Accuracy of saturated soil hydraulic conductivity estimated from numerically simulated single-ring infiltrations

Abstract

The single-ring pressure infiltrometer (PI) method is widely used to determine saturated soil hydraulic conductivity, K s , directly in the field. The original and still most common way to analyze the data makes use of the steady-state model developed by the Canadian School in the 90s and two (two-ponding-depth, TPD, approach) or more (multiple-ponding-depth, MPD, approach) depths of ponding. The so-called Wu method based on a generalized infiltration equation allows analysis of the transient infiltration data collected by establishing a single ponding depth of water on the infiltration surface. This investigation, making use of simulated infiltration runs for initially unsaturated sand to silty clay loam soils, showed that, with a run duration of practical interest (e.g., 2 h), the PI can be expected to yield more accurate estimates of K s in coarse-textured soils than in fine-textured soils even if the transient method is used instead of the steady-state method. Performing a three-level experiment and analyzing the estimated steady-state infiltration rates with both the TPD and MPD approaches is a way to predict the reliability of the estimated K s value. The K s accuracy should be acceptable if the two approaches yield similar results. Otherwise, the MPD approach should be expected to yield more accurate K s estimates than the TPD approach. The transient method does not solve the K s inaccuracy problems in fine-textured soils because obtaining accurate K s data requires that the portion of total infiltration varying linearly with time represent a high percentage of total infiltration, but this percentage is small in fine-textured soils when the run does not exceed a few hours. This investigation opens some new perspective on the use of infiltration data to make predictions on the expected reliability of the K s calculations with reference to both steady-state and transient data analysis procedures.