Use of Brooks-Corey parameters to improve estimates of saturated conductivity from effective porosity

tating a large number of samples. For this reason indirect methods have held promise as an alternative to making Effective porosity, defined here as the difference between satiated direct measurements. A further advantage of indirect total porosity and water-filled porosity at a matric potential of 33 kPa, has been shown to be a good predictor for saturated hydraulic methods is that they allow researchers to obtain an conductivity (Ks) using a modified Kozeny-Carman equation. This estimate of the variability of saturated conductivities equation is of the form of a coefficient (B ) multiplied by effective based on the variability of an easily measured predictor porosity raised to a power (n ). The purpose of this study was to variable (Ahuja et al., 1989). improve the predictive capability of the modified Kozeny-Carman A number of relationships have been developed that equation by including information from moisture release curves (soil can be used to calculate Ks with easily measured soil water content vs. matric potential relation). We fitted the Brooks- properties. Some are purely empirical and are often Corey (B-C) equation parameters (pore size distribution index and related to soil texture (Rawls et al., 1992; Puckett et al., air entry potential) to moisture release data from a large database 1985). Other relationships use physically based equa(.500 samples). Values of Ks were also available from the same tions. Ahuja et al. (1984, 1989) showed that a modified source. Inclusion of the pore size distribution index into the KozenyCarman equation improved the Ks estimation over using only effective Kozeny-Carman equation porosity, but only slightly. The improvement came through a better Ks 5 B1f n e [1] estimation of large values of Ks. We also fit a relationship for the coefficient (B) of the Kozeny-Carman equation as a function of the was applicable to a wide range of soils from the Southern two B-C parameters with a constant value of n 5 2.5 for the exponent. Region of the USA, Hawaii, and Arizona. Here fe is Overall the use of Brooks-Corey parameters from moisture retention the effective porosity calculated as saturated water condata improved estimates of Ks over using effective porosity (fe) alone. tent (us) minus the water content at 33 kPa matric potenThere is still considerable error in predicting individual Ks values, tial, and B