Subsurface Geoelectric Layers Research Articles

The Result of Electrical Resistivity Investigation of Solid Waste Landfill Conducted at Nsukka Municipality Using Electrical Resistivity Measurments

Solid waste landfill management has been a significant issue for Nigerian urban areas and other developing countries across the globe.Similar to most other cities, Nsukka also generates waste on a daily basis, much of which is dumped in poorly designed and positioned dumping sites. The majority of the disposal sites are found on roadsides, at marketplaces, on farms, and in residential neighborhoods, among other places. The road infrastructure and groundwater are under danger, and the beauty of the impacted communities are not spared. Undoubtedly, the unchecked citation of boreholes as the source of potable water in the majority of our rural and urban communities—given that the government doesn't seem to be providing water to the people—has become a significant challenge. An investigation using electrical resistivity method was conducted around a solid waste dumpsite at Nsukka in Nsukka L.G.A of Enugu State, Nigeria with an aim to investigate the level of groundwater contamination and the objectives to determine the subsurface geoelectric layers, depth to water table, lithology delineation and map out the contamination zones. The scope of this study provides an overview of some of the approaches used to assess the aquifer vulnerability and aquifer potential using Vertical Electrical Sounding (Schlumberger array) and 2D resistivity imaging (Wenner array) in different locations around Nsukka municipality dumpsite. Both methods were used for this study in order to provide a geophysical database for exploration of the study area’s groundwater resources and also they are less expensive and less time consuming. VES has proved to be effective in solving groundwater problems in most places in Nigeria (Ezeh and Ugwu, 2010; Ugwu and Ezeh, 2012; Nzemeka et al. [1,2]. Electrical Sounding (VES) and 2D resistivity imaging were carried out with a digital read out resistivity meter (ABEM SAS 1000) to acquire data in the area and were interpreted using the Schlumberger automatic INTERPEX analysis software and the RES2DINV software respectively, which generates model curves using initial layer parameters and display the variations of electrical resistivities respectively. A total of eight (8) sounding and six (6) 2D resistivity imagings were carried out in the area. A contaminant leachate plume was delineated in 2D resistivity sections as low resistivity zones while the VES shows the depth of aquifer. In 2D pseudosections where bluish colours with low resistivities (less than 20.80\(\Omega\)m) with the depth ranging from 1.28m to 17.1m in the Line 1 and 2 are seen as contaminated zones. The rest of the lines are not contaminated because of their high resistivities (greater than 20.80\(\Omega\)m). The result of the electrical resistivity survey also showed 4 - 5 layers geo-electric sections and an AA and AK type sounding curves. The VES result shows that VES 1A, 1B, 2A and 2B which are carried out on line 1 & 2 of the wenner lines showed signs of contamination with low resistivity values less than 20.80\(\Omega\)m complementing the wenner results. The contamination has not yet got to where the aquifer is located on the lines. Since the depth to the aquifer ranges from 30.26m to 155.43m while maximum depth of contamination is 17.1m. It is believed that the leachate has not percolated down to the aquiferous zones as such aquifers are presumed to be free. As such, it is recommended that boreholes around the study area should not be less than 30m deep to avoid exploiting polluted water.

Groundwater Potential Mapping Using Geophysical Techniques: a Case Study in Hosanna Area, Western Margin of The Central Main Ethiopian Rift, Ethiopia

In this study, Vertical Electrical Sounding (VES) and magnetic methods are applied for mapping the groundwater potential and aquifer system in the Gode area, the western margin of Central Main Ethiopian Rift. The VES is used to map the depth to potential aquifer zone of the groundwater and its distribution over the area, whereas, the magnetic survey is applied to delineate contact between lithologic units and geological structures. A total of 12 VES data points and more than 400 magnetic data points at about 10m station intervals along seven profiles are collected, processed and analyzed. Our results from interpretation of the VES data, geoelectric sections, and 2D magnetic modeling results respectively revealed the vertical stratification of the subsurface geoelectric layers and the presence of subsurface weak zones, which control the groundwater flow and storage system where the potential aquifer in the area obtained at a depth range from 45m to 92m. Overall, areas in the neighborhood of four VES points, i.e.VES-2, -3, -10, and -11, show good water-bearing zones in the study area associated with the highly weathered/fractured ignimbrite and pumice layers.

