639 research outputs found
Impact of sea level rise and tidal effects on flux-controlled and partially isolated shallow aquifer on the southeast coast of India
No full textA rise in sea level is the most important threat to the coastal aquifers in which the intensity of threat also depends on the local hydrogeological settings. The present study seeks to identify the impacts of sea level rise and tidal effects on the shallow and complex aquifer located south of Chennai, India. The aquifer geometry is isolated dune surfaces due to the presence of enclosing saline surface water. The freshwater is available as an elongated lens, and replenishment occurs by rainfall, with limited regional influx. Numerical simulation was carried out to understand the response of groundwater table to sea level rise until the year 2100. Initially, the tidal effects were investigated for the duration of 3 years. A sinusoidal fluctuation of groundwater table is noticed only in the northern part and the tidal impact seems infinitesimal because of steep hydraulic gradient in the south. Simulation of groundwater table without considering sea level rise predicts a decline in the elevation of groundwater table/freshwater lens by − 0.35 m in the dune surfaces. The simulation with reported sea level rise of 2 mm year −1 with the same rate of groundwater pumping results in a total increase of 0.5 m in groundwater table. The study infers that the tidal effects are high in the shallow groundwater gradient, and sea level rise will be beneficial to the isolated coastal freshwater aquifers by increasing the elevation of groundwater table/freshwater lens and further deepening the interface between seawater and freshwater
A box-model approach for reservoir operation during extreme rainfall events: A case study
No full textExtreme rainfall events in an urban area pose various challenges to the water resource managers in terms of flood mitigation, inundation, water conservation and harvesting for drinking water supply. The objective of this study is to apply the box-model approach to evaluate reservoir operation during extreme rainfall events. A large water supply reservoir in Chennai was chosen to carry out this study. A box model, based on input–output parameters, is proposed to simulate the reservoir operation and hydraulic behaviour. Hydrologic Engineering Centre-Hydrologic Modelling System (HEC-HMS) has been used to simulate the reservoir inflow hydrograph and to understand the run-off characteristics of the basin. Three extreme rainfall events occurred in past have been selected for the analysis. Three different scenarios have been framed to assess the reservoir performance. Reducing the initial storage to 50% and releasing water at the beginning of the event gives a possible solution for flood mitigation in reducing the outflow volume by 9–37% and delaying the time to peak by 1–6 h. Though the reduced outflow volume from this reservoir is less, it can help to mitigate the flood inundation to a significant extent. Thus the box-model approach presented here can be utilised as a simple tool to generate the various combinations of outflow hydrographs for any reservoir
Groundwater management in alluvial, coastal and hilly areas
No full textGroundwater plays a major role in the modern world being used for drinking, irrigation and industrial development. The increasing population and developments in agricultural and industrial sectors depends on groundwater as it is a reliable source, and so it leads to overexploitation of groundwater without due regard to the recharging capacity of the aquifers. Groundwater extraction from most of the aquifers around the world has exceeded its recharge capacity, and hence the water table has gone down drastically leading to adverse environmental consequences like land subsidence and water quality deterioration. A proper assessment of groundwater resource should be undertaken to ensure sustainable management of groundwater. Hence, the present study proposes empirical methods for the sustainable groundwater resource management in alluvial, coastal and hilly regions
Discrete Boltzmann Equation model of polydisperse shallow granular flows
No full textA polydisperse shallow mixture consisting of N p solid phases (N p ≥ 1) and one fluid phase (the ambient fluid) is a reliable model for several industrial and environmental flows, as e.g. landslides, avalanches, debris flows and fluidized beds. The description and prediction of these flows is of primary importance, mainly with respect to the mitigation and protection from natural hazards. This paper is aimed at deriving the polydisperse shallow granular flow equations by depth-averaging mass and momentum equations of the mixture and at formulating an equivalent Discrete Boltzmann Equation (hereinafter DBE) model as solution method. The reason is the simplicity and the versatility of the DBE, which consists of a set of purely advective, linear, first order partial differential equations, whose numerical integration does not need sophisticated methods. Both 1D and 2D benchmarks, concerning with the propagation of discontinuities in three-phase shallow granular flows, are obtained by applying the finite differences Lax-Friedrichs (hereinafter LF) method to the polydisperse shallow granular flow equations. The overall agreement is good, showing that the DBE and the LF numerical results are equivalent
