On the reliability of numerical solutions of brine transport in groundwater: Analysis of infiltration from a salt lake

The density dependent flow and transport problem in groundwater is solved n umerically by means of a mixed finite element scheme for the flow equation and a mixed finite element-finite volume time-splitting based technique for the transport equation. The proposed approach, spatially second order accu rate, is used to address the issue of grid convergence by solving on succes sively refined grids the salt lake problem, a physically unstable downward convection with formation of fingers. Numerical results indicate that achie vement of grid convergence is problematic due to ill-conditioning arising f rom the strong nonlinearities of the mathematical model.