Resistivity Survey Method Research Articles

Time-Lapse Geophysical Measurements for Monitoring Coastal Groundwater Dynamics in an Unconfined Aquifer.

The coastal zone, which is the interface between land and sea, is hydrodynamically very active due to the complex interactions of various hydrological controls and variable-density fluids. These forces vary over time, resulting in a state of dynamic equilibrium in the system. The major hydrological processes in coastal aquifer systems are salt water intrusion and submarine groundwater discharge, which are interdependent. Monitoring these complex processes is crucial for sustainable coastal zone management but poses a significant research challenge. In this study, we demonstrate the effectiveness of non-invasive geophysical techniques, specifically the time-lapse electrical resistivity imaging method, in conjunction with groundwater monitoring, for monitoring coastal groundwater dynamics in an unconfined aquifer at varying time scales and hydrogeological settings present at formerly glaciated sites worldwide. We generated two-dimensional baseline salt water intrusion maps for the test site, located on the coast of Rhode Island, USA. The time-lapse electrical resistivity survey method enables the rapid estimation of fresh groundwater discharge. Our approach offers insight into the mechanisms and seasonably variable salt water-freshwater interactions in unconfined heterogeneous aquifers. Although the results are site-specific, their implications are broad and may stimulate other studies related to sea to land pollution (sea water intrusion) and land to sea pollution (groundwater discharge) in heterogeneous coastal aquifer settings.

Exploration of Ground Water Potential of Federal University of Technology, Owerri and Its Environs Using Resistivity Survey

The research focused on evaluating the groundwater potential in the vicinity of Federal University of Technology Owerri (FUTO) using a resistivity survey method. The investigation involved the utilization of eleven Schlumberger vertical electrical soundings (VES). The data collection was conducted using an ABEM Terrameter SAS4000 and then processed with IPI2Win Software, which relies on the conventional theory of curve matching. This process aimed to determine the depth, quality, and subsurface formations of the groundwater. The VES interpretation results revealed the presence of 3-5 geoelectric layers above the aquiferous layers. Various curve types were identified in the study area, including monotonically ascending (AA), bowed-ascending (HA), bowl-bell (HK), and ascending-bell (AK) curves. The majority of the field curves were found to be of the A-shaped type, signifying specific aquifer characteristics. The study indicated that the depth to the water table is relatively shallow in the Ihiagwa area, with an average depth of 7.26 meters. In contrast, the aquifer's depth is deeper around Avu, Nekede, and Eziobodo areas, with a mean depth of 32.33 meters. Obinze had very deep aquifers, with an average depth of 57.75 meters. Furthermore, the study established a relationship between aquifer characteristics and geoelectric parameters, allowing for the estimation of hydraulic conductivity and transmissivity values at all the sounding locations, even in areas lacking boreholes. These hydraulic characteristics showed that the aquifer had protective capacities ranging from 0.036 to 0.509 mhos, transmissivity values ranging from 11856.32 to 28661.28 m2/day, and hydraulic conductivity ranging from 13.47 to 1009.2 m/day. These values suggested that the aquifer materials are highly permeable, facilitating fluid movement within the aquifer. This research demonstrated the effectiveness of surface geophysics in estimating aquifer hydraulic characteristics, particularly in situations where pumping test data are unavailable. It also highlighted the vulnerability of the aquifer to surface contaminants. The findings are expected to be valuable for the long-term planning of groundwater exploitation projects in the study area.

Case analysis on the characteristics of the landcreep area: focusing on Seo-myeon in Suncheon, South Korea

This study was conducted to prevent landcreep damages by examining various features such as geology, topography, and physical characteristics. The first landcreep occurred in Seo-myeon in Suncheon, South Korea, in 2000. The second occurred in 2020, the damaged surface area of the second event was approximately 21.7 times that of the first, and it was discovered that landcreep in Sunchoen was contributed to forest road construction. The study area was a typical landcreep area caused by weathered rocks, and this area belonged to a type of convex terrain ground form. As a result of analyzing the landslide hazard grade, the landcreep is found to be different from general landslides because it includes most areas of landslide hazard grade 3–5 and out of the grade. Results show that the landcreep has proceeded in the directions of S15°E, S20°E, S25°E, and S30°E, which is consistent with the direction following the flow direction of groundwater determined using the electrical resistivity survey method.

