Différence entre vitesses hydrauliques et vitesses radiométriques des eaux d'un réservoir profond : proposition d'explication pour l'aquifère miocène du bassin de Valréas (Sud-Est de la France)

Isotopic measurements on groundwaters have been carried out on the Valréas Miocene aquifer. A strong isotopic contrast exists between the recharge area and the confined aquifer, suggesting limited hydraulic communications between these two portions. In the confined aquifer, radiometric velocities are 10 to 12 times smaller (0.2–0.4 m·yr⁻¹) than hydraulic velocities (≈2.2 m·yr⁻¹). The overexploitation of the resource can have entailed a major change in the hydraulic gradients leading to a perturbation of the system and a gradual attenuation of the hydraulic barrier, which may threaten the sustainability and the quality of the resource.