WELLID is the name of the MNW2 well that is linked to the tabfile TABNAM.

MNWMAX is the maximum number of multi-node wells (MNW) to be simulated.

is a flag and a unit number:

•if IWL2CB > 0, then it is the unit number to which MNW cell-by-cell flow terms will be recorded whenever cell-by-cell budget data are written to a file (as determined by the outputcontrol options of MODFLOW).

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

•if IWL2CB < 0, then well injection or withdrawal rates and water levels in the well and its multiple cells will be printed in the main MODFLOW listing (output) file whenever cell-by-cell budget data are written to a file (as determined by the output control options of MODFLOW).

is a flag controlling the level of detail of information about multi-node wells to be written to the main MODFLOW listing (output) file. If MNWPRNT = 0, then only basic well information will be printed in the main MODFLOW output file; increasing the value of MNWPRNT yields more information, up to a maximum level of detail corresponding with MNWPRNT = 2.

is an optional list of character values in the style of “AUXILIARY abc” or “AUX abc” where “abc” is the name of an auxiliary parameter to be read for each multi-node well as part of dataset 4a. Up to 20 parameters can be specified, each of which must be preceded by “AUXILIARY” or “AUX.” These parameters will not be used by the MNW2 Package, but they will be available for use by other packages.

In addition, either of the keywords CBCALLOCATE or CBC will cause memory to be allocated for cell-by-cell budget terms.

is the name of the well. This is a unique alphanumeric identification label for each well. The text string is limited to 20 alphanumeric characters. If the name of the well includes spaces, then enclose the name in quotes.

is the number of cells (nodes) associated with this well. NNODES normally is > 0, but for the case of a vertical borehole, setting NNODES < 0 will allow the user to specify the elevations of the tops and bottoms of well screens or open intervals (rather than grid layer numbers), and the absolute value of NNODES equals the number of open intervals (or well screens) to be specified in dataset 2d. If this option is used, then the model will compute the layers in which the open intervals occur, the lengths of the open intervals, and the relative vertical position of the open interval within a model layer (for example, see figure 14 and related discussion).

is a character flag to determine the user-specified model for well loss (equation 2). Available options (that is, place one of the following approved words in this field) are:

•NONE there are no well corrections and the head in the well is assumed to equal the head in the cell. This option (hWELL = hn) is only valid for a single-node well (NNODES = 1). (This is equivalent to using the original WEL Package of MODFLOW, but specifying the single-node well within the MNW2 Package enables the use of constraints.)

•THIEM this option allows for only the cell-to-well correction at the well based on the Thiem (1906) equation; head in the well is determined from equation 2 as (hWELL = hn + AQn), and the model computes A on the basis of the user-specified well radius (Rw) and previously defined values of cell transmissivity and grid spacing. Coefficients B and C in equation 2 are automatically set = 0.0. User must define Rw in dataset 2c or 2d.

•SKIN this option allows for formation damage or skin corrections at the well: hWELL = hn + AQn + BQn (from equation 2), where A is determined by the model from the value of Rw, and B is determined by the model from Rskin and Kskin. User must define Rw, Rskin, and Kskin in dataset 2c or 2d.

•GENERAL head loss is defined with coefficients A, B, and C and power exponent P (hWELL = hn + AQn + BQn + CQnP). A is determined by the model from the value of Rw. User must define Rw, B, C, and P in dataset 2c or 2d. A value of P = 2.0 is suggested if no other data are available (the model allows 1.0 ≤ P ≤3.5). Entering a value of C = 0 will result in a “linear” model in which the value of B is entered directly (rather than entering properties of the skin, as with the SKIN option).

•SPECIFYcwc the user specifies an effective conductance value (equivalent to the combined effects of the A, B, and C well-loss coefficients expressed in equation 15) between the well and the cell representing the aquifer, CWC. User must define CWC in dataset 2c or 2d. If there are multiple screens within the grid cell or if partial penetration corrections are to be made, then the effective value of CWC for the node may be further adjusted automatically by MNW2.

is an integer flag pertaining to the location along the borehole of the pump intake (if any). If PUMPLOC = 0, then either there is no pump or the intake location (or discharge point for an injection well) is assumed to occur above the first active node associated with the multinode well (that is, the node closest to the land surface or to the wellhead). If PUMPLOC > 0, then the cell in which the intake (or outflow) is located will be specified in dataset 2e as a LAY-ROW-COL grid location. For a vertical well only, specifying PUMPLOC < 0, will enable the option to define the vertical position of the pump intake (or outflow) as an elevation in dataset 2e (for the given spatial grid location [ROW-COL] defined for this well in 2d).

