keywords: Basement aquifer, basement resistivity, reflection coefficient, water potential
Electrical resistivity survey was carried out in some parts of Abeokuta, southwestern Nigeria with the aim of delineating the resistivity characteristics of the basement groundwater yield in the study area. The study area lies within the Southwestern Basement Complex of Nigeria and it is underlain by granite gneiss, biotite gneiss and porphyroblastic gneiss rock types. Thirty (30) Vertical Electrical Sounding (VES) points were probed using the Schlumberger configuration with maximum electrode spacing (AB/2) of 100 m. The VES data were plotted and were initially interpreted with the aid of partial curve matching approach, the results were further processed using the WINREST software to produce iterated curves which were used to delineate the respective layers, resistivity and depth of the subsurface. Iterated curves showed the presence of three (3) to five (5) inferred lithological units which include the topsoil (59.4 – 914.2 Ω m), the weathered layer which include clay/sandy-clay/sand (15.4 – 544.3 Ωm) and fresh/fractured basement (123.1 – 21858.5 Ωm). The overburden thickness ranges between 3.2 to 43.7 m; while reflection coefficient ranges between 0.71 – 0.99. The consideration of basement resistivity, overburden thickness and the reflection coefficient values were used to categorize the sample point into their yield potentials as either low, medium or high and it was used to generate a groundwater potential map for the area. The combination of these three resistivity survey parameters in predicting the water potential of the area therefore enhances the accuracy of the interpretation better than using one parameter for its prediction.
Adelusi AO & Folami SL 2000. The use of very low frequency electromagnetic (VLF-EM) method in geologic mapping and hydrogeologic investigations: A case study of Abo-Oyo near Akure southwestern Nigeria. Water Resources, J. Nig. Assoc. Hydrogeol., 11: 1-6. Afolabi O & Olorunfemi MO 2004. Laboratory modelling of geoelectric response of a leaking of underground petroleum storage tank in sand formation. Global J. Geolog. Sci., 2(2): 207-220. Aina A. Olorunfemi M.O. and Ojo J .S. 1996. An integration of aeromagnetic and electrical resistivity methods in dam site investigation. Geophysics, 61(2): 349-356. Ajayi O & Abegunrin OO 1990. Causes of borehole failures in the crystalline rocks of southwestern Nigeria. Proceedings of first Biennial National Hydrology Symposium held in Maiduguri, Nigeria, pp. 466-490. Akhtar Izzaty Riwayat, Mohd Ariff Ahmad Nazri & Mohd Hazreek Zainal Abidin 2018. Application of electrical resistivity method (ERM) in groundwater exploration. Journal of Physics: Conf. Series. doi :10.1088/1742-6596/995/1/012094. Bayewu OO, Oloruntola MO & Mosuro GO 2018. Assessment of groundwater prospect and aquifer protective capacity using resistivity method in Olabisi Onabanjo University Campus, Ago-Iwoye, Southwestern Nigeria. NRIAG J. Astronomy and Geophys., 7(2): 347-360. Bayewu OO, Oloruntola MO, Mosuro GO, Laniyan TA, Ariyo SO & Fatoba JO 2017. Geophysical evaluation of groundwater potential in part of southwestern Basement Complex terrain of Nigeria. J. Appl. Water Sci., 7: 4615–4632. Bhattacharya & PatroHP 1968. Direct current Geoelectric sounding Methods in Geochemistry and Geophysics, Elsevier, Amsterdam, 135p. Braga OC, Filho WM & Dourado JC 2006. Resistivity (DC) method applied to aquifer protection studies. Brazilian J. Geophys., 24(4): 574-581. Carruthers RM & Smith IF 1992. The use of ground electrical survey for citing water supply boreholes in shallow crystalline basement terrains. In: Wright EP & Burgess WG (eds.), The Hydrogeology of Crystalline Basement Aquifers in Africa, pp. 27-34. Choudhury K & Saha DK 2004. Integrated geophysical and chemical study of saline water intrusion. Ground Water, 42(5): 671– 677. Dan-Hassan MA & Olorunfemi MO 1999. Hydrogeophysical investigation of a basement terrain in the north-central part of Kaduna State Nigeria. Journal of Mining and Geology, 35(2): 189-205. David LM & Ofrey O 1989. An indirect method of estimating groundwater level in basement complex regolith. Water Resources, J. Nig. Assoc. Hydrogeol., 1(2): 161-164. De Pasquale G, Linde N, Doetsch J & Holbrook WS 2019. Probabilistic inference of subsurface heterogeneity and interface geometry using geophysical data. Geophysical Journal International, doi:10.1093/gji/ggz055, Du-Preez JW & Barbar W 1965. The distribution and chemical quality of groundwater in Northern Nigeria. Journal of Mining and Geology, 35(2): 189-205. Fadele SI, Sule PO & Dewu BBM 2013. The Use of Vertical Electrical Sounding (VES) for Groundwater Exploration around Nigerian College of Aviation Technology (NCAT), Zaria, Kaduna State, Nigeria. Pacific J. Sci. and Techn., 14: 549-555. Gowdn Srinivasa S 2004. Electrical resistivity surveys to delineate groundwater potential aquifers in Peddavanka watershed, Anantapur District, Andhra Pradesh, India. Environmental Geology, 46: 118–131. Herman R 2001. An introduction to electrical resistivity in geophysics. American Journal of Physics, 69(9): 943–952. doi:10.1119/1.1378013. Keller GV & Frischknecht FC 1966. Electrical Methods in Geophysical Prospecting. Pergamon Press, Oxford, New York, Toronto, Sydney, Braunsckweig. Keller VG & Frischknecht FC 1996. Electrical methods in geophysical prospecting. Int. Series of Monographs on Electromag. Waves, 10: 22-27. Koefoed O 1979. Geosounding Principles 1. Resistivity Sounding Measurements, Elsevier Scientific Publishing Comp., Amsterdam, pp. 275. Kunetz, G., 1966. Principles of Direct Current Resistivity Prospecting. Gebruder Borntraeger, Berlin-Nikolassee, 103p. Maillet R 1947. The fundamental equation of electrical prospecting. Geophysics, 12: 529–556. Matzner RA 1983. Hydrogeologic and geophysical investigations of the Springfield-Blackfort area, Idaho, Pap. Presented During the Tech. Edn. Sessn. 1983, Expo. 43p. Metwaly M 2012. Groundwater exploration using geoelectrical resistivity technique at Al Quwy’yia area Central Saudi Arabia. Int. J. Physical Sci., 7(2): 317–326.