Effective hydraulic conductivities in unsaturated heterogeneous media by Monte Carlo simulation
When modeling flow and transport through unsaturated heterogeneous geological deposits, it may be neither computationally nor technically feasible to account for the actual heterogeneity in the simulations. One would fall short in terms of technical feasibility because there is simply no way that the entire spatial domain could be characterized (e.g., you cannot measure hydraulic conductivity at every location at a site). With respect to computational feasibility, the non-linear nature of the Richards equation (which is used to model the flow process) makes simulation of most sites extremely computationally intensive. The computational roadblock is being dismantled as computer hardware advances, but our inability to precisely characterize geological heterogeneity is expected to remain with us for a very long time. To address this problem, the analyst typically uses average or ‘effective’ properties to model flow and transport behavior through heterogeneous media. In this paper, a variety of approaches for developing effective unsaturated flow properties are assessed. Computational results have been obtained which give the hydraulic conductivity ratios (K parallel/K nomal) for highly nonisotropic layered materials. These results are compared with analytical models. Good agreement was obtained for all soil saturation levels except for extremely dry conditions.
Key wordsheterogeneity effective properties hydraulic conductivity
Unable to display preview. Download preview PDF.
- Ababou, R., McLaughlin, D. and Gelhar, L. W., 1988, Three-Dimensional Groundwater Flow in Random Media,Ralph Parsons Lab. Report 318, Mass. Inst. of Technology.Google Scholar
- Ababou, R., 1991, Approaches to Large Scale Unsaturated Flow in Heterogeneous, Stratified, and Fractured Geologic Media,U.S. Nuclear Regulatory Commission, NUREG/CR-5743.Google Scholar
- Bear, J., Braester, C. and Menier, P., 1987, Effective and relative permeabilities of anisotropic porous media,Transport in Porous Media 2, 301–316.Google Scholar
- Bowman, R. S., Grabka, D. P., Gibbens, J. F. and Stephens, D. B., 1990, Three-dimensional solute transport in a heterogeneous vadose zone,EOS Trans. Am. Geophys. Union 71, 514.Google Scholar
- Eaton, R. R. and Hopkins, P. L., 1992, LLUVIA-II: A Program for Two-Dimensional, Transient Flow Through Partially Saturated Porous Media,SAND90-2416, Sandia National Laboratories, Albuquerque NM, August.Google Scholar
- Frederick, R. B., 1988, A Laboratory Experiment of Uniform Infiltration into a Sloping, Stratified and Uniform Sandy Soil, M.S. Thesis, NM Institute of Mining and Technology, Socorro, NM, 102 pp.Google Scholar
- Freeze, R. A. and Cherry, J., 1979,Groundwater, Prentice-Hall Publishers.Google Scholar
- Hills, R. G. and Wierenga, P. J., 1991, Model validation at the Las Cruces Trench Site,U.S. Nuclear Regulatory Comm., NUREG/CR-5716.Google Scholar
- Polmann, D., 1990, Application of Stochastic Methods to Transient Flow and Transport in Heterogeneous Unsaturated Soils, Doctoral Dissertation, Dept. of Civil Engineering, Massachusetts Institute of Technology, 476 pp.Google Scholar
- Zimmerman and Wilson, 1990, Description of and User's Manual for TUBA: A Computer Code for Generating Two-Dimensional Random Fields via the Turning Bands Method,Scientific and Engineering Analysis Software, Albuquerque New Mexico.Google Scholar