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United States Department of Agriculture

Agricultural Research Service


item Mallants, Dirk
item Mohanty, Binayak
item Jacques, Diederik
item Feyen, Jan

Submitted to: Soil Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/30/1995
Publication Date: N/A
Citation: N/A

Interpretive Summary: Hydrological and geological processes are known to vary in space. Knowledge of spatial heterogeneity of soil hydraulic properties is, thus, important to quantify field-scale or regional-scale water and chemical migration in soil and groundwater. Saturated and unsaturated hydraulic conductivities and soil water retention functions were measured at 180 different spatial locations in a three-layered soil profil and fitted to van Genuchten model. The saturated hydraulic conductivity was found to be the most variable parameter influenced by the presence or absence of macropores. The saturated water content on the other hand was found to be one of the least variable parameters. At the field site, most hydraulic parameters were found to be correlated in space with a spatial range between 4 and 7 m. The correlation structures of hydraulic parameters can be used in practical applications such as estimating values of the selected properties at unsampled locations by means of spatial interpolation techniques such as kriging and co-kriging, or can be used in the generation of synthetic data or parameter fields, which are required for stochastic flow and transport modeling.

Technical Abstract: Moisture retention characteristic (MRC) curves and saturated hydraulic conductivity (Ks) were measured on 100-cm3 undisturbed 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. Sampling intervals in the horizontal direction were, alternately, 0.1 and 0.9 m. The drying part of the MRC curves was described by the four-parameter retention model for van Genuchten with fitting parameters, namely wcs, wcr, alpha, and n. Spatial variability of the five parameters, wcs, wcr, alpha, n, and Ks, was investigated for the three horizons using conventional statistics and geostatistical techniques. Maximum coefficient of variation (CV) was found for Ks, 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 Ks. When all three soil depths are econsidered, residual water content (wcr) and shape factor alphas showed moderate heterogeneity with a maximum CV of 156 and 53%, respectively. Small spatial heterogeneity was observed for shape factor n and saturated water content wcs with a maximum CV of 22 (for 0.1-m depth) and 8% (for 0.9-m depth), respectively. Most hydraulic parameters at different layers exhibited convex experimental semivariograms that could be described by means of spherical models, with a spatial range between 4 and 7 m.

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