U.S. Geological Survey modpath(1) NAME modpath - A particle-tracking postprocessor model for MODFLOW SYNOPSIS mpath3 [i] [filename] mplot3 [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 3.2 2000/06/14 - 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 Last change: 8 August 2000 1 U.S. Geological Survey modpath(1) 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. Last change: 8 August 2000 2 U.S. Geological Survey modpath(1) 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. 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 Distribution: U.S. Geological Survey Hydrologic Analysis Software Support Program 437 National Center Reston, VA 20192 h2osoft@usgs.gov Official versions of U.S. Geological Survey water-resources analysis software are available for electronic retrieval via the World Wide Web (WWW) at: http://water.usgs.gov/software/ and via anonymous File Transfer Protocol (FTP) from: water.usgs.gov (path: /pub/software). The WWW page and anonymous FTP directory from which the MODPATH software can be retrieved are, respectively: Last change: 8 August 2000 3 U.S. Geological Survey modpath(1) http://water.usgs.gov/software/modpath.html --and-- /pub/software/ground_water/modpath See http://water.usgs.gov/software/ordering_documentation.html for information on ordering printed copies of USGS publications. SEE ALSO contour(1) - A contouring program for gridded data modflow(1) - Modular three-dimensional finite-difference ground-water flow model Modflowp(1) - Parameter-estimation version of the modular model Last change: 8 August 2000 4