HR: 09:15h
AN: H21L-06    [Abstracts]
TI: Errors in determination of soil water content using time-domain reflectometry caused by soil compaction around wave guides
AU: * Ghezzehei, T A
EM: TAGhezzehei@lbl.gov
AF: Earth Sciences Division, Lawrence Berkeley National Laboratory, One Cyclotron Road, MS 90-1116, Berkeley, CA 94720, United States
AB: Application of time-domain reflectometry (TDR) in soil hydrology often involves the conversion of TDR-measured dielectric permittivity to water content using universal calibration equations (empirical or physically based). Deviations of soil-specific calibrations from the universal calibrations have been noted and are usually attributed with peculiar composition of soil constituents, such as high content of clay and/or organic matter. Although it is recognized that soil disturbance by TDR wave guides may have impact on measurement errors, to our knowledge, there has not been any quantification of this effect. In this presentation, we introduce a combined mechanical-hydrological method that estimates the measurement error. Our analysis indicates that soil compaction pattern depends on the mechanical properties of the soil at the time of installation. The relative error in water content measurement depends on the compaction pattern as well as the water content and water retention characteristics of the soil. Illustrative calculations based on measured soil mechanical and hydrologic properties from the literature show that the measurement errors of using a standard three-prong TDR wave guide could be up to 10 percent. We also show that the error scales linearly with the ratio of rod radius to the inter- radius spacing.
DE: 1822 Geomechanics
DE: 1859 Rocks: physical properties
SC: Hydrology [H]
MN: 2007 Fall Meeting