Présentations Colloques

Oral Presentation
2.01
Session 2.01: Groundwater in semiarid regions – a long-term view on changes in aquifer balances. Hydrogeology in developing countries.
El Mandour Abdennabi
Hydrogeological and geochemical dynamics of the Western Haouz Aquifers.Tensift Basin (Western Morocco)
The compilation of geological, hydrogeological and geophysical data reveal that the Western Haouz plain, located near Marrakech, is divided into two morphostructural synclinal units separated by the horsts of Marmouta. In the southern part, the Mejjate Syncline is very subsiding including a number of geological formations ranging from Paleozoic to Quaternary. However, in the northern part, the syncline is less developed and is constituted only by Mio-Pliocene and Quaternary. **From the hydrogeological map, the geometry of the aquifers and groundwater circulation are well controlled by subsurface geology. Two aquifers can be recognized in the southern part of the plain between the Marmouta Anticline and the foothills of the High Atlas Range- a thick Quaternary and Mio-Pliocene phreatic aquifer and a deep confined aquifer located in Turonian limestone. This latter is recharged at the level of the High Atlas Range, showing a karstic morphology and great cliff of the Turonian limestone slab. The relationship between Oxygen-18 and deuterium shows a good correlation (R2 = 0,901) and all samples are close to Global Meteoric Water Line. The isotopic signatures indicate that the aquifers are recharged from elevated altitudes ranging from 980 to 2200 m a.s.l. which correspond to the High Atlas Mountains. **Age dating of groundwater using C14 show significant differences among waters from Western Haouz aquifers+ The oldest waters (about 5000 years old) appear at the almost forty Khettaras(underground water galleries) distributed along the Assoufid Fault, the Abainou Spring and the well 397 52 exploiting the deep Turonian aquifer. This can indicate that the recharge came from distant area (e.g. High Atlas Mountains) with a relatively long residence time. In opposite way, groundwater from phreatic aquifers is much younger indicating the dominance of the recent recharge. These results can help the decision makers to more improve the water resources management in this region showing serious shortage water.**
Morocco