Geophysical Assessment of Freshwater Intrusion into Saline Aquifers Beneath Plain Reservoirs

Reservoir leakage can cause a waste of precious water resources and even severe environmental consequences. In this study, we use continuous resistivity profiling to evaluate the leakage problem of the Shuangwangcheng reservoir along the east route of the South-to-North Water Diversion Project. A numerical example was first built to validate the method's effectiveness in a saline aquifer environment. Thirty-five waterborne survey lines were then conducted with a total length of 74 km, and two ground survey lines had a length of 1.27 km each. We evaluated the quality of the overall data with the apparent resistivity of intersection points. Based on ground survey results, the resistivity value larger than 2 Ω.m at the bottom of the reservoir is regarded as leakage areas. Therefore, we divide resistivity survey results into three zones: freshwater reservoir, leakage zone, and saline aquifer. The distribution of freshwater intrusion is evaluated by fence diagram and interpolated horizontal resistivity contour maps. The delineated leakage zone is consistent with the lack of a low permeable loam layer on the north and east parts of the reservoir. The results prove that the waterborne resistivity survey method can efficiently and effectively assess leakage distribution inside a reservoir.

Groundwater Contaminants Investigation in a Basement Area of Nigeria Using 2D Electrical Surveying Methods

Some of the common methods of monitoring and mapping groundwater contaminants is by extracting and analyzing samples of the groundwater obtained from wells within the expected investigation area, although lots of limitations are encountered in this type of investigation technique (point wise method) due to the nature of most subsurface layers, which are heterogeneous and anisotropic in nature and acquiring information using this method is comparatively difficult due to the few points acquired for investigation. Common and most recent method used to overcome such type of limitation and improve ground monitoring cost-effectively, is the use of Direct Current Resistivity measurements. This method gives a comprehensive characterization of the electrical properties of the subsurface layers (volume) needed. This paper investigates the usability and advantages of the resistivity method as a better method technique in monitoring groundwater contaminants in basement area or terrains under different seasons, in monitoring programmes. The work comprises field investigations at several sanitary landfills around the basement area of Ado-Odo town, in Ogun State, Nigeria, using Wenner array configuration (tomography) technique. From the results obtained, the level/degree of contaminants are easily identified and evaluated within the subsurface layers. We therefore concluded that the use of resistivity survey method gives an improved, better and appropriate information, generally suitable for mapping and monitoring of conductive groundwater contaminants in basement area.

Analysis on Variability of Mechanical Parameters in the Process of Rock Damage

How the mechanical parameters of rock change with the development of joints and fractures is still a puzzle. It is hard to measure rock joints accurately at present. Resistivity is an important parameter of rock and its value can reflect the degree of fragmentation of rock. A new method combining measurement method of Young’s modulus with resistivity survey method is proposed in this paper. To determine the variation of mechanical parameters in the process of rock damage, the uniaxial, tri-axial compression tests and resistivity survey on rock specimens are done. The results showed that the values of resistivity were continuously increasing, but Young’s modulus and mechanical parameters were decreasing in the process of rock damage. The relationships between resistivity and mechanical parameters are established based on the experiments in the process of rock damage. Therefore, the damage state of rock and the change of mechanical parameters of rock can be determined according to the variance of resistivity. The study is helpful for design and real- time stability evaluation on rock engineering.

