RCH - Recharge Package

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Abbreviation in Name file

RCH

Purpose

The Recharge package is used to simulate a specified flux 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

•Time-varying-parameters.pdf

Related Packages

•The Well package is used to simulate a specified flux to particular cells specified in units of length3/time

•The Flow and Head Boundary package can be used to simulate a specified flux to particular cells specified in units of length3/time and varying as a function of time within stress periods.

Supported in

•MODFLOW-2000

•MODFLOW-2005

•MODFLOW-LGR

•MODFLOW-CFP

•MODFLOW-NWT

•MODFLOW-OWHM

Common Errors

•Recharge is applied to the wrong cells because NRCHOP was not set correctly.

•Precipitation is assumed to be equal to recharge

•Recharge is applied at that are unreasonable when compared with the hydraulic conductivity.

Other Notes

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

•Methods for Estimating Groundwater Recharge In Humid Regions

•When Local Grid Refinement is used, NRCHOP should not be set to 3 in the parent model unless

1.the child model extends to the base  of the parent model, or

2.there is no recharge in the area of the child model

because the recharge in the area of the child model will be applied to the first layer below the child model in addition to any recharge that is applied in the child model itself (Personal communication, Steffen Mehl and Mary Hill, 2011).

•Recharge is not the same as precipitation. Recharge includes only that portion of the precipitation that actually reaches the water table. Evapotranspiration from the unsaturated zone is not included in recharge. Recharge may also include flow into groundwater from streams or rivers if that flow is not included in the model in some other way.

Input Instructions

Input to the Recharge (RCH) Package is read from the file that has type "RCH" 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 NPRCH]

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

NPRCH—is the number of recharge 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

NRCHOP IRCHCB

NRCHOP—is the recharge option code. Recharge fluxes are defined in a layer variable, RECH, with one value for each vertical column. Accordingly, recharge is applied to one cell in each vertical column, and the option code determines which cell in the column is selected for recharge.

•1—Recharge is only to the top grid layer.

•2—Vertical distribution of recharge is specified in layer variable IRCH.

•3—Recharge is applied to the highest active cell in each vertical column. A constant-head node intercepts recharge and prevents deeper infiltration.

 

•When Local Grid Refinement is used, NRCHOP should not be set to 3 in the parent model unless

1.the child model extends to the base  of the parent model, or

2.there is no recharge in the area of the child model

because the recharge in the area of the child model will be applied to the first layer below the child model in addition to any recharge that is applied in the child model itself (Personal communication, Steffen Mehl and Mary Hill, 2011).

IRCHCB—is a flag and a unit number.

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

Repeat Items 3 and 4 for each parameter to be defined (that is, NPRCH 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 RCH Package, the only allowed parameter type is RCH, which defines values of the recharge 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 parameter. Each repetition of Item 4b is a cluster (variables Mltarr, Zonarr, and IZ). There is usually only one cluster used to define a RCH 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 cell values that are determined by a parameter. The name “NONE” means that there is no multiplier array, and the cell 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 in the layer 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

INRECH INIRCH

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

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

oIf INRECH ≥ 0, a layer variable of recharge fluxes, RECH, is read.

oIf INRECH < 0, recharge rates from the preceding stress period are used.

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

oIf INRECH > 0, INRECH is the number of parameters that will be used to define RECH in the current stress period. Item 7 defines the names of the parameters.

oIf INRECH < 0, recharge parameters from the preceding stress period are used.

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

INIRCH—is the IRCH read flag, which is read only if NRCHOP is two:

•If INIRCH ≥ 0, a layer variable of layer numbers (IRCH) is read.

•If INIRCH < 0, the variable (IRCH) used in the preceding stress period is reused.

Either Item 6 or Item 7 may be read, but not both. If Item 7 is read, it is repeated INRECH times.

Data Set 6

[RECH(NCOL,NROW)] -- U2DREL if NPRCH = 0 and if INRECH ≥ 0

RECH—is the recharge flux (LT-1). Read only if INRECH is greater than or equal to zero and if NPRCH = 0.

Data Set 7

[Pname [Iname] [IRCHPF]] -- if NPRCH > 0 and if INRECH > 0

Iname is read if Pname is a time-varying parameter. If IRCHPF 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 RECH variable in the current stress period.  Read INRECH values if NPRCH > 0 and INRECH > 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.

IRCHPF—is an optional format code for printing the RECH variable after it has been defined by parameters. The format codes are the same as those used in the U2DRELREL array reading utility module.

Data Set 8

[IRCH(NCOL,NROW)] -- U2DINT If NRCHOP=2 and if INIRCH ≥ 0

IRCH—is the layer number variable that defines the layer in each vertical column where recharge is applied. Read only if NRCHOP is two and if INIRCH is greater than or equal to zero.