Vertical Electrical Sounding Results Research Articles

Geophysical Characterization of Abandoned Dumpsite Soil Properties for Pre- Foundation Delineation at Bowen University Campus, Iwo, Nigeria

Geophysical investigation and microstudy of soil properties were carried out within Bowen University, for the characterization of the subsurface pattern in the area using vertical electrical sounding (VES) survey and evaluation of soil properties with a view to mapping subsurface geological features, such as weak and competent zones and to determine the overburden thickness of the area for pre-foundation studies for a proposed high-rise building. Four (4) VES was carried out in the study area employing schlumberger electrode configuration. The data collected were used to curve match and the results used for subsequent interpretation to reveal the depth, thickness and resistivity of the study area. In addition, soil samples were collected from three (3) selected points located at the entrance, centre and the end of the study area at about a depth 0-60 cm. Consequently, the VES results were presented as resist graph, which revealed the range of values for the depth (1.3 – 24.5), thickness (1.3 – 15.4 m) and resistivity (357.4 - 6311.6 ohms), which was later used to generated the geoelectric maps of the study area. It was also observed that the result of the soil properties revealed that all the samples taken from the study area have low bulk density (1.41 g/cm 3 , 1.26 g/cm 3 , 1.36 g/cm 3 ), high particle density (2.81 g/cm 3 , 2.94 g/cm 3 , 3.16 g/cm 3 ), and high porosity (49.64%, 57.22%, 57.03%). In conclusion, it was observed that erection of high-rise building is not advisable within the study area since the results showed that the overburden (depth to basement) is generally thick mostly greater than 15 m. Also revealed from the microstudy of soil properties is that foundation stability should be properly managed, since a porous soil does not accommodate engineering activities except when an artificial basement is put in place. Keywords : Geophysical Investigation, Soil Analysis, Foundation Studies, Subsurface Competency

Demarcation of Groundwater Possible Zones in a Hard Rock Terrain, Nagavathi Watershed of Dharmapuri District, Tamil Nadu, India—Geophysical and Geoinformatics Approach

The electrical resistivity survey has been very successful for decades in delineating prospective groundwater zones around the world. In general, the method is used to decipher the horizontal and vertical electrical resistivity distribution of the subsurface earth’s layers. In the perspective of hydrogeology, understanding the subsurface conditions and lithological variations is quite necessary to target groundwater potential zones. One-dimensional (1D) geoelectrical resistivity survey, vertical electrical sounding (VES), was carried out in selected locations across the Nagavathi watershed, Dharmapuri district of Tamil Nadu in India. The Nagavathi watershed is positioned in an undulated terrain and is dominantly underlain by charnockite and gneissic rocks. Forty-six VES using Schlumberger’s electrode arrangement were conducted over the entire Nagavathi watershed, using an equal grid method. The field data were processed by IPI2 Windows software and different types of sounding curves were identified. The lineaments such as faults, joints, and fractures act as pathways to groundwater movement, major lineaments were identified from satellite data using ArcGIS 9.3. In the study area consisting of hard rocks, groundwater prospecting is a difficult task without proper understanding of subsurface lithology. From the VES results, geoelectric layers such as topsoil, weathered, fractured, and infinitely hard rock layers were identified and eight thematic maps involving spatial distribution of resistivities and thickness were prepared, in addition to geology, hydrogeomorphology, and lineament thematic layers. The combination of the eleven thematic layers in ArcGIS resulted in a groundwater potential map, providing the information about very good (75.799 km2), good (85.595 km2), medium (134.240 km2), poor (115.124 km2), and very poor (69.336 km2) groundwater possible zones.

Evaluation of aquifer hydraulic characteristics using geoelectrical sounding, pumping and laboratory tests: A case study of Lokoja and Patti Formations, Southern Bida Basin, Nigeria

