Geoelectrical Soundings to Investigate Groundwater Potential of Orisunmibare Village in Ilorin South Area of Kwara State, Nigeria

Transcription

1 Research Paper Geoelectrical Soundings to Investigate Groundwater Potential of Orisunmibare Village in Ilorin South Area of Kwara State, Nigeria K.O. Ibrahim 1, P.I. Olasehinde 1, A.O. Akinrinmade 2 and A. Isa 2 1 Department of Geology, University of Ilorin, Ilorin 2 Department of Geology, Federal University of Technology, Minna ibrahim.ko@unilorin.edu.ng Abstract A Vertical Electrical Sounding (VES) Method was employed to determine the groundwater potential of Orisunmibare Village in the neighbourhood of federal government college, Ilorin. The purpose of this study was to determine the feasibility of a portable water borehole in the study area. Presently, there is no municipal water supply in the study area and the water source is from individual hand dug wells. A total of nine VES were carried out in different parts of the study area with DDR1 resistivity meter equipped with an SAS 2000 booster by means of Schlumberger electrode array configuration. The interpretation of the VES curve was carried out by partial curve matching method to obtain initial model parameters and computer iterations using WinResist Software. The curves reveal that the area is characterized by five classes of geoelectric layers. First, highly resistive topsoil layer has a thickness between m. The second lateritic clay layer has thickness ranges from m. Third layer is highly weathered basement with thickness of m. The fourth fractured with weathered rock layer has thickness from m, and fresh basement representing fifth layer has a thickness from 20 m and above. The results indicate the occurrence of good aquifers in the first, second, third, fourth, and fifth VES stations in the form of the weathered and fractured basement. Results also indicate that borehole drilling in the study area is achievable but to a depth of 45 meters to allow large reservoir within the aquifers. Keywords: Vertical Electrical Soundings, DDR1 Meter, Schlumberger Array, Visual Curve Inspection Win Resist Software 1. Introduction Water is one of the most valuable natural resources vital to the existence of any form of life. An adequate supply of safe water for maintaining ecosystem that supports all life and for achieving sustainable development (Topfer, 1998). As man s standard of living increase so does his need for consumption of water. However, the use of water has grown rapidly in modern times. Though, a significant portion of water resources have become unusable due to industrial and agricultural pollution. Diversions or transfer of watershed to other region have led to many ecological and human disasters (Gleick et al, 2002). Irrespective of its importance, a global paucity of safe drinking water had been established (UN, 2002; UNEP, 2002; WHO and UNICEF, 2004). Specifically UN (2002) reports that 1.1 billion people, representing 18% of the world s population, lack access to drinking water. The average amount of water used domestically each day by every person is about 190 litres (Hamill & Bell, 1986). The use of geophysics for both groundwater resource mapping and for water quality, evaluations has increased dramatically over the years. The Vertical Electrical Available online at 21

2 Soundings (VES) has proved very popular with groundwater studies due to simplicity of the technique. Groundwater has become immensely important for human water supply in urban and rural areas in developed and developing nations alike (Omosuyi, 2010). Presently, there is no municipal water supply in this area of study and the main source of water supply is from individual hand dug wells. However, the ground water conditions of this area when properly understood could be used as an effective tool in the planning of a reliable water borehole for people in the study area either through the state government, federal government, local government or private individuals. The sounding points are located between latitudes 08 o and 08 o and longitudes 4 o and 4 o in the neighbourhood of federal government college Ilorin (Figure 1). Although, many geological and hydrogeological investigations have been carried out by various scholars in most parts of Ilorin. Olasehinde (1999a) worked on preliminary results of hydrogeochemical investigations in Ilorin area i.e. South- Western Nigeria. Garba (1999) worked on the hydrogeological implications of the perched aquifer system of Ilorin. sources as an effective management tool in the planning of a reliable water supply scheme (Okurumeh & Oteze, 1996). Investigation involving detail geophysical study for groundwater potential in the area covered by this study is presently non-existent. This exigency inspired this study. Therefore, the primary objective of this study was to determine the groundwater potential and to identify suitable sites for exploitation of groundwater through drilling of boreholes in Orisunmibare Village in the neighbourhood of federal government college, Ilorin. 2. Geology and Hydrogeology of Study Area 2.1. Physiography and Climate The study area is in the intermediate zone between semiarid in the north and sub-humid climate in the south, hence characterized by two distinct seasons, that is the wet season start in late March and ends in the mid of October, while cold and dry weather due to influence of Harmattan is observed in the month of December and January. The vegetation is basically Savannah (Guinea) interspersed with tropical forest remnants (Esan, 1999). 3 1'01" 4 2'02" 5 3'03" 6 4'04" 8 3 '0 3 " 7 2 '0 2 " Kaima Rd Pakata Rd Adewole Olorunsogo Rd Ogbomoso Rd Asa River A lore St r. B a lo gu n A lan am u R d Agbooba Rd O ko -E rin R d U maru Saro Rd Abdu Azeez Ata R d O kelele St. Asa-Dam Rd S o b i R d Alimi Rd Emir's Rd Ibrahim Taiwo Rd Stadium Rd New Yidi Rd Amilegbe St. A sa R iv e r O p o m a lu Unity Rd P. O ffi c e R d R a il li n e Offa Rd Muritala Muhammed Rd Fate Rd Amodu Bello Avenue Admiralty Rd P ip e lin e R d B asin Rd Gaakanbi Rd Fate Rd University Rd Agba-Dam 8 3 '0 3 " 7 2 '0 2 " W N S E 6 1 '0 1 " Asa-Dam Offa garrage Rd 6 1 '0 1 " LEGEND 3 1'01" 4 2'02" 5 3'03" 6 4'04" Miles Road Junctions River Rail Line Dam Road Figure 1. Location Map of Study Area (Inserted is Geological Map of Nigeria) The ground water conditions in an area when properly understood could be used conjunctively with surface The rainfall is moderate with general annual average of about 1,250 mm with maximum rainfall occurring in the Available online at 22

3 months of June and August and a low humidity of about 50%. The mean annual temperature for this study area is about 27.2 o C and 31 o C, while the mean annual minimum falls between 22 o C and 23 o C. The warmest months fall between January and March with an average monthly temperature of about 28 o C and the mean annual evapotranspiration falls between 1,500 mm and 1,750 mm Isolines (Olasehinde, 1999b) Geology & Hydrogeology Orisunmibare Village, the study area, is underlain by rocks of the crystalline Nigeria basement complex, principally among which are granites and gneisses. These rocks were emplaced in Precambrian times and have over time subjected to tectonic activities characterized by large changes in temperature and the pressure resulting in fractures like joints, faults and fractures within the basement complex rocks. Such fractures are those that influence the ground water in crystalline rocks especially if they exist at depth and are over laid by a thick superficial cover (overburden). Though there is no visible outcrop seen in the area worked upon, outcrop exists in the adjoining areas such as Ilorin-Igbeti road. This is clear index to the fact that on a regional projection such rocks exist at depth beneath the thick superficial cover that are predominate in the area. This is of an immense hydrogeological interest in this investigation (Olayinka et al, 1998). 3. Geophysical Investigation For the purpose of this investigation, a total of nine (9) VES, using the Schlumberger electrode configuration, were made at different locations within the study area. DDR1 meter equipped with an SAS 2000 booster was used. As much as access allowed on the field, the maximum current electrode spacing (AB) was 100 m. The nine sounding locations numbered 1 to 9 are shown in Figure Results The sounding curves (Figure 3) were evaluated by partial curve matching method and computer iterations using WinResist. The curves shown five Geo-Electric Successions as presented in Tables 1-3. The five layers consist of a top soil with resistivity ranges between ohm-m and thickness of m followed by lateritic clay layer of resistivity ohm-m with thickness of 3.3 m-15.0 m. The third lithologic layer is characterized by highly weathered basement with resistivity ohm-m and thickness of 6.0 m-30.7 m while the fourth layer is a fractured with weathered rock of resistivity ohm-m and thickness of 20.0 m-40.2 m. The fresh basement representing the fifth layer has resistivity of ohm-m and thickness from 20.0 m and above. 5. Discussion The geophysical investigation of the study area has revealed five geo-electric units in which the aquifers occurred in the form of weathered and fractured basement. However, the results indicate the occurrence of good aquifers in the first, second, third, fourth and fifth VES stations shown from their low resistivity values. But for the rest of VES stations the resistivity values are so high indicating little or no water present in those regions. 6. Conclusion With a mean annual rainfall of 1,250 mm, maximum temperature of 31 o C and mean annual evapotranspiration of 1,750 mm (Olasehinde, 1999) adequate climatic conditions could be said to exist for groundwater recharge purpose. Also, the occurrence of joints, faults and fractures in the subsurface are indications of good aquifer in the study area. It is advisable that drilling in this area should be done to the depth of 45 meters to allow large reservoir within the aquifer References Annor, A.E., and Olasehinde, P.I. (1996) Vegetational Niche as a remote sensor of subsurface aquifer. A geological- geophysical study in Jere area, central Nigeria. Journal of NAH, 7(1&2), pp Figure 2. Sounding Locations Esan, A. (1999) The Hydrogeology and Hydrochemistry of Ground Water Source in Ilorin West Central Nigeria. M.Sc. thesis, University of Ilorin, Nigeria. Available online at 23

4 Figure 3. 3D Geoelectric Section of Vertical Electrical Sounding (VES) Point 01 to 05 Table 1. Geo-Electric Successions VES 1 VES 2 VES 3 Top Lateritic Soil Lateritic Clay Soil Weathered Rock Fractured/Weathered Rock Fresh Basement 200 > > >40.1 Table 2. Geo-Electric Successions VES 4 VES 5 VES 6 Top Lateritic Soil Lateritic Clay Soil Weathered Rock Fractured/Weathered Rock Fresh Basement 350 > > >20.4 Available online at 24

5 Table 3. Geo-Electric Successions VES 7 VES 8 VES 9 Top lateritic Soil Lateritic clay Soil Weathered Rock Fractured/Weathered Rock Fresh Basement 145 > > >35.2 Garba, A.A. (1999) Hydrogeological Implications of the Perched Aquifer System of Ilorin in West Central Nigeria. M.Sc. thesis, University of Ilorin, Nigeria. Gleick, P.R., Gary, W., Elizabeth, L., and Chalecki, R.R. (2002) The New Economy of Water: The Risk and Benefits of Globalization and the Privatization of Fresh Water. Oakland California, Pacific Institute for Studies in Development, Environment and Security. Hamill, L., and Bell, F.G (1986) Groundwater Resources Development. Cambridge, Great Britain University Press. Okurumeh, K., and Oteze, G.E. (1996) Groundwater in the Lower Benue valley, Nigeria. Journal of NAH, 7(1 &2), pp Olayinka, P.O., Nwajide, C.S., and Oni, A.O. (1998) The geology of the Ilorin Area. Federal Ministry of Solid Mineral Development. Geological Survey of Nigeria, Bulletin No. 42, pp Topfer, K. (1998) Editorial comments on freshwater. Our Planet, 9(4), p. 3. UN (2002) Facts about Water [Internet]. Proceedings of World Summit on Sustainable Development, August 26-September 4, 2002, Johannesburg, South Africa. Johannesburg, United Nation. Available from: < essreleases_factsheets/wssd4_water.pdf> [Accessed 18 June UNEP (2002) Geo 3 at a glance- freshwater. Our Planet, 3(2), p. 18. WHO and UNICEF (2004) Water Sanitation Health. Meeting the MDG Drinking Water and Sanitation Target: A Mid-Term Assessment of Progress [Internet], Geneva, WHO. Available from:< p2004/en/> [Accessed 18 June 2012]. Olasehinde, P.I. (1999a) characteristics of rain, groundwater and surface water in the area of Ilorin, Kwara State, Nigeria. Zb1. Geol. Palaont Teil 1, (3-4), pp Olasehinde, P.I. (1999b) An integrated geologic and geophysical exploration techniques for groundwater in the basement complex of west central part of Nigeria. Journal of NAH, 11, pp Omosuyi, G.O. (2010) Geoelectric assessment of groundwater prospect and vulnerability of overburden aquifers at Idanre, South Western Nigeria. Ozean Journal of Applied Sciences, 3(1), pp Onwuemesi, A.G., and Olaniyan, I.O. (1996) Hydrogeophysical Investigation of parts of Anambra State, Nigeria. Journal of NAH, 7(1&2), pp Available online at 25