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Hydraulic Functions for Macroporous Soils

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan

Citation:  Pp. 37-40 in Preferential Flow, Water Movement and Chemical Transport in the Environment, Proc. 2nd Int. Symp. (3-5 January 2001, Honolulu, Hawaii, USA), eds. D. D. Bosch and K. W. King. St. Joseph, Michigan: ASAE  701P0006.(doi:10.13031/2013.2138)
Authors:   M. Tuller and D. Or
Keywords:   liquid retention, unsaturated hydraulic conductivity, preferential flow, macroporous media

Recent progress in modeling equilibrium liquid configurations in angular pore spaces provides the basis for calculation of liquid saturation and unsaturated hydraulic conductivity in macroporous media. Medium pore space is represented as a dual-continuum made of matrix and macropores. Equilibrium liquid-vapor interfaces forming under unsaturated conditions are assumed to remain stable for slowly flowing liquid in films and corners, and are employed as boundary conditions for derivation of average liquid velocities from solutions of the Navier-Stokes equation. A linear relationship between flux density and hydraulic gradient, similar to Darcy's law, and averaging over liquid-occupied cross-sectional areas define the average hydraulic conductivities for pore-scale flow regimes within the matrix and macropore spaces. A statistical upscaling scheme based on a bimodal pore-size distribution, and weighting over matrix and macropore porosities is used to derive closed-form expressions for sample-scale unsaturated hydraulic conductivity. Soil water characteristic data, porosities of the two domains, and other physical media properties are used as input parameters for hydraulic conductivity predictions. Sample calculations for macroporous and aggregated soils reproduce a "double hump" shaped conductivity curve (typical for dual continuum media), and are in reasonable agreement with measured data. Aspects of 3-D network effects in the macropore domain are incorporated via independently measured saturated hydraulic conductivity.

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