MODPATH, "A Particle Tracking Post-Processing Package for MODFLOW, the USGS 3-D Finite-Difference Ground-Water Flow Model (MODFLOW)," is the most widely-used particle tracking program in the world. For MODPATH graphical user interfaces and complete modeling environments, see the following products:
GMS - Groundwater Modeling System
Processing MODFLOW for Windows (PMWIN)
Introduction to MODPATH
MODPATH New Features
MODPATH Input Requirements
INTRODUCTION TO MODPATH
MODPATH is a particle tracking post-processing package that was developed to compute three-dimensional flowpaths using output from steady-state or transient ground-water flow simulations by MODFLOW. MODPATH uses a semi-analytic particle tracking scheme that allows an analytical expression of the particle's flow to be obtained within each finite-difference grid cell. Particle paths are computed in MODPATH 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. Data input for MODPATH is a combination of data files and interactive keyboard input.
Output from steady-state or transient MODFLOW simulations is used in MODPATH to compute paths for imaginary "particles" of water moving through the simulated ground-water system. In addition to computing particle paths, MODPATH keeps track of the time of travel for particles moving through the system. By carefully defining the starting locations of particles, it is possible to perform a wide range of analyses such as delineating capture and recharge areas or drawing flow nets.
MODPATH NEW FEATURES
The current version of the MODPATH particle tracking package includes many new features that increase the ease of use and the analytical capabilities of the package. The most significant new features are:
Transient Flow - Previous versions of MODPATH were restricted to steady-state MODFLOW simulations. The current version of MODPATH allows forward or backward particle tracking analyses to be performed for transient as well as steady-state simulations.
Multiple Release Times for Particles - In forward tracking simulations, particles can be re-released at a regular time interval over a specified period of time. This option allows a "plume" of particles to be tracked through the ground-water flow system.
The new version of MODPATH will simulate movement of particles in a transient flow system dealt with by the original MODPATH. Output from MODPATH shows the complete paths of all particles and points of origin (starting points) for all particles discharging to a specific feature or destination points for all particles at a given location.
Because of the above attributes, MODPATH can be used to determine the contributing area of a well by calculating the path of all pathlines that end at the well. It also can be used to determine the destination of all particles in a plume by forward tracking.
MODPATH INPUT REQUIREMENTS
Input requirements to MODPATH are the output from MODFLOW, porosity and assumed starting point for particles.