Determining Soil Hydraulic Properties using Tension Infiltrometers, Time Domain Reflectometry, and Tensiometers

Abstract

AbstractTension infiltrometers have become a popular instrument for field determination of soil hydraulic properties. To develop and test different models for parameter estimation based on tension infiltrometer measurement, we obtained simultaneous measurements of transient tension infiltration rate, soil water content, and tension using small time domain reflectometry (TDR) probes and tensiometers installed at fixed locations 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 soil is an Arlington fine sandy loam (coarseloamy, mixed, thermic Haplic Durixeralf). Wooding's steady‐state approximate solution for water flow from a surface circular pond was used to estimate the saturated hydraulic conductivity (Ks) and an empirical parameter (αG) used in Gardner's exponential hydraulic conductivity function. These two parameters (i.e., Ks and αG) were then independently estimated using an integral form of the steady‐state Darcy‐Buckingham flux law. A sorptivity method was also proposed as an alternative to Wooding's steady‐state approach. Calculated Ks and αG with the Darcy‐Buckingham flux law method was in good agreement with estimates using Wooding's steady‐state approximation. The sorptivity method produced Ks estimates that were statistically similar to those obtained with Wooding's method. The K(h) inferred from measured θ(h) underestimated the conductivity close to saturation compared with estimates obtained from the infiltrometer measurements.