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Translation Settings

At the Translate step, you define the run type and property package, then generate (Translate) the input files for MODFLOW-USG.




The Model Run Type is either Steady-State or Transient

Property Packages are either LPF (default) or BCF.

The settings for some of the other packages can be adjusted as per the following sections.

For more details, please refer to the MODFLOW-USG version 1.4.00 manual, by Panday et al. (2013), which is available from the USGS website:


Layer Types

By default, the layer type is set as 4, for both the .BCF and .LPF packages. The layer types can be adjusted at the top of each respective package.


Time Steps

The number of time steps for each stress period is defined at the end of the .DISU package; simply open this tab, change the desired value, save the package, then proceed with the run.


Output Control

The OC package for MODFLOW-USG uses text keywords, make it simpler to understand the file format. By default, heads and drawdown will be saved for every time step, up to 10 time steps per stress period. If you change the number of time steps, then you may need to update the Output control, to save heads/drawdowns at the desired time steps


SMS Package

The parameters for the .SMS package are described in the MODFLOW-USG manual, and in the "MODFLOW-USG Version 1.4: Description of Model Input and Output"

Simply adjust the desired parameter values, then right-click in the window to save and update the package file, then proceed to the run.


Initial Heads

Initial Head values are saved in the .BAS package; if you want to use a Heads file from a previous MODFLOW-USG run, you can update the .BAS file with the link by following steps 1 through 8 below:


1.Run MODFLOW-USG to create the desired .HDS file

2.Open this model Run directory (in Windows Explorer), and make a copy of this file, saved with a new name (such as model-initial-heads.HDS)

3.Go back to the Translate step.

4.Select the .BAS tab

5.Browse to about the half-way point in the file, looking for the section:


"INTERNAL       1.0 (10F15.0)   -1 Initial Head layer Layer 1"


6.Delete this line, and all rows after this line (containing the default initial head arrays).

7.Insert the following line:


OPEN/CLOSE 'D:\project_directory\\MODFLOW\UnstructuredGrid2\Run1\MODFLOW-USG\initial-heads.HDS' 1 (BINARY) -1


Where the path and filename (shown in blue) match the precise location of the .HDS file from the previous MODFLOW-USG run that you wish to use.


8.Save the .BAS file, then Run


BAS Package and Discontinuous Layers

Visual MODFLOW Flex assumes that all layers have the same horizontal discretization. When there is a layer that pinches out, resulting in a cell thickness of zero, these cells will not be displayed in the 3D viewer.  During the translation to MODFLOW-USG packages, the cells with zero thickness will be marked as inactive in the basic (.BAS) package and in the .DISU (UnStructured Grid) package, those zero thickness inactive cells have no vertical connections. Their upper and lower neighbors are directly connected together, effectively bypassing the inactive cells with zero-thickness.


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