MNW1 - Multi-Node, Drawdown-Limited Well Package

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Abbreviation in Name file

MNW1

Purpose

The Multi-Node, Drawdown-Limited Well package is used to simulate wells that extend over more than one cell.  Most commonly, this would represent cells that extend over several layers.

Documentation

Halford, K.J. and Hanson R.T., 2002, User Guide for the Drawdown-Limited, Multi-Node Well (MNW) Package for the U.S. Geological Survey’s Modular Three-Dimensional Finite-Difference Ground-Water Flow Model, Versions MODFLOW-96 and MODFLOW-2000t: U.S. Geological Survey Open-File Report 02-293, 33 p.

MNW7.pdf

release.txt for MODFLOW-2005

Related Packages

Well package

MNW2 package

Head-Dependent Flux Boundary packages

Supported in

•MODFLOW-2000

•MODFLOW-2005

•MODFLOW-LGR

•MODFLOW-CFP

•MODFLOW-NWT

•MODFLOW-OWHM

Other Notes

The MNW1 and MNW2 packages can not both be used in the same simulation.

Input Instructions

Input for the multi-node, drawdown-limited well package (MNW Package) is initiated by specifying in the NAME file (Harbaugh and McDonald, 1996). Data are read from MNW Package input files as 256-character-wide, alphanumeric records to facilitate the addition of comments within the model input files and the use of keys to identify input variables. All integer, real, and character variables are read from the alphanumeric records. The records are initially read by the subroutine NCREAD. Records that begin with a ‘#’ sign in the first column are treated as comment records, are not passed to any other routines, and are discarded. Once NCREAD has acquired a valid data record, the record is checked for a ‘!!’ sign that designates the beginning of any in-line comments on a data-input record. If a ‘!!’ sign is detected, the ‘!!’ sign and all text to the right of the ‘!!’ sign are removed from the record before passing it to any other routines.

Alphanumeric strings are used in the MNW Package to identify variables (keys) and make logical decisions (flags). Specification of these keys and flags is case insensitive because all letters are capitalized before performing any logical tests. Keys precede the variable to be read, which is acquired by identifying the key and reading the first value that follows the key. Logical decisions are based on the presence (true) or absence (false) of a flag. In this report, bold, upper-case letters are used to denote the part of the key that is tested. Key:data pairs that are not delimited by parentheses are mandatory and must be included, and Key:data pairs that are delimited within parentheses and are optional because default values are used if they are not specified by the user.

The MNW Package reads input data for each simulation and for each stress period as follows:

FOR EACH SIMULATION:

Data Set 1

MXMNW IWL2CB IWELPT [NOMOITER] REFerence SP: kspref (Required record)

Format: Integer Integer Integer [Integer] Alphanumeric key Integer

MXMNW is the maximum number of well cells to be defined.

IWL2CB is a flag and a unit number.

•If IWL2CB > 0, it is the unit number on which cell-by-cell flow terms will be recorded whenever ICBCFL is set or "Save Budget" is specified in Output Control.

•If IWL2CB = 0, cell-by-cell flow terms will not be printed or recorded.

•If IWL2CB < 0, The absolute value of IWL2CB is the unit number on which cell-by-cell flow terms will be recorded whenever ICBCFL is set or "Save Budget" is specified and well recharge, water-levels in the well and cell, drawdown in the well, and the flow-rate-weighted water-quality value of the IQWGRP will be printed whenever ICBCFL is set or "Save Budget" is specified.

IWELPT is a flag. If IWELPT is not equal to 0, no well information will be printed.

Flow in MNW wells will not be calculated after NOMOITER iterations.

kspref = is the set of water levels in the HNEW matrix at the beginning of the stress period kspref that will be used as default reference values for calculating drawdown. Kspref defaults to 1 if it is not specified by the user.

Data Set 2

LOSSTYPE (PLossMNW) (Required record)

Format: Alpanumeric Real

LOSSTYPE is a flag to determine the user-specified model for well loss.

