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1.
Hydrogeology Journal - The study defines the hydrogeological framework of the Quaternary aquifer of south Bengal Basin, India, and the impact of urbanisation on the groundwater resources in and... 相似文献
2.
This article focuses on the Montello thrust system in the Eastern Southern Alps as a potential seismogenic source. This system is of particular interest because of its lack of historical seismicity. Nevertheless, the system is undergoing active deformation. We developed a finite‐element model using visco‐elasto‐plastic rheology. The free parameters of the model (essentially, the locking status of the three thrusts included in the study), were constrained by matching the observed horizontal GPS and vertical levelling data. We show that the amount of interseismic fault locking, and thus the seismic potential, is not necessarily associated with the fastest‐slipping faults. More specifically, the locked Bassano thrust has a greater seismic potential than the freely slipping Montello thrust. The findings suggest that faults with subtle evidence of Quaternary activity should be carefully considered when creating seismic hazard maps. 相似文献
3.
Data from the SESAME storm-scale network are used in computing the momentum budget of the prestorm, storm, and poststorm environment of a severe storm complex. In the prestorm period geostrophic flow dominates the environment. With progression into the storm period all terms in the momentum equation become important, as a significant ageostrophic component in the momentum field develops. Turbulent effects are estimated as a residual, and the results indicate that they are comparable in magnitude to the other terms. Their effect is to decrease the positive momentum, particularly at levels above 500 mbar, where the vertical motion is the strongest. Vertical profiles of area means ofu andv indicate that the storm is apparently redistributing momentum downwards, thus reducing the mean shear. In the poststorm period the flow once again becomes largely geostrophic, and a maximum in wind speed reappears at upper levels. 相似文献
4.
Silicon and iron isotope compositions of different physically separated components of enstatite chondrites (EC) were determined in this study to understand the role of nebular and planetary scale events in fractionating Si and Fe isotopes of the terrestrial planet-forming region. We found that the metal–sulfide nodules of EC are strongly enriched in light Si isotopes (δ30Si ≥ −5.61 ± 0.12‰, 2SD), whereas the δ30Si values of angular metal grains, magnetic, slightly magnetic, and non-magnetic fractions become progressively heavier, correlating with their Mg# (Mg/(Mg+Fe)). White mineral phases, composed primarily of SiO2 polymorphs, display the heaviest δ30Si of up to +0.23 ± 0.10‰. The data indicate a key role of metal–silicate partitioning on the Si isotope composition of EC. The overall lighter δ30Si of bulk EC compared to other planetary materials can be explained by the enrichment of light Si isotopes in EC metals along with the loss of isotopically heavier forsterite-rich silicates from the EC-forming region. In contrast to the large Si isotope heterogeneity, the average Fe isotope composition (δ56Fe) of EC components was found to vary from −0.30 ± 0.08‰ to +0.20 ± 0.04‰. A positive correlation between δ56Fe and Ni/S in the components suggests that the metals are enriched in heavy Fe isotopes whereas sulfides are the principal hosts of light Fe isotopes in the non-magnetic fractions of EC. Our combined Si and Fe isotope data in different EC components reflect an inverse correlation between δ30Si and δ56Fe, which illustrates that partitioning of Si and Fe among metal, silicate, and sulfidic phases has significantly fractionated Si and Fe isotopes under reduced conditions. Such isotope partitioning must have occurred before the diverse components were mixed to form the EC parent body. Evaluation of diffusion coefficients of Si and Fe in the metal and non-metallic phases suggests that the Si isotope compositions of the silicate fractions of EC largely preserve information of their nebular processing. On the other hand, the Fe isotopes might have undergone partial or complete re-equilibration during parent body metamorphism. The relatively uniform δ56Fe among different types of bulk chondrites and the Earth, despite Fe isotope differences among their components, demonstrates that the chondrite parent bodies were not formed by random mixing of chondritic components from different locations in the disk. Instead, the chondrite components mostly originated in the same nebular reservoir and Si and Fe isotopes were fractionated either due to gas–solid interactions and associated changes in physicochemical environment of the nebular reservoir and/or during parent body processing. The heavier Si isotope composition of the bulk silicate Earth may require accretion of chondritic and/or isotopically heavier EC silicates along with cumulation of refractory forsterite-rich heavier silicates lost from the EC-forming region to form the silicate reservoir of the Earth. 相似文献
5.
