Short Review Paper International Research Journal of Earth Sciences ISSN 2321 2527 RS and GIS based assessment of Bank Erosion in Goalparaa District part of Brahmaputra River, Assam, India Abstract G. Thakuriah * and R. Saikia Geography Department, Cotton University, Guwahati, India gthakuriah@yahoo.in Available online at: www.isca.in Received 19 th October 2017, revised 6 th March 2018, accepted 24 th March 2018 Bank erosion is a common hazard in middle course of Brahmaputra River. Bank instability mapping is an important element for planning in bank erosion affected area. Taking Goalpara district of Assam as an example, a land loss map is carried out using available satellite data and data from governmental agencies. The assessment of bank erosion in Goalpara district part of Brahmaputra River is done using Geo spatial tools. It is found from the assessment that 59 km 2 areas are loss through bank erosion in Goalpara district part of Brahmaputra River during 1970-2010. Therefore, the study area can recognize as high risk location of bank erosion and needed specific planning and development for reinstate the problem. Keywords: River morphology, Bank line migration, remote sensing and GIS. Introduction River bank erosion is an important phenomenon of channel change. It is a dynamic geomorphic process that occurs rapidly for a short duration during and after floods resulting in meandering of rivers as well as alteration of channel course. Such type of erosion affects a range of physical, social, ecological management issues in the environment. Bank erosion is a function of many interrelated factors like-flow characteristics, composition of bank materials, channel geometry etc, vegetation cover and man induced factors like human habitation near the river bank, removal of vegetation cover from the river bank area etc. Variation in water and sediment discharge causes massive lateral modification and river bank erosion 1. The shear stress associated with water steepen river bank through corrosion and finally given rise the structural failure of unstable bank 2. Extraction of river resources likes sand and gravel is a major factor of bank erosion. River banks after erosion in the Brahmaputra-Barak river of Assam are a serious problem. This is mainly caused due to intensive rainfall in upper catchment as well as plain areas during summer months, which causes high flood discharge in Brahmaputra River which is the only outlet channel towards west. Rain water released from three sides surrounded by Bhutan and Arunachal Himalaya in the north and east, Patkai-Purbanchal hill, Barail range and Karbi-Meghalaya plateau in the south into very low gradient Brahmaputra plain, causes massive flood situation in low lying area of the Brahmaputra plain. Composition of highly erodible bed and bank material became go downstairs in long time of inundation and intense flow of flood water. Moreover human habitation near the river bank, removal of vegetation cover from the river bank area and extraction of river resources likes sand and gravel is a major factor of bank erosion of Brahmaputra River. The Brahmaputra is a braided channel. Most of the sandbars and river islands are temporary in nature 3. The Brahmaputra River flows over different district boundary of Assam namely Tinsukia, Dhemaji, Dibrugarh, Lakhimpur, Majuli, Jorhat, Sibsagar, Golaghat, Biswanath, Sonitpur, Nagaon, Marigaon, Darrang, Kamrup, Barpeta, Nalbari, Goalpara, Bongaigaon, Dhubri and Mankachar. Some district have severe bank erosion problem. Goalpara is such a district located to the south bank of river Brahmaputra toward downstream. The Brahmaputra has been shifting slowly southward 4. In Goalpara district, the bank line of Brahmaputra is migrated southward through bank erosion. Remote sensing with GIS plays an important role in river morphology and river bank erosion studies 5. Therefore, river bank erosion assessment in Goalpara district part of Brahmaputra River is done at 1:50,000 scale using geospatial tools to identify high risk location of erosion. Geographically Goalpara district is extended from 25 52'59.93"N to 26 13'31.223"N latitudes and 90 07ʹ07.311"E to 91 06'07.337"E longitude (Figure-1) covering an area of 2008.1km 2. Physiographic characteristics of the district are mostly plain with isolated hills and extended parts of Garo hills uplands. The mighty river Brahmaputra flows to the northern boundary of the district. It located at subtropical monsoon belt of Lower Brahmaputra plain region. The climatic characteristic of the study area is highly seasonal rainfall, more than 77% of the total rainfall occurs during summer months May-September in the form of heavy shower leads to inundation and high soil erosion during flood period and river bank erosion during and after flood. The distribution of rainfall over the district is not uniform. The average annual International Science Community Association 1
