A geographic information system (GIS) was used in developing a graphical user interface (GUI) for use with the U.S. Geological Survey's finite difference ground-water flow model, MODFLOW. The GUI permits the construction of a MODFLOW based ground-water flow model from scratch in a GIS environment. The model grid, input data and output are stored as separate raster data sets which may be viewed, edited, and manipulated in a graphic environment. Other GIS data sets can be displayed with the model data sets for reference and evaluation.
The GUI sets up a directory structure for storage of the files associated with the ground-water model and the raster data sets created by the interface. The GUI stores model coefficients and model output as raster values. Values stored by these raster data sets are formatted for use with the ground-water flow model code. Simulations can be run and model output retrieved for visual display and analysis in the interface as raster data sets.
The use of a graphical user interface with a GIS assists in several steps of a ground-water flow model application. The development of the GIS representation of the model's spatial dimensions with other data sets defining the ground-water flow system ensures the proper placement and orientation of that mesh. Boundary conditions and model coefficients can be rapidly assigned values and input files for the model code produced. The assignment of values to model cells can be graphically reviewed and verified against other geospatial data sets during model calibration and verification. The results of model simulations can be displayed and these values contoured.
This interface and the data sets created with it assist in the preparation of the report on the ground-water flow model as called for in ASTM Standard Guide for Application of a Ground-Water Flow Model to a Site Specific Problem (ASTM D 5447). Graphics files and maps can be prepared of the values in the raster data sets and associated GIS vector data sets. Metadata prepared for the GIS data sets within the interface can provide supporting information on the values carried in the raster data sets. This information includes persons responsible for preparing the data sets, the coordinate system, and the manipulations required for the spatial representation of the ground-water flow model.