HUF2 - Hydrogeologic-Unit Flow Package

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Abbreviation in Name file

HUF2

Purpose

The Hydrogeologic-Unit Flow package is used to specify properties controlling flow between cells.  It allows you to specify these properties by "hydrogeologic unit".  The unit boundaries are not required to correspond to layer boundaries.  The properties of individual cells is synthesized from the properties of the hydrogeologic units that intersect the cell.

Documentation

•Anderman, E.R., and Hill, M.C., 2000, MODFLOW-2000, the U.S. Geological Survey Modular Ground-Water Model - Documentation of the Hydrogeologic-Unit Flow (HUF) Package: U.S. Geological Survey Open-File Report 00-342, 89 p.

•Harbaugh, A.W., 2005, MODFLOW-2005, the U.S. Geological Survey modular ground-water model -- the Ground-Water Flow Process: U.S. Geological Survey Techniques and Methods 6-A16. https://doi.org/10.3133/tm6A16

•Anderman, E.R., Kipp, K.L., Hill, M.C., Valstar, Johan, and Neupauer, R.M., 2002, MODFLOW-2000, the U.S. Geological Survey modular ground-water model -- Documentation of the Model-Layer Variable-Direction Horizontal Anisotropy (LVDA) capability of the Hydrogeologic-Unit Flow (HUF) Package: U.S. Geological Survey Open-File Report 02-409, 60 p.

•Anderman, E.R., and Hill, M.C., 2003, MODFLOW-2000, the U.S. Geological Survey modular ground-water model -- Three additions to the Hydrogeologic-Unit Flow (HUF) Package: Alternative storage for the uppermost active cells, Flows in hydrogeologic units, and the Hydraulic-coductivity depth-dependence (KDEP) capability: U.S. Geological Survey Open-File Report 03-347, 36 p.

•readme_HUF.txt

Related Packages

•The Block-Centered Flow package (BCF) and the Layer-Property Flow package (LPF) are two other packages that can be used to specify properties controlling flow between cells.

•The Horizontal Flow Barrier package (HFB) modifies the horizontal conductances between certain, specified pairs of cells.

Supported in

•MODFLOW-2000

•MODFLOW-2005

•MODFLOW-LGR

•MODFLOW-CFP

•MODFLOW-NWT

•MODFLOW-OWHM

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.

•The "Model-Layer Variable-Direction Horizontal Anisotropy" capability is provided in the LVDA input file but is part of the Hydrogeologic Unit Flow package.

•The "Hydraulic-Conductivity Depth-Dependence Capability" capability is provided in the KDEP input file but is part of the Hydrogeologic Unit Flow package.

•The "Model-Layer Variable-Direction Horizontal Anisotropy" capability (LVDA) is incompatible with the Horizontal Flow Barrier package (HFB) and with the Sensitivity (SEN) process.

•The UZF package reads values of hydraulic conductivity and specific yield from the BCF and LPF packages but not the HUF package. Therefore, the HUF2 package can not be used with the UZF package. As of MODFLOW2005 version 1.5, the UZF package can be used with the HUF2 package.

•The SFR package does not support unsaturated flow when the HUF package is used.

•See the Frequently Asked Questions for information on how to read data from binary files generated by MODFLOW.

•The SOR solver (not included in MODFLOW-2005 and MODFLOW-LGR) doesn't work well with the wetting capability.

•The vertical flow from or to a lake is calculated incorrectly when the HUF package is used. This bug is present in MODFLOW-2005 version 1.9.1 and in all earlier versions. This bug has been fixed in MODFLOW-NWT version 1.7 and MODFLOW-2005 version 1.10.

Input Instructions

Input for the Hydrogeologic Unit Flow (HUF) Package is read from the file that has type "HUF" in the name file. Free format is used for reading all values.

FOR EACH SIMULATION

Data Set 0

[#Text]

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

Text – is a character variable (199 characters) that starts in column 2. Any characters can be included in Text. The “#” character must be in column 1. Text is printed when the file is read.

Data Set 1

IHUFCB HDRY NHUF NPHUF  IOHUFHEADS IOHUFFLOWS

IHUFCB – is a flag and a unit number.

•> 0 –the unit number to which cell-by-cell flow terms will be written when "SAVE BUDGET" or a non-zero value for ICBCFL is specified in Output Control (Harbaugh and others, 2000, p. 55). The terms that are saved are storage, constant-head flow, and flow between adjacent cells.

•0 – cell-by-cell flow terms will not be written.

•< 0 – cell-by-cell flow for constant-head cells will be written in the listing file when "SAVE BUDGET" or a non-zero value for ICBCFL is specified in Output Control. Cell-by-cell flow to storage and between adjacent cells will not be written to any file.

The flow terms that will be saved are the flows through the right, front, and lower cell face. Positive values represent flows toward higher column, row, or layer numbers.

