Sayantan Das - Academia.edu (original) (raw)
Papers by Sayantan Das
<p>The Ganga&#8211;Brahmaputra&#8211;Meghna Delta (GBMD) at the nor... more <p>The Ganga&#8211;Brahmaputra&#8211;Meghna Delta (GBMD) at the northern apex of the Bay of Bengal, is the world&#8217;s largest in respect of area (c. 120 &#215; 10<sup>3</sup> km<sup>2</sup>) as well as annual discharge of sediments (c. 10<sup>9</sup> t). Contributed by the Ganga River and its numerous distributaries, the southwestern part of the GBMD is known as the Ganga Delta which spans over a number of districts in Bangladesh and West Bengal (India). The Indian state of West Bengal occupies the western portion of the GBMD, where the delta plains drained by the Ganga and its distributaries measure 42,371 km<sup>2</sup>. The estimated population residing in this region in 2021 is about 76 million. The Ganga Delta is completely enveloped by the alluviums deposited by the floods and channel deposits in the last 10,000 years. Nearly every major river in the region is embanked on their both flanks to prevent overspilling during the high stages in the monsoon season (June&#8211;September). Floods occur nonetheless in years of exceptionally high rainfalls, often brought about by tropical cyclones, when these embankments are breached or overtopped by the river water.</p><p>This study aims to delineate the flood-prone zones of the Gangetic West Bengal (GWB) based on the highest floods that occurred between 1995 and 2020, and to extract data on extension, land use and resident population of the flood-susceptible area on different administrative levels.</p><p>Using five highest-magnitude flood events for five overlapping zones, it is found that 33% of the GWB is susceptible to inundation by floodwater. Overlying the inundation area over 226 administrative blocks of 14 districts of the region reveals that 51 highly populated blocks located close to the principal rivers are susceptible to flooding. The deepest flood localities of the east&#8211;central GWB noticeably coincides with the blocks with highest percentage of inundated area (>50%) and also with the blocks having fairly large population size. 77 out of 226 blocks are susceptible to inundation of 50% or more of their total area. On a higher level, if the distribution of flood inundation across the districts constituting the GWB is considered, the districts of Nadia and Murshidabad are found to have relatively more inundation area, with almost 16% of the total flood-susceptible area of the GWB lying within each of these districts, followed by Purba Medinipur (13%) and Malda (11%). The study connotes that floods and the region&#8217;s cultural landscape&#8212;consisting of farmlands, habitations, and lines of communications&#8212;are closely related. Floods occur despite all human endeavours to prevent them, affecting approximately 14,500 km<sup>2 </sup>area and 18 million people.</p>
The Ichhamati River is well known for its transboundary flow through India and Bangladesh. A majo... more The Ichhamati River is well known for its transboundary flow through India and Bangladesh. A major part of the river traverses through North 24 Parganas District in West Bengal, which mostly comes under the tidal regime. In course of time, the non-tidal course of the Ichhamati has degenerated. However, the lower course of the river remains active throughout the year due to tidal activity. In the middle reach, tidal influence reduces significantly toward upstream along with the presence of a number of angular meandering bends. The study area, located in Baduria and Swarupnagar blocks of North 24 Parganas, is characterised by a meandering bend of Ichhamati that has changed both spatially and temporally. To show the morphological changes in this area, SoI topographical maps and satellite images have been used, complemented by field surveys. Water samples were collected to find out the variation in sediment concentration during flood and ebb tide. It is found that the alignment of the I...
Jalangi is a distributary of the Padma River which has opened up within the last few hundred year... more Jalangi is a distributary of the Padma River which has opened up within the last few hundred years to flow actively in the southern and south-western direction through the districts of Murshidabad and Nadia in West Bengal. Initially, its source was the original Jalangi offtake located near Jalangi village, Murshidabad district. Earlier, it used to meet Bhairab River at two different points 5 km apart. But due to irregular flow of water, this part of the Jalangi River has become a palaeochannel and the discharge through Jalangi River is now maintained by Bhairab River. So, the lower part of the Bhairab River is actually the present Jalangi River. It flows into the Bhagirathi-Hugli River near Mayapur in Nadia district. The part of Jalangi River in Nadia district is considered for this study which is representing the lower course of the river. Jalangi is active during the monsoon season and Nadia district is quite susceptible to the flooding of Jalangi and Bhagirathi-Hugli rivers. Jala...
Located in Garhwal Himalayas, Kedarnath (3,583 m) is one of the holiest sites of Hindu pilgrimage... more Located in Garhwal Himalayas, Kedarnath (3,583 m) is one of the holiest sites of Hindu pilgrimage. In the morning of 17 June 2013. Kedarnath village got devastated by a debris flow resulting from bursting of a marine-dammed lake called Chorabari Tal, which is located 300 m above the settlement, in the northwest. In this study estimations are made to measure the breach parameters of the lake viz. lake volume, peak flow, peak flow velocity and momentum. They were estimated from SRTM, ASTER and CartoDEM elevation models: The 9-10 m-high lateral moraine ridge of the Chorabari Glacier was breached along a 60-m wide stretch due to high water pressure in the lake after a high intensity rainfall received in its 2.7 km<sup>2</sup> catchment The amount of water released was estimated at 0.43X10<sup>6</sup> m<sup>3</sup> (SRTM), 0.25X10<sup>6</sup> m<sup>3</sup> (ASTER), and 0.63X10<sup>6</sup> m<sup>3</sup> (C...