•If LOSSTYPE is set to SKIN, head loss is defined with skin. Model is linear.

•If LOSSTYPE is set to LINEAR, head loss is defined with coefficient B. Model is linear.

•If LOSSTYPE is set to NONLINEAR, head loss is defined with coefficients B and C. Model is nonlinear.

If LOSSTYPE is nonlinear, PLossMNW represents the exponent P in equation 5. See equation 5 (p. 8) of Halford and Hanson (2002) for more information regarding PLossMNW.

Data Set Unnumbered

PREFIX:MNWNAME (Optional record)

Format: Alphanumeric header record

Prefix name of file for outputting time series data from MNW. MNWNAME may be up to 200 characters in length. MNWNAME may not contain the space character.

If MNWNAME is given as FILEPREFIX, the prefix name of the file for outputting time series data from MNW1 will be the same as the prefix name of the Name File.

If this record is omitted, the prefix name of the file for outputting time series data from MNW1 will be the "OUTput_MNW."

Data Set 3a

FILE:filename WEL1:iunw1 (Optional record)

Format: Alphanumeric header record

filename = is the name of an auxiliary output file. The file name need not be include in the Name file but it must be a unique file name.

iunw1 = is a unit number. Filename will be written to unit number iunw1. Output is a WEL1 input file with the flow rates specified at the end of each stress period. Including filename in the Name file is optional but both the file name and the unit number must be unique.

Data Set 3b

FILE:filename BYNODE:iunby ALLTIME (Optional record)

Format: Alphanumeric header record Flag

filename = is the name of an auxiliary output file. The file name need not be include in the Name file but it must be a unique file name.

iunby = is a unit number. Filename will be written to unit number iunby. Output is flow rate at each well node.

ALLTIME a flag that indicates flow rates should be written to BYNODE or QSUM at every time step regardless of the settings in the output control (OC) file.

Data Set 3c

FILE:filename QSUM:iunqs ALLTIME (Optional record)

Format: Alphanumeric header record Flag

filename = is the name of an auxiliary output file. The file name need not be include in the Name file but it must be a unique file name.

iunqs = is a unit number. Filename will be written to unit number iunqs. Output is total flow rate from each multi-node well.

ALLTIME a flag that indicates flow rates should be written to BYNODE or QSUM at every time step regardless of the settings in the output control (OC) file.

FOR EACH STRESS PERIOD:

Data Set 4

ITMP ADD

Format: I10 Alphanumeric key

ITMP is a flag.

•If ITMP < 0, wells from previous stress period will be reused and input from item 5 will not be read.

•If ITMP =, 0 no wells will be simulated and input from item 5 will not be read.

•If ITMP > 0, is the number of records of drawdown-limited well data that will be read for the current stress period. If the key ADD is not detected on record 4, the maximum number of drawdown-limited wells for the current stress period will be ITMP. If the key ADD is detected on record 4, ITMP wells will be added to the existing list of drawdown-limited wells.

ADD a flag that indicates whether or not the well cells read for the current stress period will augment or replace the well cells that were previously defined.

Data Set 5

Layer Row Column Qdes [MN or MULTI] QWval Rw Skin  Hlim Href [DD] Iwgrp Cp: C [QCUT or Q-%CUT: Qfrcmn Qfrcmx] DEFAULT   SITE: MNWsite

Format I10 I10 I10 F10.0 Flag Real Real Real Real Real Flag Integer Real Real Real Flag Alphanumeric header record

NOTE: The first four values in data item 5 for the variables Layer, Row, Column, and Qdes are read initially as a free format. If this fails, the four values are read as fixed format entries from the first 40 columns. In all instances these values must be specified. The following eight values for the remaining variables are optional, space-delimited or comma-delimited entries but must be entered in the sequence specified for item 5. The alphanumeric flags MN and DD can appear anywhere between columns 41 and 256, inclusive. Input item 5 normally consists of one record for each well cell defined or modified. If ITMP is 0 or less, item 5 is not read and should not be specified.

