Reference, completed project

Cenari-O: study of exchanges between aquifers and rivers

In 2020 BRGM, the University of Orléans Polytech and ISTO set up a collaborative research project named Cenari-O with the support of the Centre-Val de Loire Regional authorities to improve the methods for characterising exchange zones between aquifers and rivers in karstic regions.

11 October 2024

The river Loiret that gives its name to the department is a resurgence of the Loire. The water seeps into the ground and passes through the Beauce limestone aquifer, emerging in numerous resurgences, the best known of which is the Bouillon. But this is not the only aquifer that interacts with the river. Among the various underground interactions, the role of alluvial aquifers is less well known. BRGM carried out analyses at St-Pryvé-Saint-Mesmin, downstream from the Loiret, to study these relationships. A floating drone was used for these studies.

Location of low-lying areas in the Tacreniers basin, March 2022.

The need

The aims of the Cenari-O project, implemented between 2020 and 2023, were to develop methods based on multiple criteria to characterise aquifer-river exchanges in detail in the Loire-Loiret river system. These exchanges are key factors for understanding this system of watercourses as a whole.

The results

In order to develop an innovative, integrated approach to the multi-scale description of aquifer-river exchanges, several scientific methods were combined: remote sensing, piezometry, geochemical longitudinal profiling, artificial and natural water tracing and test pumping. More specifically, BRGM was responsible for developing an information system to optimise the use of the acquired data. On the basis of previous work carried out on a national scale, the concepts of a surface water-groundwater relationship database were laid. This has no international equivalent. However, specifically translating these concepts into a database required a great deal of thought and adaptation.

The complementary nature of the results (spatial and temporal variability of the water chemistry, karstic morphology of rivers and hydrodynamic properties of alluvial deposits) from the different methods used has provided an understanding of the exchanges (and mixtures) in all their spatial complexity (from source to confluence) and temporal complexity (during both flood and low-water periods). The low-lying areas are covered with aquatic vegetation, which may have originated by chance, anchoring itself in the rock or resulting from an input of nutrients from emissive low-lying areas. However, the Loiret consistently appears to be responsible for variations in the aquifer.

Acquisition of physical and chemical data and creation of longitudinal profiles of the Loiret, May 2021.

Using the results

This work yielded important results in terms of water resource management, since it showed that the water stored in the aquifer is controlled by the water level in the Loiret, which is itself very strongly influenced by the flow of the Loire. Additional information obtained on the morphology of the Loiret river bed and the chemistry of its water also point to the possible presence of springs that have not yet been identified.

The data acquired under the Cenari-O project, together with historical data relating to aquifer-river relationships in the Val d'Orléans, have been integrated into a database dedicated to surface water-aquifer relationships and transposed into a web mapping service accessible to the various stakeholders in the area. For example, they will provide input for the Centre-Val de Loire Regional Authorities as part of a Hydrology, Environment, Use and Climate (HMUC) analysis and will contribute to the operational water level management procedure of the Association Syndicale de la Rivière du Loiret (ASRL).