Determination of the preferential flows in a karstic area (Tafrata, Morocco): Contribution of satellite SAR ERS-1 and Landsat ETM+ data and of the geophysical prospection

In spite of the great number of water wells and drillings carried out in various karstic areas of Morocco, many unknown factors still remain concerning criteria for installing such works and for the final costs. To optimize future drilling campaigns, a multi-criteria method of prospecting was adopted in the karstic area of north-eastern Morocco. It is presented according to three axes: 1) the determination of hydrogeologic lineaments based on the analysis and interpretation of SAR ERS-1 and Landsat ETM+ images; 2) the application of electrical resistivity methods by (a) vertical electric soundings (VES) for the determination of the thicknesses of weathered layers and of fractures, and by (b) electric resistivity profiling for the determination of the exact location of hydrogeological lineament zones; and finally, 3) the application of Magnetic Resonance Sounding (MRS) for the verification of the presence of water. The various results of mechanical drilling carried out following this prospecting campaign show a very satisfactory rate of success.Original Abstract: Malgre le grand nombre de puits et forages d'eau realises dans les differentes regions karstiques du Maroc, de nombreux inconnus subsistent encore concernant les criteres d'implantation et le cout final des ouvrages. Afin d'optimiser les campagnes de forage a venir, une methodologie de prospection multicritere a ete adoptee dans la region karstique nord orientale du Maroc. Elle s'articule selon trois axes, a savoir : 1) determination des lineaments hydrogeologiques a partir du traitement et interpretation des images satellitaires radar SAR ERS-1 et Landsat ETM+; 2) application de la geophysique electrique par (a) sondages electriques pour la determination des epaisseurs des niveaux d'alteration et de fracturation et par (b) trainees electriques pour la localisation precise de la zone de passage des lineaments hydrogeologiques, et finalement 3) application des techniques de Sondage par Resonance Magnetique (SRM) pour la verification de la presence d'eau. Les differents resultats de sondages mecaniques realises a la suite de cette campagne de prospection montrent un taux de reussite tres satisfaisant.