2D Electrical Resistivity Tomography Research Articles

Combined 2D- and 3D ERT monitoring as a geophysical tool for investigating spatial and temporal soil moisture fluctuations in a pine-beech forest

As climate change continues, forests are increasingly suffering from drought stress, which is leading to widespread forest dieback, but also to increased mortality of individual trees. In this regard, the impact of small-scale differences in water availability on individual trees has not yet been sufficiently studied to determine possible responses of different tree species to future droughts. Since conventional soil moisture monitoring and sampling methods only consider single points or small volumes, Electrical Resistivity Tomography (ERT) is becoming increasingly important to cover a larger survey area and to detect small-scale heterogeneities with regard to soil properties and soil moisture.The current study describes the application of a combined two- and three-dimensional geoelectrical monitoring approach with daily measurements over two years (May 2021 – April 2023) in a forest ecosystem in Lower Franconia (northwestern Bavaria, Germany), which is strongly affected by climate change. Soil water content, soil matric potential, throughfall, and stem flow are also measured at the forest site as well as precipitation at an adjacent forest clearing.The seasonally (long-term) and precipitation-driven (short-term) temporal change of soil resistivity is correlated strongly with the measured soil water content and matric potential. The applied 3D-ERT approach also allowed a first three-dimensional monitoring of the subsurface below a European beech located in the middle of the measuring grid with a daily resolution. The corresponding results also provide first indications that besides soil moisture changes also chemical processes in the subsurface may influence temporal resistivity changes in the soil of forest sites.The results of this study show that daily 3D-ERT is very suitable for investigating small-scale as well as short- and long-term variations in soil moisture, which is becoming increasingly important for understanding the causal relationships considering tree mortality and the subsurface.

Monitoring of Älvkarleby test embankment dam using 3D electrical resistivity tomography for detection of internal defects

AbstractElectrical resistivity tomography (ERT) is a potential-based method for detecting internal erosion in the core of embankment dams using the electrodes installed outside. This study aims at evaluating the practical capability of ERT monitoring for detecting internal defects in embankment dams. A test embankment dam with in-built well-defined defects was built in Älvkarleby, Sweden, to assess different monitoring systems including ERT and the defect locations were unknown to the monitoring teams. Between 7500 and 14,000 ERT data points were acquired daily, which were used to create the distribution of electrical resistivity models of the dam using 3D time-lapse inversion. The inversion models revealed a layered resistivity structure in the core that might be related to variations in water content or unintentional variations in material properties. Several anomalous zones that were not associated with the defects were detected, which might be caused by unintentional variations in material properties, temperature, water content, or other installations. The results located two out of five defects in the core, horizontal and vertical crushed rock zones, with a slight location shift for the horizontal zone. The concrete block defect in the core was indicated, although not as distinctly and with a lateral shift. The two remaining defects in the core, a crushed rock zone at the abutment and a wooden block and a crushed rock zone in the filter, were not discovered. The results cannot be used to fully evaluate the capability of ERT in detecting internal erosion under typical Swedish conditions due to limited seepage associated with the defects. Furthermore, scale effects need to be considered for larger dams.

CBR Mapping Prediction from 2D Resistivity Imaging Using Regression Following Archie’s Formula

Indirect geophysical methods are increasingly associated with direct underground methods in investigating the subsurface to address environmental and geotechnical problems and reduce the cost of underground studies. These methods make it possible to explore large areas with acceptable precision, time, and cost. The present study combines the electrical resistivity method with the California Bearing Ratio for exploring an area located west of the Nouakchott port in Mauritania. The study aims firstly to verify that the thickness of the backfill layer must be less than 2 m throughout the entire study area and secondly to map areas with low California Bearing Ratio values (<80%) indicating substandard backfill compaction using 2D Electrical Resistivity Tomography imaging survey and regression. The measured Electrical Resistivity values exhibit a good nonlinear regression with California Bearing Ratio, following Archie's equation. A map of California Bearing Ratio variation was derived from the Electrical Resistivity values, indicating the distribution and variation of soil strength in the study area. The results revealed that the backfill layer did not meet the standards, with approximately 35% of the total area having a California Bearing Ratio value below 80%. The areas with poor compaction requiring treatment were primarily located in the southern sector, followed by the middle and eastern sectors.