M. A. Hoque J. M. McArthur P. K. Sikdar J. D. Ball T. N. Molla 《Hydrogeology Journal》2014,22(7):1549-1560
Dhaka, the capital of Bangladesh, is home to a population of 15 million people, whose water supply is 85% drawn from groundwater in aquifers that underlie the city. Values of Cl/Br >500 are common in groundwater beneath western Dhaka in areas <3 km from the river, and in rivers and sewers around and within the city. The study shows that groundwater beneath western Dhaka is strongly influenced by infiltration of effluent from leaking sewers and unsewered sanitation, and by river-bank infiltration from the Turag-Buriganga river system which bounds the western limit of the city. River-bank infiltration from other rivers around Dhaka is minor. Values of Cl/Br and Cl concentrations reveal that 23 % of wells sampled in Dhaka are influenced by saline connate water in amounts up to 1%. This residual natural salinity compromises the use of electrical conductivity of groundwater as a method for defining pathways of recharge by contaminated surface waters. Concentrations of As, B, Ba, Cd, Cu, F, Ni, NO3, Pb, Sb, Se and U in groundwater samples are less than WHO health-based guideline values for drinking water. 相似文献
6.
Geologic framework and isotope tracing of the arsenious Quaternary Aquifer of the southwestern North Bengal Plain,West Bengal,India 总被引：2，自引：2，他引：0
The aim of the paper is to understand the geological control of groundwater, the recharge sources, the relative age of groundwater
and the interaction between surface water and groundwater of the southwestern part of North Bengal Plain in the alluvium filled
gap between the Rajmahal hills on the west and the Garo hills on the east. The area is covered by Quaternary alluvia of two
different ages, viz. the Older Alluvium and the Newer Alluvium. The Older Alluvium of Pleistocene age is made up of argillaceous
bed reddish brown in color and interspread with ‘kankar’ and laterite debris and the Newer Alluvium is dark, loosely compacted
and has a high moisture content. A hydrostarigraphic model of the top 120 m geological column has been built by direct field
observation, constructing Fence diagram, lithofacies and isotope analyses. The model indicates an oscillating environment
of deposition of sediments from bottom to top with oxidizing at the bottom followed by reducing and then oxidizing environment
at the top. The hydrogeochemistry of groundwater also suggests a predominantly reducing condition of the aquifer with high
HCO3
−, low SO4
2− and NO3
− concentrations. The shallow groundwater at places contains heavy metals such as copper, cadmium, manganese, iron, chromium
and arsenic. The δ18O and tritium values of groundwater are within the range of monsoon precipitation composition which indicates that groundwater
is probably recharged primarily from precipitation. The plots of δ18O and δD show slight deviation from the Local Mean Water Lines suggesting that some evaporation of rainfall occurs prior to
or during infiltration. Therefore groundwater occurs under unconfined condition. Lithofacies analysis indicates that the sediments
below the depth of 40 m are the potential water bearing formation. Depletion or enrichment of δ18O and δD with depth was not observed and tritium content is also similar at various depths indicating possibility of mixing
of groundwater from various depths due to pumping which may lead to contamination of the deeper aquifer by heavy metals and
arsenic. 相似文献
7.
P. K. Sikdar Surajit Chakraborty Paulami Sahu Tulika Biswas 《Environmental Earth Sciences》2013,68(6):1673-1690
Due to the ever-increasing demand on water resource, the pressure on its judicious utilization is also increasing. Besides being precious, this resource is also complex to manage on account of its dynamic behaviour. In India emphasis is being placed on making the local-level users participate in the management of natural resources at the watershed level. Therefore, it is imperative that local-level organizations be strengthened by providing the integrated watershed management tools which are user-friendly, but still use all the scientific knowledge to arrive at the appropriate decisions. This paper demonstrates the use of GIS-based overlay method for local-level planning, incorporating the sustainability aspects of watershed development. A case study has been taken in the Lower Bhangal Micro-watershed of the outer Himalayan range to demonstrate the approach of matrix/ranking and overlay methods to delineate priority areas for watershed management plan. 相似文献
8.
