Vertical Electrical Sounding Curves Research Articles

Integrated groundwater exploration in basement complex terrain for sustainable regional water supply in Abuja, Nigeria

This study integrates geophysical and geological analyses to identify potential areas for regional water supply in newly developed sites and regions lacking coverage from the lower Usuma Dam. Covering an expanse of approximately 5200 km2, high-resolution aeromagnetic data were collected, analyzed, and interpreted alongside thirty-five (35) vertical electrical sounding (VES) data points, utilizing the Schlumberger array with current electrode separations (AB/2) ranging from 100 to 140 m and potential spacing MN/2 varying from 0.25 to 5m. The aeromagnetic data, reduced to the equator, reveal anomalies characterized by variations in magnetic susceptibility, indicative of changes in rock composition. Total magnetic field intensity ranges from 435.7 nT to 568.3 nT, with variations attributed to the presence of diamagnetic materials, specifically magnetite and quartzite in basement rocks. Residual data, ranging from −92 to 41.4 nT and high residual values correspond to granite gneiss and coarse porphyritic biotite hornblende granite. First vertical derivative results expose lineaments with lengths ranging from 894.4m to 11.627 km, supported by tilt derivative lineaments of 1.131–11.400 km these delineate potential zones for urban and regional groundwater supply, emphasizing the role of lineaments and faults in controlling structural geometry for groundwater flow. Geological mapping affirms high fracturing with conjugate faults in the area. Interpreted VES curves identify 65.7% as H-type, 22.9% as KH, and 5.7% as QH curves, with HK- and A-type curves at 2.9%. Overburden thickness varies from 6 to 44 m at specific VES points. Iso-resistivity maps exhibit high resistivity values (6000 to 9000 Ωm) due to geological outcrops, while low resistivity values result from a partially or highly fractured basement. Recommendations include drilling 31 VES points for regional water supply in Abuja's urban area, offering a diversified water source and reducing dependence on potentially vulnerable surface water supplies.

Application of Geophysical Methods for Investigation of Groundwater Potential in Layunrun Village, Ogun State, Southwestern Nigeria

An investigation of the groundwater potential of the area for tube well construction has been conducted in Layunrun village in a typical basement complex of Ogun State using electromagnetic and electrical resistivity techniques in geophysical exploration. Six (6) electromagnetic profiles were used, and twenty-eight (28) Vertical Electrical Soundings (VES) were performed along some of the profiles' potential regions. The typical partial curve matching utilized to create the VES curves was examined, and the results were used to create themed maps of the region. Within the study area, between four and six geoelectric layers were found. These layers are Topsoil, weathered layer (clay), weathered layer, fractured basement, and fresh basement. According to the findings, a bigger percentage of the land has an overburden thickness ranging from 9 to 17 m, with a maximum overburden of about 23 m. It also showed how well fractured the research area is, with thicknesses of the fractures varying from about 12 m to more than 30 m. The study area has a good chance of accumulating groundwater and, consequently, developing groundwater through digging boreholes. The outcomes also suggested that a community with similar geological settings may use the electromagnetic method in addition to the electrical resistivity method to identify places with high groundwater potentials.

Application of Vertical Electrical Sounding (VES) for the Determination of Water-Bearing Zone in Karaworo, Lokoja Kogi State, Nigeria