AbstractThe hydraulic characteristics of aquifers in Lokoja and Patti Formations were investigated using combination of vertical electrical sounding (VES), pumping and laboratory tests. A total of 20 VES (10 each in areas underlain by Lokoja and Patti Formations) were carried out at different locations with 5 pumping tests around VES stations in order to determine the geoelectric layers, thickness, depths to water table and groundwater potential of the area. 21 samples extracted fromaquiferous units of surface outcrops were also subjected to laboratory constant head and falling head permeameter tests in order to determine hydraulic conductivity (K) values using the Darcy’s law of liquid flow. The results of VES for areas underlain by Lokoja and Patti Formations revealed 4-5 geo-electrical layers. The depths to water table vary from 5.91-40.8 m. Thickness values are within the range of 7.37-27.3 m for aquiferous units of Lokoja Formation, and 10.8-20.1 m for the Patti Formation. The results of aquifer characteristics using Dar-Zarrouk Parameter gave hydraulic conductivity (K) values between 1.92-91.7 m/day and 2.15-31.8 m/day for aquifers of Lokoja and Patti Formations respectively. Transmissivity (T) values of the aquiferous units of Lokoja Formation fall within 24.97-2117 m2/day, while those of Patti Formation vary from 27.9-456.91 m2/day. There is a strong correlation between the values of measured and calculated hydraulic conductivity and transmissivity between measured and calculated transmissivity for the five wells (R2 = 0.99 and 0.92, respectively). Based on the results obtained and interpretations proffered, aquiferous units in both formations are capable of yielding optimum groundwater for private consumption and partly to small communities, and to some extent can supply water for great regional use. It is suggested that similar study should be carried out in other sedimentary basins where to aid regional planning and management of groundwater resource.

Geoelectrical study of corrosivity and competence of soils within Uburu and Okposi areas of Ebonyi State, Southeastern Nigeria

PurposeThe corrosivity and competence of soils within Uburu and Okposi areas of the Southern Benue Trough, Nigeria, were evaluated using the electrical resistivity method. This paper aims to provide information that will aid pre-design of subsurface iron/steel pipe networks for distribution of pipe-borne water and construction of subsurface structures for agricultural and environmental purposes.Design/methodology/approachIn total, 22 vertical electrical soundings (VES) in the Schlumberger configuration were acquired with Allied Ohmega™ Terrameter with a maximum half current (AB/2) electrode spacing of 200 m. Layer parameters were determined using partial curve matching techniques, using the Schlumberger master curves, while processing and modelling were done with the IPI2win™ software. The VES results were interpreted qualitatively and quantitatively to obtain various curve types and layer parameters, respectively, which were used to categorize the area into different competence and corrosivity zones. The first layer isoresistivity and competence maps were used to delineate four zones (A,B,C and D) with varying apparent resistivities and competences.FindingsIncompetent soils with resistivity values ranging from 24.3-88.7 Om are found in Zone A. The soils in Zone A are mainly expansive clays which swell on absorption of water. Zone B contains moderately competent soils with resistivity values ranging from 273-308.6 Om, while Zones C and D are underlain by sandstones and contain competent to highly competent soils with resistivity values ranging from 511-750 Om and 835-1,525 Om, respectively. Zone E contains highly corrosive (24.3 Om) to mildly corrosive (102 Om) soils; Zone F contains soils that are essentially non-corrosive with resistivity values ranging from 271-1,525 Om, while the corrosivity of soils within Zone G varies from corrosive to mildly corrosive, with resistivity values ranging from 44.3-114 Om.Research limitations/implicationsSome of the areas are not accessible because of community restrictions.Practical implicationsThese findings are essentially very significant and should be taken into consideration when materials that are susceptible to corrosion are being considered for engineering, agricultural and environmental purposes in the area.Social implicationsThe findings will aid water resource planners and developers on how to protect metal pipes from corrosion, when used for water reticulation and agricultural purposes.Originality/valueThis paper fulfils an identified need to study the corrosivity of soils in the study area with a view to providing adequate protection to metal objects when being considered for water reticulation for domestic and agricultural purposes in the area.

