HR: 1340h
AN: H23B-1132    [Abstracts]
TI: Examining the Influence of TDR-Rod-Induced Flow Disruption on Measured Water Content during Steady State Flow
AU: * Hinnell, A
EM: andrew@hwr.arizona.edu
AF: University of Arizona, 1133 E. North Campus Drive, Tucson, AZ 85721-0011
AU: Ferre, P
EM: ty@hwr.arizona.edu
AF: University of Arizona, 1133 E. North Campus Drive, Tucson, AZ 85721-0011
AU: Warrick, A
EM: aww@ag.arizona.edu
AF: University of Arizona, 1133 E. North Campus Drive, Tucson, AZ 85721-0011
AB: Time domain reflectometry (TDR) is used routinely to monitor volumetric water content in porous media. TDR is used widely because it can make rapid, automated measurements with little need for medium-specific calibration. Another advantage of the method for some applications is its relatively small sample volume, which allows for high spatial resolution of the water content. Previous studies have shown that within its support volume, TDR is most sensitive to the water content in the immediate vicinity of the TDR rods. However, this is the area that may be most susceptible to flow disruption due to the presence of the instrument. In this study, we examine the spatial distribution of TDR sensitivity during steady state flow through unsaturated porous media under unit gradient conditions. We use a numerical model, built in FEMLAB, to predict the changes in water content in the medium due to TDR rods of different size, separation, and orientation. We then use a FEMLAB-based model to determine the effect of the water content distribution on the TDR sensitivity. Finally, we use the spatial sensitivity to predict the TDR-measured water content and compare this with the water content with the homogeneous background water content. We examine the effects of soil type, flux, and rod design on the measurement errors and show that, for the wide range of cases examined, the measurement errors are acceptably small for most common TDR probe designs. This gives further support for the use of TDR to conduct high-resolution volumetric water content monitoring.
DE: 1866 Soil moisture
DE: 1875 Unsaturated zone
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting