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Define Boundary Conditions


At the Define Boundary Conditions step, you can define and edit the various boundary conditions for your model using one of the following features:







Visualizing Boundary Conditions & Style Settings

Exporting Boundary Conditions

Boundary Condition-Specific Considerations

oPumping Wells

oHead-Dependent Flux Boundary Conditions and Conductance

oRecharge and Evapotranspiration

oSurface Water


Boundary conditions can be edited in the Layer view as well as in the Row or Column views. Defining and Editing is not supported in the 3D view of finite difference models.

Under the Toolbox, use the combo box to select from the various Boundary condition types.

Use the same tools as described in the previous step to manipulate the views.



Each boundary condition group of cells will appear as its own node in the model tree. You can right click on this to adjust style settings. In addition you can load any group of boundary condition cells into a stand-alone 3D Viewer.


To delete a specific boundary condition cell group, right-click on this node in the tree, and select Delete.



To validate your boundary condition and verify that there are no warning or errors associated with a boundary condition, right-click a specific boundary condition and select Validate... and if there are any errors or warning you will be provided an option to resolve the issue as shown in the dialog below. This is available for Constant Head, River, General Head, and Drain. The validation process will check to see if the attributes of the boundary condition will place it below the bottom of the cell you assigned it to. Then it will give you options to correct this. If you choose to Ignore the errors you may encounter errors when trying to translate and run your model.


In general, each of the boundary condition types has the same set of graphical tools on the left-hand toolbar for editing the model boundary conditions. The following is a description of how to use these options. For specific descriptions of the data requirements and data entry options, refer to the sections describing each boundary condition type.



The import button allows you to import boundary condition text files in IJK format. Simply browse to the file and select Open to import the boundary condition. This option is useful when making edits to the boundary condition as described in Edit Attributes in TXT Format.



The Assign button allows you to assign new boundary conditions. You have options to assign by Polyline or Polygon, by Using Data Object or by Cells. These options are described further below.

Polygon or Polyline: Use this option to digitize one or more shapes and assign Boundary Condition attributes to the respective shapes. Use the left mouse button to start drawing. Once you have finished digitizing, double-click or right click with the mouse and select "Finish" to assign the digitized polyline or polygon to the model as shown below.



Using Data Object: Use this option when you have a polyline or polygon data object already imported into the projects and you would like to use this shape to define the geometry.  


Cells: Use this option when you want to select individual cells to assign a boundary condition.  For Recharge and Evaporation this can be useful to change only a few cells from one zone to another - as the Define Boundary Condition dialog allows you to enter zone numbers.


RThe Define Boundary Condition attributes window will appear as shown below.



Provide the desired Name and Description.


Select Next to proceed.



Define the attributes using the various methods; click Finish when you are done.


This dialog allows you to copy and paste from Excel to make defining (or editing) the attributes easy.


The following buttons are available:

Assign to current cell (F1)

Assign to column (F2)

Apply to selected cells (F3)

Interpolate values between selected cells (only available when you first create a new set of cells using a polyline feature)

Toggle automatic calculation of calculated fields

(e.g. river length x river width x river conductivity vs. explicit conductance)


The interpolate option allows you to select 2 cells (rows) and then when you select Interpolate - it will calculate the values for the cells (rows) in between using linear interpolation.

For more details on the options for defining attributes, see Define Boundary Conditions (Attributes).


If your boundary condition is transient switch the schedule drop down to transient to enter your schedule..



You can copy and paste your time schedule from Excel into this dialog to make defining your boundary condition quicker and easier.

By default the Assign to appropriate layer is selected. This means if you enter values for the attributes of a boundary condition (for example the Starting Head) which would place it into another layer - this will occur automatically once you save your boundary condition.

Please Note: When digitizing boundary conditions, Visual MODFLOW Flex will automatically assign these to the appropriate layer, based on the attributes you define.


For more details on creating a Wall (HFB) Boundary Condition, please see Define Wall (HFB).

For more details on creating Wells Boundary Condition object, please see Define Pumping Wells.



When you select the Edit... button you must select a cell containing the boundary condition you wish to edit.  The following dialog will appear (similar to defining the boundary condition).



The attributes for each cell containing the boundary condition are displayed and can be edited. The cell you selected will be highlighted in the dialog. If you select other rows in the dialog - the corresponding cell will be highlighted in the viewer.


By default the Assign to appropriate layer is selected. This means if you adjust the attributes of a boundary condition (for example the Stage) which would place it into another layer - this will occur automatically once you save your edits.


To view the attributes for Recharge or Evapotranspiration zones, see the Database section below.



