GMS:IBOUND

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Packages
Flow: BCF6, HUF, LPF, UPW
Solvers:

DE4, GMG, NWT, PCG,

PCGN, LMG, SIP, SOR,

SMS
Other:

BAS6, BFH, CHD1, CLN,

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HUF, LAK3, MNW1, MNW2,

OUT1, RCH1, RIV1, SFR2,

STR1, SUB1, SWI2, WEL1,

UZF1

The IBOUND button of the Global Options\Basic Package dialog brings up the array editor.

Values

The IBOUND array contains a value for each cell in the grid defining the type of the cell as constant head, inactive, or variable head.

Constant Head
A negative value indicates that the cell has a constant head. The value of the constant head is defined in the starting heads array.
Inactive
An IBOUND value of zero indicates that the cell is inactive (no-flow).
Variable Head
A positive IBOUND value indicates that the cell has a variable head (i.e., the head value will be computed as part of the simulation).

Editing the IBOUND Array

There are several ways to change the active/inactive status (positive vs. zero) of a cell before or after initializing the IBOUND array. One method is to directly edit the IBOUND array using the IBOUND dialog. Another method is to select the Cell Attributes command in the MODFLOW menu. In most cases, the most efficient method is to use the Activate Cells in Coverage command in the Map module. This method uses a polygon to define the active and inactive regions.

The constant head cells are typically assigned or edited in one of three ways. One method is to directly edit the IBOUND array. Another method is to select a set of cells and use the Cell Properties dialog in the MODFLOW menu. The simplest method is to define the constant head zones using feature objects as part of a conceptual model in the Map module.