This paper presents the results of a trialling of the use of Indian Remote Sensing (IRS) satellite imagery for mapping the geomorphology and physical habitat of the Brahmaputra River in Assam, India. The study was undertaken on a 110 km reach as the river emerges out of the Himalayas; a reach with a complex braid pattern and high levels of channel instability. Image analysis on four sets of IRS data encompassing a period of 13 years (1990)(1991)(1992)(1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002) was undertaken to detect basic changes in the extent and pattern of low flow channels, vegetated islands, exposed sand bars and floodplain vegetation. Simple unsupervised classification techniques were applied to the images. The water surface of the low flow braided channel network, however was mapped more accurately using the GROW facility within ENVI 4.1; a technique based upon mapping areas within a given number of standard deviations in terms of pixel values within a training area. Subsequent to this unsupervised classification of the water surface area allowed classification of the water in to three water types based on depth and separation of isolated pools and backwaters from the channels conveying flow. Overall classification accuracies of 82.5% were achieved in relation to mapping physical habitat; varying between 86 and 95% for the four different dates. Analysis of the nature of channel planform and habitat change showed that there has been a 3.7% increase in the active channel area consisting of exposed sediment and water within the river corridor. This substantiated a general awareness of an increase in the width and reduction in depth of the Brahmaputra River over the last few decades. The analysis also depicts the occurrence of a major avulsion and the highly dynamic nature of the braided channel network and sand bars.Overall the study demonstrated that simple classification methods when applied to satellite data, capturing imagery in the visible and near infra-red, can be used to measure important changes in the geomorphology and physical habitats that make up the fluvial system of the Brahmaputra River. The approach may also be more widely applicable to large river systems comprising a mosaic of water, exposed sediment and spectrally different vegetation communities.
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The present study deals with the documentation of fish diversity and fishing gears used from the wetlands of Central Assam. The study was carried out in three important wetlands of Kamrup Rural district and Kamrup Metro District, viz. Sol beel , Etila beel and Duani beel. Sol beel is situated in the Kamrup Rural district and connected to the Kulsi River, during monsoon season. Etila beel and Duani beel is situated in Kamrup Metro district and connected to Kolong and Digaru River tributary respectively. These three wetlands are perennial in nature that remains covered by water along with its aquatic flora and fauna almost throughout the year. Different types of fishes are available in these three wetlands. During the present study of Sol Beel a total number of 29 species belonging to 18 families and 7 orders have been reported. And in Etila Beel, it was recorded 38 fish species belonging to 21 families and 8 orders. In Duani Beel it was recorded 38 fish species belonging18 families and 8 orders. Dominant species of these three beels are Channa punctatus, Anabas testudineus, Colisa fasciata, Amblypharyngodon mola, Puntius sophore, Heteropneustes fossilis and less dominant species is Notopterus chitala, Notopterus notopterus, Nandus nandus, Xenentodon cancila. The study play a great role because indiscriminate killing of brood and juvenile fishes of local and commercial species and over extraction of these fishes during breeding season greatly decreasing the fish diversity of the study area.
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