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A Data Input Program (MFI) for the U.S. Geological Survey Modular Finite-Difference Ground-Water Flow Model
U.S. Geological Survey Water-Resources Investigations Report 94-468


Computer models of ground-water flow require input data in order to define the system being simulated. Most model programs read these data from one or more files rather than prompting for the data interactively. The reason for this is partly evolutionary. When ground-water models were first developed in the 1960's, the primary focus was on developing the numerical methods. The major challenge was being able to solve practical, real-world problems within the constraints of computer speed and memory. Computers were too expensive to use for data entry. Also, the simulations were generally small by today's standards, so it was relatively easy to prepare the data files using a card punch or text editor.

Today's computers can easily handle large modeling problems for which data preparation is a burdensome task. Considerable benefit can be obtained from an interactive program that helps prepare model input data. Such a program can prompt for the required data, check for errors, and ensure that files are created with the proper structure. Although it would be possible to add interactive data entry into the model program, this is not desirable because it would unnecessarily increase the required memory and increase the complexity of the program. Further, the wide variation in user preferences and needs makes it unlikely that any single method of interactive data input will meet all needs. It is better to have data entry separate from the model so that different data entry programs can be developed independently of the model program.

This report describes a data input program, called MFI, for the U.S. Geological Survey (USGS) modular three-dimensional finite-difference ground-water flow model (McDonald and Harbaugh, 1988), which is commonly called MODFLOW. MFI can also prepare data for MODPATH, which is a particle tracking program that uses flows calculated by MODFLOW (Pollock, 1994). Much of the data used by MODPATH is the same as that used by MODFLOW, so considerable redundancy is avoided by having one program prepare data for both.

Design Goals
Design Decisions

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