Hydrological connectivity from causal analysis of time series in the Lhomme Karst System, Belgium.
EGU meeting, Vienna, April 8, 2019
The hydrological behaviour of karstic systems is difficult to theorize holistically because of their specific heterogeneities leading to distinctive non-linear processes. Karstified systems present great opportunities for field exploration and hydrogeological monitoring of the vadose zone through its network of caves and conduits. These unique but explorable environments are predisposed to an inductive scientific approach where transfer processes associated with hydrological connections are directly inferred from the data. This is done conventionally using dye tracing from which connections and transfer times are undeniably revealed. However, single tests do not allow appreciating the dynamic character of the hydrological connections. Nowadays,several data analysis methods aim at the detection of causal relationships between time series allowing the investigation of dynamics and interactions. Some are designed for linear systems as the simple cross-correlation method or the Granger causality, while others are suitable for non-linear interactions, such as the Convergent Cross Mapping method. Here, these methods are applied in order to draw up causal maps and compare short-term (up to 2 days) interactions in the Lhomme Karst System in Belgium. The Lhomme Karst System has been monitored since 2013 and many time series are available: meteorological data, soil moisture, drip discharges in the caves, piezometric levels, and local gravimetric time series. In addition, dye tracing experiments revealing connections and characteristic transfer times were conducted. The different causal maps are compared and causal interactions are appreciated through the current knowledge of the system and discussed in relation to the question: can we infer true hydrological connections and processes from the empirical determination of causal relationships between hydrological time series?
Congratulations to Amaël on his PhD degree obtained on 6 September!
The underground work of the KARAG team was presented on Belgium national televion (La Une) 28th of September at 12:40 PM! The small documentary focuses on the Rochefort cave laboratory and the measurements made in the vadose zone of the Givetian karst aquifer (click on the picture to watch the video).
Don’t miss this opportunity to discover our work 😉
Amaël Poulain presented his PhD thesis last week, in the framework of the KARAG project.
Follow this link to see the Prezi presentation : https://prezi.com/view/KK6w99xScFwkSzY8t7ln/
The thesis file may be downloaded at the following URL : https://documents.unamur.be/index.php/s/NyWlXUuYjK8exeW
Remember that Arnaud Watlet will also present his PhD thesis in Geophysics this year. Stay tuned for more information !
The Grottes de Han company has just installed a board to evidence the scientific activities of the lab
The data from the iGrav019 superconducting of Rochefort are now available online on the IRIS database (www.iris.edu). The time series are available under the SG.RCHS code.
The superconducting gravimeters excel at measuring the low-frequency waves emitted by major earthquakes.
See former post: http://www.karag.be/en/the-earth-is-still-ringing/
On the 6th of September 2017, Amaël Poulain will present his PhD thesis in the framework of the KARAG project. He will present 4 years of research about phreatic and vadose zones hydrogeology in karst aquifers and specifically a focus on the Lomme Karst System in Rochefort.
The thesis jury :
- Prof. Vincent Hallet (University oy Namur – Promoter)
- Prof. Johan Yans (University of Namur – President)
- Prof. Olivier Kaufmann (University of Mons)
- Prof. Marnik Vanclooster (Catholic University of Louvain)
- Prof. Pascal Goderniaux (University of Mons)
- Prof. Hervé Jourde (University of Montpellier – France)
The defense will start at 4PM in the M01 room (Faculty of Medicine – University of Namur). Access via Place du Palais de justice (lien Street View)
Abstract in french
The defense is public
Arnaud Watlet, one of our PhD students, has recently received the renowned Ernest du Bois Doctorate Award from the King Baudouin Foundation. The Ernest du Bois PhD prize aims to encourage young engineers conducting research in the field of water to focus on the issues of water availability for human populations around the world, protection of resources, pollution problems, and treatment techniques. This therefore perfectly corresponds to the KARAG project goals. The 20.000€ PhD Prize will considerably help A. Watlet to finalize its PhD thesis. Good luck to him!
02 January 2017:
A new Ph.D. student joints the KARAG team: Ir. Damien Delforge. The supervisors are Prof. Marnik Vanclooster (UCL, Earth and Life Institute/Environmental Sciences (ELI-e)) and Dr. Michel Van Camp (Royal Observatory of Belgium, Seismology-Gravimetry). This project is supported by the Fund for Scientific Research FNRS-FRIA.
The objective of the project is to improve gravity signal processing and karst systems modelling through the use of novel data mining techniques, derived from chaos theory, known as convergent cross mapping (CCM). CCM is a statistical method to elucidate cause-effect relationships between multiple time series that seek to resolve the problem that correlation does not imply causation. Regarding the uniqueness and the complex non-linear dynamics of karst systems, the main underlying assumptions are the following: (i) data-driven tools derived from the chaos theory and CCM appears to be relevant to investigate both the relationship between the gravimetric signal and the monitored environmental variables and the hydrological behaviour of a karst system; (ii) using CCM analysis, a framework can be built to assess the realism of a hydrological model structure in complex hydrologic systems such as karst systems; and (iii) the resulting model structure can lead to a better prediction in water storage changes (WSC) and therefore to a better interpretation of the gravity signal.
Based on this assumptions, this research aims at applying advanced causal analysis to characterize the relationships between gravity signals and the locally monitored environmental variables and to assess what are the dominant hydrological processes involved in a complex Lomme karst system.