HR: 1330h
AN: H12A-0965    [PDF]
TI: Percolation- and Effective Medium-Based Models of Unsaturated Hydraulic Conductivity
AU: Ewing, R P
EM: ewing@iastate.edu
AF: Department of Agronomy Iowa State University, Department of Agronomy Iowa State University, Ames, IA 50011-1010 United States
AU: * Hunt, A G
EM: allenghunt@msn.com
AF: CIRES University of Colorado, Department of Agronomy Iowa State University, Ames, IA 50011-1010
AB: The unsaturated hydraulic conductivity function K(S) is of fundamental importance in understanding and predicting flow in the vadose zone. However, time and cost constraints typically require hydrologists to estimate K(S) rather than measuring it. Existing K(S) models are empirical; in this work we develop new theoretical models based upon percolation theory and effective medium theory. Percolation- and effective-medium-based theories have been recognized for over 25 years in the physics of transport in disordered systems as the premier means to "upscale" transport properties, i.e. to calculate system transport parameters from the variability at smaller scales. Percolation theory has recently been used to derive pressure-saturation curves, solute and gas diffusion, and the K(S) of probabilistic fractal porous media, and the results have given excellent agreement with experiment. An advantage of percolation theory vis-a-vis effective medium theory is the possibility to isolate effects of pore-sizes and the topology of the connections of pores on transport phenomena. The disadvantage of this procedure is that it can require treating different ranges of parameters, such as the moisture content, differently. The attractive aspect of effective-medium theory is its ability to handle all contributions to the physics simultaneously. We compare effective-medium and percolation theories using a model porous medium in which the pore radii are power-law distributed. In both theoretical treatments we observe a cross-over from critical pore-size dominated hydraulic conductivity at relatively large moisture contents to the dominance of the topological connections of the wetted pore space at moisture contents near the critical value for percolation.
DE: 1829 Groundwater hydrology
DE: 1832 Groundwater transport
DE: 1875 Unsaturated zone
DE: 3210 Modeling
SC: Hydrology [H]
MN: 2003 Fall Meeting