Water-table Contour Research Articles

Statistical and isotopic analysis of sources and evolution of groundwater

Investigating sources and evolution of groundwater in the Black Volta River basin is vital for understanding aquifer chemical configuration. Though resettlement has made groundwater in the region an important water supply source, its hydrochemical origin is poorly understood. Therefore, hydrochemistry was coupled with stable isotope (δ2H and δ18O) techniques to improve knowledge for effective groundwater resource management. For this purpose, 23 boreholes were sampled in the Black Volta River basin of Ghana. Major ion dominance is in the order: Na+ > Ca2+ > Mg2+ >K+ and HCO3− > Cl− > SO42− > NO3− respectively. Hydrochemical facies indicates the presence of soluble silicate minerals within aquifer. Hierarchical cluster analysis showed higher ionic concentration within aquifers which decreases towards discharge areas. This is attributed to longer residence time at lower elevations leading to interaction of water with silicate and accessory minerals. Oxygen-18 spatial plot shows recharge occurs along subsurface fractured zones which is confirmed by the water table contour of the study area. Natural geochemical processes, anthropogenic influences and the dissolution of silicate/albite components were extracted using Principal component analysis/factor analysis. These two components which explains the hydrochemistry constituted 79.5% of the total variance in the hydrochemical data and have eigen values > 1. Isotopic composition of groundwater indicates is of meteoric origin and the aquifers were recharged by precipitation. The outcome of this study provides theoretical support for the monitoring and management of groundwater, and its implication on the migration of people in arid/semi-arid regions.

Automatic Features Detection in a Fluvial Environment through Machine Learning Techniques Based on UAVs Multispectral Data

The present work aims to demonstrate how machine learning (ML) techniques can be used for automatic feature detection and extraction in fluvial environments. The use of photogrammetry and machine learning algorithms has improved the understanding of both environmental and anthropic issues. The developed methodology was applied considering the acquisition of multiple photogrammetric images thanks to unmanned aerial vehicles (UAV) carrying multispectral cameras. These surveys were carried out in the Salbertrand area, along the Dora Riparia River, situated in Piedmont (Italy). The authors developed an algorithm able to identify and detect the water table contour concerning the landed areas: the automatic classification in ML found a valid identification of different patterns (water, gravel bars, vegetation, and ground classes) in specific hydraulic and geomatics conditions. Indeed, the RE+NIR data gave us a sharp rise in terms of accuracy by about 11% and 13.5% of F1-score average values in the testing point clouds compared to RGB data. The obtained results about the automatic classification led us to define a new procedure with precise validity conditions.

Integrated vertical electrical sounding and hydrogeological approach for detailed groundwater pathways investigation: Gökpınar Dam Lake, Denizli, Turkey

Understanding the hydrodynamic systems in the dam lake surroundings is of great importance to protect the lakes feeding zones and maintain their water level. In this study, a combination of hydrogeological and geophysical surveying processes was carried out in order to distinguish the Gökpınar dam lake's recharge ways. The Gökpınar dam lake area is characterized by a very complicated hydrogeological system causing difficulty at distinguishing the groundwater flow pathways feeding the lake. Therefore, a detailed vertical electrical sounding survey was performed in accordance with the Shlumberger array in the surroundings of the Gökpınar dam lake. Results obtained from the resistivity measurements were processed using a partial curve matching technique then inverted in order to build 2D and 3D resistivity models which in their turn were corelated with the geology of the study area. In addition to the geoelectrical measurements 44 boreholes were drilled in order to confirm the vertical electrical sounding results. Data collected from these boreholes were also used for the plotting process of the water table contour map in the study area which highly correlated with the resistivity contour maps. Resistivity data evaluation led to the differentiation between water bearing and dry zones. Results showed that the Gökpınar dam lake is fed by several groundwater flows, deriving from South-West, North-West, and South-Eastern parts of the study area. These flows are generally more important near the surface than they are deeper toward the impermeable bedrock.

Recognition of Regional Water Table Patterns for Estimating Recharge Rates in Shallow Aquifers.

We propose a new method for groundwater recharge rate estimation in regions with stream-aquifer interactions, at a linear scale on the order of 10km and more. The method is based on visual identification and quantification of classically recognized water table contour patterns. Simple quantitative analysis of these patterns can be done manually from measurements on a map, or from more complex GIS data extraction and curve fitting. Recharge rate is then estimated from the groundwater table contour parameters, streambed gradients, and aquifer transmissivity using an analytical model for groundwater flow between parallel perennial streams. Recharge estimates were obtained in three regions (areas of 1500, 2200, and 3300 km2 ) using available water table maps produced by different methods at different times in the area of High Plains Aquifer in Nebraska. One region is located in the largely undeveloped Nebraska Sand Hills area, while the other two regions are located at a transition zone from Sand Hills to loess-covered area and include areas where groundwater is used for irrigation. Obtained recharge rates are consistent with other independent estimates. The approach is useful and robust diagnostic tool for preliminary estimates of recharge rates, evaluation of the quality of groundwater table maps, identification of priority areas for further aquifer characterization and expansion of groundwater monitoring networks prior to using more detailed methods.