HDRY – is the head that is assigned to cells that are converted to dry during a simulation. Although this value plays no role in the model calculations, it is useful as an indicator when looking at the resulting heads that are output from the model. HDRY is thus similar to HNOFLO in the Basic Package, which is the value assigned to cells that are no-flow cells at the start of a model simulation.

NHUF – is the number of hydrogeologic units defined using the HUF package.

NPHUF – is the number of HUF parameters.

In MODFLOW-2000, the maximum number of allowed parameters is 999.  In MODFLOW-2005,-LGR, and -CFP the maximum number of allowed parametersis 2000. In MODFLOW-OWHM, the maximum number of allowed parameters is specified in the Basic package.

IOHUFHEADS – is a flag and a unit number.

•< 0 (MODFLOW-2005 and MODFLOW-LGR only) Interpolated heads will be computed and printed to the listing file for each hydrogeologic unit, using the format defined in the output-control file when "SAVE HEADS" is specified or (equivalently) when nonzero values are specified for IHDDFL and for Hdsv in at least one layer.  (If no print format has been defined, printing will be in 10G11.4 format.) As of MODFLOW-2005 version 1.11, this option had not been implemented.

•0 – interpolated heads will not be written.

•>0 – Interpolated heads will be computed and saved to unit IOHUFHEADS for each hydrogeologic unit, using the format defined in the output-control file when "SAVE HEADS" is specified or (equivalently) when nonzero values are specified for IHDDFL and for Hdsv in at least one layer.  (If no print format has been defined, saving will be in binary format.)

IOHUFFLOWS– is a flag and a unit number.

•0 – Interpolated cell-by-cell flows will not be computed or written anywhere.

•> 0 – Interpolated cell-by-cell flows will be computed and saved to unit IOHUFFLOWS for each hydrogeologic unit, in binary format, when "SAVE BUDGET" or (equivalently) a nonzero value for ICBCFL is specified..

Data Set 2

LTHUF – is a flag specifying the layer type. Read one value for each layer; each element holds the code for the respective layer. There is a limit of 200 layers. Use as many records as needed to enter a value for each layer.

•0 – indicates a confined layer.

•not 0 – indicates a convertible layer.

Data Set 3

LAYWT – is a flag that indicates if wetting is active. Read one value per layer.

•0 – indicates wetting is inactive.

•1 – indicates wetting is active.

Data Set 4

WETFCT IWETIT IHDWET

Include Item 4 only if LAYWT indicates at least one wettable layer.

WETFCT – is a factor that is included in the calculation of the head that is initially established at a cell when the cell is converted from dry to wet. (See IHDWET.)

IWETIT – is the iteration interval for attempting to wet cells. Wetting is attempted every IWETIT iterations. If using the preconditioned conjugate gradient (PCG) solver (Hill, 1990), this applies to outer iterations, not inner iterations. If IWETIT is less than or equal to 0, it is changed to 1.

IHDWET – is a flag that determines which equation is used to define the initial head at cells that become wet:

•If IHDWET = 0, equation 3a from McDonald and others (1992) is used:

h = BOT + WETFCT (hn - BOT)

•If IHDWET is not 0, equation 3b from McDonald and others (1992) is used:

h = BOT + WETFCT (WETDRY)

Data Set 5

WETDRY(NCOL,NROW) - U2DREL

Repeat Item 5 for each layer for which LAYWET is not 0.

WETDRY – is a combination of the wetting threshold and a flag to indicate which neighboring cells can cause a cell to become wet. If WETDRY < 0, only the cell below a dry cell can cause the cell to become wet. If WETDRY > 0, the cell below a dry cell and the four horizontally adjacent cells can cause a cell to become wet. If WETDRY is 0, the cell cannot be wetted. The absolute value of WETDRY is the wetting threshold. When the sum of BOT and the absolute value of WETDRY at a dry cell is equaled or exceeded by the head at an adjacent cell, the cell is wetted. Read only if LTHUF is not 0 and LAYWT is not 0.

The Lake package requires that WETDRY be set to 0 in Lakes.

Repeat Items 6-8 for each hydrogeologic unit to be defined (that is, NHUF times).

Data Set 6

HGUNAM – is the name of the hydrogeologic unit. This name can consist of up to 10 characters and is not case sensitive.

Data Set 7

TOP(NCOL,NROW) Arrays are read by the array-reading utility module - U2DREL

TOP – is the elevation of the top of the hydrogeologic unit.

Data Set 8

THCK(NCOL,NROW) Arrays are read by the array-reading utility module - U2DREL

THCK – is the thickness of the hydrogeologic unit.

Data Set 9

HGUNAM HGUHANI HGUVANI

Repeat Item 9 for each hydrogeologic unit.

If HGUNAM is set to “ALL”, HGUHANI and HGUVANI are set for all hydrogeologic units and only one Item 9 is necessary. Otherwise, HGUNAM must correspond to one of the names defined in Item 6, and there must be NHUF repetitions of Item 9. The repetitions can be in any order.

