GMS:MODFLOW-NWT

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Starting at GMS version 8.2, GMS supports MODFLOW-NWT. MODFLOW-NWT is a version of MODFLOW based on MODFLOW-2005 that provides a different formulation of the groundwater flow equation designed to solve models that are non-linear due to unconfined cells or non-linear boundary conditions.

Choosing MODFLOW Version

Choosing to use MODFLOW 2000, MODFLOW 2005, or MODFLOW-NWT is done in the MODFLOW Global Options Dialog. At any time you can switch from one to the other.

MODFLOW Global Option Dialog

Changes to MODFLOW 2005

1. UPW Package
2. NWT Solver
3. WEL Package
  • The WEL package was modified to add an option to decrease the pumping rate as the head drops below a user-specified percentage of cell thickness. The new option is called PHIRAMP.
4. SFR Package
  • The SFR package is modified to avoid removing water from dry cells and to calculate derivatives for the Newton formulation.
5. UZF Package
  • The UZF package is modified to avoid removing water from dry cells and to calculate derivatives for the Newton formulation.
6. Other Packages
  • Poor input values for other packages can result in convergence failure. For example, an EVT extinction depth below the cell bottom elevation can result water being improperly removed from a dry cell.