Improved ERT imaging with 3-D surface-to-horizontal borehole configurations: relevance to dense non-aqueous phase liquids

SUMMARY Accurate characterization and monitoring strategies are essential for designing and implementing remedial programs for sites polluted with dense non-aqueous phase liquids (DNAPLs). Electrical resistivity tomography (ERT) is a widely used geophysical technique for mapping subsurface features and processes of interest, and exhibits desirable characteristics for DNAPL sites due to its ability to gather large volumes of continuous subsurface information in a non-invasive, cost-effective and time-efficient manner. However, ERT measured only from the surface suffers from poor imaging quality with depth. Enhanced ERT imaging can be obtained via electrodes deployed on the surface and within horizontal boreholes, but so far it has only been investigated for 2-D imaging. This study evaluates the potential of 3-D surface-to-horizontal borehole (S2HB) ERT configurations for imaging 3-D DNAPL source zones. Laboratory tank experiments were first conducted with a 3-D S2HB ERT configuration, which consisted of a surface grid and a single borehole line of electrodes, being used to monitor DNAPL migration within porous media. Results demonstrate that 3-D S2HB ERT with a single borehole provides improved sensitivity at depth, and therefore enhanced imaging compared to conventional 3-D surface ERT. Further tank experiments were performed to assess the performance of single borehole S2HB ERT when (i) the distance between surface and borehole is increased, and (ii) additional horizontal boreholes are included. The S2HB ERT with a single borehole significantly outperforms surface ERT at larger depths, and performs comparably to S2HB ERT using multiple boreholes. This study suggests that 3-D S2HB ERT with a single borehole can provide the enhanced imaging ability needed to map DNAPLs, while also being relatively practical for implementation at field sites.

3D electrical resistivity survey for reduction of groundwater drilling uncertainties in a clay-rich environment

Drilling for groundwater is expensive and challenging. It is even more challenging to find a location that will result in a high-yield well in heterogeneous environments. To tackle the heterogeneity issue, geophysical surveys can help in mapping the subsurface structure and delineating the drilling trajectory. The current study displays the effectiveness of 3D electrical resistivity tomography (ERT) to locate a permeable groundwater zone within a highly heterogeneous and clayey subsurface. Ground truthing the acquired geophysical data with in-situ sampling helps ensure accuracy in classifying groundwater zones in the final inverted 3D data set while also delineating boundaries between permeable groundwater zones and less permeable clayey structures. In-situ samples of groundwater and soil were used to measure the saturated region's resistivity in the laboratory using a column setup. Clay zones in the data set are classified from the nearby well data at similar depth ranges and from very low resistivity values from ERT data and laboratory measurements. The results display highly differentiating resistivity zones that are attributed to the scattered clay lenses (low resistivity) in conjunction with the freshwater zone (high resistivity). The distinction between clayey and nonclayey bodies is important to better inform drilling locations for optimal groundwater yield. This study concludes that with the aid of low-cost geophysical surveys and minimal in-situ sampling data correlations, permeable groundwater boundaries and clay lens volumes can be identified easily.

Delineation of the proper locations for wastewater disposal in arid regions using TEM and ERT techniques: A case study at Rubiki industrial zone, Badr City, Egypt

