Accurate determination of water content is an important aspect of most vadose zone monitoring programs. Real-time, continuous, in situ measurements of water content in relatively undisturbed conditions are usually limited to shallow soil horizons. We present a new methodology using time domain reflectometry (TDR) for water content monitoring in deep vadose zone horizons. The method uses flat, flexible, waveguides pressed against the wall of a borehole. The flexible TDR waveguides are attached to the outer side of a flexible sleeve filled with a liquid resin. The resin (e.g., a two-component urethane) generates hydrostatic pressure that forces the flexible waveguides against the borehole wall, ensuring a close fit to the irregular shape of the borehole walls. The probe can be used with either a standard TDR technique, which uses a cable tester (e.g., Tektronix 1520, Tektronix, Beaverton, OR) for collecting waveforms, or a water content reflectometer (e.g., model CS505, Campbell Scientific, Inc., Logan, UT), which provides a direct electrical output, which may be sampled using a data logger. Laboratory calibration experiments and a full-scale field experiment showed that the method is reliable and capable of providing accurate water content measurements in deep vadose zone horizons.

You do not have access to this content, please speak to your institutional administrator if you feel you should have access.