Construction of Water Table Contour Map and Geo Hydrological Studies on Krishnagiri Using GIS Techniques

Geo-hydrology and groundwater exploration manner to pick out and to find the zone of recharge of groundwater in a precise river basin or a catchment .water level contour traces (or waft traces) are much like topographic strains on a map. They fully represent "elevations" in the subsurface. Water table contour lines can be used to inform which manner groundwater will glide in a given region. Plenty of wells are drilled and the hydraulic head is measured in each one. Water desk contours are drawn that be a part of areas of identical head .The ones water table contours lines are also called equipotential strains. Bear in mind: groundwater usually movements from a place of the higher hydraulic head to an area of decrease hydraulic head, and perpendicular to equipotential traces. In our challenge, we put into effect concept of water table contour map and geohydrological studies on Krishnagiri using GIS software program which plays the essential position in contemporary technology.

Time dependent electrical resistivity tomography and seasonal variation assessment of groundwater around the Olushosun dumpsite Lagos, South-west, Nigeria

Time-lapse electrical resistivity tomography (ERT) and seasonal variation studies of the physicochemical properties of groundwater were carried out on the Olushosun dumpsite in Lagos South-western Nigeria, to monitor, track the depth of leachate contamination, and to investigate the impact of seasonal variation on groundwater quality around the dumpsite. Six 2-D resistivity imaging lines were investigated. The independent inversion of the dipole–dipole and pole-dipole resistivity data indicated that contaminated zones are characterised by resistivity values ranging from 0.63 to 12.5 Ωm, and a maximum depth of 141 m was investigated. The pole-dipole models show clear evidence of vertical migration of contaminant with time, as depth of contamination increased from 106 m in May 2014 to about 120 m in December 2015 around the investigated portion of the dumpsite. Analysis of the seasonal variation of the examined physicochemical properties of the water samples taken from wells and boreholes within and around the site showed that there is increase in concentration of TDS and EC in the dry season study and a corresponding increase in the mean concentration of pH, Ca, Mg, hardness, Cu, Cr, NO3, SO4 and Na from the dry season results. Also, there is reduction in the mean concentration of Fe, Zn, Mn, PO4, Cl, and Ni in the dry season when compared with the wet season analysis. Generally, there is a strong correlation between the ERT results and the physicochemical parameters of ground water quality viz-a-viz the contamination status of the Olushosun dumpsite. This increased trend in the dry season period could be attributed to the increase in concentration of the dissolved metals due to evaporation, and on the other hand, dilution effect of the rainfall during the wet season. South East direction of contaminant flow was established from the water table contour lines produced for the area. The research has clearly shown that the groundwater within the study area has been impacted by the leachate from the decomposed refuse at the dumpsite and may constitute danger to the life of residents living around the dumpsite.

Transient Fluid Flow Modeling in Fractured Aquifer of Sechahoon Iron Mine Using Finite Element Method

Considering the fact that a large volume of iron reserve in the Sechahoon Iron Mine in Yazd Province has located under the water table, it is necessary to conduct a comprehensive study on water flow within the pit and its surroundings. The conceptual model of the aquifer was created using the surface and underground geological information compared with water table data of the area of interest. In the data preparation stages, in order to create the numerical model, Logan and Lufran tests were carried out to determine the hydrodynamic coefficients of the layers. The precipitation and evaporation, as well as the fractures and faults of the region, as a medium for flow channels in the hard formation, were also studied. The model was created in a transient state between 2000 and 2014. To validate its results, the water table was measured 4 times in the last 4 months of 2014. Considering the complexities in the heterogeneous fractured aquifer of the study area, numerical modeling results for the basin in a transient state present 90 percent correlation with field studies. Having investigated the water balance in the region, the boundary condition of the model was determined as the input water from the eastern south and the runoff water in the western north of the region. Since the general trend of faults in the area is north-south, the water table variation is slight on northsouth and intense on the east-west direction. On the other hand, due to the fact that the maximum flow is along the faults and fractures, the water table contour lines in different locations over the region are closed.