Proper wastewater disposal is crucial for the sustainable development of rapidly growing megacities worldwide. The emergence of waterlogging near evaporation ponds (EVP) and in desert areas surrounding these cities poses a significant environmental threat. This study employs an integrated approach, combining transient electromagnetic (TEM) and 2D-electrical resistivity tomography (2D-ERT) methods with remote sensing techniques, to understand wastewater flow patterns around EVPs and identify suitable disposal sites. The research focuses on a complex subsurface structure in the Cairo-Suez district, characterized by extensive surface waterlogging. Initial monitoring relies on satellite imagery and land use-land cover maps. TEM provides an overview of subsurface layer distribution, while 2D-ERT offers detailed insights into near-surface flow paths. To address the limitations of geoelectrical methods in locating conductive layers, advanced inversion techniques (AIS) are applied. The findings reveal a four-layer subsurface composition, with waterlogging primarily attributed to the argillaceous limestone layer interbedded with shale. This layer is shallower in the eastern and northwest areas, correlating with higher instances of waterlogging. Moving northward, the argillaceous limestone layer deepens, and the upper clastic layer thickens, resulting in reduced waterlogging. The study underscores the influence of subsurface structure on near-surface layer distribution. Based on these findings, optimal wastewater disposal sites are recommended, with a focus on the northern region where the argillaceous limestone layer is deeper and the upper clastic layer is thicker. To mitigate waterlogging, the installation of disposal wells is highly advised, leveraging the insights derived from this research. This study offers a versatile and reproducible approach suitable for both pre-project planning and post-project phases in desert regions.

Estimation of Geotechnical Parameters for Coal Exploration from Quasi-3D Electrical Resistivity Measurements

Geotechnical parameters are crucial for mine planning and operation at different stages of development. However, estimating these parameters requires a large number of boreholes and subsequent detailed analysis of the samples, making it a cumbersome exercise. Moreover, even after conducting these studies, it is not possible to cover the entire operational area. To address this issue, this study presents an indirect method of estimating geotechnical parameters through mathematical relations using resistivity data. The present study incorporated 2D and 3D subsurface imaging techniques for exploring coal reserves and analyzing geotechnical parameters that define subsurface soil properties. Electrical resistivity tomography (ERT) was utilized for data acquisition, employing a Dipole–dipole array with a multielectrode ABEM Terrameter LS instrument. Six parallel profiles were conducted, each 400 m in length, with an inter-electrode spacing of 10 m and a spacing of 50 m between profiles. These profiles were combined into a 3D dataset referred to as quasi-3D ERT. The inversion process for both 2D and 3D data was performed using the Res2dinv and Res3dinv programs, respectively. This study overcame the challenges of 2D resistivity sections by evaluating horizontal depth slices in the x-z plane from layers 1 to 10, reaching a depth of 81.2 m. The geotechnical parameters, including cohesion, friction angle, moisture content, and plastic index, were derived from the resistivity data. The ERT method proved to be cost-effective and efficient in determining soil properties over a large area compared with traditional laboratory analysis of borehole samples. Additionally, the variation of geotechnical parameters with resistivity values exhibited unique characteristics. The results from both the 2D and quasi-3D ERT were well correlated with the borehole data. Such studies are valuable for resource exploration and mine planning purposes.

Electrical Resistivity Tomography Investigation of Permafrost Conditions in a Thermokarst Site in Fairbanks, Alaska

<abstract> <p>The degradation of permafrost poses severe environmental threats to communities in cold regions. As near-surface permafrost warms, extensive topographic variability is prevalent in the Arctic and Sub-Arctic communities. Geologic hazards such as thermokarst are formed due to varying rates of permafrost degradation, resulting in ground subsidence. This gradual subsidence or abrupt collapse of the earth causes a danger to existing infrastructure and the economic activities of communities in cold regions. Understanding the causes of thermokarst development and its dynamics requires imaging its underground morpho-structures and characterizing the surface and subsurface controls. In this study, we conducted a two-dimensional (2D) electrical resistivity tomography (ERT) survey to characterize the permafrost conditions in a thermokarst prone site located in Fairbanks, Alaska. To increase the reliability in the interpretability of the ERT data, borehole data and the depth-of-investigation (DOI) methods were applied. By using the 2D and three-dimensional (3D) ERT methods, we gained valuable information on the spatial variability of transient processes, such as the movement of freezing and thawing fronts. Resistivity imaging across the site exhibited distinct variations in permafrost conditions, with both low and high resistive anomalies observed along the transects. These anomalies, representing taliks and ice wedges, were characterized by resistivity values ranging from 50 Ωm and above 700 Ωm, respectively. The results from this study showed the effectiveness of ERT to characterize permafrost conditions and thermokarst subsurface morpho-structures. The insights gained from this research contribute to a better understanding of the causes and dynamics of thermokarst, which can be instrumental for engineers in developing feasible remedial measures.</p> </abstract>

