Improved design for an automated tension infiltrometer

Abstract

Automated measurements of water infiltration rates are commonly done using two gage transducers to measure water level changes in the reservoir of an infiltrometer. Previous studies have evaluated and described in detail infiltrometers automated with two gage-transducers and have shown that measurement precision and accuracy of soil hydraulic properties are improved. A previous study has also suggested the use of a single differential transducer to automate an infiltrometer to eliminate measurement error associated with air bubbles in the infiltrometer reservoir. In this study, the automation of a tension infiltrometer using a differential transducer was developed, evaluated, and applied. A single differential transducer was installed at the bottom of an infiltrometer reservoir and the other end was connected by tubing to the head-space in the reservoir. Calibration of the reservoir height measurements vs. transducer voltage output was simplified over previous methods and was even demonstrated in situ. Measurement precision was also improved by two orders of magnitude over previous methods. Measurements were also done to demonstrated the use of the single differential transducer set-up to obtain field measurements of unsaturated hydraulic conductivity and sorptivity. Unlike previous methods though, this method does not allow for the determination of the imposed potential at the soil surface unless adaptations are made.