Delineation of aquifers favorable for groundwater development using Schlumberger configuration resistivity survey techniques in Rajouri district of Jammu and Kashmir, India

The primary goal of this research is to demarcate aquifers favorable for groundwater development in the border district of Rajouri, in the Union Territory of Jammu, and Kashmir, in order to secure a long-term water supply. The Schlumberger configuration resistivity survey technique Vertical Electrical Sounding (VES) is used to investigate the characteristics of the subsurface layer and the potential of groundwater by using 30 VES sites in order to establish the optimum sites for digging a successful borehole for the qualitative and quantitative interpretations in the study area. It is determined that real resistivity values of subsurface geoelectric layers less than 35 Ohm m indicate the existence of finer sediments, whilst moderate resistivity values ranging from 35 to 100 Ohm m suggest the presence of coarser sediments favorable for groundwater development. The resistivity value between 100 and 200 Ohm m indicates weathered formation, 200–400 Ohm m, indicates fractured rock and more than 400 Ohm m represents hard formation which is devoid of any kind of groundwater development. The bedrock resistivity, nature of the curve, and overburden thickness are the parameters utilized to choose a good site for drilling tests. Based on the criteria, it was determined that nine VES sites (VES-2, VES-3, VES-4, VES-6, VES-17, VES-18, VES-19, VES-28, and VES-30) are appropriate for the installation of a tube well for irrigation and domestic purposes. The 8 sites (VES-14, VES-15, VES-20, VES-21, VES-22, VES-23, VES-24, and VES-27) were not suitable because of compact formation and harder rocks whereas the 13 VES sites (VES- 1, VES-5, VES-7, VES-8, VES-9, VES-10, VES-11, VES-12, VES-13, VES-16, VES-25, VES-26, VES-29) are partially suitable for groundwater development and only suitable for personal uses such as hand pump of shallow depth.

Geophysical Resistivity Survey (VES) for Selection of Artificial Recharge of Appropriate Artificial recharge for Augmentation of Ground Water Resources In Paithankheda Village, M. S. India

In this study the data generated while conducting electrical resistivity surveys through Vertical Electrical Sounding (VES) at 22 sites in different location along with a available geological &hydro-geological information of Paithan Kheda village were analyzed. The objective are (i)to understand the nature and extent of aquifer(ii)to find out the location and thickness of unsaturated zones and (iii)to evaluate and extent of appropriate artificial recharge structures at suitable locations across the village. Interpretation of the top sounding curves indicates presence of three to four subsurface geo-electric layers across the study area. The top soil ;layer has range of resistivity values from 2 to 30-ohm m & litho logy comprise clay with kankar,lateritic sand. This is followed by the weathered and jointed Basalt layers with resistivity values 100 300-ohm m could be identified below the depth of 45m.At some places, doleritic dykes were also observed with resistivity values >300-ohms. The interpretation of VES data when correlated with the available lithilog data indicates a prominent water bearing zone between 30 and 45 mbgl.The underlying hard and compact Basalt has very little possibility of occurrence of groundwater. The top unsaturated and unconfined granular zone up to adept of 30mts could therefore be easily recharged artificially through rainwater harvestining measures thereby augmenting the groundwater resources of the existing aquifers. Site specific artificial recharge measures from amongst counter banding ,gully plugs ,check dams, percolation tank. Recharge shafts subsurface dikes have been identified across the village for effective recharge of the aquifer especially in its north eastern &southern blockregions.Considering the deteeoriating groundwater sitution, these initiatives would be significant in catering the needs of future generations.

