A new simple statistical method for the unsupervised clustering of the hydrodynamic behavior at different boreholes: analysis of the obtained clusters in relation to geological knowledge

Karst aquifers are complex and related to numerous management issues, especially concerning flood risks or the availability of water resource. Given the stakes involved, it is necessary to obtain the best possible knowledge of the hydrodynamic behavior of these aquifers. In this context, this article presents two methodological advances concerning the hydrodynamic behavior of the water level within a borehole, based on the analysis of cumulative frequency curve of groundwater levels. First of all, a new simple semi-automated unsupervised method of borehole clustering, and second, an interpretation table of the hydrodynamic properties of these boreholes are proposed. These two advances are applied to the Cadarache site of the French Alternative Energies and Atomic Energy Commission (CEA) in south-eastern France, which is prone to rapid groundwater floods. This study, conducted on 75 boreholes, allows identifying several clusters of boreholes. Three of them appear to be representative of specific areas and show a relevant relation between each cluster and its geological structure. A punctual validation of the proposed approach is made on the cores available for a specific drilling. Thereby, the obtained clusters on the Cadarache site are consistent with the role of lineaments, NW–SE and NE–SW oriented, previously identified by regional tectonic or structural studies as preferential groundwater flow paths.