Use of the azimuthal resistivity technique for determination of regional azimuth of transmissivity

Many bedrock units contain joint sets that commonly act as preferred paths for the movement of water, electrical charge, and possible contaminants associated with production or transit of crude oil or refined products. To facilitate the development of remediation programs, a need exists to reliably determine regional-scale properties of these joint sets: azimuth of transmissivity ellipse, dominant set, and trend(s). The surface azimuthal electrical resistivity survey method used for local in situ studies can be a noninvasive, reliable, efficient, and relatively cost-effective method for regional studies. The azimuthal resistivity survey method combines the use of standard resistivity equipment with a Wenner array rotated about a fixed center point, at selected degree intervals, which yields an apparent resistivity ellipse from which joint-set orientation can be determined. Regional application of the azimuthal survey method was tested at 17 sites in an approximately 500 km2 (193 mi2) area around Milwaukee, Wisconsin, with less than 15 m (50 ft) overburden above the dolomite. Results of 26 azimuthal surveys were compared and determined to be consistent with the results of two other methods: direct observation of joint-set orientation and transmissivity ellipses from multiple-well-aquifer tests. The average of joint-set trend determined by azimuthal surveys is within 2.5 of the average of joint-set trend determined by direct observation of major joint sets at 24 sites. The average of maximum of transmissivity trend determined by azimuthal surveys is within 5.7 of the average of maximum of transmissivity trend determined for 14 multiple-well-aquifer tests.

Application of the surface azimuthal electrical resistivity survey method to determine patterns of regional joint orientation in glacial tills

Joints within unconsolidated material such as glacial till can be primary avenues for the flow of electrical charge, water, and contaminants. To facilitate the siting and design of remediation programs, a need exists to map anisotropic distribution of such pathways within glacial tills by determining the azimuth of the dominant joint set. The azimuthal survey method uses standard resistivity equipment with a Wenner array rotated about a fixed center point at selected degree intervals that yields an apparent resistivity ellipse. From this ellipse, joint set orientation can be determined. Azimuthal surveys were conducted at 21 sites in a 500-km2 (193 mi2) area around Milwaukee, Wisconsin, and more specifically, at sites having more than 30 m (98 ft) of glacial till (to minimize the influence of underlying bedrock joints). The 26 azimuthal surveys revealed a systematic pattern to the trend of the dominant joint set within the tills, which is approximately parallel to ice flow direction during till deposition. The average orientation of the joint set parallel with the ice flow direction is N77E and N37E for the Oak Creek and Ozaukee tills, respectively. The mean difference between average direct observation of joint set orientations and average azimuthal resistivity results is 8, which is one fifth of the difference of ice flow direction between the Ozaukee and Oak Creek tills. The results of this study suggest that the surface azimuthal electrical resistivity survey method used for local in situ studies can be a useful noninvasive method for delineating joint sets within shallow geologic material for regional studies.

Delineation of a Fault Zone Beneath a Riverbed By an Electrical Resistivity Survey Using a Floating Streamer Cable

Recently, the imaging of geological structures beneath watercovered areas has been in great demand because of numerous tunnel and bridge construction projects on river or lake sites. An electrical resistivity survey can be effective in such a situation because it provides a subsurface image of faults or weak zones beneath the water layer. Even though conventional resistivity surveys in water-covered areas, in which electrodes are installed on the water bottom, do give high-resolution subsurface images, much time and effort is required to install electrodes. Therefore, an easier and more convenient method is sought to find the strike direction of the main zones of weakness, especially for reconnaissance surveys.In this paper, we investigate the applicability of the streamer resistivity survey method, which uses electrodes in a streamer cable towed by ship or boat, for delineating a fault zone. We do this through numerical experiments with models of water-covered areas. We demonstrate that the fault zone can be imaged, not only by installing electrodes on the water bottom, but also by using floating electrodes, when the depth of water is less than twice the electrode spacing. In addition, we compare the signal-to-noise ratio and resolving power of four kinds of electrode arrays that can be adapted to the streamer resistivity method.Following this numerical study, we carried out both conventional and streamer resistivity surveys for the planned tunnel construction site located at the Han River in Seoul, Korea. To obtain highresolution resistivity images we used the conventional method, and installed electrodes on the water bottom along the planned route of the tunnel beneath the river. Applying a two-dimensional inversion scheme to the measured data, we found three distinctive low-resistivity anomalies, which we interpreted as associated with fault zones. To determine the strike direction of these three fault zones, we used the quick and convenient streamer resistivity survey on additional grid-style survey lines. In this way, we could delineate the strike direction of faults beneath the riverbed very efficiently.

