Natural Hazards - A hazard map is a map which shows about all the vulnerable regions present in any country or at any specific place or location which is affected or will be affected by natural... 相似文献
Hydrochemical study had been carried out on the groundwater resources of Potharlanka Island, Krishna delta, India. Groundwater
samples were collected and analyzed at 42 sites in December 2001 and October 2006. A comparative study of hydrochemical data
indicates: groundwater is mildly alkaline with a pH of 7.0–8.2; electrical conductivity (EC) varies from 605 to 5,770 μS/cm
in December 2001, and 652–5,310 μS/cm in October 2006. More than 62% of the groundwater samples in 2006 have TDS value <2,000 mg/l,
which is within permissible limit of potable water, but 57% of the samples in 2001, are higher than the maximum permissible
limit. Extremely low HCO3/Cl and variable high Mg/Ca (molar ratios) had been indicated the transformation of the fresh groundwater aquifer systems
to saline in 2001. Groundwater of this Island is mainly classified as Na–Cl and mixed types. A high percentage of Na–Cl type
of these waters indicates the possibility of seawater ingression/intrusion process during 2001 and comparatively mixed water
type indicates the dilution activities of groundwater. Excessive withdrawal of groundwater has caused the increase of saline
water intrusion. Improvement of groundwater quality in this Island due to artificial recharge structures made by NGRI under
RGNDWM project and affects of the flood due to heavy rainfall of the months of September–October 2005 are discussed in this
paper. 相似文献
Water is the most important natural resource which forms the core of the ecological system. The advent of remote sensing has
opened up new vistas in groundwater prospect evaluation, exploration and management. The groundwater resources of the study
area, Rishikesh region of Garhwal Himalayas, are under threat due to population pressure caused by expanding tourism in this
region. This entails sustainable and judicious use of this precious resource. The groundwater prospect evaluation in Rishikesh
region has been attempted based on hydrogeomorphological mapping of the area consisting of thematic maps of hydrogeomorphology,
geology, drainage, lineament, slope and relief using high resolution IRS-1C LISS III and PAN merged satellite images. The
Rishikesh region exhibits diverse hydrogeomorphological conditions where the groundwater regime is controlled mainly by topography
and geology. A probability-weighted approach has been applied during overlay analysis in ArcMap GIS environment. The overlay
analysis allows a linear combination of weights of each thematic map with respect to ground water potential. Good groundwater
prospects dominate in the area with more than 50% of the study area showing moderate to excellent potential. The study shows
that the remote sensing and geoinformatics techniques can be applied effectively for groundwater prospect evaluation. 相似文献
The variation of temporal fractal dimension D2 (t) value may be well applied for understanding the future large earthquakes. In this present analysis the time series of inter-occurrence of earthquakes of consecutive hundred events window in Himalayan region is analyzed. We observed the variation in D2 (t) values in the range of 0.19 to 0.68 indicating the variation of clustering of events with respect to time. The multifractal nature of earthquakes is also investigated by plotting Dq(t) versus q. The result shows the temporal distribution of earthquakes have multifractal structure of definitive pattern rather than random pattern. 相似文献
One of the major aspects of rock-physics forward modelling is to predict seismic behaviour at an undrilled location using drilled well data. It is important to model the rock and fluid properties away from drilled wells to characterize the reservoir and investigate the root causes of different seismic responses. Using the forward modelling technique, it is possible to explain the amplitude responses of present seismic data in terms of probable rock and reservoir properties. In this context, rock-physics modelling adds significant values in the prospect maturation process by reducing the risk of reservoir presence in exploration and appraisal phases. The synthetic amplitude variation with offset gathers from the forward model is compared with real seismic gathers to ensure the fidelity of the existing geological model. ‘Prospect A’ in the study area has been identified from seismic interpretation, which was deposited as slope fan sediments in Mahanadi basin, East Coast of India. The mapped prospect has shown class-I amplitude variation with offset response in seismic without any direct hydrocarbon indicator support. The existing geological model suggests the presence of an excellent gas reservoir with proven charge access from the fetch area, moderate porosity and type of lithology within this fan prospect. But, whether the seismic response from this geological model will exhibit a class-I amplitude variation with offset behaviour or ‘dim spot’ will be visible; the objective of the present study is to investigate these queries. A rock-physics depth trend analysis has been done to envisage the possibilities of class-I reservoir in ‘Prospect A’. Forward modelling, using a combination of mechanical and chemical compaction, shows the synthetic gas gathers at ‘Prospect A’, which are class I in nature. The study has also depicted 2D forward modelling using lithology and fluid properties of discovery well within similar stratigraphy to predict whether ‘dim spot’ will be seen in seismic. The estimated change in synthetic amplitude response has been observed as ∼5% at contact, which suggests that the changes will not be visible in seismic. The study connects the existing geological model with a top-down seismic interpretation using rock-physics forward modelling technique to mature a deep-water exploratory prospect. 相似文献
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.
