Integrated approach for identification of potential groundwater zones in Seethanagaram Mandal of Vizianagaram District,Andhra Pradesh,India

Identifying a good site for groundwater exploration in hard rock terrain is a challenging task. In hard rocks, groundwater occurs in secondary porosity developed due to weathering, fracturing, faulting, etc., which is highly variable within short distance and contributing to near-surface inhomogeneity. In such situations topographic, hydrogeological and geomorphological features provide useful clues for the selection of suitable sites. Initially, based on satellite imagery, topographical, geomorphological and hydrogeological features, an area of about 149 km² was demarcated as a promising zone for groundwater exploration in the hard rock tract of Seethanagaram Mandal, Vizianagaram District, Andhra Pradesh, India. A total of 50 Vertical Electrical Soundings (VES) were carried out using Wenner electrode configuration. An interactive interpretation of the VES data sharpened the information inferred from geomorphological and hydrogeological reconnaissance. Ten sites were recommended for drilling. Drilling with Down-The-Hole Hammer (DTH) was carried out at the recommended sites down to 50 to 70 m depths. The interpreted VES results matched well with the drilled bore well lithologs. The yields of bore wells vary from 900 to 9000 liters per hour (lph).     

The gravity method in groundwater exploration in crystalline rocks: a study in the peninsular granitic region of Hyderabad, India

The application of variations in the earth's gravity in groundwater exploration on a regional scale, especially in sedimentary basins, metamorphic terrains, valley fills, and for buried alluvial channels, is well established. However, its use in hard crystalline rocks is little known. In granite, for example, the upper weathered layer is a potential primary aquifer, and the underlying fractured rock can form a secondary aquifer. Fracturing and weathering increases the porosity of a rock, thereby reducing the bulk density. Changes in gravity anomalies of 0.1–0.7 mGal for granites, due to weathering or variations in lithology, can be detected. To test the use of gravity as a groundwater exploration tool for crystalline rocks, a gravity survey of the peninsular shield granites underlying Osmania University Campus, Hyderabad, India, was undertaken. At the site, gravity anomalies reflect variations in the lithology and in the thickness of weathered zones. These anomalies also define the position of intrusives and lineaments. Areas of more deeply weathered granite that contain wells of higher groundwater yield are represented by negative gravity values. In the weathered zone, well yield has an inverse relation to the magnitudes of residual gravity. The study confirms the feasibility of gravity as a tool for groundwater exploration in crystalline rocks. Electronic Publication     

Integrated geophysical interpretation for the area located at the eastern part of Ismailia Canal, Greater Cairo, Egypt

The integrated geophysical interpretation for the different geophysical tools such as resistivity and gravity is usually used to define the structural elements, stratigraphic units, groundwater potentiality, and depth to the basement rocks. In the present work, gravity and resistivity data were utilized for detecting the groundwater aquifer and structural elements, as well as the upper and lower surfaces of the subsurface basaltic sheet in an area located at the eastern side of Ismailia Canal, northeastern Greater Cairo, Egypt. Two hundred and ten gravity stations were measured using an Autograv instrument through a grid pattern of 50?×?50 m. The different required corrections were carried out, such as drift, elevation, tide, and latitude corrections. The final corrected data represented by the Bouguer anomaly map were filtered using high- and low-pass filters into regional and residual gravity anomaly maps. The resulting residual gravity anomaly map was used for gravity modeling to calculate the depths to the upper and lower surfaces of the basaltic sheet. The resulting gravity models indicated that the depths to the upper surface of the basaltic sheet are ranged between 26 and 314 m, where the shallower depths were found around the southern and eastern parts. The depths to the lower surface of the basaltic sheet are varied from 86 to 338 m, and the thickness of the basaltic sheet is ranged from 24 to 127 m, where the biggest thicknesses were found around the southern and northern parts of the study area. Forty-two vertical electrical soundings (VES) were carried out using Schlumberger configuration with AB/2 spacings ranged from 1.5 to 500 m. 1D quantitative interpretation was carried out through manual and analytical interpretations. The VES data were also inverted assuming a 3D resistivity distribution. The results from the 3D resistivity inversion indicated that the subsurface section consists of sand, sandstone, and sandy–clays of Miocene deposits overlying the basalts. Such basaltic features (of Oligocene age) are underlain by Gabal Ahmar Formation of Oligocene deposits, which are composed of sand and sandstone. Therefore, two aquifers were deduced in the area. The first is the Miocene aquifer (shallower) and the other is the Oligocene aquifer (deeper).     

