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This article in SSSAJ

  1. Vol. 63 No. 5, p. 1086-1092
    Received: Nov 24, 1997

    * Corresponding author(s): dtimlin@asrr.arsusda.gov
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Use of Brooks-Corey Parameters to Improve Estimates of Saturated Conductivity from Effective Porosity

  1. D. J. Timlin *a,
  2. L. R. Ahujab,
  3. Ya. Pachepskyc,
  4. R. D. Williamsd,
  5. D. Gimeneze and
  6. W. Rawlsf
  1. a USDA-ARS Systems Research Lab, Bldg. 007, Rm 116, 10300 Baltimore Ave, Beltsville, MD 20705 USA
    b USDA-ARS Great Plains Systems Research Unit, P.O. Box E, Ft. Collins, CO 80522 USA
    c Dept of Botany, Duke University, Durham, NC 27708 USA
    d USDA-ARS Grazing Lands Research Laboratory, P.O. Box 1199, El Reno, OK 73036-1199 USA
    e Dept. of Environmental Sciences, Rutgers, The State University of NJ, 14 College Farm Rd., New Brunswick, NJ 08901 USA
    f USDA-ARS Hydrology Laboratory, Bldg 007, Rm 112, 10300 Baltimore Ave., Beltsville, MD 20705 USA


Effective porosity, defined here as the difference between satiated total porosity and water-filled porosity at a matric potential of 33 kPa, has been shown to be a good predictor for saturated hydraulic conductivity (K s) using a modified Kozeny-Carman equation. This equation is of the form of a coefficient (B) multiplied by effective porosity raised to a power (n). The purpose of this study was to improve the predictive capability of the modified Kozeny-Carman equation by including information from moisture release curves (soil water content vs. matric potential relation). We fitted the Brooks-Corey (B-C) equation parameters (pore size distribution index and air entry potential) to moisture release data from a large database (>500 samples). Values of K s were also available from the same source. Inclusion of the pore size distribution index into the Kozeny-Carman equation improved the K s estimation over using only effective porosity, but only slightly. The improvement came through a better estimation of large values of K s We also fit a relationship for the coefficient (B) of the Kozeny-Carman equation as a function of the two B-C parameters with a constant value of n = 2.5 for the exponent. Overall the use of Brooks-Corey parameters from moisture retention data improved estimates of K s over using effective porosity (ϕe) alone. There is still considerable error in predicting individual K s values, however. The best forms of the equation was when λ was included in the term for the coefficient for the modified Kozeny-Carman equation. The next best form was when λ was included in the exponent for ϕe The two best models appeared to better preserve the mean, standard deviation and range of the original data.

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