Groundwater Prospectivity Assessment of a Field of Hand-Dug Wells in the Area Around the Murtala Muhammed Postgraduate Hall OAU, Ile-Ife, Using Geoelectric Parametric Soundings

摘要

This paper presents the results of geoelectric parametric soundings carried out on a field of hand-dug wells within the Murtala Muhammed Postgraduate Hall in Obafemi Awolowo University (OAU), Ile-Ife, Southwest Nigeria, with a view to assessing the groundwater potential and establishing the feasibility of increasing the well depths, for enhanced groundwater yield. The Vertical Electrical Sounding (VES) utilized the Schlumberger array whose curves were interpreted quantitatively by partial curve matching and computer assisted 1D forward modeling. The VES interpretation results were used to generate 2D geoelectric sections and thematic maps of overburden thickness, aquifer resistivity and basement bedrock relief. Using multi-criteria evaluation in a GIS environment, the thematic maps were integrated to evolve the groundwater potential of the study area. The feasibility of increasing the well depths was based on the current well depths, estimates of water column in the wells and estimated aquifer thicknesses. The topsoil; laterite; clay/sandy clay weathered layer; partly weathered/fractured basement and the fresh basement bedrock constitute the underlying geologic layers. The weathered layer constitutes the main aquifer unit. The depths to the basement bedrock ranged from 4.5 - 44.3 m but are generally >19.1 m except beneath wells 1 and 2 (<7.2 m). The groundwater potential rating for the study area ranged from very low (4.1%) to low (79%) and moderate (16.9%). The well depths ranged from 7.55 to 12.63 m which for most wells barely or rarely penetrated the 6.85 - 32.8 m thick weathered layer aquifer. The study concluded that there is prospect for enhanced and sustainable groundwater yield if the well depths are increased to a minimum of 19 m.