A Geophysical Survey Involving Twelve Vertical Electrical Sounding (VES), Lokoja Areas Council Kogi State (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
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.
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 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.
ABSTRACT Vertical Electrical Sounding (VES) technique using Schlumberger configuration and the 2D resistivity imaging (Wenner array) were carried out to delineate the freshwater aquifer in the Golden Estate of Elegushi community in Lekki, Eti-Osa local government area of Lagos State. Twenty four (24) VES and six (6) 2-D Resistivity data were acquired within the study area using PASI Terrameter (model 16GL). Partial curve-matching technique was used for the processing of the VES data to generate the first order geoelectric parameters and the models obtained were iterated using WinResist (1.0) to create models of perfect fit indicating layer thicknesses and resistivity values for the lithologic layers present in the subsurface, as well as the depth. The 2-D resistivity data were processed using DIPROWIN software (4.0). The interpreted VES data and the 2D images were integrated which delineated four geoelectric layers which include the topsoil, sandy clay, clay and sand. The topsoil has thickness ranging from 0.5 to 3.6 m with its resistivity values ranging from 706 to 5706Ωm. The Sandy clay layer has resistivity values ranging from 68 to 926 Ωm, and thickness ranging from 9.5m to 143.1m. The resistivity values of the sand layer ranges from 185 to 2598Ωm and its thickness ranges from 1.3 to 121.4m. The clay layer has resistivity values ranging from 11 to 39.4Ωm and thickness ranging from 3.4 to 178m. The depth to sand layer which is the aquifer ranges from 35.4m at VES 3 to 81.1 m at VES 1. The depth to the aquifer ranges from 63.7m at VES 6 to 197.3m at VES 8. The depth to the water bearing layer ranges from 18.4 m at VES 10 to 83.2m at VES 12. The aquifer was encountered at a depth range of 16.7 m at VES 14 to 91.4 m at VES 15. The depth to aquifer fluctuates between 25.5 m at VES 19 to 148.7 m at VES 20 and finally, the depth to the aquifer ranges from 26.0 m at VES 24 to 52.2m at VES 21. Generally, the depths to the aquifer fluctuates between 18.4 to 197.3m across the study area. The 2D resistivity structures revealed the lateral and the vertical subsurface information with resistivity values ranging from 13 to 245Ωm. The resistivity values correspond to the topsoil, sandy clay, clay and sand along all the traverse. The results of the 2D resistivity imaging complement the VES results except with slight variations in their layer thickness and resistivity values. Fresh groundwater exploitation through borehole drilling is feasible only at VES 3, 9, 10, 13, 14, 19, 22, and 24 at depths of not less than 36 m, 64 m, 102 m, 90 m, 138 m, 110 m, 95 m, and 67 m respectively. Further studies should be carried out with wider spread in order to map deeper aquifers.
Hydrogeophysical study was carried out in the Basement Complex area of Kogi State Polytechnic, Osara Campus, to investigate the groundwater potential of the subsurface layers. Acute water shortage and challenges of abortive and non-functional open and closed wells has prompted this study on the development of the groundwater resources. This work involves using the electrical resistivity method to investigate concealed fractures within the area with the aim of delineating near surface/subsurface geological layers to determine the depths, thickness, structural trends and spatial distribution of basement rocks as potential sources of groundwater. A total of thirty six vertical electrical sounding (VES) using the Schlumberger configuration was employed for the study. The depth and resistivity of the subsurface layers were determined. The interpreted results of the geo electrical sections indicates the presence of four subsurface layers: top soil of thickness and resistivity values ranging from 0.2 – 5.0m and 169 – 3728 ohms meter, weathered basement ranging from 5 – 12m and 100 – 914 ohms meter, fractured basement ranging from 6.2 – 196 meters and 42-196 ohms meter the fresh rock bedrock ranging from infinity in thickness and 741 – 3691 ohms metres. Geo electric sections, overburden Isopach maps of the area were drawn with basement depressions and elevations, the basement depressions are the priority areas for groundwater abstraction within the study area.