Combined ground-penetrating radar (GPR) and electrical resistivity applications exploring groundwater potential zones in granitic terrain

Frequent failures of monsoons have forced to opt the groundwater as the only source of irrigation in non-command areas. Groundwater exploration in granitic terrain of dry land agriculture has been a major concern for farmers and water resource authorities. The hydrogeological complexities and lack of understanding of the aquifer systems have resulted in the failure of a majority of the borehole drillings in India. Hence, a combination of geophysical tools comprising ground-penetrating radar (GPR), multielectrode resistivity imaging (MERI), and vertical electrical sounding (VES) has been employed for pinpointing the groundwater potential zones in dry land agricultural of granitic terrain in India. Results obtained and verified with each other led to the detection of a saturated fracture within the environs. In GPR scanning, a 40-MHz antenna is used with specifications of 5 dielectric constant, 600 scans/nS, and 40 m depth. The anomalies acquired on GPR scans at various depths are confirmed with low-resistivity ranges of 27–50?Ω m at 23 and 27 m depths obtained from the MERI. Further, drilling with a down-the-hole hammer was carried out at two recommended sites down to 50–70 m depth, which were complimentary of VES results. The integrated geophysical anomalies have good agreement with the drilling lithologs validating the MERI and GPR data. The yields of these bore wells varied from 83 to 130 l/min. This approach is possible and can be replicated by water resource authorities in thrust areas of dry land environs of hard rock terrain around the world.     

Geoelectrical method in the investigation of groundwater resource and related issues in Ophiolite and Flysch formations of Port Blair, Andaman Island, India

Geoelectrical resistivity investigation using Vertical Electrical Sounding (VES) technique was conducted at Port Blair, South Andaman Island, to locate the fractures in different formations and to decipher its groundwater potential. A total of 40 VES were carried out covering the entire study area using Schlumberger electrode configuration out of which 34 VES fall in Andaman Flysch formations and the remaining VES in Ophiolite formations. The interpreted resistivity results were integrated with nine borehole lithologs for the subsurface analysis. The combination of VES with borehole litholog data has provided a close correspondence on subsurface hydrogeological conditions. The interpreted VES data of various formations showed drastic variations in the resistivity ranging from higher in Ophiolite, moderate in Andaman Flysch and very low in valleys of Andaman Flysch formations. The study further revealed that the weathered and fractured volcanics of Ophiolite groups of rocks and sandstone that occur in the Andaman Flysch formations constitute the productive water bearing zones categorized as good groundwater potential zone. Based on the geoelectrical parameters, viz., thickness of layers and the layer resistivity values, a groundwater potential map was prepared, in which good, moderate, and poor groundwater zones were demarcated. Further, numerical, spatial and litho-geoelectric models of resistivity were analyzed in terms of groundwater potential and these models have thus enabled to prepare a comprehensive groundwater development and management plans proving its efficacy in this art of exploratory investigations.     

