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1.
This study has been conducted to find out the aquifer characteristics of Bagerhat Sadar and adjacent areas in Bangladesh using geoelectrical resistivity method and borehole logs. The interpretation of resistivity soundings (14 nos.) shows that the sub-surface lithological sequence can be divided into four geoelectric units. The deepest geoelectric unit (with resistivity from 8 Ohm-m to 18 Ohm-m) represents the deep aquifer with usually fresh water. Resistivity values of 12 ?m or more for this unit may indicate formation water as acceptable for coastal people. In the study area, the shallow aquifer inferred is not suitable for groundwater development.  相似文献   

2.
As Suqah area is a NW–SE trending wadi present in the west central part of the Arabian Shield. It comprises Precambrian–Cambrian basement rocks, Cretaceous–Tertiary sedimentary succession, Tertiary–Quaternary basaltic lava flows, and Quaternary–Recent alluvial deposits. The magnetic anomalies indicated the presence of many recent local buried faults. These affected the distribution of the clastic sedimentary succession and seem to have controlled the deep groundwater aquifers. Groundwater movement is towards the west and northwest, following in general the surface drainage system. Hydraulic gradient varies greatly from one point to another depending on the pumping rates and cross-sectional area of the aquifer in addition to its transmissivity. The detailed results of the resistivity and seismic measurements were integrated with those obtained from test holes drilled in the study area. Groundwater occurs mainly in two water-bearing horizons, the alluvial deposits and within the clastic sedimentary rocks of Haddat Ash Sham and Ash Shumaysi formations. The shallow zone is characterized with a saturated thickness of 3–20 m and water is found under confined to semi-confined conditions. Water levels were encountered at depths varying from 3 to 16 m in the alluvial wadi deposits and from 18 to 62 m in the sedimentary succession. The combinations of vertical electrical sounding, horizontal electrical profiling, and drilling led to the identification of groundwater resources in the study area. Resistivity soundings clearly identified the nature of the lithological depth and proved useful at identifying water-bearing zones. Significantly, the majority of the groundwater was found within the deep confined aquifer gravelly sandstone, rather than in the shallow unconfined aquifer.  相似文献   

3.
This study focusses on the hydrogeology of Urema Graben, especially possible interactions between surface water and groundwater around Lake Urema, in Gorongosa National Park (GNP). Lake Urema is the only permanent water source for wildlife inside GNP, and there are concerns that it will disappear due to interferences in surface-water/groundwater interactions as a result of changes in the hydraulic environment. As the lake is the only permanent water source, this would be a disaster for the ecosystem of the park. The sub-surface geology in Urema Graben was investigated by 20 km of electrical resistivity tomography (ERT) and three magnetic resonance sounding (MRS) surveys. The average depth penetration was 60 and 100 m, respectively. The location of the ERT lines was decided based on general rift morphology and therefore orientated perpendicular to Urema Graben, from the transitional areas of the margins of the Barue platform in the west to the Cheringoma plateau escarpments in the east. ERT and MRS both indicate a second aquifer, where Urema Lake is a window of the first upper semi-confined aquifer, while the lower aquifer is confined by a clay layer 30–40 m thick. The location and depth of this aquifer suggest that it is probably linked to the Pungwe River which could be a main source of recharge during the dry season. If a dam or any other infra-structure is constructed in Pungwe River upstream of GNP, the groundwater level will decrease which could lead to drying out of Urema Lake.  相似文献   

4.
Aquifer sediments from areas of low- and high-As groundwater were characterized mineralogically and geochemically at a field site in the Nadia district of West Bengal, India. Leaching experiments and selective extraction of the sediments were also carried out to understand the release mechanism of As in the sub-surface. The correlation between measured elements (major, minor and trace) from low- and high-As groundwater areas are only significant for As, Fe and Mn. The borehole lithology and percentage of silt and clay fraction demonstrates the dominance of finer sediments in the high-As aquifer. Multivariate analysis of the geochemical parameters showed the presence of four different mineral phases (heavy-mineral fraction, phyllosilicates/biotite/Fe-oxyhydroxides, carbonates and sulphides) in the sediments. Selective extraction of sediment reveals that amorphous Fe-oxyhydroxide acts as a potential sink for As in the sub-surface. The result is consistent with microbially mediated redox reactions, which are controlled in part by the presence of natural organic matter within the aquifer sediments. The occurrences of As-bearing redox traps, primarily formed of Fe- and Mn-oxides/hydroxides, are also important factors that control the release of As into groundwater at the study site.  相似文献   

