MXADRT—is the maximum number of drain-return cells in use during any stress period. MXADRT includes cells that are defined using parameters as well as cells that are defined without using parameters. Recipient cells are not included in MXADRT.

IDRTCB—is a flag and a unit number.

•If IDRTCB > 0, it is the unit number to which DRT1-Package cell-by-cell flow terms will be written when “SAVE BUDGET” or a non-zero value for ICBCFL is specified in Output Control (Harbaugh and others, 2000). IDRTCB must be a unit number associated with a file listed with type “DATA(BINARY)” or “DATAGLO(BINARY)” in the name file.

•If IDRTCB = 0, DRT1-Package cell-by-cell flow terms will not be written.

•If IDRTCB < 0, drain leakage for each drain-return cell and return flow to each recipient cell will be written to the LIST file when “SAVE BUDGET” or a non-zero value for ICBCFL is specified in Output Control.

NPDRT—is the number of drain-return parameters.

In MODFLOW-2005,-LGR, and -CFP the maximum number of allowed parametersis 2000.

MXL—is the maximum number of drain-return cells that will be defined using parameters. Recipient cells are not included in MXL. MXL must equal or exceed the sum of NLST×N for all parameters, where N is the greater of 1 and NUMINST.

Option—is an optional list of character values.

•“AUXILIARY abc” or “AUX abc” – defines an auxiliary variable (Harbaugh and McDonald, 1996a, p. 9, Item 4), named "abc," which will be read for each drain as part of Items 3 and 5. Up to 20 variables can be specified, each of which must be preceded by "AUXILIARY" or "AUX." These variables will not be used by the Groundwater Flow Process, but they will be available for use by other processes. The auxiliary variable values will be read after the Rfprop variable.

Auxiliary parameters are used with MODPATH and the Groundwater Transport process.  In MODPATH, the variable IFACE is specified with an auxiliary parameter.  In the Groundwater Transport process, concentration is specified with an auxiliary parameter.  The option COMPACT BUDGET AUXILIARY must be used in the Output Control when IFACE is used for MODPATH.

•“RETURNFLOW”—activates the return-flow option of the DRT1 Package. If “RETURNFLOW” is listed as an option, LayR, and, optionally, RowR, ColR, and Rfprop are read from items 3 and(or) 5.

•NOPRINT—suppresses the printing of cell lists.

•

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 DRT1 Package, the only allowed parameter type is “DRT,” which defines values of the drain hydraulic conductance.

Parval—is the parameter value. This parameter value may be overridden by a value in the PVAL file.

NLST—is the number of drain-return cells included in a non-time-varying parameter or in each instance of a time-varying parameter.

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 list of drain-return cells, associated recipient cells, and properties. 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.

Layer—is the layer number of the cell containing the drain.

Row—is the row number of the cell containing the drain.

Column—is the column number of the cell containing the drain.

Elevation—is the elevation of the drain.

Condfact—is the factor used to calculate drain hydraulic conductance from the parameter value. The conductance (L2/T) is the product of Condfact and the parameter value.

See also "What is conductance?"

LayR—is a flag and, if greater than 0, a layer number. If auxiliary variables are being read, LayR must be greater than zero, so that RowR, ColR, and Rfprop are read. LayR is not read if “RETURNFLOW” is not listed as an option in item 1.

•If LayR > 0, it is the layer number of the recipient cell.

•If LayR = 0, there is no return flow for the drain cell, and RowR, ColR, and Rfprop are not read unless there are auxiliary variables defined.

RowR is defined by the value of LayR that is read. RowR is not read if “RETURNFLOW” is not listed as an option in item 1.

•If LayR > 0, RowR is the row number of the recipient cell that will receive the drain water as recharge.

•If LayR = 0, RowR is NOT read, and there is no return flow for the drain cell, and the water leaves the model.

ColR is defined by the value of LayR that is read. ColR is not read if “RETURNFLOW” is not listed as an option in item 1.

•If LayR > 0, ColR is the column number of the recipient cell that will receive the drain water as recharge.

•If LayR = 0, ColR is NOT read, and there is no return flow for the drain cell.

Rfprop—is the return-flow proportion. Valid values are in the range 0.0 to 1.0, inclusive. Rfprop is the proportion of the drain flow, if any, calculated for the drain-return cell simulated as returning to the recipient cell. If Rfprop equals 0.0, the return-flow capability is deactivated for the cell. Rfprop is not read if “RETURNFLOW” is not listed as an option in item 1.

[xyz]—is up to 20 auxiliary variables for a drain-return cell that have been defined in item 1. The auxiliary variables must be present in each repetition of items 3 and 5 record if they are defined in item 1.

ITMP—is a flag and a counter.

•If ITMP < 0, non-parameter drain-return data from the last stress period will be reused.

•If ITMP ≥0, ITMP will be the number of non-parameter drain-return cells read for the current stress period.

NP—is the number of drain-return parameters in use in the current stress period.

Layer—is the layer number of the cell containing the drain.

Row—is the row number of the cell containing the drain.

Column—is the column number of the cell containing the drain.

Elevation—is the elevation of the drain.

Cond—is the hydraulic conductance of the interface between the aquifer and the drain.

See also "What is conductance?"

LayR—is a flag and, if greater than 0, a layer number. If auxiliary variables are being read, LayR must be greater than zero, so that RowR, ColR, and Rfprop are read. LayR is not read if “RETURNFLOW” is not listed as an option in item 1.

•If LayR > 0, it is the layer number of the recipient cell.

•If LayR = 0, there is no return flow for the drain cell, and RowR, ColR, and Rfprop are not read unless there are auxiliary variables defined.

RowR is defined by the value of LayR that is read. RowR is not read if “RETURNFLOW” is not listed as an option in item 1.

•If LayR > 0, RowR is the row number of the recipient cell that will receive the drain water as recharge.

•If LayR = 0, RowR is NOT read, and there is no return flow for the drain cell, and the water leaves the model.

ColR is defined by the value of LayR that is read. ColR is not read if “RETURNFLOW” is not listed as an option in item 1.

•If LayR > 0, ColR is the column number of the recipient cell that will receive the drain water as recharge.

•If LayR = 0, ColR is NOT read, and there is no return flow for the drain cell.

Rfprop—is the return-flow proportion. Valid values are in the range 0.0 to 1.0, inclusive. Rfprop is the proportion of the drain flow, if any, calculated for the drain-return cell simulated as returning to the recipient cell. If Rfprop equals 0.0, the return-flow capability is deactivated for the cell. Rfprop is not read if “RETURNFLOW” is not listed as an option in item 1.

[xyz]—is up to 20 auxiliary variables for a drain-return cell that have been defined in item 1. The auxiliary variables must be present in each repetition of items 3 and 5 record if they are defined in item 1.

Pname—is the name of a parameter being used in the current stress period. NP parameter names will be read.

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.