Groundwater floods: linking the hydrodynamic characterisation of the karst aquifer at the Cadarache CEA centre (South of France) to the karst structure using statistical analysis of temperature.

Karst environments can be subject to rising water tables leading to rapid kinetic floods (a few hours) of great amplitude (about tens of meters) due to heavy rainfall. The Cadarache centre of the French Alternative Energies & Atomic Energy Commission (CEA), located in the French Mediterranean region (Bouches-du-Rhône), is subject to this type of underground flooding. For example, in November 2011, a cumulative rainfall of 225 mm in 72 hours was recorded at the centre, leading the Cretaceous limestone water table to a rise of nearly 40m, locally. The Cadarache centre of 1,600 hectares, has an exceptional hydrogeological monitoring network of 8 rain gauges and more than 400 piezometers, including 230 equipped with pressure/temperature sensors (115 measuring the Cretaceous aquifer). This dense monitoring network has enabled the acquisition of a large database (rainfall, water-level and temperature) over more than 15 years.

The goal of this study is to improve the understanding of the Cretaceous karst aquifer hydrodynamic behaviour by analysing temperature data. This would allow an improvement of groundwater floods prediction on the site. This variable is little studied but it can provide interesting information on the aquifer hydrodynamic response and specifically the role of karst structures on pressure and mass transfers at kilometer scale.

For this purpose, statistical analyses were conducted on measured temperature data in various piezometers defined as representative of the aquifer. Sorted temperature data and correlations analyses were made for different types of rainy events. This study aims to: i. Identify potential flow dynamics (deep or superficial flows), ii. Compare the temperature signal with those of rainfall and water levels.