Impact of Farakka barrage on the hydrology and fishery of Hoogly estuary     

M. Sinha  M. K. Mukhopadhyay  P. M. Mitra  M. M. Bagchi  H. C. Karamkar 《Estuaries and Coasts》1996,19(3):710-722

Construction of the Farakka barrage on the Ganga River in April 1975 to augment water supply to the Calcutta port has brought about a significant increase in freshwater discharge in its distributary, the Hoogly estuary. This has naturally resulted in major changes in the ecology of this estuary, causing modifications in the structure of its fishery resources, fishing pattern, and fish production. This paper presents observations on salinity, plankton, bottom biota, fishery resource, and fish production of different zones of the Hooghly estuary during the period 1982–1992. Comparison with similar studies made before and immediately after commissioning of the Farakka barrage (1975–1977) has revealed that the increased freshwater discharge has resulted in considerable decrease in salinity throughout the estuary. The freshwater zone now extends toward the mouth of the estuary. The true estuarine zone has moved seaward and the marine zone has been restricted to the area near the mouth of the estuary. This has effected major changes in plankton dynamics, sharp decline in the fishery of marine and neritic species in the upper estuary, caused a significant increase in catch ofTenualosa ilisha and an over twofold increase in the average annual fish landings from the estuary as a whole. New zonations have been proposed based on the presently, observed salinity values, which are the most significant factor in determining the fishery of any estuary. An interdisciplinary study of the ecology of the new zones is needed to establish their correct biological characteristics.  相似文献   

On the propagation of plane waves in a porous visco-elastic material containing a fluid and deformed by a magnetic field     

Dilip K. Sinha 《Pure and Applied Geophysics》1964,59(1):27-32

Summary In the present note, an attempt has been made to investigate the wave-motions in a poro-viscoelastic medium traversed by a static magnetic field, by using the equations ofMaxwell, and those ofBiot.  相似文献   

Isotopic evolution of common lead     

A.Krishna Sinha  George R. Tilton 《Geochimica et cosmochimica acta》1973,37(8):1823-1849

The isotopic composition of lead from galenas and feldspars of granitic rocks covering a time span of 3600 m.y. is reviewed. Hew data are combined with data from the literature, all ratios being normalized to a fixed value for the isotopic composition of lead in an inter-laboratory reference sample. Comparison of feldspar and galena results show that the isotopic composition of initial lead in granitic rocks may be identical to, or more radiogenic than, that in coeval stratiform (or ‘single stage’) ore deposits. The isotopic evolution of terrestrial lead over the past 3600 m.y. deduced from the stratiform ore data does not fit the closed system source. The data are best fitted to evolution models in which the value of μ (U²³⁸/Pb²⁰⁴ normalized to the present day) in the source has increased either over approximately the past 3.6 billion years or since the time of formation of the Earth. A limited number of high precision data for strontium likewise indicate open system isotopic evolution. In this system the Rb/Sr ratio appears to have decreased as a function of time. Physical models that explain the data are presented. Either mantle differentiation or crustal contamination processes could account for the change in μ in the source for the lead. The strontium data and some detailed studies of the isotopic composition of lead in oceanic volcanic rocks support mantle differentiation rather than crustal contamination. The exact nature of the mantle differentiation process cannot be specified, although empirical data favoring the existence of such a process are given. The best estimate of the age of the Earth, calculated with the data from 2750 and 3290 m.y.-old lead ores, is 4660 m.y.  相似文献   

An elegant coupled model     

Chanchal Guha-Roy  Dilip Kumar Sinha 《大气科学进展》1993,10(2):257-260

This paper deals with a new family of coupled wave equations which are basically nonlinear in nature. An analyt-ical study enables us to show that these equations exhibit solitary wave profiles. Finally some remarks are drawn from the standpoint of atmospheric problem.  相似文献   

Geomorphology and landuse of Pasighat-Jonai bazar area-A photo based study in a part of Dihang river basin,Arunachal pradesh and Assam     

K. K. Sinha  A. U. Khan 《Journal of the Indian Society of Remote Sensing》1981,9(2):21-26

Photo-interpretation coupled with systematic field checks over an area of about 1500 sq. km has led to the identification of various landform units and their characteristic landuse pattern in part of the submontaneous tract of Arunachal Pradesh and Assam in the Dihang river basin. Four major geomorphic units have been mapped and their respective lithounits are studied in detail. Present landuse and the land’s capability inrespect of each of the major geomorphic units have been noted. Suggestions have been made for better utilisation of land.  相似文献   

A note on visual interpretation of landsat imagery to locate possible locust habitat in a part of Rajasthan     

P. P. Sinha 《Journal of the Indian Society of Remote Sensing》1980,8(2):7-10

Visual interpretation of Landsat data from an area in Rajasthan desert has been used to delineate vegetation and other associated parameters helpful for locust breeding and development. The results indicate the usefulness of Landsat in date locust surveys by reducing time and cost involved.  相似文献   

On the random motion of a uniform beam in a magnetic field     

D. K. Sinha 《Pure and Applied Geophysics》1972,99(1):94-98

Summary The present note is concerned with the investigation of responses under random processes of a beam-plate placed in a magnetic field which is transverse in nature. The distinctive features of the motion have been pointed out.  相似文献   

Transmission of elastic waves through a second-order fluid layer sandwiched between elastic media     

Arabinda Biswas  S. B. Sinha 《Pure and Applied Geophysics》1970,78(1):42-47

Summary The present paper is concerned with the transmission of elastic waves through a second-order fluid layer sandwiched between homogeneous elastic media having identical properties. It is concluded that the transmission ratio increases with the increasing absolute values of visco-elastic co-efficient and also with the wavelength of the wave transmitted.  相似文献   

Induction of thymine dimers by solar radiation in natural freshwater phytoplankton assemblages in Patagonia, Argentina     

Manfred Klisch  Rajeshwar P. Sinha  E. Walter Helbling  Donat-P. Häder 《Aquatic Sciences - Research Across Boundaries》2005,67(1):72-78

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Landscape level disturbance gradient analysis in daltonganj south forest division     

R. K. Sinha  Arabinda Sharma 《Journal of the Indian Society of Remote Sensing》2006,34(3):233-243

Disturbance, man-made or natural, is an innate process of any landscape. Disturbance gradient analysis provides insight into the disturbance status of forest which is useful for forest management. In the present study new landscape metrics are introduced through FRAGSTATS 3.3 software for analyzing both anthropogenic and natural disturbance pattern of Daltonganj south forest division of Jharkhand state. Various landscape indices were used for natural disturbance analysis. Anthropogenic disturbance was measured as function of the proximity of landscape to roads and settlements. It was observed that the forests of the study area are experiencing varied degrees of disturbances. The software in combination with ARC VIEW Spatial Analyst was found to be a cost effective and user friendly landscape analysis tool.  相似文献