Steady convective flow in an unsaturated state dependent anisotropic soil profile: Analysis of the affected zone from a contaminating point source

Anisotropy of the medium plays a dominant role in shaping the flow pattern in the soil profile. This study analyses the effect of anisotropy on the horizontal spreading of the flow trajectories from a contaminating source point at the soil surface to a high water table. It considers a phreatic aquifer with infinite lateral extension and uniform sedimentary-layered soil profile, where a state dependent anisotropy factor (SDAF) – A(ψ), and anisotropy model might be applicable. The numerically calculated streamlines portray the effect of anisotropy, and allow discernment among various anisotropic media. Different flow cases are analyzed with regard to their dependence on A(ψ), as well as their dependence on the infiltration rate, and on the orientation of the principal axes. Theory indicates that the flux direction is dependent on the capillary head and thus on the flow rate. Consequently, it is the infiltration rate, which determines the particular path line from the contaminant source point to the ground water table. Accordingly, we have defined the “affected domain” as the domain within the unsaturated profile which is vulnerable to contamination from a source point at the soil surface, and the “affected segment” as the segment on the phreatic surface where pollutants may potentially reach the ground water aquifer. Both are determined with respect to anisotropy, infiltration rate, and depth. The non-linear horizontal shift of the contaminant trajectory indicates that a substantial error may result when adopting a constant anisotropy factor.