GMS is the most sophisticated and comprehensive groundwater modeling software available!

Used by thousands of people at U.S. Government agencies, private firms, and international sites in over 90 countries, it has been proven to be an effective and exciting modeling system. GMS provides tools for every phase of a groundwater simulation including site characterization, model development, calibration, post-processing, and visualization. GMS supports both finite-difference and finite-element models in 2D and 3D including MODFLOW 2000, MODPATH, MT3DMS/RT3D, SEAM3D, ART3D, UTCHEM, FEMWATER, PEST, UCODE, MODAEM and SEEP2D. Regardless of your modeling needs, GMS has the tools!

The program's modular design enables the user to select modules in custom combinations, allowing the user to choose only those groundwater modeling capabilities that are required. Additional GMS modules can be purchased and added at any time. The software will dynamically link to these subsequent modules at run time—automatically adding additional modeling capability to the software.

Groundwater Flow & Transport Options

The variety of modeling options in GMS is unparalleled! Rather than being limited to one main model (such as MODFLOW) and accompanying "add-on" codes, GMS provides interfaces to a wide range of 2D or 3D models. Here is a brief overview of the options available to you:

2D Flow

• Perform fast, easy modeling with the MODAEM analytical element model integrated into GMS!
• 2D finite-element seeepage modeling is supported in the SEEP2D model - perfect for dams, levees, cutoff trenches, etc.

3D Flow

• 3D finite difference modeling with MODFLOW 2000 (saturated zone)
• 3D finite-element modeling with FEMWATER (saturated and unsaturated zone)

Solute Transport

• Simple analytical transport modeling with ART3D
• Simple 3D transport with MT3D, MODPATH, or FEMWATER
• Reactive 3D transport with RT3D or SEAM3D
• Multi-phase reactive transport with UTCHEM

Unsaturated Zone Flow and Transport

• Fully 3D unsaturated/saturated flow and transport modeling with FEMWATER or UTCHEM.

GIS-based Model Conceptualization
One of GMS's greatest strengths traditionally has been the conceptual model approach. This approach makes it possible to build a conceptual model in the GMS Map Module using GIS feature objects (points, arcs, and polygons). The conceptual model defines the boundary conditions, sources/sinks, and material property zones for a model. The model data can then be automatically discretized to the model grid or mesh. The conceptual model approach makes it possible to deal with large complex models in a simple and efficient manner.

You can transfer the results (material properties) of a solid model direclty to a numerical model such as a MODFLOW grid or a FEMWATER mesh.  You can also direclty generate MODFLOW 2000 HUF data - GMS is the only system that allows you to do this!

Site Visualization
GMS is a powerful graphical tool for model creation and visualization of results. Models can be built using digital maps and elevation models for reference and source data. During the model building process, the graphical representation of the model allows quick review and presentation of your work. Fully 3D views, with contouring and shading, of your model allow anyone to see and understand the domain and parameters of your analysis.

A groundwater model can be displayed in plan view or 3D oblique view, and rotated interactively. Cross-sections and fence diagrams may be cut arbitrarily anywhere in the model. Hidden surface removal, and color and light source shading can be used to generate highly photorealistic rendered images. Contours and color fringes can be used to display the variation of input data or computed results. Cross-sections and iso-surfaces can be interactively generated from 3D meshes, grids, and solids, allowing the user to quickly visualize the 3D model.

Both steady-state and transient solutions can be displayed in an animated format (as if viewing a movie) using either vector, iso-surface, color fringe, or contour animation. For example, animation of a transient solution allows the user to observe how head, drawdown, velocity, and contaminate concentration vary with time. In addition, GMS can also sweep an iso-surface through the 3D model. The minimum and maximum iso-surface values are determined from the model and the program will then linearly interpolate and display multiple iso-surfaces in rapid succession. This allows the user to quickly understand the spatial variation of a contaminant plume, for example.

Risk Assessment (Stochastic) Modeling
One of the most exciting features in GMS is a suite of tools for performing stochastic simulations with MODFLOW and accompanying transport models.

The Risk Analysis Wizard is a new tool associated with the stochastic modeling tools in GMS. Two types of analysis are currently supported: probabilistic threshold analysis and probabilistic capture zone delineation. This wizard allows you to quantify the risk of a contaminant exceeding critical levels in groundwater or the risk of a capture zone including key areas at a site. Such analysis helps determine appropriate action to be taken in design or remediation.

Two approaches are supported for setting up stochastic simulations: parameter randomization and indicator simulation. The parameter randomization can be done using either a "Monte Carlo" or a "Latin Hypercube" approach. The indicator simulation approach randomizes the spatial distribution of the parameter zones using the T-PROGS software. The T-PROGS software is used to perform transition probability geostatistics on borehole data. The output of the T-PROGS software is a set of N material sets on a 3D grid. Each of the material sets is conditioned to the borehole data and the materials proportions and transitions between the boreholes follows the trends observed in the borehole data. These material sets can be used for stochastic simulations with MODFLOW.

