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Online Guide to MODFLOW-NWT

Navigation: Groundwater Flow Process > Groundwater Flow Packages

UPW - Upstream Weighting Package

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Abbreviation in Name file



The Upstream Weighting package is used to specify properties controlling flow between cells in MODFLOW-NWT


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

Hanson, R.T., Boyce, S.E., Schmid, Wolfgang, Hughes, J.D., Mehl, S.M., Leake, S.A., Maddock, Thomas, III, and Niswonger, R.G., 2014, One-Water Hydrologic Flow Model (MODFLOW-OWHM): U.S. Geological Survey Techniques and Methods 6–A51, 120 p.,

Related Packages

The LPF package has nearly identical input.

The NWT Solver is required in the UPW package is used.

Supported in



Other Notes

Every model must  use one and only one of the four packages (BCF6, LPF, HUF2, and UPW) that are used to specify properties controlling flow between cells. UPW is only available in MODFLOW-NWT and MODFLOW-OWHM.

Input data types and formats described below are nearly identical to those for the LPF Package and described on pages 8-28 through 8-31 of the MODFLOW-2005 manual (Harbaugh, 2005). However, the input variable LAYWET should be set to zero for all layers because all layers that are specified as convertible (that is, LAYTYP>0) are assumed to be wettable in the UPW Package. The model will stop and print an error statement to the main Listing file if LAYWET is non-zero for any layers. Options are not allowed in the UPW Package, as they are in the LPF Package, and the variable IPHDRY is new to the UPW Package.

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

Cell property data are read from the file that is type “UPW” in the Name File. Free format is used for reading all values.

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.


Data Set 2.

Data Set 3.

Data Set 4.

Data Set 5.

Data Set 6.


(Item 6 should always be set to zero in the UPW Package because all layers with LAYTYP(NLAY)>0 are assumed to be wettable)

Repeat Items 7-8 for each parameter to be defined (that is, NPUPW times).

Data Set 7.


Each repetition of Item 8 is called a parameter cluster. Repeat Item 8 NCLU times.

Data Set 8.

[Layer Mltarr Zonarr IZ]

A subset of the following two-dimensional variables is used to describe each layer. All variables that apply to layer 1 are read first, followed by layer 2, followed by layer 3, and so forth. A variable not required due to simulation options (for example, Ss and Sy for a completely steady-state simulation) must be omitted from the input file.

These variables are either read by the array-reading utility subroutine, U2DREL, or they are defined through parameters. If a variable is defined through parameters, then the variable itself is not read; however, a single line containing a print code is read in place of the control line. The print code determines the format for printing the values of the variable as defined by parameters. The print codes are the same as those used in a control line. If any parameters of a given type are used, parameters must be used to define the corresponding variable for all layers in the model.

Data Set 9.


If any HK parameters are included, read only a print code.

Data Set 10.


Include item 10 only if CHANI is less than or equal to 0. If any HANI parameters are included, read only a print code.

Data Set 11.


If any VK or VANI parameters are included, read only a print code.

Data Set 12.


Include item 12 only if at least one stress period is transient. If there are any SS parameters, read only a print code.

Data Set 13.


Include item 13 only if at least one stress period is transient and LAYTYP >0. If any SY parameters are included, read only a print code.

Data Set 14.


Include item 14 only if LAYCBD (in the Discretization File) is not 0. If any VKCB parameters are included, read only a print code.

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