Delineation of groundwater prospective zones from a delta region of India, using geoelectrical and water quality approach

Geoelectrical survey was carried out in the western delta region of River Vasista Godavari, Andhra Pradesh, India, for delineation of groundwater prospective zones due to acute shortage of water supply for various purposes. Forty-six vertical electrical soundings (VES) were done, employing the Schlumberger configuration with a maximum AB/2 of 160 m. The interpreted results of VES show four to five layers with variable thicknesses, such as topsoil zone (1.5–3 m), clay zone (0.84–32 m), finer sand zone (2–72 m), medium to coarse sand zone (4 to 28.8 m) and clay zone (1.2–∞ m), indicating a multi-aquifer system. These results are corroborated with the known lithologs of the study area. Further, the resistivity is also compared with electrical conductivity (EC) of groundwater observed nearby shallow wells representing buried channel (BC), flood plain (FP) and coastal (C) zones, which indicate slightly brackish to brackish water (EC: 1470–6010 µS/cm), whereas the groundwater observed from deep wells shows the fresh (EC: 726–1380 µS/cm), fresh to brackish (EC: 1010 to 3250 µS/cm), and brackish water (EC: 3020 to 4170 µS/cm) located in BC, FP and C zones, respectively. This survey reveals the prospective aquifer zones with potable water at VES locations of 4–6, 8, 10, 11, 14, 16–28, 33–36, 39 and 42–44, where the resistivity values vary from 10 to 40 Ω m. The slightly brackish and brackish water zones are also observed from the resistivity of less than 10 Ω m at shallow depth in BC (VES-22, 37, 38 and 46), FP (VES-1, 2, 7, 29, 30 and 40) and C (VES-3, 4, 9, 12, 13, 15, 31, 32, 41 and 45) zones. As a result, the present investigation has delineated the freshwater zones at shallow (< 12 m) and also at deeper depths (30–45 m) as prospective areas, where BC zone occurs. Freshwater pockets also identified in FP (VES-8 and 39) and C (VES-11, 14 and 15) zones. Thus, this study helps to solve the drinking and irrigation water problems.

Geoimaging of subsurface fabric in Awgbagba, Southwestern Nigeria using geomagnetic and geoelectrical techniques

The heterogeneous nature of the earth has given rise to variations experienced in the subsurface. Some parts are good for hydrological exploration while others are good for civil engineering activities. These variations experienced in the subsurface could not be detected except through geophysical survey and analysis. Integration of ground magnetic and Vertical Electrical Sounding (VES) techniques were carried out in Awgbagba to image the subsurface fabric with a view to mapping subsurface geological features, such as the weak and competent zones, to determine the overburden thickness, and suitability of Awgbagba for civil engineering and hydrogeological purposes. Ten ground magnetic traverses were established in W-E and N-S azimuths. Twenty VES points were randomly sounded for the study in order to cover the entire study area. The magnetic residual field anomaly values ranged from -1, 600 to 700 nT. The study area is grouped into low, average, and high magnetic zones. The depth to magnetic sources ranged from 8.1 to 48.9 m with a mean value of 17.4 m. Three planar feature orientations in the study area are in NE-SW, NW-SE, and SE-NW orientations. VES results showed 7 QH-curve type, 6 HA-curve type, 4 KH-curve type, 1 AA-curve type, 1 HK-curve type and 1 QQ-curve type respectively. The ratio of thin-to-thick overburden and fresh-to-fractured bedrock are 3:7 and 2:3 respectively. It is concluded that the study area cannot withstand high-rise building constructions. However, the mapped fracture zones in the study area would serve as promising zones for borehole development.

Lithologic characterisation of the basement aquifers of Awe and Akinmorin areas, Southwestern Nigeria

Just like many communities in Nigeria, people living in Awe and Akinmorin areas rely on groundwater supply for their domestic water need. However, these areas are underlain by impermeable crystalline rocks that included migmatite, schist and quartzite that can only transmit water when fractured and where there is sufficient weathered regolith overlying the bedrocks. Therefore, a total of twenty-five vertical electrical soundings (VES) was conducted across the study area with the aim of investigating the lithological characteristics of the regolith and the underlying bedrocks for groundwater prospect. An aggregate of nine soundings were conducted on quartzite terrains and eight each across terrains underlain by migmatite and schist. From the VES results, the dominant curves across the study areas were the H and KH types. These geo-electric curves indicate that the middle (saprolite) layers are more conductive and the bedrocks are more resistive. The total regolith thickness ranged from 11.9 to 50.9m with an average of 26.4m on migmatite terrains, 11.7 to 28.8m and average of 19.4m on schist terrain and 8.4 to 41m with an average of 22.3m on quartzite terrain. From the lithologic characterisation, 70% of the saprolite layers are interpreted as fine grained with resistivities of less than 100Ωm, which is an indication of deep and intense weathering across the study area. The occurrences of fractured and fresh bedrocks are almost of the same proportions. However, there is more dominant of partially weathered bedrocks than those that are either fresh or fractured. Altogether, bedrocks resistivities of more than half of the surveyed area are <1500Ωm and were either fractured or slightly weathered. This increased groundwater prospect across the study area, particularly within terrains underlain by fractured bedrocks. Generally, the potential for groundwater development in the study area is reasonably credible. Although, the saprolite units are mostly fine grained and may not be the best groundwater bearing zone, they may act as confining units for areas underlain by fractured or partially weathered bedrocks. In addition, the fairly thick fine grained saprolite layer may reduce the risk of groundwater contamination from direct recharge.