Evaluation of Topsoil Competence, Aquifer Types, Groundwater Prospect and Flow Pattern using Geoelectric Characterization for Part of Ogbomoso, Nigeria

Part of Ogbomoso Southwestern Nigeria was assessed using electrical resistivity method with a view to obtaining the subsurface geoelectric parameters (resistivities and thicknesses), categorizes the topsoil into different competence zones and evaluates the aquifer types, groundwater prospect and flow pattern. Fifty-four Vertical Electrical Sounding (VES) data were quantitatively interpreted using the partial curve matching technique to obtain the preliminary layer parameters which were further refined through 1-D forward modelling WinResist software package. The resulting final layer parameters were used to generate 2D geoelectric sections, isopach and isoresistivity maps and subsequently used to categorize the study area into different topsoil Competence, Aquifer types and Groundwater Potential zones. Static water levels of hand-dug wells in the area were used to generate the groundwater flow pattern. Four subsurface geoelectric layers were delineated. These were the topsoil, laterite, weathered/partly weathered layer (main aquifer) and fractured/fresh bedrock. The resistivities and thicknesses of the layers were 76-1858, 649-2021, 17-880 and 260-33385 Ωm and 0.4-4, 0.7-1.9 and 1.9-25.2 m respectively. The groundwater flow pattern in the area was NE-SW. The study concluded that incompetent to highly competent topsoil, weathered bedrock (main) aquifer unit/partly weathered/fractured bedrock aquifer and generally low groundwater potential with NE-SW flow direction underlay the study area.

2D Electrical Resistivity Imaging (ERI) for Subsurface Evaluation of a Pre-engineering Construction Site in Akure, Southwestern Nigeria

2D electrical resistivity imaging (ERI) and vertical electrical sounding (VES) were integrated to map the subsurface lithology at a pre-engineering construction site in Akure, southwestern Nigeria, in order to ascertain the competence and suitability of the site for engineering structures. Four 2D horizontal profiling (Wenner array) was used to qualitatively study and interprete the geoinformation of the lithological nature of each geoelectric layer within the study site. Four vertical electrical sounding were also conducted using Schlunberger configuration. The VES data were processed and inverted using master curves and WinResist computer software, while the 2D inversion was done using Diprowin. The results of the 2D horizontal profiling revealed that the study area is composed of four subsurface geo-electric layers with resistivities ranging between 6.91Ωm to 93.6Ωm. These results revealed an expansive clay formation to the depth probed. While the VES results showed a three subsurface geo-electric layers with resistivities ranging between 8.4Ωm to 640Ωm with the second layers where the foundation is supposed to be laid confirmed the presence of clay with resistivities ranging between 8.4Ωm to 13.0Ωm with depth ranging between 4.9m to 7.9m. The results revealed the site to be an expansive clay formation and showed that shallow foundation may not be feasible or advisable for massive engineering structures because of the presence of clay materials in the area. But small or light engineering structures may be recommended.

Evaluation of groundwater potentials of Orogun, South\u2013South part of Nigeria using electrical resistivity method

An investigation has been made of the groundwater potentials of Orogun Town, Ughelli North Local Government Area of Delta State, Nigeria, using electrical resistivity survey. This study motivated to determine electrical resistivity parameters of the area. The aim of this work is to use electrical resistivity method to explore the groundwater potentials of Orogun Town with the determination of its Dar Zarrouk parameters. A total of eight vertical electrical sounding (VES) were conducted with maximum electrode spacing of 150 m. The data were acquired using ABEM SAS 4000 Terrameter and processed using IPI2win and Interpex softwares. The groundwater potentials of the area are evaluated based on the longitudinal conductance (S), transverse resistance (T), coefficient of electrical anisotropy (λ), resistivity for the formation (rho_{text{m}}), reflection coefficient (RC) and resistivity contrast (FC). The results reveal four subsurface geoelectric layers in seven of the eight VES while one VES revealed three subsurface geoelectric layers. Resistivity values for all the layers in the study area are very high, higher than what is expected in a sedimentary basin as we have in the study area. The resistivity values range from 8470 Ωm (layer 1, VES 7) to 118,030,000 Ωm (layer 3, VES 8). Depth to aquifer in the study area ranged from 1.61 m (VES 2) to 12.41 m (VES 1), while resistivity values of the aquifer ranged from 64,182 Ωm (VES 3) to 118,030,000 Ωm (VES 8). The results from the formation parameters evaluated showed that the area has good groundwater potential but might have been highly contaminated, especially from hydrocarbon sources and other man-made pollutants. The suggested contamination of the aquifer is as a result of the high values of resistivity of the aquifer layers.

