Application of Statistical Approaches to Piezometry to Improve the Understanding of the Karst Aquifer Hydrodynamic Behaviours at the Cadarache CEA Centre (France)

Abstract

Located in the French Mediterranean region, the French Alternative Energies and Atomic Energy Commission (CEA) Cadarache Centre is subject to significant rainfall events which can lead to groundwater floods with rapid kinetics and high amplitude. This study aims to improve the understanding of the aquifer’s heterogeneity and piezometric responses at the scale of the Cadarache centre (900 ha) in order to better apprehend the groundwater floods. The deployed method consists in: (i) taking an inventory of reliable data; (ii) conducing a preliminary study of the spatial variability of rainfall at the centre scale with the method of double-mass curves and the comparison of the rainfall amounts of the different stations; and (iii) conducting a comprehensive statistical study of piezometric data (graphs of sorted piezometric data for three different flood events, definition of an original clustering method using an automatic feature detection). The results are of two kinds: (i) several clusters were identified; three appeared to be representative of specific areas; (ii) for each specific area, piezometers were linked with different plurikilometric NW–SE and NE–SW lineaments identified by previous bibliographic studies. This extensive study on nearly 80 piezometers has thus allowed to define a method of automatic feature extraction of the sorted groundwater levels, and to establish a clustering of piezometers according to their statistical behaviour. Even if the statistical “black box” method was applied without any prerequisite on the location of the boreholes, it allowed establishing a very relevant relation between sorted water height and geological structure constraining the flows.