Hydrochemical framework of the aquifer in and around East Kolkata Wetlands,West Bengal,India

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.     

Microwave D-InSAR technique for assessment of land subsidence in Kolkata city,India

An effective microwave Differential Interferometric Synthetic Aperture Radar (D-InSAR) technique was used to rapidly assess the potential land subsidence with high precision by exploiting the phase difference of two temporally separated SAR data in the region of Kolkata city, India. The objective of this study is to assess land subsidence using D-InSAR technique and to delineate the regions of land subsidence caused by over exploitation of groundwater by minimising the errors by applying topographic and atmospheric corrections. The study area forms a part of Indo-Gangetic plain. Three ENVISAT Advanced Synthetic Aperture Radar ?(ASAR) images of the years 2003, 2007 and 2010 were acquired to study the temporal evolution of land subsidence in the study area. The phase changes due to topography in the interferograms were removed by using Shuttle Radar Topography Mission (SRTM) degital elevation model data. Medium Spectral Resolution Imaging Spectrometer (MERIS) data were applied to remove the atmospheric noise in the interferogram. The deformation fringes were observed in the northern and central part of the study area where the land subsidence was 12 and 18 mm during the years of 2003–2007 and 2007–2010. The regional variation in the piezometric head compares well with the fringes of the interferogram. This confirms over extraction of groundwater is the main cause for land subsidence in this region. Hence, it is necessary to reduce groundwater pumping and to augment rainfall recharge in northern part of the study area.     

Factors influencing willingness to comply with HIV/AIDS prevention measures by female college students in Kolkata,West Bengal,India

With a 2.4 million people living with Human Immunodeficiency Virus (HIV), India is among the countries in the world most vulnerable to the spread of HIV. This study focuses on understanding what makes female college students (ages 18–24) in Kolkata, India willing to comply with HIV/AIDS preventive measures; these students are widely believed to be at low risk of infection with HIV. Through a questionnaire survey, the data used in this study was collected from 232 female students attending five higher education institutes. Multiple regression analysis reveals that religion, household income, perception of whether preventive measures would hamper freedom, and respondents’ perception of the effectiveness of preventive measures all influence the students’ willingness to comply with preventive measures. Based on its findings, the study makes several recommendations to improve HIV/AIDS prevention in Kolkata and West Bengal, India.     

Study of subsurface geology in locating arsenic-free groundwater in Bengal delta,West Bengal,India

Over a large area of the Bengal delta in West Bengal, India, arsenic distribution patterns in groundwater were studied. One hundred and ten boreholes at different target locations were made, subsurface sediments were logged and analysed, and arsenic values in sediments vis-à-vis groundwater were compared. The study elucidates the subsurface geology of the western part of Bengal delta and characterises the sediments that were intersected in different boreholes with contrasting values of arsenic in groundwater. It reveals an existence of multiple aquifers stacked over each other. Depending on the color and nature of aquifer-sands and their overlying clay beds six aquifer types (Type-1 to Type-6) are classified and described. Sediment-arsenic for all the varieties of aquifer sands are near similar but the groundwater-arsenic of these six aquifers varies widely. Type-2 and Type-5 aquifers host arsenic-contaminated groundwater whereas the other four aquifers are arsenic-free. Type-2 and Type-5 aquifers are capped by a grey to dark grey soft organic matter-rich clay unit which makes these aquifers semi-confined to leaky-confined. These contribute in releasing arsenic from the sediments. The results of this study are employed in a proposed georemedial measure against this hazardous toxic element.     

Geochemistry of groundwater,Burdwan District,West Bengal,India

Hydrogeochemical investigations are carried out in the different blocks of Burdwan district, West Bengal, India in order to assess its suitability for drinking as well as irrigation water purpose. Altogether 49 representative groundwater samples are collected from bore wells and the water chemistry of various ions viz. Ca²⁺, Mg²⁺, Na⁺, K⁺, CO₃²⁻, HCO₃⁻, Cl⁻, SO₄²⁻ and NO₃⁻ are carried out. The chemical relationships in Piper and Gibbs diagram suggest that the groundwater mainly belongs to alkali type and Cl⁻ group and are controlled by rock dominance. A comparison of groundwater quality in relation to drinking water quality standards proves that most of the water samples are suitable for drinking water purpose whereas groundwater in some areas of the district has high salinity and high sodium adsorption ratio (SAR), indicating unsuitability for irrigation water and needs adequate drainage.     

广州金沙洲地面沉降成因分析

广州金沙洲是地面沉降危害较严重的地区之一,目前已形成7个沉降区域,沉降总面积约71×104m2,2007年起至2009年3月,是金沙洲地面沉降地质灾害的高发期,这一时期正是某高铁隧道在金沙洲施工阶段。据广州市地质调查院地下水动态监测及地面沉降监测结果,地下水的波动变化与地面沉降具有良好的对应关系,沉降区域沿区内北东向断裂带展布,地面沉降量等值线的展布方向与断裂走向大致一致。各沉降区域沉降中心大多位于断裂带或断裂的交汇部位等特点,据调查,金沙洲地面沉降与软土、正长斑岩风化土、砂土、断裂构造及地下水等因素有关。研究结果表明:复杂的地质环境条件是金沙洲发生地面沉降的客观因素,某高铁隧道施工大量抽排地下水是诱发和加剧地面沉降的主要因素。     

Assessment of land-use change and its impact on the environment using GIS techniques: a case of Kolkata Municipal Corporation,West Bengal,India

It is axiomatically true that urbanization in India's metropolises and large cities has been exacerbated since the beginning of the millennium, consuming the natural and semi-natural ecosystem on the outskirts of the city, resulting in a zone with a distinct climate known as urban climate. Such a climate—the result of a built-up environment is distinctly different from the natural climate as the paved surface and concrete skyscrapers not only destroy the natural ecosystem, it peculiarly induce a different kind of insolation, cooling and air drainage were lacking in green space, water bodies and open space cannot accommodate with environmental rhythm properly, resulting into the accumulation of heat, ecological derangement of subsurface soil which can easily be predicted by GIS analysis. This paper is an attempt to measure urban growth and its impact on the environment in the metropolitan city Kolkata. The use of satellite data and GIS techniques to detect urban expansion is a highly scientific strategy. Using geospatial techniques, the current study attempts to examine major urban changes in Kolkata and its surroundings from 1988 to 2021. Landsat 5 TM and Landsat 8 OLI temporal data are used to identify land-use change through unsupervised classification; Spectral Radiance Model and Split Window Algorithm method are used for identifying land surface temperature change. SRTM DEM (30 m) has been used to identify flood risk zones and several spectral indices like Normalized Difference Vegetation Index and Modified Normalized Difference Water Index are a further extension for environmental assessment. By all such suitable methods, a clearer change in an urban environment is detected within the period of 33 years (1988–2021). The result shows that the population changes, vegetation cover and built-up area, and accessibility are at a rapid rate. These changes are causing major environmental degradation in the city. The classification result indicates that appropriate land use planning and environmental monitoring are required for the long-term exploitation of these resources.

     

GPS-measured land subsidence in Ojiya City, Niigata Prefecture, Japan

Land subsidence caused by compression of clay layers in Ojiya City, Japan was measured by global positioning system (GPS) between 1 April 1996 and 31 December 1998.

Three baselines were selected in and around the city, and height difference on a WGS-84 ellipsoid was measured by GPS on each baseline. The ground at the GPS station in the city subsides and rebounds 7 cm every winter and spring, respectively. Measurement accuracy was 9.5 mm standard deviation. Ground water level was observed at a well near the GPS station. Regression analysis between total strain, calculated as ratio of the height difference displacement to the total thickness of the clay layers, and the layers' effective stress change with ground water level change gave good correlation. The slope of regression line 7.0×10⁻¹¹ m²/N was obtained as an average apparent coefficient of volume compressibility of the layers.     

Deeper groundwater chemistry and geochemical modeling of the arsenic affected western Bengal basin,West Bengal,India

A regional scale hydrogeochemical study of a ∼21,000-km² area in the western Bengal basin shows the presence of hydrochemically distinct water bodies in the main semiconfined aquifer and deeper isolated aquifers. Spatial trends of solutes and geochemical modeling indicate that carbonate dissolution, silicate weathering, and cation exchange control the major-ion chemistry of groundwater and river water. The main aquifer water has also evolved by mixing with seawater from the Bay of Bengal and connate water. The isolated aquifers contain diagenetically altered water of probable marine origin. The postoxic main aquifer water exhibits overlapping redox zones (metal-reducing, sulfidic and methanogenic), indicative of partial redox equilibrium, with the possibility of oxidation in micro-scale environments. The redox processes are depth-dependent and hydrostratigraphically variable. Elevated dissolved As in the groundwater is possibly related to Fe(III) reduction, but is strongly influenced by coupled Fe–S–C redox cycles. Arsenic does not show good correlations with most solutes, suggesting involvement of multiple processes in As mobilization. The main river in the area, the Bhagirathi–Hoogly, is chemically distinctive from other streams in the vicinity and probably has little or no influence on deep groundwater chemistry. Arsenic in water of smaller streams (Jalangi and Ichamati) is probably introduced by groundwater discharge during the dry season.     

