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MODFLOW-NWT: A Newton Formulation for MODFLOW-2005

June 1, 2022

Overview of MODFLOW-NWT

Example layer-bottom altitudes from MODFLOW-NWT.
Distribution of layer-bottom altitudes for an example problem from the MODFLOW-NWT documentation.

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.


Download Current Version of MODFLOW-NWT


Documentation for MODFLOW-NWT

Additional documentation can be found in the 'doc' subdirectory in the MODFLOW-2005 distribution.


Find MODFLOW-Related Software

Visit the MODFLOW and Related Programs page for a list of MODFLOW-related software.


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., http

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

Publication Year 2022
Title MODFLOW-NWT: A Newton Formulation for MODFLOW-2005
Product Type Software Release
Record Source USGS Digital Object Identifier Catalog