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

Effective porosity, defined here as the difference between satiated total p orosity 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) us ing a modified Kozeny-Carman equation. This equation is of the form of a co efficient (B) multiplied by effective porosity raised to a power (n). The p urpose of this study was to improve the predictive capability of the modifi ed Kozeny-Carman equation by including information from moisture release cu rves (soil water content vs. matric potential relation). We fitted the Broo ks-Corey (B-C) equation parameters (pore size distribution index and air en try 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 i mprovement 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 a s 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 ret ention data improved estimates of K-s over using effective porosity (phi(c) ) alone. There is still considerable error in predicting individual K-s val ues, however, The best forms of the equation was when lambda was included i n the term for the coefficient for the modified Kozeny-Carman equation. The next best form was when lambda was included in the exponent for phi(c) The two best models appeared to better the mean, standard deviation and range of the original data.