Thunderstorm overshooting is rare but not an unusual phenomenon in a metropolitan of India, Kolkata (22.57° N; 88.36° E) during the pre-monsoon months (April–May). An attempt is made in this study to identify the important parameters differentiating the thunderstorms in overshooting and non-overshooting categories through data analytics from 2000 to 2015. The present investigation on parametric classification would facilitate in estimating the predictability of thunderstorms with overshooting which subsequently might assist in operational forecast of thunderstorm severity over Kolkata. The altitudes of lifting condensation level (LCL), wind shear, bulk Richardson number (BRN), gust speed, boundary layer characteristics and their correlation with thunderstorm cloud top height (CTH) and also their variation and distribution during overshooting (OTS) and non-overshooting (TS) thunderstorms are analyzed in this study. The result depicts that over Kolkata the intensity of storms during OTS is higher than during TS though the frequency of OTS is less than that of TS. The results further show that the potential temperature (θ), equivalent potential temperature (θe), mixing ratio (es) in the boundary layer, convective available potential energy, convective inhibition energy, BRN and gust speed play significant roles in regulating the CTH during OTS and TS thunderstorms over Kolkata.
We study the radiation properties of an accretion disc around a rotating black hole. We solve the hydrodynamic equations and calculate the transonic solutions of accretion disc in the presence of shocks. Then we use these solutions to generate the radiation spectrum in the presence of radiative heating and cooling processes. We present the effect of spin parameter of the black hole on the emitted radiation spectrum. In addition, attention has also been paid to the variation in energy spectral index with Kerr parameter and accretion rate. We find that spectral index becomes harder as the spin parameter changes from negative (accretion disc is counter-rotating with respect to the black hole spin) to a positive value. Finally, we compute and compare the spectral characteristics due to a free-fall flow and a transonic flow. We notice significant differences in high energy contributions from these two solutions. 相似文献
A major problem of the islanders is the availability of fresh water for drinking purpose. Groundwater is the only source of fresh water for the islanders. The demand for groundwater is increasing very year due to growing population and urbanization. A proper understanding of the groundwater condition is important in order to meet this increasing demand and to formulate future development and management strategies. It is in this context, principal hydrogeologic units; water table fluctuation pattern, general groundwater potential, existing groundwater withdrawal structures and draft, water quality, etc. have been studied in an elliptical shape Andrott Island of Union Territory of Lakshadweep, India, through field investigation and secondary data collection. Groundwater occurs under phreatic condition and seawater is in hydraulic continuity with the groundwater as evidenced by the tidal influence in almost all the wells. Groundwater level fluctuation due to seasonal variation varies from 0 to 0.542 m depending on the distance of the well from the coast. Depth to groundwater level varies from less than 1.234 to 3.520 m depending on the topography. Groundwater level fluctuation is due to the combination of factors like rainfall, tidal activities, sub-surface runoff, and draft. Large diameter dug wells are the main groundwater extraction structures in this island. There are 2,143 dug wells with almost each family having its own well and the density of the dug wells is about 437/km2. The stage of groundwater development is estimated as 37% and hence “Safe” for further groundwater development in this island. However, considering the very limited fresh-water resources and also the growing demand for groundwater, various management strategies such as rainwater harvesting, artificial recharge of groundwater, public participation in water conservation and wise use of groundwater, etc., have been suggested. 相似文献
