A DISPARITY BETWEEN EROSIONAL HAZARD AND ACCRETION OF THE SUNDARBANS WITH ITS ADJACENT EAST COAST, BANGLADESH: A REMOTE SENSING AND GIS APPROACH (original) (raw)
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Remote Sensing of Environment, 2011
The Sundarbans is the world's largest remaining single block of mangrove forest, covering approximately 1 million ha (~10,000 km 2) of the Ganges-Brahmaputra delta along the coastal areas of India and Bangladesh. Sea level rise and alteration of water flows of the Himalayan headwaters are among the major disturbances threatening these coastal areas. But very few studies exist on the dynamics or current status of the Sundarbans coastline. We used Landsat images spanning from 1973 to 2010, and an algorithm that we developed, to consistently estimate the spatiotemporal dynamics of erosion and accretion for four different time intervals and the whole study period. Our results show that the direction and extent of erosion and accretion rates varied throughout the different periods. Erosion was the highest in the 1973-1979 interval, with 23.2 km 2 year −1 of land loss. However, that rate substantially declined in the following periods, reaching a rate of 7-10 km 2 year −1. Accretion showed a rate of 10 km 2 year −1 between 1973 and 1989, but substantially declined to~4 km 2 year −1 between 1989 and 2010. Accretion rate has declined in the recent years but erosion rate has remained relatively high. As a result the delta front has undergone a net erosion of~170 km 2 of coastal land in the 37 years of our study period. These numbers are significantly higher than the previously reported rates and magnitudes of erosion in this area. The methods and maps developed in this study may be helpful in management planning of this vulnerable coastline.
Predictive assessment on landscape and coastal erosion of Bangladesh using geospatial techniques
Elsevier Journal- Remote Sensing Applications: Society and Environment, 2019
Coastal erosion, land use and land cover (LULC) changes analysis using remote sensing is a dynamic, relatively low cost based precise method using now a day. Coastal districts of Bangladesh occupied by naturally grown mangrove forest which are susceptible to rapid land cover (LC) changes and natural erosion. Barguna and Patuakhali districts of Bangladesh deserve special attention for conserving coastal mangrove forest named Tengragiri Wildlife Sanctuary and variety of human forces income. The core objective of this research is to analyze the LULC change along with coastal erosion analysis from 2000 to 2017. Combination of four years Landsat satellite image analysis, primary field data, geo-tag photography, secondary information, utilization of forest carbon inventory 2015 data, and semi-structured questionnaire are the key approaches adopted in the study. K-means cluster based unsupervised and maximum likelihood supervised classification by using ERDAS Imagine 2014 found the total study area is 33,361 ha. Random sampling (40 points/class) based accuracy assessment and verification by google earth pro 7.1 found overall accuracy 88.15% and Kappa coefficient is 0.867. Python coding program and overlay operation tested for conversion analysis any found weighted overlay provide best results. An intensive RS analysis of 33,564 ha mangrove forest and community landscapes generated six (6) distinct land cover class and sub-classes, e.g. Forest, agriculture & grassland, plantation, sandbar, settlement and waterbody. During 2000-2017, agriculture and grassland were decreasing 23 ha/year. Out of 11,831 ha (in 2000) Agri-grass land 9,326 ha remained intact while remaining 2,246 ha converted to settlement mixed with homestead plantation class. This study also presents the landscape erosion-accretion due to natural, quasi-natural and anthropogenic interventions which shows that, along the river flow and at the confluence at the Nishanbaria Union (local name Khouttar Char & Fakir hat) to lower side of the Tengragiri WS locations are susceptible to high trend of land erosion whereas accretions are prominent on the reverse sides named Baliatali Union, Barabagi Union and so on. These results of the study and developed maps will be helpful for the community people, line departments, national and international policy maker and the researchers' community for monitoring coastal geomorphology including erosion and accretion of this landmass.
