Determination of wetting soil water characteristics curve from disk infiltrometer measurements

Department of Civil Engineering, Indian Institute of Technology, Guwahati, India

^* Corresponding author: aparimita@iitg.ac.in

Abstract

A wetting soil water characteristic curve (SWCC_w) is necessary for understanding and interpreting the re-distribution of infiltrated rainwater, percolation rate, and contaminant transport. Direct determination of SWCC_w is tedious and needs destructive sampling and invasive sensor installation. This study demonstrates an indirect method for determining SWCC_w based on infiltration measurements using a mini disc infiltrometer (MDI). Under controlled initial conditions, infiltration tests were conducted, coupled with real-time soil moisture and matric potential measurements using sensors. Sensor data facilitated assessment and cross-verification of SWCC_w indirectly determined from MDI measurements. The indirect estimation involved inverse analysis and optimization of SWCC_w parameters (α and n of the van Genuchten model) based on measured cumulative infiltration (CI) -versus-time response along with the knowledge of final volumetric water content (VWC_f). The optimized SWCC_w from MDI-infiltration matched the sensor-measured SWCC_w reasonably well. The statistical tests using ANOVA proved that the CI measurements from MDI, together with VWC_f information, are reliable input for inverse estimation of SWCC_w and its parameters. Based on a realistic wetting process in the unsaturated zone beneath the disc infiltrometer, this study demonstrates the utility of a compact MDI for a quick, non-destructive measurement of SWCC_w.