河北省廊坊市地面沉降调查

文章首次系统调查了河北省廊坊市区地面沉降灾害。结果显示，廊坊市区存在较为严重的地面沉降灾害，灾害程度大体可以分为重度、中度和轻度，主要表现为井台相对抬升、拉裂，井房地面鼓起，抽水管变形弯曲。沉降灾害点集中分布在市区西北和东北两个区域，与地下水位降落漏斗相吻合，证明地面沉降是由于开采地下水所致。根据大地水准测量资料分析，自1966年以来廊坊市区地面累积沉降量近800mm，沉降发展分为4个阶段，1966～1978年地壳自然垂直波动阶段、1979～1983年地壳波动下降阶段、1984～1992年地壳持续下降阶段以及1992年以后的地壳加速下降阶段。根据沉降灾害形迹推算，1990～2004年期同累积沉降量120mm，并在近年有加速发展趋势。廊坊地面沉降还处于灾害发展的初期发展阶段。建议制定包括地下水源取代、井位优化分布、采水方案优化、节约用水等措施的综合防治对策，为廊坊城市社会经济的可持续发展提供一个良好的基础环境。     

Implementing Vetiver grass-based riverbank protection programmes in rural West Bengal,India

The largely impoverished rural communities of India are unable to bear the costs involved in creating and maintaining substantial structural measures for riverbank protection. The monsoonal nature of the country’s streams and an agrarian economy based on intensive cultivation further heighten the risk posed by annual peak flows and shifting stream courses. Mitigating this requires urgent, sustainable and cost-effective means of conserving valuable farmlands and stabilising channel boundaries. Towards this, riverbank erosion mitigation using Vetiver grass has been a recent development in the country and has been experimented with in a few areas. In this article, we examine how such riparian buffers are created through riverbank modification, planted and nurtured and the effectiveness of the grass in mitigating erosion, taking a small case study from rural West Bengal as an example. We especially focus on the government policies and frameworks and local stakeholder involvements that facilitate such an undertaking, with particular emphasis on the organisational workflow and the ground-level perception of such endeavours, as these are crucial to the success and effectiveness of such schemes. The marked successes achieved through the use of the Vetiver grass in abating erosion and the hindrances encountered in implementing such mitigation projects are outlined, along with the importance of such community-based approaches to river management and monitoring. This case study can be a microcosm for similar such endeavours, particularly in the rural global south.

     

佛山市瓷海国际陶瓷城地面沉降成因分析

佛山市瓷海国际陶瓷城自2008年起出现地面沉降现象,随着周边人类工程活动增多,地面沉降现象日趋严重.结合研究区地质背景,并运用InSAR地表形变监测技术,从自然因素和人类工程活动两方面研究了该地区地面沉降的形成原因.结果表明,引起地面沉降的内部物质条件为填土和软土的压密固结,尤其是软土分布广、厚度大、埋藏浅,为地面沉降...     

Regional hydrostratigraphy and groundwater flow modeling in the arsenic-affected areas of the western Bengal basin, West Bengal, India

The first documented interpretation of the regional-scale hydrostratigraphy and groundwater flow is presented for a ～21,000-km² area of the arsenic-affected districts of West Bengal [Murshidabad, Nadia, North 24 Parganas and South 24 Parganas (including Calcutta)], India. A hydrostratigraphic model demonstrates the presence of a continuous, semi-confined sand aquifer underlain by a thick clay aquitard. The aquifer thickens toward the east and south. In the south, discontinuous clay layers locally divide the near-surface aquifer into several deeper, laterally connected, confined aquifers. Eight 22-layer model scenarios of regional groundwater flow were developed based on the observed topography, seasonal conditions, and inferred hydrostratigraphy. The models suggest the existence of seasonally variable, regional, north–south flow across the basin prior to the onset of extensive pumping in the 1970s. Pumping has severely distorted the flow pattern, inducing high vertical hydraulic gradients across wide cones of depression. Pumping has also increased total recharge (including irrigational return flow), inflow from rivers, and sea water intrusion. Consequently, downward flow of arsenic contaminated shallow groundwater appears to have resulted in contamination of previously safe aquifers by a combination of mechanical mixing and changes in chemical equilibrium.     

