A Framework for Monitoring Soil Hydraulic Properties of Undisturbed Soil Samples and Modeling Unsaturated Zone Water Flow

Abstract

Soil structure is the predominant factor of water, gases, and nutrients movement within the unsaturated zone. Despite the growing interest in the influence of structured soil media on soil-water dynamics, there is a gap in explicit technical documentation on monitoring soil hydraulic properties in undisturbed soil samples. This study proposes a new framework to measure and monitor soil hydraulic properties in undisturbed soil samples, in parallel optimizing falling head and centrifuge method for structured soil samples. Both unimodal and bimodal soil hydraulic functions are used to describe Soil Water Retention Curve (SWRC) data derived from laboratory experiments, and a modified one is introduced to integrate all the possible distinct pore domains of the soil matrix. The description SWRC data by the modified soil hydraulic equation coincides with Durner equation, while provides important insights on the saturated water content of each sub-pore domain. Water flow models in the unsaturated zone have been developed in Hydrus 1D, applying hydraulic parameters that correspond to soil hydraulic properties obtained from experimental data and the Rosetta Pedotransfer function. The combined used of optimized methods on undisturbed soil samples provided an insightful description of soil hydraulic properties, while water flow models with conceptualized soil hydraulic properties and data assimilation (DA) outperformed every other method. Water flow models using bimodal hydraulic function achieved the greater accuracy in each observation node of the soil column (10 cm: 0.074 cm³cm⁻³, 50 cm: 0.0756 cm³cm⁻³).