DETERMINING SOIL HYDRAULIC-PROPERTIES USING TENSION INFILTROMETERS, TIME-DOMAIN REFLECTOMETRY, AND TENSIOMETERS

Tension infiltrometers have become a popular instrument for field dete rmination of soil hydraulic properties, To develop and test different models for parameter estimation based on tension Infiltrometer measure ment, we obtained simultaneous measurements of transient tension infil tration rate, soil water content, and tension using small time domain reflectometry (TDR) probes and tensiometers installed at fixed locatio ns relative to the infiltrometer disk. infiltration was made with 10- and 20-cm-diam. disks under 1 and 5 cm of water supply tensions. The s oil is an Arlington fine sandy loam (coarse-loamy, mixed, thermic Hapl ic Durixeralf). Wooding's steady-state approximate solution for water now from a surface circular pond was used to estimate the saturated hy draulic conductivity (K-s) and an empirical parameter (alpha G) used i n Gardner's exponential hydraulic conductivity function. These two par ameters (i.e., K-s and alpha(G)) were then independently estimated usi ng an integral form of the steady-state Darcey-Buckingham flux law. A sorptivity method was also proposed as an alternative to Wooding's ste ady-state approach, Calculated K-s and alpha(G) with the Darcy-Bucking ham flux law method was in good agreement with estimates using Wooding 's steady-slate approximation. The sorptivity method produced K-s esti mates that were statistically similar to those obtained with Wooding's method, The K(h) inferred from measured theta(h) underestimated the c onductivity close to saturation compared with estimates obtained from the infiltrometer measurements.