ESTIMATION OF THE WATER-BALANCE OF ALLUVIAL AQUIFERS IN REGION OF HIGH ISOTOPIC CONTRAST - AN EXAMPLE FROM SOUTHEASTERN FRANCE

The much contrasted orographic and climatic characters of southeastern France serve to establish a hydrological balance of the porous aquife rs in the region. Comparing a regional average gradient of O-18 conten t versus elevation, which was calculated on low-water period karst wat ers content, with a -10.5 parts per thousand average delta of Alpine r ivers, an estimate of the percentages brought to these aquifers is pro posed under the form of an abacus. It appears that the main groundwate rs of the Var, the Durance and the Rhone are fed by an average of 20-3 0% of Provencal underground contribution, and 70-80% shallow contribut ion from the Alpine rivers. These figures reveal that local supplies r ange between 25 and 10% of the average yearly discharge flowing in the porous and shallow aquifers. (C) 1998 Elsevier Science B.V. All right s reserved.