A METHOD FOR ESTIMATING UNSATURATED HYDRAULIC-PROPERTIES OF VERTICALLY HETEROGENEOUS SOILS FROM TRANSIENT CAPILLARY-PRESSURE PROFILES

The hydraulic properties of soil are represented by the relationship b etween the volumetric water content a and the soil capillary pressure psi and the relationship between the hydraulic conductivity K and psi. A method to estimate the hydraulic properties for each horizontal lay er of a soil profile was developed by combining the instantaneous prof ile method to compute K(psi) values and Mualem's model to derive the K -psi relationship from the soil water retention characteristic. With t his method, three parameters that are contained both in the theta-psi and K-psi models are optimized by an iterative procedure using transie nt capillary pressure profiles during water redistribution. Two hypoth etical soil columns were used to test the parameter estimation procedu re, and it was shown that the proposed method can be applied to soil p rofiles which have homogeneous or heterogeneous hydraulic properties w ith depth.