The importance of water in our various communities and the difficulties faced so far to get good and clean water for both domestic consumption and industrial purposes can never be overemphasized. For these purposes to be accomplished, it is necessary to survey the area of study to know more about the geology of the area, which is characterized by the Lokoja Formation, Patti Formation, and Agbaja Ironstone and the possible reasons why there is a lack of water in the area. The geoelectric survey was conducted at Karaworo with the objective of determining the sedimentary formation's geoelectrical features and analyzing the potential of the groundwater in the study area. The most frequently used type of array for Vertical Electrical Sounding (VES) is the Schlumberger array, which needs a lot of space at both ends to yield deeper subsurface information. The Schlumberger configuration was used for data acquisition. About fifteen (15) VES points were acquired at different locations within the study area. For the different VES positions, the maximum AB/2 is within 100m to 180m. Partial curve matching was used to determine the layer parameters as part of the quantitative interpretation of the VES curves. The IP2WIN software was used in the final data analysis. The depth sounding interpretation revealed subsurface layers which comprises of topsoil/clay with a resistivity range between 1.42 ohm-m to 81.0ohm-m and a thickness of 0.253 m to 70.4 m, lateritic clay with a resistivity range between 01.06ohm-m to 1730 ohm-m and a thickness of 0.236 m to 19.2 m, siltstone with resistivity range between 0.423 ohm-m to 5069 ohm-m and a thickness of 4.09 m to 28 m and sandstone with resistivity range between 0.664 ohm-m to 137 ohm-m with the thickness at infinity. Sandstone constituted the aquiferous zone. In conclusion, different types of curves which include HA-type, H-type, KH-type, QH-type and HAK-type characterize the area and hence it is suggested that boreholes be placed in low resistivity zones and considerable depth and thickness as revealed in VES 4 and VES 8 but those with low resistivity without considerable depth, for example, VES 2, VES 5, VES 6, VES 7, etc. can be developed into a hand dug well.

Characteristics of soils for civil engineering foundations in part of North Central Nigeria, using electrical resistivity method

A geophysical investigation was carried out using Vertical Electrical Sounding (VES) in part of North Central Nigeria to evaluate the subsoil thickness, competence, and corrosivity for civil engineering foundations. A total of 60 VES stations were covered within the study area using the Schlumberger configuration array with half current electrode separation (AB/2) varying from 1m to a maximum of 100m while the half potential electrode spacing (MN/2) varied by 0.3 m to a maximum of 5m. The analysis of data was done using IP2win and Surfer 12 softwares. The first layer has resistivity values between 4.728 Ωm to 4210 Ωm and varied in thickness between 0.15 m to 1.42 m, the second layer has resistivity values between 24.7Ωm to 355000 Ωm and varied in thickness between 0.0355 m to 8.983 m while the third layer has resistivity values ranging between 8.361 Ωm to151,608 Ωm and varied in thickness between 1.05 m to 34.2 m, the fourth layer which is the last of the geoelectric layers has resistivity values between 27.95 m to 77000 m. The subsoil within the study area is composed of clay, sandy clay, clayey sand, sand, and laterite. From the qualitative interpretation of the Isoresistivity and Isopach maps, the Southwestern, Southeastern and Northwestern parts of the study area are moderately corrosive to extremely corrosive subsoil with resistivity values ranging between 4.728 Ωm and 50.48 Ωm. The third layer consists of an incompetent low resistivity soft material that underlain the entire study area except at the central region which is essentially noncorrosive and highly competent. VES curves interpretations revealed the thickness and depths of the geoelectric layers within the study area. The results of this research could enable civil engineers to ascertain the requisite depth of soil evacuation for the sustainability of structures within the study area.

Application of Vertical Electrical Sounding for Subsurface Characterization to Determineslope Instability at Perizie, Nagaland

Vertical Electrical Sounding (VES) technique which employs the Schlumberger depth sounding method was used to investigate the subsurface conditions at the landslide in Perizie colony, Kohima. The interpretation of the VES curves shows differing lithology consisting of weathered shales with associated clay, which is considered an important factor for slope instability. The shear strength of the slope materials, including the country rocks and the soil cover, is also significantly reduced and easily detached due to the effects of weathering and erosion, causing the landslides. Three to six possible geo-electric layers are delineated from the variations in the resistivity values, with the lithologies consisting of topsoil followed by alternate layers of weathered and fractured rocks of varying thickness. The analysis also points to the presence of a weak zone at a depth of about 10 m, which is not apparent from the surface. The formation of groundwater aquifers in the fractured zones indicates high risk for slope failure as this accelerates the weak country rocks to weather. The results obtained by this study correspond well with the available borehole data of the area.

