Calibration of a model with particle tracking observations

Dear all,

Is it possible to use particle tracking results to calibrate a FEFLOW model?
Can particle tracking results be automatically calculated and exported?
Does anyone have experience with this?

Thanks in advance for your answers/comments,

Olivier

An automation to generate particle tracks is not possible with the current FEFLOW 7.0. This missing feature makes a PEST calibration impossible in case you want to use fieldlines.

As an alternative, I suggest to use Age-based simulations you can directly use in FEFLOW/FePEST. On top of that, age-based computations are more accurate in a physical sense than generic particle tracking techniques.

While standard streamlines are solely based on advection, other processes as such as diffusion and dispersion are simply neglected. Of course, Random Walk Particle Tracks (RWPT) mimic the additional effects diffusion and dispersion. However, both methods are based on a flow solution, because no advective-diffusive transport equation is taken into account. Moreover, these methods provide a visual inspection only. A quantitative evaluation can only be indirectly derived (second order).

Age-based computations provide a powerful alternative. Age computations do not only allow a visual inspection, but they also take budget quantities into account as driven by advection, dispersion and diffusion.

Let’s assume you are interested in delineating catchment zones. In this context you may work with the age-species Exit Propability (EP). You may prescribe Dirichlet BC’s for the EP (equal to 1.0) to nodes where water leaves the system (e.g. wells). A value of 1 at exit points corresponds to an exit probability of 100 %.

The EP is taken into account as a concentration, because internally FEFLOW solves a mass transport equation involving advection, dispersion and diffusion. During the computations FEFLOW reverses the flow field (vectors) in the advective terms of the transport equation. Accordingly, extraction wells become injection wells. These “injection wells” inject water with a “unit concentration” of 1 for the EP. This “concentration” is then transported within the porous medium and a plume may evolve. This plume can be used to delineate the capture zone.

The EP is available in FEFLOW as a process variable and in FePEST as an observation.

Hi Bjorn,

Thanks a lot for your answer. I will give it a try.

Regards,

Olivier

Great Olivier, give it a try and please let me know if you have further questions.

Since the EP is solved as a process variable you have a remarkable degree of freedom to automatize the post-processing component of modelling. On top of that, you may intersect nodal EP's distributions as derived by multiple simulations you carry out with geological units by using boolean operators. That's a "nice" alternative to overlaying vertices of field lines over a fixed raster and calculating the frequency.