Geoelectric evaluation of groundwater potential within sunshine garden estate, akure southwestern Nigeria

The Vertical Electrical Resistivity surveys in the Sunshine Garden Estate have contributed to a better understanding of the basement complex of Southwestern Nigeria. Nine (9) vertical electrical sounding (VES) using the Schlumberger electrode array were interpreted and the results shows three (3) subsurface geoelectric layers within the study area. These are the weathered layer, topsoil, fresh/fractured basement. Groundwater pockets such as fractured zones, valley fills/basement depressions, and weathered zones were delineated in the study area. Weathered/partially weathered layer and weathered basement/fractured basement were the two major aquifer mapped out and these aquifers are characterized by thick overburden, found within basement depressions. The groundwater potential of the study area was zoned into low, medium and high potentials. Zones where the overburden thickness (which constitutes the main aquifer unit) is greater than 13m and of low clay composition (average resistivity value between 200 - 400Ωm) are considered zones of high groundwater potential. Area where the thickness of the aquifer ranges from 11-13m with less clay composition are considered to have medium groundwater potential and the areas where the thickness of the aquifer is less than 11m are considered to have a low groundwater. The VES station underlained by high and medium groundwater potential zones are envisaged to be viable for groundwater development within the area. Â

Groundwater Level Fluctuation in Response to Climatic Variation and its Geotechnical Implication in Part of Awgu Shale, Central Benue Trough, Nigeria

The role of climate variation on groundwater level and its geotechnical implication was studied. Static water levels (SWL) and elevations of 57 dug wells and boreholes were measured during dry and wet seasons. The differences between the SWL for dry and wet season was used to establish the depth of groundwater fluctuation, while geophysical investigation was conducted to delineate the subsurface geo-electric layers. This information is vital for groundwater assessment and evaluation, however, this research is biased towards its geotechnical implications. SWL varied between 5.5 – 13 and 2.2 - 9.2 meters below sea level (mbsl), while groundwater elevation ranges from 131.8 – 157.2 and 136-160 meters above sea level (masl) for dry and wet seasons respectively. The depth of fluctuation (active zone) lies between 1.1 – 5.9 mbsl. The wells showed a direct rapid response to short term seasonal precipitation attributable to climate variation, which implies a shallow aquifer. Groundwater flows from the northern parts towards the southern parts. Foundations in the study area are underlain by sandy-clays, clays and sands as revealed by geophysical investigations. Engineering structures with shallow foundation may be prone to shrink-swell behavior, and should be laid beyond active zone.

Geophysical characterization of the role of fault and fracture systems for recharging groundwater aquifers from surface water of Lake Nasser

The role of the fracture system is important for enhancing the recharge or discharge of fluids in the subsurface reservoir. The Lake Nasser is consider one of the largest artificial lakes all over the world and contains huge bulk of storage water. In this study, the influence of fracture zones on subsurface fluid flow in groundwater reservoirs is investigated using geophysical techniques including seismicity, geoelectric and gravity data. These data have been utilized for exploring structural structure in south west Lake Nasser, and subsurface discontinuities (joints or faults) notwithstanding its related fracture systems. Seismicity investigation gave us the comprehension of the dynamic geological structure sets and proposing the main recharging paths for the Nubian aquifer from Lake Nasser surface water. Processing and modelling of aerogravity data show that the greater thickness of sedimentary cover (700 m) is located eastward and northward while basement outcrops occur at Umm Shaghir and Al Asr areas. Sixty-nine vertical electrical soundings (VES’s) were used to delineate the subsurface geoelectric layers along eight profiles that help to realize the subsurface geological structure behind the hydrogeological conditions of the studied area.

