EVT - Evapotranspiration Package

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Abbreviation in Name file

EVT

Purpose

The Evapotranspiration package is used to simulate a head-dependent flux out of the model distributed over the top of the model and specified in units of length/time.  Within MODFLOW, these rates are multiplied by the horizontal area of the cells to which they are applied to calculate the volumetric flux rates.

Documentation

•Harbaugh, A.W., Banta, E.R., Hill, M.C., and McDonald, M.G., 2000, MODFLOW-2000, the U.S. Geological Survey modular ground-water model -- User guide to modularization concepts and the Ground-Water Flow Process: U.S. Geological Survey Open-File Report 00-92, 121 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

•Merritt, M.L., and Konikow, L.F., 2000, Documentation of a Computer Program to Simulate Lake-Aquifer Interaction Using the MODFLOW Ground-Water Flow Model and the MOC3D Solute-Transport Model: U.S. Geological Survey Water-Resources Investigations Report 00-4167, 146 p.

•Time-varying-parameters.pdf

Related Packages

Evapotranspiration Segments

Riparian Evapotranspiration

Head-Dependent Flux Boundary packages

Supported in

•MODFLOW-2000

•MODFLOW-2005

•MODFLOW-LGR

•MODFLOW-CFP

•MODFLOW-NWT

•MODFLOW-OWHM

Common Errors

Evapotranspiration is applied to the wrong cells because NEVTOP was not set correctly.

Other Notes

•The UZF package simulates evapotranspiration so the EVT package is not normally included in a model that includes the UZF package or at least not in the same locations.

•The evapotranspiration simulated by the EVT package only includes evapotranspiration from the saturated zone. Recharge is sometime calculated as precipitation minus losses between the land surface and the water table. Evapotranspiration from the unsaturated zone would be one such loss. Another such loss would be surface runoff.

Input Instructions

Input to the Evapotranspiration (EVT) Package is read from the file that is type "EVT" in the name file. All single-valued variables are free format if the option “FREE” is specified in the Basic Package input file; otherwise, the variables have 10-character fields.

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. Except for the name file, lines beginning with # are restricted to these first lines of the file. Text is printed when the file is read.

Data Set 1

[ PARAMETER NPEVT]

This optional item must start with the word “PARAMETER”.

NPEVT—is the number of evapotranspiration 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.

Data Set 2

NEVTOP IEVTCB

NEVTOP—is the evapotranspiration (ET) option code. ET variables (ET surface, maximum ET rate, and extinction depth) are specified in layer variables, SURF, EVTR, and EXDP, with one value for each vertical column. Accordingly, ET is calculated for one cell in each vertical column. The option codes determine the cell within a column for which ET will be calculated.

•1—ET is calculated only for cells in the top grid layer.

•2—The cell for each vertical column is specified by the user in variable IEVT.

•3—Evapotranspiration is applied to the highest active cell in each vertical column. (This option is described in Merritt and Konikow (2000).)

IEVTCB—is a flag and a unit number.

•If IEVTCB > 0, it is 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.

•If IEVTCB ≤ 0, cell-by-cell flow terms will not be written.

Repeat Items 3-4 for each parameter to be defined (that is, NPEVT times).

Data Set 3

[PARNAM PARTYP Parval NCLU [INSTANCES NUMINST]]

If PARNAM is to be a time-varying parameter, the keyword INSTANCES and a value for NUMINST must be entered.

PARNAM—is the name of a parameter to be defined. This name can consist of 1 to 10 characters and is not case sensitive; that is, any combination of the same characters with different case will be equivalent. All parameter names must be unique.

PARTYP—is the type of parameter to be defined. For the EVT Package, the only allowed parameter type is EVT, which defines values of the maximum ET flux.

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 a non-time-varying parameter or one instance of a time-varying parameter. Each repetition of Item 4b is a cluster (variables Mltarr, Zonarr, and IZ). There is usually only one cluster used to define an EVT non-time-varying parameter or instance of a time-varying parameter; however, it is acceptable to have more than one cluster.

INSTANCES – is an optional keyword that designates a parameter as time varying. The keyword is case-insensitive; that is, it may be entered in any combination of upper- and lower-case letters. If INSTANCES is present, it must be followed by a value for NUMINST. If INSTANCES is absent, PARNAM is non-time-varying and NUMINST should not be present.

NUMINST – is the number of instances that are included in the definition of a time-varying parameter, where each instance is a series of NCLU clusters. If the keyword INSTANCES is present, NUMINST must be present and must be at least 1. If the keyword INSTANCES is absent, NUMINST should not be present.

