Impact of human intervention on assessing downstream channel behaviour of Ichamati River on the lower Gangetic Plain of West Bengal, India (original) (raw)
Related papers
International Journal of Science and Research, 2019
Channel shifting is very common aspect of the flood plain environment all over the world. Bank erosion is the immediate effect of channel shifting. A rapid rate of river bank line shifting is found in the study area. The changing character of land use is being accentuated due to river bank erosion or channel shifting. In this study, the changes in Land use and Land Cover (LULC) driven by bank erosion were studied using P.S map and Google Earth map. The present study is mainly oriented towards the morphometric measurement of river through temporal changes during 1937, 2019 P.S map and Google Earth map data. In this paper an attempt has been made to get the nature of shifting, direction of shifting, sinuosity of the river channel has also been calculated.
Earth Systems and Environment, 2020
Rapid infrastructural development, triggered by the economic policies implemented in 1991, subsequently modified the river channel planform of the Terai region of northern West Bengal, India, through perceptible channel fragmentation, excessive in-channel sediment mining and rampant landuse alterations of the floodplains. In this context, this study has attempted to assess the impacts of anthropogenic interventions on fluvial regime of the lower reaches of Balason and Mahananda River of the sub-Himalayan region over the last 30 years by adopting a combined methodological framework of remote sensing and field survey. Results showed that initially the naturally vegetated areas had converted into crop land and grass land, tea plantation or bare land, and afterwards, the majority of it had been converted into built-ups. Besides, a noticeable amount of channel narrowing was directly proportionate to unrestricted sediment mining and embanking of the river channels, evidenced between 1987 and 2017. Comparison of measured multi-temporal channel width along with cross-profiles showed remarkable channel narrowing (18.8 m/year) as well as significant bed lowering (3.15 m). Studies reveal that the rivers have started showing signs of losing their existing equilibrium condition and if that happens then that will lead to the sinking of the ground water table, decreasing flood occurrence interval, destabilization of existing infrastructures associated with rivers, and destruction of river ecology. In order to restore the state of socio-hydrological as well as eco-hydrological amenities of these rivers, certain recommendations have also been made towards promoting the wise use of riverine resources by the local communities and policy makers.
The Ganga/Ganges 1 is an important river system in South Asia which supports the life and livelihoods of millions of people both in India and Bangladesh. The system has a number of names throughout its length. Below its con-fluence with the Brahmaputra at Aricha it is known as the Padma, which in turn merges with the Upper Meghna at Chandpur below which the channel is known as the Lower Meghna. There is a growing concern about this large river system because its channels are subject to frequent migration, threatening engineering structures and resulting in various environmental and social consequences which may be compounded by climatic variability, land use change, and agricultural intensification as the basin experiences rapid population growth. Concerns have been expressed that the construction of a barrage just upstream of the Indo–Bangladesh border has adversely affected the Ganges reach in Bangladesh. Partly in order to investigate this, the planform changes of the Ganges and the Padma within Bangladesh was analysed over the period 1973 to 2011 using multitemporal Landsat images and long–term flow data in eight epochs with an average duration of 4.5 years. The Padma reach is less affected by the barrage and provides a useful control study. Areas of erosion and deposition were determined from sequential changes in the bankline positions. Mean channel width, sinuosity and braiding index were analysed using a Geographic Information System (GIS). Flood frequency, duration and magnitudes were studied using long-term discharge records. Generally, channel planform evaluation indicated that both the Gan-ges and the Padma experienced contraction, expansion and readjustment in configuration over the last 38 years. Erosion and deposition statistics of the Ganges indicate that 57 km 2 of land was lost along the right bank whereas around 59 km 2 has been gained along the left bank during the assessment period, suggesting that the erosion and accretion of both banks is roughly balanced with a general movement towards the right bank. The width of the Ganges varied from a maximum of 5.36 to a minimum of 3.23 km during the observation period. Changes to sandbar area are, in general, much more radical than changes to the overall width and area of the channel. Measurement of areas of erosion and accretion showed that both banks of the Padma experienced considerable loss of land. The total net loss for left bank and right bank was 155 and 28 km 2 , respectively. The Padma is approximately twice the width of the Ganges and the changes to its channel area are not as temporally dynamic as the Ganges. The relationship between bank curvature and erosion/accretion of the river banks for both rivers was analysed and the results contradict established meander theory. Regression analysis between bank erosion rates, annual average discharge and mean flood flow data showed that bank erosion was significantly correlated with annual average discharge for the Padma (r 2 = 0.6283) and that the Ganges bank erosion rate is influenced by mean flood flow (r 2 = 0.6738). The flood frequency shows generally good stability across the first eight of the nine epochs for the Ganges but for the Padma the frequency showed even greater stability. We were unable to support the widely held belief that the upstream barrage has a deleterious effect on the Ganges but note that there is a slight effect due to the periodic release of sediment through scour sluices.
Journal of Geography & Natural Disasters, 2013
Channel changes with respect to time and space play a significant role in stream flow dynamics. The rambling and trailing of channels in the studied region has been studied through systematic analysis and interpretation of diverse channel configuration and multi-channel orientation using multi-temporal Topographical maps and Satellite images for a period spanning nearly 80 years (1930-2011). For this specific purpose lower course of Diana River in the Jaldhaka-Diana river system has been selected in the Duars region of the Jalpaiguri district, West Bengal which is virtually a zone of transition between the Himalayan Mountains and the North Bengal plain. The prime objective of the study is to reveal the spatio-temporal sequences of channel changes, consequent movement of confluence point and the factors and causes of such movement. For this particular extraction, Base map has been generated with the help of SOI Topographical maps and satellite images of the respective area. For this purpose updated version of ERDAS Imaging is employed as image processing tool for enhancing, merging and to update the spatial information of channel configuration and Arc GIS for final product generation. Following the specific objective of the study it has been deduced that during this span the confluence point has moved and reoriented both upstream and downstream on a historical time scale and new confluence points have been created by repeated shifting and migration of channels. No definite trend is observed in the movement of the confluence points. However, but it is noticed that some distinct flow dynamics and channel maintaining processes are actively performing in this spatio-temporal analysis of channel changes.
