Modeling Groundwater Flow in Unconfined Conditions: Numerical Model and Solvers’ Efficiency

A mathematical model for variably saturated flow in unconfined conditions is presented. The model is based on pseudo-unsaturated approach using Richards equation with piecewise linear dependencies between hydraulic head, water content and relative permeability. It is implemented in GeRa (Geomigration of Radionuclides) software package, which is designed for modeling groundwater flow and contaminant transport in porous media and uses finite volume methods on unstructured grids. We consider two nonlinear solvers for nonlinear equations arising from discretization of the Richards equation, namely Newton and Picard methods. A special method for correction of hydraulic head values within the iterations of nonlinear solvers is proposed. The developed numerical techniques are applied to two test cases: dam seepage and real-world groundwater flow problems. © 2018, Pleiades Publishing, Ltd.