Field Report: Upper Reach of the Brahmaputra Valley, Assam (original) (raw)
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Journal of The Indian Society of Remote Sensing, 2007
The Burhi Dining river flows in a meandering course for about 220 km through alluvial plains of Assam including a short rocky and hilly tract in between. Sequential changes in the position of banklines of the river due to consistent bank erosion have been studied from Survey of India topographic maps of 1934 and 1972, and digital satellite data of 2001 and 2004 using GIS. Two broad kinds of changes have been observed, e.g. alteration of direction of flow due to neck cut-off and progressive gradual change of the meander bends that accounts for translational, lateral, rotational, extensional and other types of movement of the meander bends. Study of bankline shift due to the bank erosion has been carried out for the periods 1934–1972, 1972–2001, 2001–2004 and 1934–2004 at 13 segments spaced at 5′ longitude interval (average 15 km) as the river course trends nearly east to west. The amounts of the bank area lost due to erosion and gained due to sediment deposition are estimated separately. The total area eroded in both banks during 1934–1972 was more (26.796 km2) as compared to sediment deposition (19.273 km2), whereas total sediment deposition was more (34.61 km2) during 1972-2001 as compared to erosion (23.152 km2). Erosion was again more in 2001–2004 (7.568 km2) as compared to sediment deposition (2.493 km2). During the entire period (1934–2004) of study the overall erosion on the both banks was 31.169 km2 and overall sediment deposition was 30.101 km2. The highest annual rates of bank erosion as well as bank building of the river are 21055.47 m2/km in 2001–2004 and 9665.81 m2/km in 1972-2001, respectively. Similarly the highest average annual rates of erosion as well as sediment deposition in both banks are observed during 2001–2004 and 1972–2001, respectively. The hard rocks of the hilly tract situated in between result in development of entrenched meandering and this tract has suffered minimum bank erosion.
Bank Erosion: Middle Diana River Basin , Jalpaiguri, West Bengal
Riverbank erosion is one of the most unpredictable and critical type of fluvial hazard that takes tolls less in lives but more in livelihood such as agricultural land and homesteads along with other livelihood options that are evacuated. River Diana, the main right bank tributary of the Jaldhaka, originates in Bhutan and flows south-westward into Jalpaiguri. The present study concentrates on middle Diana basin where intense problems of bank erosion and spilling exist. Channel migration and severe bank failures have taken place almost every year that have severe impact on surrounding areas. Because of the dynamic nature of the braided river and the failure of structural measures, the sufferings of the people continue. Avulsed Rivers, Flow pattern Change, Flow Diversion Strea bank failure and subsequent land loss is a destructive Aey words-Erosion and Accretion, Bank line Shifting,
Riverbank erosion is one of the most unpredictable and critical type of disasters that takes tolls less in lives but more in livelihood such as agricultural land and homesteads along with other livelihood options that are evacuated. River Diana, the main right bank tributary of the Jaldhaka, originates in Bhutan and flows south-westward into Jalpaiguri. The present study concentrates on Khairkata Village, a small village on the right bank of Diana where severe problems of bank erosion and spilling exist. Channel migration and severe bank failures have taken place almost every year that threatens the only livelihood option of the population. In addition, severe flooding destroys standing crops and disrupts communication. Because of the dynamic nature of the braided river and the failure of structural measures, the sufferings of the people continue. Long-term policies should be taken to cope up with the bank erosion taking into account the social and institutional adjustment measures. Introduction Stream bank erosion is a natural process that over time has resulted in the formation of the productive flood plains and alluvial terraces common in the middle and lower reaches of many river systems. Events like flooding can trigger dramatic and sudden changes in rivers and streams. However, land use and stream management can also trigger erosion responses. The responses can be complex, often resulting in accelerated rates of erosion and sometimes affecting stability for decades. Over-clearing of catchment and stream bank vegetation, poorly managed sand and gravel extraction, and stream straightening works are examples of management practices which result in accelerated rates of bank erosion. Human activities have altered the natural processes in the present day rivers. The activities in one location (riverbank protection, riverbed excavation) can alter the flow velocity patterns and thereby affect erosion on the opposite bank and the scouring/sedimentation process of the downstream riverbed (Miyazawa, Sunada & Sokhem, 2008).
