Présentations Colloques

Oral Presentation
8.05
Session 8.05: Karst aquifers
Chedeville Stéphane
Multiscale karst sediment dynamic study- from the flood scale to the pluriannual scale Example with Bruisseresse spring, Normandy, France
Karstification is an azonal process occuring in different kind of bioclimatic settings and weatherable rocks. Karst processes create voids both on the surface (e.g., sinkhole) and within the bedrock (i.e., karstic conduit) in relation to chemical weathering and or mechanical erosion. Depending on the geomorphological setting, hydrodynamics and sediment sources, karst systems may be filled with (i) allochtonous material (supply of sediments by mechanical erosion), (ii) autochthonous deposits (insoluble residues from chemical weathering of the bedrock) or (iii), a mixture of both.**Usually, turbidity is the parameter used to study sediment transport in karst. Few or no work has been published on sediment dynamics using an approach coupling in situ monitoring of hydrological variables (flow, rainfall, ...) and sedimentary (altimeter mesurments, sediment cores) to identify main sediment transport or deposit controls in a karst network.****Acquisition of high-frequency hydro-meteorological data coupled with sedimentary signal measurments (turbidity, sediment cores and records of high-frequency altimetric data of a sedimentation area) allows to characterize sediment transfert controls from flood scale to annual scale. Sedimentary organisation and nature can be explained by the intensity of turbid flood events.**The use of signal analysis tools on long times series allows to understand sediment transport and deposition controls at the pluriannual scale. In detail, wavelet analysis of rainfalls, piezometric level and turbidity, as well as sediment archive, all show common modes of variability. A common spectral composition emphasizes the climate control. The comparison of the wavelet spectra with the North Atlantic Oscillation (NAO) spectrum clearly highlights the control of the latter on hydro-meteorological variables at the regional level. **
France