Journal of Geography, Environment and Earth Science International, 2018
Sundarban mangrove delta represents one of world's delta where the Tidal action is extremely active. This unique tropical ecosystem has been delineated as almost vulnerable and disaster prone area in the world due to several aggressive natural hazards like sea level rise, cyclone, coastal erosion, salinization etc. Coastal erosion is the one of the most important hazards. This paper aimed to evaluate the coastal erosion in this area. It also attempted to find out the causes and consequences of coastal erosion in this area. Another objective of this study is to measure and quantify the rate and pattern of coastal erosion. Gobardhanpur and its surrounded mouzas (Mouza is the least administrative area in India. It is also called as a village) have been chosen for the study area. This village is most affected area due to coastal erosion in this region. Descriptive types of research method, literature survey, and questionnaire survey methods have been applied to this work. Questionnaire has prepared by 4 point Likart scale. Satellite data, mouza map and topographical map have been used for chronological analysis and determination of the rate of erosion. The maps and satellite images have been processed to digital images and superimposed for exploration of a pattern of coastal erosion through image processing software. The result shows that the Gobardhanpur and Plot G 6 th portion are the most affected area. Another finding is that the Plot G 6 th Portion almost vanished from the map. The cause of the coastal erosion of this area is
TIJ's Research Journal of Science & IT Management - RJSITM, 2014
Natural resources of off shore island of Bay of Bengal (BoB) have been used for multiple purposes and have strongly influenced socioeconomic development. Conventional methods of collecting information about coastal area are relatively costly, time consuming and inaccurate. On the other hand Remote Sensing (RS) observation with its unique capability provides cost-effective support in compiling the latest information about the environment of coastal area, while Geographic Information System (GIS) facilitates uses for multidisciplinary analysis and decision support. Integrated analysis of RS and GIS can gives a vital input for better planning for exploration, exploitation, conservation and management of resources. In this study Sandwip Island of the BoB has been selected as study area. Landsat MSS (80 m) data of 1973, Landsat TM (30 m) data of 1989 and 2010 were used to generate digital data base of different time period, analysis of erosion and accretion and finally produced digital map of Sandwip island of Bangladesh in different time period. For land water layer generation, near-infrared band of (0.76 to 0.90 μm) has been used to develop an algorithm. In this study DN values of water in band 4 of Landsat-TM have been collected carefully from the histogram of the selected images and applied in the developed algorithm. Erosion and accretion map has been produced using raster base GIS and ArcGIS analysis. The study reveals that about 7068 ha area has been disappeared in the sea during 37 year (1973-2010) of which during 1973 to 1989 the rate of erosion per year was about 316 ha but during 1989 to 2010 it was reduced to 24 ha only.
The numerous tidal river systems have made Sundarban delta one of the most dynamic geomorphic regions of the world. Through time morphological shape and extent of shoreline and river bank configurations have changed considerably through intense erosional and depositional processes by the longshore current and tidal flow pattern in Sundarban. The present study has made an assessment of morpho-dynamic behavior of bank lines for the time-period between 1925-26 and 2014 to identify nature and extent of erosion and deposition of different geomorphic units through consultation and preparation of geo-spatial database comprised of old maps and recent satellite images. Besides, detailed field investigations have also been carried out to understand different processes regarding the bank line changes. Finally different erosion hazard zones have been identified based on the net areal changes.
Quantitative techniques, statistical methods and mathematical rules make the geospatial analysis more systematic, accurate and precise. In order to measure the intensity of the ongoing processes on the earth surface, evaluate the spatio—temporal changes in geographical attributes, highlight the principal factors for any geographic events and to identify the future possibilities , quantitative techniques are for most dependable. In the present article sequential changes of the shoreline, spatio—temporal extent of erosion and depositional processes of Sundarban region, West Bengal, India, have been measured following the selected quantitative techniques. The Sundarban is one of the most dynamic geomorphic units in the earth surface, situated in the northern apex of Bay of Bengal. The region has formed, sculptured and modified due to continuous sedimentation of the Ganga and the Brahmaputra systems, intense tidal hydro dynamic behavior, climatic disturbances and anthropogenic activitie...