Status of Rivers in Tamil Nadu: Problems and Perspectives, 2015
ABSTRACT West Bengal (88,752 km2) is the only Indian state that extends from the Himalaya to the ... more ABSTRACT West Bengal (88,752 km2) is the only Indian state that extends from the Himalaya to the Bay of Bengal. It can be divided into nine physiographic provinces of which the Himalayas, the western plateaus, the northern and western alluvial fans and the Ganga delta are the most important. The development of the river system of the state was largely governed by tectonic evolution of the eastern Himalaya and western edges of the Bengal basin. The characteristics of the rivers as well as a number of aspects of water resources of the state can be linked to its physiographic regions. The principal issues associated with water in West Bengal include river degeneration, channel shifting, flood, urban waterlogging, drought, pollution, groundwater depletion and inland navigation. The management of water is practised by river impoundment projects in various scales and by drainage schemes. It is estimated that the western and eastern parts of the state are the most water stressed regions due to climatic and human factors respectively. The solutions for many of the water-related problems of West Bengal, progressive or cyclic, can be achieved by putting emphasis on participatory management besides organisational intervention.
Geomorphology, 2015
Rudra (2014, Geomorphology, 227, 87-100) presented a review of geomorphic changes of the Indian p... more Rudra (2014, Geomorphology, 227, 87-100) presented a review of geomorphic changes of the Indian part of the Ganga-Brahmaputra delta (GBD) during the last ~240 years, emphasising deterioration of distributary channels, effects of discharge augmentation from the Farakka barrage project into the Bhagirathi-Hugli river and the patterns of coastal erosion. The work contained many inconsistencies, improper understanding, and misrepresentation of facts. The principal of these involved (1) usage of nomenclature like GBD, Bengal basin, and their delineation; (2) discussions made on evolution and current status of the deltaic distributaries; and (3) generation and presentation of data on discharge, tides, and sea level. Besides this, most figures of the work contained positional inaccuracies and/or errors in survey years. We systematically addressed all these issues in the present discussion and offered corrected and up-to-date information wherever applicable.
Geography of the physical environment, 2022
The Indian part of the Upper Ganga Delta (UGD) is traversed by the Ganga River and its distributa... more The Indian part of the Upper Ganga Delta (UGD) is traversed by the Ganga River and its distributary system. As most of these distributaries, in their present condition, are unable to contain the monsoon discharge within their banks, the region is susceptible to frequent flood hazards. The topography of the UGD is mainly characterized by natural levee systems and earthen dykes alongside the rivers. Embankment-induced channel sedimentation, in some parts, has raised the elevation of riverbeds above the surroundings, causing stagnation of floodwater till it percolates down or drains out through the abandoned river courses. The levees often act as barriers and prevent the spilled water from getting back into the main channel. The largest flood in living memory occurred here at the turn of the millennium, in 2000. In September 2000, the remnant of a cyclonic depression triggered heavy downpours in the northwestern part of the UGD and the adjacent Chhotanagpur Plateau. This caused an unprecedented flood that inundated 46% of the UGD region and kept the area waterlogged for more than a month. Breaching the left bank embankment of the Bhagirathi-Hugli River, the floodwater surged southward following non-descript palaeodistributaries like the Gobra Nala and caused significant damages in the districts of Murshidabad and Nadia. Besides this, analysis of elevation models revealed some water movement paths that are undetectable on the ground. Following regional slope, the floodwater then moved across the Jalangi, Mathabhanga-Churni, and Ichhamati river courses to flow southeastward into the North 24 Parganas District, and eventually to Bangladesh. The waters took about a week to cover ~150 km. The pre-, syn-, and post-event satellite images related to the Millennium Flood detected only a few alterations in channel orientations and floodplain morphology. This suggests that the existing channel configuration and floodplain morphology of the UGD are the outcome of slower and lower magnitude fluvial processes. Most inhabitants, residing in the channel bars and near the rivers, have become accustomed to living with the floods during the monsoons. Construction of shelters on the higher areas detachable from the syn-flood images and elevation models can render further protection to these people. [] Das, S., Bandyopadhyay, S., 2022. The Millennium Flood of the Upper Ganga Delta, West Bengal, India: A remote sensing based study. In: Mandal, S., Maiti, R., Nones, M., Beckedahl, H.R. (editors) Applied Geomorphology and Contemporary Issues. Geography of the Physical Environment. Springer, Cham, 499–517. https://doi.org/10.1007/978-3-031-04532-5_26
Mula-Mutha basin is one of the rapidly urbanizing watersheds, wherein two major urban centers – P... more Mula-Mutha basin is one of the rapidly urbanizing watersheds, wherein two major urban centers – Pune and Pimpri-Chinchwad have developed at an alarming rate in the last two decades or so. In order to bring out the changes in land use/land cover within this watershed, two images spanning over 19 years were analyzed. This data were supplemented by the field observations and other ancillary data layers which served as the basic sources of data for land cover change detection maps. It was observed that there was a net increase of around 5.33% in the built up area. However this increase is with respect to the entire basin and the actual sprawl is observed near the main urban cores. Most of the development in terms of built up is observed all along the fringe areas of the major settlements and major highways crawling out of the city in all the directions. A significant decrease of 12% was noticed in barren land which is the result of the ever growing city limits and thus the built up area...
