Options Tab

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The Options tab on the MODFLOW Options dialog box is used to specify a variety of options in MODFLOW.

CHTOCH determines whether or not flow between adjacent specified-head cells is calculated. Activating this option will slow down MODFLOW slightly. CHTOCH should be activated if solute transport is simulated with the Ground-Water Transport (GWT) process.

If PRINTTIME is active, MODFLOW will print the beginning, ending, and elapsed time required for the model to execute.

If STOPERROR is active, MODFLOW will continue to run even if the closure criteria are not met so long as the overall budget error does not exceed STOPER. This is similar to the USE_NONCONVERGENCE_CONTINUE option in the Surface-Water Routing process but it applies only to the groundwater flow process. See also the CONTINUE option in the NWT solver.

HNOFLO is the value that will be printed or saved for head in cells that were inactive since the beginning of the simulation. It is generally best to specify a value outside the range of heads that will be calculated by the model. In MODFLOW-6, the user does not specify HNOFLO. It is set automatically to 1E30

HDRY is the value that will be printed or saved for head in cells that have converted to a dry state since the beginning of the simulation. It is generally best to specify a value outside the range of heads that will be calculated by the model. In MODFLOW-6, the user does not specify HNOFLO. It is set automatically to -1E30

STOPER is the budget error that must be exceeded for execution to stop when STOPERROR is active.

LENUNI and ITMUNI are the length and time units respectively used in the model for all input and output. For example, if the length of the cells is measured in meters and the time steps are measured in days, the units for the pumping rate in wells would have to be specified in m3/d.

MUNIT is the mass unit used in MT3DMS. The mass unit is used for labeling. It does not affect the calculations. It is not used in MODFLOW.

Open listing file in text editor when model is done. If this check box is checked, the text editor specified in the MODFLOW Program Locations dialog box will be used to open the main output file from the model once the model is finished.

Binary file containing initial heads (optional). Usually, the initial heads for a transient model are generated using an initial steady state stress periods. In rare cases, it may be desirable to generate the initial heads for the model using a different model. In such cases, the name of the file containing the initial heads is specified here. Certain conditions must be strictly observed for this to work properly.

•The heads must have been saved in a binary file.

•Both models must have the same number of columns, rows, and layers.

•The model that reads the binary head file must not also generate a file with the same name as the one it is reading.

•The first heads saved in the file must be the heads to be used as the initial heads. Thus if the other model has multiple time steps or stress period, only the heads for the very last time step should be saved to the file.

In GSFLOW, the format for the SFR package and and Discretization input file are slightly different from the format used by MODFLOW-2005. If you are generating input for GSFLOW, you should check the Use GSFLOW format check box. The new SFR format is used automatically for MODFLOW-NWT.

Write binary grid file (MODFLOW-6) suppresses printing the NOGRB option in MODFLOW 6 discretization files. If the NOGRB is used, MODFLOW will not create a binary grid file. Thus when this checkbox is checked a binary grid file will be created by MODFLOW 6. Binary grid files are used by post-processors such as MODPATH and ZONEBUDGET.