Unsaturated Flow and Solute Transport During Infiltration and Evaporation Cycles: Influence of Soil Heterogeneity and Gravity Fingers

Infiltration and evaporation processes in porous media are crucial for understanding the hydrologic cycle and managing water resources, particularly in the context of climate change. Studying these processes requires models that accurately represent experimental and field measurements.

This work focuses on understanding flow and transport during water infiltration and evaporation cycles, considering factors such as soil heterogeneity, the non-linearity of its properties, and the formation of gravity fingers. We aim to improve the modeling of infiltration and evaporation processes in soils to accurately predict water flow and solute transport behavior, and to characterize the impact of soil heterogeneity, non-linear properties, and gravity fingers on these processes.

To address the effect of these factors, we simulate water infiltration and evaporation cycles, and solute transport in unsaturated soil. Two modeling approaches are compared: the traditional Richards’ equation and the fourth-order derivative in space model proposed by Cueto-Felgueroso and Juanes (2009), which is able to reproduce the formation of fingers and preferential flow during water infiltration. The flow and transport problems are solved using the finite element library FEniCS.

Soil heterogeneity is represented by Gaussian random permeability fields, with different correlation lengths and variance. To evaluate how heterogeneity affects dispersion and mixing during the solute transport, we analyze solute breakthrough curves at different depths, we calculate dispersion coefficients, concentration distribution and segregation index.

 

Keywords: infiltration and evaporation cycles, unsaturated flow, heterogeneity, gravity fingers, finite element method, solute transport, mixing.

References:

Cueto-Felgueroso, L., and R. Juanes (2009). A phase field model of unsaturated flow. Water Resources Research, 45, W10409. https://doi.org/10.1029/2009WR007945