Define Groundwater Boundary Condition Properties

If the Groundwater Method = Steady State (finite element seepage analysis) in the Groundwater tab of the Project Settings dialog, the properties of the hydraulic boundary conditions are defined with the Define Groundwater Boundary Condition Properties option.

To define steady-state groundwater seepage analysis boundary conditions:

1. Select the Groundwater workflow tab.
2. Select Define Groundwater Boundary Condition Properties from the toolbar or the Groundwater menu.
3. You will see the Groundwater Properties dialog. In this dialog:

• • select the Type of groundwater boundary condition to apply.
  • if applicable, enter the Value of the boundary condition.
  • if applicable, select the Seepage face condition option.
  • if applicable, select the Stage Factors option.
  • use the Add new property option to define the properties of a new boundary condition.

See below for details about the options in the Groundwater Properties dialog.

1. When finished defining the groundwater boundary condition properties, select OK to close the dialog.

Boundary Condition Type

The following boundary conditions can be assigned for steady-state groundwater seepage analysis. Depending on the boundary condition, you may be required to enter a value or select a seepage face condition, and have the option of selecting to stage factors of the boundary condition, as summarized in the table below.

	Value	Seepage Face Option	Stage Factors Option
None	no	no	no
Total Head (H)	yes	no	yes
Zero Pressure (P=0)	no	no	no
Nodal Flow Rate (Q)	yes	yes	yes
Normal Infiltration (q)	yes	yes	yes
Vertical Infiltration (q)	yes	yes	yes
Unknown (P=0 or Q=0)	no	no	no
Pressure Head (PH)	yes	no	yes
Pore Pressure (u)	yes	no	yes

INFILTRATION BOUNDARY CONDITIONS

Unlike other groundwater boundary conditions, Infiltration boundary conditions can only be applied to surfaces, and not along edges or points. This is because Infiltration is, by definition, specified over an area.

Notice that the units of Infiltration are distance / time (e.g. meters / sec ). This is because Infiltration represents a volume of fluid, entering (or leaving), an area of a boundary. Example: ( m3 / sec ) / (m2) = ( m / sec).

Infiltration can be specified in the Vertical direction, or Normal to boundaries. In most cases you will be specifying a Vertical Infiltration (e.g. rainfall on a slope). Normal Infiltration may be required in some cases (for example, if you need to specify Infiltration on a vertical boundary).

Value

All groundwater boundary conditions require a value to be input except for None, Zero Pressure, and Unknown, which do not require a value.

Seepage Face Condition

For Nodal Flow Rate and Infiltration boundary conditions, you can specify that the boundary is a seepage face. This ensures that the total head calculated at a node does not exceed the elevation head of the node. To enforce the Seepage Face condition, select the Seepage face condition checkbox.

Stage Factors

If the boundary condition requires a Value (e.g. Total Head), then you can use the Stage Factors option to increase or decrease the value of the boundary condition at any stage. To do this select the Stage Factors checkbox and select the Add Stage button for each stage and enter a Factor for the boundary condition value at each stage. The Factor is multiplied by the Value to obtain the actual value used at each stage.

If your groundwater boundary condition is staged, it is a good idea to select the Stage Tabs after adding the boundary condition, to check that the boundary condition is applied at the correct stages, and that the values are correct. If not, then edit the boundary condition using the Properties Pane, and make sure that the correct Factors have been applied at the correct stages.