Detection of crustal inhomogeneity in the Nojima Fault zone using earth current noise

Abstract A resistivity survey method using artificial telluric noise was examined and applied to a field of a fault zone. The electric earth current was measured at 50 sites in the Nojima Fault zone, which is in the northwestern part of Awaji Island, southwestern Japan. The dominant component of the observed electric field is supposed to be leakage currents from DC electric railways running outside the island. Amplitude and polarization of the stray current were systematically investigated and were revealed to represent the subsurface electrical structure of the study area. Some features on the fault zone’s electrical structure have been pointed out, including: (i) an electrical boundary that corresponds to a geological one between granite (resistive) and sediments (conductive); and (ii) a low resistivity spot on the surface rupture of the earthquake fault. The structure estimated in the present study is both qualitatively and quantitatively consistent with previous resistivity surveys done using other methods pursued in the same area. It shows the validity of the ‘stray current method’ as one that is easy and uses low‐cost resistivity exploration tools in a region where the effect of artificial noise caused mainly by leakage currents from electrical railways cannot be ignored.

Use of the EM-34 instrument in groundwater exploration in the Shepparton region

Since the late 1970's, the Rural Water Commission of Victoria (RWC) has been offering a groundwater exploratory drilling service to landholders in the irrigation areas of the Shepparton Region. The aim of this service has been to encourage exploration for shallow aquifers in the Shepparton Formation and in turn to encourage groundwater pumping for water-table control. The selection of drilling sites in early exploration programs was based on geomorphological expressions of prior stream activity. Later, the dipole-dipole resistivity survey method was used. While giving good resolution of targets in the sedimentary profile, this method was found to be too restrictive in covering large areas of a property. In 1986, the RWC acquired a Geonics EM-34 unit to become the main geophysical tool in groundwater exploration. Since this time, the unit has been used on over 60 individual properties, as well as being used for broader scale exploration surveys on the Riverine Plains. The EM-34 unit has proved to be a useful tool in defining areas where shallow sand aquifers occur in the Upper Shepparton Formation. The RWC uses the horizontal dipole technique with a constant coil separation of 20 m. This technique has allowed good line coverage of up to 7500 m in a day, while allowing fair resolution of the target within the top 15-20 m of the Shepparton Formation. Experience has shown that a number of non-rigorous categories can be applied to the various ranges of conductivity readings. Such categories aid in the interpretation and selection of drilling targets.

地温測定による旧河道調査の有効性について

Electrical Resistivity survey has been carried out hitherto in order to find out places being easy to flow ground water in an old-river channel. According to the interpretation of the results, all of high resistivity zones have had to be regarded as places being easy to flow ground water. Therefore we had to consider very wide zone as flowing ground water with unsatisfactory. Accordingly, the survey method was not so desirable in the case of considering a concrete counterplan for conservation of banks. It was necessary to improve such a condition.We adopted a new method “Investigation Method by Measuring Underground Temperature” in order to detect places being easy to flow ground water in a old-river channel which had possibility to have bad influence on banks. It was shown the some abnormal temperature parts existed in the high resistivity zone by the results of the new method. In this fact, it is elucidated that places being easy to flow ground water is detected more accurately by carrying out the underground temperature survey than by carrying out the electrical resistivity survey.Some bore holes were dug in each parts of an abnormal temperature part and a normal temperature part in a same high resistivity zone with the object of inspecting this point, and a few test which were concerned with ground-water (observation of ground-water level, temperature logging, different temperature logging, and pumping test) were carried out by using these bore holes. By the results of these test, we could recognized clearly flowing ground water in an abnormal temperature part, but could not recognized flowing ground water in a normal temperature part in the same high resistivity zone.As mentioned above, we estimated that the investigation method by measuring underground temperature was better than the electrical resistivity survey method in order to detect places being easy to flow ground water in old-river channels.