Assessment of seawater mixing in a coastal aquifer by high resolution electrical resistivity tomography
No full textSeawater intrusion is a major problem in urbanized coastal regions of India which is due to over exploitation of groundwater for various purposes. This study was carried out with the objective of assessing the zone of mixing between seawater and groundwater in the coastal aquifer in south of Chennai, Tamil Nadu, India using high resolution electrical resistivity tomography. High resolution electrical resistivity tomography was carried out in five profiles perpendicular to the sea using IRIS make SYSCAL Pro-96 system with 2.5 m or 5 m inter-electrode separation. The maximum length of the profile was 170 m which resulted in a depth of investigation of 28.7 m. The apparent resistivity measured in this area varies from 0.3 ohm-m to 30,000 ohm-m. The apparent resistivity of saturated zone decreases towards the sea, indicating the influence of seawater. This was also confirmed by measuring the electrical conductivity of groundwater, which gradually increases from 156 μS/cm to 3430 μS/cm towards the sea. Further, the concentration profiles of electrical conductivity, sodium, chloride and chloride / bicarbonate ratio are compared with the high resolution electrical resistivity tomography profile. The distance of influence of seawater is comparatively high in northern part than in southern part of the area. The high resolution electrical resistivity tomography was effectively used to determine the effect of seawater mixing with groundwater. © IRSEN, CEERS, IAU
INITIAL PRODUCTION OF DEFECTS IN ALKALI-HALIDES - F AND H CENTER PRODUCTION BY NON-RADIATIVE DECAY OF SELF-TRAPPED EXCITON
No full textRadiation damage in KCl can be produced by the decay of a self-trapped exciton into an F centre and an H centre. The authors present calculations of the energies of the states involved for various stages in the evolution of the damage. These lead to important conclusions about the very rapid damage process, and support strongly Itoh and Saidoh's suggestion (1973) that damage proceeds through an excited hole state. The results also help in understanding the prompt decay of F and H pairs at low temperatures, the thermal annihilation of F and H centres, the effects of optical excitation of the self-trapped exciton, and some of the trends within the alkali halides. The calculations use a self-consistent semi-empirical molecular-orbital method. A large cluster of ions is used (either 42 or 57 ions) plus long-range Madelung terms. The ion positions were obtained from separate lattice-relaxation calculations with the HADES code. The choice of CNDO parameters and the adequacy of the method were checked by a number of separate predictions
Quantum chemical and dynamical approaches to intra and intermolecular kinetics: The CnH2nO (n = 1, 2, 3) molecules
No full textAn account is given of isomerization and decomposition paths in the title molecules, as obtained by characterizing stable isomers and transition states using quantum chemistry and reaction rate theories. For n 1⁄4 1 (formaldehyde) intrinsic reaction paths are calculated to provide rates for decomposition mechanisms dominated by quantum mechanical tunneling. The n 1⁄4 2 closed shell isomers are acetaldehyde, ethylene oxide, and vinyl alcohol, which interconvert and decompose through alternative paths. For n 1⁄4 3, the very large number of isomers are characterized using an efficient automatic search algorithm recently made available by Ohno and Maeda. Interconversion paths are also found, including those involving chiral change mechanisms for propylene oxide
Temperature Dependence of Chemical and Biphysical Rate Processes: Phenomenological Approach to Deviation from Arrhenius Law
No full textM(P) M(W) M M(S) (s1) ���� M(T) M∗(s2) �� M M(V)
No full textii This thesis is the result of my own work and includes nothing which is the outcome of work done in collaboration except where specifically indicated in the text. This work has not been submitted for a higher degree to any other university or institution
Depth averaged modelling of loose rectangular granular piles collapsing in water
No full textThe collapse of a submerged granular pile under the action of the gravity force is investigated by means of a depth averaged model (hereinafter DAM). The granular pile is a mixture of solid particles and ambient liquid, totally covered by a layer of ambient liquid. The DAM is obtained by depth-averaging the mass and momentum equations of the mixture and the ambient fluid and is aimed at providing estimates of technical quantities regarding the considered phenomenon. The DAM is numerically solved by adopting an equivalent Discrete Boltzmann Equation model (hereinafter DBE) as solution method. The main advantage yielded by the DBE is the possibility to turn the original system of strongly non linear partial differential equations, which would require the resort to complex numerical schemes, into a purely advective, linear, first order one. Previously published experimental and numerical data, relative to the collapse of loose rectangular granular piles in water, are reproduced by the proposed model and a satisfactory agreement is found, revealing that the DAM is able to describe reliably the overall dynamics, in terms of quantities of technical interest as the height of the submerged granular flow and the instantaneous position of its front
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