Electrical Resistivity Sounding for Subsurface Delineation and Evaluation of Groundwater Potential of Araromi Akungba-Akoko Ondo State Southwestern Nigeria (original) (raw)
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Abstract The objective of this geophysical survey is to evaluate the hydrological characteristics of the study area. This includes the availability of groundwater, depth of aquifer, determining whether the underlying geology is competent basement/weathered basement or fractured bedrock and the delineation of the subsurface into various geo-electric layers. The availability of groundwater in an area is controlled by varying geological factors such as hydrogeological units, stratigraphical faults/folds, and geological sequences The methodology used is the direct current method using the schlumberger configuration. In this electrical resistivity method, artificially-generated electric currents are introduced into the ground and the resulting potential differences are measured at the surface. Deviations from the expected pattern of potential differences from homogeneous ground provide information on the lithological formations and electrical properties of subsurface anomalies. A total of 10 vertical electric sounding was carried out on the study area, which covers the entire community and the data plotted and computer software designed by Vander Velpen BPA was used to iterate the result. This removes the noise and field errors incorporated in the data. The result of the VES curve reveals that there are three major geoelectric layers The fist layer has an intermediate resistivity implying a sandy soil. Very low resistivity corresponds to clayey/clayey sand (VES 4, VES 5, and VES 6) while exceedingly high resistivity (VES 10) implies a lateritic cover. The second layer is the weathered layer sub-divided into minor geoelectric layers such as clays, gravels and weathered rocks. The weathered layers have low resistivity values, possibly due to the presence of conduction fluids such as water. The third layer is the basement or bedrock which may be fractured basement or fresh bedrock. Ajaokuta has more of fresh unfractured bedrocks except in some cases (VES 2 and VES 4) The resistivity of topsoil varies from 12.6Ω to 3247.9Ω with a mean of 657.1Ω ± 947.7. The thickness of topsoil is within the range of 0.4m to 14.9m with a mean of 2.2m ± 4.2. The resistivity of weathered layer ranges from 27.9Ω to 175.5Ω with a mean of 59.2Ω ± 43.5. The thickness of the weathered layer is from minimum of 5.8m to maximum of 37.0 m having a mean of 12.4m ± 9.5. The depth to basement varies from 6.2m to 37.5m with a mean of 13.38 ± 9.07. The resistivity of the basement in the area varies from 183.3Ωm to 4294.2Ωm with a mean 0f 905Ωm ± 1170.The thickness of the topsoil is very low except for (VES 4) The average depth to basement is 13.38m±9.07. Keywords: Boreholes, Ajaokuta, schlumberger configuration, resistivity, VES
International Journal of Geosciences, 2022
This report evaluates the use of electrical method and borehole data to investigate the subsurface to delineate the groundwater potential in Enugu metropolis and the environs, southeastern Nigeria other than rely only on resistivity method which could lead to interpretation error. Integrating these 2 data sets is key in this study. The study area is located in the Anambra Basin and is underlain by Nkporo/Enugu Shale which is overlain by the Mamu Formation. It is bounded by Latitudes 6˚2 0'00"N to 6˚30'00"N and Longitudes 7˚25'00"E to 7˚35'00"E and covers surface area of about 342 m 2. Thirty-one vertical electrical soundings (VES) were carried out across the area using the Schlumberger electrode array with current electrode separation from 2 to 500 m to identify the depths and resistivity values of the identified geo-electric layers. Through data analysis using WinResist software, the apparent resistivity, thicknesses and depths and the thicknesses of the aquifers were generated. The resistivity and depths were modelled to generate resistivity map and depth map. The resistivity of the aquiferous zone within the study area varied from 20.55-427.8 ohm-m at depths of between 10.7-40.05 m. Depth to the water table appears to be shallow at the south western part of the map. The interpreted geo-electric layers show a sequence of lateritic top soil, shale, sand and shale. The frequency distribution of the VES curves generated shows the presence of 3 to 5 layers with HK type as the highest. Also, a 2D model was generated using the correlation of VES to VES data and borehole data to VES data to show the underlying stratigraphy beneath the study area as well as the direction of ground water flow. Result of the VES curve analysis reveals that the sub-surface is underlain by three lithological layers namely: lateritic top soil, shale, sand and shales with NW direction of groundwater flow from the 2D model. Groundwater prospective zones can be seen along NW, SW and
IOSR journal of applied geology and geophysics, 2017
