HydroGeoSphere

HydroGeoSphere (HGS) is a 3D control-volume finite element groundwater model, and is based on a rigorous conceptualization of the hydrologic system consisting of surface and subsurface flow regimes. The model is designed to take into account all key components of the hydrologic cycle. For each time step, the model solves surface and subsurface flow, solute and energy transport equations simultaneously, and provides a complete water and solute balance. The original name for the code was FRAC3DVS, which was created by René Therrien in 1992. The code was further developed jointly at the University of Waterloo and the Laval University, and was primarily used for academic research. It was renamed to HydroGeoSphere in 2002 with the implementation of 2D surface water flow and transport. In 2012, the software became commercialized under the support and management of Aquanty Inc. In order to accomplish the integrated analysis, HydroGeoSphere utilizes a rigorous, mass conservative modeling approach that fully couples the surface flow and transport equations with the 3-D, variably saturated subsurface flow and transport equations. This approach is significantly more robust than previous conjunctive approaches that rely on linkage of separate surface and subsurface modeling codes. HydroGeoSphere assumes that the subsurface flow equation in a porous medium is always solved during a simulation, either for fully saturated or variably saturated flow conditions. The subsurface flow equation can be expanded to incorporate discrete fractures, a second interacting porous continuum, wells, tile drains and surface flow. The following assumptions are made for subsurface flow: The fluid is essentially incompressible. The porous medium and fractures (or macropores), if present, are non-deformable. The system is under isothermal conditions. The air phase is infinitely mobile. The Richards’ equation is used to describe three-dimensional transient subsurface flow in a variably saturated porous medium: The fluid flux, , is represented by the Darcy's law shown as: where is the volumetric fraction of the total porosity occupied by the porous medium, is the internal fluid exchange rate (e.