Field Determination of Saturated and Unsaturated Hydraulic Conductivities Using the IP Method

An instantaneous profile (IP) test was conducted at Sandia National Laboratories, Albuquerque, New Mexico. The IP method was used to determine the field-saturated and unsaturated hydraulic conductivities of a natural soil profile. The soil profile was instrumented with two neutron probe access tubes and three clusters of paired tensiometers and time domain reflectometry (TDR) probes. The soil profile was flooded for a period of 48 hours. Flooding was discontinued when the soil was field-saturated. Neutron probe and tensiometer data were acquired on a continual basis for 890 days and 200 days, respectively. As the soil profile was allowed to drain, soil moisture and suction data were recorded throughout the soil profile. These data from the IP test were used to calculate the unsaturated hydraulic conductivity as a function of the volumetric moisture content of the soil profile. The curves representing hydraulic head, H, change with depth, z, exhibit a clear change in slope between 90 cm and 120 cm due to a caliche layer. Values of hydraulic conductivity were calculated from the slope of the ∂H/∂z curves corresponding to a given depth and time. The hydraulic conductivity of the soil profile is represented by a family of curves that represent the variations in soil characteristics within this soil profile.