MODELING TASK DESCRIPTION
In reality, aquifers are not homogenous but have preferential flow paths, low-conductive clay lenses or fracture networks. Apart from the often applied equivalent permeability approach, in some cases it may be necessary to implement hydraulic conduits, drains, faults or fractures as separate structures in groundwater models. FEFLOW offers one- and two-dimensional features to represent such heterogeneity.
SOLUTION
High-conductive structures can be implemented in FEFLOW as discrete features which each can have an individual parameterization. They can be assigned along element edges (1D), element faces (2D) or they can connect two arbitrary nodes within the mesh.
The workflow to include discrete features in a FEFLOW model is as follows:
Step #01 - In the Selection Toolbar, activate the target geometry for Discrete Feature assignment (Slice or Join Edges, Slice or Join Faces) - see Fig. 1
Fig. 1 - Selection of toolbar options
Step #02 - Use one of the selection tools of the Selection Toolbar to create a 1D horizontal/vertical or 2D planar/subvertical selection - see Fig. 2
Fig. 2 - Selection for 1D Discrete Feature
Step #03 - To convert the selection into a discrete feature, go to the Discrete Features panel, open the context menu of 'Discrete Features' and select Add...Feature Element and the preferred flow law - see Fig. 3
Fig. 3 -Discrete Feature panel while creating a Discrete Feature from a selection
Step #04 - The Discrete Feature is now added to the Discrete Features panel as 'Feature 1'. It will also appear as a new section in the Data panel under /Discrete Features that contains the specific parameter options of the discrete features, as shown in the lower part of Fig. 4. The chosen flow law and geometry type are displayed behind the feature's name.
Fig. 4 - Discrete Feature and Data Panels after the creation of the Feature
Step #05 - The parameterization of the discrete features can be edited any time with a double click on the feature parameter in the Data Panel, followed by a normal parameter assignment. To select all edges/faces belonging to the desired discrete feature, double-click on the feature's name in the Discrete Features Panel.
Special case - Arbitrary node path
Arbitrary node paths connect two or more nodes without any hydraulic exchange in between these nodes. This can be used to model culverts of closed pipes for example. To create an arbitrary discrete feature, the option Select Arbitrary Node Path is available in the Selection Toolbar - see Fig. 5
Fig. 5 - "Select Arbitrary Node Path"
For an arbitrary node path with one in- and outlet, only the nodes at the ends of the discrete feature should be selected - see Fig. 6. Be aware that only these nodes will exchange fluid/mass with the model domain. If more nodes are defining the arbitrary node path, all the nodes exchange fluid/mass.
Fig. 6 - Selected nodes only will exchange mass and fluid with the model domain
FURTHER INFORMATION & USEFUL LINKS
Manuals and Guidelines
FEFLOW 10.0 Documentation - Discrete Features Panel
FEFLOW 10.0 Documentation - Discrete Feature Elements