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Online Guide to MODFLOW

Abbreviation in Name file

DRN

Purpose

The Drain package is used to simulate head-dependent flux boundaries to simulate the effects of features such as agricultural drains, which remove water from the aquifer. In the Drain package, if the head in the cell falls below a certain threshold, the flux from the model cell to the drain drops to zero.

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

release.txt

modpath.txt

Related Packages

See: Head-Dependent Flux Boundary Packages

Drain Observation input file

Drain Return package

Supported in

MODFLOW-2000

MODFLOW-2005

MODFLOW-LGR

MODFLOW-CFP

MODFLOW-NWT

MODFLOW-OWHM

Other Notes

Special care must be taken when constructing the DRN package input file if the observations are used.  See discussion of "Observations at Cells Having More Than One Head-Dependent Boundary Feature Represented by the Same Package" in the DROB input file.

Input Instructions

Input to the Drain (DRN) Package is read from the file that has type "DRN" in the name file. Optional variables are shown in brackets. All variables are free format if the option “FREE” is specified in the Basic Package input file; otherwise, the non-optional variables have 10-character fields and the optional variables are free format.

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 NPDRN MXL]

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

Data Set 2

MXACTD IDRNCB [Option]

Repeat Items 3 and 4 for each NPDRN parameter.

Data Set 3

[PARNAM PARTYP Parval NLST [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, NLST repetitions of Item 4b are read.

Data Set 4b

Layer Row Column Elevation  Condfact [xyz]

NLST repetitions of Item 4b are required; they are read by module ULSTRD. (SFAC of the ULSTRD utility module applies to Condfact). The NLST repetitions of Item 4b follow each repetition of Item 4a when PARNAM is time-varying.

FOR EACH STRESS PERIOD

Data Set 5

ITMP NP

Data Set 6

Layer Row Column Elevation  Cond [xyz]

ITMP repetitions of Item 6 are read by module ULSTRD if ITMP > 0. (SFAC of the ULSTRD utility module applies to Cond.) Item 6 is not read if ITMP is negative or 0.

Data Set 7

[Pname [Iname]]

Item 7 is repeated NP times. It is not read if NP is negative or 0. Iname is read if Pname is a time-varying parameter.

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