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Techniques and Methods 6–A41

User Guide for MODPATH Version 6—A Particle-Tracking Model for MODFLOW

By David W. Pollock

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ABSTRACT

MODPATH is a particle-tracking post-processing model that computes three-dimensional flow paths using output from groundwater flow simulations based on MODFLOW, the U.S. Geological Survey (USGS) finite-difference groundwater flow model. This report documents MODPATH version 6. Previous versions were documented in USGS Open-File Reports 89–381 and 94–464.

The program uses a semianalytical particle-tracking scheme that allows an analytical expression of a particle's flow path to be obtained within each finite-difference grid cell. A particle's path is computed by tracking the particle from one cell to the next until it reaches a boundary, an internal sink/source, or satisfies another termination criterion.

Data input to MODPATH consists of a combination of MODFLOW input data files, MODFLOW head and flow output files, and other input files specific to MODPATH. Output from MODPATH consists of several output files, including a number of particle coordinate output files intended to serve as input data for other programs that process, analyze, and display the results in various ways.

MODPATH is written in FORTRAN and can be compiled by any FORTRAN compiler that fully supports FORTRAN-2003 or by most commercially available FORTRAN-95 compilers that support the major FORTRAN-2003 language extensions.

First posted June 14, 2012

For additional information contact:
Office of Groundwater
U.S. Geological Survey
Mail Stop 411
12201 Sunrise Valley Drive
Reston, VA 20192
phone: (703) 648–5001

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Suggested citation:

Pollock, D.W., 2012, User guide for MODPATH version 6—A particle-tracking model for MODFLOW: U.S. Geological Survey Techniques and Methods, book 6, chap. A41, 58 p.



Contents

Abstract

Introduction

Method

Semianalytical Tracking Algorithm

Special Cases

Backward Tracking

Transient Flow

Solute Retardation

Limitations

MODPATH Overview

Time Concepts

Flow Boundaries

Terminating Particles

Model Input

Model Output

Program Portability and Compatibility

Input Instructions

General Structure of Input Data

Simulation File

Basic Data File

Name File

Starting Locations File

Particle Output File Structure

Endpoint File

Pathline File

Timeseries File

Advective Observations File

Example Problem

References

Appendix 1. MODPATH Output Examiner


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