A Canadian environmental engineer friend of mine asked me a consultancy on Groundwater Mathematical Modelling; water seepage through levees, in his case.

I took this occasion for updating my personal list of softwares (free, partially free, and not free) that perform groundwater calculations.

Details of mathematical models herein described are taken from their own web-sites.

**MODFLOW**: MODFLOW is the name that has been given the USGS (United States Geological Survey) Modular Three-Dimensional finite-difference Groundwater Flow Model. MODFLOW can represent the effects of wells, rivers, streams, drains, horizontal flow barriers, evapotranspiration, and recharge on flow. Potentiality of MODFLOW is that it can include many other modules to perform specific calculation, e.g. MOC3D a three-dimensional method-of-characteristics ground-water flow and transport model; MODPATH a particle tracking post-processing package; ZONEBDGT a computer program for calculating subregional water budgets. But many others tools are available that can fit your needs. It is widely used 2000 version of MODFLOW, but recently this version was upgraded by 2005 version. The standard version of MODFLOW is public-domain.

**SEEP2D**: SEEP2D is a 2-D finite-element flow model designed to compute seepage on profile models, such as for earthen dam and levee cross sections. SEEP2D can be used to model confined, partially confined, and unconfined flow situations. For partially-confined and unconfined flow situations, both the saturated and unsaturated flow is simulated and the phreatic surface determined. SEEP2D is a steady-state flow model and it computes the flow value at each node of the finite-element mesh. You have to pay for SEEP2D model. Anyhow it is easy to use: SEEP2D makes few things, but it works well.

**Z_SOIL. PC**: is a finite element package designed for solving geotechnical problems in two and three dimensions. The program can represent, among others: gravity fields and initial stress conditions, water table and water pressures under steady state or transient conditions, including time dependent boundary conditions, drained and undrained soil conditions, unloading control for convergence analysis in tunnels. In Demo version, Z_SOIL.PC can solve problems unlimited in time but limited in size to: 400 nodes and/or 25 structural elements (beams, trusses, membranes) for 2D problems; 600 nodes and/or 50 structural elements (beams, trusses, membranes, shells) for 3D problems. Prices varies between 2D and 3D version, and for academic and professional users.

**GSM**: GSM is a comprehensive graphical user environment for performing groundwater simulations. The entire GMS system consists of a graphical user interface (the GMS program) and a number of analysis codes (MODFLOW, MT3DMS, RT3D, SEAM3D, MODPATH, MODAEM, SEEP2D, FEMWATER, WASH123D, UTCHEM). The GMS interface was developed by the Environmental Modeling Research Laboratory of Brigham Young University in partnership with the U.S. Army Engineer Waterways Experiment Station. GMS was designed as a comprehensive modeling environment. Several types of models are supported and facilities are provided to share information between different models and data types. GSM is a nice tool. My favorite, absolutely, above all the last version 6.0. GSM is not for free (see prices). In DEMO mode you can work freely, but you can’t save your project.

In my opinion, the funniest way to model groundwater flows is implementing your own code, e.g in Matlab language. Just Matlab has the Partial Differential Equation Toolbox (PDE), an environment for the study and solution of partial differential equations in two space dimensions and time. The equations are discretized by the Finite Element Method (FEM). An easy-to-use Graphical User Interface (typing *pdetool* at the Matlab command line) completes this Matlab toolbox.