The Mula-Mutha watershed is located in the western Maharashtra which nests Pune urban agglomerati... more The Mula-Mutha watershed is located in the western Maharashtra which nests Pune urban agglomeration at its central part. For the assessment of impervious surface growth of this watershed, satellite images of 1989 and 2008 have been used. An integrated application of remote sensing techniques using Normalized Difference Vegetation Index (NDVI) and Geographic Information System (GIS) has been carried out to identify the amount of impervious surface and its variations. The Impervious surface analysis reveals<br> that there has been almost three-fold increase of the built up area under very high impervious class representing the Pune city and its surroundings between 1989 and 2008. The entire scenario is indicating the requirement of immediate remediation through pollutant mitigation and resource restoration in those areas.
SpringerPlus, 2016
Background: With myriad geospatial datasets now available for terrain information extraction and ... more Background: With myriad geospatial datasets now available for terrain information extraction and particularly streamline demarcation, there arises questions regarding the scale, accuracy and sensitivity of the initial dataset from which these aspects are derived, as they influence all other parameters computed subsequently. In this study, digital elevation models (DEM) derived from Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER V2), Shuttle Radar Topography Mission (SRTM V4, C-Band, 3 arc-second), Cartosat-1 (CartoDEM 1.0) and topographical maps (R.F. 1:250,000 and 1:50,000), have been used to individually extract and analyze the relief, surface, size, shape and texture properties of a mountainous drainage basin. Results: Nestled inside a mountainous setting, the basin is a semi-elongated one with high relief ratio (>90), steep slopes (25°-30°) and high drainage density (>3.5 km/sq km), as computed from the different DEMs. The basin terrain and stream network is extracted from each DEM, whose morphometric attributes are compared with the surveyed stream networks present in the topographical maps, with resampling of finer DEM datasets to coarser resolutions, to reduce scale-implications during the delineation process. Ground truth verifications for altitudinal accuracy have also been done by a GPS survey. Conclusions: DEMs derived from the 1:50,000 topographical map and ASTER GDEM V2 data are found to be more accurate and consistent in terms of absolute accuracy, than the other generated or available DEM data products, on basis of the morphometric parameters extracted from each. They also exhibit a certain degree of proximity to the surveyed topographical map.
Natural Hazards, 2015
ABSTRACT Kedarnath (3,533 m, 30°44′05″N, 79°04′02″E) is situated within a kilometre of the termin... more ABSTRACT Kedarnath (3,533 m, 30°44′05″N, 79°04′02″E) is situated within a kilometre of the termini of the Chorabari and Companion glaciers in the Indian Himalaya. An outburst flood from a lake (3,845 m) formed by right lateral moraine of the former caused severe damage to the village on 17 June 2013. We determined various physical parameters of the lake from three digital elevation datasets (CartoDEM, SRTM and ASTER) and selected the SRTM-derived data as they appeared to portray the region more accurately. The obtained parameters were used in predictive equations suggested by different authors to estimate peak discharge of the flood. We also compared high-resolution images of 10 December 1965 (Corona), June 2011 (Bing) and 25 June 2013 (Catrosat-1 Pan + LISS-4mx) to assess the damage caused to the village besides other geomorphic changes. The results showed that at least 149 mm of rainfall in its 291-ha catchment was required to fill up the lake, without considering the presence of antecedent water and loss from seepage and evaporation. At the point of breaching, the lake released 0.43 × 106 m3 of water with a peak discharge of 1,352 cumecs. The north-western section of Kedarnath village was on the direct path of the debris flow triggered by the flood and was almost completely destroyed. The southern and south-eastern sections were least affected. Out of 37,299 m2 of pre-event roof area of Kedarnath (259 structures), 44.2 % were obliterated and 26.7 % were partly damaged, representing 138 and 56 structures, respectively. Only one-quarter of the structures of the village emerged intact or slightly affected after the event.
The longitudinal profile of a river is one of the most popular indicators for assessing the degre... more The longitudinal profile of a river is one of the most popular indicators for assessing the degree of tectonic and structural control in a fluvial system. Sensitive to long-term tectonic, structural and climatic regimes, long profiles have been employed all over the globe and the anomalies in the long profiles are often been interpreted as evidence of active tectonic deformation. With the advent of high-resolution DEM datasets such as, SRTM, ASTER, etc. many large rivers of the world have been studied and analysed with respect to structure and tectonics. The present study is one such attempt for the Himalayan Rangit River in Eastern India. Physiographically located in the Eastern Himalayan Division of the Himalayas, this river is a small, steep-gradient tributary of the Tista River, debouching its waters into the Tista River near Melli (27°04'47"N, 88°25'56"E). SRTM DEM (30 m) was procured for the study area and the drainage network and the watersheds of the major ...
Geomorphology, 2021
Avulsions involve switching of fluvial discharge through a new channel from an existing course an... more Avulsions involve switching of fluvial discharge through a new channel from an existing course and occur over varied timeframes ranging from hours to decades. With a peak discharge above 100,000 m^3/s, the Brahmaputra (2900 km) is one of the largest rivers in the world. Its lower course through the Ganga–Brahmaputra–Meghna (GBM) Delta of Bangladesh was first mapped in 1764–73 as a broad eastward-swinging curvature skirting the subsiding Sylhet Wetlands and falling into the Meghna River. Beginning from the late eighteenth century, the river started to avulse into a linear, more direct, southward passage into the Ganga called the Jamuna and decreased its length by 46 k (14.2%) from its former course to the Bay of Bengal. Examination of the established timeline and procedure of the avulsion event using maps and images from 1764–73, 1830–34, 1854–60, 1907–24, and 2014, in addition to evidence from contemporary literature and tree-ring reconstructed long-term discharge data, connoted cer...
