Présentations Colloques

    Session 8.05: Karst aquifers
    Miche (orateur)
    Geochemical and isotopical analyzes of groundwater in a karst system - the case study of Fez-Meknès basin ( Morocco)
    The karst Middle Atlas Causses reservoir mainly composed of Liasic dolomitic limestone, overlying Triassic clays, evaporates and basalts, is the main drinking water supply in Fez-Meknès region (Saïs Basin). Because of the increase in population, the number of drilling for irrigation of agricultural land and some longer drought periods in recent years, the issue of sustainable groundwater management arises. Recent analyzes have shown a decline in its chemical quality and punctually some turbidity problems.**In order to enhance understanding of this hydrosystem and the interactions between the different main springs of Liasic and Triassic origin, and their connections to the major spring (Bittit), an integrated hydrogeochemical study was conducted coupled to isotopic analyzes of delta O-18, delta+D and Radon-222. Four surveys were performed in fall and spring seasons (2009-2011).**Water geochemistry shows two kinds of water- a major Liasic origin along the transition between the Causses and the Saïs basin, and a major Triassic origin for El Mir, Sbaa, and Maarouf springs located at the southern border of Saïs basin extremities. Deuterium excess highlights a local recharge while delta O-18 versus delta D characterize two aquifers with different evaporations. Radon-222, underlined the existence of areas of rapid exchange between waters of Liasic aquifer characterized by low Radon activity (3500 Bq m3) and waters in contact with Triassic aquitard characterized by a high Radon activity (> 15000 Bq m3). The transit time is less than two weeks to surface. The waters renewal is only conducted by major rainfalls. Four recharge zones of different altitudes have been found and two main mixing zones (limits of Saïs Basin).**


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