Neotectonics and bank erosion of the Brahmaputra River around Rohmoria, Assam, India
Bank erosion of the Brahmaputra River and geomorphology around Rohmoria area in Assam, India, are found to be related to neotectonics as revealed by a study carried out using GIS based on topographic maps surveyed in 1916 and 1963, seismotectonic map as well as remote sensing data of the amount of bank area eroded by the river around Rohmoria in km 2 were 51.372, 18.522, 34.507, 1.468, 1.321 and 1.289, respectively. The rate of bank erosion in km 2 /year were highest (2.731) during 1983-1996 and lowest (0.220) during 2001-2007 and 0.645 in the present years during 2007-2009. Subsidence due to movement along the neotectonic fault during these two periods of higher bank erosion was the main cause of rampant bank erosion of Rohmoria area, which is augmented by direct action of the river current and presence of a thick unconsolidated sand horizon at the base of the bank.
Hazard, Vulnerability and Risk on the Brahmaputra Basin: A Case Study of River Bank Erosion
The Open Hydrology Journal, 2010
The authors present an assessment of risk from river bank erosion in the Brahmaputra river basin. The concept of risk is conceptualised in the context of socioeconomic vulnerability, and the potential for exposure to hazard. By addressing both the physical hazard and the variations across the socioeconomic surface the approach presented attempts to spatially combine these parameters to provide a risk surface for use by policy makers and decision makers at a number of administrative levels. The concept of vulnerability and risk as a description of the status of a society with respect to an imposed hazard such as flooding or the associated bank erosion exacerbated by climate change is deep rooted in a very broad research effort and its associated publications. In part, this reflects the complex evolution of the underlying notion of hazard-which itself shows the concurrent evolution of a series of strands each representing one disciplinary tradition. The concept of vulnerability has been very widely treated in the literature, and for present purposes an acceptable approach to vulnerability may be to start with an influential (but still controversial) established model by IPCC (2001) who have developed working definition-and then explore its ramifications in order to develop a set of working definitions and operational indicators for the project. This provides a pragmatic route towards a realistic target. It also offers a possible buffer against the common experience that the more sophisticated indices of vulnerability are strongly sensitive to contingent local/historical circumstances. This approach is explored within this chapter. The hazard posed by unabated bank erosion has been analysed with the help of satellite imagery based data and through adoption of Plan Form Index along with its threshold values developed for the Brahmaputra. The land loss to erosion is depicting a significantly rising trend which has contributed to the impoverishment of the riverine population. The attendant uncertainties of climate change on hydrological and hydraulic river behaviour may exacerbate the channel instability of the Brahmaputra.
Bank Erosion and Bankline Shifting of Dhansiri River In Golaghat District, Assam (1999-2019
ECOLOGY ENVIRONMENT AND CONSERVATION, 2024
The Dhansiri River is the main river of the Golaghat District of Assam. However, unpredictable shifts of the river, serve erosion and frequent flooding have major adverse effect on the economy and ecology, affecting and threatening key villages, agricultural lands, school, and natural heritage sites. Erosion displaces a large number of the population often rendering them poor and landless. This study is aimed to investigate the flood erosion and bed aggradations scenarios of the Dhansiri River in the Golaghat district, Assam. Most of the villages in Golaghat district have been submerged by flood water and people and animal are taking shelter on the roadside and on the highlands. Golaghat in upper Assam has been most flood affected, where over 1, 19,179 people of 109 villages under Khumtai, Dergaon, Golaghat and Bokakhat revenue circle in Golaghat district have been affected by floods due to rise water of Brahmaputra and Dhansiri rivers. There are many problems being faced by this flood affected are due to river bank erosion: social, economic, health, education and political. The major impact of erosion is social, i.e., homelessness due to land erosion which compels people to migrate. After forced migration they suffer economic crisis, namely loss of occupation and loss of property.
