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Online Guide to MODFLOW-NWT

Abbreviation in Name file



The Newton solver is used to solve the finite difference equations in each step of a MODFLOW-NWT stress period.


Niswonger, R.G., Panday, Sorab, and Ibaraki, Motomu, 2011, MODFLOW-NWT, A Newton formulation for MODFLOW-2005: U.S. Geological Survey Techniques and Methods 6-A37, 44 p.

release.txt for MODFLOW-NWT

Related Packages


The NWT solver can only be used with the Upstream Weighting (UPW) package

Supported in



Other Notes

All numeric variables are free format if the option “FREE” is specified in the Basic Package input file; otherwise, all variables have 10-character fields. Values in brackets are specified only for some input options. If the OPTIONS keyword is specified as “SIMPLE,” “MODERATE,” or “COMPLEX,” then all solver input variables following OPTIONS in item 1 are not required to be specified and are set to default values. If OPTIONS is specified as “SPECIFIED,” then all input variables are required; however, residual-control variables are only required if BACKFLAG is set to one. The residual-control option can only be used if OPTIONS is specified as “SPECIFIED.” It is recommended that users refer to table 2 and the discussion on “Example Input for the NWT Input File” for guidance on values that might be identified for each input variable.

The optional variable PHIRAMP in the Well package can be specified in MODFLOW-NWT.

If the Lake package is used, more iterations may be required.

Input to the Newton (NWT) Solver Package is read from the file that is type “NWT” in the Name File.

For Each Simulation

Data Set 0.


Item 0 is optional—“#” must be in column 1. Item 0 can be repeated multiple times.

Data Set 1.


If LINMETH = 1 and OPTIONS is set to “SPECIFIED” read the following line:

Data Set 2a.


If LINMETH = 2 and OPTIONS is set to “SPECIFIED” read the following line:

Data Set 2b.


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