Dam-break flood simulation under various likely scenarios and mapping using GIS: Case of a proposed dam on River Yamuna, India

The precision modeling of dam break floods can lead to formulation of proper emergency action plan to minimize flood impacts within the economic lifetime of the assets.Application of GIS techniques in integration with hydrological modeling for mapping of the flood inundated areas can play a momentous role in further minimizing the risk and likely damages.In the present study,dam break analysis using DAMBRK model was performed under various likely scenarios.Probable Maximum Flood (PMF)calculated for a return period of 1000 years using deterministic approach was adopted for dam break analysis of the proposed dam under various combinations of breach dimensions.The available downstream river cross-sections data sets were used as input in the model to generate the downstream flood profile.Dam break flow depths generated by the DAMBRK model under various combinations of structural failure are subsequently plotted on Digital Elevation Model(DEM)of the downstream of dam site to map the likely affected area.The simulation results reveals that in one particular case the flood without dam may be more intense if a rainfall of significant intensity takes place.     

Study of high and low amplitude wave trains of cosmic ray diurnal variation during solar cycle 23

A detailed study has been conducted on the long-term changes in the diurnal variation of cosmic rays in terms of high and low amplitude wave trains event (HAEs/LAEs) during the period 1996–2008 (solar cycle 23), using the neutron monitor data from Kiel neutron monitoring station. As such, 17 HAE and 48 LAE cases have been detected and analyzed. These HAEs appear quite dominantly during the declining phase as well as near the maximum of the solar activity cycle 23. In contrast, the low amplitude events (LAEs) are inversely correlated with solar activity cycle. In fact, LAEs appear quite dominantly during the minimum phase of the solar activity. When we compare our results for diurnal phase with that observed on an annual average basis, we notice no significant diurnal phase shift for HAEs as well as for LAEs. Moreover, we find that the high-speed solar wind streams (HSSWS) do not play any significant role in causing these variations. These results are discussed on the basis of that observed in earlier cycles.     

Mean sea level determination from satellite altimetry

The primary experiment on the Geodynamics Experimental Ocean Satellite‐3 (GEOS‐3) is the radar altimeter. This experiment's major objective is to demonstrate the utility of measuring the geometry of the ocean surface, i.e., the geoid. Results obtained from this experiment so far indicate that the planned objectives of measuring the topography of the ocean surface with an absolute accuracy of ±5 m can be met and perhaps exceeded. The GEOS‐3 satellite altimeter measurements have an instrument precision in the range of ±25 cm to ±50 cm when the altimeter is operating in the “short pulse”; mode. After one year's operations of the altimeter, data from over 5,000 altimeter passes have been collected. With the mathematical models developed and the altimeter data presently available, mapping of local areas of ocean topography has been realized to the planned accuracy levels and better. This paper presents the basic data processing methods employed and some interesting results achieved with the early data. Plots of mean sea surface heights as inferred by the altimeter measurements are compared with a detailed 1^o × 1° gravimetric geoid.     

Evolution of Ganges–Brahmaputra western delta plain: Clues from sedimentology and carbon isotopes

Sedimentology, carbon isotope and sequence stratigraphic analysis of subsurface sediments from western part of Ganges–Brahmaputra (GB) delta plain shows that a Late Quaternary marine clay and fluvial channel-overbank sediments of MIS 5 and 3 highstands are traceable below the Holocene strata. During the Last Glacial Maximum (LGM) sea-level lowering of >100 m produced a regional unconformity (type 1), represented by palaeosols and incised valley. C4 vegetation expanded on exposed lowstand surface in an ambient dry glacial climate. At 9 ka transgression inundated the lowstand surface pushing the coastline and mangrove front 100 km inland. Simultaneous intensification of monsoon and very high sediment discharge (4–8 times than modern) caused a rapid aggradation of both floodplain and estuarine valley fill deposits between 8 and 7 ka. The Hoogli River remaining along its present drainage possibly acted as the main conduit for transgression and sediment discharge that was subsequently abandoned. C3 vegetation dominated the delta plain during this time. From 7 ka onward progradation of delta plain started and continued till recent. This period experienced a mixed C3–C4 vegetation with localized mangroves in the mid-Holocene to dominant return of C4 vegetation in the late Holocene period. The study indicates that while the initiation of western part of GB delta occurred at least 1 ka earlier than the global mean delta formation age, the progradation started at 7 ka, at least 2 ka earlier than thought before. The terrestrial vegetation change was modulated by changes in depositional environment, specific ecological niches and climate rather than pCO₂.     