International Research Journal of Earth Sciences ISSN 2321 2527 rainfall in lower reaches has 180cm where as the upper reaches toward south rises up to 225cm. Methodology The assessment of river bank erosion of Goalpara district is carried out using high resolution (IRS LISS IV) satellite imagery and other auxiliary data for identifying land loss area. The location map of Goalpara district is delineated from SOI, toposheet at scale 1:50,000. The remote sensing data has the ability to provide spatial-temporal temporal measurement of many hydrological variables, which is time consuming and expensive to measure with available traditional methods metho and tools. In this paper, it is investigated how the geospatial technology can implement for bank erosion affected area. Figure-1: Study area map. Table-1: Details of data base. Data base type Data base Toposheet No6 78J/4, 78J/8, 78J/12, 78J/16, 78N/4 78K/01, 78K/05, 78K/09, 78K/13 & 78O/01 Rainfall data7 Station- Goalpara, Boko, Williumnagar, Dhubri, Bongaigaon and Barpeta Thematic map Soil map8 Satellite image9 IRS LISS IV, 09/03/2010 Village Map10 Revenue village International Science Community Association 2
Results and discussion The bank erosion of Brahmaputra River in Goalpara district is a natural phenomenon in summer months. It is a combine effect of high seasonal rainfall, structure and composition of soil, topography and drainage network and land use and land cover etc. These contributing factors of bank erosion of Brahmaputra in Goalpra district are analyzed in details: Rainfall: North East India is an area of high rainfall 11. High rate of recurrence and magnitude of rainfall over the Garu Hill and human interfering activities on natural environment are main causes of flood in Goalpara district 12. In Goalpara, the intensity of rainfall was rise up to 32.4cm in an hour on 22 nd September 2014. Total and average hourly rainfalls for the same day are 191.2cm and 7.96cm respectively 12. High intensity of rainfall in upper catchment area causes flood in downstream and consequent land loss of Brahmaputra river bank in the Goalpara district 12. Soil: Soil characteristics are an important constituent factor of bank instability and resultant flood susceptibility 13. In Goalpara district of Assam, there are nine different soil textures are found with including three parent matters i.e. Alluvium, Gneiss and Sandstone. The bank of the Brahmaputra in Goalpara district is composed of highly erodible alluvium soil, coarse-silty soil texture with taxonomy Aeric Fluvaquents. Therefore, unstable bank material causes bank erosion of each flood period in Brahmaputra River bank of Goalpara district. Figure-2: Soil map of Goalpara district. Figure-3: Drainage map of Goalpara district. International Science Community Association 3
Drainage: Tributaries and their connected distributaries are also main reason for flood risk as well as river bank erosion 14. Nature of drainage network in Goalpara district is another important contributing factor of bank erosion. The important tributaries of Brahmaputra in Goalpara district are Dudhnoi, Krishnai, Jinari or Balbola, Jinjiram. Out of which Dudhnoi, krishnai and Jinari river are originate from Garo hills of Meghalaya Plateau in southeastern boundary of the district and flow toward north and meet Brahmaputra. But Jinjiram River originate from Meghalaya Plateau and flow toward west and parallel to the Brahmaputra and meet Brahmaputra in Mancachar part of Dhubri district in Assam. The general slope of landscape is south to north in eastern part of the district, but it is towards west from central part of the district. There are numbers of riverine wetlands form in western part. In summer, these wetlands are linked with streams and Brahmaputra River. Therefore, the bank line of river Brahmaputra tends towards south after each flood inundation and bank erosion. Land use: Type of land use in bank side and their nature is another important weighted factor of bank erosion. Land use map of Goalpara district is prepared from satellite data using supervised interpretation technique in ERDAS 9.3 software 15. Field verification is done before interpretation and necessary information about the ground truth are collected. There are seven different land use /land cover are identified i.e. settlement, cropland, forest, scrub land, sand bar, water bodies specially wetland, pond and river etc. The erosion affected area of Goalpara district is covered by settlement and crop land. Area Assessment: The district boundary map is prepared from SOI toposheet, at scale 1:50,000 in Arc GIS software. The district map of Goalpara of Assam with Brahmaputra