In Situ Characterization of Unsaturated Soil Hydraulic Properties at the Maricopa Environmental Monitoring Site

Abstract

Characterization of the unsaturated hydraulic properties is fundamental in modeling soil water flow and contaminant transport in the vadose zone. The objective of this study was to develop a database of in situ determined unsaturated hydraulic properties for a 50 x 50 meter field site. Two infiltration experiments were conducted. Neutron probe and tensiometers were used to determine soil water content and soil water potential to a depth of 10 meters throughout the irrigation and redistribution phases of both experiments. Unsaturated hydraulic conductivity was determined from changes in soil water content using the instantaneous profile method with a simplified unit gradient approach. Hydraulic properties determined from the redistribution phase of experiment 1 were evaluated by means of a one-dimensional forward simulation of wetting front arrival times at the 3, 5 and 10 m depths for experiment 2. It was found that predictions of wetting front arrival times at 10 m were late by an average of 15%. The hydraulic gradient averaged 0.97 throughout the redistribution phase of experiment 1, thus the unit gradient assumption, used to determine unsaturated hydraulic properties for nine locations and 40 depths within the 50 x 50 m field plot, was justified for this deep layered profile.