5.
An electrical resistivity method has been used to determine aquifer parameters in the Ganga-Yamuna interfluve in northern India. An existing relationship between the geoelectrical and hydraulic parameters has been modified for the case of an anisotropic aquifer. The hydrogeological framework in the upper part of the Ganga-Yamuna interfluve is evaluated by using existing relationships between hydraulic parameters and geoelectrical parameters for alluvial aquifers. On the basis of aquifer geometry, the area has been divided into two hydraulic units: the western Yamuna flood plain and the Ganga flood plain towards the east. The resistivity data collected in parts of the study area are first interpreted in terms of true resistivity and thicknesses of subsurface layers. The electrical parameters (resistivity and thicknesses) are subsequently correlated with the available pumping test data. Distinct correlations between transmissivity and modified transverse resistance are obtained for the two hydraulic units. A four-parameter model consisting of hydraulic conductivity, modified longitudinal resistivity, modified transverse resistance and hydraulic anisotropy is presented for the anisotropic aquifer underlain by conductive fine grained sediments. The model has been validated at a number of locations, where aquifer parameters are known from pumping test data.  相似文献   

6.
Kuttanad near the western coast of Kerala is a low lying area below mean sea level. The hydrogeological scenario in this wet land dominated tract, known as kole lands, was investigated by using the lithological and geophysical data generated under the R&D exploration programme of Central Ground Water Board (CGWB) during the year 2000, as also other related data generated till the year 2009. The hydrogeology of the tract is complex, and the presence of carbonaceous and organic matter in the soil and sub-soil influences the geochemical and geo-electric characteristics of the sub-surface geological formations as reflected by SP and resistivity logs. The lithologs and geophysical logs of bore wells were used to define the aquifer geometry. While the lateral and vertical variations of the aquifer systems identified were high, the bottom aquifer was relatively brackish over a large area. The gamma log behavior in these granular zones is anomalous and misguiding in nature. The radioactivities recorded against clay horizons were in the range of 130 to 200cps and in the granular zones 150 to 350 cps. The presence of monazite bearing sands at certain depths was responsible for anomalously high gamma counts against granular zones. The water quality in the granular zones was inferred from the electrical logs. The depth of occurrence of high radiation sand beds was also demarcated.  相似文献   

7.
A large number of valleys and basin systems are present in the northwestern part of the Himalayas in Pakistan which form significant aquifers in the region. Hydrogeophysical investigations in the western part of Nowshera District, a part of the intermontane Peshawar basin, were undertaken to help to determine the availability of groundwater resources in the region. Thirty vertical electrical resistivity soundings (VES) were acquired using a Schlumberger expanding array configuration with a maximum current electrode spacing (AB/2) of 150 m in delineating the groundwater potential in the study area. The results of the interpreted VES data using a combination of curve matching technique and computer iterative modeling methods suggest that the area is underlain by 3 to 5 geo-electric layers. The interpretation results showed that the geo-electrical succession consists of alluvium comprising of alternating layers of clay, silty clay, fine to coarse sands, sand with gravels and gravels of variable thickness. High subsurface resistivity values are correlated with gravel–sand units and low resistivity values with the presence of clays and silts. The modeled VES results were correlated with the pumping tests results and lithological logs of the existing wells. The pumping test suggests the transmissivity of the aquifer sediments is variable corresponding to different sediments within the area. The gravel–sand intervals having high resistivity value show high transmissivity values, whereas clay–silt sediments show low transmissivities. It is concluded that majority of the high resistive gravel–sand sediments belong to an alluvial fan environment. These gravel–sand zones are promising zones for groundwater abstraction which are concentrated in the central part of the study area.  相似文献   

