Using geophysical anomalies for locating rural groundwater supplies in crystalline basement environments of Gbêkè region, center of Côte d’Ivoire

Résumé

 Hard rock aquifers are characterized by high heterogeneity, which leads to difficulties in groundwater prospecting, boreholes implementation and water resources management in rural areas of Gbêkè Region. Satisfying people's drinking water needs is therefore linked to a better knowledge of the geometry of discontinuous aquifers. This study focuses on the location of the discontinuities of hydrogeological interest in the crystalline bedrock through the examination of resistivity data from 66 horizontal profiling and 36 vertical electrical sounding employing the Schlumberger. Conducting anomalies founded in the crystalline bedrock were of U, V, W and K shape. Their wide and tight conductor compartments represent 73% and 27% respectively. These correspond to discontinuities and geologic structures such as vein zones, fractures, faults and geological contacts. The chances of having a positive borehole are higher when they oriented to N 5-44° (N-S), N 46-84° (NE-SO), N 137-178° (N-S) et N 183-218°(NE-SO). Electrical soundings reveal three main forms of electrical sounding curves (A, H and KH) with different productivity (p <0.05). The curves “boat bottom”(H) were more productive than the other two types. These correspond to an alteration profile composed from top to bottom of a thin clay lateritic armor with resistivities varying from 98 and 1356 Ω.m, of a fissured-altered conductive zone which has a thickness between 8.5 and 40 meters and healthy bedrock with higher resistivities up to 87721 Ω.m. The "resistivity" parameter therefore determines the alteration profile of the site and characterizes the fracturing zones favorable to the presence of aquifers and the implantation of boreholes.