Determination of groundwater potential by using geoelectrical method and petrographic analysis in Rawalakot and adjacent areas of Azad Kashmir,sub-Himalayas,Pakistan

The current study is carried out for the determination of groundwater potential in District Rawalakot Azad Jammu and Kashmir (AJ&K) Pakistan by using electrical resistivity method and petrographic analysis of the area. The tape-compass-clinometers method was used in section measurement to understand the facies and depositional environment. The electrical resistivity survey was carried out in the project area in sub-Himalayan Siwaliks system of Pakistan to overcome water scarcity in a few regions. The area was chartered with the Schlumberger configuration up to the AB/2 depth of 150 m. The ABEM Terrameter SAS 4000 (Sweden) and accessories were used to acquire vertical electrical soundings in 24 locations. The results obtained through the 2D and 3D isoresistivity maps of apparent resistivity for 15, 45, and 130 m spacings, the 3D isoresistivity maps of transverse resistance and anisotropy, the VES curve types, and the measured stratigraphic section of surface rocks revealed the confined or semi-confined type aquifers within sedimentary formations. The petrographic analysis indicates the clues of the secondary porosity and fluid migrations through the rocks.     

1D geoelectrical resistivity survey for groundwater studies in coastal area: A case study from Pearl city,Tamil Nadu

Geoelectrical resistivity method involving vertical electrical sounding (VES) was carried out in a sedimentary environment to determine the suitability of the method for sub-surface groundwater investigations. The EC and TDS hydrochemical data in the study area clearly showed the influence of seawater intrusion. The abundance of the major cations and anions are in the following order, Na⁺ > Ca²⁺ > Mg ²⁺ > K⁺ = Cl^- > HCO₃^- > SO₄^2- > CO₃ > NO₃ > PO₄. Results suggest that the groundwater in this study area is very hard and alkaline in nature. As indicated by Piper trilinear diagram, NaCl and Ca²⁺ - Mg²⁺–Cl^- - SO₄^2- facies are the dominant hydrochemical facies in the groundwater of Pearl city. The VES method by Schlamberger electrode array was applied in 12 locations, which is expected to represent the whole area. The resistivity meter (aquameter CRM 5OO) was used to collect the VES data by employing a Schlumberger electrode configuration, with half current electrode spacing (AB/2) ranging from 2 to 180 m and the potential electrode (MN) from 1 to 50 m. The resistivity data is then interpreted by WINSEV 1-D inversion program geoelectric software to entirely describe the aquifer system as well as the occurrence of groundwater. The outputs of sub-surface layers with resistivities and thickness presented in contour maps and 2-D views by using SURFER software were created. Accordingly, three zones with different resistivity values were detected, corresponding to three different formations: (1) a transition zone of sandy soil (aeolian deposits) thick formation, (2) strata’s saturated with fresh groundwater in the east disturbed by the presence of sandy shell limestone horizons, (3) a water-bearing formation in the west containing low saltwater horizons. The bedrock is encountered at an average depth of 95m. This study indicates that the groundwater reservoirs are mainly confined to the alluvial aquifer.     

Vertical electrical sounding to delineate the potential aquifer zones for drinking water in Niamey city,Niger, Africa

Niger is a landlocked African country and the only source of surface water is the Niger River which flows in the western part of Niger and only few villages near to the river gets benefited from it, leaving most of the areas dependent on groundwater solely. The groundwater resources in Niger are mainly used for drinking, livestock and domestic needs. It can be observed that the water exploitation is minimal there due to several factors like undeveloped areas, less population, limited wells, rain-fed irrigation, etc. The delineation of potential aquifer zones is an important aspect for groundwater prospecting. Hence, the direct current (DC) resistivity soundings method also known as vertical electrical sounding (VES) is one of the most applied geophysical techniques for groundwater prospecting that was used in the capital city, Niamey of Niger. Twelve VES surveys, each of AB spacing 400 m were carried out in lateritic and granitic rock formations with a view to study the layer response and to delineate the potential zones. Potential aquifer zones were at shallow depth ranging from 10 to 25 m for the drilled borehole depth of 80–85 m in every village. Analysis of the result showed a good correlation between the acquired data and the lithologs.     