Characterization of Crystalline Aquifers in Ouaddaï Division (East of Chad) Using Electrical Resistivity Method: A Case Study of Waguiré and Anourchi

This study aimed to locate suitable aquifers that can be exploited with their structural and hydraulic characteristics. So for this aim, combination of geoelectrical and drilling techniques was used. Eight electrical trailing and Vertical Electrical Soundings (VES) were carried out with Syscal R1 - Plus resistivimeter, using Schlumberger array. VES data were interpreted using the Ipi2win software, and geohydraulic parameters (conductivity, transmissivity, and porosity) were estimated based on geoelectric parameters computed. Results show four favorable shapes of electrical trailing (W, U, V, and H -shapes) and four types of VES curves (H, HA, QH and HKH). Three to five geoelectric layers were delineated from analysis of VES curves with aquifer resistivity influenced by clay content, varying from 6.09 to 33.84 Ω.m and thickness from 5.54 to 17.35 m. Computed hydraulic conductivity, transmissivity, and porosity vary from 14.19 to 70.93 m/day, 92.36 to 429.13 m²/day, and 37.44 to 44.68% respectively. The groundwater potential of the area ranges from moderate to high potential. Based on these geohydraulic parameters, two points (VES4 and VES7) were chosen to drill a hole. Drillings were a success and yield ranging from 2.72 m3/h to 3.12 m3/h. This study reveals that geohydraulic parameters could be an alternative to choose where to drill a positive borehole in the area with a similar geological context.

Geophysical Investigation of Groundwater Potentials of the Nanka Sand in Obosi and Its Environs, Anambra State Nigeria

Geophysical investigation for Groundwater which entails the use of vertical electrical sounding (VES) methods was carried out in parts of the Idemili area of Anambra State, Nigeria. Geologically the study area falls within the Nanka Sand, belonging to the Ameki Group in the Tertiary Niger Delta Basin. The investigation intends amongst others to assess the groundwater potential of the area, find out the existence of possible aquifer(s) within the area, and estimate the possible depth of a borehole. 15 VES stations were established at the site using Ohmega System Tetrameter and Schlumberger electrode configuration with current electrode spacing (AB/2) of 350 meters. The geologic parameters, such as the number of geo-electric layers, the thickness of the geo-electric units, and their resistivities were interpreted from the VES curves. A qualitative assessment of the curves shows that a model with 5 layers would sufficiently model the field curves. The thickness value ranged from 0.1 to 86 m, the resistivity ranged from 258 to 13,258 Ωm, and the depth ranged between 1.2 and 109 m. Quantitative interpretation of field curves involved inversion with appropriate parameters using Zond Res1D software.

Electrical Resistivity Sounding for Groundwater Investigation around Enugu Metropolis and the Environs, Southeast Nigeria

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, south-eastern 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 m2. 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 central parts of the study area which have low resistivity values.

Assessment of Groundwater Yield Potentials Zones of Idi-Ayunre using Vertical Electrical Sounding and Geographic Information System (GIS)

To fully harness the increasing number of observations and variant data sets available and put them to efficient use in geological studies aimed at solving earth science-related problems, GIS technique is a veritable tool. The dynamic techniques and the complex nature of earth sciences is a serious cause for worry for geologists. In this work vertical electrical sounding (VES) was integrated with geographic information system (GIS) to delineate subsurface characteristics and evaluate groundwater potential zones in Idi Ayunre, Oluyole Local Government Area, Oyo State. The results of the VES curves obtained from the partial curve matching were used to constrain the interpretation by the computer using iteration software known as WINRESIST® and extended analysis on the data set was done using geostatistical analysis tool on archGIS 10.0®. The Root Mean Square (RMS) errors for the analysis were found to be very low with an average of 2.96% . This underscores the reliability of the analysis tool for this type of work. The area is dominated predominantly by Type-H curves which amassed twenty (20) out of the twenty-one (21) VES and one (1) VES producing a type-K curve. The VES results revealed a maximum of three geo-electric layers, viz: topsoil, weathered layer, bedrock respectively. The yields of wells dug in most of these locations may be insufficient, even for domestic use because of its relatively small thicknesses. However, at a depth of 7.8 m, a fractured zone occurs in VES 10 with resistivity value of 21.2 Ωm suggesting the presence of groundwater, which may be considered the main aquifer units suitable for groundwater exploration.