River Bank erosion has emerged to be one of the most annoying environmental hazards these days. It is a complex process which incorporates actions of several complex processes and cannot be attributed to any single process. At present, the average quantum of land engulfed by the rivers is about 800 hectares in West Bengal. River Bhagirathi –Hooghly, the most prominent river of the state has resorted to large scale bank slumping and flood in Shantipur, Nadia, the birth place of Vaishnavism. Though there has been immense study on the erosional activity of this river in the state, Shantipur has not got enough importance on this matter. Eminent national and international scholars have detected the causes of such erosional activities to be the typical flow properties of the river, the structural and compositional properties of the bank and climatic characteristics of the concerned area. This paper tries to throw some light upon the factors which have probably acted jointly to produce such large scale wearing away of land in this part of the planet.
Copernicus Publications on behalf of the European Geosciences Union Earth Syst. Dynam. Discuss., 3, pp. 1085–1106, 2012, 2012
The Kaziranga National Park is a forest-edged riverine grassland inhabited by the world’s largest population of one-horned rhinoceroses, as well as a wide diversity of animals. The park is situated on the southern bank of the Brahmaputra River at the foot of the Mikir 5 Hills. National Highway 37 forms the southern boundary and the northern boundary is the river Brahmaputra and covers an area of about 430km2. The Brahmaputra River flows by Kaziranga National Park in a braided course for about 53 km. Sequential changes in the position of banklines of the river due to consistent bank erosion have been studied from Survey of India topographic maps of 1912–1916 and 10 1972, satellite IRS LISS III images from 1998 to 2008 using GIS. Study of bank line shift due to the bank erosion around Kaziranga has been carried out for the periods 1912–1916 to 1972, 1972 to 1998 and 1998 to 2008. The amounts of the bank area lost due to erosion and gained due to sediment deposition are estimated separately. The total area eroded during 1912–1916 to 1972 was more (84.87 km2) as compared 15 to accretion due to sediment deposition (24.49 km2), the total area eroded was also more in 1972–1998 (44.769 km2) as compared to accretion (29.47 km2) and the total area eroded was again more in 1998–2008 (20.41 km2) as compared to accretion (7.89 km2). The rates of erosion during 1912–1916 to 1970, 1970 to 1998, and 1998 to 2008 were 1.46, 1.59 and 1.021 km2 per year, respectively. During the entire period 20 (1912–1916 to 2008) of study the erosion on the whole was 150.04 km2 and overall accretion was 61.86km2 resulting in a loss of 88.188km2 area of the park. The maximum amounts of shift of the bankline during 1912–1916 to 1970, 1970 to 1998, and 1998 to 2008 were 4.58 km, 3.36 km, and 1.92 km, respectively, which amount to the rates of shift as 0.078, 0.12 and 0.096km per year, respectively. A lineament and a few faults 25 have controlled the trend of the course of the Brahmaputra around Kaziranga area. The main cause of erosion of the Brahmaputra is the loose non-cohesive sediments of the bank throughout the park. The braided channel of the river strikes the bank directly and undermines the silty bank causing overhanging blocks to be carried away easily by the river current. In future deposition is likely to be more in upstream or eastern part of Kaziranga and erosion in middle part of Kaziranga national park area due to the river Brahmaputra. Antierosion measures have been adopted only in a few places to check bank erosion at Kaziranga.
IAEME PUBLICATION, 2020
The problem of bank erosion by the river is becoming very serious day by day. The state of Assam in India is such a flood affected region which bears the brunt of bank erosion by the mighty river Brahmaputra and its tributaries in every rainy season. The flood and bank erosion by the river Jia Bharali, a right bank tributary of the Brahmaputra, have been creating havoc in the Panchmile area of Tezpur town for the last few decades. Due to its increasing erosive intensity day by day the Panchmie area is now under severe threat of erosion and the river start to shift towards northwest, if it’s shifting continues then it will be a thinkable matter for the people of Tezpur town in near future. Keeping this in mind, an attempt to study about the bank erosion problem of Panchmile area and its consequent impact in details with the help of geo-spatial tools is made.