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Water Software > Groundwater Software > MODFLOW and Related Programs > MODFLOW-NWT

MODFLOW-NWT: a Newton Formulation for MODFLOW-2005

Overview of MODFLOW-NWT

The USGS MODFLOW-NWT is a Newton-Raphson formulation for MODFLOW-2005 to improve solution of unconfined groundwater-flow problems. MODFLOW-NWT is a standalone program that is intended for solving problems involving drying and rewetting nonlinearities of the unconfined groundwater-flow equation.

MODFLOW-NWT must be used with the Upstream-Weighting (UPW) Package for calculating intercell conductances in a different manner than is done in the Block-Centered Flow (BCF), Layer Property Flow (LPF), or Hydrogeologic-Unit Flow (HUF) Packages. Flow-property input for the UPW Package is designed based on the LPF Package and material-property input is identical to that for the LPF Package except that the rewetting and vertical-conductance correction options of the LPF Package are not available with the UPW Package. Input files constructed for the LPF Package can be used with slight modification as input for the UPW Package.

The NWT linearization approach generates an asymmetric matrix, which is different from the standard MODFLOW formulation that generates a symmetric matrix. Because all linear solvers presently available for use with MODFLOW-2005 solve only symmetric matrices, MODFLOW-NWT includes two previously developed asymmetric matrix-solver options. The matrix-solver options include a generalized-minimum-residual (GMRES) Solver and an Orthomin / stabilized conjugate-gradient (CGSTAB) Solver.

MODFLOW-NWT is described in the documentation report by Niswonger and others (2011). The Surface-Water Routing (SWR1) and Seawater Intrusion (SWI2) Packages, which are included with MODFLOW-NWT are documented in Hughes and others (2012) and Bakker and others (2013), respectively.

MODFLOW-NWT Information and Downloads

[Image: Cover of software documentation report. ]

Software Downloads

Note: Users are encouraged to read the documents that are provided in the 'doc' directory of this software distribution.

Documentation of MODFLOW-NWT

Example USGS Applications of MODFLOW-NWT

Allander, K.K., Niswonger, R.N., and Jeton, A.E., 2014, Simulation of the Lower Walker River Basin hydrologic system, west-central Nevada, Using PRMS and MODFLOW models: U.S. Geological Survey Scientific Investigations Report 2014-5190, 93 p.,

Davis, K.W., and Putnam, L.D., 2013, Conceptual and numerical models of groundwater flow in the Ogallala aquifer in Gregory and Tripp Counties, South Dakota, water years 1985-2009: U.S. Geological Survey Scientific Investigations Report 2013-5069, 82 p.

Eggleston, J.R., Carlson, C.S., Fairchild, G.M., and Zarriello, P.J., 2012, Simulation of groundwater and surface-water interaction and effects of pumping in a complex glacial-sediment aquifer, east central Massachusetts: U.S. Geological Survey Scientific Investigations Report 2012-5172, 48 p.

Feinstein, D.T., Fienen, M.N., Kennedy, J.L., Buchwald, C.A., and Greenwood, M.M., 2012, Development and application of a groundwater/surface-water flow model using MODFLOW-NWT for the Upper Fox River Basin, southeastern Wisconsin: U.S. Geological Survey Scientific Investigations Report 2012-5108, 124 p.

Huntington, J.L. and Niswonger, R.G., 2012, Role of surface-water and groundwater interactions on projected summertime streamflow in snow dominated regions: An integrated modeling approach: Water Resources Research, v. 48, 20 p.

Kennedy, J. R. and Ferré, T. P., 2016, Accounting for time-and space-varying changes in the gravity field to improve the network adjustment of relative-gravity data: Geophysical Journal International, vol. 204, no. 2, pp. 892-906,

Morway, E.D., Gates, T.K., Niswonger, R.G., 2013, Appraising options to reduce shallow groundwater tables and enhance flow conditions over regional scales in an irrigated alluvial aquifer system: Journal of Hydrology, v. 495, pp. 216-237.

Morway, E. D., Niswonger, R. G., and Triana, E., 2016, Toward improved simulation of river operations through integration with a hydrologic model: Environmental Modelling & Software, v. 82, pp. 255-274,

Niswonger, R.G., Allander, K.K., and Jeton, A.E., 2014, Collaborative modelling and integrated decision support system analysis of a developed terminal lake basin: Journal of Hydrology, doi: 10.1016/j.jhydrol.2014.05.043. Avalaible online at

Tanvir Hassan, S.M., Lubczynski, M.W., Niswonger, R G., and Su, Z., 2014, Surface-groundwater interactions in hard rocks in Sardon Catchment of Western Spain: an integrated modeling approach: Journal of Hydrology, doi: 10.1016/j.jhydrol.2014.05.026. Avalaible online at

Point of Contact

Support is provided for correcting bugs and clarification of how MODFLOW-NWT is intended to work. Only limited assistance can be provided for applying MODFLOW-NWT to specific problems by contacting the points of contact listed below:

Richard Niswonger
U.S. Geological Survey
National Research Program - Western Branch
U.S. Geological Survey
345 Middlefield Road
Mail Stop 470
Menlo Park, CA 94025

Other USGS Groundwater Software

The USGS develops groundwater, water-quality, surface-water, and other water-resources software for use by the USGS in fulfilling its mission. Most of this software is available online for download at no charge.

Disclaimers and Notices

This software has been approved for release by the U.S. Geological Survey (USGS). Although the software has been subjected to rigorous review, the USGS reserves the right to update the software as needed pursuant to further analysis and review. No warranty, expressed or implied, is made by the USGS or the U.S. Government as to the functionality of the software and related material nor shall the fact of release constitute any such warranty. Furthermore, the software is released on condition that neither the USGS nor the U.S. Government shall be held liable for any damages resulting from its authorized or unauthorized use. Also refer to the USGS Water Resources Software User Rights Notice for complete use, copyright, and distribution information.

Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.

See also, USGS policy on linking to non-Federal web sites.

Software License and Purchase Information

This software is a product of the U.S. Geological Survey, which is part of the U.S. Government.


This software is freely distributed. There is no fee to download and (or) use this software.


Users do not need a license or permission from the USGS to use this software. Users can download and install as many copies of the software as they need.

Public Domain:

As a work of the United States Government, this USGS product is in the public domain within the United States. You can copy, modify, distribute, and perform the work, even for commercial purposes, all without asking permission. Additionally, USGS waives copyright and related rights in the work worldwide through CC0 1.0 Universal Public Domain Dedication ( [Link exits USGS]).

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