Ground-Water Flow Process

The Ground-Water Flow process is required for all MODFLOW models. The Ground-Water Flow process includes the following

•	The Basic package (required)

•	The Discretization file (required)

•	Multiplier arrays (optional)

•	Zone arrays (optional)

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Ground-Water Flow packages (Of the primary ground-water flow packages (BCF, LPF, HUF2), one and only one must be selected. The Horizontal-Flow Barrier package can be used to modify the groundwater flow variables. The Unsaturated-Zone Flow package can be added to simulate vertical, unsaturated flow above the saturated zone.)

•	Boundary Condition packages (optional but at least one is almost always used.)

•	Solvers (One and only one must be selected.)

•	Output Control (optional)

•	Subsidence packages (optional)

Some packages allow "parameters" to be used to specify input values. When parameters are used several input values may be linked because they are both controlled by the same parameter. In the Ground-Water Flow process, parameters are simply another way of specifying input. However, parameters make automatic model calibration possible through the use of the Observation, Sensitivity, and Parameter-Estimation processes.