SpringerPlus, 2016
Background: With myriad geospatial datasets now available for terrain information extraction and ... more Background: With myriad geospatial datasets now available for terrain information extraction and particularly streamline demarcation, there arises questions regarding the scale, accuracy and sensitivity of the initial dataset from which these aspects are derived, as they influence all other parameters computed subsequently. In this study, digital elevation models (DEM) derived from Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER V2), Shuttle Radar Topography Mission (SRTM V4, C-Band, 3 arc-second), Cartosat-1 (CartoDEM 1.0) and topographical maps (R.F. 1:250,000 and 1:50,000), have been used to individually extract and analyze the relief, surface, size, shape and texture properties of a mountainous drainage basin. Results: Nestled inside a mountainous setting, the basin is a semi-elongated one with high relief ratio (>90), steep slopes (25°–30°) and high drainage density (>3.5 km/sq km), as computed from the different DEMs. The basin terrain and stream network is extracted from each DEM, whose morphometric attributes are compared with the surveyed stream networks present in the topographical maps, with resampling of finer DEM datasets to coarser resolutions, to reduce scale-implications during the delineation process. Ground truth verifications for altitudinal accuracy have also been done by a GPS survey. Conclusions: DEMs derived from the 1:50,000 topographical map and ASTER GDEM V2 data are found to be more accurate and consistent in terms of absolute accuracy, than the other generated or available DEM data products, on basis of the morphometric parameters extracted from each. They also exhibit a certain degree of proximity to the surveyed topographical map.
Natural Hazards, Jan 29, 2015
Kedarnath (3,533 m, 30°44′05″N, 79°04′02″E) is situated within a kilometre of the termini of the ... more Kedarnath (3,533 m, 30°44′05″N, 79°04′02″E) is situated within a kilometre of the termini of the Chorabari and Companion glaciers in the Indian Himalaya. An outburst flood from a lake (3,845 m) formed by right lateral moraine of the former caused severe damage to the village on 17 June 2013. We determined various physical parameters of the lake from three digital elevation datasets (CartoDEM, SRTM and ASTER) and selected the SRTM-derived data as they appeared to portray the region more accurately. The obtained parameters were used in predictive equations suggested by different authors to estimate peak discharge of the flood. We also compared high-resolution images of 10 December 1965 (Corona), June 2011 (Bing) and 25 June 2013 (Catrosat-1 Pan + LISS-4mx) to assess the damage caused to the village besides other geomorphic changes. The results showed that at least 149 mm of rainfall in its 291-ha catchment was required to fill up the lake, without considering the presence of antecedent water and loss from seepage and evaporation. At the point of breaching, the lake released 0.43 × 106 m^3 of water with a peak discharge of 1,352 cumecs. The north-western section of Kedarnath village was on the direct path of the debris flow triggered by the flood and was almost completely destroyed. The southern and south-eastern sections were least affected. Out of 37,299 m^2 of pre-event roof area of Kedarnath (259 structures), 44.2 % were obliterated and 26.7 % were partly damaged, representing 138 and 56 structures, respectively. Only one-quarter of the structures of the village emerged intact or slightly affected after the event.
Geomorphology, Elsevier, 2015
Rudra (2014, Geomorphology, 227, 87-100) presented a review of geomorphic changes of the Indian p... more Rudra (2014, Geomorphology, 227, 87-100) presented a review of geomorphic changes of the Indian part of the Ganga–Brahmaputra delta (GBD) during the last ~ 240 years, emphasising deterioration of distributary channels, effects of discharge augmentation from the Farakka barrage project into the Bhagirathi–Hugli river and the patterns of coastal erosion. The work contained many inconsistencies, improper understanding, and misrepresentation of facts. The principal of these involved (1) usage of nomenclature like GBD, Bengal basin, and their delineation; (2) discussions made on evolution and current status of the deltaic distributaries; and (3) generation and presentation of data on discharge, tides, and sea level. Besides this, most figures of the work contained positional inaccuracies and/or errors in survey years. We systematically addressed all these issues in the present discussion and offered corrected and up-to-date information wherever applicable.
Geological Society of India Special Publication No. 3, 2014
West Bengal (88,752 km²) is the only Indian state that stretches from the Himalaya to the Bay of ... more West Bengal (88,752 km²) is the only Indian state that stretches from the Himalaya to the Bay of Bengal. It can be divided into nine physiographic provinces of which the Himalayas, the western plateaus, the northern and western alluvial fans and the Ganga delta are most important. The development of the river system of the state was largely governed by tectonic evolution of the eastern Himalaya and western edges of the Bengal basin. The characteristics of the rivers as well as a number of aspects of water resources of the state can be linked to its physiographic regions. The principal issues associated with water in West Bengal include river degeneration, channel shifting, flood, urban waterlogging, drought, pollution, groundwater depletion and inland navigation. The management of water is practised by river impoundment projects in various scales and by drainage schemes. It is estimated that the western and eastern parts of the state are most water stressed regions due to climatic and human factors, respectively. The solution to many of the water-related problems of West Bengal, progressive or cyclic, can be addressed by putting emphasis on participatory management besides government intervention.