Applying of High-Resolution Geophysical Techniques for Drainage Investigations at El-Basateen Cemetery Area, Cairo, Egypt

Due to the collapse of some cemetery in Basateen area, South of Cairo, this paper presents the application of geoelectrical resistivity sounding and imaging, as well as ground penetrating radar techniques for outlining the reasons and the presence of draining water and groundwater at the investigated area. A Vertical Electrical Sounding (VES) survey was performed at 3 points through the studied site to investigate the vertical extent of the subsurface sequence and the saturation levels. A total of 9 Dipole-Dipole imaging profiles were surveyed to determine the lateral distribution of saturation of drain water and infiltrated groundwater, and a total of 6 GPR profiles with 100- and 200- MHz antennae were surveyed to evaluate and determine the depth and the degree of saturation of the subsurface layer/s. The qualitative and quantitative interpretation of the acquired VES's and dipole-dipole imaging profiles showing easily the levels of saturations at the studied site. From the interpretation of GPR profiles, it was possible to locate and determine the saturated zones and the level of the groundwater through the area. The radar signals are penetrated enough and enabled the identification of the subsurface reflectors. The results of GPR, VES's and Resistivity imaging showed a good agreement. The integrated interpretations were verified by local geology and information from several bores. Also, the study was supported by a chemical analysis from the drain water and Ein El-Seera spring (close to studied site), to determine the main source of the drain and infiltrated water at the studied site.

Preliminary Geotechnical Characterization of a Site in Southwest Nigeria using Integrated Electrical and Seismic Methods

ABSTRACT Geophysical investigation using Vertical Electrical Sounding (VES), Electrical Resistivity Tomography (ERT) and Seismic Refraction at a proposed conference center site along Ajibode-Labani road, Ibadan, southwestern Nigeria has been carried out. The investigation aims at characterizing and delineating the sub-surface strata to understand the weathered profile at the site. Understanding the weathered profile is essential in determining the suitability of the site for engineering construction of the future conference center. A total of 25 VES and 10 ERT profiles were acquired in a systematic grid pattern using both Schlumberger and Wenner configurations with Allied omega terrameter. The VES data were processed and analyzed using WinResist and the ERT data were inverted using RES2DINV. The data were combined to form a 3-D data set of the site and RES3DINV was used to produce the depth slices. Seismic refraction data were also acquired with an ABEM seismograph and processed using SeisImager and Fajseis software. Seismic data were used in understanding the velocity distribution and thickness. The results of VES, ERT and seismic refraction show good correlation. Four sub-surface layers were delineated: top layer of reworked sand, clayey sand/ lateritic hard pan, clay/ sandy clay and fracture/ fresh basement. The 3-D model permits a pictorial view of the sub-surface in relation to materials that overlie the basement. The thickness of unconsolidated materials to bedrock varies from 2.7 m to 12.2 m which revealed inhomogeneity in weathering under the shallow sub-surface. It is found that the integrated geophysical tool is well suited to characterize and delineate sub-surface structure (weathered profile) for engineering site characterization.

Comparison of Thickness and Depth Resolution Power of Wenner and Schlumberger Arrays: A Case Study of Temidire Quarters, Akure, Nigeria

An electrical resistivity sounding investigation was carried out within the vicinity of some hand dug wells at Temidire Quarters in Akure, Ondo State, Nigeria. The aim of this study was to compare depth and thickness resolution power of Schlumberger and Wenner arrays. The investigation involved twenty-four vertical electrical soundings (VES) which consisted of twelve Schlumberger array VES and twelve Wenner array VES. The VES results delineated geoelectric layers beneath each VES locations, their layer resistivities, layer thicknesses and depth to aquifer layer(s). Depth to aquifer layer was also determined from static water level measurement and this aided the aquifer layer delineation from VES results. The geoelectric sounding results showed that the study area is dominated by a KH-curve type which consists of top soil, clay/weathered layer, fractured basement and fresh basement. Results from both Schlumberger and Wenner array data were correlated with the static water level measurement; Schlumberger array was found to have higher correlation value than Wenner array.