Application of Geophysics in Post Foundation Study: A Case Study of the Faculty of Social Science Building, Phase I, Federal University, Oye-Ekiti, Southwestern, Nigeria

Post foundation study of the causes of distress on the Faculty of Social Science building, Phase I, Federal University, Oye-Ekiti was carried out using geophysical approach. The geophysical methods used were the magnetic and electrical resistivity. The magnetic measurements were taking at an interval of 5 m along the established three traverses. The magnetic data were presented as profiles and interpreted using Euler deconvolution software. The Vertical Electrical Sounding data were quantitatively interpreted using partial curve matching technique and 1-D forward modelling with Win Resist software. The dipole-dipole data were inverted using DIPPROTM software. The magnetic profiles delineated two subsurface layers; the overburden and the Basement bedrock. Series of geological linear structures were delineated by the ground magnetic. The VES results reveal three subsurface geoelectric layers. These include; the topsoil with resistivity ranging from 20-290 Ωm and thickness ranging from 0.4-2.5 m; the weathered layer with resistivity ranging from 2.6-122Ωm and thickness ranging from 0.9-23 m; and the Basement bedrock with resistivity ranging from 83-∞Ωm. The low resistivity values of the Basement bedrock in places indicate an intense fractured basement rock. The 2-D resistivity structure also delineated three geoelectric sequences; the topsoil, the weathered layer and the Basement rock which correlate with the geoelectric sections. Geological linear features were also delineated by the 2-D resistivity imaging which was correlated with the magnetic results. The depth on which the foundation of the investigated building was hosted is not known but it is suspected to have been hosted within the weathered layer. This layer predominantly composed of clayey formation which are of high swelling potential and may be subjected to subsidence under heavy load. The causes of distress on the investigated building may have being precipitated by the clayed nature of the layer where the structure is founded and the presence of linear structure suspected to be fractured or fault within the basement.

Surface DC resistivity survey of contamination Beneath Ido-Osun dumpsite, southwestern Nigeria

Surface DC resistivity techniques have been used to investigate the subsoil characteristics around an abandoned dumpsite in Ido Osun, Southwestern Nigeria. The aim was to delineate groundwater contamination, identify lithologic layers, locate possible leachate plumes, and assess the risk of groundwater pollution. Schlumberger vertical electrical sounding (VES) and Dipole-dipole resistivity profiling data were acquired at 20 m and 10 m intervals respectively along three northwest-southeast geophysical traverses. The geoelectric sections revealed four probable subsurface geoelectric layers which were considered to be topsoil, laterite, weathered/fractured bedrock and competent/fresh bedrock based on previous works. The weathered/fractured bedrock forms the groundwater reservoir in the area as interpreted from the over 98% occurrence of H, KH geoelectric curve types. The dipole-dipole sections showed several distinct low resistivity zones which extends into the weathered/fractured bedrock. These were interpreted as probable contamination plumes beneath the dumpsite.

Geophysical and Hydrochemical Evaluation of Groundwater Potential and Character of Abeokuta Area, Southwestern Nigeria

Hydrogeological assessment of groundwater resources of part of Abeokuta area was carried out with a view to highlighting the potential of the aquifers to provide portable water supply, chemical character and provenance of the groundwater resources of the area. Seventy-five Vertical Electrical Soundings (VES) were distributed across areas underlain by different rock types. This was complemented with fifty groundwater samples collected from wells and analyzed for the major ions and seventy two minor constituents. Three to five sub-surface geo-electric layers were delineated from the VES...