Geophysical investigation of dambo groundwater reserves as sustainable irrigation water sources: case of Linthipe sub-basin

The geophysical investigation of dambo groundwater reserves using electrical resistivity methods was conducted in Linthipe 4B sub basin in Central region of Malawi. With the increasing over-utilization of shallow wells in dambos for smallholder irrigation, this study was carried out to investigate whether dambo groundwater reserves could serve as sustainable irrigation water sources and to examine the aquifer characteristics in Linthipe sub basin. Vertical Electrical Sounding (VES) points were established in the basin using the Schlumberger configuration array. Data was analysed using IPI2win and Surfer software applications. Contrary to other commercial software applications which are costly for government departments when analysing geophysical data, partial curve matching and one dimensional (1-D) computer iteration techniques were used to interpret the VES curves and the pseudo-cross section resistivity profiles due to their simplicity and cost-effectiveness. The study has revealed that the aquifer properties in the basin are exceptionally variable in terms of state of weathering, depth, thickness, lithology, aquifer recharge configuration, geologic material and hydraulic gradients. These variations showed that the shallow wells in the basin have significant fractures suggesting high water potential for climate smart irrigation usage in the study area. The potential groundwater zones for climate smart irrigated farming were detected at VES 1, 2, 3, 4, 5 and 6 noted by low aquifer resistivity with high values of aquifer thickness. However, VES points, 7, 8 and 9 were likely to be zones of low water bearing potential because they had high values of aquifer resistivity with low aquifer thickness. The findings also validated the effectiveness, timeliness, and efficiency of using vertical electrical resistivity technique in exploring groundwater for irrigation. The results from this study have highlighted that feasible shallow well depth for a sustainable irrigation system is a function of geologic resistance and aquifer thickness when the geologic material has low resistance and broader thickness. This study noted that knowledge of aquifer recharge rates in dambos is required in order to effectively control abstraction rates for sustainable irrigation in basins. There is a need to promote the usage of geophysical studies, reforestation, river basin management trainings and aquifer recharge technologies in exploring sites for shallow well development for irrigation. The study further recommends the usage of geographical information systems (GIS) and Artificial Intelligence (AI) in improving the results of groundwater monitoring studies in Malawi.

Delineation of groundwater potential zones in Logbadjeck, Cameroun: an integrated geophysical and geospatial study approach

The locality of Logbadjeck, located in the littoral region of Cameroon, has been investigated using the vertical electrical soundings with a Schlumberger configuration. Eighty vertical electric soundings have been carried out along fourteen profiles oriented in the southwest-northeast direction. The lateral and vertical variations of resistivity in the area were mapping and made it possible to infer the internal structure and determine the presence of aquifers in order to solve the problem of drinking water in the study area. Resistivity maps highlighted the conducting properties of the subsoil. This zone is made up of 3 to 5 layers and the Vertical Electrical Sounding curves obtained were of the KH, K, H, AK and Q types. The resistivity generally varied between 11 Ω.m and 8131 Ω.m and decrease with increasing depth. In addition, areas with discontinuities which can be associated to a fracture, a zone of water infiltration or a very conducting body were also identified and could be potential zones for groundwater prospecting. The very resistive bodies observed in the study area suggest the presence of gneiss. The subsoil of the study area, in turn, highlights the presence of two principal aquifers: shallow aquifers at depths of approximately 6 m and deep aquifers lying between 28 and 56 m of depth. Hydraulic conductivity ranges from 0.1 m/day to 16 m/day while transmissivity ranges from 5 $$m^{2} /day$$ to 600 $$m^{2} /day$$ . The transmissivity results obtained show that the study area is rated low to moderate groundwater potentials. The longitudinal conductance ranging from 0.2 $$\Omega^{ - 1}$$ to 1.24 $$\Omega^{ - 1}$$ enabled the protective capacity of the aquifer to be classified as moderate to good. The estimated aquifer, protective capacity and the various constructed contour maps, will serve as a useful guide for groundwater exploration and development in the study area.