An integrated use of geo-electrical resistivity soundings and hydrogeologic methods were employed in the investigation for groundwater resource,evaluation and development around Obu-Okpella, nearBuacement factory, Southwestern Nigeria. The study area is underlain by Basement Complex rocks which consist of migmatites, granite gneiss and pegmatites.A total of 35 vertical electric soundings (VES) and four exploratory boreholes were carried out in the study. The geo-electric resistivity sounding datawere interpreted using IXD interpexsoftware and the VES interpretation revealed 4 geo-electric layers/lithologic units from the geo-electric parameters. The geo-electric layers are-(1) Topsoil from 0 to 2.5m, (2) weathered basement from 3.3 to 49m, (3) Slightly weathered/Fresh basement from 5m to ∞, (4) Fractured basement (≥5 to 150m) and are characterised by resistivity value range of 14 to 297 ohm-m, 16 to 98 ohm-m, >1000 ohm-m and < 50 to 31056 ohm-m respectively. Four exploratory boreholes numbered BH1, BH2, BH3, and BH4 were drilled on VES 1, 17, 18 and 31 to a depth of 180, 150, 58 and 110m respectively. The VES interpretation and boreholelithologic logs were well correlated. The main aquifer is in the deep and highly fractured basement rocks with average depth of 50-150m. The pumping test results for the boreholes number BH1, BH2, BH3 and BH4 were 0.8l/s, 1.87l/s, 1.2l/s and 1.7l/s respectively with very maximum dynamic water level of <10m.Transitivity value of the aquifer for BH1, BH2, BH3 and BH4 are 2.58m 2 /day, 21.43 m 2 /day, 55.62 m 2 /day, and 37.98 m 2 /day respectively indicates that the lithostrata constituting the aquifer is fair in transmitting the groundwater. With a volume of 12,000 l/day, 97,000 l/day, 91,000 l/day and 51,840 l/day for BH1, BH2, BH3 and BH4, the total volume of water for the four boreholes is 253,560 l/day.
Ethiopian Journal of Environmental Studies and Management, 2013
A geo-resistivity exploration has been carried out for groundwater within the Akobo catchment of the ancient city of Ibadan. The area lies within the basement rock terrain of South Western Nigeria and bounded by longitudes 3 o 51′-3 o 53′E and latitudes 7 o 22′-7 o 24′N. The exploration was done using SYSCAL KID meter while a total of 10 VES with an average of 46m station interval were completed in 3 profiles by means of Schlumberger configuration with total current electrode spread of 160m. The results revealed that the area is underlain by four geo-electric layers. The top lateritic soil has resistivity values ranging from 28.1 to 481.8 Ωm and thickness of 0.8 to 5.7m. The second layer has sand/clay intercalation with resistivity values varying between 47.7 and 192.5 Ωm and thickness varying between 2.8 and 19.4 m. The weathered/fractured basement has resistivity values from 106.2 to 846.8 Ωm with thickness of 13.2 to 24.9m while the partly weathered/fresh basement layer has resistivities ranging from 130 to 856.4 Ωm. The distribution of resistivities in the area shows that the weathered basement has a relatively low resistivity (< 200 Ωm) values in the northeastern and northwestern axis coupled with high thickness values (> 20 m) which suggests the presence of an aquiferous zone. Therefore, this portion of the study area could be highly hydro-geologically promising and maybe recommended for siting groundwater tube.
Electrical Resistivity Survey for Predicting Aquifer at Onicha-Ugbo, Delta State, Nigeria
A geoelectric survey employing the vertical electrical sounding (VES) was carried out in parts of Onicha-Ugbo in Aniocha North Local Government Area of Delta State using Abem Terrameter SAS 300C together with SAS 2000 booster. The study was carried out with the aim of delineating the subsurface geologic sequence present in the study area, determining their geoelectrical parameters (layer thicknesses and resistivities), and delineating the structural and geomorphological features present beneath the subsurface. The results of the survey suggest that the subsurface comprises of 5 - 6 layers and that clay and silt content varies vertically and horizontally, thus influencing the apparent resistivity of the area. The geoelectric section developed shows that the subsurface units are dominantly sandy underlying loamy sandy topsoil which is relatively dry. The depth to water table from the sites is above 150 m and suggests that groundwater exploration is encouraging.A geoelectric survey employing the vertical electrical sounding (VES) was carried out in parts of Onicha-Ugbo in Aniocha North Local Government Area of Delta State using Abem Terrameter SAS 300C together with SAS 2000 booster. The study was carried out with the aim of delineating the subsurface geologic sequence present in the study area, determining their geoelectrical parameters (layer thicknesses and resistivities), and delineating the structural and geomorphological features present beneath the subsurface. The results of the survey suggest that the subsurface comprises of 5 - 6 layers and that clay and silt content varies vertically and horizontally, thus influencing the apparent resistivity of the area. The geoelectric section developed shows that the subsurface units are dominantly sandy underlying loamy sandy topsoil which is relatively dry. The depth to water table from the sites is above 150 m and suggests that groundwater exploration is encouraging.