West Bengal Coast / Sundarban by Sayantan Das
<p>The Ganga&#8211;Brahmaputra&#8211;Meghna Delta (GBMD) at the nor... more <p>The Ganga&#8211;Brahmaputra&#8211;Meghna Delta (GBMD) at the northern apex of the Bay of Bengal, is the world&#8217;s largest in respect of area (c. 120 &#215; 10<sup>3</sup> km<sup>2</sup>) as well as annual discharge of sediments (c. 10<sup>9</sup> t). Contributed by the Ganga River and its numerous distributaries, the southwestern part of the GBMD is known as the Ganga Delta which spans over a number of districts in Bangladesh and West Bengal (India). The Indian state of West Bengal occupies the western portion of the GBMD, where the delta plains drained by the Ganga and its distributaries measure 42,371 km<sup>2</sup>. The estimated population residing in this region in 2021 is about 76 million. The Ganga Delta is completely enveloped by the alluviums deposited by the floods and channel deposits in the last 10,000 years. Nearly every major river in the region is embanked on their both flanks to prevent overspilling during the high stages in the monsoon season (June&#8211;September). Floods occur nonetheless in years of exceptionally high rainfalls, often brought about by tropical cyclones, when these embankments are breached or overtopped by the river water.</p><p>This study aims to delineate the flood-prone zones of the Gangetic West Bengal (GWB) based on the highest floods that occurred between 1995 and 2020, and to extract data on extension, land use and resident population of the flood-susceptible area on different administrative levels.</p><p>Using five highest-magnitude flood events for five overlapping zones, it is found that 33% of the GWB is susceptible to inundation by floodwater. Overlying the inundation area over 226 administrative blocks of 14 districts of the region reveals that 51 highly populated blocks located close to the principal rivers are susceptible to flooding. The deepest flood localities of the east&#8211;central GWB noticeably coincides with the blocks with highest percentage of inundated area (>50%) and also with the blocks having fairly large population size. 77 out of 226 blocks are susceptible to inundation of 50% or more of their total area. On a higher level, if the distribution of flood inundation across the districts constituting the GWB is considered, the districts of Nadia and Murshidabad are found to have relatively more inundation area, with almost 16% of the total flood-susceptible area of the GWB lying within each of these districts, followed by Purba Medinipur (13%) and Malda (11%). The study connotes that floods and the region&#8217;s cultural landscape&#8212;consisting of farmlands, habitations, and lines of communications&#8212;are closely related. Floods occur despite all human endeavours to prevent them, affecting approximately 14,500 km<sup>2 </sup>area and 18 million people.</p>
The Ichhamati River is well known for its transboundary flow through India and Bangladesh. A majo... more The Ichhamati River is well known for its transboundary flow through India and Bangladesh. A major part of the river traverses through North 24 Parganas District in West Bengal, which mostly comes under the tidal regime. In course of time, the non-tidal course of the Ichhamati has degenerated. However, the lower course of the river remains active throughout the year due to tidal activity. In the middle reach, tidal influence reduces significantly toward upstream along with the presence of a number of angular meandering bends. The study area, located in Baduria and Swarupnagar blocks of North 24 Parganas, is characterised by a meandering bend of Ichhamati that has changed both spatially and temporally. To show the morphological changes in this area, SoI topographical maps and satellite images have been used, complemented by field surveys. Water samples were collected to find out the variation in sediment concentration during flood and ebb tide. It is found that the alignment of the I...
Jalangi is a distributary of the Padma River which has opened up within the last few hundred year... more Jalangi is a distributary of the Padma River which has opened up within the last few hundred years to flow actively in the southern and south-western direction through the districts of Murshidabad and Nadia in West Bengal. Initially, its source was the original Jalangi offtake located near Jalangi village, Murshidabad district. Earlier, it used to meet Bhairab River at two different points 5 km apart. But due to irregular flow of water, this part of the Jalangi River has become a palaeochannel and the discharge through Jalangi River is now maintained by Bhairab River. So, the lower part of the Bhairab River is actually the present Jalangi River. It flows into the Bhagirathi-Hugli River near Mayapur in Nadia district. The part of Jalangi River in Nadia district is considered for this study which is representing the lower course of the river. Jalangi is active during the monsoon season and Nadia district is quite susceptible to the flooding of Jalangi and Bhagirathi-Hugli rivers. Jala...
Located in Garhwal Himalayas, Kedarnath (3,583 m) is one of the holiest sites of Hindu pilgrimage... more Located in Garhwal Himalayas, Kedarnath (3,583 m) is one of the holiest sites of Hindu pilgrimage. In the morning of 17 June 2013. Kedarnath village got devastated by a debris flow resulting from bursting of a marine-dammed lake called Chorabari Tal, which is located 300 m above the settlement, in the northwest. In this study estimations are made to measure the breach parameters of the lake viz. lake volume, peak flow, peak flow velocity and momentum. They were estimated from SRTM, ASTER and CartoDEM elevation models: The 9-10 m-high lateral moraine ridge of the Chorabari Glacier was breached along a 60-m wide stretch due to high water pressure in the lake after a high intensity rainfall received in its 2.7 km<sup>2</sup> catchment The amount of water released was estimated at 0.43X10<sup>6</sup> m<sup>3</sup> (SRTM), 0.25X10<sup>6</sup> m<sup>3</sup> (ASTER), and 0.63X10<sup>6</sup> m<sup>3</sup> (C...