An Integrated Microgravity and Soil Analysis Methods to Assist the Resistivity Profiles Interpretation in an Engineering Site Southern Baghdad, Iraq

A 2D Electrical Resistivity Imaging survey was conducted at the Al-Jadiriya Campus of Baghdad University. The 2D resistivity survey was achieved on two profiles using the Wenner- Schlumberger configuration. The length of each profile is 80 meters, and the spacing between adjacent electrodes is 1 mr. The obtained resistivity data were interpreted using the RES2DINV program. Both profiles show high resistivity anomaly at depths more than 6 meters, extending from a distance of 32-44 m and 37-44 mrs for profiles 1 and 2, respectively. In addition to the deep anomalies, there are many shallow high-resistivity anomalies. A microgravity survey was carried out for a distance of 20- 60 m along the two profiles to check the nature of the deep high resistivity anomaly. The gravity profiles showed many positive gravity anomalies reflected the effect of shallow sources, which coincide with the shallow relatively high resistivity anomalies. Many soil samples were analyzed chemically and sedimentologically to investigate soil homogeneity. It is found that the soil is homogenous, composed mainly of silt and clay. According to the integrated interpretation of resistivity, gravity, and soil analyses, it is found that the high resistivity anomaly is related to dry compacted soil mass, which is indicated in the gravity study. This study confirms the importance of integrated research to access better geophysical interpretation. The water table level in the study sites ranges 5.6–6.2 ms.

Determination Water Level by Electrical Resistivity and Comparing Results with Drilled Well in Al-Naharwan, Baghdad

The 2D electrical resistivity imaging survey was done in Al-Naharawan area within Baghdad city for unknown subsurface to give a best location for digging a new well. Electrical resistivity imaging survey is implemented for along four lines that are 120 m long and all have 1m electrode separation. Measurements done with wenner-Schlumberger array and interpreted data by using RES2DINV program. The results for drilling the well at electrodes 62 and 63 in line 1 showed exactly corresponds to the lithological order of the well Fadhel Abass. Electrical resistivity imaging results showed high and low resistivity values, although they both contain clay, which corresponds to variances in water content. One Groundwater sample was taken from the new well and analyzed chemically to determine the concentration of the major ions. water analysis shows high TDS, electrical conductivity, and most parameters affecting human life out of permissible limits, so it is not suitable for human drinking. SAR =21.695, RSC=-474, which indicates the risk from sodium is improbable and lies within permissible ranges. PI% within Class II, meaning the water quality is good for irrigation. The findings indicated that the 2D imaging method is an effective and powerful enough tool for identifying new well with water table and detecting subsurface.

Characterization of seepage in an earthfill dam by the integration of geophysical surveys and geotechnical data

Seepage is a common phenomenon in earthfill dams, and one that typically warrants episodic assessment and monitoring by regulatory agencies. Geophysical surveys provide a convenient, cost-effective, and convenient means for assessing seepage, but only if they are applied in effective combinations and if the data are analyzed properly. In the present study, a self-potential survey of streaming potential and a 2D electrical resistivity tomography survey were notably successful in detecting seepage under the embankment of the nearly 90-year-old Standing Rock Dam No. 1 in South Dakota, USA. Self-potential (SP) measurements show a localized negative anomaly of up to 27 mV on the upstream side of the dam, which we interpret to be the inlet or recharge zone for seepage, and a positive anomaly of up to 20 mV on the downstream side, which we interpret to be the outlet or discharge zone. The spatial correlation between our resistivity models, SP data, and topography was excellent. Water-saturated, conductive deposits in the dam's embankment match a negative SP amplitude in the inlet or recharge area. Similarly, water-saturated electrically conductive sediments are characterized by a positive SP amplitude in the discharge area where surface seepage occurs in a topographic low. Six years of water-level measurements in the existing piezometers interpreted relative to the properties and spatial distribution of coarser-grained alluvium (sand and gravel) underneath the dam's embankment fill, suggest that most seepage occurs under the dam. Our approach to assessing seepage in this project should be widely applicable to earthfill dams worldwide, and our modeled results constitute a valuable case study.