River channel changes of the Subansiri in Assam, India
Geomorphology, 1999
The sequential changes in the position of banklines as a result of bank erosion, as well as various changes in the channel have been studied in the Subansiri river in Assam, India. The study was carried out from available topographic maps of 1920, 1970 and satellite imagery of 1990. The types of changes taking place in the Subansiri river channel as observed from Ž. the above-mentioned maps and imagery are grouped into four categories: 1 alteration of the direction of flow due to neck Ž. Ž. Ž. cutoff , 2 widening of a channel in response to bar development, 3 development and subsequent abandonment of Ž. anabranches, and 4 progressive shifting of meander bends. The river channel has become substantially wider during the period of 1970-1990. There has also been a progressive increase in the number and area of mid-channel bars with a corresponding decrease in the number and area of point bars during 1920-1990. These periodic and progressive changes are responsible for a change in channel pattern of the river. A study made on nature and amount of change in the banklines of Ž. the Subansiri river by dividing the channel 84 km in 1970 into 10 equal segments reveals that the types of change are varied, and in some cases chaotic in nature. Study of the bankline shift of the Subansiri determined separately for the periods 1920-1970, 1970-1990 and 1920-1990 at 20 evenly spaced transverse sections reveals that there has been a substantial westward shift of both the banklines, up to a maximum of 6 km, in the three upstream sections during 1920-1970. However, shifting of banklines in both directions and the unequal amount of shifting in the same direction have caused a marked increase in channel width during 1970-1990. It is found that due to bankline migration, the total amount of area eroded along the entire course under study during 1920-1970 and 1970-1990 are 107.90 and 57.50 km 2 , respectively. The overall sinuosity which was 1.51 in 1920 has decreased to 1.30 in 1970, while the corresponding braiding intensity has increased from 0.79 to 1.32. The river channel seems to make a remarkable change from a meandering pattern in 1920 towards a braided pattern by 1990 as seen from gradual increase in overall braiding intensity.
The Egyptian Journal of Remote Sensing and Space Science, 2017
Channel migration becomes the main characteristic of the Khowai River of Tripura. A study on bank erosion and channel migration of the present course of the Khowai River through the synclinal valley of Atharamura and Baramura Hill Ranges indicates that the area is under active erosion since long back. In this study, the rate of channel migration has been assessed and variation of sinuosity index and radius of curvature have also been calculated. The study of the active channel width and channel position from 1975 to 2014 indicates that a large portion of land along both the banks of the Khowai River has already been eroded away. This work also documented land use changes in its surrounding flood plain area using supervised image classification. Overall accuracy of the land use classification ranges between 88% and 93%. The whole study is being done utilising the remote sensing imagery (2014), SOI topographical map (1975) and GIS technology. The land use classification shows that there is an increase in built up area and decrease in net sown area. The channel migration directly affects the land use and land use change has direct effect on the flood plain dwellers of the study area. All the assessments of this study highlight a significant message of immense vulnerability of Khowai River and also provide news about geomorphological instabilities of the study area.
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.
Riverbank Erosion and Channel Width Adjustments across a Meandering Channel of North Bengal, India
Earth Science India
Bank erosion as a natural agent of channel change owes special attention in geosciences arena. Indeed it is not only a process behind riverine dynamics but also is a quagmire for the river engineers, watershed planning agencies and especially to the coexisting human communities. An attempt has been made to reveal the processes and trends of riverbank erosion and channel width adjustments for the middle and lower course of the Duduya river belonging to the fertile North Bengal plains (with portions of upper reach fall within the highly dynamic Sub-Himalayan piedmont) of northern parts of West Bengal for a span of 24 years (1990-2014) primarily based on field observations along with the aid of Geographic Information System (GIS). Investigations cleared it out that the bank erosion trend was erratic. Recent bank erosion rate (5.99 meters/year during 2009-14) has shown signs of gradual decline from its earliest records (7.94 meters/year during 1990-2001). Primarily, riverbank composition, riparian vegetation and seasonal discharge variations have been found as the significant controllers of the bank erosion processes along with certain moderating effects of human interventions. Similarly, channel width adjustments were also been random, tended towards expansion along lower courses while headed for contraction along the middle one, guided predominantly by the opposite processes of erosion-deposition.
A Study on Channel Migration of the Subansiri River in Assam Using Remote Sensing and GIS Technology
Current Science, 2014
The Subansiri is a major Trans Himalayan tributary of the River Brahmaputra, characterized by its extremely dynamic and unstable alluvial channel in Assam. In this study, the pattern of channel shifting as well as various other changes of the Subansiri river have been studied for the period from 1828 to 2011. Five different types of channel shift have been observed in the Subansiri river. They are (i) alternate barinduced shifting, (ii) neck cut-off, (iii) chute cut-off, (iv) meander shift and (v) avulsion or rapid diversion. The channel pattern of the Subansiri river in Assam changes continuously with large number of channels being abandoned and new channels developed in the course of a few years. Large discharge and heavy sediment load during floods cause the river to be extremely unstable, because of which it consistently migrates laterally from the eastern side to the western side of the basin abandoning the earlier channels.
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).