Conceptual Modeling Workflow > Defining Boundary Conditions

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Define Boundary Conditions

At this step, define the boundary conditions for the conceptual model.


Quick Overview



Define hydrological boundaries (sources/sinks) for the model


Structural Zones have been created.

Property Zones have been created.

You have imported and/or created the data objects you want to use for defining boundary conditions. For example, polylines for the geometry or Surfaces or time schedule for defining the attributes.


A "conceptual" boundary condition object is created

Next Steps:

Create Finite Difference Grid,

Create Unstructured Grid, or

Create Finite Element Mesh



Every conceptual model requires an appropriate set of boundary conditions to represent the system’s relationship with the surrounding systems. In the case of groundwater flow model, boundary conditions will describe the exchange of flow between the model and the external system.

Specified Head


General Head





Specified Flux

Wall (Horizontal Flow Barrier)

Pumping Well


The workflow for defining a pumping well boundary conditions and a Wall (Horizontal Flow Barrier) is different than that of defining other boundary conditions such as recharge, specified head, river, etc. Please see the following section for information on defining pumping well boundary conditions. For information on how to define all other types of boundary conditions, please skip to "Defining Other Boundary Conditions" section.


Defining Boundary Conditions

In Visual MODFLOW Flex, the boundary condition types are separated into the following categories:

Boundary Conditions (standard) (Constant Head, Rivers, Drains, General Head, Recharge, EVT, etc.)

Wall (Horizontal Flow Barrier)

Pumping Wells


Modifying Boundary Conditions

From the Model Explorer tree, right-click on the desired boundary condition, and select Edit Boundary Condition... from the pop-up menu.

The Edit Boundary Condition dialog box will display on your screen, allowing you modify the input parameters for the boundary condition. For more information on defining parameter attributes, please refer to "Boundary Conditions Overview" section

Once modifications have been made to the input parameters, click the [Finish] button to save the changes.


Deleting Boundary Conditions

To delete a boundary condition, follow the steps below:

From the Model Explorer tree, right-click on the desired boundary condition and select Delete from the pop-up menu.

You will prompted with a confirmation message. Click the [Yes] button to delete the boundary condition.


Please be aware that there is no undo function to recover a deleted boundary condition. Please exercise caution when deleting boundary condition



Parameters for Transport Boundaries (Sinks/Sources)

If you need to include contaminant transport in your model, then the species concentrations for transport sinks/sources must also be defined while you create your conceptual boundary conditions. By default, species concentrations will be undefined when you create a new boundary condition.  An undefined value is identified by the value "-1" for the species concentration (eg. Conc001, Conc002).  If you with to assign a contaminant mass to a specific boundary condition object, then replace the default -1 value with a representative contaminant concentration.



In Visual MODFLOW Flex you can create boundary conditions in the conceptual model and in the numerical model. When you edit a conceptual boundary condition object, its corresponding numerical representation will not get updated; likewise, when you update a numerical boundary condition, its corresponding conceptual representation will not get updated. The one exception to this rule is Pumping Wells.


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