HGUHANI – is a flag and a horizontal anisotropy value for a hydrogeologic unit. Horizontal anisotropy is the ratio of hydraulic conductivity along columns to hydraulic conductivity along rows. Read one value for each hydrogeologic unit unless HGUNAM is set to ALL.

•0 – indicates that horizontal anisotropy will be defined using a HANI parameter.

•>0 – HGUHANI is the horizontal anisotropy of the entire hydrogeologic unit.

HGUVANI – is a flag that indicates whether array VK is vertical hydraulic conductivity or the ratio of horizontal to vertical hydraulic conductivity. Read only one value for each hydrogeologic unit unless HGUNAM is set to ALL.

•0 – indicates VK is hydraulic conductivity (VK parameter must be used).

•>0 – indicates VK is the ratio of horizontal to vertical hydraulic conductivity and HGUVANI is the vertical anisotropy of the entire hydrogeologic unit. Value is ignored if a VANI parameter is defined for the corresponding hydrogeologic unit.

Repeat Items 10-11 for each parameter to be defined (that is, NPHUF times).

Data Set 10

PARNAM PARTYP Parval NCLU

PARNAM – is the name of a parameter to be defined. This name can consist of up to 10 characters and is not case sensitive. All parameter names must be unique.

PARTYP – is the type of parameter to be defined. For the HUF Package, the allowed parameter types are:

•HK – defines variable HK, horizontal hydraulic conductivity.

•HANI – defines variable HANI, horizontal anisotropy.  When using the LVDA capability, HANI values need to be less than or equal to 1. (Horizontal anisotropy is the hydraulic conductivity in the Y or column direction divided by the hydraulic conductivity in the X or row direction.)

•VK – defines variable VK, vertical hydraulic conductivity, for units for which HGUVANI is set to zero.

•VANI – defines variable VANI, vertical anisotropy, for units for which HGUVANI is set greater than zero. If the Hydraulic-Conductivity Depth-Dependence Capability is used, the vertical hydraulic conductivity changes according to the changes in the horizontal hydraulic conductivity. (Vertical anisotropy is the ratio of hydraulic conductivity in the X or row direction to the hydraulic conductivity in the Z or layer direction.)

•SS – defines variable Ss, the specific storage.

•SY – defines variable Sy, the specific yield.

•SYTP – when all model layers are confined, defines the storage coefficient for the top active cell at each row, column location. The value specified is not multiplied by model layer thickness. When SYTP is specified as the parameter type, HGUNAM of item 11 needs to be set to SYTP.

Parval—is the parameter value. This parameter value may be overridden by a value in the PVAL file, the Sensitivity Process (SEN) input file, or by a value generated by the Parameter-Estimation (PES) Process.

NCLU – is the number of clusters required to define the parameter. Each Item-11 record is a cluster (variables HGUNAM, Mltarr, Zonarr, and IZ).

Data Set 11

HGUNAM Mltarr Zonarr IZ

Each Item 11 record is called a parameter cluster. Repeat Item 11 NCLU times.

HGUNAM – is the hydrogeologic unit to which the parameter applies. When PARTYP = SYTP, HGUNAM must be set to SYTP.

Mltarr – is the name of the multiplier array to be used to define array values that are associated with a parameter. The name “NONE” means that there is no multiplier array, and the array values will be set equal to Parval.

Zonarr – is the name of the zone array to be used to define array elements that are associated with a parameter. The name “ALL” means that there is no zone array and that all elements in the hydrogeologic unit are part of the parameter.

IZ – is up to 10 zone numbers (separated by spaces) that define the array elements that are associated with a parameter. The first zero or non-numeric value terminates the list. These values are not used if Zonarr is specified as “ALL”.

Data Set 12

PRINT HGUNAM PRINTCODE PRINTFLAGS

Item 12 is optional and is included only for hydrogeologic units for which printing is desired. Item 12 must start with the word PRINT.

If HGUNAM is set to ALL, PRINTCODE and PRINTFLAGS are set for all hydrogeologic units, and only one Item 12 is necessary. Otherwise, HGUNAM must correspond to one of the names defined in Item 6.

PRINTCODE – determines the format for printing the values of the hydraulic-property arrays for the hydrogeologic unit as defined by parameters. The print codes are the same as those used in an array control record (Harbaugh and others, 2000, p. 87). If PRINTCODE is set to zero, the array will not be printed.

PRINTFLAGS – determines the hydraulic-property arrays to be printed and must be set to “ALL” or any of the following: “HK”, “HANI”, “VK”, “SS”, or “SY”. Arrays will be printed only for those properties that are listed. When VK is specified, the property printed depends on the setting of HGUVANI. All the PRINTFLAGS for a hydrogeologic unit must be specified on the same line.