Analytical Method to Determine Soil Hydraulic Properties from Vertical Infiltration Experiments

Abstract

Core Ideas
• A new method was proposed to determine Brooks‐Corey (BC) model parameters.
• Only a vertical infiltration experiment and simple measurements were required.
• The new method has great potentials to be applied in situ on various scales.

Soil hydraulic properties are basic inputs for simulating water and solute transport in the vadose zone. Many methods have been developed to directly measure or indirectly estimate soil hydraulic properties. However, low‐cost, simple and robust methods are still scarce even in a laboratory. Here we present a new analytical method, based on an approximate solution to the one‐dimensional vertical infiltration problem that can be used to determine Brooks–Corey model parameters. Measurements include cumulative infiltration, wetting front advance with time, and initial and final upper boundary water contents, during a one‐dimensional vertical infiltration experiment. Infiltration experiments with twelve disturbed soils were performed to test the new method. The results indicated that the estimated saturated hydraulic conductivities from transient infiltration processes were consistent with those measured with a constant‐head method. The estimated soil water retention curves (SWRCs) by the analytical method for the twelve soils were in agreement with those measured by a direct method in which soil water potentials were measured through tensiometers. The root mean square error (RMSE) of the estimated soil water contents by the new method were less than 0.045 cm³ cm^–3 for the twelve soils. Compared to most direct methods, the new method is inexpensive, rapid and easy to use, and thus can be a substitute for direct methods in a laboratory. Although how to monitor representative wetting front remains unsolved, the new method has a potential for use in the future in determining in situ soil hydraulic properties where lateral flows are negligible.