Indented Interfaces between Soil Strata: Analytical and HYDRUS2D Modeling of 2-D Seepage Towards a Wedge

Abstract: Formation of soil horizon boundaries are commonly qualitatively described, their formation and time evolution are rarely quantified by adequate mathematical modeling. In this paper, analytical (using conformal mappings) and numerical (involving HYDRUS2D simulations) methods are employed to model 2D infiltration-induced Darcian flows within a layered fine/coarse soil substrate system featuring a wedge-shaped interface, considering both saturated and unsaturated conditions. Initial-boundary value problems to the Richards (in particular, Laplace’s) partial differential equations are set in domains with geometry of interfaces more complex than in regular soil profiles. The patterns of 2D distribution of physical characteristics (streamlines, isobars, velocities, etc.) are found in two variants of such a system (loam/gravelly non-capillary material, loam/sand), with comparison of analytical and numerical models. The novelty of the results is in the analysis of concentrating streamlines with maximum water flow rates and fastest travel time of advected marked particles at the tops of the jagged interface of the soil textures and the unsaturation of the underlying coarse-dispersed substrates during pressure infiltration of water in such systems. Also, if the soil surface is subject to small infiltration fluxes, the opposite phenomenon of capillary barrier, i.e. diversion of the infiltration flux from the top of the interface of the coarse substratum, is demonstrated in HYDRUS2D simulations. Prediction of morphological variations of soil profiles with non-horizontal interfaces, which undergo time-factor controlled anthropogenic drivers, is important for theoretical soil hydrophysics and hydrological and soil/geotechnical engineering.