8.
This study investigated the relationship between near-surface lithology and the spatial variability of As concentrations using sediment grain-size analysis and electromagnetic induction survey in the southeast Bangladesh. It has been observed that the aquifers overlain by finer sediments have higher concentrations of As in groundwater, whereas As concentrations are remarkably low in aquifers having permeable sandy materials or thinner silt/clay layer at the surface. The near-surface lithology acts as a controlling factor for spatial distributions of groundwater As within the very shallow depths (<15 m). Shallow alluvial aquifers can provide low-As drinking water in many areas of the country when tube wells are properly installed after investigation of the overlying near-surface sediment attributes and hydraulic properties.  相似文献   

9.
The geophysical characterization of a previously unstudied endorheic karstic system is presented. The studied area, known as the Esta?a Lakes, is located in the Pyrenean Marginal Sierras, northern Spain. The Esta?a Lakes are a set of natural water ponds on a bedrock of Triassic evaporites, lutites and carbonates. This wetland is included in the Natura 2000 European network of nature protection areas as a “Site of Community Importance”. Two geophysical techniques were used, magnetic resonance sounding (MRS) and electrical resistivity tomography (ERT), to map the subsurface geology and characterize the aquifer layers and the hydraulic links between the aquifers and lakes. The geophysical data were integrated with the surface geology and data from six boreholes. Ten electrical profiles were performed to identify the thickness of the units and lithological changes, whereas the MRS was used to determine the top of the saturated zone. As result, the aquifer in the Esta?a Lakes system and surrounding area has been identified as Middle Triassic carbonates, which does not correspond with the regional aquifer in the area (Upper Cretaceous and Eocene). This work shows the power of geophysical methods in poorly understood and tectonically complex areas in addition to the standard aquifer tests to evaluate hydraulic properties.  相似文献   

10.
复杂山区近地表调查技术是制约地震资料品质的主要因素。这里利用地质雷达和高密度电法相配合,在四川南江山区进行了近地表结构综合调查。地质雷达探测精度高,高密度电法探测深度大且能有效补充介质电性信息。通过微测井数据进行标定,建立了近地表结构的深度和速度模型,为地震静校正提供了依据。经研究结果表明,采用近地表调查数据进行静校正的地震品质得到了提高。  相似文献   

11.
The potential health impact of As in drinking water supply systems in the Mississippi River Valley alluvial aquifer in the state of Arkansas, USA is significant. In this context it is important to understand the occurrence, distribution and mobilization of As in the Mississippi River Valley alluvial aquifer. Application of surface complexation models (SCMs) to predict the sorption behavior of As and hydrous Fe oxides (HFO) in the laboratory has increased in the last decade. However, the application of SCMs to predict the sorption of As in natural sediments has not often been reported, and such applications are greatly constrained by the lack of site-specific model parameters. Attempts have been made to use SCMs considering a component additivity (CA) approach which accounts for relative abundances of pure phases in natural sediments, followed by the addition of SCM parameters individually for each phase. Although few reliable and internally consistent sorption databases related to HFO exist, the use of SCMs using laboratory-derived sorption databases to predict the mobility of As in natural sediments has increased. This study is an attempt to evaluate the ability of the SCMs using the geochemical code PHREEQC to predict solid phase As in the sediments of the Mississippi River Valley alluvial aquifer in Arkansas. The SCM option of the double-layer model (DLM) was simulated using ferrihydrite and goethite as sorbents quantified from chemical extractions, calculated surface-site densities, published surface properties, and published laboratory-derived sorption constants for the sorbents. The model results are satisfactory for shallow wells (10.6 m below ground surface), where the redox condition is relatively oxic or mildly suboxic. However, for the deep alluvial aquifer (21-36.6 m below ground surface) where the redox condition is suboxic to anoxic, the model results are unsatisfactory.  相似文献   