Journal of the Geological Society of India, 2022
The coastal region is one of the most sensitive areas on earth. This region has a diversified ecosystem. Erosion and accretion are common natural phenomena that can be seen in this region. In some circumstances, these changes become hazardous to the coastal ecosystem. Natural processes such as rainfall, flood, cyclone, longshore drift, and tectonic shifts can trigger irregular coastal changes. Similarly, anthropogenic factors such as urbanization, unscientific land usage, mining, etc., enhance coastal dynamics and make larger changes. Hence identification of such region has great importance. Geospatial technology has brought various advanced methods for shoreline change studies. It has decreased the huge effort for getting an accurate result for a larger area. Landsat satellite imageries with 30 m spatial resolution have been used for studying the changes in the shoreline of Ramanathapuram for the years 2000, 2005, 2010, 2015 and 2020. In Geographic Information System (GIS) software, the Digital Shoreline Analysis System (DSAS) tool is added for shoreline change analysis. DSAS will build the baseline transects. The rate of shoreline change was calculated using the MATLAB feature runtime function for ArcGIS. Based on the DSAS output, the region of high erosion, low erosion, stable, and low accretion, high accretion zones have been identified on the shore. The results reveal that 5.1% of the shoreline, around 9.3 km is under high erosion, 11.5% of the shoreline, which is around 20.8 km, is under low erosion, 71% of the shoreline, around 128 km, is a stable region, 6.7% of shorelines, around 12 km, have low accretion, and 5.6% of shorelines, around 10.1 km, have high accretion. The coastal villages, namely, Mayakulam, Keelakakrai, Periapattinam, Mandapam, West-Pamban, and East-Rameswaram, have a high erosion with a maximum rate of change between 2.29 to 5.11 m/y. The coastal villages Ervadi, Kalimankund, Sattankonvalsai, South-Pamban and South- Rameswaram have high accretion with a maximum rate of change between 2.34 to 5.24 m/y.
Indian Journal of Geo Marine Sciences, 2021
Shoreline change study is very challenging for any coastal scientists because of its dynamic changes. Erosion and accretion processes directly control the shoreline and coastal landforms. The present study is attempted to assess the shoreline changes between the Vembar and Tharuvaikulam coast of the Thoothukudi district, Tamil Nadu, India. Both the places were regarded as two zones viz. Vembar and Tharuvaikulam zone. These zones are further subdivided into three grids to understand and mark the erosion and deposition zones. The shorelines were digitized from satellite images of Landsat-5 (1997) and Landsat-8 (2018), and also the base details were extracted from a survey of India (SOI, 1968). These shorelines were taken to Geographic Information System for overlay analysis to determine the extent of erosion and accretion in the study area. The result of this study shows that during the period 1968-1997, Vembar and Tharuvaikulam zones have noticed accretion with a rate of 6.9 m 2 /y and 4.5 m 2 /y, respectively. Whereas, during the period 1997-2018, the Vembar zone was subjected to erosion with a rate of-1 m 2 /y. While in the Tharuvaikulam zone, the accretion process has reduced with a rate of 0.1 m 2 /y. The study results have shown that the Vembar zone has undergone erosion, whereas; the Tharuvaikulam zone has undergone both erosion and accretion. The accretion process rate is less compared to the erosion process during 1968-1997. The study concludes that the erosion is increasing due to natural and human intervention.
Estimation of Areal Changes along the Coastline of Bangladesh due to Erosion and Accretion
International Journal of Engineering Sciences, 2019
The present study focuses on the entire coastline of Bangladesh, which was analyzed for the last thirty years, with a five years' interval in between, to identify the changes in the shoreline position due to erosion or accretion. Shoreline positions for the time period 1989-2019, were manually digitized using multi-temporal Landsat satellite images of 30m resolution and comparable tidal conditions. A polygon-based approach was then employed in Arc GIS to determine the areal changes in the three different exposed coastal zones. The central zone was found to be the most dynamic in terms of both erosion and accretion. The western zone was mostly characterized by erosion, whereas only the eastern zone experienced a net land gain in this time span. Periodic reversal from erosion or accretion was also noted in several locations. The outcome of this study regarding the general trend (erosional or depositional) along the coastline, is expected to aid the proper planning and land management of the coastal zones in Bangladesh.