Resistivity Contrast and the Phenomenon of Geophysical Anomaly in Groundwater Exploration in A Crystalline Basement Environment, Southwestern Nigeria (original) (raw)
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International Journal of Earth Sciences Knowledge and Applications, 2020
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.
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...
2018
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 2252 m and 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 resi...
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.
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
Saudi Journal of Engineering and Technology
The study integrates electrical resistivity tomography (ERT) and vertical electrical sounding (VES) methods for investigation of the groundwater potential of the study area. Five ERT was conducted to determine the variation in resistivity of the shallow subsurface rocks both vertically and laterally in order to infer aquifer zones therefrom while twenty-four VES was carried out to compliment the information obtained from the ERT, determine vertical variation in resistivity, infer lateral variation in resistivity, identify depth to aquifer and infer groundwater prospect of the area. Three geoelectric layers were obtained with layer resistivity and thickness increasing northwards with shallower depth to aquifer obtained at Kutigi. K (ρ1<ρ2>ρ3) and Q (ρ1>ρ2>ρ3) resistivity type curves constitute 75% of obtained curves signifying increasing groundwater saturation and salinity, and are indication of increasing aquifer prospect with depth. The groundwater prospects in the area...
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.
Pacific Journal of Science and …, 2009
Hard rocks occupy large parts of the earth's crust. These rocks are devoid of primary porosity and permeability. Most crystalline rock areas of Nigeria are located in areas of high relief; as a result, run off is high and infiltration rates very low. Most often, the occurrence of groundwater in this terrain is localized and confined to weathered/fractured zones. Hence detailed predrilling geophysical investigations become inevitable. This present work gives a brief geological background of the hard rock encountered in the study areas and explains the usefulness of the electrical resistivity method, most especially vertical electrical sounding, in locating weathered/fractured zones that are the major source of groundwater development in the study area. A total of twenty-eight such vertical electrical sounding locations were probed in the study area and the interpreted result gives an overview of various aquifers that are present in the area which are weathered/fractured basement and the groundwater situation of these hard rock units in the study area.
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...