Browsing by Author "Sarkar, Subir"

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Open Access
A study on the impact of environmental degradation on river behaviour in jaldhakaduduya watershed, jalpaiguri district, West Bengal
(University of North Bengal, 2023) Sarkar, Sriparna; Sarkar, Subir
A watershed or a drainage basin consists of a main or trunk river, with several tributary river channels, both perennial and non-perennial, converging with the trunk river and spreading both water and sediments throughout the area covered by the entire network of channels. Movement of water and sediments, controlled by several geologic, physiographic, meteorological and anthropological factors may be affected by alterations in any of these factors, affecting thus, the entire fluvial dynamics of the watershed itself. This applies especially to watersheds located in areas, having a propensity to delicate ecological balance. Watersheds located between physical units with different structural and physiographic characteristics, or threshold regions are marked by more frail ecological balance, having long term effects on economy and livelihood of an entire region. The Jaldhaka- Duduya Watershed situated at the heart of the Eastern Himalayan Foothills known as Duars or Dooars, covering parts of Jalpaiguri and Alipurduar districts of West Bengal, India provides a typical example of such an area. Interaction of physical and anthropogenic factors leading to land degradation, riverbank erosion and soil erosion, causing hardships for the agro- based economy of the watershed. Qualitative and quantitative assessment of the problems through reconnaissance surveys, extensive field surveys were done to study the both the causes and effect of environmental degradation on river behavior within the selected study area.The Jaldhaka- Duduya watershed, is made up of two broad physiographic regions, which may be stated as micro- thresholds, located within a short longitudinal distance (<100km). These are the distal alluvial fan surface region of the northern plains in the north and the floodplain of Jaldhaka and Duduya in the south has marked differences in rainfall regime, soils and natural vegetation, clearly visible within relatively short distance from the mountain front, which marks the northern boundary. The piedmont terraces lying at the base of the mountain front marks the active alluvial fan surface. The Jaldhaka River, originating from the Lesser Himalayas of Sikkim, is the main river of Jaldhaka, while River Duduya originating from the piedmont terrace region lying at the base of Himalayan Foothills is the main river of the Duduya watershed. The northern part, constituted by quaternary deposits of various sizes forms the entire piedmont and the escarpments bordering them. The floodplain consists of mostly sandy soil, mixed with silt, with slight increase of clay at the extreme south. The Jaldhaka and its major tributaries flow through north-south trending faults and fault lineaments which were created due to neo-tectonic activities in Bhutanese Lesser Himalayan zone. The Rethi, which constitutes the Lesser Himalayan and the piedmont section of R. Duduya, also follows quaternary fault lineaments. Relief zones of the Jaldhaka- Duduya watershed show rapid change of elevation within small distances; a very small area in the extreme north in Sikkim with >4000m elevation from sea level, forming the source region of Jaldhaka. About 25% of the northern and north-eastern part of the watershed located in Bhutan’s territory, has 2500-1000m elevation from sea level, marking the source regions of the major tributaries of Jaldhaka, namely, Daina, Chamurchi and Rethi Rivers. More than 50% of the Jaldhaka- Duduya watershed has 50- 100m above sea level, forming the southern floodplain. The Jaldhaka- Duduya watershed experiences tropical warm and moist climate, receiving copious monsoon rainfall. High rainfall mostly occurs due to formation and stationing of the monsoon trough over the neighbouring Sikkim or Bhutan Himalayas, or from low pressure areas, which are created during the monsoon, bringing in heavy and clustered rainfall or causing rainstorms. Monsoon rainfall received at the northern part, situated at the base of the mountain front, is more than twice the monsoon rainfall received at the floodplain section in the south. Due to such variations of rainfall six rainfall zones may be found within a northsouth distance of 100 km and west-east distance of <50 km. High intensity rainfall received during rainstorms lead to flash floods in different parts of the Jaldhaka- Duduya watershed. Simple statistical techniques have been used to identify characteristics of rainfall within the watershed, for which both rainfall data collected by selected tea gardens and data collected from registered website of Indian Meteorological Department have been used . Parameters like seasonal and daily rainfall, average 24hour rainfall frequencies, maximum 24 hour rainfall have been used. Time series analysis of annual rainfall of some selected tea gardens of the area show little or no variation for the first decade (1923-1952), distinct rising trend during the second decade (1971- 2000) and finally, a clear decreasing trend for the third decade (2001-2019), which is further substantiated by calculation of standard deviation of decadal rainfall. Annual rainfall has decreased throughout the watershed, as proven by mean rainfall calculated for the post- 2000-s period. There is, thus, a change in rainfall pattern within the Jaldhaka- Duduya watershed; the prevailing change is increasing frequencies of rainstorms, occurring both in the piedmont and floodplain sections. Longitudinal profiles constructed for