The Influence Of Precambrian Metamorphic Rocks On Groundwater In The Chyulu Area,Kenya

The Chyulu Area is characterized by an extensive contact between the Precambrian metamorphic rocks and the overlying volcanic rocks. The area underlain by metamorphic rocks is characterized by lowlands with an average altitude of between 400–900m above mean sea level (amsl) and the area underlain by volcanic rocks forms the Chyulu Hills with an altitude of between 1200m and 2000m amsl. The area is bounded by latitudes 2°5’ and 3°5’ south and longitudes 37°20’ and 38°35’ east. The geology of the area has been critically examined to evaluate its impact on groundwater. Springs at the contact zone are located at specific points that could have either geological or paleogeographic control. The chemical quality of the groundwater varies with rock type. This indicates that the metamorphic and volcanic rock aquifers are not interconnected. Although the groundwater is important for present and future tourism and agricultural development of the area, its quantity has not been satisfactorily assessed. There is an urgent need to quantify the groundwater resource of the area in order to ensure its optimum development and utilization.     

Identifications of fractured zones in part of hard rock area of Sonebhadra District,U.P., India using integrated surface geophysical method for groundwater exploration

Surface geophysical methods were used to determine the locations of fracture zones in part of the hard rock area in Sonebhadra District of Uttar Pradesh, India. The survey comprises three DC resistivity profile using the gradient profiling technique and ten very low frequency electromagnetic (VLF-EM) traverses profiles. The methods were used over survey lines extending between 200 and 400 m; the results were correlated to locate fracture zones for the purpose of groundwater exploration. Qualitative interpretation of the VLF-EM was carried out using Fraser and Karous–Hjelt filters. The result of the interpretation revealed a number of subsurface zones with high real component current density that defines the potential subsurface features (probably fracture zones). The subsurface feature concurred with the low resistive zones indentified from the gradient resistivity profiling. The zones where further inferred quantitatively using data obtained from DC resistivity sounding at some selected anomalous points. The result obtained proves the efficiency of integrating both methods in detecting fractures zones in hard rock area.     

The use of vertical electrical sounding resistivity method for the location of low salinity groundwater for irrigation in Chaj and Rachna Doabs

A geoelectrical resistivity survey using vertical electrical sounding (VES) was conducted at Chaj Doab (land between rivers Jhelum and Chenab, Pakistan) and Rachna Doab (land between rivers Chenab and Ravi, Pakistan), with the objective of investigating groundwater conditions. A total of 90 sites were selected with 43 sites in Chaj and 47 sites in Rachna Doabs. The resistivity meter (ABEM Terrameter SAS 4000, Sweden) was used to collect the VES data by employing a Schlumberger electrode configuration, with half current electrode spacings (AB/2) ranging from 2 to 180 m and the potential electrode (MN) from 1 to 40 m. The field data were interpreted using the Interpex IX1D computer software and the resistivity versus depth models for each location was estimated. The outputs of subsurface layers with resistivities and thickness presented in contour maps and 3-D views by using SURFER software were created. A total of 102 groundwater samples from nearby hydrowells at different depths were collected to develop a correlation between the aquifer resistivity of VES and the electrical conductivity (EC) of the groundwater and to confirm the resulted geophysical resistivity models. From the correlation developed, it was observed that the groundwater salinity in the aquifer may be considered low and so safe for irrigation if resistivity >45 Ω m, and marginally fit for irrigation having resistivity between 25 and 45 Ω m. The study area has resistivities from 3.9 to 2,222 Ω m at the top of the unsaturated layer, between 1.21 and 171 Ω m, in the shallow aquifers, and 0.14–152 Ω m in the deep aquifers of the study area. The results indicate that the quality of groundwater is better near the rivers and in the shallow layers compared to the deep layers.     