Geophysics for underground engineering

The growth of underground engineering brought a need for the use of geophysical methods for research of underground constructions rather different in approach compared to that of civil engineering. These changes relate to surface measurement on the one hand and the development of new specialised methods used for underground work on the other. The results of a complete documentation of mining work, the application of the resistivity methods used underground and also the use of 3D electrical resistivity tomography, are all presented here.

The Geophysical Investigation of Leachate Formation in Mgbuka Obosi, Idemili North Local Government Area of Anambra State, Nigeria

The contamination of leachates (a polluted liquid made up of various toxic substances) from landfills is a significant environmental concern, especially in developing countries.This contaminated fluid is formed when rainwater interacts with refuse and travels through the pore spaces in soil. Constant migration of this fluid poses a significant threat to the quality of both surface and groundwater in and close to the landfill area. To determine the extent of leachate formation, the study used both Very Low-Frequency Electromagnetic (VLF-EM) and Electric Resistivity Tomography (ERT) to locate and define the spatial distribution of the leachate plume migration pathway at Mkpuka Obosi Dumpsite in Idemili North LGA of Anambra, Nigeria. Seven profiles were surveyed for both the VLF-EM and ERT. The VLF-EM survey, with a profile length of 100 to 200m and a 10m interstation spacing, revealed the presence of a conductive pollutant (leachate plume) in the subsurface. The results from the 2D ERT survey that employed a Wenner array with a profile length of 100 to 200m and an electrode spacing of 5m, divided the subsurface into six zones with an unusually low resistivity ranging from 0-250\(\Omega\)m. The leachate plumes were interpreted as the zone with the lowest resistivity of 0 to 25\(\Omega\)m, having an average thickness of approximately 10m and extending beyond the probed depth of 50m. Additionally, the percentage of leachate was found to be concentrated primarily at the center of the landfill and gradually decreasing proportionally from the center. Thus, emphasizing the importance of addressing the issues in landfill management.

Study on Resistivity Imaging of Urban Landfill Leachate Channel Using 3D Electrical Resistivity Tomography with Annular Electrode Configuration

Urban garbage landfills are distributed mostly in a nearly circular shape with complex internal and external environments. The conditions on the top of the landfills are not conducive to the layout of electrical measuring lines and electrodes, resulting in difficulties in using the conventional linear or rectangular mesh high density electrical surveying system to achieve good results for the detection of leachate channel under the garbage body. This paper proposed 3D electrical resistivity tomography (ERT) method by annular electrode configuration with electrodes placed around the landfill. Through numerical simulation and indoor physical simulation experiments, we have discussed the feasibility and effectiveness of this method for circling the pollution range and channel location of landfill leachate. The study shows that the 3D ERT method with annular electrode configuration can effectively detect the spatial location and extension of garbage leachate channel, reflect the leakage of garbage leachate in landfills, and thus provide technical support for the fine detection of garbage leachate channel.

Application of electrical resistivity tomography and geotechnical techniques for identification and characterization of collapsible soils in Bafoussam (Western, Cameroon)

Road failure catastrophes have increased in frequency in the West Cameroon area. The collapsed soil characteristics that contribute to these phenomena in Bafoussam have been investigated using the geophysical investigation combined with geotechnical tests. The result of electrical resistivity tomography shows water conditions and heterogeneity of road foundation materials: resistivity values higher than 200 Ωm indicate dry materials, values between 30 and 200 Ωm define wet materials, and values lower than 30 Ωm indicate the very wet or water-saturated materials. These water-saturated materials can therefore move, bounded by a sliding surface of high-resistivity materials. Geotechnical properties analysis shows that these materials are clayey-sensitive water (64% clay fraction; A-7-6), very plastic (liquid limit: 46–63% plasticity limit: 29–39%), compressible, with high porosity (e > 0.8), low shear strength, and high friction angle (24–37°). The quality of foundation materials associated with high slopes (> 40°) and heavy rainfall in wet seasons (July–October) means that seepage water is the main factor responsible for the mass movement observed on the road of Western Cameroon. The construction or rehabilitation of these roads should be carried out in compliance with the natural conditions of the project site.Article highlights- 2D Electrical Resistivity Tomography method is able to determine the nature, subsurface structure and water conditions of road foundation soils.- Geotechnical test can be used to define the physical and mechanical properties of road foundation soils.- These two techniques complement each other to understand the mass movement observed on two sections of road failures caused by seepage water.