P. K. Sikdar P. Sahu S. P. Sinha Ray A. Sarkar S. Chakraborty 《Environmental Earth Sciences》2013,70(4):1863-1879
A heterogeneous anisotropic steady-state groundwater flow model for the multi-aquifer system of a part of southern Bengal Basin shows that human intervention has changed the natural groundwater flow system. At present, the shallow groundwater flow is restricted within the aquifer, with very short travel time of tens of years and vertical path length. The deep aquifer is fed by surface water or rainwater from distant locations with travel time of thousands of years and has no hydraulic connection with the arsenic-rich shallow aquifer. Numerical simulations indicate that the future pumping of deep groundwater is not likely to drive in arsenic from the shallow aquifer. Therefore, new wells may be installed in the deep aquifer. High pumping of shallow unpolluted aquifer consisting of brown sand will drive in groundwater containing organic matter from the post-Last Glacial Maximum aquifer-aquitard system. The organic matter drives reduction of manganese oxides at strip interfaces between palaeo-channel and palaeo-interfluve. After the completion of manganese reduction, FeOOH reduction may take place in the marginal palaeo-interfluvial aquifer and release sorbed arsenic. Arsenic then moves into the interior of palaeo-interfluvial aquifer polluting its fresh groundwater. Arsenic migration rates ranges between 0.21 and 6.3 and 1.3 × 10?2 and 0.4 m/year in horizontal and vertical directions, respectively. Therefore, palaeo-interfluvial aquifer will remain arsenic-free for hundreds to thousands of years to supply safe drinking water. 相似文献
9.
Hydrochemical framework of the aquifer in and around East Kolkata Wetlands,West Bengal,India 总被引：1，自引：0，他引：1
The area lies between Hugli river in the northwest and Bidyadhari river in the east and includes the East Kolkata Wetlands.
The East Kolkata Wetlands is included in the List of Wetlands of International Importance (“Ramsar List”), as per the Convention
on Wetlands signed in Ramsar, Iran, in 1971. This wetland has been declared as a Ramsar site on the 19th August 2002 (Ramsar
site no. 1208) and therefore has acquired an international status. The area is a part of the lower deltaic plain of the Bhagirathi–Ganga
river system and is generally flat in nature. The sub-surface geology of the area is completely blanketed by the Quaternary
fluviatile sediments comprising a succession of clay, silty clay, sand and sand mixed with occasional gravel. The Quaternary
aquifer is sandwiched between two clay sequences. The confined aquifer is made up of moderately well sorted sand and reflects
fluviatile environment of deposition. The regional groundwater flow direction is from east to west. Detailed geochemical investigations
of 40 groundwater samples along with statistical analysis (for example, correlation and principal component analysis) on these
chemical data reveal: (i) four types of groundwater quality, for example, good, poor, very poor and water unsuitable for drinking
purpose, (ii) four hydrochemical facies which may be assigned to three broad types such as “fresh”, “blended”, and “brackish”
waters, (iii) the evolution of the “blended” water is possibly due to hydraulic mixing of “fresh” and “brackish” waters within
the aquifer matrix and/or in well mixing, and (iv) absence of Na–Cl facies indicates continuous flushing of the aquifer. 相似文献
10.
AbstractWater supply to the world’s megacities is a problem of quantity and quality that will be a priority in the coming decades. Heavy pumping of groundwater beneath these urban centres, particularly in regions with low natural topographic gradients, such as deltas and floodplains, can fundamentally alter the hydrological system. These changes affect recharge area locations, which may shift closer to the city centre than before development, thereby increasing the potential for contamination. Hydrogeological simulation analysis allows evaluation of the impact on past, present and future pumping for the region of Kolkata, India, on recharge area locations in an aquifer that supplies water to over 13 million people. Relocated recharge areas are compared with known surface contamination sources, with a focus on sustainable management of this urban groundwater resource. The study highlights the impacts of pumping on water sources for long-term development of stressed city aquifers and for future water supply in deltaic and floodplain regions of the world.Editor D. KoutsoyiannisCitation Sahu, P., Michael, H.A., Voss, C.I., and Sikdar, P.K., 2013. Impacts on groundwater recharge areas of megacity pumping: analysis of potential contamination of Kolkata, India, water supply. Hydrological Sciences Journal, 58 (6), 1340–1360. 相似文献