Effects of fracture lineaments and in-situ rock stresses on groundwater flow in hard rocks: a case study from Sunnfjord, western Norway

Systematic field mapping of fracture lineaments observed on aerial photographs shows that almost all of these structures are positively correlated with zones of high macroscopic and mesoscopic fracture frequencies compared with the surroundings. The lineaments are subdivided into zones with different characteristics: (1) a central zone with fault rocks, high fracture frequency and connectivity but commonly with mineral sealed fractures, and (2) a damage zone divided into a proximal zone with a high fracture frequency of lineament parallel, non-mineralized and interconnected fractures, grading into a distal zone with lower fracture frequencies and which is transitional to the surrounding areas with general background fracturing. To examine the possible relations between lineament architecture and in-situ rock stress on groundwater flow, the geological fieldwork was followed up by in-situ stress measurements and test boreholes at selected sites. Geophysical well logging added valuable information about fracture distribution and fracture flow at depths. Based on the studies of in-situ stresses as well as the lineaments and associated fracture systems presented above, two working hypotheses for groundwater flow were formulated: (i) In areas with a general background fracturing and in the distal zone of lineaments, groundwater flow will mainly occur along fractures parallel with the largest in-situ rock stress, unless fractures are critically loaded or reactivated as shear fractures at angles around 30° to σ_H; (ii) In the influence area of lineaments, the largest potential for groundwater abstraction is in the proximal zone, where there is a high fracture frequency and connectivity with negligible fracture fillings. The testing of the two hypotheses does not give a clear and unequivocal answer in support of the two assumptions about groundwater flow in the study area. But most of the observed data are in agreement with the predictions from the models, and can be explained by the action of the present stress field on pre-existing fractures.     

Palynofacies,Organic Thermal Maturation and Source Rock Evaluation of Nanka and Ogwashi Formations in Updip Niger Delta Basin,Southeastern Nigeria

For the deep underground pump house complex engineering geological and geotechnical investigations were carried out. The area was investigated through detailed engineering geological mapping, exploratory drilling, in-situ stress measurements and laboratory testing. Surface mapping was done on 1:500 scales with 0.5 m contour interval and drill holes logging was done on 1:100 scale. The rock mass properties, i.e. joint sets, weathering grade, RQD etc. of the rock masses to be encountered during the excavation of cavities have been analyzed in detail. Core samples from the exploratory drill holes drilled at the surge pool and pump house area were tested for physico-mechanical properties of rocks in the laboratory. To evaluate the stress regime at the proposed underground pump house complex area, stress measurements were carried out by hydrofracturing method inside the borehole. The mapping details indicated that cavities will be excavated through fresh, coarse to very coarse grained, hard and jointed granites. The average depth recorded of fresh rock from the surface was 15.7 m. The uniaxial compressive strength of the rock mass range from 221 to 246 MPa. The orientation of the long axis of the cavities recommended is N150°. Classification of rock mass using Tunnelling Quality Index Q is attempted and the values are range from 3.58 to 16.40.     

Electrical and electromagnetic surveys to locate possible causes of water seepage to ground surface at a quarry open pit near Helwan city,Egypt

Water seepage to ground surface at a limestone quarry located at Wadi Garawy about 20 km south-east of Helwan city in Egypt posed a real threat to the mining activity at the quarry. The quarry area is known to be very dry for decades and away from water utilities and infrastructures that may cause water leaks to the quarry. Geophysical investigation including 1D Vertical Electrical Sounding (VES), 2D Electrical Resistivity Tomography (ERT) and 1D Transient Electromagnetic (TEM) surveys were conducted to characterize the rock sequence and locate what could be a possible source of water seepage to the quarry. The resistivity profiles generated from the VES and TEM surveys mapped the rock units in the area down to depths exceeded 100 m. The ERT profiles acquired from the quarrying zone close to the water seepage spot have imaged the top of groundwater level at few meters below the ground surface at the quarry open pit. The spot of groundwater seepage seemed to occur at an area of limestone dissolution that were filled by finer sediments. The finer sediments acted as a hydrological conduit that allowed an upward seepage of groundwater to ground surface under the capillary action effect.     

