Coupled River Boundary (CRB) Module: FFTools Plug-In

Main FFTools Page | Description | Input File Format | Example

Description

This module allows the use of FEFLOW's "Coupled River Boundary" (CRB) condition nodes. CRB nodes can be used to simulate a Cauchy, or third-type, boundary condition. Examples are rivers with bed material too small to represent in the model, drains with a conductance layer too small to represent in the model or the influence of a distant boundary external to the model. CRB nodes are similar to FEFLOW's standard "Fluid-transfer BC" with the following exceptions:

• CRB nodes are only available via IFM or Python modules (there is currently no CRB-specific documentation available), and
• A single CRB node is sufficient to simulate the boundary condition (for a single "Fluid-transfer BC" condition to be active, FEFLOW requires that all nodes at the corners of the target element face be defined as "Fluid-transfer BC" nodes).

Suggested FEFLOW Configuration

The CRB module has been tested on models with the following characteristics:

• FEFLOW versions 7.x
• Three-dimensional mesh using layered prismatic elements (prismatic elements having a triangular shape in horizontal cross section)
• All slices set to "fixed" in FEFLOW's "3D Layer Configuration..." editor
• FEFLOW Problem Class: Richard's equation for variably-saturated media
• State: Transient

Format of the CRB Setup File

CRB nodes are configured by importing a formatted Comma-Space-Variable (CSV) file. The format is:

• Input 1, Identifies this as a CRB setup file:

  CRB

• Input 2, For each CRB node:

  Node,Stage,Area,Thick,K_CRB,Chk_Budget

where:

• Node is the FEFLOW number of the node at which a CRB condition will be defined (-)
• Stage is the specified water level of the modeled feature (for example, the stage at a point along a river) (L)
• Area is the area across which water flows to or from the CRB node (for example, the area of riverbed in contact with the node at which the CRB condition is specified) (L²)
• Thick is the thickness of the material between the groundwater system and the CRB node (for example, the thickness of the riverbed material) (L)
• K_CRB is the hydraulic conductivity of the material between the groundwater system and the CRB node (for example, the hydraulic conductivity of the riverbed material) (L/T)
• Chk_Budget is an integer flag for setting a constraint on the CRB node:
  • 0 = CRB flow to/from groundwater is unconstrained, or
  • 1 = No flow from the CRB node to the aquifer is allowed. For example, for a flowing stream that is above the water table, the user can use this option to specify that no water will leak from the stream's channel into the groundwater system.

If the user saves simulation data in a FEFLOW DAC output file, flows for CRB nodes will be available in that file:

• For any saved time-step, the status of CRB boundary conditions can be viewed in FEFLOW's interface by displaying FEFLOW's "Fluid-Tranfer BC" data.
• FEFLOW's "Rate Budget" and "Period Budget" panels can be used to evaluate flows to and from CRB nodes by selecting some or all of the nodes. Using such selections, FEFLOW will compute the flows for the selected nodes.

Future releases of the CRB module may allow more flexibility with regard to constraints.

Example

See the Tailing Impoundment and Mine Pit example that uses the CRB module. An example input file:

CRB
1,874,0.25,1,250,0
2392,874,0.5,1,250,0
3588,874,0.25,1,250,0