Geo-electrical Method Applied to Evaluation of Groundwater Potential and Aquifer Protective Capacity of Overburden Units

Aims: This study was designed to determine different subsurface Geo-electric layers, the aquifer units, determination of Dar-Zarrouk parameter (Longitudinal conductance(S) and Transverse resistance (R)) as well as identifying suitable areas with poor, weak, moderate and excellent aquifer protective capacity rating. Study Design: The study area, Sabo in Kaduna state lies approximately between latitudes 10o25’N and 10o30’N and longitudes 7o25’E and 78o30’E covering an area of about 500,000m. Methodology: A total of sixty-six (66) vertical electrical soundings (VES) using Schlumberger electrode array were acquired with a maximum electrode separation of AB/2=100 m, using the ABEM Terrameter SAS 300C. Results: Maximum of five lithologies were identified namely, topmost layer which consists of lateritic clay, river sand and gravel, clayey sand, weathered transition zone/ fractured layer and the fresh basement. Qualitative interpretation indicates that the weathered layer and weathered/fractured basement constitutes the main aquifer units. These aquifers are characterized by thick overburden found within basement depressions with maximum value of 65 m and resistivity values between 10 ohm.m and 756 ohm.m. Original Research Article British Journal of Applied Science & Technology, 4(14): 2024-2037, 2014 2025 The Dar-Zarrouk parameters evaluated are total longitudinal unit conductance (S) and total transverse resistance (T) with values ranging from 0.005 – 0.65 mhos and 2000 – 32000 ohm.m. Conclusion: The results show that the lithology of the aquifer is dominated by clay/clayey sand and sandy materials with attendant low and high transmissivity. About 80 % of the area has longitudinal conductance value greater than 0.3 mhos due to high content of clay/lateritic clay indicating moderate protective capacity rating, hence vulnerable to contamination.

Hydrogeophysical study for additional groundwater supplies in El Heiz Area, Southern part of El Bahariya Oasis, Western Desert, Egypt

El Bahariya Oasis is a part of the great groundwater reservoir of the Western Desert of Egypt. The different stratigraphic units, the water-bearing zones, aquifer potentiality conditions, and the favorable locations for drilling new wells were evaluated by carrying out 24 Schlumberger vertical electrical soundings (VESs), along with the data of some wells drilled in the near vicinity of the measuring sites. The results of the interpreted field data revealed the presence of ten distinctive subsurface geoelectric layers; a thin surface, dry loose sand and gravel, sandy clay and shale interclations, saturated coarse sand layer, shale and clay, and saturated fine sandstone and saturated coarse sandstone. The aquifer is a multilayer aquifer with different thicknesses represented by the fourth, sixth, eighth, and tenth geoelectric layers. Results also revealed that the thicknesses of the water-bearing horizons increase towards the east direction, consequently the aquifer potentiality increases. Therefore, the best production well locations are in that direction. Depth to water starts from 40 m at VES no. 14 and increases gradually toward the east to reach 66 m at VES no. 5. Hydrogeochemical analysis of two groundwater samples taken from Ein El Ezza and well no. 2 showed that groundwater in the study area is suitable for agricultural purposes but not for human consumption due to the high iron content. Recommendations concerning site selection for drilling new productive groundwater wells are given.

Estimating aquifer transmissivity from geo-electrical sounding

A geophysical survey was carried out at Kaduna Polytechnic Senior Staff Quarters using Direct Current Electrical Resistivity method. The objectives were to determine different subsurface geoelectric layers, the aquifer units and the estimation of Transmissivity of the aquifer. Sixty-six Schlumberger Vertical Electrical Soundings (VES) were carried out using a maximum electrode separation of 200m.Data analysis and interpretation of the field curves by computer modeling proposes a distinctive 3-4 geoelectric layer situations. This includes the topmost layer which consists of laterite, river sand and gravel. This formation is followed in succession by clayey sand, weathered transition zone/ fractured layer and the fresh basement. Qualitative interpretation indicates that the weathered/fractured Basement constitutes the main aquifer unit. Aquifer resistivity range from 4.26 ohm-m to 755.3 ohm-m with maximum thickness of 52.25m. A maximum 55.52m depth- tobasement was obtained in the study area. Based on the model obtained, aquifer Transmissivity was calculated and was used to delineate the study area into prospective low and high groundwater potential zones. In order to test the reliability of the results, the calculated Transmissivity values were compared with those obtained from pumping test analysis, and a linear regression coefficient of 0.94 was obtained.

