All posts by Michel Van Camp

EGU meeting: about the non-linear interactions in a karst system

Hydrological connectivity from causal analysis of time series in the Lhomme Karst System, Belgium.
Damien Delforge, Michel Van Camp, Marnik Vanclooster, Vincent Hallet, Olivier Kaufmann, Amaël Poulain, and Arnaud Watlet

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?

9 November: PhD thesis of Arnaud Watlet

On 9 November 2017, Arnaud Watlet will defend his PhD thesis dedicated to the de FNRS KARAG project of Rochefort.
Arnaud will present 4 years of results on the saturated and non-saturated zones of the karst aquifers.
The jury will be composed of the following members:
Supervisors:
Prof. Olivier Kaufman, Université de Mons
Dr. Michel Van Camp, Observatoire Royal de Belgique
Jury:
Pr Jean-Marc Baele, Université de Mons
Pr Thierry Camelbeeck, Observatoire Royal de Belgique
Pr Konstantinos Chalikakis, Université d’Avignon
Pr Cédric Champollion, Université de Montpellier
Pr Olivier Francis, Université de Luxembourg
Pr Pascal Goderniaux, Université de Mons
The dissertation defense will take place at 15 pm at U. Mons, Salle Académique, Bd Dolez, 31 (2e étage), 7000 Mons. The defense is public.
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A new Ph.D. student for KARAG

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.

KARAG at the AGU Fall meeting 2016, San Francisco

  • Watlet, A., Kaufmann, O., Van Camp M., Triantafyllou, A., Fadel Cisse, M., Quinif, Y., P. Meldrum, P.B. Wilkinson, J.E. Chambers, Electrical Resistivity Tomography monitoring reveals groundwater storage in a karst vadose zone, AGU Fall meeting (poster), 12-16 Dec 2016.
  • Van Camp M., Watlet, A., Poulain, A., Hallet, V., Rochez, G., Quinif, Y., Meus, P., Kaufmann, O., Francis O., Continuous gravimetric monitoring as an integrative tool for exploring hydrological processes in the Lomme Karst System (Belgium), AGU Fall meeting (poster), 12-16 Dec 2016.

Eurokarst 2016

Arnaud Watlet proudly presents the latest results from the Rochefort Cave Laboratory at the 2016 Eurokarst meeting, Neuchâtel (CH), September 5. (picture: (c) Eurokarst 2016)
In particular, he comments on the gravity measurements, electric tomography profiles and hydrogeological investigations performed by the Royal Observatory of Belgium, U. Mons and U. Namur.

Arnaud Watlet presenting on September 5 at the Eurokarst 2016 workshop. Picture (c) Eurokarst 2016
Arnaud Watlet presenting on September 5 at the Eurokarst 2016 workshop. Picture (c) Eurokarst 2016

Abstract:

Present knowledge of karst systems has evidenced the importance of the vadose zone on the water dynamics. Temporary perched aquifers can appear in the subsurface, especially in the epikarst layer, due to changes of weather conditions, reduced evapotranspiration and the vertical gradients of porosity and permeability. Seasonal water variations in the infiltration zone of a karst system should then be observable with geophysical techniques. Monitoring these variations may help separate the hydrological signature of the vadose zone from that of the saturated zone.

Although many difficulties are usually encountered when studying karst environments due to their heterogeneities, cave systems offer an outstanding opportunity to investigate vadose zone from the inside. We present results covering two years of hydrogeological and geophysical monitoring at the Rochefort Cave Laboratory (RCL), located in the Variscan fold-and-thrust belt (Belgium), a region that shows many karstic networks within Devonian limestone units.

Hydrogeological data such as flows and levels monitoring or tracer tests performed in both vadose and saturated zones bring valuable information on the hydrological context of the studied area. Combining those results with geophysical measurements allows validating and imaging them with more integrative techniques.

A microgravimetric monitoring involves a superconducting gravimeter continuously measuring at the surface of the RCL. Early in 2015, a second relative gravimeter was installed in the underlying cave system located 35 meters below the surface. This set up allows highlighting vadose gravity changes. These relative measurements are calibrated using an absolute gravimeter. 12 additional stations (7 at the surface, 5 in the cave) are monitored on a monthly basis by a spring gravimeter.

To complete these gravimetric measurements, the site has been equipped with a permanent Electrical Resistivity Tomography (ERT) monitoring system comprising an uncommon array of surface, borehole and cave electrodes. Although such an unconventional ERT setup is challenging in terms of data processing and interpretation, it provides valuable data for inferring variations of the vadose zone saturation rate