ERT investigation of mud volcanoes: detection of mud fluid migration pathways from 2D and 3D synthetic modelling

Mud volcanoes are geological structures observed throughout the world that arise from the upwelling of deep fluids along discontinuities in the subsoil. The detection of mud fluid migration pathways can be challenging, even when using Electrical Resistivity Tomography (ERT) as detectability issues may arise from complex geological settings. This paper presents new results from 2D and 3D ERT synthetic modelling for the investigation of the shallow, internal structure of terrestrial mud volcanoes. This study revealed the internal structure of the ‘Cenerone-Pineto’ mud volcano (Central Italy) and provided further clues as to its internal structure. The main results of the study are: the presence of a mud chamber, which represents the last phase of mud accumulation before final emission, not located beneath the crater but laterally offset, as well as the presence of a narrow, shallow feeder channel; these findings represent evidence of a much more complex structure than one would expect. This means that the mud volcano is not supplied with mud fluids directly from below as would be the case with an uprising of deep fluid along a near-vertical open fracture and that the shallow mud fluid reservoir is not correlated to the distribution of any mud volcano observed on the surface. Findings from this study are consistent with the observed structural features already noted in ERT and seismic field data collected at the ‘Cenerone-Pineto’ mud volcano and may be helpful in explaining the mechanisms and processes involved in mud volcanism in similar geological settings.

New Insights from Geophysical, Hydrogeological and Borehole Data into the Deep Structure of the Louta Phosphatic Deposit (Gantour Basin, Morocco): Mining Implications

The Gantour Phosphatic Basin (GPB) is formed by a sedimentary series of Maastrichtian to the Eocene age, which consists of alternating phosphate layers and sterile levels. This series outcrops in the northern part of the basin, where it is exploited in open-pit mines. The exploration methodology employed by the Office Chérifien des Phosphates (OCP) group to investigate the GPB is based on direct recognition with boreholes drilled on a 500 × 500 m grid. This research is concerned with the compilation and analysis of data collected during several drilling campaigns conducted on the central segment of the GPB, namely the Louta deposit. This research also includes acquiring, processing, and interpreting new geophysical and hydrogeological data. Its main objective is to provide a better understanding of the deep structure of the phosphatic series. Therefore, the present study was carried out according to a multidisciplinary approach that comprises three parts. (i) The first one involves geological modeling of the exploration borehole data using Datamine Studio RM software (version 1.4), developed by Datamine Corporate Ltd., (Bristol, United Kingdom). It results in establishing a series of geological cross-sections that display a detailed view of the deep structure of the phosphatic series and its lateral variations. (ii) The second part is related to the hydrogeological study, whose purpose was to elaborate on an accurate and updated piezometric map of the study area. The new map helps understand the groundwater flow in the Louta deposit. Furthermore, the superimposition of the piezometric level with the geological sections throws light on the flooded volume of phosphate in this deposit. (iii) The third part of the study focuses on implementing the Electrical Resistivity Tomography (ERT) method. The interpretation of the recorded geoelectrical data not only highlights the main features controlling the mode and the proportion of the phosphate series deepening under the Plio-Quaternary cover but also confirms the evolution of the overall structure of the studied area. The obtained 2D ERT models generally corroborate the cross-sections produced by geological modeling. They also correlate with the information provided by the hydrogeological study. Such information will help guide future hydrogeological and mining extraction planning in the studied area.