IOSR Journal of Applied Physics, 2012
Over thirty Vertical Electrical Sounding survey were carried out in Tofa and Rimin Gado local government areas of Kano state. Dynamic water level from open wells was also collected and was used as a guide for the selection of the electrode spread. The schlumberger array with a maximum electrode spread of 100 m was employed in all the points. Results from the sounding data indicates that the area is generally underlain by five geoelectric or geologic section which include Lateritic top soil or Lateritic sand, Silty sand or Sandy clay, Weathered basement or Clayey sand, Fractured basement and Fresh basement. Based on the result obtained the weathered as well as the fractured basements forms the aquiferous zone within the study area, with the weathered being more promising. The resistivity of these zones varies from 9 to 1640 Ωm with an average value 255 Ωm, while the thickness varies from a value of 1.66 to 28 m with an average value of 10.67 m. Depth to this zone varies from 5 to 31 m with an average value of 8.1 m. The study also shows that the Rimin Gado area appears to have more potential for groundwater development as compared with the Tofa area.
International journal of water resources and environmental engineering, 2013
Onicha Olona, Atuma Iga and Akwukwu-Igbo have experienced severe hardship in getting reliable boreholes over many years due to their high topography. They are transition towns as it is from here that marked variations in subsurface structures and topography commence. Although the entry point at onicha Olona which is tied to Issele Uku is a flat land by contouring, the western end of the town has evidence of intermittently occurring deep valleys. It is important to study and ascertain the formation strata and groundwater occurrence in these towns. Hence, this study was made in Onicha Olona, Atuma Iga and Akwukwu-Igbo Delta State Nigeria. Seven vertical electrical sounding (VES) stations were sounded using Schlumberger configuration. The apparent resistivity values obtained in the field were plotted against half current electrode spacings. Interpretations of data were done qualitatively and quantitatively from which seven to eight layers with complex curve types of HAK, HAH, HK, QHK, QKHK, HKHKQ and QHKHA were mapped. Parches of springs from faults in the weathered rocks within the valleys at depths of about 30 m and low yield aquifers at depths of 125 m and beyond are delineated in Onicha Olona. Akwukwu-Igbo and Atuma Iga have sustainable aquifers at depths of 85 to 105 m due to topographic variation.
2013
The Wenner offset system of electrical resisitivity sounding and its multicore cable was used to carry out resistivity survey, in parts of Kaduna town and environs in the Basement Complex of Northern Nigeria. The study is aimed at preliminary appraisal of the groundwater potential of the study area. Thirteen sounding points were taken at various point of interest using Abem terrameter SAS1000.The readings were at spacings of 0.5, 1, 2, 3, 4, 8, 16, 32, 64, and 128m. The field obtained were plotted and subjected to quantitative and qualitative analysis. The layers, resistivities, thicknesses, the depth to basement, and the groundwater potential were deduced. The study area revealed four to six geoelectric layers, consisting of topsoil (laterite, sand and clay), lateritic clay, sand and clay), (sandy clay) highly weathered basement, partially weathered/fractured basement rocks units and fresh basement rock or bedrock. The highly weathered basement/partially weathered and fractured lay...
Central European Journal of Geosciences, 2013
Vertical electrical sounding (VES), employing a Schlumberger electrode configuration, was used to investigate the sediments and aquifer repositories in Itu Local Government Area of Akwa Ibom state, southern Nigeria. This was done in sixteen (16) locations/communities with the maximum current electrode spread ranging between 800–1000m. The field data were interpreted using forward and iterative least square inversion modeling, which gives a resolution with 3–5 geoelectric layers. The observed frequencies in curve types include 31.25% of AKH, 18.8% of AAK and HK and 6.25% of K, QHK, AKH, KA and KHQ, respectively. These sets of curves show a wide range of variabilities in resistivities between and within the layers penetrated by current. The presence of K and H curve types in the study area indicates the alteration of the geomaterials with limited hydrologic significance to the prolific groundwater repository. A correlation of the constrained nearby borehole lithology logs with the VES...