Numerical Simulation of the Effect of Vegetation on Infiltration in Soil Covers of Potash Tailings Piles

Potash tailings piles from the mining of potassium salts present considerable environmental challenges concerning surface and groundwater. Uncovered piles are primarily composed of saline residues such as sodium chloride, magnesium sulfate and magnesium chloride. To mitigate the interaction between saline residues and rainwater, some piles have been covered by different soil types in some regions of the world, including Germany, to act as a physical barrier to prevent water-salt contact. In this way, the amount of infiltrated water is reduced, thereby reducing the amount of salts that can be leached and transported to the underlying water bodies. The extent to which the soil cover prevents the contact of infiltrated rainwater will depend on the hydraulic parameters of each soil type, how many soil layers make up the overall soil cover, how the soil layers are distributed, and on the hydrological situation of each region. While climatic factors such as precipitation are fundamental controlling factors, the type and distribution of vegetation play a crucial role in the efficiency of the pile cover. The objective of this research is therefore to quantify the effect of vegetation on infiltration and evapotranspiration in a vegetated soil cover over a hypothetical potash tailings pile by numerical simulation. For this purpose, different types of vegetation are analyzed, represented by their hydrological parameters leaf area index, depth and root density. The seasonal variations of the vegetation represented by temporally changing parameter values are also taken into consideration. Different depths of the cultivation layer for vegetation, the stabilization layer, the drainage layer and the sealing layer are regarded. The numerical simulation is carried out with the Advanced Terrestrial Simulator (ATS), a software which allows surface-subsurface coupling through continuity conditions of pressure in both zones. The software solves the diffusion wave equation for surface flow and Richard’s equation for the subsurface flow. Additionally, ATS implements the Priestley-Taylor model for potential evapotranspiration. Together with vegetation parameters, this enables the calculation of actual evapotranspiration and, subsequently, the water balance of the soil cover. Results from 2D simulations demonstrate the ability of the model to represent the relevant coupled processes outlined above. The simulated infiltration patterns provide valuable insights for optimizing cover design and vegetation selection, contributing to the development of more effective solutions for groundwater protection in potash tailings piles areas.