part is delineating from toposheets, surveyed in 1970-71 and satellite Imagery, 8/02/2010 (IRS LISS IV) separately in Figure-5. From the figure, the bank erosion prone areas are identified properly. It is evaluate from the figure that the Brahmaputra River became wider 2km-4.7km more in 2010 than in 1070-71 through erosion of south bank. It is observed from the table 2 that 294.1km 2 area covered by Brahmaputra river and riverine landform developed by the river especially sand bars locally known as char, chaporis and river island etc during the survey, 1970-71 by SOI (Survey of India). These areas occupy 179 revenue village of the district which is shown in Figure-6. After forty years, these areas are increased up to 353.1km 2 and covered 231 revenue village of the district (Figure-7). During these periods, it is observed from the Figure-8 that 52 revenue villages in south bank of Brahmaputra in Goalpara district was loss through bank erosion in flood period and form new sand bars in dry season through deposition of sediment in river bed and bank of Brahmaputra River. Figure-4: Land use map. International Science Community Association 4
Table-2: Land cover change from 1970 to 2010. Level-I Level-II Area (in km 2 ) 1970-71 2010 Change rate (in Per cent) Brahmaputra River Water Body 120.9 113.5-6.12 Sand Bar 173.2 239.6 38.33 Other Other land use 1714.0 1655.0-3.44 Total 2008.1 2008.1 Figure-5: Bank erosion affected area. International Science Community Association 5
Figure-6: 179 village boundary of Goalpara district in Brahmaputra River, 1070-71. Figure-7: Village boundary of Goalpara district in Brahmaputra River, 2010. Figure-8: Overlay map of village boundary. International Science Community Association 6
Figure-9: Bank line migration in Goalpara district part of Brahmaputra River. Bank line migration: The bank line of Brahmaputra in Goalpara district is migrated gradually toward south through south bank erosion. It is observed from SOI, toposheet that bank line of the Brahmaputra River in lower Goalpara is flow from 33m to 30m BM at the distance of about 37.6km. The general slope of south bank is 7.79cm/km. In 2010, the bank line is shifted toward 2-4.7km south of line in 1970-71. Jinjiram River of Goalpara District flow toward west and parallel to the Brahmaputra and meet Brahmaputra in Mancachar part of Dhubri district in Assam. The general slope of landscape is towards west from central part of the district. There are numbers of riverine wetlands are form in western part of the district. In summer, these wetlands are linked with streams and Brahmaputra River. Therefore, the bank line of river Brahmaputra tends towards south after each flood inundation and bank erosion. Conclusion It may be concluded that the bank erosion is a natural phenomena which is very severe problem in Brahmaputra River. High intensity rainfall and resultant flood event, highly erodible bank material, soil characteristics, drainage system, slope, land use and land cover change are considered most important contributing factors of river bank erosion in Goalpara district part of Brahmaputra River. Maps of erosion affected areas are identified and prepared in GIS environment. It is found from the study that there are 52 revenue villages covering 59km 2 areas in south bank of Brahmaputra in Goalpara district was loss through bank erosion within forty years. The study area needs corrective measure, appropriate planning and governmental support for stabilize of bank line and protect from river bank erosion. References 1. Guite L.T.S. and Bora A. (2016). Impact of River Bank Erosion on Land Cover in Lower Subansiri River Flood Plain. International Journal of Scientific and Research Publications, 6(5), 480-486. 2. Islam M.S. (2008). River Bank Erosion and Sustainable Protection Strategies. Fourth International Conference on Scour and Erosion, 316-323. 3. Patil J.K., Lal J., Prakash K. and Bhusan R. (2008). Spatiotemporal shift of western bank of the Ganga River at Allahabad city and its implications. Indian Soc. of Remote Sensing, 36(3), 289-297. 4. Taher M. and Ahmed P. (1998). Geography of North East India. Natural Hazard, Mani Manik Prakash, Guwahati, 54-64. 5. Thakur P.K., Laha C. and Aggarwal S.P. (2011). River bank erosion hazard study of river Ganga, upstream of Farakka barrage using remote sensing and GIS. Natural Hazards, 61(3), 967-987. http:// dx.doi.org/10.1007/ s11069-011-9944-z. 6. Survey of India (1967) 7. Meteorological and Oceanographic Satellite Data Archiving Centre, ISRO (2014) 8. Department of Agriculture, Government of Assam (1999) 9. National Remote Sensing Agency (NRSA), Hyderabad, (2010) 10. District Commission Office, Goalpara (1991) International Science Community Association 7
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