Ground water potential in fractured aquifers of Ophiolite formations,Port Blair,South Andaman Islands using Electrical Resistivity Tomography (ERT) and Vertical Electrical Sounding (VES)

Ground water occurs in weathered formations of unsaturated zone and fractured rocks of saturated zone. The ground water occurring in the unsaturated zone is not sustainable while the ground water occurring in the fractured rocks are sustainable if properly exploited. But, targeting the productive fractured rocks needs careful evaluation and systematic approach of geophysical survey owing to the heterogeneity, magmatic and metamorphic activities of multiple episodes of rocks. Hence, judicious planning in ground water exploration is warranted because of the huge money involved in drilling, manpower and time factor. In this context, an attempt has been made to locate the fractured rocks of ground water potential in the Ophiolite formations of Port Blair, South Andaman Islands using Electrical Resistivity Tomography (ERT) and Vertical Electrical Soundings (VES) since the ground water database of Andaman and Nicobar islands is poor as not much work has been carried out so far and the ground water is not properly utilised. The ERT have been carried out along different azimuth of fractures to ascertain the resistivities in vertical and horizontal direction and the conductivity and/or the resistivity of the varied fractures was also evaluated by spot VES. The 2-D Electrical Resistivity Images in conjunction with the geoelectrical parameters brought out by VES revealed that E-W fractures are expected to be productive fractures showing more conductivity as it is compared with the NE-SW and NW-SE fractures. The potentiality of the E-W fractures was also validated with the borehole data.     

基于分布式光纤温度示踪探测裂隙岩体地下水渗流特征

认识深部裂隙岩体中的地下水渗流特征(流速、渗流路径等),是深部地质工程开发建设的重要前提。近年来,分布式光纤测温技术作为识别深部裂隙岩体地下水渗流特征的有效方法,在国外开展了大量的研究,但在国内鲜少见在实际场地开展的相关工作。本研究以我国首个地下实验室场址甘肃北山新场花岗岩岩体中的两个钻孔(BSQ02及BSQ03)为试验对象,开展基于分布式光纤测温(Fiber-Optic Distributed Temperature Sensing, FO-DTS)的现场温度-水力试验,实现了对钻孔地下水温度的高精度、连续性观测。通过分析现场试验获取的钻孔温度-深度剖面随时间的变化,推断BSQ02在试验过程中存在外源地下水的流入,然后结合钻孔柱状图对钻孔中的入流导水裂隙进行了定位;基于现场观测数据建立了钻孔的渗流-传热耦合数值模型,反演估算出钻孔中地下水平均流速为0.01 m·s^-1,通过裂隙流入地下水温度小于钻孔中原地下水温度,两者之间的温度差为0.7℃,通过裂隙流入的地下水流速为1×10^-5 m·s^-1,获取了地下水的渗流特征。该...     

重力场特征与砂岩型铀矿的关系及地质意义

重力场变化特征能够较好地反映地下地质体信息,砂岩型铀矿分布特征与重力场具有一定联系。我国砂岩型铀矿主要分布在我国布格重力异常场中-西北部区,且砂岩型铀矿床大多位于重力场由高向低变化的梯度带上,但靠近重力场高值区。结合砂岩型铀矿成矿机理,分析中-西北部区主要含铀盆地构造演化、地层结构等特征,认为位于中-西北部区的含铀盆地所经历的“次造山运动”及其后期相对稳定的构造环境有利于砂岩型铀矿成矿。斜坡的适度抬升有利于富铀岩体风化剥蚀,含铀含氧流体运移、断裂等因素控制砂岩型铀矿成矿,斜坡处地形改变形成重力场变化梯度带,地下断裂、岩石组分变化使重力等值线产生同形扭曲或错断现象。因此,重力场变化特征对划定砂岩型铀矿勘探靶区具有一定的借鉴作用,并以松辽盆地西南部钱家店铀矿床为例,探讨其成矿条件与重力场变化特征的关系,体现其实际应用性。     

Delineation of shallow resistivity structure around Malvan, Konkan region, Maharashtra by neural network inversion using vertical electrical sounding measurements

