SPATIAL VARIABILITY OF HYDRAULIC-PROPERTIES IN A MULTILAYERED SOIL-PROFILE

Unsaturated hydraulic properties of field soils are needed for water f low and solute transport calculations in variably saturated soils. The purpose of this study was to quantify the spatial variability and spa tial crosscorrelation of estimated parameter values of a flexible rete ntion model that was fitted to measured retention data. Moisture reten tion characteristic (MRC) curves were measured on 100-cm(3) undisturbe d soil cores collected at 180 locations along a 31-m-long transect in a three-layered soil profile at depths of 0.1, 0.5, and 0.9 m. Samplin g intervals in the horizontal direction were, alternately, 0.1 and 0.9 m. Saturated hydraulic conductivity (K-s) was determined on the same soil cores using a constant head permeameter. The drying part of the M RC curves was described by the four-parameter retention model of van G enuchten with fitting parameters, namely theta(r), theta(s), alpha, an d n. Spatial variability of the five parameters, theta(r), theta(s), a lpha, n, and K-s, was investigated for the three horizons using conven tional statistics and geostatistical techniques. Maximum coefficient o f variation (CV) was found for K-s, i.e., 599%, 322%, and 897% for the 0.1-, 0.5-, and 0.9-m soil depths, respectively. Macropores and small sampling volume contributed to this large variability of K,. When all three soil depths are considered, residual water content (theta(r)) a nd shape factor cw showed moderate heterogeneity with a maximum CV of 156 and 53%, respectively. Small spatial heterogeneity was observed fo r shape factor n and saturated water content theta(s), with a maximum CV of 22 (for 0.1-m depth) and 8% (for 0.9-m depth), respectively. Mos t hydraulic parameters at different layers exhibited convex experiment al semivariograms that could be described by means of spherical models , with a spatial range between 4 and 7 m. The correlation scales for c ross-semivariograms for pairs of cross-correlated parameters were foun d to be of similar magnitude to those pertaining to the direct semivar iograms of correlated variables.