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Online Guide to MODFLOW-LGR

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.

Data Set 1

[ PARAMETER NPRCH]

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

Data Set 2

NRCHOP IRCHCB

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.

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.

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.

FOR EACH STRESS PERIOD

Data Set 5

INRECH INIRCH

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

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.

Data Set 8

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

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