Regional land subsidence simulation in Su-Xi-Chang area and Shanghai City, China

Su-Xi-Chang area and Shanghai City, located in the south of Yangtze Delta, China, has subsided due to groundwater overpumping. Because of the regional scale of the groundwater exploitation, cone of depression and land subsidence at present, Su-Xi-Chang area and Shanghai City are treated as a single area for land subsidence study to avoid the uncertainty of boundary condition due to the regionalism. The characteristics of aquifer system compaction are complex because of the difference in the types, compositions and structures of the soils that the hydrostratigraphic units are composed of, and in the histories of groundwater level change the hydrostratigraphic units have experienced. Considering the fact that different hydrostratigraphic units have different kinds of deformation and that an identical unit may also present different deformation characteristics, such as elasticity, elasto-plasticity, and visco-elasto-plasticity, at different sites of the cone of depression or in different periods, corresponding constitutive laws have been adopted. This avoids the shortcomings of the previous research that the same constitutive law was adopted in all the hydrostratigraphic units during the entire time period. A coupled flow and subsidence model, which includes a three-dimensional flow model with variable coefficients and a one-dimensional (vertical) subsidence model, is built according to the complicated hydrological condition in the region. The simulation model is calibrated using observed data, which include compression of individual strata from groups of extensometers and groundwater levels from observation wells from 1995 to 2002. The model reproduced that the primary subsidence layer in Shanghai shifts from the shallow aquitard to the fourth confined aquifer because of the groundwater yield variations and the change of exploitation aquifers. However the third aquitard was the primary subsidence layer in Su-Xi-Chang area and the compaction deformation of the sandy aquifers was remarkable. The simulation results could provide some reasonable advice about groundwater exploitation in the future.     

上海地面沉降研究的过去、现在与未来

地面沉降是我国东部沿海平原地区城市化进程中,资源与环境如何由对立走向统一的焦点之一.上海地面沉降具有一定的代表性,经几代地质工作者的努力,在地面沉降监测、研究与防治方面取得了一定的经验与成绩.本文初步总结了上海地面沉降研究与防治工作的现状与存在的问题,并分析了我们在新世纪所面临的机遇和挑战.     

哈尔滨市地面沉降预测分析

针对哈尔滨市区地面沉降特点,根据地面沉降痕迹调查,利用岩土工程勘察规范中的“分层总和”法,分别对两个漏斗中心重型机器厂和菅草岭的沉降量进行计算。结果表明,不同的释水厚度、不同的表层黏性土厚度所产生的地面沉降量亦有所不同。到2000年哈尔滨市区两漏斗中心沉降量分别达15.38cm和6.69cm。     

Geochemical evolution of groundwater in southern Bengal Basin: The example of Rajarhat and adjoining areas,West Bengal,India

Detailed geochemical analysis of groundwater beneath 1223 km² area in southern Bengal Basin along with statistical analysis on the chemical data was attempted, to develop a better understanding of the geochemical processes that control the groundwater evolution in the deltaic aquifer of the region. Groundwater is categorized into three types: ‘excellent’, ‘good’ and ‘poor’ and seven hydrochemical facies are assigned to three broad types: ‘fresh’, ‘mixed’ and ‘brackish’ waters. The ‘fresh’ water type dominated with sodium indicates active flushing of the aquifer, whereas chloride-rich ‘brackish’ groundwater represents freshening of modified connate water. The ‘mixed’ type groundwater has possibly evolved due to hydraulic mixing of ‘fresh’ and ‘brackish’ waters. Enrichment of major ions in groundwater is due to weathering of feldspathic and ferro-magnesian minerals by percolating water. The groundwater of Rajarhat New Town (RNT) and adjacent areas in the north and southeast is contaminated with arsenic. Current-pumping may induce more arsenic to flow into the aquifers of RNT and Kolkata cities. Future large-scale pumping of groundwater beneath RNT can modify the hydrological system, which may transport arsenic and low quality water from adjacent aquifers to presently unpolluted aquifer.