Delineation of sinkhole in evaporite deposits using electrical resistivity survey: a case study of southern Kohat Plateau, Pakistan

Vertical electrical sounding (VES) is a non-destructive geophysical technique which provides fast subsurface lithological investigations and it is widely used in exploration of water, mineral resources, and its characterization. The present study work has been focused on subsurface imaging over evaporite deposits in Bahadarkhel area, Karak, Pakistan where multiple VES points along three profile lines have been acquired using Schlumberger electrode configuration to delineate subsurface lithology and structure of the area. The VES curves have been modeled and interpreted which resulted in true resistivities, depths, and thicknesses of layers. These VES points have been stacked along their respective profile lines for pseudosections and resistivity cross section preparation. Five distinct geoelectrical units have been identified depending upon their true resistivity values. Iso-resistivity 3D surfaces at 30 m and 60 m depths have been generated using the interpreted data which exhibits salt diapiric structure and dissolution of salt at depth by the action of infiltrating water from nearby ephemeral stream. Dar-zarrouk parameter calculations yield transverse resistance, longitudinal conductance, and anisotropy maps which infer that the area is mostly covered with rock salt and the presence of clay beds and calcareous sediments increases the resistivity values.

Groundwater Occurrence and Aquifer Vulnerability Assessments in Coastal Settlements of Araromi Seaside and its Environ, Southwestern Nigeria

The groundwater potential and aquifer vulnerability study of Araromi Seaside are reported in this study using a combination of Vertical Electrical Sounding (VES) and Electrical Resistivity Tomography (ERT). Double dipole with minimum electrode spacing of 20 m and maximum length of 400 m were employed to acquire twelve (12) ERT data while Schulumberger configuration with maximum half current electrode separations of 500 m was used to obtain the twelve (12) VES data at the mid-point of each ERT traverse. ERT data was inverted using DIPPRO for window software why VES curves were iterated using WINRES software. Interpretation of the ERT results show promising groundwater potential points under ERT line 1, 4, 6, 8, 11 and 12, while the VES result revealed good sandy / clayey sand aquifers with good aquifer thickness under VES 1, 2, 3, 6, 7, 10, 11 and 12. In terms of aquifer vulnerability capacity, VES 3, 5, 8 and 11 show poor capacity, VES 10 and 12 weak capacity, VES 2, 4, 7 moderate and VES 1, 6, 9 show good capacity. For healthy water supply, groundwater boreholes should be developed in areas with good aquifer parameters and good protective capacity. Juxtaposing the two parameters we suggested VES 1, 2, 6 and 7 which have both groundwater potential and vulnerability capacity for groundwater borehole development. Considering spatial result that the ERT affords, other possible point like surface position 170 m on Profile 4 is also recommended, because it satisfies the two conditions of good aquifer and good vulnerability capacity.

Hydrogeophysical Investigation of Groundwater Systems in Otukpo, Benue State, North-Central Nigeria

Hydrogeophysical investigation of groundwater systems in Otukpo, Benue State, Nigeria has been carried out using vertical electrical sounding (VES) technique to delineate the groundwater potentials across the study area. Ten (10) vertical electrical soundings were carried out during the geophysical survey using the Schlumberger configuration of electrical resistivity method with maximum current and potential electrode spacing of 600 meters and 80 meters respectively. The VES data was qualitatively and quantitatively interpreted using the conventional curve matching and computer iteration methods. The result of qualitative interpretation depicts that the VES curves obtained within the study area are mainly the QH and KQH which are typically indicative of a sedimentary terrain. The results of the quantitative interpretation reveal that the resistivity values from shallow subsurface to the depth of about 500 m of the VES stations ranges from 3 Ωm to 1250 Ωm. The VES results also show that the study is characterized by seven (7) different inferred lithological layers namely; topsoil, sand/silt, laterite, clay, shale, sandstone and the basement rock. The result also reveals that the depth to water-saturated unit ranges from 450 to 500 meters within the study area. Two distinguished aquifer types were obtained within the area namely; unconfined and confined aquifers. The findings reveal that the future borehole drillers should target the confined aquifers situated between the depths of 450meters to 500 meters beneath the surface for sustainable groundwater yield across the study area.