Geoelectrical Investigation of the Groundwater Potential at Laniba, Akinyele Local Government area of Ibadan, Oyo State

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 fractured layer has resistivity ranging from 51.5 to 1178.0 \(\Omega\)m, the fresh basement (bedrock) has resistivity value ranging from 39.1 to 1010.2 \(\Omega\)m with infinite depth. However, the depth from the earth surface to the bedrock surface varies from 3.1 to 35.5 m.

Hydrological Characterization of Budge Budge and Dum Dum Areas of South and North 24 Parganas Districts, West Bengal Using Geoelectric and Geochemical Methods

Abstract: Integrated geoelectric, geological and geochemical investigations are carried out in Budge Budge and Dum Dum areas of south and north 24 Parganas district for ascertaining the prevailing hydrological condition and aquifer characteristic with chemical qualities of groundwater for drinking and irrigation purposes. The proposed areas are constituted of alluvium and marine sediments of Quaternary age being a part of Gangetic delta. Vertical electrical soundings (VES) of Budge Budge have delineated four to six layers consisting of top soils, the brackish water zone, clay layer, first fresh water zone, another clay layer and the bottom-most(sixth layer) second fresh water bearing zone. The first fresh water zone is located at a depth of 128 m with thickness of 43 m having resistivity range of 32 ohm.m to 37 ohm.m for VES locations BB2 and BB3. The resistivity of the deeper second fresh water bearing zone is varying from 47 ohm.m to 51 ohm.m. The interpreted VES results significantly correspond with the borehole litholog of Budge Budge area. Similar VES results are also obtained for Dum Dum area showing promising potential aquifer zone especially for VES locations DD3 and DD4. A litho-resistivity relation is also determined for the area. Total TDS content of Budge Budge ground water samples are ranging from 720 mg/l to 4400 mg/l and same is ranging from 1012 mg/l to 1930mg/l for Dum Dum ground water samples. According to IS standard, the value of major cations and anions are near to the permissible limit for Dum Dum but same is not observed in Budge Budge for drinking and irrigation purpose excepting location G7. According to Piper trilinear diagram, the ground water in Budge Budge area is sulphate rich type and in Dum Dum it is fresh in nature. Chemically, the groundwater samples from Dum Dum and Budge Budge is classified as (Ca+Mg+Cl+SO4) facies. The geochemical parameters like total hardness (TH), sodium adsorption ratio (SAR), soluble sodium percentage (SSP), Kelly’s ratio (KR), magnesium ratio (MR), residual sodium carbonate (RSC), corrosivity ratio (CR), Gibb’s ratio-I&amp;II (GR-I &amp; GR-II), chloro alkaline indices (CAI-I &amp; CAI-II), permeability index (PI), sea water contamination (SWC) are also determined for better understanding of the quality of groundwater in the above areas.

Estimating geohydraulic parameters, protective strength, and corrosivity of hydrogeological units: a case study of ALSCON, Ikot Abasi, southern Nigeria

