Dynamiques d’infiltration karstique et spatialisation de la vidange aquifère en milieu crayeux : exemple du bassin de la vesle en amont de Reims (Champagne Sèche/France)

Karstic infiltration dynamics and spatialisation of chalk aquifer drain: Example of the upper Vesle basin (Dry Champagne, France)

EA 3795 G.E.G.E.N.A. (Groupe d’Étude sur les Géomatériaux et les Environnements Naturels et Anthropiques), UFR Lettres et Sciences Humaines, 57 rue Pierre Taittinger, 51096 Reims Cedex

Auteurs de correspondance : alain.devos@univ-reims.fr olivier.lejeune3@libertysurf.fr edith.chopin@univ-reims.fr

Reçu : 10 Mai 2006
Accepté : 22 Janvier 2007

Résumé

Dans le cadre d’un programme de recherche sur les pollutions diffuses en milieu rural (AQUAL) et du bassin Vesle, bassin atelier du Piren-Seine, le GEGENA a mis en évidence le rôle des fronts de karstification sur la vulnérabilité des aquifères à la pollution hydrique en milieux crayeux. Les méthodes des profils hydrologiques et de la cartographie des rendements par bassins élémentaires permettent de montrer l’hétérogénéité spatiale des écoulements en période d’étiage inhérent à l’anisotropie de l’aquifère de la craie au niveau du front de karstification. Ces méthodes constituent une nouvelle approche de la vidange aquifère et un exemple original en Champagne Sèche où le comportement hydrodynamique des cours d’eau indigènes à la craie est habituellement homogène.

Abstract

As part of a research program on diffuse pollution in rural environment, the role of karstification fronts on chalk aquifer suceptibility to water pollution was established. This front, which is part of the Ile de France cuesta system (Montagne de Reims), overlooks the central part of the Vesle’s left bank. The karst was located at different altitudes and could be found from the Cretaceous chalk to the Thanetian sandstones. Diffuse infiltrations, localised and concentrated losses, and epikarst and chalk aquifer draining fed the saturated zone. The Vesle draining the chalk aquifer, the study of its flow helped to determine the aquifer hydrodynamical behaviour. However, lack of direct measurements prevented to establish the karst influence. Therefore, flow and other physical and chemical parameters were measured during low-water season to determine aquifer drain spatial distribution. These measurements combined with hydrological profiles and unit basin outputs mapping showed flow spatial heterogeneity during low-water season, which was due to chalk aquifer anisotropy at karstification front level. The Vesle has a wide variety of flow along its course. Losses and dry-ups due to infiltration occured upstream, while elevated hydrological outputs characterised its central part where the stream cuts through the saturated zone, which was fed y karstic infiltration. Each slope change on hydrological profiles represented flow changes characterising the location of the stream using Mangin karstic aquifer model. Temperature and conductivity profiles allowed better interpretation of hydrological profiles. Specific flow rate mapping showed that spatial heterogeneity could be linked to basin geomorphological differences. Base levels were determined. They controlled underground water mass transfers between basins located at different altitudes. Study of piezometric highs, when compared to aquifer supply, showed that these transfers could occur in low-water seasons. These methods represent a new approach for aquifer drain study. They provided unusual results for Dry Champagne where streams hydrodynamical behaviours are usually homogeneous. They allowed extrapolation of flow rates measured at hydrometric stations. However, they must be coupled to physical and chemical measurements at some outfalls in order to determine the influence of each of Mangin model zones on the flow.