Pierre Chauve

Turbidity mechanism of water from a karstic spring: example of the Ain Asserdoune spring (Beni Mellal Atlas, Morocco)

To understand the turbidity phenomenon that occurs during floodwater periods in the water of some karstic aquifers, a study was carried out on the Ain Asserdoune spring in the Beni Mellal Atlas. The application of correlation and spectral analyses to turbidity, rainfall and discharge rate with a daily sampling for three hydrological cycles showed that the Ain Asserdoune turbidity corresponded to the beginning of the unclogging of the karstic conduits affecting the saturated area. The appearance of turbidity during the increased flow rate was due to instability in the chaotic regime that was represented by suspended matter, which was evacuated independent of the discharge rate. This phenomenon only appears in polyphase karst, which is frequently found, and thus must be taken into account when karstic water is used for drinking as it could become unfit for human consumption.

Utilisation du rapport Br/Cl pour déterminer l'origine de la salinité des eaux souterraines: exemple de la plaine du Souss (Maroc)

Abstract The use of bromide anion contents is an essential complement to chloride measurements in order to explain the salinity anomalies in groundwaters. Thanks to the relationship Br = ƒCl) and to the molar ratio Br/Cl, it allows marine influence areas (the Ocean, precipitation, aerosols, sedimentary paleosalinity) to be distinguished from evaporitic or anthropogenic influence areas, which are impoverished in Br as opposed to the oceanic domain. Applied to the Souss alluvial plain, and thanks to this methodology, we can interpret phenomena which are responsible for conductivity anomalies in groundwaters: present salt encroachment, sedimentary paleosalinity or wastewaters downstream; evaporites, recycling of irrigation waters in the mean Souss.

Apports des méthodes hydrodynamiques à l’étude du fonctionnement des aquifères karstiques de l’Atlas de Beni-Mellal (Maroc)

ResumeLe massif karstique de Beni-Mellal, dans le Haut Atlas (Maroc), est constitue essentiellement par des calcaires dolomitiques du Lias qui presentent en surface des figures de dissolution spectaculaires. Le massif est situe entre 500 m et 2 400 m d’altitude et alimente plusieurs sources dont la plus importante est celle d’Ain Asserdoune. La quasi-totalite des sources emergent au niveau des contacts chevauchants qui limitent le Jurassique calcaire des formations tertiaires sousjacentes du piemont. L’etude des debits classes et du tarissement ainsi que l’analyse correlatoire et spectrale des chroniques pluies – debits du systeme karstique draine par la source d’Ain Asserdoune permettent de caracteriser cet aquifere. Il s’agit d’un aquifere inertiel qui assure le flot de base. Cet aquifere est caracterise par l’existence de reserves dynamiques importantes. Il est influence par un karst superficiel fonctionnant en periode de hautes eaux ainsi que par des apports lateraux provenant des compartiments voisin...