}$ in the Carrizo aquifer from the outcrop to the discharge area. Results also suggest that the solution for groundwater flow simulations based on calibration of hydraulic heads depends on the ratio between hydraulic conductivities of different formations, showing that an infinite number of solutions are available for calibration of 3-D groundwater flow models. Understanding how geological processes directly affect the 3-D hydraulic conductivity field at the regional scale is essential not only to hydrogeological applications, but also at improving our understanding of the Earth\'{ }s crust and mantle dynamics by allowing for a more accurate quantification of helium and heat fluxes. Castro M. C., and Goblet P. (2003). Calibration of regional groundwater flow models - working toward a better understanding of site-specific systems. Water Resour. Res., 39(6), 1172, doi:10.1029/2002WR001653. Manning C. E., and Ingebritsen S. E. (1999). Permeability of the continental crust; implications of geothermal data and metamorphic systems. Rev. Geophys., 37(1), p. 127-150. Saar M. O., and Manga M. (2004). Depth dependence of permeability in the Oregon Cascades inferred from hydrogeologic, thermal, seismic, and magmatic modeling constraints. J. Geophys. Res., 109(B4), B04204, doi:10.1029/2003JB002855.
DE: 5114 Permeability and porosity
DE: 3210 Modeling
DE: 1829 Groundwater hydrology
DE: 1832 Groundwater transport
DE: 1040 Isotopic composition/chemistry
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting