Get 20M+ Full-Text Papers For Less Than $1.50/day. Start a 14-Day Trial for You or Your Team.

Learn More →

Geophysical evaluation of groundwater potential in part of southwestern Basement Complex terrain of Nigeria

Geophysical evaluation of groundwater potential in part of southwestern Basement Complex terrain... Appl Water Sci (2017) 7:4615–4632 https://doi.org/10.1007/s13201-017-0623-4 O R I G IN AL ARTI CL E Geophysical evaluation of groundwater potential in part of southwestern Basement Complex terrain of Nigeria 1 2 1 • • • Olateju O. Bayewu Moroof O. Oloruntola Ganiyu O. Mosuro 1 1 3 • • Temitope A. Laniyan Stephen O. Ariyo Julius O. Fatoba Received: 22 April 2017 / Accepted: 12 September 2017 / Published online: 18 September 2017 The Author(s) 2017. This article is an open access publication Abstract The geophysical assessment of groundwater in Keywords Groundwater potential  Resistivity survey Awa-Ilaporu, near Ago Iwoye southwestern Nigeria was VES  VLF-EM  Fracture  Geoelectric layer carried out with the aim of delineating probable areas of high groundwater potential. The area falls within the Crystalline Basement Complex of southwestern Nigeria which is pre- Introduction dominantly underlain by banded gneiss, granite gneiss and pegmatite. The geophysical investigation involves the very In hard rock terrains, groundwater potential mapping is rel- low frequency electromagnetic (VLF-EM) and Vertical atively complex due largely to highly variable nature of the Electrical Sounding (VES) methods. The VLF-EM survey geological terrain (Kellgren 2002: Anbazhagan et al. 2011) was at 10 m interval along eight traverses ranging between extensive hydrogeological investigations are required in 290 and 700 m in length using ABEM WADI VLF-EM unit. basement complex environment to understand groundwater The VLF-EM survey was used to delineate areas with con- conditions (Solomon and Quiel 2006; Balamurugan et al. ductive/fractured zones. Twenty-three VES surveys were 2008;Pradhan 2009). Evans and Myers 1990; Sener et al. carried out with the use of Campus Ohmega resistivity meter 2005; Singh and Singh 2009;Sharmaand Kujur 2012 all at different location and at locations areas delineated as high noted that several methods commonly adopted in delineating conductive areas by VLF-EM survey. The result of VLF-EM groundwater potential depending on the available data which survey along its traverse was used in delineating high con- include remote sensing and Geological Information Sys- ductive/fractured zones, it is, however, in agreement with the tem(GIS). Several statistical methods can also be adopted for delineation of the VES survey. The VES results showed 3–4 groundwater mapping where adequate information on dif- geoelectric layers inferred as sandy topsoil, sandy clay, clayey ferent influencing parameters to groundwater accumulation and fractured/fresh basement. The combination of these two and movement are available. These include frequency ratio methods, therefore, helped in resolving the prospecting (Davoodi et al. 2013), multi-criteria decision evaluation location for the groundwater yield in the study area. (Murthy and Mamo 2009; Kumar et al. 2014), logistic regression model (Ozdemir 2011), weights-of-evidence model (Ozdemir 2011; Pourtaghi and Pourghasemi 2014), random forest model (Rahmati et al. 2016 Naghibi et al. 2016), maximum entropy model (Rahmati et al. 2016), & Olateju O. Bayewu boosted regression tree (Naghibi et al. 2016; Naghibi and tejubpositive@yahoo.com Pourghasemi 2015), classification and regression tree (Naghibi et al. 2016), multivariate adaptive regression spline Department of Earth Sciences, Olabisi Onabanjo University, Ago Iwoye, Nigeria model (Zabihi et al. 2016), certainty factor model (Zabihi et al. 2016), evidential belief function (Pourghasemi and Department of Geosciences, University of Lagos, Lagos, Beheshtirad 2015; Naghibi and Pourghasemi 2015), and Nigeria generalized linear model (Naghibi and Pourghasemi 2015). Department of Applied Geophysics, Federal University Oye, These information are lacking in many third world country Oye Ekiti, Nigeria 123 4616 Appl Water Sci (2017) 7:4615–4632 Fig. 1 The location map of the study area hence proper understanding of hydrogeological characteristics subsurface layering and ensures a higher degree of accu- for successful exploitation of groundwater in basement areas racy in the location of hydro resources (Omosuyi et al. depend largely on geophysical methods. 2003). They are important in the search and location of Various forms of water exploratory projects are used in suitable groundwater potentials either singly or combined. the provision of potable water for human usage and great Various combinations of geophysical methods have been importance is geophysics which serves as important tool in used with an accompanying increase in the degree of exploration. Offodile (1983) documented that careful accuracy in the location of suitable groundwater reservoir. studies accompanied by improved drilling techniques yield A combination of the electromagnetic method and the favorable results even in problematic areas. Geophysical electrical resistivity gave a higher rate of 90% as opposed methods, therefore, play an important role in the explo- to 82% by the electromagnetic method and the 85% by the ration of suitable and productive groundwater reservoirs. resistivity method (White 1986). The geophysical survey is employed to determine geo- In areas underlain by crystalline rocks, groundwater electric parameters of formations, identify aquifer units and occurs in fracture zone or in highly weathered basement also determine its depth and lateral extent (Telford et al. (Olorunfemi and Fasuyi 1993; Ariyo et al. 2003). The 1976). electromagnetic and resistivity methods are both respon- The types of geophysical method used for a survey sive to water bearing basement fracture columns due to the depends mainly on the extent or size of area to be surveyed, relatively high bulk electric conductivities, both methods the cost of the survey, geology of the area and the ease of were, therefore, found relevant and were hence integrated the interpretation of data obtained. It also provides infor- in the geophysical investigation. The VLF-EM method was mation on the depth of water table, the lithology in the adopted as a fast reconnaissance tool to map possible linear 123 Appl Water Sci (2017) 7:4615–4632 4617 Fig. 2 Map of the study area showing the location of the VES points and VLF Traverse in the study area Fig. 3 The VLF-EM traverse and Karous–Hjelt pseudosection for Traverse 1 123 4618 Appl Water Sci (2017) 7:4615–4632 Fig. 4 The VLF-EM traverse and Karous–Hjelt pseudosection for Traverse 2 features such as; fault, and fracture zones while the elec- The aim of this study is, therefore, to delineate the trical resistivity method was used to investigate prominent groundwater potentials in Awa-Ilaporu, near Ago Iwoye electromagnetic anomalies and provide a geo-electric southwestern Nigeria, by determining the depth of occurrence image or section of the subsurface sequence. of suitable aquifers; and also to provide background infor- In spite the many studies (Olorunfemi and Olorunniwo mation for the future development of groundwater within the 1985; Olayinka and Olorunfemi 1992; Okwueze 1996; area by delineating potential areas for borehole drilling. Oladapo and Akintorinwa 2007; Oloruntola and Adeyemi 2014) on groundwater potential in many parts of Nigeria, most of the studies were carried out in urban centers such Location of the study area and geological setting as Lagos, Abeokuta, Ibadan where hydrogeological infor- mation is readily available. Awa-Ilaporu, SW is located The study area (Fig. 1) is located in Awa-Ilaporu, near Ago within the Basement Complex terrain of southwestern Iwoye, south western Nigeria; it falls between latitude 0 0 0 Nigeria like many areas in southwestern Nigeria it is a 657 to 659 North of the Equator and longitudes 3 55 community of indigenous rural people and students of a and 3 57 East of the Greenwich Meridian. The drainage non-residential Olabisi Onabanjo University, which lacks shows a dendritic drainage pattern and the major river in municipal water supply. The inhabitants rely mainly on low the area is River Ome and all other tributaries take their yield, pollution prone shallow wells many of which dries source from this river. It is located within the tropical rain up during dry season. Most of the attempts to construct forest which is characterized by a tropical climate with deeper borehole have either failed outrightly or produced alternating wet and dry season, within the year. According low yield borehole. As a result of this, the need to explore to Onakomaiya et al. (1992), the wet season spans from other promising high water yield areas to supplement water March to October and peaks in June/July while the dry supply mostly during the dry season or drought is obvious, season spans from November to February. The mean hence the need for a more detailed evaluation of the annual rainfall ranges from 100 to 1500 mm with average groundwater potential of the community. rainfall of about 100 mm. Ogunrayi et al. (2016) observed fluctuations in rainfall and temperature pattern of Akure 123 Appl Water Sci (2017) 7:4615–4632 4619 Fig. 5 The VLF-EM traverse and Karous–Hjelt pseudosection for Traverse 3 which is part of southwestern Nigeria, the climate of the The VLF-EM survey region indicates that the beginning of rainfall is becoming earlier which implies possible longer rainy season in the The VLF-EM is a type of continuous wave field electro- magnetic method and it is most widely used in the recon- area. The temperature on the other hand, showed an increasing trend indicating warming throughout the year. naissance mode. VLF traverses can be run quickly and inexpensively to anomalous areas which may require fur- There are lots of vegetation covers such as trees, shrubs and grasses. The temperature of the area ranges from 18 to ther investigation either with more detailed geophysical measurement and/or drilling and sampling (Telford et al. 34 C (Iloeje 1986). The area is found within the southwestern crystalline 1976). This was one of the methods employed in this Basement Complex of Nigeria. Geologically, it is made up research work. of three major rock types; granite gneiss, banded gneiss and The VLF-EM survey was carried out at different stations pegmatites which serves as an intrusive body. Awa-Ilaporu and were surveyed at 10 m interval along eight traverses and environs were in the past agrarian communities with approximately east–west direction ranging from 290 to 700 very low population. However, the establishment of the metres in length using ABEM WADI VLF-EM unit. The VLF-EM was used to initially delineate areas with con- then Off-Campus Ogun State University (now Olabisi Onabanjo University) led to rapid geometric increase in the ductive or fractured zone. VLF systems make use of the energy emanating from population of the communities. distant powerful radio transmitters and measure the per- turbations in plane-wave radio signal (15–30 kHz). These Materials and methods low frequency signals are trapped between the earth and the ionosphere. Two geophysical methods were used for this work; the The primary field (the transmitted radio signal) causes very low frequency electromagnetic (VLF-EM) and verti- eddy currents to be induced in conductive geological units cal electrical sounding (VES). The location and arrange- or structure. Faraday’s principle of EM induction shows ment of the two methods in the area is shown in Fig. 2. that any oscillating magnetic field (e.g. the radio wave) will 123 4620 Appl Water Sci (2017) 7:4615–4632 Fig. 6 The VLF-EM traverse and Karous–Hjelt pseudosection for Traverse 4 produce an electric field and electric current in a conduc- filtered real are determined. Anomalous areas are iden- tive media. Those eddy currents in turn create a secondary tified and a gross characterization attached to the magnetic field which is measured by the VLF receiver. The anomaly (e.g. steeply dipping conductor or thickening secondary or perturbed field may be phase shifted and conductive overburden). Some simple modeling may be oriented in a different direction than the primary field carried out for simple geometric structures (McNeil and depending on the shape or geometry of the conductor, the Labson 1992). orientation of the conductor and conductivity contrast with Data filtering are applied in other to eliminate errors and the surrounding material (e.g. the host rock). The instru- enhance interpretation of data. This is done by applying a ment measures two components of magnetic field or filter operator (Q) which transform true anomaly inflection equivalently the ‘‘tilt angle’’ and ellipticity of the field. to peak positive anomalies also referred to as conductivity Some instruments also measure the third magnetic com- because they are proportional (Parasnis 1986). The filter ponent and/or the electric field. The electrical field is operation is given by Fraser (1969): measured by inserting two probes in the ground spaced F1 ¼½ ðÞ U þ U ðÞ U þ U Fraser filtering; 3 4 1 2 about 5 meters (McNeil and Labson 1992). VLF interpre- tation is generally qualitative or subjective in nature and where A , A , A and A are consecutive readings of the 1 2 3 4 sometimes may be subjected to quantitative interpretation measured raw data obtained on the field. with the aid of filtering technique from which the true 123 Appl Water Sci (2017) 7:4615–4632 4621 Fig. 7 The VLF-EM traverse and Karous–Hjelt pseudosection for Traverse 5 Vertical electrical sounding (VES) survey results obtained from the exercise were used as input- model for the eventual computer aided iteration using The second type of geophysical survey method used is the WINRESIST program. electrical resistivity method using the schlumberger elec- The reflection coefficient of each station in the area was trode configuration. Twenty-three (23) Vertical Electrical calculated using the method of Bhattacharya and Patra Sounding stations were carried out in the field using (1968), Olayinka (1996). Loke (1997) and Olasehinde and OHMEGA resistivity meter which investigates the sub- Bayewu (2011): surface resistivity conditions by passing electric current K ¼ðq  q Þ=ðq þ q Þ; n n n1 n n1 into the ground through a pairs of current electrodes and where K is reflection coefficient for the nth layer, n is the measuring the resulting voltage differences between pair’s n number of layers, q is the layer resistivity of the nth layer potential electrodes. Repeated measurements of current and and q is the layer resistivity overlying the nth layer. potential difference were made at these same points using a n1 larger current electrode separation (AB/2) in each succes- sive electrode probe to determine the depth to the bed rock. Results and discussion In the probe, the spacing AB/2 was varied in a line direction to a maximum of 100 m in a station, keeping the Very low frequency-electromagnetic method (VLF- center of the electrode configuration fixed. The values EM) obtained were then plotted on a log–log paper as points with the resistivity values being on the vertical axis and the Traverse 1 is 400 m in length (Fig. 3). The filtered real current electrode spacing (AB/2) on the horizontal axis. value ranges from -131.7 to 118.0 Siemens, while the The points were joined and curve marched manually using filtered imaginary ranges from -30.3 to 68.9 Siemens. The pre-calculated master curves and their auxiliaries. The 123 4622 Appl Water Sci (2017) 7:4615–4632 Fig. 8 The VLF-EM traverse and Karous–Hjelt pseudosection for Traverse 6 traverse shows the maximum peak at both positive and overburden T2 is identified at distance between 310 and negative region with a more prominent filtered real peak at 350 m where the positive peak of filtered real and imagi- horizontal distance of 70–100 m. This usually signifies or nary coincide. In the Karous–Hjelt filtering pseudo-section, corresponds to the area of high conductivity or area with the extent of the fractured identified is below 40 m depth, the presence of fracture. This is marked F1 on the graph. this can either be a localized zone of fracture or thick The correspondent Karous–Hjelt pseudosection filtering clayey materials in the region. confirms the moderately high conductivity which extends Traverse 3 is 600 m in length (Fig. 5). The filtered real below 50 m depth. This conductivity could be due to the values ranges from -28.7 to 69.2 Siemens, while the fil- presence of fracture or accumulation of clayey materials. tered imaginary ranges from -67.5 to 100.7 Siemens. A (McNeil and Labson 1992). Also at horizontal distance positive anomalous value of filtered real is observed at between 200 and 250 m, there is an observation of the distance between 100 and 140 m and it is identified as a filtered real and filtered imaginary both positively peaking fracture F3. Area of thick overburden is observed at dis- together; this usually signifies a relatively thick overburden tance interval of 600 and 650 m and marked as T3. The (McNeil and Labson 1992). This area is, therefore, marked Karous–Hjelt pseudosection also agrees with the plot and T1. showed the extent of the identified fracture to be 40 m deep Traverse 2 (Fig. 4) is 700 m long (Fig. 4). The filtered while the thick overburden is about 30 m deep. real values ranges from -57.6 to 53.0 Siemens, while the Traverse 4(Fig. 6) is 400 metres in length. The filtered filtered imaginary ranges from -52.0 to 51.5 Siemens. A real values ranges from -305.4 to 142.2 Siemens, while fracture F2 is observed where the positive peak of the fil- the filtered imaginary values ranges from -17.8 to 20.7 tered real coincides with the negative peak of the imagi- Siemens. The profile shows a maximum peak at the posi- nary at station 635 meters on the traverse. Also a thick tive region with a more prominent filtered real peak at 123 Appl Water Sci (2017) 7:4615–4632 4623 Fig. 9 The VLF-EM traverse and Karous–Hjelt pseudosection for Traverse 7 285 m, which also correspond to high conductive region. shallow overburden. Fractures F6 and F7 are observed on There are occurrences of fracture between at 270–290 m the traverse at 5–30 and 200–230 m, respectively. The (F4a) and at 310–330 m (F4b) along this traverse. This also Karous–Hjelt pseudosection showed that the extent of the shows in the Karous–Hjelt filtering pseudo-section and identified fracture F6 extended to about 20 m deep while reveal that the fractures extend to more than 50 m. F7 extended to 45 m deep. Traverse 5 (Fig. 7) is also 400 m in length. The filtered Traverse 7 (Fig. 9) is 400 m. The filtered real value real values ranges from -53.0 to 48.5 Siemens, while the ranges from -73.5 to 552.1 Siemens, while the filtered filtered imaginary values ranges from -31.7 to 28.9 Sie- imaginary ranges from -6.6 to 6.6 Siemens. The traverse mens. The profile shows a maximum peak at positive shows a maximum peak of filtered real at 30 m along the region with a more prominent filtered real peak at 260 m. traverse with width of about 40 m; this is thus corre- The fracture, thick overburden, and shallow overburden are sponded to fracture F8 and fracture F9 was observed at marked as F5, T4 and S2, respectively. The Karous–Hjelt 320 m of the traverse with the width of about 30 m. The pseudosection showed the extent of the identified fracture Karous–Hjelt pseudosection showed the extent of the to be inclined and also extended to more than 50 m deep identified fracture F8 to be about 28 m deep while F9 is while the thick overburden is about 40 m deep. 40 m deep. Traverse 6 (Fig. 8) is 290 metres in length. The filtered Traverse 8 (Fig. 10) is 400 m long. The filtered real real values range from -47.5 to 34.2 Siemens, while the values range from -203.7 to 146.8 Siemens, while the filtered imaginary values ranges from -36.7 to 36.7 Sie- filtered imaginary ranges from 0.0 to 0.9 Siemens. The high mens. On the profile is S3 at point 230 metres with maximum peak of the positive filtered real implies frac- approximately width of 22 m and correspond to area of tured zones, F10 was observed at 200 m of the traverse of 123 4624 Appl Water Sci (2017) 7:4615–4632 Fig. 10 The VLF-EM traverse and Karous-Hjelt pseudosection for Traverse 8 width of about 30 m and F11 at point 280 m with width of Typical iterated curves generated from the field mea- about 30 m, respectively. The Karous–Hjelt pseudosection surements in the area are shown in Fig. 11. Table 1 showed the identified fractures F10 and F11 to be inclined revealed the geoelectric parameters of the various layers and they are also interconnected. They are extended to and showed the inferred lithologies from the geoelectric more than 40 m deep. interpretation. The geoelectric interpretation revealed 3-5 geoelectric layers: top soil (66–870 Xm), the weathered layer which Vertical electrical sounding (VES) data comprises of clay/clayey sand/sand/laterite (28.3–2342.7 Xm), underlying this layer is the fractured basement The areas delineated as high conductive/fracture zones and (480.0–1415.9 Xm) and the fresh basement thick overburden along the traverse were considered as (655.9–18,265.4 Xm). The fractured and fresh basement points of interest in the VES survey. layers were differentiated using the values of reflection Interpretation of VES data is both quantitative and coefficient obtained from each VES point, which is the qualitative, it involves the determination of the thickness measure of competence of the basement layer. (Olayinka and resistivity of different horizons and the inference of 1996; Olasehinde and Bayewu 2011). From the calculated their lithologies based on their resistivity and reflection reflection coefficient, the reflection coefficient map was coefficient values. produced (Fig. 12) and shows a value range of (0.59–0.98). The curve types observed in the area are 3-layer H-type Olayinka (1996) observed that an area of lower reflection (26%); 4-layer HA-type (9%) and KH (52%); and 5-layer coefficient value (\0.8) exhibits weathered or fractured HKH-type (13%). The curve types include KH, HA, HKH basement rock thus, favors a high water potential. There- and H. The KH type is the most predominant and it is fore, areas with relatively lower reflection coefficient typical of tropics area (Olayinka and Olorunfemi 1992). It (i.e. \0.8) represents areas where the bedrock is fractured/ is often possible to make qualitative hydrologic deduction or intensely weathered. from curve type (Worthington 1993). 123 Appl Water Sci (2017) 7:4615–4632 4625 Fig. 11 Typical VES curve types observed in the study area (a-d) Table 1 Results of vertical electrical sounding No. of VES No. of layers Resistivity Thickness Depth Reflection coefficient Description 1 1 192.8 0.7 0.7 0.98 Sandy top soil 2 421.5 1.1 1.9 Sandy layer 3 57.2 6.0 7.9 Clayey layer 4 5691.9 Infinite Infinite Fresh basement 2 1 285.0 1.4 1.4 0.94 Sandy top soil 2 30.2 8.0 9.3 Clay layer 3 1005.1 Infinite Infinite Fresh basement 3 1 326.9 1.1 1.1 0.59 Top soil 2 768.1 3.5 4.6 Sandy layer/laterite 3 420.4 1.7 6.3 Weathered basement 4 580.2 Infinite Infinite Fractured basement 4 1 334.5 0.9 0.9 0.92 Top soil 2 392.8 1.3 2.2 Sandy layer 3 73.7 4.2 6.4 Clay layer 4 1018.9 Infinite Infinite Fresh basement 5 1 704.5 1.2 1.2 0.31 Top soil 2 28.3 8.3 9.4 Clay layer 123 4626 Appl Water Sci (2017) 7:4615–4632 Table 1 continued No. of VES No. of layers Resistivity Thickness Depth Reflection coefficient Description 3 746.2 23.2 32.6 Fractured basement 4 1415.9 Infinite Infinite Fresh basement 6 1 126.4 0.4 0.4 0.87 Top soil 2 44.8 6.3 6.8 Clay layer 3 665.5 Infinite Infinite Fresh basement 7 1 98.2 0.7 0.7 0.89 Top soil 2 44.4 1.5 2.2 Clay layer 3 458.8 39.8 42.0 Fractured basement 4 7956.5 Infinite Infinite Fresh basement 8 1 157.4 0.9 0.9 0.95 Top soil 2 305.4 2.6 3.5 Sandy layer 3 64.9 20.7 24.2 Clay layer 4 2449.2 Infinite Infinite Fresh basement 9 1 92.5 0.9 0.9 0.96 Top soil 2 153.3 6.6 7.5 Sandy layer 3 88.0 18.2 25.7 Clayey layer 4 4711.2 Infinite Infinite Fresh basement 10 1 217.4 0.5 0.5 0.92 Top soil 2 49.1 10.8 11.4 Clayey layer 3 1173.5 Infinite Infinite Fresh basement 11 1 66.1 1.8 1.8 0.91 Top soil 2 288.6 7.0 13.9 Sandy layer 3 99.7 21.4 30.4 Weathered basement 4 2035.1 Infinite Infinite Fresh basement 12 1 144.5 1.9 1.9 0.64 Top soil 2 396.4 22.6 22.5 Sandy layer 3 140.6 41.1 65.6 Clayey sand 4 708.6 Infinite Infinite Fractured basement 13 1 733.4 0.9 0.9 0.98 Top soil 2 1012.7 3.1 3.9 Lateritic rock 3 77.0 11.5 15.4 Clayey layer 4 9302.6 Infinite Infinite Fresh basement 14 1 133.7 1.0 1.0 0.98 Sandy top soil 2 161.9 2.6 3.6 Sandy layer 3 35.4 8.7 12.3 Clayey layer 4 4783.0 Infinite Infinite Fresh basement 15 1 82.1 0.7 0.7 0.96 Clayey sand 2 288.5 1.6 2.3 Sandy layer 3 52.7 8.6 10.9 Clayey layer 4 3181.0 Infinite Infinite Fresh basement 16 1 183.4 1.0 1.0 0.94 Top soil 2 141.3 5.7 6.7 Clayey sands 3 306.9 9.4 16.0 Sandy layer 4 202.1 16.8 32.8 Weathered or fractured rock 5 6560.2 Infinite Infinite Fractured basement 17 1 466.0 1.2 1.2 0.59 Sandy top soil 2 263.3 2.3 3.5 Clayey sand 3 654.5 12.8 16.3 Sandy layer 123 Appl Water Sci (2017) 7:4615–4632 4627 Table 1 continued No. of VES No. of layers Resistivity Thickness Depth Reflection coefficient Description 4 328.9 13.1 29.4 Weathered basement 5 1293.5 Infinite Infinite Fractured basement 18 1 97.4 1.1 1.1 0.88 Top soil 2 40.8 10.5 11.6 Clayey layer 3 655.9 Infinite Infinite Fresh basement 19 1 55.0 0.7 0.7 0.76 Top soil 2 303.3 3.9 4.6 Sandy layer 3 64.6 13.1 17.7 Clayey layer 4 480.0 Infinite Infinite Fractured basement 20 1 277.1 0.6 0.6 0.96 Top soil 2 1833.3 1.8 2.4 Sandy layer 3 115.2 10.5 12.9 Weathered rock 4 6694.7 Infinite Infinite Fresh basement 21 1 174.6 1.6 1.6 0.99 Top soil 2 28.8 5.0 6.7 Clayey layer 3 6166.4 Infinite Infinite Fresh basement 22 1 870.2 0.6 0.6 0.98 Sandy top soil 2 345.5 1.4 2.0 Sandy layer 3 2342.7 4.7 6.8 Lateritic layer 4 18,265.4 Infinite Infinite Fresh basement 23 1 475.0 1.5 1.5 0.92 Sandy top soil 2 94.1 7.7 9.3 Sandy clay 3 2208.1 Infinite Infinite Fresh basement Fig. 12 Map of the reflection coefficient in the study area 123 4628 Appl Water Sci (2017) 7:4615–4632 Fig. 13 The Iso-resistivity map of the study area The apparent resistivity values of the area were con- deduced that VES 5, VES 7, VES 8, VES 9, VES 11, VES toured to produce the isoresistivity map (Fig. 13) and it 12, VES 16, VES 17 and VES 19 are the most promising revealed that the apparent resistivity increases radially areas for the sitting of boreholes based on consideration of from the central part of area outwardly. The resistivity resistivities of the last layer, overburden thickness, or its ranges between 150-850 Xm. respective reflection coefficient according to Olayinka The overburden thickness in the area varies between 6.3 (1996). and 65.6 m. The isopach map of the area (Fig. 14) showed overburden thickness range of 20–50 m at the northern, eastern and some part at the south of the study area, while Groundwater potential evaluation the relatively thin overburden thickness of about 5–15 m were noticed virtually around the central and western part The groundwater potential of a basement complex area is study area. The overburden thickness is shallow in most determined by a complex inter-relationship between the part of the probing stations, which indicates the closeness geology, post emplacement tectonic history, weathering of the basement to the surface. Therefore, groundwater processes and depth, nature of the weathered layer, occurrence in this area will largely depend on the occur- groundwater flow pattern, recharge and discharge pro- rence of fractures in areas where there is thin overburden cesses (Olorunfemi et al. 2004). Decrease in the reflection thickness. From the VES interpreted result, it can be coefficient and relatively high overburden thickness 123 Appl Water Sci (2017) 7:4615–4632 4629 Fig. 14 Isopach map of the overburden in the study area enhance the productivity of boreholes in some parts of the i. Areas with high yield: These are the areas with basement complex of southwestern Nigeria (Olorunfemi overburden thickness greater than 13 m and/or with and Olorunniwo 1985). reflection coefficient less than 0.8. ii. Areas with medium yield: (i) Areas with overburden The present evaluation of the groundwater potential of the study area has been based on aquifer geoelectrical thickness greater than 13 m but less than 30 m and with reflection coefficient greater than or equal to 0.8 parameters obtained from VES interpretation result. Some of the factors that are considered for groundwater potential iii. Areas potential with low yield are: (i) Areas with in the study area are, overburden thickness, reflection overburden thickness less than 13 m and or with coefficient and presence of fractures and these are reflection coefficient greater than or equal to 0.8. expressed in Table 2. Based on these criteria, the northern, northeastern and Based on the aforementioned factors, groundwater eastern areas have the highest and brightest potential for potential map of the study area was produced from the data future groundwater exploration and development in addi- in Table 2, and the potential of groundwater in the study tion to the existing ones in the study area, while the area is delineated into three (3) segments: the high medium and the low yield water potential are found at the groundwater potential, the medium groundwater potential western and central part of the area. and the low groundwater potential. Three basic criteria Apart from the hand dug wells in this area, two were considered in evaluating promising points for prominent water boreholes are present and were dug by groundwater potential: 123 4630 Appl Water Sci (2017) 7:4615–4632 Table 2 Groundwater Potential across the 23 VES stations VES Station Overburden thickness (m) Reflection coefficient Presence of fracture/weathered rock Remark 1 7.8 0.98 – Low yield 2 9.4 0.94 – Low yield 3 6.3 0.59 Fracture available Medium yield 4 6.4 0.92 – Low yield 5 32.7 0.62 Fracture available High yield 6 6.7 0.87 Weathered rock High yield 7 42.0 0.89 Weathered rock High yield 8 24.2 0.95 – High yield 9 25.7 0.96 – Medium yield 10 11.3 0.92 Weathered rock Medium yield 11 30.2 0.91 Weathered rock High yield 12 65.6 0.64 Fracture available High yield 13 23.6 0.98 – Medium yield 14 12.3 0.98 Weathered rock Medium yield 15 10.9 0.96 Weathered rock Medium yield 16 33.0 0.94 Weathered rock High yield 17 29.4 0.59 Fracture available High yield 18 11.6 0.88 Weathered rock Medium yield 19 17.7 0.76 Partially Fractured High yield 20 12.9 0.96 Weathered rock High yield 21 6.6 0.99 – Low yield 22 6.7 0.98 – Low yield 23 9.2 0.92 – Low yield individuals to get a more hygienic and good quality water from VLF-EM anomaly curves were confirmed by geo- to drink. These wells are located in the part of the study electric subsurface information developed from interpre- area shown in Fig. 15. Well 1 has a low yield. Most times, tation results of vertical electrical soundings. Three (3) to it is usually pumped twice in a day (Early morning and five (5) major subsurface geoelectric layers were delineated evening) into a storage tank and the quantity of water per from VES interpretation result; these include the top soil community member is strictly controlled as a result of the (mostly sandy), sandy or lateritic layer clay or sandy clay low yield. Well 2, however, is located in area classified as (partly weathered to weathered layer) and the basement having high groundwater potential. Unlike Well 1, Well 2 bedrock (fractured/fresh basement). Other VES stations yield is higher and quantity of water per community have appreciable groundwater within the weathered layer member is not controlled and the well is left for the com- but because of high reflection coefficient ([0.8) which munity to fetch continuously unregulated. The existing indicates that the basement beneath is fresh, it might not wells confirm the reliability of the groundwater potential harbor or store adequate or sufficient groundwater, the map, hence the map provides a useful guide for further borehole, when drilled might not be productive enough. groundwater development. Integration of VLF-EM and electrical resistivity sounding results enabled identification of good site for productive borehole and groundwater in a typical crystalline terrain as Conclusion the studied area. The Groundwater potential map produced shows a reliable agreement with the groundwater discharge The combination of electromagnetic profiling and vertical from existing boreholes within the study area. electrical resistivity surveys in the study area has con- It is, however, recommended that detailed studies which tributed to a better understanding of the groundwater might involve the use of multiple approach such as statis- occurrence in this part of basement complex of South- tical modeling coupled with remote sensing data should be western Nigeria. Geological features suspected to be used to predict the groundwater potential of the covered basement fractures (zones of high conductivities) identified areas more accurately and faster. This will also help to 123 Appl Water Sci (2017) 7:4615–4632 4631 Fig. 15 Groundwater potential map of the study area remote sensing technology and applications with Specia lEm- cover wider area extent and, therefore, help the commu- phasis on microwave remote sensing and annual convention of nities locally and on regional basis. Indian Society of Remote Sensing (ISRS). Ahmedabad, Gujarat, India Open Access This article is distributed under the terms of the Bhattacharya PK, Patra HP (1968) Direct current geoelectric sound- Creative Commons Attribution 4.0 International License (http:// ing methods in geochemistry and geophysics. Elsevier, Amster- creativecommons.org/licenses/by/4.0/), which permits unrestricted dam, p 135 use, distribution, and reproduction in any medium, provided you give Davoodi MD, Rezaei M, Pourghasemi HR, Pourtaghi ZS, Pradhan B appropriate credit to the original author(s) and the source, provide a (2013) Groundwater spring potential mapping using bivariate link to the Creative Commons license, and indicate if changes were statistical model and GIS in the Taleghan watershed Iran. Arab J made. Geosci. doi:10.1007/s12517-013-1161-5 Evans BM, Myers WL (1990) A GIS-based approach to evaluating regional groundwater pollution potential with DRASTIC. J Soil Water Conserv 45(2):242–245 References Fraser DC (1969) Contouring of VLF-EM data. Geophysics 34(6):958–967 Anbazhagan S, Balamurugan G, Biswal TK (2011) Remote sensing in Iloeje LP (1986) A new geography of Nigeria New Revised Edition. delineating deep fracture aquifer zones. In: Anbazhagan S, Longman Group, London, p 115 Subramanian SK, Yang X (eds) Geoinformatics in APPLIED Kellgren N (2002) Applicability of remote sensing techniques to GEOMORPHOLOGY. CRC Press, Taylor and Francis, groundwater exploration in semi-arid hard rock terrain—a pp 205–229 systematic approach. PhD thesis, Chalmers Publication Ariyo SO, Oduwole MG, Mosuro GO (2003) Hydro-geophysical Library-Chalmers University of Technology, Gotebor evaluation of groundwater potentials of Awa-Ijebu, southwestern Kumar T, Gautam AK, Kumar T (2014) Appraising the accuracy of Nigeria. J Niger Assoc Hydrogeol 14:13–21 GIS-based Multi-criteria decision making technique for delin- Balamurugan G, AnbazhaganS, Biswal TK (2008) Remote sensing eation of Groundwater potential zones. Water Resour Manag for delineating deep aquifer zones, Hosur-Rayakottai region, 28:4449–4466. doi:10.1007/s11269-014-0663-6 India. In: 2008 (Ed.), National Symposium on Advances in 123 4632 Appl Water Sci (2017) 7:4615–4632 Loke MH (1997) Electrical Imaging surveys for Environmental and Onakomaiya SO, Oyesiku OO, Jegede FI (eds) (1992) Ogun State in Engineering Studies. A partial guide to 2-D and 3-D surveys. maps. Rex Charles Publication, Ibadan, p 187 Minden Heights, 11700, Penang, Malaysia Ozdemir A (2011) GIS-based groundwater spring potential mapping McNeil JD, Labson VF (1992) Geological mapping using VLF radio in the Sultan Mountains (Konya, Turkey) using frequency ratio, fields. In: Nabighian M (ed) Electromagnetic methods in applied weights of evidence and logistic regression methods and their geophysics, vol 2. Society of Exploration Geophysicists, Tulsa, comparison. J Hydrol 411(3–4):290–308 pp 10–12 Parasnis DS (1986) Principles of applied geophysics. Chapmans and Murthy KSR, Mamo AG (2009) Multi-criteria decision evaluation in Hall, London groundwater zones identification in Moyale-Teltele subbasin, Pourghasemi HR, Beheshtirad M (2015) Assessment of a data driven South Ethiopia. Int J Remote Sens 30:2729–2740 evidential belief function model and GIS for groundwater Naghibi A, Pourghasemi HR (2015) A comparative assessment potential mapping in the Koohrang watershed, Iran. Geocarto between three machine learning models and their performance Int 30(6):662–685. doi:10.1080/10106049.2014.966161 comparison by bivariate and multivariate statistical methods for Pourtaghi ZS, Pourghasemi HR (2014) GIS-based groundwater spring groundwater potential mapping in Iran. Water Resour Manag potential assessment and mapping in the Birj and Township, 29(14):5217–5236. doi:10.1007/s11269-015-1114-8 southern Khorasan Province, Iran. Hydrogeology 22:643–662. Naghibi SA, Pourghasemi HR, Dixon B (2016) Groundwater spring doi:10.1007/s10040-013-1089-6 potential using boosted regression tree, classification and Pradhan B (2009) Groundwater potential zonation for basaltic regression tree, and random forest machine learning models in watersheds using satellite remote sensing data and GIS tech- Iran. Environ Monit Assess 188:44. doi:10.1007/s10661-015- niques. Cent Eur J Geosci 1(1):120–129 5049-6 Rahmati O, Pourghasemi HR, Melesse A (2016) Application of GIS- Offodile ME (1983) The occurrence of exploitation groundwater in based data driven random forest and maximum entropy models Nigeria Basement rocks. Nig J Min Geol 20:131–146 for groundwater potential mapping: a case study at Mehran Ogunrayi AO, Akinseye FM, Goldberg V, Bernhofer C (2016) Region, Iran. Catena 137:360–372. doi:10.1016/j.catena.2015. Descriptive analysis of rainfall and temperature trends over 10.010 Akure, Nigeria. J Geogr Reg Plann 9(11):195–202 Sener E, Davraz A, Ozcelik M (2005) An integration of GIS and Okwueze EE (1996) Preliminary findings of the groundwater resource remote sensing in groundwater investigations: a case study in potentials from a regional geo-electric survey of the Obudu Burdur, Turkey. Hydrogeol J 13(5–6):826–834 basement area. Nig Global J Pure Appl Sci 2(2):201–211 Sharma MP, Kujur A (2012) Application of Remote Sensing and GIS Oladapo MI, Akintorinwa OJ (2007) Hydrogeophysical study of for groundwater recharge zone in and around Gola Block, Ogbese, southwestern Nigeria. Glob J Pure Appl Sci Ramgargh district, Jharkhand, India. Int J Sci Res Publ 2(2):1–6 13(1):55–61 Singh PK, Singh UC (2009) Water resource evaluation and manage- Olasehinde PI, Bayewu OO (2011) Evalution of Electrical resistivity ment for Morar River Basin, Gwalior district, Madhya Pradesh, anisotropy in geological mapping: a case study of Odo Ara, west using GIS e-journal. Earth Sci India 2(III):174–186 central Nigeria. Afr J Environ Sci Technol 5(7):553–556 Solomon S, Quiel F (2006) Groundwater study using remote sensing Olayinka AI (1996) Non uniqueness in the interpretation of bedrock and geographic information systems (GIS) in the central resistivity from sounding curve and its hydrological implica- highlandsof Eritrea. Hydrogeol J 14(5):1029–1041 tions. Water Resour J NAH 7(1&2):55–60 Telford WM, Geldart LP, Sheriff RE, Keys DA (1976) Applied Olayinka AI, Olorunfemi MO (1992) Determination of geoelectrical geophysics. Cambridge University Press, Cambridge, p 282 characteristics in Okene area and implication for borehole White IF (1986) An assessment of geophysical method applied to setting. J Min Geol 28:403–412 basement aquifer studies in Masvingo Province, Zimbabwe. Olorunfemi MO, Fasuyi SA (1993) Aquifer types and the geoelectric/ Commonwealth Science Council Technical Paper 273, vol 11, hydrologic characteristics of part of the central basement terrain pp 14–32 of Nigeria (Niger State). J Afr Earth Sci 16:309–317 Worthington PF (1993) The Uses and abuses of archie equations: the Olorunfemi MO, Olorunniwo MA (1985) Geoelectric parameter and formation factor—porosity relationship. J Appl Geophys aquifer characteristics of some parts of southwestern Nigeria. 30:215–228 Geol Appl E Hydrogeol Part 2:99–109 Zabihi M, Pourghasemi HR, Pourtaghi ZS, Behzadfar M (2016) GIS- Olorunfemi MO, Afolayan JF, Afolabi O (2004) Geoelectric/electro- based multivariate adaptive regression spline and random forest magnetic VLF survey for groundwater in a Basement Terrain: a models for groundwater potential mapping in Iran. Environ Earth case Study. Ife J Sci 6(1):74–78 Sci 75:665. doi:10.1007/s12665-016-5424-9 Oloruntola M, Adeyemi GO (2014) Geophysical and hydrochemical evaluation of groundwater potential and character of Abeokuta area, southwestern Nigeria. J Geogr Geol 6(3):162–177 Publisher’s Note Omosuyi GO, Ojo JS, Enikanselu PA (2003) Geophysical investiga- Springer Nature remains neutral with regard to jurisdictional claims in tion for groundwater of Obanla-Obakekere in Akure Area within published maps and institutional affiliation. the Basement Complex of South Western Nigeria. J Min Geol 3(2):109–116 http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Applied Water Science Springer Journals

Geophysical evaluation of groundwater potential in part of southwestern Basement Complex terrain of Nigeria

Download PDF
18 pages

Loading next page...
 
/lp/springer_journal/geophysical-evaluation-of-groundwater-potential-in-part-of-OyeZ7T2aHf

References (43)

Publisher
Springer Journals
Copyright
Copyright © 2017 by The Author(s)
Subject
Earth Sciences; Hydrogeology; Water Industry/Water Technologies; Industrial and Production Engineering; Waste Water Technology / Water Pollution Control / Water Management / Aquatic Pollution; Nanotechnology; Private International Law, International & Foreign Law, Comparative Law
ISSN
2190-5487
eISSN
2190-5495
DOI
10.1007/s13201-017-0623-4
Publisher site
See Article on Publisher Site

Abstract

Appl Water Sci (2017) 7:4615–4632 https://doi.org/10.1007/s13201-017-0623-4 O R I G IN AL ARTI CL E Geophysical evaluation of groundwater potential in part of southwestern Basement Complex terrain of Nigeria 1 2 1 • • • Olateju O. Bayewu Moroof O. Oloruntola Ganiyu O. Mosuro 1 1 3 • • Temitope A. Laniyan Stephen O. Ariyo Julius O. Fatoba Received: 22 April 2017 / Accepted: 12 September 2017 / Published online: 18 September 2017 The Author(s) 2017. This article is an open access publication Abstract The geophysical assessment of groundwater in Keywords Groundwater potential  Resistivity survey Awa-Ilaporu, near Ago Iwoye southwestern Nigeria was VES  VLF-EM  Fracture  Geoelectric layer carried out with the aim of delineating probable areas of high groundwater potential. The area falls within the Crystalline Basement Complex of southwestern Nigeria which is pre- Introduction dominantly underlain by banded gneiss, granite gneiss and pegmatite. The geophysical investigation involves the very In hard rock terrains, groundwater potential mapping is rel- low frequency electromagnetic (VLF-EM) and Vertical atively complex due largely to highly variable nature of the Electrical Sounding (VES) methods. The VLF-EM survey geological terrain (Kellgren 2002: Anbazhagan et al. 2011) was at 10 m interval along eight traverses ranging between extensive hydrogeological investigations are required in 290 and 700 m in length using ABEM WADI VLF-EM unit. basement complex environment to understand groundwater The VLF-EM survey was used to delineate areas with con- conditions (Solomon and Quiel 2006; Balamurugan et al. ductive/fractured zones. Twenty-three VES surveys were 2008;Pradhan 2009). Evans and Myers 1990; Sener et al. carried out with the use of Campus Ohmega resistivity meter 2005; Singh and Singh 2009;Sharmaand Kujur 2012 all at different location and at locations areas delineated as high noted that several methods commonly adopted in delineating conductive areas by VLF-EM survey. The result of VLF-EM groundwater potential depending on the available data which survey along its traverse was used in delineating high con- include remote sensing and Geological Information Sys- ductive/fractured zones, it is, however, in agreement with the tem(GIS). Several statistical methods can also be adopted for delineation of the VES survey. The VES results showed 3–4 groundwater mapping where adequate information on dif- geoelectric layers inferred as sandy topsoil, sandy clay, clayey ferent influencing parameters to groundwater accumulation and fractured/fresh basement. The combination of these two and movement are available. These include frequency ratio methods, therefore, helped in resolving the prospecting (Davoodi et al. 2013), multi-criteria decision evaluation location for the groundwater yield in the study area. (Murthy and Mamo 2009; Kumar et al. 2014), logistic regression model (Ozdemir 2011), weights-of-evidence model (Ozdemir 2011; Pourtaghi and Pourghasemi 2014), random forest model (Rahmati et al. 2016 Naghibi et al. 2016), maximum entropy model (Rahmati et al. 2016), & Olateju O. Bayewu boosted regression tree (Naghibi et al. 2016; Naghibi and tejubpositive@yahoo.com Pourghasemi 2015), classification and regression tree (Naghibi et al. 2016), multivariate adaptive regression spline Department of Earth Sciences, Olabisi Onabanjo University, Ago Iwoye, Nigeria model (Zabihi et al. 2016), certainty factor model (Zabihi et al. 2016), evidential belief function (Pourghasemi and Department of Geosciences, University of Lagos, Lagos, Beheshtirad 2015; Naghibi and Pourghasemi 2015), and Nigeria generalized linear model (Naghibi and Pourghasemi 2015). Department of Applied Geophysics, Federal University Oye, These information are lacking in many third world country Oye Ekiti, Nigeria 123 4616 Appl Water Sci (2017) 7:4615–4632 Fig. 1 The location map of the study area hence proper understanding of hydrogeological characteristics subsurface layering and ensures a higher degree of accu- for successful exploitation of groundwater in basement areas racy in the location of hydro resources (Omosuyi et al. depend largely on geophysical methods. 2003). They are important in the search and location of Various forms of water exploratory projects are used in suitable groundwater potentials either singly or combined. the provision of potable water for human usage and great Various combinations of geophysical methods have been importance is geophysics which serves as important tool in used with an accompanying increase in the degree of exploration. Offodile (1983) documented that careful accuracy in the location of suitable groundwater reservoir. studies accompanied by improved drilling techniques yield A combination of the electromagnetic method and the favorable results even in problematic areas. Geophysical electrical resistivity gave a higher rate of 90% as opposed methods, therefore, play an important role in the explo- to 82% by the electromagnetic method and the 85% by the ration of suitable and productive groundwater reservoirs. resistivity method (White 1986). The geophysical survey is employed to determine geo- In areas underlain by crystalline rocks, groundwater electric parameters of formations, identify aquifer units and occurs in fracture zone or in highly weathered basement also determine its depth and lateral extent (Telford et al. (Olorunfemi and Fasuyi 1993; Ariyo et al. 2003). The 1976). electromagnetic and resistivity methods are both respon- The types of geophysical method used for a survey sive to water bearing basement fracture columns due to the depends mainly on the extent or size of area to be surveyed, relatively high bulk electric conductivities, both methods the cost of the survey, geology of the area and the ease of were, therefore, found relevant and were hence integrated the interpretation of data obtained. It also provides infor- in the geophysical investigation. The VLF-EM method was mation on the depth of water table, the lithology in the adopted as a fast reconnaissance tool to map possible linear 123 Appl Water Sci (2017) 7:4615–4632 4617 Fig. 2 Map of the study area showing the location of the VES points and VLF Traverse in the study area Fig. 3 The VLF-EM traverse and Karous–Hjelt pseudosection for Traverse 1 123 4618 Appl Water Sci (2017) 7:4615–4632 Fig. 4 The VLF-EM traverse and Karous–Hjelt pseudosection for Traverse 2 features such as; fault, and fracture zones while the elec- The aim of this study is, therefore, to delineate the trical resistivity method was used to investigate prominent groundwater potentials in Awa-Ilaporu, near Ago Iwoye electromagnetic anomalies and provide a geo-electric southwestern Nigeria, by determining the depth of occurrence image or section of the subsurface sequence. of suitable aquifers; and also to provide background infor- In spite the many studies (Olorunfemi and Olorunniwo mation for the future development of groundwater within the 1985; Olayinka and Olorunfemi 1992; Okwueze 1996; area by delineating potential areas for borehole drilling. Oladapo and Akintorinwa 2007; Oloruntola and Adeyemi 2014) on groundwater potential in many parts of Nigeria, most of the studies were carried out in urban centers such Location of the study area and geological setting as Lagos, Abeokuta, Ibadan where hydrogeological infor- mation is readily available. Awa-Ilaporu, SW is located The study area (Fig. 1) is located in Awa-Ilaporu, near Ago within the Basement Complex terrain of southwestern Iwoye, south western Nigeria; it falls between latitude 0 0 0 Nigeria like many areas in southwestern Nigeria it is a 657 to 659 North of the Equator and longitudes 3 55 community of indigenous rural people and students of a and 3 57 East of the Greenwich Meridian. The drainage non-residential Olabisi Onabanjo University, which lacks shows a dendritic drainage pattern and the major river in municipal water supply. The inhabitants rely mainly on low the area is River Ome and all other tributaries take their yield, pollution prone shallow wells many of which dries source from this river. It is located within the tropical rain up during dry season. Most of the attempts to construct forest which is characterized by a tropical climate with deeper borehole have either failed outrightly or produced alternating wet and dry season, within the year. According low yield borehole. As a result of this, the need to explore to Onakomaiya et al. (1992), the wet season spans from other promising high water yield areas to supplement water March to October and peaks in June/July while the dry supply mostly during the dry season or drought is obvious, season spans from November to February. The mean hence the need for a more detailed evaluation of the annual rainfall ranges from 100 to 1500 mm with average groundwater potential of the community. rainfall of about 100 mm. Ogunrayi et al. (2016) observed fluctuations in rainfall and temperature pattern of Akure 123 Appl Water Sci (2017) 7:4615–4632 4619 Fig. 5 The VLF-EM traverse and Karous–Hjelt pseudosection for Traverse 3 which is part of southwestern Nigeria, the climate of the The VLF-EM survey region indicates that the beginning of rainfall is becoming earlier which implies possible longer rainy season in the The VLF-EM is a type of continuous wave field electro- magnetic method and it is most widely used in the recon- area. The temperature on the other hand, showed an increasing trend indicating warming throughout the year. naissance mode. VLF traverses can be run quickly and inexpensively to anomalous areas which may require fur- There are lots of vegetation covers such as trees, shrubs and grasses. The temperature of the area ranges from 18 to ther investigation either with more detailed geophysical measurement and/or drilling and sampling (Telford et al. 34 C (Iloeje 1986). The area is found within the southwestern crystalline 1976). This was one of the methods employed in this Basement Complex of Nigeria. Geologically, it is made up research work. of three major rock types; granite gneiss, banded gneiss and The VLF-EM survey was carried out at different stations pegmatites which serves as an intrusive body. Awa-Ilaporu and were surveyed at 10 m interval along eight traverses and environs were in the past agrarian communities with approximately east–west direction ranging from 290 to 700 very low population. However, the establishment of the metres in length using ABEM WADI VLF-EM unit. The VLF-EM was used to initially delineate areas with con- then Off-Campus Ogun State University (now Olabisi Onabanjo University) led to rapid geometric increase in the ductive or fractured zone. VLF systems make use of the energy emanating from population of the communities. distant powerful radio transmitters and measure the per- turbations in plane-wave radio signal (15–30 kHz). These Materials and methods low frequency signals are trapped between the earth and the ionosphere. Two geophysical methods were used for this work; the The primary field (the transmitted radio signal) causes very low frequency electromagnetic (VLF-EM) and verti- eddy currents to be induced in conductive geological units cal electrical sounding (VES). The location and arrange- or structure. Faraday’s principle of EM induction shows ment of the two methods in the area is shown in Fig. 2. that any oscillating magnetic field (e.g. the radio wave) will 123 4620 Appl Water Sci (2017) 7:4615–4632 Fig. 6 The VLF-EM traverse and Karous–Hjelt pseudosection for Traverse 4 produce an electric field and electric current in a conduc- filtered real are determined. Anomalous areas are iden- tive media. Those eddy currents in turn create a secondary tified and a gross characterization attached to the magnetic field which is measured by the VLF receiver. The anomaly (e.g. steeply dipping conductor or thickening secondary or perturbed field may be phase shifted and conductive overburden). Some simple modeling may be oriented in a different direction than the primary field carried out for simple geometric structures (McNeil and depending on the shape or geometry of the conductor, the Labson 1992). orientation of the conductor and conductivity contrast with Data filtering are applied in other to eliminate errors and the surrounding material (e.g. the host rock). The instru- enhance interpretation of data. This is done by applying a ment measures two components of magnetic field or filter operator (Q) which transform true anomaly inflection equivalently the ‘‘tilt angle’’ and ellipticity of the field. to peak positive anomalies also referred to as conductivity Some instruments also measure the third magnetic com- because they are proportional (Parasnis 1986). The filter ponent and/or the electric field. The electrical field is operation is given by Fraser (1969): measured by inserting two probes in the ground spaced F1 ¼½ ðÞ U þ U ðÞ U þ U Fraser filtering; 3 4 1 2 about 5 meters (McNeil and Labson 1992). VLF interpre- tation is generally qualitative or subjective in nature and where A , A , A and A are consecutive readings of the 1 2 3 4 sometimes may be subjected to quantitative interpretation measured raw data obtained on the field. with the aid of filtering technique from which the true 123 Appl Water Sci (2017) 7:4615–4632 4621 Fig. 7 The VLF-EM traverse and Karous–Hjelt pseudosection for Traverse 5 Vertical electrical sounding (VES) survey results obtained from the exercise were used as input- model for the eventual computer aided iteration using The second type of geophysical survey method used is the WINRESIST program. electrical resistivity method using the schlumberger elec- The reflection coefficient of each station in the area was trode configuration. Twenty-three (23) Vertical Electrical calculated using the method of Bhattacharya and Patra Sounding stations were carried out in the field using (1968), Olayinka (1996). Loke (1997) and Olasehinde and OHMEGA resistivity meter which investigates the sub- Bayewu (2011): surface resistivity conditions by passing electric current K ¼ðq  q Þ=ðq þ q Þ; n n n1 n n1 into the ground through a pairs of current electrodes and where K is reflection coefficient for the nth layer, n is the measuring the resulting voltage differences between pair’s n number of layers, q is the layer resistivity of the nth layer potential electrodes. Repeated measurements of current and and q is the layer resistivity overlying the nth layer. potential difference were made at these same points using a n1 larger current electrode separation (AB/2) in each succes- sive electrode probe to determine the depth to the bed rock. Results and discussion In the probe, the spacing AB/2 was varied in a line direction to a maximum of 100 m in a station, keeping the Very low frequency-electromagnetic method (VLF- center of the electrode configuration fixed. The values EM) obtained were then plotted on a log–log paper as points with the resistivity values being on the vertical axis and the Traverse 1 is 400 m in length (Fig. 3). The filtered real current electrode spacing (AB/2) on the horizontal axis. value ranges from -131.7 to 118.0 Siemens, while the The points were joined and curve marched manually using filtered imaginary ranges from -30.3 to 68.9 Siemens. The pre-calculated master curves and their auxiliaries. The 123 4622 Appl Water Sci (2017) 7:4615–4632 Fig. 8 The VLF-EM traverse and Karous–Hjelt pseudosection for Traverse 6 traverse shows the maximum peak at both positive and overburden T2 is identified at distance between 310 and negative region with a more prominent filtered real peak at 350 m where the positive peak of filtered real and imagi- horizontal distance of 70–100 m. This usually signifies or nary coincide. In the Karous–Hjelt filtering pseudo-section, corresponds to the area of high conductivity or area with the extent of the fractured identified is below 40 m depth, the presence of fracture. This is marked F1 on the graph. this can either be a localized zone of fracture or thick The correspondent Karous–Hjelt pseudosection filtering clayey materials in the region. confirms the moderately high conductivity which extends Traverse 3 is 600 m in length (Fig. 5). The filtered real below 50 m depth. This conductivity could be due to the values ranges from -28.7 to 69.2 Siemens, while the fil- presence of fracture or accumulation of clayey materials. tered imaginary ranges from -67.5 to 100.7 Siemens. A (McNeil and Labson 1992). Also at horizontal distance positive anomalous value of filtered real is observed at between 200 and 250 m, there is an observation of the distance between 100 and 140 m and it is identified as a filtered real and filtered imaginary both positively peaking fracture F3. Area of thick overburden is observed at dis- together; this usually signifies a relatively thick overburden tance interval of 600 and 650 m and marked as T3. The (McNeil and Labson 1992). This area is, therefore, marked Karous–Hjelt pseudosection also agrees with the plot and T1. showed the extent of the identified fracture to be 40 m deep Traverse 2 (Fig. 4) is 700 m long (Fig. 4). The filtered while the thick overburden is about 30 m deep. real values ranges from -57.6 to 53.0 Siemens, while the Traverse 4(Fig. 6) is 400 metres in length. The filtered filtered imaginary ranges from -52.0 to 51.5 Siemens. A real values ranges from -305.4 to 142.2 Siemens, while fracture F2 is observed where the positive peak of the fil- the filtered imaginary values ranges from -17.8 to 20.7 tered real coincides with the negative peak of the imagi- Siemens. The profile shows a maximum peak at the posi- nary at station 635 meters on the traverse. Also a thick tive region with a more prominent filtered real peak at 123 Appl Water Sci (2017) 7:4615–4632 4623 Fig. 9 The VLF-EM traverse and Karous–Hjelt pseudosection for Traverse 7 285 m, which also correspond to high conductive region. shallow overburden. Fractures F6 and F7 are observed on There are occurrences of fracture between at 270–290 m the traverse at 5–30 and 200–230 m, respectively. The (F4a) and at 310–330 m (F4b) along this traverse. This also Karous–Hjelt pseudosection showed that the extent of the shows in the Karous–Hjelt filtering pseudo-section and identified fracture F6 extended to about 20 m deep while reveal that the fractures extend to more than 50 m. F7 extended to 45 m deep. Traverse 5 (Fig. 7) is also 400 m in length. The filtered Traverse 7 (Fig. 9) is 400 m. The filtered real value real values ranges from -53.0 to 48.5 Siemens, while the ranges from -73.5 to 552.1 Siemens, while the filtered filtered imaginary values ranges from -31.7 to 28.9 Sie- imaginary ranges from -6.6 to 6.6 Siemens. The traverse mens. The profile shows a maximum peak at positive shows a maximum peak of filtered real at 30 m along the region with a more prominent filtered real peak at 260 m. traverse with width of about 40 m; this is thus corre- The fracture, thick overburden, and shallow overburden are sponded to fracture F8 and fracture F9 was observed at marked as F5, T4 and S2, respectively. The Karous–Hjelt 320 m of the traverse with the width of about 30 m. The pseudosection showed the extent of the identified fracture Karous–Hjelt pseudosection showed the extent of the to be inclined and also extended to more than 50 m deep identified fracture F8 to be about 28 m deep while F9 is while the thick overburden is about 40 m deep. 40 m deep. Traverse 6 (Fig. 8) is 290 metres in length. The filtered Traverse 8 (Fig. 10) is 400 m long. The filtered real real values range from -47.5 to 34.2 Siemens, while the values range from -203.7 to 146.8 Siemens, while the filtered imaginary values ranges from -36.7 to 36.7 Sie- filtered imaginary ranges from 0.0 to 0.9 Siemens. The high mens. On the profile is S3 at point 230 metres with maximum peak of the positive filtered real implies frac- approximately width of 22 m and correspond to area of tured zones, F10 was observed at 200 m of the traverse of 123 4624 Appl Water Sci (2017) 7:4615–4632 Fig. 10 The VLF-EM traverse and Karous-Hjelt pseudosection for Traverse 8 width of about 30 m and F11 at point 280 m with width of Typical iterated curves generated from the field mea- about 30 m, respectively. The Karous–Hjelt pseudosection surements in the area are shown in Fig. 11. Table 1 showed the identified fractures F10 and F11 to be inclined revealed the geoelectric parameters of the various layers and they are also interconnected. They are extended to and showed the inferred lithologies from the geoelectric more than 40 m deep. interpretation. The geoelectric interpretation revealed 3-5 geoelectric layers: top soil (66–870 Xm), the weathered layer which Vertical electrical sounding (VES) data comprises of clay/clayey sand/sand/laterite (28.3–2342.7 Xm), underlying this layer is the fractured basement The areas delineated as high conductive/fracture zones and (480.0–1415.9 Xm) and the fresh basement thick overburden along the traverse were considered as (655.9–18,265.4 Xm). The fractured and fresh basement points of interest in the VES survey. layers were differentiated using the values of reflection Interpretation of VES data is both quantitative and coefficient obtained from each VES point, which is the qualitative, it involves the determination of the thickness measure of competence of the basement layer. (Olayinka and resistivity of different horizons and the inference of 1996; Olasehinde and Bayewu 2011). From the calculated their lithologies based on their resistivity and reflection reflection coefficient, the reflection coefficient map was coefficient values. produced (Fig. 12) and shows a value range of (0.59–0.98). The curve types observed in the area are 3-layer H-type Olayinka (1996) observed that an area of lower reflection (26%); 4-layer HA-type (9%) and KH (52%); and 5-layer coefficient value (\0.8) exhibits weathered or fractured HKH-type (13%). The curve types include KH, HA, HKH basement rock thus, favors a high water potential. There- and H. The KH type is the most predominant and it is fore, areas with relatively lower reflection coefficient typical of tropics area (Olayinka and Olorunfemi 1992). It (i.e. \0.8) represents areas where the bedrock is fractured/ is often possible to make qualitative hydrologic deduction or intensely weathered. from curve type (Worthington 1993). 123 Appl Water Sci (2017) 7:4615–4632 4625 Fig. 11 Typical VES curve types observed in the study area (a-d) Table 1 Results of vertical electrical sounding No. of VES No. of layers Resistivity Thickness Depth Reflection coefficient Description 1 1 192.8 0.7 0.7 0.98 Sandy top soil 2 421.5 1.1 1.9 Sandy layer 3 57.2 6.0 7.9 Clayey layer 4 5691.9 Infinite Infinite Fresh basement 2 1 285.0 1.4 1.4 0.94 Sandy top soil 2 30.2 8.0 9.3 Clay layer 3 1005.1 Infinite Infinite Fresh basement 3 1 326.9 1.1 1.1 0.59 Top soil 2 768.1 3.5 4.6 Sandy layer/laterite 3 420.4 1.7 6.3 Weathered basement 4 580.2 Infinite Infinite Fractured basement 4 1 334.5 0.9 0.9 0.92 Top soil 2 392.8 1.3 2.2 Sandy layer 3 73.7 4.2 6.4 Clay layer 4 1018.9 Infinite Infinite Fresh basement 5 1 704.5 1.2 1.2 0.31 Top soil 2 28.3 8.3 9.4 Clay layer 123 4626 Appl Water Sci (2017) 7:4615–4632 Table 1 continued No. of VES No. of layers Resistivity Thickness Depth Reflection coefficient Description 3 746.2 23.2 32.6 Fractured basement 4 1415.9 Infinite Infinite Fresh basement 6 1 126.4 0.4 0.4 0.87 Top soil 2 44.8 6.3 6.8 Clay layer 3 665.5 Infinite Infinite Fresh basement 7 1 98.2 0.7 0.7 0.89 Top soil 2 44.4 1.5 2.2 Clay layer 3 458.8 39.8 42.0 Fractured basement 4 7956.5 Infinite Infinite Fresh basement 8 1 157.4 0.9 0.9 0.95 Top soil 2 305.4 2.6 3.5 Sandy layer 3 64.9 20.7 24.2 Clay layer 4 2449.2 Infinite Infinite Fresh basement 9 1 92.5 0.9 0.9 0.96 Top soil 2 153.3 6.6 7.5 Sandy layer 3 88.0 18.2 25.7 Clayey layer 4 4711.2 Infinite Infinite Fresh basement 10 1 217.4 0.5 0.5 0.92 Top soil 2 49.1 10.8 11.4 Clayey layer 3 1173.5 Infinite Infinite Fresh basement 11 1 66.1 1.8 1.8 0.91 Top soil 2 288.6 7.0 13.9 Sandy layer 3 99.7 21.4 30.4 Weathered basement 4 2035.1 Infinite Infinite Fresh basement 12 1 144.5 1.9 1.9 0.64 Top soil 2 396.4 22.6 22.5 Sandy layer 3 140.6 41.1 65.6 Clayey sand 4 708.6 Infinite Infinite Fractured basement 13 1 733.4 0.9 0.9 0.98 Top soil 2 1012.7 3.1 3.9 Lateritic rock 3 77.0 11.5 15.4 Clayey layer 4 9302.6 Infinite Infinite Fresh basement 14 1 133.7 1.0 1.0 0.98 Sandy top soil 2 161.9 2.6 3.6 Sandy layer 3 35.4 8.7 12.3 Clayey layer 4 4783.0 Infinite Infinite Fresh basement 15 1 82.1 0.7 0.7 0.96 Clayey sand 2 288.5 1.6 2.3 Sandy layer 3 52.7 8.6 10.9 Clayey layer 4 3181.0 Infinite Infinite Fresh basement 16 1 183.4 1.0 1.0 0.94 Top soil 2 141.3 5.7 6.7 Clayey sands 3 306.9 9.4 16.0 Sandy layer 4 202.1 16.8 32.8 Weathered or fractured rock 5 6560.2 Infinite Infinite Fractured basement 17 1 466.0 1.2 1.2 0.59 Sandy top soil 2 263.3 2.3 3.5 Clayey sand 3 654.5 12.8 16.3 Sandy layer 123 Appl Water Sci (2017) 7:4615–4632 4627 Table 1 continued No. of VES No. of layers Resistivity Thickness Depth Reflection coefficient Description 4 328.9 13.1 29.4 Weathered basement 5 1293.5 Infinite Infinite Fractured basement 18 1 97.4 1.1 1.1 0.88 Top soil 2 40.8 10.5 11.6 Clayey layer 3 655.9 Infinite Infinite Fresh basement 19 1 55.0 0.7 0.7 0.76 Top soil 2 303.3 3.9 4.6 Sandy layer 3 64.6 13.1 17.7 Clayey layer 4 480.0 Infinite Infinite Fractured basement 20 1 277.1 0.6 0.6 0.96 Top soil 2 1833.3 1.8 2.4 Sandy layer 3 115.2 10.5 12.9 Weathered rock 4 6694.7 Infinite Infinite Fresh basement 21 1 174.6 1.6 1.6 0.99 Top soil 2 28.8 5.0 6.7 Clayey layer 3 6166.4 Infinite Infinite Fresh basement 22 1 870.2 0.6 0.6 0.98 Sandy top soil 2 345.5 1.4 2.0 Sandy layer 3 2342.7 4.7 6.8 Lateritic layer 4 18,265.4 Infinite Infinite Fresh basement 23 1 475.0 1.5 1.5 0.92 Sandy top soil 2 94.1 7.7 9.3 Sandy clay 3 2208.1 Infinite Infinite Fresh basement Fig. 12 Map of the reflection coefficient in the study area 123 4628 Appl Water Sci (2017) 7:4615–4632 Fig. 13 The Iso-resistivity map of the study area The apparent resistivity values of the area were con- deduced that VES 5, VES 7, VES 8, VES 9, VES 11, VES toured to produce the isoresistivity map (Fig. 13) and it 12, VES 16, VES 17 and VES 19 are the most promising revealed that the apparent resistivity increases radially areas for the sitting of boreholes based on consideration of from the central part of area outwardly. The resistivity resistivities of the last layer, overburden thickness, or its ranges between 150-850 Xm. respective reflection coefficient according to Olayinka The overburden thickness in the area varies between 6.3 (1996). and 65.6 m. The isopach map of the area (Fig. 14) showed overburden thickness range of 20–50 m at the northern, eastern and some part at the south of the study area, while Groundwater potential evaluation the relatively thin overburden thickness of about 5–15 m were noticed virtually around the central and western part The groundwater potential of a basement complex area is study area. The overburden thickness is shallow in most determined by a complex inter-relationship between the part of the probing stations, which indicates the closeness geology, post emplacement tectonic history, weathering of the basement to the surface. Therefore, groundwater processes and depth, nature of the weathered layer, occurrence in this area will largely depend on the occur- groundwater flow pattern, recharge and discharge pro- rence of fractures in areas where there is thin overburden cesses (Olorunfemi et al. 2004). Decrease in the reflection thickness. From the VES interpreted result, it can be coefficient and relatively high overburden thickness 123 Appl Water Sci (2017) 7:4615–4632 4629 Fig. 14 Isopach map of the overburden in the study area enhance the productivity of boreholes in some parts of the i. Areas with high yield: These are the areas with basement complex of southwestern Nigeria (Olorunfemi overburden thickness greater than 13 m and/or with and Olorunniwo 1985). reflection coefficient less than 0.8. ii. Areas with medium yield: (i) Areas with overburden The present evaluation of the groundwater potential of the study area has been based on aquifer geoelectrical thickness greater than 13 m but less than 30 m and with reflection coefficient greater than or equal to 0.8 parameters obtained from VES interpretation result. Some of the factors that are considered for groundwater potential iii. Areas potential with low yield are: (i) Areas with in the study area are, overburden thickness, reflection overburden thickness less than 13 m and or with coefficient and presence of fractures and these are reflection coefficient greater than or equal to 0.8. expressed in Table 2. Based on these criteria, the northern, northeastern and Based on the aforementioned factors, groundwater eastern areas have the highest and brightest potential for potential map of the study area was produced from the data future groundwater exploration and development in addi- in Table 2, and the potential of groundwater in the study tion to the existing ones in the study area, while the area is delineated into three (3) segments: the high medium and the low yield water potential are found at the groundwater potential, the medium groundwater potential western and central part of the area. and the low groundwater potential. Three basic criteria Apart from the hand dug wells in this area, two were considered in evaluating promising points for prominent water boreholes are present and were dug by groundwater potential: 123 4630 Appl Water Sci (2017) 7:4615–4632 Table 2 Groundwater Potential across the 23 VES stations VES Station Overburden thickness (m) Reflection coefficient Presence of fracture/weathered rock Remark 1 7.8 0.98 – Low yield 2 9.4 0.94 – Low yield 3 6.3 0.59 Fracture available Medium yield 4 6.4 0.92 – Low yield 5 32.7 0.62 Fracture available High yield 6 6.7 0.87 Weathered rock High yield 7 42.0 0.89 Weathered rock High yield 8 24.2 0.95 – High yield 9 25.7 0.96 – Medium yield 10 11.3 0.92 Weathered rock Medium yield 11 30.2 0.91 Weathered rock High yield 12 65.6 0.64 Fracture available High yield 13 23.6 0.98 – Medium yield 14 12.3 0.98 Weathered rock Medium yield 15 10.9 0.96 Weathered rock Medium yield 16 33.0 0.94 Weathered rock High yield 17 29.4 0.59 Fracture available High yield 18 11.6 0.88 Weathered rock Medium yield 19 17.7 0.76 Partially Fractured High yield 20 12.9 0.96 Weathered rock High yield 21 6.6 0.99 – Low yield 22 6.7 0.98 – Low yield 23 9.2 0.92 – Low yield individuals to get a more hygienic and good quality water from VLF-EM anomaly curves were confirmed by geo- to drink. These wells are located in the part of the study electric subsurface information developed from interpre- area shown in Fig. 15. Well 1 has a low yield. Most times, tation results of vertical electrical soundings. Three (3) to it is usually pumped twice in a day (Early morning and five (5) major subsurface geoelectric layers were delineated evening) into a storage tank and the quantity of water per from VES interpretation result; these include the top soil community member is strictly controlled as a result of the (mostly sandy), sandy or lateritic layer clay or sandy clay low yield. Well 2, however, is located in area classified as (partly weathered to weathered layer) and the basement having high groundwater potential. Unlike Well 1, Well 2 bedrock (fractured/fresh basement). Other VES stations yield is higher and quantity of water per community have appreciable groundwater within the weathered layer member is not controlled and the well is left for the com- but because of high reflection coefficient ([0.8) which munity to fetch continuously unregulated. The existing indicates that the basement beneath is fresh, it might not wells confirm the reliability of the groundwater potential harbor or store adequate or sufficient groundwater, the map, hence the map provides a useful guide for further borehole, when drilled might not be productive enough. groundwater development. Integration of VLF-EM and electrical resistivity sounding results enabled identification of good site for productive borehole and groundwater in a typical crystalline terrain as Conclusion the studied area. The Groundwater potential map produced shows a reliable agreement with the groundwater discharge The combination of electromagnetic profiling and vertical from existing boreholes within the study area. electrical resistivity surveys in the study area has con- It is, however, recommended that detailed studies which tributed to a better understanding of the groundwater might involve the use of multiple approach such as statis- occurrence in this part of basement complex of South- tical modeling coupled with remote sensing data should be western Nigeria. Geological features suspected to be used to predict the groundwater potential of the covered basement fractures (zones of high conductivities) identified areas more accurately and faster. This will also help to 123 Appl Water Sci (2017) 7:4615–4632 4631 Fig. 15 Groundwater potential map of the study area remote sensing technology and applications with Specia lEm- cover wider area extent and, therefore, help the commu- phasis on microwave remote sensing and annual convention of nities locally and on regional basis. Indian Society of Remote Sensing (ISRS). Ahmedabad, Gujarat, India Open Access This article is distributed under the terms of the Bhattacharya PK, Patra HP (1968) Direct current geoelectric sound- Creative Commons Attribution 4.0 International License (http:// ing methods in geochemistry and geophysics. Elsevier, Amster- creativecommons.org/licenses/by/4.0/), which permits unrestricted dam, p 135 use, distribution, and reproduction in any medium, provided you give Davoodi MD, Rezaei M, Pourghasemi HR, Pourtaghi ZS, Pradhan B appropriate credit to the original author(s) and the source, provide a (2013) Groundwater spring potential mapping using bivariate link to the Creative Commons license, and indicate if changes were statistical model and GIS in the Taleghan watershed Iran. Arab J made. Geosci. doi:10.1007/s12517-013-1161-5 Evans BM, Myers WL (1990) A GIS-based approach to evaluating regional groundwater pollution potential with DRASTIC. J Soil Water Conserv 45(2):242–245 References Fraser DC (1969) Contouring of VLF-EM data. Geophysics 34(6):958–967 Anbazhagan S, Balamurugan G, Biswal TK (2011) Remote sensing in Iloeje LP (1986) A new geography of Nigeria New Revised Edition. delineating deep fracture aquifer zones. In: Anbazhagan S, Longman Group, London, p 115 Subramanian SK, Yang X (eds) Geoinformatics in APPLIED Kellgren N (2002) Applicability of remote sensing techniques to GEOMORPHOLOGY. CRC Press, Taylor and Francis, groundwater exploration in semi-arid hard rock terrain—a pp 205–229 systematic approach. PhD thesis, Chalmers Publication Ariyo SO, Oduwole MG, Mosuro GO (2003) Hydro-geophysical Library-Chalmers University of Technology, Gotebor evaluation of groundwater potentials of Awa-Ijebu, southwestern Kumar T, Gautam AK, Kumar T (2014) Appraising the accuracy of Nigeria. J Niger Assoc Hydrogeol 14:13–21 GIS-based Multi-criteria decision making technique for delin- Balamurugan G, AnbazhaganS, Biswal TK (2008) Remote sensing eation of Groundwater potential zones. Water Resour Manag for delineating deep aquifer zones, Hosur-Rayakottai region, 28:4449–4466. doi:10.1007/s11269-014-0663-6 India. In: 2008 (Ed.), National Symposium on Advances in 123 4632 Appl Water Sci (2017) 7:4615–4632 Loke MH (1997) Electrical Imaging surveys for Environmental and Onakomaiya SO, Oyesiku OO, Jegede FI (eds) (1992) Ogun State in Engineering Studies. A partial guide to 2-D and 3-D surveys. maps. Rex Charles Publication, Ibadan, p 187 Minden Heights, 11700, Penang, Malaysia Ozdemir A (2011) GIS-based groundwater spring potential mapping McNeil JD, Labson VF (1992) Geological mapping using VLF radio in the Sultan Mountains (Konya, Turkey) using frequency ratio, fields. In: Nabighian M (ed) Electromagnetic methods in applied weights of evidence and logistic regression methods and their geophysics, vol 2. Society of Exploration Geophysicists, Tulsa, comparison. J Hydrol 411(3–4):290–308 pp 10–12 Parasnis DS (1986) Principles of applied geophysics. Chapmans and Murthy KSR, Mamo AG (2009) Multi-criteria decision evaluation in Hall, London groundwater zones identification in Moyale-Teltele subbasin, Pourghasemi HR, Beheshtirad M (2015) Assessment of a data driven South Ethiopia. Int J Remote Sens 30:2729–2740 evidential belief function model and GIS for groundwater Naghibi A, Pourghasemi HR (2015) A comparative assessment potential mapping in the Koohrang watershed, Iran. Geocarto between three machine learning models and their performance Int 30(6):662–685. doi:10.1080/10106049.2014.966161 comparison by bivariate and multivariate statistical methods for Pourtaghi ZS, Pourghasemi HR (2014) GIS-based groundwater spring groundwater potential mapping in Iran. Water Resour Manag potential assessment and mapping in the Birj and Township, 29(14):5217–5236. doi:10.1007/s11269-015-1114-8 southern Khorasan Province, Iran. Hydrogeology 22:643–662. Naghibi SA, Pourghasemi HR, Dixon B (2016) Groundwater spring doi:10.1007/s10040-013-1089-6 potential using boosted regression tree, classification and Pradhan B (2009) Groundwater potential zonation for basaltic regression tree, and random forest machine learning models in watersheds using satellite remote sensing data and GIS tech- Iran. Environ Monit Assess 188:44. doi:10.1007/s10661-015- niques. Cent Eur J Geosci 1(1):120–129 5049-6 Rahmati O, Pourghasemi HR, Melesse A (2016) Application of GIS- Offodile ME (1983) The occurrence of exploitation groundwater in based data driven random forest and maximum entropy models Nigeria Basement rocks. Nig J Min Geol 20:131–146 for groundwater potential mapping: a case study at Mehran Ogunrayi AO, Akinseye FM, Goldberg V, Bernhofer C (2016) Region, Iran. Catena 137:360–372. doi:10.1016/j.catena.2015. Descriptive analysis of rainfall and temperature trends over 10.010 Akure, Nigeria. J Geogr Reg Plann 9(11):195–202 Sener E, Davraz A, Ozcelik M (2005) An integration of GIS and Okwueze EE (1996) Preliminary findings of the groundwater resource remote sensing in groundwater investigations: a case study in potentials from a regional geo-electric survey of the Obudu Burdur, Turkey. Hydrogeol J 13(5–6):826–834 basement area. Nig Global J Pure Appl Sci 2(2):201–211 Sharma MP, Kujur A (2012) Application of Remote Sensing and GIS Oladapo MI, Akintorinwa OJ (2007) Hydrogeophysical study of for groundwater recharge zone in and around Gola Block, Ogbese, southwestern Nigeria. Glob J Pure Appl Sci Ramgargh district, Jharkhand, India. Int J Sci Res Publ 2(2):1–6 13(1):55–61 Singh PK, Singh UC (2009) Water resource evaluation and manage- Olasehinde PI, Bayewu OO (2011) Evalution of Electrical resistivity ment for Morar River Basin, Gwalior district, Madhya Pradesh, anisotropy in geological mapping: a case study of Odo Ara, west using GIS e-journal. Earth Sci India 2(III):174–186 central Nigeria. Afr J Environ Sci Technol 5(7):553–556 Solomon S, Quiel F (2006) Groundwater study using remote sensing Olayinka AI (1996) Non uniqueness in the interpretation of bedrock and geographic information systems (GIS) in the central resistivity from sounding curve and its hydrological implica- highlandsof Eritrea. Hydrogeol J 14(5):1029–1041 tions. Water Resour J NAH 7(1&2):55–60 Telford WM, Geldart LP, Sheriff RE, Keys DA (1976) Applied Olayinka AI, Olorunfemi MO (1992) Determination of geoelectrical geophysics. Cambridge University Press, Cambridge, p 282 characteristics in Okene area and implication for borehole White IF (1986) An assessment of geophysical method applied to setting. J Min Geol 28:403–412 basement aquifer studies in Masvingo Province, Zimbabwe. Olorunfemi MO, Fasuyi SA (1993) Aquifer types and the geoelectric/ Commonwealth Science Council Technical Paper 273, vol 11, hydrologic characteristics of part of the central basement terrain pp 14–32 of Nigeria (Niger State). J Afr Earth Sci 16:309–317 Worthington PF (1993) The Uses and abuses of archie equations: the Olorunfemi MO, Olorunniwo MA (1985) Geoelectric parameter and formation factor—porosity relationship. J Appl Geophys aquifer characteristics of some parts of southwestern Nigeria. 30:215–228 Geol Appl E Hydrogeol Part 2:99–109 Zabihi M, Pourghasemi HR, Pourtaghi ZS, Behzadfar M (2016) GIS- Olorunfemi MO, Afolayan JF, Afolabi O (2004) Geoelectric/electro- based multivariate adaptive regression spline and random forest magnetic VLF survey for groundwater in a Basement Terrain: a models for groundwater potential mapping in Iran. Environ Earth case Study. Ife J Sci 6(1):74–78 Sci 75:665. doi:10.1007/s12665-016-5424-9 Oloruntola M, Adeyemi GO (2014) Geophysical and hydrochemical evaluation of groundwater potential and character of Abeokuta area, southwestern Nigeria. J Geogr Geol 6(3):162–177 Publisher’s Note Omosuyi GO, Ojo JS, Enikanselu PA (2003) Geophysical investiga- Springer Nature remains neutral with regard to jurisdictional claims in tion for groundwater of Obanla-Obakekere in Akure Area within published maps and institutional affiliation. the Basement Complex of South Western Nigeria. J Min Geol 3(2):109–116

Journal

Applied Water Science – Springer Journals

Published: Sep 18, 2017

There are no references for this article.