Status of Rivers in Tamil Nadu: Problems and Perspectives, 2015
ABSTRACT West Bengal (88,752 km2) is the only Indian state that extends from the Himalaya to the ... more ABSTRACT West Bengal (88,752 km2) is the only Indian state that extends from the Himalaya to the Bay of Bengal. It can be divided into nine physiographic provinces of which the Himalayas, the western plateaus, the northern and western alluvial fans and the Ganga delta are the most important. The development of the river system of the state was largely governed by tectonic evolution of the eastern Himalaya and western edges of the Bengal basin. The characteristics of the rivers as well as a number of aspects of water resources of the state can be linked to its physiographic regions. The principal issues associated with water in West Bengal include river degeneration, channel shifting, flood, urban waterlogging, drought, pollution, groundwater depletion and inland navigation. The management of water is practised by river impoundment projects in various scales and by drainage schemes. It is estimated that the western and eastern parts of the state are the most water stressed regions due to climatic and human factors respectively. The solutions for many of the water-related problems of West Bengal, progressive or cyclic, can be achieved by putting emphasis on participatory management besides organisational intervention.
Geomorphology, 2015
Rudra (2014, Geomorphology, 227, 87-100) presented a review of geomorphic changes of the Indian p... more Rudra (2014, Geomorphology, 227, 87-100) presented a review of geomorphic changes of the Indian part of the Ganga-Brahmaputra delta (GBD) during the last ~240 years, emphasising deterioration of distributary channels, effects of discharge augmentation from the Farakka barrage project into the Bhagirathi-Hugli river and the patterns of coastal erosion. The work contained many inconsistencies, improper understanding, and misrepresentation of facts. The principal of these involved (1) usage of nomenclature like GBD, Bengal basin, and their delineation; (2) discussions made on evolution and current status of the deltaic distributaries; and (3) generation and presentation of data on discharge, tides, and sea level. Besides this, most figures of the work contained positional inaccuracies and/or errors in survey years. We systematically addressed all these issues in the present discussion and offered corrected and up-to-date information wherever applicable.
Geography of the physical environment, 2022
The Indian part of the Upper Ganga Delta (UGD) is traversed by the Ganga River and its distributa... more The Indian part of the Upper Ganga Delta (UGD) is traversed by the Ganga River and its distributary system. As most of these distributaries, in their present condition, are unable to contain the monsoon discharge within their banks, the region is susceptible to frequent flood hazards. The topography of the UGD is mainly characterized by natural levee systems and earthen dykes alongside the rivers. Embankment-induced channel sedimentation, in some parts, has raised the elevation of riverbeds above the surroundings, causing stagnation of floodwater till it percolates down or drains out through the abandoned river courses. The levees often act as barriers and prevent the spilled water from getting back into the main channel. The largest flood in living memory occurred here at the turn of the millennium, in 2000. In September 2000, the remnant of a cyclonic depression triggered heavy downpours in the northwestern part of the UGD and the adjacent Chhotanagpur Plateau. This caused an unprecedented flood that inundated 46% of the UGD region and kept the area waterlogged for more than a month. Breaching the left bank embankment of the Bhagirathi-Hugli River, the floodwater surged southward following non-descript palaeodistributaries like the Gobra Nala and caused significant damages in the districts of Murshidabad and Nadia. Besides this, analysis of elevation models revealed some water movement paths that are undetectable on the ground. Following regional slope, the floodwater then moved across the Jalangi, Mathabhanga-Churni, and Ichhamati river courses to flow southeastward into the North 24 Parganas District, and eventually to Bangladesh. The waters took about a week to cover ~150 km. The pre-, syn-, and post-event satellite images related to the Millennium Flood detected only a few alterations in channel orientations and floodplain morphology. This suggests that the existing channel configuration and floodplain morphology of the UGD are the outcome of slower and lower magnitude fluvial processes. Most inhabitants, residing in the channel bars and near the rivers, have become accustomed to living with the floods during the monsoons. Construction of shelters on the higher areas detachable from the syn-flood images and elevation models can render further protection to these people. [] Das, S., Bandyopadhyay, S., 2022. The Millennium Flood of the Upper Ganga Delta, West Bengal, India: A remote sensing based study. In: Mandal, S., Maiti, R., Nones, M., Beckedahl, H.R. (editors) Applied Geomorphology and Contemporary Issues. Geography of the Physical Environment. Springer, Cham, 499–517. https://doi.org/10.1007/978-3-031-04532-5_26
Mula-Mutha basin is one of the rapidly urbanizing watersheds, wherein two major urban centers – P... more Mula-Mutha basin is one of the rapidly urbanizing watersheds, wherein two major urban centers – Pune and Pimpri-Chinchwad have developed at an alarming rate in the last two decades or so. In order to bring out the changes in land use/land cover within this watershed, two images spanning over 19 years were analyzed. This data were supplemented by the field observations and other ancillary data layers which served as the basic sources of data for land cover change detection maps. It was observed that there was a net increase of around 5.33% in the built up area. However this increase is with respect to the entire basin and the actual sprawl is observed near the main urban cores. Most of the development in terms of built up is observed all along the fringe areas of the major settlements and major highways crawling out of the city in all the directions. A significant decrease of 12% was noticed in barren land which is the result of the ever growing city limits and thus the built up area...
