Hydraulic Interfaces from Soil Compaction: Evidence from Experiments and Numerical Simulation

Agricultural tillage and compaction create abrupt hydraulic interfaces in the vadose zone by forming contrasting tilled (loose) and untilled (compacted) soil layers with differing bulk densities. These interfaces influence pore connectivity, hydraulic conductivity, and water redistribution, thereby controlling infiltration and deep percolation in agricultural fields. This study used HYDRUS-2D to evaluate the performance of the single-porosity van Genuchten–Mualem model (VGM) against the dual-porosity Durner model (DM) for simulating water flow across a compacted interface in a two-layer silty loam profile representative of field conditions.  Hydraulic parameters were obtained by inverse modeling of laboratory hood–tension disc infiltrometer experiments conducted under varying suction heads with and without intermittent stop-flow periods. Model performance was evaluated for both continuous and intermittent infiltration scenarios. A global Sobol sensitivity analysis was performed to identify the most influential hydraulic parameters across suction regimes. The dual-porosity Durner model markedly outperformed the single-porosity VGM, especially in capturing sharp wetting front advancement, preferential flow cessation during redistribution, and water partitioning between macropore and matrix domains during stop-flow periods. The VGM tended to overly smooth the hydraulic contrast at the interface, resulting in unrealistic infiltration behavior. Sobol analysis revealed that compaction shifts parameter sensitivity: at lower suction, macropore parameters (α, n) dominate due to reduced macroporosity, whereas at higher suctions, matrix-region parameters (α₁, n₁, w₂) in the DM become more influential as flow transitions to matrix-dominated conditions. These results emphasize the critical role of density-driven hydraulic interfaces in controlling infiltration and redistribution and strongly support the use of dual-porosity models such as the Durner for predicting water flow prediction in heterogeneous, compaction-affected agricultural soils. The results have direct implications for improved modeling of water dynamics and agrochemical movement under realistic field management practices.