3D Resistivity Imaging Investigation for Engineering Construction Project Studies at Al-Muthana Airport in Baghdad, Iraq

     Engineering project assessment at Al-Muthana Airport in Baghdad, Iraq, has been studied using a 3D electrical resistivity imaging survey. The site investigation is crucial for assessing the future of the region's infrastructures since it reveals the location of buried facilities or weak zones below the surface and measures localized groundwater levels. Wenner-Schlumberger array was used to conduct four parallel 2D electrical resistivity spreads (MU1 to MU4). Each spread line was 100 m in length with 1 m electrode spacing and an average spacing of 9 meters between any two adjacent lines. The depth of the investigation was around 23.8 m. Survey lines were drawn going from northwest to southeast. These spreads were combined to provide a 3D image of a 2700 m2 space.The robust inversion method and the inverse model generated using the standard least-squares method showed horizontal slices identified three zones with resistivity distribution ranging from 2 to 45.5 ohm.m. The first zone, from surface to 3.37 m, had relatively high resistivity of sandy silty clay soil with relatively low moisture content; the second zone, approximately from 3.37 to 12.2 m, had very low resistivity representing groundwater table; and the third zone, from 12.2 to 23.8 m representing high stiffness and density and relatively high resistivity due to gravel presence in the deposits. The second zone highlights potential risk zones for construction projects; as a result, it is advised that the zone surrounding the foundation be filled with a low permeability layer and that the towers be built on deep foundations.

Evaluating topsoil salinity via geophysical methods in rice production systems in the Vietnam Mekong Delta

AbstractThe Vietnam Mekong Delta (VMD) is threatened by increasing saltwater intrusion due to diminishing freshwater availability, land subsidence, and climate change induced sea level rise. Through irrigation, saltwater can accumulate in the rice fields and decrease rice production. The study aims at evaluating topsoil salinity and examining a potential link between topsoil salinity and rice production systems in a case study in the Tra Vinh province of the VMD. For this, we applied two geophysical methods, namely, 3D electrical resistivity tomography (ARES II) and electromagnetic induction (EM38‐MK2). 3D ARES II measurements with different electrode spacings were compared with EM38‐MK2 topsoil measurements to evaluate their respective potential for monitoring topsoil salinity on an agricultural scale and the relationship between land‐use types and topsoil salinity. Results show that EM38‐MK2 is a rapid and powerful tool for obtaining high‐resolution topsoil salinity maps for rice fields. With ARES II data, 3D maps up to 40 m depth can be created, but compared with EM38‐MK2 topsoil maps, topsoil salinity was underestimated due to limitations in resolution. Salt contamination of above 300 mS m−1 was found in some double‐cropped rice fields, whereas in triple‐cropped rice fields salinity was below 200 mS m−1. Results clearly show a relation between topsoil salinity and proximity to the saline water sources; however, a clear link between rice production and topsoil salinity could not be established. The study proved that geophysical methods are useful tools for assessing and monitoring topsoil salinity at agricultural fields scale in the VMD.

Assessment of groundwater potential zones using an integration of Remote Sensing, GIS and 2D Electrical Resistivity imaging in the Echway watershed, Baro River Basin, Southwest Ethiopia

The objective of this study is to delineate and identify the groundwater potential zone of degraded land in the Echway watershed, southwest Ethiopia, employing a combined approach that includes 2D electrical resistivity, the analytical hierarchy process (AHP), geographic information systems (GIS) and remote sensing (RS). Using a geographic information system (GIS) and remote sensing data, groundwater potential zones were identified by taking into account the soil types, drainage density, geology, lineament density, Land use and land cover, rainfall and slope. Using the AHP method, calculate the weight of thematic layers and rank of subclasses based on the effects of various thematic layers on groundwater potential. A significant weight was provided on the geology of the research region, total annual rainfall, and lineament density. Due to significant effects on groundwater potential zones, only three of the seven theme levels were assigned significant weight in this analysis. The weighted overlay analysis was used to construct the diagram of the zones with groundwater potential. 2D electrical resistivity was utilized to find the groundwater aquifer, and four major electrical layers were discovered: clayey silt, sand, moderately weathered/fractured rock, and basement parent rock. The groundwater potential zones in the study area have been classified into five categories: very low (22.97%), low (13.43%), moderate (32.50%), high (25.12%), and very high (5.98%) covered, respectively. The groundwater potential zone image was created by combining GIS, remote sensing, AHP, and an electrical survey