Geological and geophysical evaluation of the Ajana area's groundwater potential, southwestern Nigeria

• Published in: Earth sciences research journal 2011-07, Vol.15 (1), p.35-40
• Main Authors: Ariyo, Stephen O, Folorunso, Adetayo F, Ajibade OM
• Format: Article
• Language: English
• Subjects: Anisotropy; Aquifers; Electric properties; GEOSCIENCES, MULTIDISCIPLINARY; Permeability; Porosity; Water, Underground
• ISSN: 1794-6190; 2339-3459

A combined geological and geophysical evaluation was made of the groundwater potential of the Ajana, Remo North area in south-western Nigeria; the geology and other structural features of the rocks there strongly influenced and correlated the aquifers' storability and transmissivity. Geological mapping revealed that the area was made up of granite, quartzite and varieties of gneiss, some of which have good secondary porosity and permeability. Ten vertical electric soundings (VES) stations were established using a Schlumberger electrode array. Five geoelectric layers consisting of topsoil, sand, clayey-sandy, fractured/weathered basement and fresh bedrock were delineated. The aquifer layers were the 38.3m thick 283 ?m resistivity sand/sandy clay and 55-518 ?m resistivity fractured/weathered basement. Other geoelectric parameters used in evaluating the area's hydrogeological potential included curve type, anisotropy coefficient and reflection coefficient--The QH curve type was predominant in the area. The anisotropy Coefficients suggested VES stations having high groundwater potential ranging from 1.4-1.56; while the reflection coefficients for the area ranged from 0.21-0.99. The overall results showed that VES stations 8,9 and 10 could be possible groundwater sources having high expected yield. Keywords: Reflection Coefficient, Anisotropy Coefficient, Geoelectric Layers, Groundwater Potential, Mapping, Ajana Se realizo una evaluacion geologica--geofisica del potencial hidrogeologico en Ajana, Remo North en la zona suroeste de Nigeria; la geologia y las fracturas en las rocas estan estrechamente relacionadas con la capacidad de almacenamiento y transmisividad de los acuiferos. El mapeo geologico revela que el area esta conformada por granitos, cuarcitas y variedades de gneis, algunos con buena porosidad secundaria y permeabilidad. Se realizaron diez Sondeos Electricos Verticales (SEV) en configuracion Schlumberger, donde se establecieron cinco capas: Suelo, arena, arcilla arenosa, basamento fracturado meteorizado y roca fresca. Las capas acuiferas tiene espesores de 38.2m con resistividades de 283 ωm para arenay arcilla arenosa, y resistividades entre 55-518 ωm para el basamento meteorizado. Otros parametros geoelectricos utilizados en laevaluacion delpotencialhidrogeologico de la zonaincluyen eltipo de curva, elcoeficiente de anisotropia yelcoeficiente de reflexion--Las curvas tipo ωH fueronpredominantes en la zona. Los coeficientes de anisotropia sugiriere