Mixed finite elements for accurate particle tracking in saturated groundwater flow

Saturated groundwater flow can often be described by the law of mass conservation and Darcy's law, i.e. by a potential flow problem. An accurate approximation of the specific discharge can be determined by the mixed finite element method. In this article the lowest-order mixed method is presented including its hybridization, which results in a sparse symmetric positive definite system of linear equations. This system can be solved efficiently by the preconditioned conjugate gradient method. After approximating the specific discharge, streamlines and residence times can be determined easily and accurately. The applicability and advantages of the mixed finite element method are illustrated for three potential flow problems for HYDROCOIN Level 1.