The state of toxicity and cause of elevated Iron and Manganese concentrations in surface water and groundwater around Naga Thrust of Assam-Arakan basin, Northeastern India

An alarming situation of exceedingly high Fe and Mn concentrations in both surface water and groundwater has been identified in a tectonically active region located in Assam-Arakan basin of northeast India. Cross plots, Pearson correlation, principal component analysis and flow net methods were applied to elucidate the present state and possible sources of Fe and Mn contamination. Out of 32 water samples collected for the study, all of them found exceeding 28 times more for Fe and 136 times more for Mn than EPA limit. Correlation and cross plots of pH, TDS, EC, Fe, Mn, Cu, Zn suggest the reduction of both Fe-hydroxides and Mn-oxides in redox condition into dissolve states leading to Fe and Mn elevations in groundwater. Principal component analysis exhibits three PC factors in which PC1 and PC3 reflected oxidized condition and PC2 reflected reducing environment that controlled Fe and Mn concentrations. The study also revealed that source of high Fe and Mn contaminations was controlled by groundwater flows. Water table contour flow net suggests that the Chathe river acts as influent stream and supplies elevated Fe and Mn water into the shallow aquifers. Baseflow from the discharge areas into low lying areas causes accretion of Fe and Mn in pond, oxbow lake, backswamp and shallow aquifers.

Analysis on Groundwater Dynamic Characteristics and Causes in Yao Ba Oasis

According to the monitoring data from 1984 to 2014 of the groundwater table in Yao Ba oasis, Alax League, Inner Mongolia of China, analysis the annual and interannual variation of the groundwater table and its genesis in the irrigation area. In addition, use the Surfer11 to draw the water-table contour and restore the cone of depression. Analytical results show that the dynamic type in the irrigation area is artificial exploitation type. Groundwater exploitation is a major factor causing the groundwater table dynamic change, the groundwater table characteristics and the cone of depression mainly depend on the size of exploitation.

Evolution characteristics and influence factors of deep groundwater depression cone in North China Plain, China—A case study in Cangzhou region

The North China Plain (NCP) is one of the global hotspots of groundwater depletion, groundwater is almost the only source of water for agricultural, industrial and drinking water in this region. After long-term’s over-exploitation of deep groundwater, there appeared several deep groundwater depression cones, such as Cangzhou cone, Dezhou cone, Hengshui cone, Tianjin cone, etc., in which the Cangzhou cone is one of the typical cones for its special geography and hydrogeology conditions. In this study, the authors intended to analyze the evolution characteristics and influence factors of deep groundwater depression cone in Cangzhou region, especially the No. III aquifer depression cone, which is the main exploitation zone in this region. Analysis of the evolution of the groundwater depression cone of the No. III aquifer group in Cangzhou region showed that this process can be divided into four stages, namely, development, stable development, rapid expansion, and gradual recovery. The shape and evolution characteristics of the depression cone at different stages are described by analyzing the evolution of the −30, −40, and −50 contours of the groundwater table, for example the closed area of water table contour of −50 m has been enlarged from 95 km2 in 1985 to 6 528.5 km2 in 2005. The dominant factors that affect the evolution characteristics at different stages are proposed. The results showed that relatively long dry periods with less precipitation, special geological and hydrogeological conditions, and sharply increased water consumption for industrial and agricultural development are the main factors that cause the formation of deep groundwater depression cones. Meanwhile, an environmental response against groundwater exploitation is presented, and rational solutions are suggested to avert water crisis.

Hydrogeomorphic Classification and Aquifer Disposition in the Markanda River Basin, Northwestern India – Hydrogeological Approach

Abstract The regional hydrogeological aspects of the Markanda river basin in the Himalayan foothills, NW India have been attempted. The basin has been hydro-geomorphologically analyzed as ridge, piedmont zone, alluvial plain, flood plain and palaeochannel. Groundwater prospect in the alluvial plain, flood plain and palaeochannel areas were found to be promising. Water table contour maps of the basin revealed that groundwater flows from northeast to southwest. Groundwater permeability is low in the northern part and is high towards the southern part of the basin. The areas of recharge were identified in the northern part of the basin, while the areas of discharge were identified in the central and lower parts of the basin. Hydrogeologic transects across and along the basin indicate that aquifer horizons are made up of fine sand, medium sand and gravelly sand. These aquifer layers are laterally extensive but limited in thickness. They occur as multistoried sand bodies with pinch and swell behavior. The overall study gives an understanding of the present regional hydrogeological scenario of the Markanda basin. Such detailed integrated approach would help to locate productive groundwater areas before installing a new tubewell in the region. Also, it would help in planning future groundwater management of the region.

