FINIFLUX 2.1

A quantitative understanding of groundwater-surface water interactions is vital for sustainable management of water quantity and quality. The Noble gas Radon-222 (Rn) is becoming increasingly used as a sensitive tracer to quantify groundwater discharge to wetlands, lakes and rivers; a development driven by technical and methodological advances in Rn measurement equipment. However, quantitative interpretation of this data is not trivial, and the current methods are usually based on the simplest solutions to the mass-balance equation (e.g. first order finite difference, inversion, trial and error).

FINIFLUX is an implicit Finite Element model that numerically solves the steady state mass balance equation for 222Rn in lotic (rivers, streams) systems. Degassing is represented using two popular models which originally are from O'Connor and Dobbins (1958) and Negulescu and Rojanski (1969) with modifications (mostly unit conversions from feet to meter) from Cartwright et al. (2011). Alternatively, FINIFLUX also can work with degassing fluxes specified by the user, which can either be measured directly (e.g. using gas tracer experiments, e.g propane) or some other empirical equation (recommended for headwater or very turbulent streams). FINIFLUX is intended to estimate groundwater fluxes into river systems as well as hyporheic exchange characteristics based on measured 222Rn concentrations and discharge data. The model is coupled to the optimisation software package BEOPEST (Doherty 2010, Principia Mathematica, Inc.) for inverse parameter estimation. BEOPEST allows for the parallelisation of the model, and can even be run on multiply machines via TCP/IP protocols. FINIFLUX is intended to help scientists and authorities that use the 222Rn technique to estimate groundwater - surface water exchange for river systems at the reach (meters to km) scale.

UPDATE 1: FINIFLUX 2.1: We have had some particularly difficult datasets where PEST fails to find a good fit to the data. In particular modelled Rn activities are considerably higher than the measured ones. We have found that a regularisation program available on the PEST site can solve this problem and again produce very good fits. In version 2.1 we have added these two files. I will make a video in the near-future, but in the meantime, copy the Add.bat and addreg1.exe files into the main directory and each of the slaves after pre_pest.exe is run. Type 'Add.bat' at the command prompt of first the main directory, and then each of the slaves. Then start FINIFLUX as usual. Enjoy!

Update 2: the plotting program plot_output.exe has been disabled. Use pest_tracker.exe instead.

Note: recently, a few people have had problems with the pre_pest routine. The pre_pest does not copy any files into the slaves because msvcp110.dll is missing. This has been hard for us to solve as we could not reproduce this problem on our computers. A colleague in Portugal, Gustavo Santiago Luis, has found a solution (Thanks!). He installed both the x64 and x86 versions of Visual Studio 2012, which can be found here: https://www.microsoft.com/en-us/download/details.aspx?id=30679

If using FINIFLUX please cite the papers:
Frei, S., and B. S. Gilfedder (2015), FINIFLUX: An implicit finite element model for quantification of groundwater fluxes and hyporheic exchange in streams and rivers using radon, Water Resour. Res., 51, 6776-6786, doi:10.1002/2015WR017212.

Adyasari, D., Dimova, N. T., Dulai, H., Gilfedder, B. S., Cartwright, I., McKenzie, T., and Fuleky, P.: (2023): Radon-222 as a groundwater discharge tracer to surface waters, Earth-Science Reviews, 104321, https://doi.org/10.1016/j.earscirev.2023.104321.