Characterizing Water and Solute Movement by Time Domain Reflectometry and Disk Permeametry
1996
Vogeler, Iris | Clothier, Brent E. | Green, Steven R. | Scotter, David R. | Tillman, Russell W.
To investigate a rapid, nondestructive way of characterizing solute transport properties, time domain reflectometry (TDR) and disk permeametry have been used in combination. Calibration measurements had previously related TDR measurements to both the volumetric water content and the pore water concentration of Cl⁻. Laboratory measurements from a horizontal TDR probe were used to estimate transport parameters in a soil column by applying a one-dimensional numerical model in an inverse sense. A vertical TDR probe was used to provide independent verification of these parameters. A repacked column of Ramiha silt loam (an Andic Dystrochrept) was used under unsaturated, transient flow conditions. The disk permeameter, set to a pressure head of −50 mm and containing a solution of 0.032 M KCl, was placed straight onto the repacked soil column, which had an initial water content of 0.32 m³ m⁻³. The soil wet to 0.60 m³ m⁻³. However, in the columns only an envelope of Cl⁻ concentration could be obtained, due to exchange between the initially resident Ca²⁺ and the invading K⁺. This illustrates why cation exchange needs to be considered when TDR is used to infer solute dispersivity and the retardation were found to be 2.3 mm and 1.2, respectively. The retardation is shown to be due to the anion-exchange capacity varying with the concentration of the invading soil solution.
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