If preferred, you can make your boundary condition edits by using the Script option. On this tab you will find the script for any edits you make on the Edit cells tab allowing you to learn the script language. You can re-use the script to "replay" your edits to your boundary conditions.

You can also build expressions using the Expression Builder.



The Erase button allows you erase the boundary condition assigned to either a single cell or a group of cells. This option is available for all boundary conditions (except Recharge and Evapotranspiration) as well as Walls and Pumping Wells.



The Copy / Layer/Row/Column option is used to copy all of the boundary data from a selected boundary group to one or more selected model layers, rows, or columns (based on the active view). This option is available for: Constant Head, River, General Head, Drain, Specified Flux and Constant Concentration.  When this option is launched, you will see only those boundary condition groups that are in the currently selected layer. Please use caution when copying boundary conditions for an LGR model, as you cannot copy boundary conditions from layers in a parent grid to layers in a child grid; you can only copy boundary conditions within the grid in which that it lies (within parent grid layers/rows/columns or within child grid layers/rows/columns).




The Database button becomes active when you select either Recharge or Evapotranspiration for the Boundary Condition type. This will load the zone database window as shown in the following figure.



In this grid, you can modify the values for existing zones.


Specifying Active/Inactive Time Periods

For Constant Head, River, Drain, General-Head, and Specified Flux, you can disable selected Time Periods by removing the check marks from the Active column (see below), which “turns off” the boundary condition for that particular Time Period. The corresponding package will have no attributes defined for those cells covered by that boundary condition, for that specific stress period. For Recharge and Evapotranspiration zones, you can define a zero rate for those cells in those time periods.



By default, Visual MODFLOW Flex uses the following color scheme for Boundary Condition Cells

Boundary Condition Type


Constant Head




General Head





Light blue


Varies (zone based)


Varies (zone based)

Unsaturated Zone (UZF)

Varies (zone based)

Seepage Face

Bright Blue

Specified Flux


Time Varying Material


Wall (Horizontal Flow Barrier)



Light red


Adjusting Style Settings

The style settings of some of the Boundary condition cells

Right click on the desired Boundary condition cell group from the model tree and select 'Settings'.

The Settings dialog will appear; the settings are similar to described in Points.


Exporting Boundary Conditions

The boundary condition cell locations (and attributes) be exported to shapefile; see Export for more details.


Boundary-Condition Specific Considerations

Since each boundary condition is intended to simulate different processes, there are functions/behaviors that are unique to certain boundary condition types. For more information on each boundary condition type, please refer to the Boundary Condition Theory section.


Pumping Wells

Pumping Wells are treated differently than other boundary conditions and are pseudo-conceptual boundary conditions that are not tied directly to the finite difference grid. To edit a well set:

Select "Well" from the Boundary Condition list.

Be sure you are in the correct layer where your well is screened.

Select [Edit >] Single from the toolbox.

Select the desired well cell.

You will see a window similar to the one below:



Please Note: if you make edits to the well pumping rates in this screen, these changes are not propagated back to the raw (original) wells data object in the Data Explorer.


For more information about wells, please refer to the Editing Wells, Well Data, and Theory sections.


Head Dependent-Flux Boundary Conditions - Default Conductance

For Drain, River, General Head, and Lake boundary conditions, you will find an options to Use Default Conductance within the Define Boundary Condition dialog.

This allows you to enter attributes more easily measured and have the conductance calculated for you. For example, when assigning a River using a polyline (digitized or data object), you need to provide the River width, Riverbed thickness and Riverbed Conductivity - and the Conductance will be calculated for you based on these fields and the length of the polyline that intersects each cell.



If you unselect the Use default conductance button, you will need to specify the Conductance values explicitly:


Recharge and Evapotranspiration

Recharge and Evapotranspiration have additional settings for rendering the cells by either ZoneID or Rate (either Recharge or Evapotranspiration). To access these settings, right-click on the Recharge (or Evapotranspiration) node in the model tree and select Settings. The following dialog will appear:



From the tree on the left side of this window, select Colors under Style/Recharge. In the main window, under "Attribute" you can then change this between Zone or Rate; as you change this, the color range in the grid will refresh. Upon clicking Apply or OK, the 2D/3D views will be refreshed.


Surface Water  (SFR2)

The Surface Water workflow only includes the option to "Edit..." the boundary condition.  Selecting the "Edit..." option will launch a new Surface Water workflow or the existing workflow if one was previously created.  Since the workflow includes topology data (i.e. the interconnections) of surface water features, there can only be a single Surface Water workflow per model run.  The Surface Water workflow is described in detail in the Surface Water workflow section.



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