The study area, characterized by prolific surface and groundwater repositories, is faced with the challenges of surface and groundwater pollutions. These pollutions need good management practices to avoid waterborne diseases. In an attempt to solve this problem, the integration of vertical electrical sounding (VES) method with laboratory analysis of borehole water was undertaken to size up the contour of groundwater geohydraulic parameter distributions and their dispositions. These Parameters are fraught with information concerning contaminant plume. Aquifer repositories characterized by fine to coarse sands have resistivity ranging from 166.3–2332.5 Ωm, delineated through the use of manual and electronic processing aided by software packages such as WINRESIST and SURFER. Thickness ranged from 2.6–170.3 m. Using the VES results and water resistivity, porosities were determined using Archie’s model. Estimated porosities were employed in the Kozeny–Carman–Bear’s Model to estimate the hydraulic conductivity for all the VES stations and good fits were obtained with pump test results. The K values were combined with Dar Zarrouk parameters to infer the hydraulic transmissivity. The results indicate that fractional porosity varies from 0.102 to 0.198. The hydraulic conductivities ranged from 7.48 × 10−6 to 5.33 × 10−5 m/s, while the transmissivity values vary between 7.938 × 10−5 and 3.389 × 10−3 m2/s. The tortuosity of the aquifer also varies from 1.12 to1.35 while the conductance of aquifer per day varies from 259 to 15,575 μS/day. The hydrogeological units are generally prone to interaction with brackish/saline water from the Imo River and corrosion from surface sources due to the high permeability of the layers surrounding the geometries of water repositories. The ranges of parameters estimated are consistent with literatures for studies conducted in other areas with similar geomaterials, therefore indicating the efficacy of the method.

Geoelectric assessment as an aid to geotechnical investigation at a proposed residential development site in Ilubirin, Lagos, Southwestern Nigeria

The study focuses on the application of electrical resistivity methods as a guide for a detailed geotechnical investigation due to the inhomogeneity of the soil materials cum inability of the drilling beyond 38 m from the three initially drilled geotechnical boreholes which did not allow for proper foundation decisions and thus necessitated the research. Two-dimensional (2D) electrical resistivity data were acquired using the Wenner array along ten (10) traverses of about 500 m long, and forty-four (44) vertical electrical sounding (VES) data were acquired along the various traverses using the Schlumberger array with a maximum spread of 620 m. The VES data were interpreted using partial curve matching technique and one-dimensional (1D) computer iteration using WinRESIST software. The 2D dataset were processed using DIPROWin software. The inversion of the 2D resistivity data was constraint by the VES results and available borehole data. The results of the interpretation of the electrical resistivity data reveal that the lithological units underlying the study area compose of clay/peat, clayey sand, sandy clay, and sand. The results of the interpretation of the electrical resistivity data guided by the range of resistivity (ρ) values and knowledge of the geology of the area reveal that the lithological units underlying the study area are composed of peat (ρ ρ ρ ρ 300 Ωm). The various layers are intercalated with each other, and thickness values vary from one location to another up to a maximum depth of 70 m. The VES results show that the clayey material underlies the sand-filled topsoil and there are indications of competent sand layers at depth beneath these clayey layers in the study area. The 2D pseudosections reflect that the different lithological units are intercalated with varying thicknesses across the study area. Thus, the study reveals that the subsoil within the study area is quite inhomogeneous and great care and expertise is required for developing the site. Anonymously low-resistivity areas delineated along each of the traverses are locations recommended for targeted geotechnical investigation prior to construction.

Application of Electrical Resistivity and Ground Penetrating Radar Techniques in Subsurface Imaging around Ajibode, Ibadan, Southwestern Nigeria

Integrated geophysical investigation involving Electrical Resistivity (ER) and Ground Penetrating Radar (GPR) techniques were carried out around a site underlined by Basement Complex rocks of southwestern Nigeria. The study was aimed at imaging the subsurface lithological units and delineating shallow geologic structures for the purpose of characterizing the area for construction suitability. A total of twenty five (25) Vertical Electrical Sounding (VES) data using Schlumberger array, ten (10) traverses of Electrical Resistivity Imaging (ERI) using Wenner array and Ground Penetrating Radar (GPR) surveys were carried out along the established traverse lines within the area. The VES data were quantitatively interpreted using partial curve matching technique and subsequently improve upon by inversion software using IPI2Win, to obtain the layer geoelectric parameters. The ERI data was inverted and interpreted using Res2Dinv and Res3Dinv inversion software’s respectively to generate 2D and 3D resistivity image of the subsurface. The GPR data was processed into radar section using RadExplorer software. Vertical electrical sounding results delineates typically three to four geologic layers which are the topsoil/lateritic hardpan, weathered basement (consisting clay and sandy clay) and fractured/fresh basement with layer resistivity value ranges of 10-2684 Ωm, 12-242 Ωm and 229-3213 Ωm respectively and thickness value ranges of 0.5-2.1 m and 4.0-14.1 m respectively. 2-D inverted resistivity results also delineated three major geologic layers which are the topsoil, weathered basement and fresh basement and correlates well with the results obtained from the VES results. Layers 1 to 3 of 3D inverted resistivity slice results show high degree of variation in resistivity distribution at shallow depth, consisting of highly resistive material towards the eastern part with low resistivity material concentrating at the south-western part. Results of the GPR survey also delineated three to four geologic layers which include the topsoil/lateritic hardpan, weathered basement and fractured/ fresh basement. The study area was categorized to have semi-competent to competent basement rock based on the resistivity value of the underlying material within the area. Bedrock depression delineated at some location could pose threat of differential settlement to construction works within the study area. Thus, it should be ensured that foundation is designed to sit comfortably on the competent bedrock or by employing suitable foundation work, such as piling to ensure foundation stability and prevent structural failure. Thus, electrical resistivity and ground penetrating radar techniques are versatile tools in site characterization.