Modeling resistivity profiles, especially from hard rock areas, is of specific relevance for groundwater exploration. A method based on Bayesian neural network (BNN) theory using a Hybrid Monte Carlo (HMC) simulation scheme is applied to model and interpret direct current vertical electrical sounding measurements from 28 locations around the Malvan region, in the Sindhudurg district, southwest India. The modeling procedure revolves around optimizing the objective function using the HMC based sampling technique which is followed by updating each trajectory by integrating the Hamiltonian differential equations via a second order leapfrog discretization scheme. The inversion results suggest a high resistivity structure in the north-western part of the area, which correlates well with the presence of laterites. In the south-western part, a very high conductive zone is observed near the coast indicating an extensive influence of saltwater intrusion. Our results also show that the effect of intrusion of saline water diminishes from the south-western part to the north-eastern part of the region. Two dimensional modeling of four resistivity profiles shows that the groundwater flow is partly controlled by existing lineaments, fractures, and major joints. Groundwater occurs at a weathered/semi-weathered layer of laterite/clayey sand and the interface of overburden and crystalline basement. The presence of conduits is identified at a depth between 10 and 15 m along the Dhamapur–Kudal and Parule–Oros profiles, which seems to be potential zone for groundwater exploration. The NW–SE trending major lineaments and its criss-cross sections are indentified from the apparent and true resistivity surface map. The pseudo-section at different depths in the western part of the area, near Parule, shows extensive influence of saltwater intrusion and its impact reaching up to a depth of 50 m from the surface along the coastal area. Further, the deduced true electrical resistivity section against depth correlates well with available borehole lithology in the area. Present analyses suggest that HMC-based BNN method is robust for modeling resistivity data especially in hard rock terrains. These results are useful for interpreting fractures, major joints, and lineaments and crystalline basement rock and also for constraining the higher dimensional models.     

Measuring fracture orientation at exposed rock faces by using a non-reflector total station

Measurements of fracture orientation are usually taken by using a compass-inclinometer device on exposed rock faces. The drawbacks when using this method is that it is time-consuming if many fractures are measured and that measurement might be impossible if the rock face cannot be safely reached physically. To improve field mapping of rock fractures, a method for applying a non-reflector total station to measuring fracture orientation is presented in this paper. A non-reflector total station is a geodetic device that captures three-dimensional co-ordinates of target points without using a reflector. Therefore, physical touching the rock surfaces is no longer required. To determine a fracture orientation, co-ordinates of a set of points on the exposed fracture surface are captured at a distance from the rock face. The best-fit plane of the exposed fracture surface is defined by the co-ordinates of the target points, and the orientation (e.g. dip angle and dip direction) of the fracture surface is determined as that of its best-fit plane. This paper presents the technical procedure and a portable system designed for the field mapping of fracture orientation. Results of a case study performed at an exposed rock face are also included.     

Comparison between 2D imaging and vertical electrical sounding in aquifer delineation: a case study of south and south west of Samawa City (IRAQ)

The vertical electrical sounding (VES) survey was carried out by using Schlumberger array in (12) points distributed along two profiles, except VES 6 was not located within any profile. The 2D imaging survey was carried out using Wenner array in four stations. The VES results revealed the presence of two groundwater aquifers. The first is Euphrates aquifer and the second is Dammam aquifer. While the results of 2D imaging survey distinguished two secondary aquifers in addition to previous aquifers located within Dammam formation. Also, 2D imaging gave a more accurate picture for the distribution of electrical horizons especially for the depths which ranges between 2.5 and 73 m. While the VES gives information for larger depths than that of 2D, which ranges between the earth’s surface and a depth 140 m. The geo-electrical sections of VES showed electrical horizons (layers) with sharp boundaries. But the 2D inverse models revealed the lateral and vertical variations of the resistivity within each horizon especially for shallow depths due to large volume of data available in 2D measurement. These variations were not shown in the geo-electrical sections of VES points. Comparison of VES and 2D imaging techniques revealed that the 2D imaging was the best for determined the shallow aquifers as observed from this study. It can be concluded that 2D resistivity imaging and VES can provide very useful guide for borehole drilling particularly where there is no existing well.