Vertical electrical sounding in the investigation of subsurface gravel deposits in arid environments—a case study, El-Salhayia plain, West Ismailia area, Egypt

The vertical electrical sounding (VES) is a common geophysical technique which depends mainly on the clear difference in the electrical resistivity between the causative body and the hosting sediments. These conditions could be achieved in the arid environmental zone of Egypt. The VES technique has been tested and used in the El-Salhayia plain in order to locate the subsurface accumulations of dry gravels. Twenty soundings have been measured in the plain by using the Schlumberger array. Interpretation of the VES curves showed that they are of 3-layer K-type where the dry gravel bodies represent the middle layer and occurred as lenses that gave high electrical resistivity relative to the hosting dry sand sediments. The estimation of the transverse resistance (i.e., one of the Dar-Zarrouk parameters) of the expected subsurface gravel layer detected three promising sites for quarrying operations in the El-Salhayia plain, where the depths and thicknesses of the gravel deposits could be estimated. The grain size analysis of some drilling samples from four available water wells in the study area confirmed the occurrence of gravel deposits with different sizes (i.e., granules and pebbles). Accordingly, the vertical electrical sounding technique can be highly recommended as an effective tool for gravel prospecting in similar conditions.

Electrical resistivity in the delineation of groundwater potential zones: a case study from Kota, Rajasthan, India

A geophysical investigation using electrical resistivity method is carried out in the eastern part of Sangod Block, Kota District, Rajasthan, India. A total of twenty-one vertical electrical sounding (VES) data were collected using Schlumberger sounding configuration with the aim of determining subsurface layer parameters (resistivities and thicknesses) and delineating the groundwater potential zones in the area. The automatic interpretation of the sounding data has been carried out, which gives layer parameters (i.e., apparent resistivities and thicknesses) of different layers. The interpreted layer parameters are used to generate the geo-electrical cross-sections representing the possible geological formation in the area. The interpretation of the results reveals that there are maximum five layers in the study area, and most of the VES curves are combination of A-type such as AA, HA, and HAA types representing a successively hard rock formation in the area. The obtained VES results have been correlated with the available litho-log data in the area, and a good agreement is found between the sounding results and lithology data. From study it is inferred that the loose pockets of sands and fractured or semi-fractured zones in the area could be the possible potential zones of groundwater in Sangod Block of Kota District, Rajasthan, India.

Hydrogeophysical assessment and protective capacity of groundwater resources in parts of Ezza and Ikwo areas, southeastern Nigeria

Geoelectrical investigations were carried to determine the aquifer potentials and protective capacity of Ezza and Ikwo areas, Ebonyi State, Southeastern Nigeria. A total of thirty-five (35) Vertical Electrical Sounding survey was conducted using the Schlumberger configuration to evaluate the character of the aquifers in the studied locations. Geoelectric sections derived from the modeling of the sounding data reveal 4 to 7 subsurface layers. The Vertical Electrical Sounding curves obtained were QH, QHK, QHKH, QQH, KHK, QHAK, and QQHK. The third and fourth layers constitute the aquiferous zones. The aquifer resistivity ranges from 11.7 to 814 Ωm, while the aquifer thickness and depth range from 99.2 to 3.4 m and 8.7 to 105.8 m respectively. The Dar Zarrouk (longitudinal conductance and transverse resistance) parameters were determined from the results. The longitudinal conductivity ranges from 0.004975 to 2.9573 mhos, whereas the transverse resistance ranges from 70.1 to 17,161.6 Ωm2. Furthermore, the aquifer potentials of the study area were shown to differ with aquifer size, structure and characteristics are influenced by the underlying geology generally. From the study, it was concluded that the western axis of the study area underlying the Ebonyi Formation has a higher aquifer potential compared to the eastern axis underlying the Abakaliki Formation. This is supported by the geology of the area with the Abakaliki Formation dominated by shales that have very low permeability, while the Ebonyi Formation consists of shales with alternations of sandstone which supports good aquifer conditions. The study area has a moderate aquifer protective capacity.