Data Set 4a

INSTNAM

Item 4a is read only if PARNAM is time-varying. NUMINST repetitions of Item 4 (parts a and b) are read. After each repetition of Item 4a, NCLU repetitions of Item 4b are read.

INSTNAM – is the name of an instance associated with parameter PARNAM specified in the corresponding Item 3. The name can consist of 1 to 10 characters and is not case sensitive. That is, any combination of the same characters with different case will be equivalent. Names entered for INSTNAM must be unique for any given parameter, but names may be reused for instances associated with different parameters.

Data Set 4b

[Mltarr Zonarr IZ]

Repeat Item 4b NCLU times. Each repetition of Item 4b is called a parameter cluster. The NCLU repetitions of Item 4b follow each repetition of Item 4a when PARNAM is time-varying.

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

Zonarr—is the name of the zone array to be used to define the cells that are associated with a parameter. The name “ALL” means that there is no zone array, and all cells are associated with the parameter.

IZ—is up to 10 zone numbers (separated by spaces) that define the cells that are associated with a parameter. These values are not used if Zonarr is specified as “ALL.” Values can be positive or negative, but 0 is not allowed. The end of the line, a zero value, or a non-numeric entry terminates the list of values.

FOR EACH STRESS PERIOD

Data Set 5

INSURF INEVTR INEXDP INIEVT

INSURF—is the ET surface (SURF) read flag.

•If INSURF ≥ 0, a layer variable containing the ET surface elevation (SURF) will be read.

•If INSURF < 0, the ET surface from the preceding stress period will be reused.

INEVTR—is the EVTR read flag. Its function depends on whether or not parameters are being used.

•If no parameters are being used (NPEVT=0):

oIf INEVTR ≥ 0, a layer variable containing the maximum ET rate (EVTR) will be read.

oIf INEVTR < 0, the maximum ET rate from the preceding stress period will be reused.

•If parameters are being used (NPEVT>0):

oIf INEVTR > 0, INEVTR is the number of parameters that will be used to define EVTR in the current stress period. Item 8 defines the names of the parameters.

oIf INEVTR < 0, EVT parameters from the preceding stress period are used.

oINEVTR = 0 is not allowed. That is, when parameters are used, at least one parameter must be specified each stress period

INEXDP—is the extinction depth (EXDP) read flag.

•If INEXDP ≥ 0, a layer variable containing the extinction depth (EXDP) will be read.

•If INEXDP < 0, the extinction depth from the preceding stress period will be reused.

INIEVT—is the layer indicator (IEVT) read flag. It is read only if the ET option (NEVTOP) is equal to two.

•If INIEVT ≥ 0, a layer variable containing the layer indicators (IEVT) will be read.

•If INIEVT < 0, layer indicators used during the preceding stress period will be reused.

Data Set 6

[SURF(NCOL,NROW)] -- U2DREL If INSURF ≥ 0

SURF—is the elevation of the ET surface. This variable is read only if INSURF ≥ 0

Either Item 7 or Item 8 may be read, but not both. If Item 8 is read, it is repeated INEVTR times.

Data Set 7

[EVTR(NCOL,NROW)] -- U2DREL If NPEVT = 0 and if INEVTR ≥ 0

EVTR—is the maximum ET flux [volumetric flow rate per unit area (LT-1)]. This variable is read only if INEVTR ≥ 0 and if NPEVT = 0.

Data Set 8

[Pname [Iname] [IEVTPF]] -- if NPEVT > 0 and if INEVTR > 0

Iname is read if Pname is a time-varying parameter. If IEVTPF is specified for a non-time-varying parameter, Iname must be omitted.

Pname—is the name of a parameter that will be used to define the EVTR variable in the current stress period. Read INEVTR values if NPEVT > 0 and INEVTR > 0.

Iname – is an instance name that is read only if Pname is a time-varying parameter. Multiple instances of the same time-varying parameter are not allowed in a stress period.

IEVTPF—is an optional format code for printing the EVTR variable after it has been defined by parameters. The format codes are the same as those used in the U2DREL array reading utility module.

Data Set 9

[EXDP(NCOL,NROW)] -- U2DREL If INEXDP ≥ 0

EXDP—is the ET extinction depth. This variable is read only if INEXDP ≥ 0. This is the distance from SURF, not an elevation.

Data Set 10

[IEVT(NCOL,NROW)] -- U2DINT If NEVTOP = 2 and if INIEVT ≥ 0

IEVT—is the layer indicator variable. For each horizontal location, it indicates the layer from which ET is removed. It is read only if the ET option is equal to two and if INIEVT ≥ 0.