is an integer flag that indicates whether the water level (head) in the well will be used to constrain the pumping rate. If Qlimit = 0, then there are no constraints for this well. If Qlimit > 0, then pumpage will be limited (constrained) by the water level in the well, and relevant parameters are constant in time and defined below in dataset 2f. If Qlimit < 0, then pumpage will be limited (constrained) by the water level in the well, and relevant parameters can vary with time and are defined for every stress period in dataset 4b.

is an integer flag that determines whether the calculated head in the well will be corrected for the effect of partial penetration of the well screen in the cell. If PPFLAG = 0, then the head in the well will not be adjusted for the effects of partial penetration. If PPFLAG > 0, then the head in the well will be adjusted for the effects of partial penetration if the section of well containing the well screen is vertical (as indicated by identical row-column locations in the grid). If NNODES < 0 (that is, the open intervals of the well are defined by top and bottom elevations), then the model will automatically calculate the fraction of penetration for each node and the relative vertical position of the well screen. If NNODES > 0, then the fraction of penetration for each node must be defined in dataset 2d (see below) and the well screen will be assumed to be centered vertically within the thickness of the cell (except if the well is located in the uppermost model layer that is under unconfined conditions, in which case the bottom of the well screen will be assumed to be aligned with the bottom boundary of the cell and the assumed length of well screen will be based on the initial head in that cell).

is an integer flag and value that determines whether the discharge of a pumping (withdrawal) well (Q < 0.0) will be adjusted for changes in the lift (or total dynamic head) with time. If PUMPCAP = 0, then the discharge from the well will not be adjusted on the basis of changes in lift. If PUMPCAP > 0 for a withdrawal well, then the discharge from the well will be adjusted on the basis of the lift, as calculated from the most recent water level in the well. In this case, data describing the head-capacity relation for the pump must be listed in datasets 2g and 2h, and the use of that relation can be switched on or off for each stress period using a flag in dataset 4a. The number of entries (lines) in dataset 2h corresponds to the value of PUMPCAP. If PUMPCAP does not equal 0, it must be set to an integer value of between 1 and 25, inclusive.

are the layer, row, and column numbers of each model cell (node) for the current well. If NNODES > 0, then a total of NNODES model cells (nodes) must be specified for each well (and dataset 2d must contain NNODES records). In the list of nodes defining the multi-node well, the data list must be constructed and ordered so that the first node listed represents the node closest to the wellhead, the last node listed represents the node furthest from the wellhead, and all nodes are listed in sequential order from the top to the bottom of the well (corresponding to the order of first to last well nodes). A particular node in the grid can be associated with more than one multi-node well.

are the top and bottom elevations of the open intervals (or screened intervals) of a vertical well. These values are only read if NNODES < 0 in dataset 2a. The absolute value of NNODES indicates how many open intervals are to be defined, and so must correspond exactly to the number of records in dataset 2d for this well. In the list of intervals defining the multi-node well, the data list must be constructed and ordered so that the first interval listed represents the shallowest one, the last interval listed represents the deepest one, and all intervals are listed in sequential order from the top to the bottom of the well. If an interval partially or fully intersects a model layer, then a node will be defined in that cell. If more than one open interval intersects a particular layer, then a length-weighted average of the cell-to-well conductances will be used to define the well-node characteristics; for purposes of calculating effects of partial penetration, the cumulative length of well screens will be assumed to be centered vertically within the thickness of the cell. If the well is a single-node well by definition of LOSSTYPE = NONE and the defined open interval straddles more than one model layer, then the well will be associated with the cell where the center of the open interval exists.

if the relevant variables were set to a negative value in dataset 2c, then that means that they vary in value among nodes (or open intervals, if NNODES < 0) and should be defined here in dataset 2d according to the definitions given under dataset 2c. Which values are specified here, if any, depends on which were set to a negative value in dataset 2c.

Rw

Rskin

Kskin

B C P

CWC

is the fraction of partial penetration for this cell (see PPFLAG in dataset 2b). Only specify if PPFLAG > 0 and NNODES > 0.

are the layer, row, and column numbers, respectively, of the cell (node) in this multi-node well where the pump intake (or outflow) is located. The location defined in dataset 2e should correspond with one of the nodes listed in 2d for this multi-node well. These variables are only read if PUMPLOC > 0 in 2b.

is the elevation of the pump intake (or discharge pipe location for an injection well). Zpump is read only if PUMPLOC < 0; in this case, the model assumes that the borehole is vertical and will compute the layer of the grid in which the pump intake is located.

is the limiting water level (head) in the well, which is a minimum for discharging wells and a maximum for injection wells. For example, in a discharging well, when hWELL falls below Hlim, the flow from the well is constrained.