12.
DRASTIC indexing and integrated electrical conductivity (IEC) modeling are approaches for assessing aquifer vulnerability to surface pollution. DRASTIC indexing is more common, but IEC modeling is faster and more cost-effective because it requires less data and fewer processing steps. This study aimed to compare DRASTIC indexing with IEC modeling to determine whether the latter is sufficient on its own. Both approaches are utilized to determine zones vulnerable to groundwater pollution in the Nile Delta. Hence, assessing the nature and degree of risk are important for realizing effective measures toward damage minimization. For DRASTIC indexing, hydrogeological factors such as depth to aquifer, recharge rate, aquifer media, soil permeability, topography, impact of the vadose zone, and hydraulic conductivity were combined in a geographical information system environment for assessing the aquifer vulnerability. For IEC modeling, DC resistivity data were collected from 36 surface sounding points to cover the entire area and used to estimate the IEC index. Additionally, the vulnerable zones identified by both approaches were tested using a local-scale resistivity survey in the form of 1D and 2D resistivity imaging to determine the permeable pathways in the vadose zone. A correlation of 0.82 was obtained between the DRASTIC indexing and IEC modeling results. For additional benefit, the obtained DRASTIC and IEC models were used together to develop a vulnerability map. This map showed a very high vulnerability zone, a high-vulnerability zone, and moderate- and low-vulnerability zones constituting 19.89, 41, 27, and 12%, respectively, of the study area. Identifying where groundwater is more vulnerable to pollution enables more effective protection and management of groundwater resources in vulnerable areas.  相似文献   

13.
Siliyin spring is one of the many natural fresh water springs in the Western Desert of Egypt. It is located at the central part of El-Fayoum Delta, which is a potential place for urban developments and touristic activities. Integrated geoelectrical survey was conducted to facilitate mapping the groundwater resources and the shallow subsurface structures in the area. Twenty-eight transient electromagnetic (TEM) soundings, three vertical electrical soundings (VES) and three electrical resistivity tomography (ERT) profiles were carried out around the Siliyin spring location. The dense cultivation, the rugged topography and the existence of infra structure in the area hindered acquiring more data. The TEM data were inverted jointly with the VES and ERT, and constrained by available geological information. Based on the inversion results, a set of geoelectrical cross-sections have been constructed. The shallow sand to sandy clay layer that forms the shallow aquifer has been completely mapped underneath and around the spring area. Flowing of water from the Siliyin spring is interconnected with the lateral lithological changes from clay to sand soil. Exploration of the extension of Siliyin spring zone is recommended. The interpretation emphasizes the importance of integrating the geoelectrical survey with the available geological information to obtain useful, cheap and fast lithological and structural subsurface information.  相似文献   

14.
Near-surface geophysical methods are commonly used to solve a wide class of geological, engineering and environmental problems. In this study, a geoelectrical survey was performed to investigate an alluvial aquifer. The study area is located in the southwest of the Çubukluda? graben, situated in the south of ?zmir, Turkey. The geophysical studies included the electrical resistivity imaging and self-potential (SP) methods. The resistivity data were acquired along eight profiles in the northern part of the study area by a Wenner-Schlumberger electrode configuration and the data processing was achieved by a tomographic inversion technique. The SP data were collected by gradient technique along 16 profiles. Total field values were calculated for each profile by addition of the successive gradient values, then a total field SP map was obtained. The water-saturated zone in the northern part of the study area was clearly revealed by the electrical resistivity imaging and the SP survey yielded useful information on the subsurface fluid movement.  相似文献   

15.
This paper presents the combination of two complementary methods, magnetic and joint inversion of resistivity/TEM data, as an effective approach to characterize groundwater reservoirs. Twenty stations of transient electromagnetic (TEM) and vertical electrical soundings (VES) were measured and interpreted using a joint inversion technique to evaluate the subsurface low resistivity zones connected to the groundwater reservoir. A complementary survey including 871 land magnetic stations was carried out at the same area to detect the upper surface of the basaltic sheet, which represents the bottom of the Miocene aquifer in the study area. The geological log from one borehole drilled in the zone was used to partially calibrate the calculated models. The results revealed that the study area consists of five different geological units with ages ranging from Paleogene (Oligocene) to Quaternary. The methodology provides good results at a very low cost when compared with drilling boreholes.  相似文献   