Application of Electrical Resistivity Method in Groundwater Exploration

Vertical Electrical Sounding (VES) was carried out in Alode Community of Eleme Local Government Area in Rivers State, Nigeria to determine the geo-electrical and hydrogeological characteristics of aquifers present in the area, also to delineate the geo-electric stratigraphy of each VES station. A total of three (3) VES were carried out with the ABEM Terrameter SAS 300C, using the Schlumberger Configuration. Maximum half-current electrode spread (AB/2) of 1m up to 150m was used, while the half potential electrode separation (MN/2) was maintained between 0.5m and 7.5m. The VES curves were quantitatively interpreted by partial curve matching and computer iteration techniques, using the IP1 WIN computer software. The results of the interpreted VES data confirm the following stratigraphies: top soil (40.2-65.2Ωm), shale (32.2-86.3Ωm), fine-medium sand (172-204Ωm), medium-coarse sand (532Ωm), and medium sand (417Ωm). Geo-electric sections reveal that the aquiferous units are mostly confined, with depth to aquifer range of 60m (154.2ft) for VES 1 and 63m (206.7ft) for VES 2 and 65m (213.3ft) for VES 3.

Geophysical characterization and hydraulic properties of unconsolidated floodplain aquifer system in Wamako area, Sokoto State, north-western Nigeria

The subsurface internal geometry of Rima River floodplain located in north-western area of Nigeria was investigated using 2D resistivity imaging, vertical electrical sounding (VES) and laboratory analyses. Four profiles were acquired using Wenner array. The apparent resistivity computed was used to produce 2D electrical resistivity pseudosections using RES2DINV software. A total of nine VESs were acquired along the four profiles in the study area with AB/2 of 1 to 100 m. Quantitative interpretation of VES curves was done by partial curve matching and computer-assisted 1D forward modelling with the WinResist version 1.0 software. Five pits were dug along the profiles to confirm the interpreted results from the geophysical surveys. Soil samples were collected from the pits at various depths, and hydraulic conductivity (K) was estimated in the laboratory using the constant head permeability test following standard procedure. Interpretations of electrical resistivity technique show three to four subsurface layers including topsoil, sandy material and clay/saturated clayey materials. The sandy material is believed to be saturated with water with appreciable amount of porosity and permeability. This layer was further confirmed by pitting around the study area. From the laboratory and empirical estimation of K, it was discovered that the K value ranges from 10−2 to 10−6 m/s, which shows that the sample is clean sand which is moderately to highly permeable. The grain size analysis revealed from the cumulative plot that the sample falls predominantly within medium-sized sand, which makes the study area a good aquifer system.

Groundwater Vulnerability Assessment using Electrical Resistivity Method in the Northern part of Ado-Ekiti, Southwestern Nigeria

Over the years, the demand for clean and safe water has skyrocketed globally in response to rising population. Since groundwater is a more reliable source of potable water, assessment of aquifer vulnerability becomes a necessity. This research therefore aimed at delineating geo-electric parameters inform of layer resistivity and thickness, towards generating a second order geo-electric section. This study employed the use of electrical resistivity method to evaluate the vulnerability of aquifers to contamination in the northern part of Ado-Ekiti, southwestern Nigeria. Forty Vertical Electrical Sounding (VES) locations were studied using the Schlumberger array with current electrodes spacing (AB/2) of 150m. ABEM SAS 300 Resistivity Meter was useful for collecting the VES data which were presented as VES curves and quantitatively interpreted through partial curve matching and Computer Assisted 1-D forward modeling using the WinResist software. Geo-electric section along five (5) traverses, iso-resistivity map of the weathered layer and an isopach map showing the depth to aquifer were generated. Seven (7) different types of VES curves were identified, namely A, H, K, KA, HA, QA and KH types. The four geo-electric layers delineated include the topsoil (resistivity values between 29 – 1176 Ωm; thickness from 0.5 – 4.4 m), lateritic layer (resistivity values between 138– 3787 Ωm; thickness between 1.0 – 63.6m), weathered layer (resistivity values between 6 – 298 Ωm; thickness between 0.7 – 17.8 m), and fresh basement (resistivity values between 331 – 7479 Ωm). The total longitudinal unit conductance (S) values obtained range from 0.009 to 2.972 mhos. This suggests that most parts (northern, central, western and eastern portions of the area) have medium to high protective capacity rating; except the eastern portion. Therefore, most parts (80%) of the study area appear to be less vulnerable to contamination.