the Jaldhaka and the major rivers of the watershed reveal variations of relief and degree of concavity. Least square regressions were done to fit longitudinal profiles, showing elevation-distance data, which show concavity for all rivers and breaks of slope, indicating tectonic control, except Duduya, which originates from the piedmont terrace. The Streamlength Gradient Index (SLGI) developed by Hack was also used to calculate degree of structural control on the rivers, which indicate youthful stage for major rivers, except Duduya. Transects constructed across major rivers at selected sites and at selected time intervals, bring out preponderance of braiding activity in Jaldhaka, Daina and Rethi Rivers, with propensity of bank attrition and toe erosion, especially, following rainstorms or periods of clustered monsoon rainfall. Evidences of north- south shifting of the confluence of Jaldhaka and Daina is noted from satellite images and Google maps. Only River Duduya has a comparatively stable channel, with comparatively lower degree of bank erosion. Increased sedimentation within the channels of major rivers and their tributaries, specially rivers with source regions lying deep within the Bhutanese Lesser Himalayan zone causes increased braiding, accumulation of lag deposits within channels in the piedmont and alluvial fan sections, lying within Indian territory. This is found to occur due to unplanned mining activities, mainly within Bhutanese territory, gratuitous lifting of sand and gravel from beds of Daina and Rethi within Indian territory, resulting in steady raising of beds of both tributaries and the trunk river itself, increasing thus, the risk of floods, during periods of active or vigorous monsoon or during rainstorms. Rapid urbanization in and around the Jaldhaka- Duduya watershed, necessitating construction and refurbishment of communication network of the region, construction and extension of settlements and tea garden areas in upper catchment and source regions of rivers, have increased amount and frequencies of slope wash, slope failures and landslides, debris being transported downstream, choking smaller channels and further increasing sedimentation and braiding activities. All of these have led to fertile agricultural lands becoming flood- prone and barren for considerable periods. Thus, general land and environmental degradation throughout the watershed has set in, affecting the chiefly agrarian economy of the area. Hydrographs could, however, be constructed only for Jaldhaka, which is the main river of the watershed. It is observed, that, rainstorms lasting for two or three days at maximum, are capable of triggering peak discharge resulting in flood flows followed by a series of events, ranging from soil and riverbank erosion, or even avulsion, which decrease rapidly, almost immediately after rainfall decreases or stops altogether. Return period of floods with very high discharge has remained the same, but return period of floods with medium to moderately high discharge seems to be increasing during recent years. Risk of floods has increased during recent years due to environmental degradation, in spite of the changing rainfall pattern, that indicates somewhat decreased annual rainfall. Flooding and inundation have become annual phenomena, for bigger and smaller rivers alike. Popular measures of protection from floods, like construction of flood embankments have been successful, only initially. With increasing demand for regional development, need for improved transport and communication system, improved housing and certain amenities cannot be denied to local people. Sustainable development measures for regional development, with minimized effects of the delicate ecological balance are suggested for the Jaldhaka- Duduya watershed.
Open Access
Addressing poverty through appropriate local level technologies : a case study of Jalpaiguri district
(University of North Bengal, 2009) Subbiah, A; Bairagi, Goutam; Sarkar, Subir
Open Access
Application of geo-informatics in micro level development planning: a case study in Dhupguri block of Jalpaiguri district, West Bengal
(University of North Bengal, 2010) Rana, Shrabani; Sarkar, Subir
Open Access
Changing pattern in agriculture ; a case study of Koch Behar district
(University of North Bengal, 2009) Roy, Ranjan; Sarkar, Subir
Open Access
Environmental degradation : problems and prospects A Study in Kurseong Sub-Division of Darjeeling Himalaya
(University of North Bengal, 1999) Bhutia, Pop Tshering; Sarkar, Subir
Open Access
Flood hazards in Jalpaiguri district and its management
(University of North Bengal, 2011) Roy, Suprakash; Sarkar, Subir
Open Access
Forest resources: it`s problems and prospects a study of Darjeeling and Jalpaiguri district West bengal
(University of North Bengal, 2003) Rakshit, Swapan Kumar; Sarkar, Subir
Open Access
A Geo- environmental Appraisal of The Upper Mahananda Basin of The Darjeeling Himalaya West Bengal
(University of North Bengal, 1989) Sarkar, Subir; Basu, S R
Open Access
Geographical study on urbanization and associated problems in North Bengal
(University of North Bengal, 2018) Basak, Arindam; Sarkar, Subir
Open Access
Geospatial analysis of road transport network of Siliguri City, Darjeeling District, West Bengal
(University of North Bengal, 2023) Paul, Biswajit; Sarkar, Subir