Automated Model Calibration
Calibration is the process of modifying the input parameters to a groundwater model until the output from the model matches an observed set of data. GMS includes a suite of tools to assist in the process of calibrating a groundwater model to point and/or flux observations. When a computed solution is imported to GMS, the point and flux residual errors are plotted on a set of calibration targets and a variety of plots can be generated showing overall calibration statistics. Most of the calibration tools can be used with any of the models in GMS.

Automated parameter estimation is supported in GMS for the MODFLOW simulations using MODFLOW PES, PEST, and UCODE. These are sometimes called "inverse models". Most of the steps involved in setting up an inverse model in GMS are the same regardless of the selected inverse model. The basic process for inverse modeling is:

• Build a base model with MODFLOW
• Input observed data (point or flux data)
• Indicate the model input parameters that the inverse model can adjust to make the model match the observations.
• Let the inverse model run - it will adjust input parameters and run the MODFLOW simulation repeatedly until the best match betweeen computed data and observed data is obtained.

Graphical User interface
Thanks to the graphical tools of GMS, with standard MS Windows functionality, building models and viewing results is very easy and intuitive. All modeling parameters are entered through interactive graphics and easy-to-use dialog boxes. Though the software reads and writes native model input/output files, there is no need to worry about formatting text files to get the models to run nor will you need to search through text output files to find the results from the model run.

The Data Tree Window of GMS has been developed to give you GIS-style, quick access to data layers and display settings. By simply clicking on data layers you can: Turn display on/off Convert data to other formats/types Project data to a different coordinate system Control display settings Set the active data set for editing. The Data Tree Window also allows you direct access to modeling parameters/tables for control of your groundwater model. You will find that managing data for modeling is easier than ever before in this specialized system. Thanks to simple CAD/GIS style tools and functionality, you will find that manipulating digital terrain data, GIS data, and subsurface data to build model geometry and compute model input parameters is very smooth. Further, presentation of results of your work will be impressive and easy to understand.

Graphics and Visualization
GMS is a powerful graphical tool for model creation and visualization of results. Models can be built using digital maps and elevation models for reference and source data. During the model building process, the graphical representation of the model allows quick review and presentation of your work. Fully 3D views, with contouring and shading, of your model allow anyone to see and understand the domain and parameters of your analysis.

GMS now utilizes the OpenGL graphics engines for all 3D visualization, both wireframe and shaded. This means that all displays are rendered using hardware acceleration. Fully shaded 3D images can now be rendered instantaneously. Complex 3D objects can be rotated in real time in either shaded or wireframe mode.

A groundwater model can be displayed in plan view or 3D oblique view, and rotated interactively. Cross-sections and fence diagrams may be cut arbitrarily anywhere in the model. Hidden surface removal, and color and light source shading can be used to generate highly photorealistic rendered images. Contours and color fringes can be used to display the variation of input data or computed results. Cross-sections and iso-surfaces can be interactively generated from 3D meshes, grids, and solids, allowing the user to quickly visualize the 3D model.

Both steady-state and transient solutions can be displayed in an animated format (as if viewing a movie) using either vector, iso-surface, color fringe, or contour animation. For example, animation of a transient solution allows the user to observe how head, drawdown, velocity, and contaminate concentration vary with time. In addition, GMS can also sweep an iso-surface through the 3D model. The minimum and maximum iso-surface values are determined from the model and the program will then linearly interpolate and display multiple iso-surfaces in rapid succession. This allows the user to quickly understand the spatial variation of a contaminant plume, for example.

GMS Supported Models
Numerical models are programs that are separate from GMS that are used to run an analysis on a model. The models can be built in GMS, and then run through the numerical model program. GMS can then read in and display the results of the analysis. GMS also has the option of using a "model wrapper" to run the model and display real-time results of during the model simulation.

The following numerical models are currently supported in GMS. Each model is included with the GMS installation (model executable files and documentation) and is fully linked with the GMS software.

GMS Modules
The GMS interface is separated into several modules; these modules contain tools that allow manipulation and model creation from different data types. The modules of GMS are:

• Map module
• GIS module
• TIN module
• Solids module
• 2D grid module
• 3D grid module
• 2D mesh module
• 3D mesh module
• 2D/3D scatter point module.

Module
The Map module provides a suite of tools for using GIS objects to build conceptual models, adding annotation to a plot, displaying digital background maps, and displaying CAD drawings.

