MOC3D adapted to simulate 3D density-dependent groundwater flow

Abstract

The three-dimensional computer code MOC3D (Konikow et al., 1996) is adapted for density differences: MOCDENS3D. As a result, it is possible to model transient three-dimensional groundwater flow in large-scale hydrogeologic systems where non-uniform density distributions occur. A special field of application is the simulation of salt water intrusion in coastal aquifers. The groundwater flow equation is solved by the MODFLOW module of MOCDENS3D. Density differences are taken into account through adding buoyancy terms to the RHS term of the basic groundwater flow equation of MODFLOW. The advection-dispersion equation is solved by the MOC module, using the method of characteristics. Advective transport of solutes is modeled by means of particle tracking and dispersive transport by means of the finite difference method. An advantage of applying the method of characteristics is that the condition of spatial discretisation is not strict. As a consequence, the displacement of fresh, brackish and saline groundwater in large-scale hydrogeologic systems can easily be modeled. Finally, the evolution of a freshwater lens at a circular sandy island is shortly discussed.