Piezometric modeling in precambrian fractured metamorphosed hard-rock: case of the Sassandra watershed (South-Western Côte d'Ivoire)
The piezometric levels in hard-rock from Côte d'Ivoire are poorly understood because of the complexity of the geological substratum. This work aims to model the piezometric level of aquifers located in crystalline and crystallophyllian basement, particularly in the Sassandra Watershed (south-western Côte d'Ivoire). By exploiting, on the one hand the method of linear correlation between the elevation of ground surface and base surface of thalwegs, and on the other hand the difference in elevation between the piezometric surface and the base surface thalwegs, we have established equations to determine groundwater levels and thereby compensate gaps in our knowledge. This study is based on field data, drilling datasheet, maps (topographic and geological) and an extract of the Digital Elevation Model (DEM) in south-western Cote d’Ivoire. The mathematical interpretation of the results, using established equations, helped us to calculate directly the piezometric level at any point in the study area. The piezometric map obtained shows that groundwater level is on average 7 m below ground when we take as reference the base surface of the thalwegs. The piezometric surface iscorrelated with the topographic surface. On the scale of the analysis carried out, the superposition of the piezometric map on the hydrographic network shows that flow of groundwater is modeled on that of the surface water. This observation supports the idea that hydrogeological and topographical watersheds overlap. This is logical considering the low permeability of hard-rock media and the relative homogeneity of their hydrodynamic properties on the scale of this approach. This result may help the integrated management of groundwaterand surface water resources, especially regarding their vulnerability to pesticides, which are frequently used in the study area.