Geophysical and geochemical approach to identify the groundwater quality in Agastheeswaram Taluk of Kanyakumari District, Tamil Nadu, India

A combined study of both geoelectrical and geochemical methods was used to find the quality of groundwater in the Agastheeswaram Taluk of Kanyakumari District, Tamil Nadu, India. The vertical electrical sounding (VES) method was applied to identify the variations in electrical resistivity of the subsurface. Three to five geoelectric layers are interpreted in the study area from the observed VES data. The aquifer was mostly found in the second or third layer. Analytical results from the 14 groundwater samples collected near the VES stations are in good correlation with the VES outcomes. Also, the interpreted results of VES data collected from the field were compared with the existing subsurface data and correlation was made, which proved the consistency of the VES method. Iso-resistivity contour maps for different depths and pseudo cross sections showing the resistivity distribution with depth are prepared for detailed analysis. More than 50 % of the area is having aquifer resistivity value less than 10 Ωm. This indicates that the aquifer is found to get polluted by saline water intrusion or some other anthropogenic activities, like intense agricultural practices and poor sewage management. From the geochemical analysis of the groundwater samples, it is found that the Na+ and Cl− are the dominant cation and anion in the study area. Evaporation and rock-water interaction are found to be the major processes controlling the ion concentration in the groundwater. The results obtained from geochemical analysis are in good correlation with the VES results.

Integrated Geophysical and Hydrochemical Approach for Locating Fresh Water Locations in a Coastal Terrain

An integrated geophysical investigation viz., Vertical Electrical Sounding (VES), Electrical Resistivity Tomography (ERT) and Ground Penetrating Radar (GPR) were carried out in a coastal terrain at Vizag Steel Plant (VSP), Visakhapatnam, Andhra Pradesh., India for locating fresh water locations. The entire area was underlain by recent alluvial of varying thickness consists of sand, clay and silt with basement as Kondalite rock formation consisting of saline water in some parts of the area. Locating favorable groundwater locations in such a terrain is a difficult task. The area consists of saturated clay, saturated silt and saline water has the same resistivity signature and misleads resistivity data interpretation for identifying and recommending the suitable groundwater locations in a coastal terrain. To overcome these uncertainties, a second geophysical approach or combinations of geophysical methods become necessary to resolve these resistivity ranges in a more reliable and better fruitful interpretation of sub-surface layers. In order to pin-point the groundwater locations at VSP; VES, ERT and GPR investigations were carried out. Interpreted results of VES, ERT pseudo-section and GPR images (radargram) were correlated with each other to ascertain confidently the geophysical signature of the sub-surface. Combination of geophysical methods gives better resolution or interpretation of sub-surface information before made any recommendations for drilling of borewell. Based on integrated geophysical investigation few borewell sites were recommended and drilled. The observed drilled lithologs was well correlated with the VES, ERT and GPR data. Besides, this hydrochemical analysis of water samples was carried out from the existing borewells and dugwells. Total Dissolved Solids (TDS) and chloride concentration were ranges from 189 to 3398 mg/l and 5 to 1610 mg/l. The eastern and north-eastern part of the area has elevated concentration of TDS and chloride indicating intrusion of saline water. TDS concen- tration of drilled borewell was found to range from 400 to 500 mg/l. The observed yield of drilled borewells ranges from 104 to 3623 gal/hr.