Map objects are used to provide GIS capabilities within GMS. These objects include points, arcs, and polygons. Feature objects can be grouped into layers or coverages. A set of coverages can be constructed representing a conceptual model of a groundwater modeling problem. This high level representation can be used to automatically generate MODFLOW and MT3DMS numerical models. Feature objects can also be used for automated mesh generation for FEMWATER or SEEP2D numerical models.

Images are scanned maps or aerial photos imported from TIFF or JPEG files. Images are displayed in the background for on-screen digitizing or model placement or simply to enhance the display of a model. Images can also be draped over surfaces and texture mapped to generate highly realistic shaded images. DXF files are CAD drawings which can be imported into GMS and displayed in the Graphics Window to assist in model placement or simply to enhance the display of a model. DXF objects can also be converted to feature objects. The Map Module of GMS allows you to use data from many other software systems. Some of the file formats that GMS can read/write for this type of data are: ArcGIS Shapefiles USGS DLG files CAD DXF files Georeferenced or regular TIFF files Georeferenced or regular JPEG files

Module
A new "GIS Module" has been added to version 5.0. This module greatly simplifies the process of importing and converting GIS data from external sources. To fully utilize the GIS module, a license of ArcGIS (formerly ArcView) version 8.0 is required. In this case, portions of ArcGIS are effectively run inside of GMS using the new ArcObjects library. This makes it possible to use the GIS module to open virtually ANY GIS database supported by ArcGIS

Once a GIS database is opened, the data are displayed in the GMS window using the ArcGIS map rendering engine. This results in beautiful, professional looking maps that can be displayed in the background of a GMS modeling project. The user has access to all of the standard ArcGIS tools for modifying the display of the map.

Once a GIS database is imported and displayed, the user can select a portion of the map using either a simple graphical selection or an SQL query. The selected data can then be converted to standard GMS feature objects using a simple and intuitive GIS Property Mapping Wizard. The user is prompted to indicate how each of the columns in the GIS attribute data should be mapped to corresponding GMS feature object properties.

TIN Module
The Triangulated Irregular Network (TIN) module is used for surface modeling. TINs are formed by connecting a set of XYZ points (scattered or gridded) with edges to form a network of triangles. The surface is assumed to vary in a linear fashion across each triangle. TINs can be used to represent the surface of a geologic unit or the surface defined by a mathematical function.

Several TINs can be modeled at once in GMS. A TIN may be created within GMS by several methods or can be imported from other systems. TINs can be used in GMS to build solid models and 3D meshes or they can be converted to other types of data such as scatter point for interpolation to grids.

Solids Module
The Solid module of GMS is used to construct three-dimensional models of stratigraphy using solids. Once such a model is created, cross sections can be cut anywhere on the model and the solid model can be shaded to generate realistic images. The new "Horizons Method" of constructing solids is the most advanced tool available for creating solids quickly and accurately.

Solids are used for site characterization and visualization. Solids can also be used to define layer elevation data for MODFLOW models using the Solids -> MODFLOW command or Solids to HUF and to define a layered 3D mesh using the Solids -> Layered Mesh.

2D Grid Module
The 2D Grid module is used for creating and editing two-dimensional Cartesian grids. 2D grids are primarily used for surface visualization and contouring. This is accomplished by interpolating to the grid and then shading the grid. The figure below is an example of interpolating contaminant concentration data to a 2D grid and then shading the 2D grid.

3D Grid Module
The 3D Grid module is used to create 3D Cartesian grids. These grids can be used for interpolation, iso-surface rendering, cross sections, and finite difference modeling.

Interfaces to the following 3D finite difference models are provided in this module. Clcik below for a more complete description of each model:

 - MODFLOW
 - MODPATH
 - MT3DMS
 - RT3D
 - SEAM3D
 - UTCHEM
 - ART3D

2D Mesh Module
The 2D Mesh module is used to construct two-dimensional finite element meshes. Numerous tools are provided for automated mesh generation and mesh editing. 2D meshes are used for SEEP2D modeling and to aid in the construction of 3D meshes. The figures below show an example of a SEEP2D model.

3D Mesh Module
The 3D Mesh module is used to construct three-dimensional finite element meshes. Numerous tools are provided for automated mesh generation and mesh editing. These meshes can be used for interpolation, iso-surface rendering, cross sections, and finite element modeling with FEMWATER.

2D / 3D Scatter Point Module
The 2D Scatter Point module is used to interpolate from groups of 2D scattered data to other objects (meshes, grids, TINs). Several interpolation schemes are supported, including kriging. Interpolation is useful for setting up input data for analysis codes and for site characterization. The interpolation methods supported by the 3D Scatter Point module are:

• Linear
• Inverse Distance Weighted
• Clough-Tocher
• Natural Neighbor
• Kriging.

• Linear
• Inverse Distance Weighted
• Clough-Tocher
• Natural Neighbor
• Kriging.

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