Layer is the layer number of the model cell that contains the well.

Row is the row number of the model cell that contains the well.

Column is the column number of the model cell that contains the well.

Qdes is the desired volumetric pumping or recharge rate. A positive value indicates recharge and a negative value indicates discharge. The actual volumetric recharge rate will range from 0 to Qdes and is not allowed to switch directions between discharge and recharge conditions during any stress period.

(MN) a flag that indicates this entry is part of a multi-node well. The flag MN is not included on the first entry of a multi-node well and is exclusive of the flag MULTI.

(MULTI) a flag that indicates this entry is the end of a multi-node well and all intervening nodes between this entry and the previous MULTI flag are part of a multi-node well. Intervening nodes will be assigned the same cell-to-well conductance that was specified in this entry. The flag MULTI is not included on the first entry of a multi-node well and is exclusive of the flag MN.

Both the following examples specify a multi-node well in Column 5, Row 5 that extends from layer 1 to layer 3.

Example 1

         1        5        5       0.1

         3        5        5       0.1 MULTI

Example 2

         1        5        5       0.1

         2        5        5       0.1 MN

         3        5        5       0.1 MN

When MULTI is used, the well should always be aligned along a column, row, or layer.

QWval is the water-quality value that is to be flow-rate averaged amongst wells in the same Iqwgrp. Negative water-quality values and positive flow terms are not averaged. Water-quality values can be respecified for each stress period.

Rw is a flag and a variable used to define the cell-to-well conductance.

•If Rw > 0, The variable represents the radius of the well and the cell-to-well conductance is calculated with eq. 5 as formulated by Peaceman (1983).

•If Rw = 0, the head in the cell is assumed to be equivalent to the head in the well and the cell-to-well conductance is set to 1,000 times the transmissivity of the cell. The cell is NOT allowed to be part of a multi-node well.

•If Rw < 0, the absolute value of the variable is the cell-to-well conductance.

Skin defines the friction losses to the well owing to the screen and to formation damage. The variable is either a skin or the coefficient B depending on the LOSSTYPE, and is used in eq. 5 when Rw > 0.

Hlim is the limiting water level, which is a minimum for discharging wells and a maximum for recharging wells. If the flag DD is set, the value of Hlim read is a drawdown from the reference elevation. For Qdes < 0, Hlim = Href - Hlim and for Qdes > 0, Hlim = Href + Hlim.

Href is the reference elevation. If the value of Href read is greater than the maximum water level from the HNEW matrix at the beginning of the stress period kspref, Href is set to the simulated water level at the location of the drawdown-limited well.

DD a flag that indicates the value of Hlim read is a drawdown or build-up from the reference elevation.

Iqwgrp is a water-quality group identifier. Flow-rate averaged water-quality values are reported for each group of wells with the same lqwgrp and Qwval entries that are not negative.

Cp:C is coefficient for nonlinear head losses (eqn. 2). The variable is used only when the LOSSTYPE is NONLINEAR. Default value is 0 if not specified.

QCUT a flag that indicates pumping limits will be specified as a rate (L3 /T).

Q-%CUT a flag that indicates pumping limits will be specified as a percentage of the specified rate.

Qfrcmn minimum pumping rate that a well must exceed to remain active.

Qfrcmx minimum potential pumping rate that must be exceeded to reactivate a well.

DEFAULT a flag that sets this entry of Qfrcmn and Qfrcmx as the new default values.

(SITE: is an optional label for identifying wells. An individual file of time, discharge, water level MNWsite) in well, concentration, net-inflow, net-outflow, and node-by-node flows will be written for each well with a unique MNWsite label. Individual well files are tab delimited. Only one label should be applied to a multi-node well. MNWsite can be up to 32 characters in length. MNWsite can not contain space or tab characters.