The Application of Vertical Electrical Sounding (VES) for Groundwater Exploration in Tudun Wada Kano State, Nigeria

A new simple and quick geophysical method for groundwater exploration in the crystalline rocks of Tudun Wada Kano State, Nigeria has been developed. A geophysical evaluation using Electrical Resistivity method for groundwater exploration at the study area was carried out which involved the utilization of Vertical Electrical Sounding (VES) technique with schlumberger array system. The study area is located within the sedimentary rocks, igneous, and metamorphic with alluvial as common types of rocks. The data acquired from six (6) VES stations using ABEM terrameter (SAS 300) was tabulated in a table which shows the resistivity, the thicknesses and the number of layers for each VES station. The data was analyzed using computer software called IPI2win, which yield an automatic interpretation of the apparent resistivity. The VES results revealed heterogeneous nature of the subsurface geological sequence. The geological profile sequence in the study area include the topsoil, weathered layer, fractured basement and fresh basement. The value for topsoil ranges from 16 Ωm to 550 Ωm with thickness varies from 1.45 m to 6.05 m. The weathered layer resistivity ranges from 14 Ωm to 541 Ωm and thickness of 5.70 m to 33.00 m. The fractured basement ranges in value from 189 Ωm to 785 Ωm with thickness ranges from 11 m to 20 m. The fresh or bedrock basement has a resistivity of 1011 Ωm to 3006 Ωm which move down infinitely. Therefore the depth of the bedrock from the topsoil or earth’s surface ranges from 2 m to 45 m.

Geohydrological investigation using Schlumberger sounding in part of hard rock and alluvial area of Ahraura region, Mirzapur district, Uttar Pradesh, India

The study area is located in the part of hard rock and alluvial area of Ahraura region, Mirzapur district, Uttar Pradesh, India. Twenty-two vertical electrical soundings (VES) were conducted using Schlumberger configuration at suitable locations in study area for geohydrological or groundwater investigation. The VES data were interpreted using both techniques: curve matching technique and automatic iterative method. Geoelectrical cross section along the five profiles was conducted based on the results of vertical electrical soundings using Schlumberger configuration. A priori information, detailed survey, and appropriate locations of vertical electrical sounding were done using satellite imagery and integrated geophysical methods. The different types of hydro-resistivity maps are prepared based on the results of VES such as contour map of total transverse resistance and total longitudinal conductance, 3-D surface map of total transverse resistance and total longitudinal conductance, contour map of substratum, and one-grid vector resistant substratum map, giving the information about lithological changes and subsurface geology.

An Assessment of the Influences of Surface and Subsurface Water Level Dynamics in the Development of Gullies in Anambra State, Southeastern Nigeria

Abstract Gully erosion–induced problems have been challenging the people and government of Anambra State in southeastern Nigeria for a long time. In spite of the numerous geoscientific and engineering studies so far conducted in the area, the underlying causes of these problems still remain poorly understood. In an attempt to contribute to the understanding of the underlying processes responsible for the persistent gully erosion problems in Anambra State, an integrated study utilizing hydrological, geomorphological, and geophysical data was undertaken. Results of the analyses show that bulk density, pH, and organic matter content of the soil range from 1610 to 1740 kg m−3, 5.10 to 5.30, and 0.32% to 0.46%, respectively. Particle size analyses results show that the soils are dominated by coarse sand materials (50%–68%). Variations in the Atterberg limit parameters (liquid limit, plastic limit, and plasticity index) also point to the dominance of coarse materials in the shallow subsurface. Vertical electrical sounding results capture the shallow surface as being dominated by resistive sandy materials that are underlain by lowly resistive clayey materials. Thus, the area is dominated by porous, friable, and poorly cemented coarse materials that are located on a long and steeply sloping terrain of the tectonically elevated Awka–Orlu cuesta. Both overland and subsurface flow processes are responsible for the gully erosion problems confronting the area. Human activities (e.g., deforestation, uncontrolled urbanization, and absence of requisite legislation to protect the environment) and the high elevation of the Awka–Orlu cuesta have aggravated the severity of the problems. An aggressive reforestation program particularly with native trees, promulgation of necessary legislation to protect the environment, and setting up and empowering an enforcement agency should be vigorously pursued. Also, necessary enlightenment campaigns on best agricultural practices that can reduce surface runoff in soil and water conservation may also be helpful in changing the mindset of people.