The Mula-Mutha watershed is located in the western Maharashtra which nests Pune urban agglomerati... more The Mula-Mutha watershed is located in the western Maharashtra which nests Pune urban agglomeration at its central part. For the assessment of impervious surface growth of this watershed, satellite images of 1989 and 2008 have been used. An integrated application of remote sensing techniques using Normalized Difference Vegetation Index (NDVI) and Geographic Information System (GIS) has been carried out to identify the amount of impervious surface and its variations. The Impervious surface analysis reveals<br> that there has been almost three-fold increase of the built up area under very high impervious class representing the Pune city and its surroundings between 1989 and 2008. The entire scenario is indicating the requirement of immediate remediation through pollutant mitigation and resource restoration in those areas.
SpringerPlus, 2016
Background: With myriad geospatial datasets now available for terrain information extraction and ... more Background: With myriad geospatial datasets now available for terrain information extraction and particularly streamline demarcation, there arises questions regarding the scale, accuracy and sensitivity of the initial dataset from which these aspects are derived, as they influence all other parameters computed subsequently. In this study, digital elevation models (DEM) derived from Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER V2), Shuttle Radar Topography Mission (SRTM V4, C-Band, 3 arc-second), Cartosat-1 (CartoDEM 1.0) and topographical maps (R.F. 1:250,000 and 1:50,000), have been used to individually extract and analyze the relief, surface, size, shape and texture properties of a mountainous drainage basin. Results: Nestled inside a mountainous setting, the basin is a semi-elongated one with high relief ratio (>90), steep slopes (25°-30°) and high drainage density (>3.5 km/sq km), as computed from the different DEMs. The basin terrain and stream network is extracted from each DEM, whose morphometric attributes are compared with the surveyed stream networks present in the topographical maps, with resampling of finer DEM datasets to coarser resolutions, to reduce scale-implications during the delineation process. Ground truth verifications for altitudinal accuracy have also been done by a GPS survey. Conclusions: DEMs derived from the 1:50,000 topographical map and ASTER GDEM V2 data are found to be more accurate and consistent in terms of absolute accuracy, than the other generated or available DEM data products, on basis of the morphometric parameters extracted from each. They also exhibit a certain degree of proximity to the surveyed topographical map.
Natural Hazards, 2015
ABSTRACT Kedarnath (3,533 m, 30°44′05″N, 79°04′02″E) is situated within a kilometre of the termin... more ABSTRACT Kedarnath (3,533 m, 30°44′05″N, 79°04′02″E) is situated within a kilometre of the termini of the Chorabari and Companion glaciers in the Indian Himalaya. An outburst flood from a lake (3,845 m) formed by right lateral moraine of the former caused severe damage to the village on 17 June 2013. We determined various physical parameters of the lake from three digital elevation datasets (CartoDEM, SRTM and ASTER) and selected the SRTM-derived data as they appeared to portray the region more accurately. The obtained parameters were used in predictive equations suggested by different authors to estimate peak discharge of the flood. We also compared high-resolution images of 10 December 1965 (Corona), June 2011 (Bing) and 25 June 2013 (Catrosat-1 Pan + LISS-4mx) to assess the damage caused to the village besides other geomorphic changes. The results showed that at least 149 mm of rainfall in its 291-ha catchment was required to fill up the lake, without considering the presence of antecedent water and loss from seepage and evaporation. At the point of breaching, the lake released 0.43 × 106 m3 of water with a peak discharge of 1,352 cumecs. The north-western section of Kedarnath village was on the direct path of the debris flow triggered by the flood and was almost completely destroyed. The southern and south-eastern sections were least affected. Out of 37,299 m2 of pre-event roof area of Kedarnath (259 structures), 44.2 % were obliterated and 26.7 % were partly damaged, representing 138 and 56 structures, respectively. Only one-quarter of the structures of the village emerged intact or slightly affected after the event.
The longitudinal profile of a river is one of the most popular indicators for assessing the degre... more The longitudinal profile of a river is one of the most popular indicators for assessing the degree of tectonic and structural control in a fluvial system. Sensitive to long-term tectonic, structural and climatic regimes, long profiles have been employed all over the globe and the anomalies in the long profiles are often been interpreted as evidence of active tectonic deformation. With the advent of high-resolution DEM datasets such as, SRTM, ASTER, etc. many large rivers of the world have been studied and analysed with respect to structure and tectonics. The present study is one such attempt for the Himalayan Rangit River in Eastern India. Physiographically located in the Eastern Himalayan Division of the Himalayas, this river is a small, steep-gradient tributary of the Tista River, debouching its waters into the Tista River near Melli (27°04'47"N, 88°25'56"E). SRTM DEM (30 m) was procured for the study area and the drainage network and the watersheds of the major ...
Geomorphology, 2021
Avulsions involve switching of fluvial discharge through a new channel from an existing course an... more Avulsions involve switching of fluvial discharge through a new channel from an existing course and occur over varied timeframes ranging from hours to decades. With a peak discharge above 100,000 m^3/s, the Brahmaputra (2900 km) is one of the largest rivers in the world. Its lower course through the Ganga–Brahmaputra–Meghna (GBM) Delta of Bangladesh was first mapped in 1764–73 as a broad eastward-swinging curvature skirting the subsiding Sylhet Wetlands and falling into the Meghna River. Beginning from the late eighteenth century, the river started to avulse into a linear, more direct, southward passage into the Ganga called the Jamuna and decreased its length by 46 k (14.2%) from its former course to the Bay of Bengal. Examination of the established timeline and procedure of the avulsion event using maps and images from 1764–73, 1830–34, 1854–60, 1907–24, and 2014, in addition to evidence from contemporary literature and tree-ring reconstructed long-term discharge data, connoted cer...
