Geoelectrical Investigations for Groundwater Exploration in Crystalline Basement Terrain, SW Nigeria: Implications for Groundwater Resources Sustainability (original) (raw)
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IOP Conference Series: Earth and Environmental Science
This research involves the subsurface geological characterization for groundwater potential assessment within the campus of the Polytechnic of Ibadan, southwestern Nigeria. The study is directed towards groundwater resources exploration, development and management in the campus. Five 2D resistivity imaging traverses were conducted using Wenner array in addition to five VES surveys using Schlumberger array that provide layering information and geoelectrical parameters. Three geologic layers delineated from the 2D resistivity inversion models include predominantly clayey sand/ sandy clay top soil (overburden), partly weathered or fractured basement and fresh basement. Their inverse model resistivity values ranges 6.68-98.6 m , 68.0-929 m and 2252 m with bottom depths ranges 3.8-6.4 m and 6.4-10 m respectively. 1D model inversion from VES results also delineate three lithologies classifying both topsoil and some part of the partly weathered basement as overburden with resistivity and thickness range 483-1746.9 m , 1.1-1.8 m; partly weathered or fractured basement 60.3-93.5 m , 8.4-12.9 m and fresh basement 984.6-2078.9 m . The saturated portion of the partly weathered or fractured basement at depth will favour groundwater exploration and development in this area, while the relatively shallow overburden thickness would serve as the protective layer and recharge for the fractures.
International Journal of Earth Sciences Knowledge and Applications, 2021
In absence of magnetic, gravity, electromagnetic and seismic refraction tools, Lateral Resistivity Profiling (LRP) has been engaged as major tool in the study of deep-seated geological structures for the evaluation of structural trend and settings for groundwater exploration in a complex geologic environment of Southwestern Nigeria. Twenty LRP using wenner configuration was used to delineate zones of resistivity contrast anomaly (weak zone) diagnostic of fracture, fault, cracks, joints and highly weathered geologic materials. Thirtythree Vertical Electrical Sounding (VES) using schlumberger configurations was carried out on the zones of resistivity contrast (weak zones) to delineate geoelectric sequence and layer stratification. The results from the VES were used to generate geoelectric section, geoelectric maps and also to determine the second order parameters. Groundwater potential map was also generated from the integration of geoelectric parameters using Multi-Criteria Evaluation Techniques (MCDA). The model was classified into low, moderate, high and very high groundwater potential zones and all identified points was drilled and the boreholes was very productive, which were used to validate the accuracy of the groundwater potential map. Mformula was used to determine the groundwater yield index value to model the groundwater yield map. All the result obtained has been found to be very relevant in groundwater evaluation of the study area and thereby justifying the relevance of LRP as a major tool in groundwater exploration before carrying out VES
Geoelectrical characterisation of basement aquifers: the case of Iberekodo, southwestern Nigeria
Hydrogeology Journal, 2017
Basement aquifers, which occur within the weathered and fractured zones of crystalline bedrocks, are important groundwater resources in tropical and subtropical regions. The development of basement aquifers is complex owing to their high spatial variability. Geophysical techniques are used to obtain information about the hydrologic characteristics of the weathered and fractured zones of the crystalline basement rocks, which relates to the occurrence of groundwater in the zones. The spatial distributions of these hydrologic characteristics are then used to map the spatial variability of the basement aquifers. Thus, knowledge of the spatial variability of basement aquifers is useful in siting wells and boreholes for optimal and perennial yield. Geoelectrical resistivity is one of the most widely used geophysical methods for assessing the spatial variability of the weathered and fractured zones in groundwater exploration efforts in basement complex terrains. The presented study focuses on combining vertical electrical sounding with two-dimensional (2D) geoelectrical resistivity imaging to characterise the weathered and fractured zones in a crystalline basement complex terrain in southwestern Nigeria. The basement aquifer was delineated, and the nature, extent and spatial variability of the delineated basement aquifer were assessed based on the spatial variability of the weathered and fractured zones. The study shows that a multiple-gradient array for 2D resistivity imaging is sensitive to vertical and near-surface stratigraphic features, which have hydrological implications. The integration of resistivity sounding with 2D geoelectrical resistivity imaging is efficient and enhances near-surface characterisation in basement complex terrain.
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...
Gidan Kwano campus of the Federal University of Technology, Minna, is located within the basement complex terrain of North-Central Nigeria and is underlain by Pre-Cambrian basement rocks of which granites are predominant. Vertical Electrical Sounding (VES) employing the Schlumberger electrode configuration was used to provide information about the subsurface lithology and structures with the aim of evaluating its groundwater potential. A total of 48 VES was made along eight profiles with six sounding stations per profile within an area of about 10km2. A combination of VES, Horizontal Resistivity Profile and Sounding – Profiling produced a subsurface geological appraisal of the study area. Results of the interpretations of VES data were used to produce fracture map and isopach map of depth to basement which has a mean value of 35 m. Interpreted fractures coincide with the direction of stream flow suggesting a structurally controlled drainage system. VES curves reveal that the area is generally characterized by three geoelectric layers. Top soil layer thickness range from 0.2m to 7.4 m while the weathered layer thickness range from 0.3 m to 58.8 m. Out of the 48 VES made, 8 VES stations have been selected as priority locations for the development of groundwater resources. The study area has been found to have a very high potential for groundwater development. Despite all the limitations of the VES technique, it has been found to be reliable for groundwater exploration in the basement complex terrain particularly when the Schlumberger Configuration combined with geological and computer - aided interpretation for the survey data is implemented. Keywords Crystalline Basement, Vertical Electrical Sounding (VES), Horizontal Resistivity Profiling (HRP), Sounding-Profiling (Pseudosection), Groundwater Potential.