Journal of Geography and Geology, 2020
From the results, three to four electrostratigraphic layers with resistivity value ranging from 44 to 997 ohm/m and thickness ranging from 0.5 to 39.7 m were observed in the study area. The top loose rocks, the weathered conductive zone, the fractured basement rock and the fresh basement rock of older granite suite were encountered respectively. From this research, it can be deduce that, the thicker top soil and deeper weathered basement rock at the depth of 30 to 45 meters within this area produce a productive site for sitting future borehole. Insufficient groundwater supply in some places leading to scarcity is noticed in VES 10, VES 12 and VES 13. H, I, and A curve types are generally the most common in the area and are typical of basement complex area. Geographical Positioning System tool (model: GPSmap 76CSx), was used to locate the VES points. Fifteen VES points with electrode spacing [AB/2] of 100 meters separation around Ndanaku and environs were undertaken using Schlumberge...
Journal of Informatics and Mathematical Sciences, 2017
Vertical Electrical Sounding (VES) was carried out at Laniba area, Ibadan, Oyo state, Nigeria in order to study the subsurface geologic layer with view of determining the depth to the bedrock and thickness of the geologic layers. The ABEM terrameter (SAS 300B) was used for data acquisition in twenty two (22) VES stations. The field data obtained has been analyzed using computer software (IPI2win) which gives an automatic interpretation of the apparent resistivity. The VES results revealed heterogeneous nature of the subsurface geological sequence.\ The geologic sequence beneath the study area is composed of hard pan topsoil (clayed and sandy lateritic weathered layer), partly weathered or fractured basement and fresh basement. The resistivity value for the topsoil layer varies from 36.1 to 185.0 \(\Omega\)m with thickness ranging from 0.1 m to 1.4 m, the weathered basement has resistivity value ranging from 98.0 to 1098.8 \(\Omega\)m and thickness of between 0.1 m to 1.4 m, the frac...
2010
Groundwater occurrence and distribution in Basement Complex is localized and confined to weathered /fractured zones. Hence exploration for groundwater in such terrains posses a great challenge to groundwater development agencies as in most cases the risk of failure of such projects is very high. This study was carried out with the aim of demonstrating the application of vertical electrical sounding method of investigation in the exploration for groundwater in Rimin Gado town and environs. A total of 16 VES points were probed located in 4 settlements spread at a distance of 200-300m apart. ABEM SAS 300C terameter was used to generate field data applying the Schlumberger Array with an AB/2 of 1.5-100m. The field data were simulated using Zhody and OFFIX software. The results show that there are 2-4 Geo-electric layers: topsoil (sandy/lateritic), highly weathered Basement (clay and sandy clay), slightly weathered/ fractured Basement (Clay,sand/clayey sand) and Fresh bed rock. Three bas...
A Vertical Electrical Sounding (VES) Method was employed to determine the groundwater potential of Orisunmibare Village in the neighbourhood of federal government college, Ilorin. The purpose of this study was to determine the feasibility of a portable water borehole in the study area. Presently, there is no municipal water supply in the study area and the water source is from individual hand dug wells. A total of nine VES were carried out in different parts of the study area with DDR1 resistivity meter equipped with an SAS 2000 booster by means of Schlumberger electrode array configuration. The interpretation of the VES curve was carried out by partial curve matching method to obtain initial model parameters and computer iterations using WinResist Software. The curves reveal that the area is characterized by five classes of geo-electric layers. First, highly resistive topsoil layer has a thickness between 0.2-1.0 m. The second lateritic clay layer has thickness ranges from 3.3-15.0 m. Third layer is highly weathered basement with thickness of 6.0-30.7 m. The fourth fractured with weathered rock layer has thickness from 20.0-40.2 m, and fresh basement representing fifth layer has a thickness from 20 m and above. The results indicate the occurrence of good aquifers in the first, second, third, fourth, and fifth VES stations in the form of the weathered and fractured basement. Results also indicate that borehole drilling in the study area is achievable but to a depth of 45 meters to allow large reservoir within the aquifers.