U.S. Geological Survey                                 modpath(1)



NAME
     modpath - A particle-tracking postprocessor model for
     MODFLOW

SYNOPSIS
     mpath4 [i] [filename]

     mplot4 [i] [filename]

ABSTRACT
     MODPATH is a particle-tracking postprocessing package that
     was developed to compute three-dimensional flow paths using
     output from steady-state or transient ground-water flow
     simulations by MODFLOW, the U.S. Geological Survey finite-
     difference ground-water flow model.  The particle tracking
     package consists of two Fortran computer codes: (1) MODPATH,
     which calculates particle paths, and (2) MODPATH-PLOT, which
     displays results graphically.

OPTIONS
     i          Tells the program to prompt for all input
                interactively.  A "response file" is produced
                which records user responses for the execution of
                the program.

     filename   The name of an existing "response file."

     If no option is given, the program will prompt for the name
     of a "response file".  If none is given, the program will
     proceed in the interactive mode.  Response files can be made
     to include interactive prompts by adding the string "(?)" to
     the end of the last line of a prompt message.  This is
     useful, for example, when plots are needed for multiple
     reference times with all other responses the same.

METHOD
     MODPATH uses a semi-analytical particle tracking scheme that
     allows an analytical expression of the particle's flow path
     to be obtained within each finite-difference grid cell.
     Particle paths are computed by tracking particles from one
     cell to the next until the particle reaches a boundary, an
     internal sink/source, or satisfies some other termination
     criterion.  Both steady-state and transient ground-water
     flow systems can be analyzed with MODPATH.

HISTORY
     Version 4.3 2003/07/03 - Fixed problem that prevented MODPATH
       from working with mixed steady-state and transient stress
       periods.  Fixed problem in which recharge and ET were sometimes
       applied to the wrong cells when COMPACT BUDGET was used.
       Fixed problem with displaying contours.  Added a check for
       negative cell thickness.
     Version 4.2 2001/04/18 - Modified to improve use on personal
       computers.  The code was modified to make it possible to use
       non-standard compiler options for opening unformatted head
       and budget files. This can make it possible for MODPATH and
       MODPATH-PLOT to read head and budget files generated by MODFLOW
       runfiles that were created by a different compiler than the one
       used to compile MODPATH and MODPATH-PLOT.
       Also, a new version of Interacter has been loaded with the PC
       version of MODPATH-PLOT, which supports more graphics devices.
     Version 4.1 2000/07/06 - Modified to work with MODFLOW-2000.
       MODPATH version 4 has been modified to read the cell elevations
       from the MODFLOW-2000 discretization file.  The discretization
       file also defines the number and length of stress periods, so
       this information is no longer read from MODPATH's main data file.

       Another change involves the way MODPATH determines information about
       stresses.  MODPATH versions 3.2 and earlier read the MODFLOW input
       files for stresses.  These were read in order to identify the locations
       of stresses and the faces to which a stress is applied (variable IFACE).
       For the WEL and RCH Packages, the stress input files were also read
       to define the stress flow rate rather than using data in the budget
       file. MODPATH version 4 no longer reads any stress files.
       Instead, the stress information is obtained entirely from
       the budget file.  MODFLOW-2000 has been modified to save AUXILIARY
       variables in the budget file, and MODPATH uses AUXILIARY variable
       IFACE to define the IFACE variable that was previously read from
       the MODFLOW input files for stresses.

     Version 3.2 1999/06/14 - Dynamic memory allocation added to
        allow for very large problems and minimize the need for
        source-code recompilation.  Additional graphical output
        options provided in precompiled MODPATH-PLOT.  Fixed
        problem causing MODPATH to fail when trying to read the
        MODFLOW head file for cases where the MODFLOW-96 XSECTION
        option was used to save the heads as a single 2D cross
        section.  Fixed problem causing end-of-file error when
        reading the cell-by-cell budget file when list-oriented
        stress packages (e.g. rivers, drains, etc.) had zero
        entries for one or more stress periods.  Fixed bug
        causing the automatic particle generation option to fail
        for transient simulations where the number of columns was
        larger than the number of rows.