Effectiveness of groundwater nitrate removal in a river riparian area: the importance of hydrogeological conditions

Riparian areas are often considered important ecological ecotones that decrease the nitrate load of groundwater discharging into rivers. In this paper, the effectiveness of nitrogen removal from groundwater in a riparian area has been evaluated. We used a quantitative hydrogeological approach which delimited homogeneous stream tubes based on the water table contour. We constructed water and mass balances and used the results to estimate the mass of nitrogen removed by biological processes. Nitrogen removal effectiveness was calculated as the ratio of nitrogen removed to the total nitrogen mass flowing through the riparian area. This approach requires knowledge of the hydrogeological settings and coverage of an area larger than the study site. The removal we observed was seasonally variable, ranging between 2.2 and 7.6 mg N m −2 day −1, and represented up to 95% of the total nitrogen mass entering the riparian area in late summer. Removal effectiveness was only 27–38% in winter, due to the combination of a high nitrogen input and a low plant uptake. Nitrogen removal was highest in spring, but effectiveness was about 60% because the input was as high as in winter. Rainwater infiltrating the riparian area could represent almost the same quantity as groundwater input. Under such conditions, the dilution effect is very important in riparian areas that are not nitrate sources and it is essential to maintain this non-nitrate-emissive use. This study showed that the effectiveness of nitrogen removal in a riparian area is highly dependent on the pathway of water movement through its biologically active layers.

Airborne Magnetic Lineament, Groundwater Potentiality and Basement Structures in S-E Part of Vindhyan Basin

Abstract Airborne total intensity magnetic survey flown at a height of approximately 152 m in central India has delineated several linear magnetic anomalies of 200-400 nT aligned together to form a large magnetic lineament approximately 1 km wide and 100 km long. The nature of magnetic anomalies suggest the lineament to be a fracture zone with basic intrusives at places. Magnetic and resistivity surveys on ground provide large magnetic (600-800 nT) and low resistivity anomalies along this lineament suggesting a fracture zone with basic intrusive rocks at places and very good groundwater potentiality along it.. Existing wells close to the lineament yield good amount of water, while those away from it show poor yield. Water table contour map of the area shows contours parallel to the lineament indicating pumping of more water from this zone causing lateral flow of groundwater. This lineament does not find reflection in the ground gravity survey; instead it delineated some second order small dome and basin structures around Damoh and Jabera which are not recorded in the airborne total intensity map referred to above. This suggests that while linear features are better reflected in the airborne magnetic surveys small-scale three-dimensional basement structures are better reflected in the ground gravity surveys. This indicates the need for an integrated airborne and ground exploration programme for delineating subsurface structures/tectonics and to quickly assess the groundwater resources of a region.

Fracture pattern and electrical resistivity studies for groundwater exploration

The occurrence, movement and control of groundwater, particularly in hard-rock areas, are governed by different factors such as topography, lithology, structures like fractures, faults and nature of weathering. An attempt is made in the present study to investigate the extent of the influence of structures such as fractures and thereby delineate the nature of subsurface lithology with the help of an electrical resistivity method. For this study, the Upper Gunjanaeru River basin, Cuddapah district Andhra Pradesh was chosen to determine groundwater potentials. In order to understand the significance of the fracture pattern, geological, hydrogeomorphological and lineament maps were prepared based on the field data and also from the LANDSAT TM imagery. Further, electrical resistivity surveys were conducted to determine the subsurface lithology and also to confirm the studies of LANDSAT imagery. The isoresistivity contour map has been prepared based on the 45 VES conducted to determine the resistivity variations in the study area. The isoresistivity contours obtained were found to conform to the structural trends obtained by geological studies and also confirm the relationship between the structure and secondary porosity present in the rocks. The lineaments in the area have two preferred directions. One set is a NE-SW direction (N 30°–70° E; S 30°–70° W) and another is a NW-SE direction (N 0°–30° W; S 0°–30° E and N 60°–80° W; S 60°–80° E). The water-table contour map shows that the direction of groundwater flow is south to north.

Digital Terrain Modeling of Geologic Data for a Ground-Water Monitoring Program

Geologists from Southern Company Services, Inc., Birmingham, Alabama, were required to develop, in a compressed time frame, ground-water monitoring plans for sites in Florida. The Map Information Management System (MIMS), from Synercom Technology, Inc., and the Contour Interpolation Package (CIP), from Wild Heerbrugg, were used to define the geology and hydrogeology of the areas. Specifically MIMS and CIP were used to generate multiple structure, isopach, and water-table contour maps and geologic cross sections for the areas. Computer-aided geology has the following advantages: it frees the geologist from the mechanics of map preparation, thereby allowing more analysis and problem solving; frees drafters from hours of tracing and lettering; provides flexibility in the types and numbers of maps generated; pinpoints errors in data readily; and allows quick revisions and updates. These advantages result in a more efficient, cost-effective job.

Design of Interceptor Drains in Heterogeneous Soils

Approximate method for including variable permeability in design procedure is presented; use of water table contour map for transposing flow system in heterogeneous soil to equivalent system having constant permeability throughout; reverse-transformation of prediction from uniform soil system to field problem gives expected condition after drainage facilities are installed.