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MODELING TASK DESCRIPTION

FEFFLOW offers a wide range of result analyses including spatial visualization of process variables, water balance calculations, time-series charting and particle tracking. To delineate catchments for drinking water production wells, identify contaminant plumes or follow water infiltration paths, particle tracking can be performed in various approaches. FEFLOW enables forward and backward streamline calculations for steady-state models as well as pathline calculations for transient simulations. The following workflow instructions guide you through the process how to display particle tracks and how to interpret them.  

 

SOLUTION

Step #01 - Store a nodal selection for particle tracks to start (or end)
Particle tracks are calculated in forward or backward manner from either one or multiple nodes. Create a nodal selection (e.g. the nodes capturing a river section with infiltrating conditions) and store the selection. Activate this selection with a double-click on the nodal selection in the ‘Selections' panel.  See Fig. 1.
 

Fig. 1 – Preparation of a nodal selection for the calculation of forward streamlines. The blue lines mark a river and a smaller tributary and the red circles indicate irrigation well locations. 

 
 
 
Step #02 - Open the parameter Streamlines and choose the display components
Activate the parameter Streamlines (Forward/Backward) in the 'Data' panel  /Process Variables/Fluid Flow/Streamlines/Forward/. Now, select Traces or Period Sections in the ‘View Components’ panel - see Fig. 2. 
Fig. 2 – Parameter Forward Streamlines in the ‘View Components’ panel
 
 
 
Step #03 - Parameterize the streamlines
In order to see the streamlines a couple of parameter settings have to be adjusted:

a) choose the number of seeds per node (number of particles released from each node)
b) increase the radius by clicking on "Default" (capture zone of seeds around a node)
c) select an appropriate time range and color scheme 
See Fig. 3.

Please note : the options “surface only” and “spherical input” have the effect of either evenly distributing the seeds over the spherical surface or within its volume. The “flux-weighted” option creates a seed distribution based on the amount of flux, e.g. most seeds are placed where fluxes are highest, typically applied when backward streamlining from a pumping well.
 
 
Fig. 3 – Forward Streamlines of the nodal selection with Period Sections of every hundred days travel time. 
 
 
Assuming the selected nodes capture an infiltrating river section, the particle tracks can be used to evaluate which wells would be affected and how long it will take until a potential contamination in the river will reach these wells. In the above example, the contamination will first reach the well north of the infiltration after approximately 100 days. Another well located further East will be reached after around 300 days and a third well far northeast of the river may be reached after 2000 days.  

The described workflow works identically for any backward streamlines or for transient pathline or Random-Walk calculations. Please note, that streamlines/pathlines are displayed only, if the simulation is running or using .dac files. Once the simulation is stopped in the .fem model file, all streamlines/pathlines disappear. 
 
Be aware that FEFLOW uses the parameters of the "Particle-tracking Computation" Tab in the Problem settings to calculate the particle times. In this Tab, parameters such as porosity, diffusion and dispersivities can be defined. 
 
FURTHER INFORMATION & USEFUL LINKS

Manuals and Guidelines
FEFLOW 10.0 Documentation - Particle Tracking
FEFLOW 10.0 Documentation - Particle Tracking Workflow

FEFLOW 10.0 Documentation - Particle Tracking Computation and Additional Settings
 
 
 
Keywords: particle tracking, transport, FEFLOW, contaminants, catchment, calculation
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