Hydrogeophysical Study Of The Groundwater Potential Of Ilara-Mokin Southwestern Nigeria

Geoelectric study of the groundwater potential of Ilara-Mokin in Ondo State Southwestern Nigeria was carried out using electrical resistivity (Vertical Electrical Sounding) method with the view to providing adequate information on the different sub-surface geoelectric layers, structural configuration of the concealed basement rocks and the groundwaterpotential of the study area. Forty-one Schlumberger vertical electrical soundings (VES) were conducted across the study area. The computerassisted VES data interpretation enabled generation of geoelectric curves, sections and overburden thickness map which were used in the delineation of key hydrogeologic features like the topsoil, weathered basement, fractured basement and the fresh basement. Resistivity values range from 21 Ω-m to 798 Ω-m in the topsoil, 14 Ω-m to 209 Ω- m in the weathered basement, 51 Ω-m to 209 in the partially weathered/fractured basement and 312 Ω-m to ∞ within the fresh basement. Layer thickness values also vary from 0.3 m to 6.1 m in the topsoil and 0.9 m to 28.6 m in theweathered basement. The depth to the resistive bedrock ranges from 0.3 m to 29.3 m across the study area. The study revealed that greater part of Ilara-Mokin town is underlain by marginally thick overburden thus constituting shallow aquifer units with poor to marginal groundwater potential. Partially weathered/fractured basement were delineated in isolated cases with tendency for low to marginal groundwater yield around central and northeastern areas of the town. The results reasonably provide basic information that is expected to assist in the future development of groundwater resources in Ilara-Mokin.

Computer model study of the effect of resistive topsoil on interpretation results of subsurface geoelectric layers' parameters

This paper investigates the effect of resistive topsoil (upper layer) on interpreted subsurface layers’ geoelectric parameters. Five hypothetical computer geoelectric models were employed for this study. Model A is a three-layered model with constant thicknesses and varied topsoil resistivity of 100 ohm-m to 2500 ohm-m. Model B is a threelayered model with constant resistivities and varied topsoil thicknesses from 2 to 12 m. Model C is a four-layered model with constant thicknesses and varied topsoil resistivities from 250 to 2500 ohm-m. Model D is a four-layered model with constant thicknesses and varied second layer resistivities from 1000 to 10000 ohm-m. Model E is a four-layered model with constant resistivities and varied second layer thicknesses from 2.0 to 20.0 m. A total of forty theoretical Vertical Electrical Sounding (VES) curves of the A, H, HA, and KHtype were generated and interpreted using the conventional partial curve matching method and computer assisted 1-D iterative forward modeling with the RESIST 1.0 (Vander-Velpen, 1988) software. Statistical analysis of percentage deviations between model and final interpretation

Subsurface Structures and Hydrogeologic Aquifers at the Western Side of Lake Nasser, Southwestern Desert, Egypt

This work deals with the detection of water aquifers and the delineation of subsurface structures predominant in the basement rocks, and their relationship with these aquifers, at west Lake Nasser, southwestern desert, Egypt. An integrated study using geoelectric, geomagnetic, and well logging methods was conducted. Geoelectric surveys were initially performed to obtain vertical electrical sounding (VES) profiles to identify the subsurface geoelectric layers predominant in the area. This was followed by land magnetic surveys using a proton precession magnetometer in a mesh-like network covering the area of investigation. These surveys allowed us to determine the depth to basement rock, and establish the subsurface structures and their relation with the detected aquifers. To confirm the results, more than 20 boreholes were drilled and logged within the study area to determine the distribution of the subsurface water reservoirs and geological sequences in the area. The results indicate that the depth to the main water aquifer, represented by saturated Nubian sandstone, ranges from [Formula: see text]. The thickness of this reservoir varies from [Formula: see text]. The Nubian sandstone formation consists of three members (layers) that unconformably overlie the basement rocks. The depth to the basement rocks ranges from [Formula: see text]. The structure trend analyses indicate that the dominant tectonic trends are NW, NE, and Aqaba trends. These structures play an important role in the water supply from Lake Nasser and recharging the main water aquifer.