Effect of the presence of a conducting channel between India and Sri Lanka Island on the features of the equatorial electrojet

Summary. Transient geomagnetic variations like SSCs, Bays, Sq and storm-time variations show anomalously large Z amplitudes at the three permanent magnetic observatories in India under the equatorial electrojet. Our earlier studies have shown that these anomalies cannot be explained in terms of the usual coastal effect. Another unique feature of this area is the small equatorial enhancement of all magnetic fluctuations, which still remains to be completely understood. It is also noticed that Z/H ratio at Annamalainagar is very large for night-time variations but becomes insignificant for day-time fluctuations, whereas no such large difference is seen at Trivandrum, the other coastal station. All the above features have been explained here by introducing the presence of a conducting channel in the lower crust or upper mantle between India and Sri Lanka Island. The anomalies of the equatorial electrojet in the Indian region thus do not necessitate the conducting surface of the mantle to be deeper in this area as has been suggested by earlier workers. A less conducting mantle in the Indian region otherwise could be difficult to incorporate in the present theories of mantle convection when this area is known to be tectonically active. The presence of the conducting channel is further confirmed by analogue model experiments of Papamastorakis. We further observe that the equatorial electrojet does have an associated internal part in the Indian region.     

Heat and mass transfer of an oscillatory flow with Hall current,II

An analysis of Hall current on the combined effects of thermal and mass diffusion of an electrically conducting liquid past an infinite vertical porous plate is performed. Analytical expressions for the transient velocity, the transient temperature in the boundary layer and the skin-friction on the plate are derived. The effects of various parameters on the velocity, temperature, shearing stresses and rate of heat transfer are shown by graphs and tables.     

Evidence of low density sub-crustal underplating beneath western continental region of India and adjacent Arabian Sea: Geodynamical considerations

The known high mobility of the Indian subcontinent during the period from 80 to 53 Ma has evoked considerable interest in recent times. It appears to have played an important role in shaping the subcontinental structures of western India and the adjoining Arabian Sea. During this period, a major catastrophic event took place in the form of Deccan volcanism, which coincides with the biological mass extinction at the K-T boundary, including the death of dinosaurs. The origin of Deccan volcanism is still being debated.Geophysically, western India and its offshore regions exhibit numerous prominent anomalies which testify to the abnormal nature of the underlying crust-lithosphere. In this work, we develop a two-dimensional structural model of these areas along two long profiles extending from the eastern basin of the Arabian Sea to about 1000 km inland. The model, derived from the available gravity data in the oceanic and continental regions, is constrained by seismic and other relevant information in the area, and suggests, for the first time, the presence of an extensive low-density (2.95–3.05 g/cm³) sub-crustal underplating. Such a layer is found to occur between depths of 11 and 20 km in the eastern basin of the Arabian Sea, and betweeen 45 and 60 km in the continental region where it is sandwiched in the lower lithosphere. The low density may have been caused as a result of serpentinization or fractionation of magma by a process related in some way to the Deccan volcanic event. Substantial depletion of both oceanic and continental lithosphere is indicated. We hypothesize that the present anatomy of the deformed lithosphere of the region at the K-T boundary is the result of substantial melt generated owing to frictional heat possibly giving rise to a hot cell like condition at the base of the lithosphere, resulting from the rapid movement of the Indian subcontinent between 80 and 53 Ma.     

Palaeoclimate,stratigraphy and prehistory in north and west Rajasthan

Quaternary formations in western Rajasthan are of fluvial, locustrinal and aeolian origins. Fossil gravel ridge of Jayal in Nagaur District is one of the earliest quaternary formations so far recorded in the region. A rich lower palaeolithic habitation-cum-workshop site has been discovered in association with the gravel ridge. Multiple evidence for climatic change in the area during the quaternary period is discussed.     

X-Ray emission from the pleiades cluster

Detection of a new X-ray source and its identification with the Pleiades cluster is reported here. The new X-ray source has an X-ray luminosity of ～10³² ergs s^?1 in the 0.15–3.0 keV energy band. The observed X-ray emission could be explained as integrated emission from a large number of stars in the cluster.