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Online Guide to MODFLOW

Abbreviation in Name file



The UZF package simulates vertical flow of water through the unsaturated zone to the saturated zone.


Niswonger, R.G., Prudic, D.E., and Regan, R.S., 2006, Documentation of the Unsaturated-Zone Flow (UZF1) Package for modeling unsaturated flow between the land surface and the water table with MODFLOW-2005: U.S. Geological Techniques and Methods Book 6, Chapter A19, 62 p.


release.txt for MODFLOW-NWT


Hughes, J.D., Langevin, C.D., Chartier, K.L., and White, J.T., 2012, Documentation of the Surface-Water Routing (SWR1) Process for modeling surface-water flow with the U.S. Geological Survey Modular Ground-Water Model (MODFLOW-2005): U.S. Geological Survey Techniques and Methods, book 6, chap. A40 (Version 1.0), 113 p.

Related Packages

Rejected recharge can be routed to the SFR or LAK packages.

Supported in






Other Notes

When the UZF package is used, the RCH, EVT, and ETS packages are not normally used  or at least not used in the same locations because the UZF simulates recharge and evapotranspiration. However, MODFLOW does not prevent UZF being used in conjunction with the the RCH, EVT, and ETS packages.

Because the UZF package can simulate both groundwater flow, infiltration, and evapotranspiration, it is a combination of a groundwater flow package and a boundary condition package.

Because the UZF1 Package delays recharge to the water table, changes in stress do not necessarily correspond to the beginning of a stress period. Consequently, caution should be used when simulating time steps that increase during a stress period (specifying the variable TSMULT>1.0 in the data input for the Discretization file; Harbaugh, 2005) because water percolating through the unsaturated zone may reach the water table at the end of a stress period, when the time step length is a maximum.

In addition to lakes in the LAK package and streams in the SFR package, overland flow in the UZF package can be directed to reaches in the SWR package of MODFLOW-NWT.

If the Farm Process in MODFLOW-OWHM is active FINF should be set to zero.


Percolation of water through an unsaturated zone is activated by including a record in the MODFLOW name file using the file type (Ftype) “UZF” to indicate that relevant calculations are to be made in the model and to specify the related input data file. The UZF1 Package is compatible with MODFLOW-2005 (Harbaugh, 2005), but not with earlier versions of MODFLOW. The user can optionally specify unsaturated-zone water budgets and water content profiles for selected model cells by including a record in the MODFLOW name file using the file type (Ftype) “DATA” that specifies the relevant output data file name for each model cell. The row and column cell indices for each selected model cell are included in the UZF output file. Three types of information may be printed to the specified file for each model cell depending on the OUTTYPE option specified. The three OUTTYPE options are: option 1 prints volumes of water entering, leaving, and stored in the unsaturated zone; option 2 prints volumes and rates for water entering, leaving, and stored within the unsaturated zone; and option 3 prints the water content profile between land surface and the water table. Additionally, a time series of infiltration, unsaturated zone evapotranspiration, recharge, and groundwater discharge summed over the model domain may be printed to a specified file.

Unsaturated-Zone Flow Package Input Data

The UZF1 Package input file consists of items numbered from 0 through 16, each consisting of one or more records. These data are used to specify information about the hydraulic properties of the unsaturated zone, the infiltration rate, evapotranspiration, and certain output control options. All input variables are read using free format unless indicated otherwise. In free format, variables are separated by one or more spaces or by a comma and optionally one or more spaces. A blank field cannot be used to set a variable value to zero. Units of length (L) and time (T) are used to define the dimensions of each variable.

The UZF1 Package relies on the specific yield values as specified in the Layer-Property Flow (LPF) Package or the Block-Centered Flow (BCF) Package. Thus, the option for unsaturated flow is only available when either the LPF or BCF Package is used in the simulation. (As of MODFLOW-2005 version 1.5, the UZF package is compatible with LPF, BCF6 and HUF2 packages.) When the option to use vertical hydraulic conductivity in the LPF Package is specified, the layer(s) that contain cells where unsaturated flow will be simulated must be specified as convertible. That is, the variable LAYTYP specified in the LPF Package must not be equal to zero, otherwise the model will print an error and stop execution. The variable VKA in LPF may be specified as the ratio of horizontal to vertical hydraulic conductivity (LAYVKA is not zero) or as the vertical hydraulic conductivity (LAYVKA=0). When using the BCF Package, the right digit of LTYPE (LAYCON) must be greater or equal to one or the model will print an error and stop execution. Neither parameter estimation nor solute transport can be simulated with the UZF1 Package.

For Each Simulation

Data Set 0


Data Set 1a



Note that the keywords must be entered in the order shown. For example, if keywords “SPECIFYTHTR” and “NOSURFLEAK” are specified, then “SPECIFYTHTR”  must precede “NOSURFLEAK”. Alternatively, if only “SPECIFYTHTI”  is specified, then the other two keywords should not be specified.

Data set 1a can only be specified in MODFLOW-2005 and MODFLOW-NWT.

Data Set 1b


NTRAIL2 and NSETS2 are only read if IUZFOPT is greater than zero.

Data Set 2


If IRUNFLG > 0: Read item 3

Data Set 3


IF the absolute value of IUZFOPT = 0 or 1: Read item 4.

Data Set 4


If SPECIFYSURFK is specified;

Data Set 4b MODFLOW-2005 version 1.12 and MODFLOW-NWT version 1.1


hmtoggle_plus0        SURFK


Data sets 5-7 are only read if IUZFOPT is greater than or equal to 1.

Data Set 5


hmtoggle_plus0        EPS

Data Set 6a


hmtoggle_plus0        THTS

If the keyword SPECIFYTHTR is specified, read data set 6b. SPECIFYTHTR can only be specified in MODFLOW-2005 and MODFLOW-NWT.

Data Set 6b


hmtoggle_plus0        THTR


THTI should not be specified for simulations with a steady-state stress period unless the keyword SPECIFYTHTI is specified. SPECIFYTHTI can only be specified in MODFLOW-2005 and MODFLOW-NWT.

Data Set 7


hmtoggle_plus0        THTI

If NUZGAG>0: Item 8 is repeated NUZGAG times

Data Set 8


hmtoggle_plus0        Explanation of variables

For Each Stress Period

Data Set 9

hmtoggle_plus0        NUZF1

If NUZF1 0:

Data Set 10


hmtoggle_plus0        FINF

If IETFLG > 0: Read Items 11 through 16

Data Set 11

hmtoggle_plus0        [NUZF2]

If NUZF2 0:

Data Set 12


hmtoggle_plus0        PET

Data Set 13

hmtoggle_plus0        [NUZF3]

If NUZF3 0:

Data Set 14


hmtoggle_plus0        EXTDP

Data Set 15

hmtoggle_plus0        [NUZF4]

If NUZF4 0:

Data Set 16


hmtoggle_plus0        EXTWC

If the character variable CAPILLARYUZET is specified in the options block, then items 17-22 are specified. (MODFLOW-NWT only)

Data Set 17

hmtoggle_plus0 [NUZF5]


If NUZF5>0, then air entry pressure values are specified.

Data Set 18


hmtoggle_plus0 AIR_ENTRY


Data Set 19

hmtoggle_plus0 [NUZF6]


If NUZF6>0, then root pressure values are specified.



hmtoggle_plus0 H_ROOT

Data Set 21

hmtoggle_plus0 [NUZF7]

If NUZF7>0, then root activity values are specified.

Data Set 22


hmtoggle_plus0 ROOTACT



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