Subsurface Structural Mapping for Groundwater Resource Development of a Part of Tudun-Fulani North- Central Nigeria Using Radial Vertical Electrical Sounding Technique

Abstract

The primary target for the development of groundwater resources in crystalline rocks of the basement complex are fractures which aid in enhancing their secondary porosities thus, making them aquiferous. It is to this end that Radial Vertical Electrical Sounding (RVES) in combination with detailed geologic and hydrogeologic mapping was employed to provide information about the subsurface structure and lithology with the aim of evaluating the groundwater potential of Tudun-Fulani area in Minna, North-central Nigeria. The study area is composed entirely of granitic rocks. A total of Nine RVES were made along three profiles of three sounding stations each within an area of 2km2. Geophysical sounding data obtained were used to produce Vertical Electrical Sounding (VES) curves, electrical pseudosections, geoelectrical sections and anisotropy polygons of the area. VES curves reveal that the area is generally characterised by three geo-electric layers. Resistivities and depths of top soil layer range from 15 Ωm to 167 Ωm and 1.3 m to 17.5 m respectively. The middle layer consisting of slightly weathered rocks have resistivity values ranging from 26 Ωm to 777 Ωm and depths of 4.6 m to 27.7 m. Generally, the area has not undergone appreciable weathering which is evident from the isopach map which showed that the average depth to basement is about 10 m. Iso-resistivty map show a trend of increasing resistivity values from the north-western portion of the map to the south-eastern part. Anisotropy polygons showed no definite joint direction which is in complete agreement with measurements made at the surface. RVES has been able to prove its usefulness in resolving the orientation of subsurface structures. However, the area does not have good groundwater potential because fractures mapped were not deep seated and interconnected.