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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

Parameters Shared Between MODFLOW and MODPATH

Many parameters are shared between MODFLOW and MODPATH. In MFI, these shared parameters are entered only within MODFLOW's data editing screens. That is, the shared parameters are not included as part of the screens used for MODPATH's data. These shared parameters are:

NLAY
NROW
NCOL
NPER
NSTP
PERLEN
TSMULT
HNOFLO
HDRY
LAYCON
DELR
DELC
TOP for layer types 2 and 3
BOT for layer types 1 and 3
Names of budget file, head file, and data files for stress packages
Note that IBOUND is not shared by MODPATH and MODFLOW even though both MODFLOW and MODPATH have a parameter named IBOUND. The reason is that MODPATH makes expanded use of IBOUND. In addition to indicating boundary conditions as in MODFLOW, MODPATH uses IBOUND to indicate zones for the purpose of controlling which particles and pathlines are displayed and their colors. There are situations in which different IBOUND values may be desired for MODFLOW and MODPATH. Thus, these are viewed as separate arrays, except that when MODPATH is first activated, any MODFLOW IBOUND arrays that are constant or package arrays are copied to MODPATH's IBOUND. Further, whenever IBOUND is modified in MODFLOW or MODPATH, the values are checked for consistency (no flow, constant head, and variable head at the same locations). If there are inconsistencies, the user is notified, but nothing is done to attempt to remedy the situation. No consistency checking is done for any layers for which IBOUND is specified as being in a separate file in either MODFLOW or MODPATH.

MODPATH includes the ability to specify which cell face receives a particular stress. This capability is incorporated in MFI through the screens in which stress data are entered. When MODPATH is active, the stress screens include an extra parameter to indicate the cell face for the stress. For the River, Well, Drain, and General-head Boundary stresses, the stress face is specified in the list of stresses each stress period. For Recharge and Evapotranspiration stresses, the face is specified as a single value for all cells for the entire simulation. Thus, it is more efficient to activate MODPATH prior to entering stress data if the user knows that MODPATH will eventually be used. This will allow the stress faces to be entered when the other stress data are entered. If stress data are entered prior to activating MODPATH, then the stress screens will need to be reentered after MODPATH is activated if there is a need to specify specific faces to recieve stresses.

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