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Analytic Element Model (MODAEM)

One of the more exciting new features in GMS v5.0 is an interface to a new analytic element model called MODAEM.  Unlike finite difference and finite element models, analytic element models do not require a discretization of the problem domain.  Rather the model is completely defined by boundary conditions, source/sink terms, and material property zones represented by points, polylines (arcs), and polygons.  Since GMS users are already in the habit of building conceptual models in the Map Module using points, arcs, and polygons, analytic element modeling is a natural fit for GMS.

The MODAEM interface is supported in the GMS Map Module.  The model input is defined completely from a conceptual model.  Once the conceptual model is defined, there is no need to discretize the model using a "Map -> MODAEM" command.  Rather, the user can simply select the F5 key or the "Run MODAEM" command from the MODAEM menu and the MODAEM model is solved.  In most cases, the solution is very rapid and the results are immediately plotted.  Although it is not used in the solution process, GMS captures the MODAEM output on a background grid so that the results can be contoured.  Output includes heads, pathlines, and flows at source/sink objects.  Observation wells can be used with MODAEM for calibration.

One of more powerful features associated with the MODAEM interface is regional to local model conversion.  A regional model can be built with MODAEM and then linked to a local scale MODFLOW model.  When the local scale model is being constructed using the GMS Map Module, the user can choose to mark some or all of the local model boundaries as "AEM Head" boundaries.  Then when the Map -> MODFLOW command is selected, the MODAEM model is queried and the head from the regional model is computed at the center of each of the cells along the local scale model boundary.  Furthermore, the total flow rate through the boundary is computed by MODAEM and applied as an observed flow to the MODFLOW model.

The MODAEM model is developed by Vic Kelson of Wittman Hydro Planning Associates in Bloomington, Indiana.