     1994 - version 3 released (no version 2 was released)

     1989 - version 1 released

DATA REQUIREMENTS
     Data input for MODPATH and MODPATH-PLOT is a combination of
     data files and interactive keyboard input.  Keyboard input
     also can be redirected to a data file.  Both programs are
     designed to work with MODFLOW.  The number of new data files
     required by MODPATH is minimized by making use of MODFLOW
     data files whenever possible.

OUTPUT OPTIONS
     Output from MODPATH is in the form of a variety of numerical
     data files containing spatial coordinates of particles and
     traveltime.  Output from MODPATH-PLOT is primarily
     graphical.  The graphical output is dependent on the
     capabilities of the GKS graphics system installed on the
     computer system.

SYSTEM REQUIREMENTS
     MODPATH and MODPATH-PLOT are written primarily in standard
     Fortran 77; a few Fortran 90 statements have been added for
     dynamic array allocation.  The code can be compiled with any
     standard Fortran 90 compiler.  The code can also be compiled
     using a standard Fortran 77 compiler when alternate Fortran
     77 statements for static array dimensioning are uncommented.
     In addition to a Fortran compiler, MODPATH-PLOT requires a
     graphics subroutine library known as GKS (Graphical Kernel
     System).  GKS is a standardized set of graphics routines
     that are available commercially for most computer systems.
     The code has been used on UNIX-based computers and on DOS-
     and Windows-based computers.

APPLICATIONS
     The MODPATH package has been widely applied to MODFLOW-based
     ground-water flow simulation studies.  It is useful as a
     visualization tool to help understand flow patterns in
     simulated ground-water flow systems.  It also has been
     widely used to delineate sources of water to discharge sites
     and aquifers in systems simulated with MODFLOW.



DOCUMENTATION
     Pollock, D.W., 1994, User's Guide for MODPATH/MODPATH-PLOT,
        Version 3: A particle tracking post-processing package
        for MODFLOW, the U.S. Geological Survey finite-difference
        ground-water flow model: U.S. Geological Survey Open-File
        Report 94-464, 234 p.


Revised 4 Input Instructions for Version 4:

MODFLOW-2000 input files

1.  When point stresses are applied to faces, declare IFACE as an
Auxilary Variable in each point-stress input file, and use the COMPACT
BUDGET AUXILIARLY option in Output Control.  The IFACE values are only
written into the budget file if this Output Control option is used.


MODPATH Name File

1.  The MODFLOW discretization file must be included in the name file. 
Its file type is DIS.

2.  The stress packages should no longer be included in the name file. 
If they are included, they will be ignored.


MODPATH MAIN data file

1.  MAXSIZ HNOFLO  HDRY  NPART  IRCHTP  IEVTTP

IRCHTP indicates where recharge (if used in the model) is applied
          0 indicates distributed
          not 0 indicates the top face
IEVTTP indicates where evapotranspiration (if used in the model) is applied
          0 indicates distributed
          not 0 indicates the top face

2.  Options -- same as before

3.  LAYCON(NLAY)
          0 indicates confined
          not 0 indicates convertible or water table

4.  IBOUND(NCOL,NROW)
      Read one array for each layer

5.  POR(NCOL,NLAY)
      Read one array for each layer

Items 6A and 6B are required only for transient simulations:

6A.  TBEGIN

6B.  BeginPeriod  BeginStep  End Period  EndStep



RELATED DOCUMENTATION
     Pollock, D.W., 1994, Source Code and Ancillary Data Files
        for the MODPATH Particle Tracking Package of the Ground-
        Water Flow Model MODFLOW -- Version 3, Release 1: U.S.
        Geological Survey Open-File Report 94-463, 2 p., two
        3.5-inch diskettes.

TRAINING
     Training in the use of MODPATH is included in the USGS
     MODFLOW training courses Modeling of Ground-Water Flow Using
     Finite-Difference Methods (GW2096TC) and Advanced Finite-
     Difference Modeling of Ground-Water Flow (GW3099TC), offered
     annually at the USGS National Training Center.

CONTACTS
     Operation:
           U.S. Geological Survey
           Office of Ground Water
           David Pollock
           411 National Center
           Reston, VA 20192

           dwpolloc@usgs.gov


     See
     http://water.usgs.gov/software/ordering_documentation.html
     for information on ordering printed copies of USGS
     publications.


SEE ALSO
     modflow(1) - Modular three-dimensional finite-difference
                  ground-water flow model
