USGS Home
Contact USGS
Search USGS

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

Constraints in MFI that are not in MODFLOW and MODPATH

1. MFI does not allow a steady-state simulation to have more than one stress period.

2. The precision of data values in files created by MFI is controlled by MFI. In most cases, values will be written with at least four significant digits. If the precision used is inadequate, MFI cannot be used or must be modified.

3. If output does not occur at regular intervals (every time step, end of every stress period, or end of simulation), then a maximum of 47 times can be entered at which output will occur.

4. If specific layers for printing or saving head or drawdown are listed rather than using the default of having this information output for all layers, a maximum of 15 layers can be specified.

5. When MODPATH is used, each TOP and BOT array that is in a separate (external) file must be in a file by itself. This constraint is needed in order to insure that MODFLOW and MODPATH can share the same arrays. MODFLOW and MODPATH cannot share multiple TOP and BOT arrays from the same external file because they read these arrays in a different order.

6. A maximum of 92 file units can be used for MODFLOW files -- units 1-92. A maximum of 77 file units can be used for MODPATH files -- units 1-4 and 7-79.