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NOTES

Flexible Time Domain Reflectometry Probe for Deep Vadose Zone Monitoring

^a Desert Research Institute, Reno, NV, and The Jacob Blaustein Institute for Desert Research, Dep. of Environmental Hydrology & Microbiology, Ben-Gurion University of the Negev, Sede Boqer Campus, 84990, Israel
^b Desert Research Institute, Reno, NV
^c Desert Research Institute, Las Vegas, NV
^* Corresponding author (odahan{at}bgumail.bgu.ac.il)

Received 9 September 2002.

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.

Abbreviations: PVC, polyvinyl chloride • TDR, time domain reflectometry

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