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Online Guide to MODFLOW-NWT

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Online Guide to MODFLOW-NWT

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Compiled by Richard B. Winston

Revised: 1/31/2022


The purpose of these web pages is to provide a unified description of the formats for MODFLOW-NWT input files.  These descriptions have been copied from the original reports in which they were published and supplemented with materials found in the "doc" directory of the MODFLOW-NWT distribution file. These web pages are not substitute for or a definitive guide to MODFLOW-NWT.  They may contain errors that are not in the original documents.  In case of doubt, consult the original documents or examine the source code.

In a few cases, obvious typographical errors in the original documents have been corrected in the version of the input instructions presented on these web pages.  Such changes are not marked.

Some packages, such as the Interbed Storage package, were originally published as part of MODFLOW-88.  In such cases, the instructions for including these package in a MODFLOW-NWT model have been updated to reflect how the input is specified in MODFLOW-NWT.

In a few cases, the instructions have been supplemented by additional material not found in the original input instructions.  Such materials are shown in a different type face like this.  The sources of such additional material include examination of the source code, correspondence with the authors of a package, and experience.

Keywords in the input files that must be entered exactly as shown (in a case-insensitive manner) are displayed in these web pages in bold and italics like this.

Please send comments and corrections to Richard B. Winston (

This guide reflects MODFLOW-NWT version 1.1.3.

Guides to other versions of MODFLOW can be found at the following locations





Combined guide to MODFLOW-2000, -2005, -LGR -CFP, -NWT, and OWHM

An indication of the different capabilities of the various versions of MODFLOW can be found in Input Files Supported in Various Versions of MODFLOW.

The input and output files for MODFLOW 6 are described in


Although every effort is made to provide timely and accurate information, the authors, the U.S. Geological Survey (USGS), and the U.S. Government make no warranty, expressed or implied, as to the timeliness or accuracy of the contents of this web site, which may be updated and revised at any time.  Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply endorsement by the U.S. Government.  Any links to non-Government web sites are provided for convenience only and do not imply endorsement by the U.S. Government.


You can download a copy of the Online Guide to MODFLOW-NWT in the form of an Windows help file from . Windows may block the content of the help file because it was downloaded from the internet. To fix this problem, copy the *.chm file to a flash drive and then back to your computer.

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