Surface water and groundwater are two interrelated components, where the influence of one automatically affects the quantity and quality of the other. These exchange flows are robustly influenced by some mechanisms such as permeability, lithological nature of the soil, landscape, in addition to the difference between the hydrometric height of the river and the piezometric level of groundwater. The study area of Bou Ahmed plain is vulnerable to intensive pumping mainly in the coastal fringe. The increase in water demand, due to demographic development, is accompanied by pressure on groundwater abstraction which causes significant drops of the groundwater level. The main objectives of this study are to develop Geographic Information System database and mathematical models to analyze spatial and temporal hydrogeological characteristics and hydrodynamic functioning of groundwater flow of the Bou Ahmed aquifer. The present work exhibits the characteristics of the river-groundwater exchanges in an alluvial plain. Therefore, we quantified the flows exchanged between a river and its groundwater using GIS tools along with measurements of parameters obtained by the differential gauging, which was carried out in the field, and hydrogeological boreholes data. These quantified flows, moreover, enabled us to eventually estimate the uncertainties related to the use of the GIS method. These results will also be used to support a set of groundwater simulations based on MODFLOW code in the Bou Ahmad aquifer. These models also associated with develop Geographic Information System will help to better plan, manage and control the groundwater resources of this aquifer.
The Bou Ahmed plain, which is part of the internal area of the Rif, is located along the Mediterranean coast, 30 kilometers of Oued Laou town. This basin is made up by a quaternary filling mainly formed by detrital fluvial facies, channeled conglomerates surmounted by fluvial sand interlayered with pebbles; these facies can be new potential aquifers formations areas. Therefore, the main goal of this study is to build a lithostratigraphic three dimensional model to identify the hydrogeological units and the reservoir geometry of the Bou Ahmed plain. In order to achieve this goal, we have created a database made up by Vertical Electrical Sounding surveys and drilling data integrated into a Geographic Information System. This database allowed us to establish a three-dimensional model of the bottom, geoelectric cross-sections, isopach and isoresistivity maps of new potential aquifers units. This approach allowed us to explain the modalities of deposition for the quaternary deposits of the Bou Ahmed plain and to identify potential hydrogeological reservoirs. These results will also be used to develop a hydrodynamic model based on MODFLOW code in the Bou Ahmed aquifer.
Résumé :Le bassin côtier du Rharb s'étend entre la ville Rabat et la ride de Lalla Zahra sur une distance de 100 km. Il est limité au Nord et au Sud le domaine rifain instable et au NE par le domaine mésétien "relativement stable". Les dépôts du plio-quaternaire sont, pour l'essentiel, fluviatiles, estuariens et alluviaux. Le présent travail a pour objectif de reconstituer, moyennant les outils géophysiques, leur évolution spatiotemporelle et les critères qui augmentent leur vulnérabilité. Selon le modèle établi, la géométrie de ces dépôts se présente en deux configurations, la première sous la dépendance du soulèvement de la méséta, la seconde sous celle de l'avancement, depuis le Miocène moyen, des rides prérifaines. Ces dépôts sont représentés par trois niveaux géoélectriques très discontinus au Nord alors qu'ils sont organisés en électroséquences au Sud. Le croisement des données géophysiques permet de mettre en évidence les zones préférentielles d'intrusion saline, la principale est celle du couloir de Oulad Mahdi. Ces nouveaux résultats permettent d'ouvrir de nouvelles perspectives à l'étude du cadre sédimentaires des dépôts plio-quaternaires, à l'évaluation de leur ressources en eau et à l'étude des effets des aménagements futurs sur les ressources de subsurface.
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