Data in Brief
This article consists of geoelectrical resistivity data sets for thirty (30) vertical electrical sounding (VES) and four (4) traverses of 2D electrical resistivity imaging (ERI) collected within Iyesi, Ota, southwestern Nigeria for about five (5) weeks between December, 2016 and January, 2017 using an ABEM Terrameter (SAS1000/ 4000). The observed apparent resistivity data sets for the VES were processed using WinResist to obtain geoelectric layer parameters while those of the 2D ERI were processed with RES2DINV to obtain 2D inverse model resistivity images. The geoelectric parameters for the VES and the inverse models for the 2D ERI were integrated to characterise the subsurface and delineate the underlying aquifer units.
IOSR Journals , 2019
he School of Earth and Mineral Sciences (SEMS) of the Federal University of Technology, Akure Nigeria is facing an acute water shortage. At the moment the entire school depends only on a seasonal hand dug well and several hydro-geophysical surveys carried in the environment to locate possible point for groundwater development were unsuccessful. This study combined two techniques of electrical resistivity method; the Wenner-Schlumberger (a 2-Dimensional resistivity technique) and Schlumberger arrays (vertical electrical survey). The Wenner-Schlumberger array was deployed as a reconnaissance tool to determine probable locations for the vertical electrical sounding (VES) survey. The Wenner-Schlumberger survey was done along 8 traverses. Nine (9) VES points were selected based on the qualitative interpretation of Wenner-Schlumberger pseudo-sections. The vertical electrical sounding (VES) survey results delineated 3 - 4 geoelectric layers across the study area which corresponds to the topsoil, weathered layer, partially weathered/partially fractured basement and the presumed fresh bedrock. The layers’ resistivity varies from 52 - 132 Ωm, 29 - 513 Ωm, 24 - 76 Ωm and 1869 - 36,227 Ωm in topsoil, weathered layer, partially weathered/partially fractured basement and the presumed fresh bedrock respectively. The layer thickness varies from 1.0 - 2.5 m, 0.7 - 9.3 m and 10.1 m - infinity in the topsoil, weathered layer and partially weathered/partially fractured basement. The geoelectric section along north-south direction reveals the presence of bedrock depression beneath VES 2 and this correlate well with traverse 1 Wenner-Schlumberger pseudosection. VES 2 has a highly saturated weathered layer with resistivity value of 24 Ωm and thickness of 10.1 m. The partially weathered basement layer can also serve as an aquifer based on its lower resistivity value (205 Ωm). VES 1 can also be considered for groundwater development since it has 3 subsurface layers that can serve as aquifer layer; the weathered layer, partially weathered basement and partially fractured basement. The resistivity of the weathered layer is 92 Ωm with thickness of 9.3 m. The partially weathered basement and partially fractured basement have resistivity values of 24 and 76 Ωm respectively, while the thickness value of the former is 10.2 m. VES 1 and VES 2 can be developed into a motorized borehole. VES 3 can also be considered for groundwater development due its low resistive (106 Ωm) weathered layer, but the layer is thin (5.6 m) and thus VES3 can only be considered for a hand dug well.
SEG Technical Program Expanded Abstracts 2018
A knowledge of hydrogeophysical parameters of aquifers is essential for groundwater resource assessment, development and management. Traditionally, these parameters are estimated using pumping test carried out in boreholes or wells; but this is often costly and time consuming. Surface geophysical measurements can provide a cost effective and efficient estimates of these parameters. In the present work, geoelectrical resistivity data has been used to characterize and evaluate the aquifer potential at Covenant University, Ota, southwestern Nigeria. Some thirty-five vertical electrical soundings (VESs) were conducted using Schlumberger array with a maximun half-current electrode spacing (AB/2) of 240 m. The geoelectrical parameters obtained were used to estimate longitudinal conductance and transverse resistance of the delineated aquifer. Both the longitudinal conductance and transverse resistance, which qualitatively reflects the hydraulic properties of the aquifer, indicate that the aquifer unit is characterized with high values of hydraulic parameters; consequently a good groundwater potential. Thus, groundwater resource development and management in the area can be effectively planned based on these parameters.
2015
Geoelectric soundings using the symmetric Schlumberger configuration were carried out to investigate the groundwater potential in fifteen communities of Kajuru local government area within the Northern Nigerian Basement Complex. The project employed the acquired vertical electrical soundings (VES) data and hydrogeophysical expression of structural features and aquiferious zones to model groundwater prospects in the area. Model layers correspond to weathered, fractured and fresh basement zones of varied thickness and lithology. The VES curves obtained were predominantly KH and QH type curves. The topsoil, laterites and pebbles have thicknesses from 2-7m with a resistivity range of 2807m-3600 Ωm. Following this layer is a progression into mainly sandy clay units with a weathered denser sandier base. The thickness of the zone varies from 8-20m and resistivity range of 198-406 Ωm. The partially weathered and fractured portions of the basement have thickness ranges of 9-26m and resistivi...