MODPATH is a particle tracking code that is used in conjunction with MODFLOW. After running a MODFLOW simulation, the user can designate the location of a set of particles. The particles are then tracked through time assuming they are transported by advection using the flow field computed by MODFLOW. Particles can be tracked either forward in time or backward in time. Particle tracking analyses are particularly useful for delineating capture zones or areas of influence for wells.
A complete description of MODPATH is beyond the scope of this help file, however, because of the user-friendly interface in GMS, an intimate knowledge of MODPATH is not required to effectively do particle tracking in GMS. For a more complete knowledge of MODPATH, refer to the MODPATH documentation (Pollock, 1994).
MODPATH was developed by the U.S. Geological Survey. Version 4.2 of MODPATH is supported in GMS. The version of MODPATH distributed with GMS is the original public domain version distributed by the USGS, with minor modifications to accommodate GMS.
Before you can do particle tracking with MODPATH, you must have:
A MODFLOW simulation in memory.
A MODFLOW solution in memory computed using MODFLOW 2000 with a valid head and flow field.
Once you have a MODFLOW solution, all that is necessary to do particle tracking is to:
Create particle starting locations.
As soon as you create the particle starting locations GMS immediately does a number of things: saves the MODPATH input files, launches MODPATH and passes it the input files, waits for MODPATH to compute the pathlines, then reads in and displays the pathlines. All this is done automatically and behind the scenes and usually takes just a second or two. Thus, pathlines will appear almost immediately after you define the particle starting locations. If MODPATH encountered problems attempting to generate the path lines, the errors will be displayed in the MODPATH Errors dialog.
There are two ways to generate particle starting locations in GMS, both available via the MODPATH menu:
Related Links:
Building a MODPATH Conceptual Model
Generate Particles at Wells
Generate Particles at Selected Cells