Critical Evaluation of Viability of Mini Disc Infiltrometer for Determining the Unsaturated Hydraulic Conductivity Function

The soil hydraulic conductivity function [K(ψ)] is generally estimated from a known soil-water characteristic curve and saturated hydraulic conductivity because of its cumbersome and time-intensive procedure. The need for a quick determination of K(ψ) along with the generation of comparable K(ψ) using available methods has motivated this research work. This study demonstrates the utility of a handy mini disc infiltrometer (MDI) as a nondestructive and noninvasive method to determine K(ψ) relationship with the assistance of laboratory tests on disturbed soil samples. The main objective is to critically evaluate MDI measurements [cumulative infiltration (CI) versus time] to generate K(ψ), followed by its comparison with two existing methods [instantaneous profile method (IPM) and wetting front advancing method (WFAM)]. The methodology involves MDI infiltration tests in soil columns and the utilization of its surficial infiltration measurements to generate K(ψ) using a numerical inversion technique. Additionally, the spatial and temporal volumetric water content (θ) and matric suction (ψ) profiles recorded during a one-dimensional (1D) wetting process under identical conditions are employed to obtain K(ψ) using IPM and WFAM methods and, further, to validate K(ψ) from MDI data inversion. The results show that MDI tests considerably reduce the wetting period (<24 h) and enable determining K(ψ) for a wide range of ψ. The IPM and WFAM also exhibit matching K(ψ) when analyzed using the same θ-ψ profiles. Further, the normalized root mean square error between all the methods used for K(ψ) determination is <16%, which is deemed appropriate for real soil conditions.