Hydrogeological Characterization of the Upper Drâa Catchment: Morocco

Sébastien Cappy, B Reichert, Zweiter Gutachter, B Diekkrüger
2006 unpublished
I -ABSTRACT The Drâa valley located in the south of Morocco is a typical semi-arid area facing water scarcity problems. This Ph.D. thesis is part of the interdisciplinary research project IMPETUS (integrated approach to the efficient management of scarce freshwater resources in West Africa), which is a project of the universities of Bonn and Cologne (Germany). The IMPETUS project is part of the GLOWA program (global change of the water cycle) funded by the German BMBF (Federal Ministry of
more » ... l Ministry of Education and Research) and focuses on the development of integrated strategies for an efficient and sustainable freshwater resource management. Groundwater is one of the primordial components of the hydrological cycle. Therefore the aim of this work is to characterize and quantify the hydrogeological properties of the aquifer system prevailing in the Upper Drâa catchment down to the Mansour Eddahbi reservoir (15,200 km 2 ). ABSTRACT -II - the basin is not significant. Additionally, the steady state simulation with MODFLOW of the alluvial aquifer system of the Basin of Ouarzazate proves an efficient recharge of the alluvial aquifers by river bed infiltration over the whole model domain averaging 85 % of the total recharge (~ 27 Mio m³/a). Only the remaining 15% of the total recharge are provided by the infiltration of precipitation. The hydrochemical characterization of the groundwater of local aquifers developed in the Mio-Pliocene multi-layer aquifer in the Basin of Ouarzazate shows various origins according to their hydraulic connections with the overlying alluvial aquifers. But, the recharge of those small deeper aquifers is not effective as proved by groundwater ages older than 50 years. The confined aquifer of Infracenomanian in the Tikirt area shows a heterogeneous character in regard to the groundwater chemistry due to some local leakage from the alluvial aquifer of the Imini Wadi. This confined aquifer is mainly recharged in the High Atlas as confirmed by the isotopic composition. Due to the fact that the volume of this confined aquifer is small and that the tritium ages reveal groundwater older than 50 years, the productivity of this aquifer is not suitable for exploitation. Precambrian rocks in the Skoura Mole located in the northern part of the basin embody old groundwater dated between 500 to 2,800 years with the carbon-14 method. The unproductive character of those fissured rocks is explained by a low rate of infiltration and a low permeability confirming the aquitard role of these formations. The groundwater in the Upper Drâa catchment presents a high variability in quality, which often do not meet the international standards for drinking water due to a high mineralization. This high mineralization results only from the leaching of evaporitic minerals (gypsum, halite and sylvite) naturally present in the various geological formations (Trias, Cretaceous, Eocene and Mio-Pliocene). This is confirmed by the isotopic signatures of the groundwater, which do not show any evaporation effect. In the High Atlas, chemical processes such as dedolomitization associated with the leaching of gypsum influence the groundwater chemistry. In the Basin of Ouarzazate, the exhalation of CO 2 along faults in the Precambrian rocks has also local impact on the composition of the groundwater. This study provides specific hydrogeological data for the interdisciplinary research. Thus, it supports tasks such as hydrological modelling, anthropological investigations, development of an integrated information system, and the future implementation of Decision Support Systems in the IMPETUS project. KURZFASSUNG -III -KURZFASSUNG Das Drâa Tal im Süden Marokkos ist ein typisch semi-arides Gebiet, in dem die Wasserknappheitsproblematik die Motivation der vorliegenden Forschungsarbeit liefert. Diese Dissertation ist eingebettet in das interdisziplinäre Forschungsprojekt IMPETUS (Integratives Management-Projekt für einen Effizienten und Tragfähigen Umgang mit Süßwasser in Westafrika), das gemeinsam von den Universitäten Bonn und Köln durchgeführt wird. Das IMPETUS Projekt ist Teil des GLOWA (Globaler Wandel des Wasserkreislauf) Schwerpunktprogramms der Bundesrepublik Deutschland mit dem Forschungsziel der Entwicklung integrierter Strategien für eine nachhaltige und vorausschauende Bewirtschaftung von Wasser und Gewässern im regionalen Maßstab. Grundwasser ist einer der bedeutsamsten Bestandteile des hydrologischen Kreislaufes. Daher ist es ein Ziel dieser Arbeit die hydrogeologischen Eigenschaften der vom oberen Drâa Einzugsgebiet bis hinunter zum Mansour Eddahbi Stausee (15200 km 2 ) vorkommenden Aquifere zu charakterisieren und zu quantifizieren. ACKNOWLEDGMENTS VII ACKNOWLEDGMENTS