The gorges of the river cèze - development of a chronological model based on geological data: implications for hydrogeology

The content presented in this article is an integral part of the research work carried out with the aim of characterizing, evaluating and modeling theexchanges between the Cèze River and its karstic system that it crosses in the middle part of the valley [Chapuis, 2017]. This paper presents the Cèze watershed with a lithological description of the terrain to lead to a chronological model in order to better understand the implication on the flow of water.Geological analysis reveals a significant diversity of watershed-wide formations in its downstream portion, leading to the identification of shifting hydrological boundaries over time. Through the threedimensional representation of the study area as a chronological model, there is a structural evolution of the lower Cretaceous limestone from its setting up to the orogenic phases of the Miocene. The analysis of this complex geology, combined with successive tectonic deformations, provides a better understanding of the current arrangement of karst aquifers in the studied area. From the western edge of the Alès graben to the upper Cretaceous formations east of the plateau of Méjannes-le-Clap, geological formations capable of infiltrating surface waters are emerging. These infiltrated waters can be directly connected to the exutory of karst springs by the karstic network itself. However, it is possible that these springs do not return all of the infiltrated waters. This groundwater could therefore have flow beyond the boundaries of the study area and reaches the eastern Rhone Valley.