16.
Integrated geophysical techniques including resistivity image, vertical electrical sounding (VES), and seismic refraction have been conducted to investigate the Wadi Hanifah water system. The groundwater in Wadi Hanifah has problems caused by the high volumes of sewage water percolating into the ground. The combination of VES, resistivity image, and seismic refraction has made a valuable contribution to the identification of the interface between the contaminated and fresh water in Wadi Hanifah area. The contaminated groundwater has lower resistivity values than fresh groundwater due to the higher concentration of ions which reduces the resistivity. Resistivity image and sounding in this area clearly identified the nature of the lithological depth and proved useful at identifying water-bearing zones. Fresh groundwater was found in the study area at a depth of 100 m within the fractured limestone. Water-bearing zones occur in two aquifers, shallow contaminated water at 10 m depth in alluvial deposits and the deeper fresh water aquifer at a depth of about 100 m in fractured limestone. The interface between the contaminated water (sanitary water) and fresh water marked out horizontally at 100 m distance from the main channel and vertically at 20 m depth.  相似文献   

17.
A saltwater intrusion study using electrical resistivity distribution was conducted in a coastal aquifer system in the southeastern part of Busan, Korea. This aquifer system is divided into four layers according to the hydrogeologic characteristics, and the horizontal extent of intruded saltwater is determined at each layer through the geostatistical interpretation of electrical resistivity data. Intrinsic random function of order k (IRF-k) kriging is performed with covariance models to produce the plane of spatial mean resistivities. The kriged estimates are evaluated by cross validation, and they showed a good agreement with the true values. The statistics of cross validation represented low errors for the estimates. In the resistivity contour maps more than 5 m below the surface, a dominant direction of saltwater intrusion was observed beginning from the east side. These results led the authors to conclude that the application of geostatistical technique to electrical resistivity data is useful for assessing saltwater intrusion in a coastal aquifer system.  相似文献   

18.
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- > SO42- > 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- - SO42- 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.  相似文献   

19.
Detailed local geological, geophysical, and hydrogeological investigations were carried out for the alluvial aquifer in the Kangavar basin, West Iran to delineate the architecture of different subsurface geological horizons using lithologs and generated vertical electrical sounding (VES) data. An attempt has also been made to estimate aquifer transmissivity from resistivity data. Forty VESs were recorded with the Schlumberger electrode configuration in the study area; 28 of these were selected for evaluation. The maximum current electrode spacing was 400–500 m. The data obtained were interpreted by computer iterative modeling with curve matching for calibration purposes. In order to ascertain the subsurface geological framework, the general distribution of resistivity responses of the geological formations was obtained and geoelectrical sections along a number of lines were prepared. Probable aquifer horizons from these sections were identified. The transmissivity of the unconfined aquifer was computed by determining the Dar-Zarrouk parameters (longitudinal unit conductance and transverse unit resistance) and were compared with the actual field transmissivity. The results showed a direct relation between aquifer transmissivity and modified transverse resistance.  相似文献   

20.
Integrated geoelectrical and hydrochemical surveys were used to investigate and delineate different types of groundwater in the Kuala Selangor alluvial aquifer. Previous hydrogeological borehole investigation showed that this aquifer contains several types of groundwater in relation to its salinity. The high salinity of the groundwater in some areas is believed to be due to either saltwater intrusion from the nearby sea or river infiltration during high tide season. The vertical electrical sounding (VES) method was employed to study and map the subsurface variation of resistivity in the area. For each sounding measurement, a total spread length of 300 m was obtained with a vertical depth penetration of about 60 to 75 m. Chemical analysis of the groundwater samples taken from both shallow and deep boreholes was carried out for the water quality determination. A total of 45 VES stations were succesfully established along three parallel roads with a direction almost perpendicular to the coastal line. The distance between stations varies from 1 to 2 km with a maximum length of about 60 km surveyed line. Results of the vertical electrical soundings as well as the hydrochemistry of the groundwater samples show that the soil and groundwater in the study area can be grouped into fresh and brackish water zones. The subsurface resisitivity sections derived from the VES study suggest that the area is dominated by brackish soil and groundwater zones, especially in the area towards the coast. This result appears to agree well with the groundwater pumped from boreholes scattered around in the area. Water drawn from boreholes near the coast showed higher salinity compared to the water pumped from inland boreholes. Chloride values greater than 250 mg/L are considered to represent the brackish zones whilst values less than 250 mg/L represents zones of fresh soil and groundwater.  相似文献   

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