NRCHOP—is the recharge option code. Recharge fluxes are defined in a layer variable, RECH, with one value for each vertical column. Accordingly, recharge is applied to one cell in each vertical column, and the option code determines which cell in the column is selected for recharge.

•1—Recharge is only to the top grid layer.

•2—Vertical distribution of recharge is specified in layer variable IRCH.

•3—Recharge is applied to the highest active cell in each vertical column. A constant-head node intercepts recharge and prevents deeper infiltration.

•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).

IRCHCB—is a flag and a unit number.

•If IRCHCB > 0, it is the unit number to which cell-by-cell flow terms will be written when "SAVE BUDGET" or a non-zero value for ICBCFL is specified in Output Control.

•If IRCHCB ≤ 0, cell-by-cell flow terms will not be written.

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 RCH Package, the only allowed parameter type is RCH, which defines values of the recharge flux.

Parval—is the parameter value. This parameter value may be overridden by a value in the PVAL file, the Sensitivity Process (SEN) input file, or by a value generated by the Parameter-Estimation (PES) Process.

NCLU—is the number of clusters required to define a parameter. Each repetition of Item 4b is a cluster (variables Mltarr, Zonarr, and IZ). There is usually only one cluster used to define a RCH non-time-varying parameter or instance of a time-varying parameter; however, it is acceptable to have more than one cluster.

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 series of NCLU clusters. 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.

Mltarr—is the name of the multiplier array to be used to define cell values that are determined by a parameter. The name “NONE” means that there is no multiplier array, and the cell values will be set equal to Parval.

Zonarr—is the name of the zone array to be used to define the cells that are associated with a parameter. The name “ALL” means that there is no zone array, and all cells in the layer are associated with the parameter.

IZ—is up to 10 zone numbers (separated by spaces) that define the cells that are associated with a parameter. These values are not used if Zonarr is specified as “ALL.” Values can be positive or negative, but 0 is not allowed. The end of the line, a zero value, or a non-numeric entry terminates the list of values.

INRECH—is the RECH read flag. Its function depends on whether or not parameters are being used.

•If no parameters are being used (NPRCH = 0):

oIf INRECH ≥ 0, a layer variable of recharge fluxes, RECH, is read.

oIf INRECH < 0, recharge rates from the preceding stress period are used.

•If parameters are being used (NPRCH > 0):

oIf INRECH > 0, INRECH is the number of parameters that will be used to define RECH in the current stress period. Item 7 defines the names of the parameters.

oIf INRECH < 0, recharge parameters from the preceding stress period are used.

oINRECH = 0 is not allowed. That is, when parameters are used, at least one parameter must be specified each stress period.

INIRCH—is the IRCH read flag, which is read only if NRCHOP is two:

•If INIRCH ≥ 0, a layer variable of layer numbers (IRCH) is read.

•If INIRCH < 0, the variable (IRCH) used in the preceding stress period is reused.

Pname—is the name of a parameter that will be used to define the RECH variable in the current stress period.  Read INRECH values if NPRCH > 0 and INRECH > 0.

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.

IRCHPF—is an optional format code for printing the RECH variable after it has been defined by parameters. The format codes are the same as those used in the U2DRELREL array reading utility module.