THE DEPENDENCE OF THE ELECTRICAL-CONDUCTIVITY MEASURED BY TIME-DOMAINREFLECTOMETRY ON THE WATER-CONTENT OF A SAND

We present paired measurements of the water content and electrical con ductivity collected in a laboratory column packed with a homogeneous, clean sand over a wide range of water content and pore water electrica l conductivity (EC) conditions. The EC was determined using the method of Nadler et al. [1991] from waveforms collected with two-rod time do main reflectometry (TDR) probes with and without baluns and with three -rod probes without baluns. Following Heimovaara et al. [1995], we cal ibrated the probes in saline solutions to account for the series resis tance of the cable and connectors. The calibrated EC shows a nonlinear dependence on the water content that is well described by a simple po wer relationship [Archie, 1942]. Recognizing that calibration in salin e solutions is impractical for some TDR probes, we demonstrate that th e EC response can be calibrated directly using the results of drainage events, incorporating only a separate calibration of the cable resist ance. None of the probe designs shows any clear advantage for EC measu rement.