SpringerPlus, 2016
Background: With myriad geospatial datasets now available for terrain information extraction and ... more Background: With myriad geospatial datasets now available for terrain information extraction and particularly streamline demarcation, there arises questions regarding the scale, accuracy and sensitivity of the initial dataset from which these aspects are derived, as they influence all other parameters computed subsequently. In this study, digital elevation models (DEM) derived from Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER V2), Shuttle Radar Topography Mission (SRTM V4, C-Band, 3 arc-second), Cartosat-1 (CartoDEM 1.0) and topographical maps (R.F. 1:250,000 and 1:50,000), have been used to individually extract and analyze the relief, surface, size, shape and texture properties of a mountainous drainage basin. Results: Nestled inside a mountainous setting, the basin is a semi-elongated one with high relief ratio (>90), steep slopes (25°–30°) and high drainage density (>3.5 km/sq km), as computed from the different DEMs. The basin terrain and stream network is extracted from each DEM, whose morphometric attributes are compared with the surveyed stream networks present in the topographical maps, with resampling of finer DEM datasets to coarser resolutions, to reduce scale-implications during the delineation process. Ground truth verifications for altitudinal accuracy have also been done by a GPS survey. Conclusions: DEMs derived from the 1:50,000 topographical map and ASTER GDEM V2 data are found to be more accurate and consistent in terms of absolute accuracy, than the other generated or available DEM data products, on basis of the morphometric parameters extracted from each. They also exhibit a certain degree of proximity to the surveyed topographical map.
Natural Hazards, Jan 29, 2015
Kedarnath (3,533 m, 30°44′05″N, 79°04′02″E) is situated within a kilometre of the termini of the ... more Kedarnath (3,533 m, 30°44′05″N, 79°04′02″E) is situated within a kilometre of the termini of the Chorabari and Companion glaciers in the Indian Himalaya. An outburst flood from a lake (3,845 m) formed by right lateral moraine of the former caused severe damage to the village on 17 June 2013. We determined various physical parameters of the lake from three digital elevation datasets (CartoDEM, SRTM and ASTER) and selected the SRTM-derived data as they appeared to portray the region more accurately. The obtained parameters were used in predictive equations suggested by different authors to estimate peak discharge of the flood. We also compared high-resolution images of 10 December 1965 (Corona), June 2011 (Bing) and 25 June 2013 (Catrosat-1 Pan + LISS-4mx) to assess the damage caused to the village besides other geomorphic changes. The results showed that at least 149 mm of rainfall in its 291-ha catchment was required to fill up the lake, without considering the presence of antecedent water and loss from seepage and evaporation. At the point of breaching, the lake released 0.43 × 106 m^3 of water with a peak discharge of 1,352 cumecs. The north-western section of Kedarnath village was on the direct path of the debris flow triggered by the flood and was almost completely destroyed. The southern and south-eastern sections were least affected. Out of 37,299 m^2 of pre-event roof area of Kedarnath (259 structures), 44.2 % were obliterated and 26.7 % were partly damaged, representing 138 and 56 structures, respectively. Only one-quarter of the structures of the village emerged intact or slightly affected after the event.
Geomorphology, Elsevier, 2015
Rudra (2014, Geomorphology, 227, 87-100) presented a review of geomorphic changes of the Indian p... more Rudra (2014, Geomorphology, 227, 87-100) presented a review of geomorphic changes of the Indian part of the Ganga–Brahmaputra delta (GBD) during the last ~ 240 years, emphasising deterioration of distributary channels, effects of discharge augmentation from the Farakka barrage project into the Bhagirathi–Hugli river and the patterns of coastal erosion. The work contained many inconsistencies, improper understanding, and misrepresentation of facts. The principal of these involved (1) usage of nomenclature like GBD, Bengal basin, and their delineation; (2) discussions made on evolution and current status of the deltaic distributaries; and (3) generation and presentation of data on discharge, tides, and sea level. Besides this, most figures of the work contained positional inaccuracies and/or errors in survey years. We systematically addressed all these issues in the present discussion and offered corrected and up-to-date information wherever applicable.
Geological Society of India Special Publication No. 3, 2014
West Bengal (88,752 km²) is the only Indian state that stretches from the Himalaya to the Bay of ... more West Bengal (88,752 km²) is the only Indian state that stretches from the Himalaya to the Bay of Bengal. It can be divided into nine physiographic provinces of which the Himalayas, the western plateaus, the northern and western alluvial fans and the Ganga delta are most important. The development of the river system of the state was largely governed by tectonic evolution of the eastern Himalaya and western edges of the Bengal basin. The characteristics of the rivers as well as a number of aspects of water resources of the state can be linked to its physiographic regions. The principal issues associated with water in West Bengal include river degeneration, channel shifting, flood, urban waterlogging, drought, pollution, groundwater depletion and inland navigation. The management of water is practised by river impoundment projects in various scales and by drainage schemes. It is estimated that the western and eastern parts of the state are most water stressed regions due to climatic and human factors, respectively. The solution to many of the water-related problems of West Bengal, progressive or cyclic, can be addressed by putting emphasis on participatory management besides government intervention.