An understanding of the potential traffic effects associated with the development of a well-managed transportation system is typically provided by a transportation network analysis, which contributes to overall urban development. The transportation system in Siliguri City includes both roads and railroads; however, roads are the predominate means for carrying a significant amount of the traffic produced in the city. Rapid urban transportation systems like the metro and local trains are not an option in the city. Because commuters are unable to use alternative modes of transportation, the city becomes extremely congested, reducing both human and technological productivity. The current study examines the condition of the Road Transport Network in Siliguri City of Darjeeling District (West Bengal), using both primary and secondary data and information. Some of the methodologies adopted are: descriptive statistics, Wilcoxon signed rank test, Kolmogorov-Smirnov and Shapiro-Wilk test, segment delay, delay rate, relative delay rate, delay ratio, average travel speed, density of vehicles, graph theoretic measures, volume of traffic/hour, PCUs/hour, day-of-week variability pattern, Single factor ANOVA, composite score, and Spearman’s rank correlation. The study area includes the entire Siliguri Municipal Corporation, covering an area of 41.9 square kilometres and 47 wards. Four objectives are met in order to examine the current conditions of the city's major roads, such as, Physical and functional characteristics of the major arterial roads; examining the degree of accessibility and connectivity of the major roadway network; analysis of the traffic flow along the major arterial roads and the relationship between road transport and various service facilities of Siliguri city. As the city has already begun to experience intense and protracted traffic congestion at key intersections, causing the average travel time to multiply within a few years, Siliguri urgently needs to pay attention to its urban road and traffic management. By examining the connection between road development and urban services, the study considers the road transport system from both a geographical and an overall developmental perspective. Additionally, the study aims to offer some suggestions and recommendations for addressing Siliguri's traffic issues in a methodical and effective manner. There are a number of findings established from both the qualitative and quantitative analysis in the previous chapters. Following are the major findings made from the analyses: Hill Cart Road is the busiest and most important road in Siliguri, holding the maximum share of daily PCUs per hour. The primary mode of transportation is private two-wheelers or motor cycles. The proportion of slow moving vehicles, consisting of e-rickshaws, bicycles, and rickshaws, is the second-highest mode of commutation, resulting in traffic V congestion along the arterial road sections. Except for AH 2 (30-45 km/h) and the Eastern Bypass Road (> 45 km/h), the average travel speed remains below 30 km/h on most arterial roads. Throughout the day, vehicle density on Hill Cart Road between Safdar Hasmi Chowk and Gurunanak Chowk remains high (> 11000 vehicles per hour or kilometre). Considering the alpha index, which is used for checking the network connectivity, it is seen that ward no 11 has the highest index value i.e. 0.33, Ward 28 has an index value of 0.29 and Ward 12 has 0.2. Other than these three wards all the other 44 wards in the city have alpha index value ‘0’ (table 4.3). Beta index has been calculated for the road networks in the city, according to the different existing wards (47 in number). It is seen that ward 20 and 23 has the lowest beta index value, ‘0’ and the highest value is in ward number 28, i.e. 1.17. Ward 11 and 12 have a similar beta index value i.e. 1. Whereas gamma index calculated shows that wards 13, 16, 19, 20,21, 22, 23, 30,36, 37 have the lowest index value, i.e. 0, the highest index value can be seen in wards 5,9, 11,29, 25,39 And 44. In case of the eta index calculated Ward Number 20 and 23 have the lowest value 0. Whereas the ward 42 of the city has the highest value 1.39. Like the other indices that have been calculated and discussed prior to this. We see in case of the pi index calculated, Ward 20 has the lowest value and ward 11 the highest. Road density in terms of major roads is maximum in the Ward Number 14 whereas road density is highest in Ward Number 18 considering all major and local roads. Nodal density is also highest in Ward Number 18. Ward Number 8 and 18 recorded with highest composite connectivity score whereas the low zone of connectivity includes 55.32 % of the 47 wards. Out of 41.9 square kilometres area, 11.65 square kilometres falls in most accessible physical zone of accessibility. In terms of total accessibility Safdar Hasmi Chowk and Mahabirsthan placed first position with more than 280000 scores representing most accessible nodes of the city. Inadequate transportation could also be responsible for traffic jams, congestion, travel delays, environmental degradation, and loss of productivity. Arterial roads are very few in Siliguri, the total length of arterials is 28.68 kilometres out of 547.81 kilometres of total length. An effective plan has to be made by the authority for balanced distribution in order to improve overall connectivity and accessibility. Siliguri has become one of the fastest growing cities in India because of its geographical significance and is the gateway to the north eastern states of India and the Eastern Himalayan region. Despite having a number of arterial roads that have been widened and facilitated with road dividers, Hill Cart Road holds the maximum share of overall traffic.
Open Access
Land use changes and its impact on increasing flood frequency and magnitude in Jalpaiguri district (undivided), West Bengal
(University of North Bengal, 2023) Maitra, Kaustabi; Sarkar, Subir
Open Access
Study of the enviromental geomorphology in the Balasan Basin,Darjeeling
(University of North Bengal, 2003) Lama, Indira Lepcha; Sarkar, Subir