is an integer flag that indicates how pumping limits Qfrcmn and Qfrcmx will be specified. If pumping limits are to be specified as a rate (L3/T), then set QCUT > 0; if pumping limits are to be specified as a fraction of the specified pumping rate (Qdes), then set QCUT < 0. If there is not a minimum pumping rate below which the pump becomes inactive, then set QCUT = 0.

is the minimum pumping rate or fraction of original pumping rate (a choice that depends on QCUT) that a well must exceed to remain active during a stress period. The absolute value of Qfrcmn must be less than the absolute value of Qfrcmx (defined next). Only specify if QCUT ≠ 0.

is the minimum pumping rate or fraction of original pumping rate that must be exceeded to reactivate a well that had been shut off based on Qfrcmn during a stress period. The absolute value of Qfrcmx must be greater than the absolute value of Qfrcmn. Only specify if QCUT ≠ 0.

is the reference head (or elevation) corresponding to the discharge point for the well. This is typically at or above the land surface, and can be increased to account for additional head loss due to friction in pipes.

is the value of lift (total dynamic head) that exceeds the capacity of the pump. If the calculated lift equals or exceeds this value, then the pump is shut off and discharge from the well ceases.

is the value of lift (total dynamic head) corresponding to the maximum pumping (discharge) rate for the pump. If the calculated lift is less than or equal to LIFTqmax, then the pump will operate at its design capacity, assumed to equal the user-specified value of Qdes (in dataset 4a). LIFTqmax will be associated with the value of Qdes in the first stress period in which Qdes for the well is less than 0.0.

is a minimum absolute value of change in the computed water level in the well allowed between successive iterations; if the value of hWELL changes from one iteration to the next by a value smaller than this tolerance, then the value of discharge computed from the head capacity curves will be locked for the remainder of that time step. It is recommended that HWtol be set equal to a value approximately one or two orders of magnitude larger than the value of HCLOSE, but if the solution fails to converge, then this may have to be adjusted.

is a value of lift (total dynamic head) that corresponds to a known value of discharge (Qn) for the given pump, specified as the second value in this line.

is the value of discharge corresponding to the height of lift (total dynamic head) specified previously on this line. Sign (positive or negative) is ignored.

must correspond with one of the names defined in dataset 2a. Including WELLID in this dataset means it will be an active well during this stress period.

is the actual (or maximum desired, if constraints are to be applied) volumetric pumping rate (negative for withdrawal or positive for injection) at the well (L3/T). Qdes should be set to 0 for nonpumping wells. If constraints are applied, then the calculated volumetric withdrawal or injection rate may be adjusted to range from 0 to Qdes and is not allowed to switch directions between withdrawal and injection conditions during any stress period. When PUMPCAP > 0, in the first stress period in which Qdes is specified with a negative value, Qdes represents the maximum operating discharge for the pump; in subsequent stress periods, any different negative values of Qdes are ignored, although values are subject to adjustment for CapMult. If Qdes ≥ 0.0, then pump-capacity adjustments are not applied.

is a flag and multiplier for implementing head-capacity relations during a given stress period. Only specify if PUMPCAP > 0 for this well. If CapMult ≤ 0, then head-capacity relations are ignored for this stress period. If CapMult = 1.0, then head-capacity relations defined in datasets 2g and 2h are used. If CapMult equals any other positive value (for example, 0.6 or 1.1), then head-capacity relations are used but adjusted and shifted by multiplying the discharge value indicated by the head-capacity curve by the value of CapMult.

is the concentration in the injected fluid. Only specify used if Qdes > 0 and GWT process is active.

represents a list of up to 20 auxiliary variables for a multi-node well that have been defined in dataset 1. The auxiliary variables must be present in each repetition of dataset 4a if they are defined in dataset 1.

is the limiting water level (head) in the well, which is a minimum for discharging wells and a maximum for injection wells. For example, in a discharging well, when hWELL falls below Hlim, the flow from the well is constrained.

is an integer flag that indicates how pumping limits Qfrcmn and Qfrcmx will be specified. If pumping limits are to be specified as a rate (L3/T), then set QCUT > 0; if pumping limits are to be specified as a fraction of the specified pumping rate (Qdes), then set QCUT < 0. If there is not a minimum pumping rate below which the pump becomes inactive, then set QCUT = 0.

is the minimum pumping rate or fraction of original pumping rate (a choice that depends on QCUT) that a well must exceed to remain active during a stress period. The absolute value of Qfrcmn must be less than the absolute value of Qfrcmx (defined next). Only specify if QCUT ≠ 0.

is the minimum pumping rate or fraction of original pumping rate that must be exceeded to reactivate a well that had been shut off based on Qfrcmn during a stress period. The absolute value of Qfrcmx must be greater than the absolute value of Qfrcmn. Only specify if QCUT ≠ 0.