Estimation of Areal Changes along the Coastline of Bangladesh due to Erosion and Accretion (original) (raw)
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Ocean & Coastal Management, 2018
This paper draws upon the application of GIS and remote sensing techniques to investigate the dynamic nature and management aspects of land in the coastal areas of Bangladesh. The geomorphological characteristic of the coastal areas is highly dynamic where land erosion and accretion with different rates remain a constant phenomenon. This study focuses on three coastal zones: western, central and eastern that comprise the entire coastal area of the country. At its core, this study uses the past 30 year Landsat satellite images. This research reveals that the rate of accretion in the study area is slightly higher than the rate of erosion. Overall land dynamics indicate a net gain of 237 km² (7.9 km² annual average) of land in the area for the whole period from 1985 to 2015. The results also demonstrate that the rates of both erosion and accretion are higher in the central zone compared to the western and the eastern zones of the coastal area. This is the first time that the entire coastal areas of Bangladesh have been considered for assessment. This study also recommends that coastal managers, planners and policymakers to consider the identified dynamic trends of coastal land before opting for any specific measure. Constant monitoring using the GIS and remote sensing techniques would be a viable management for this purpose. This study has identified some causes of land dynamics, particularly for the three coastal zones, that might be helpful for policymakers in identifying the nature of interventions needs to be taken for specific coastal zones.
Rates of shoreline change along the coast of Bangladesh
Bangladesh, at the confluence of the sediment-laden Ganges and Brahmaputra Rivers, supports an enormous and rapidly growing population (>140 million in 2011), across low-lying alluvial and delta plains that have accumulated over the past few thousand years. It has been identified as one of the most vulnerable places in the world to the impacts of climate change and sea-level rise. Although abundant sediment supply has resulted in accretion on some parts of the coast of Bangladesh, others are experiencing rapid erosion. We report a systematic assessment of rates of shoreline change over a 20-year period from 1989 to 2009, using Landsat satellite images with pixel resolution of 30 m on the ground. A Band ratio approach, using Band-5 divided by Band-2, discriminated the water line on images that were largely cloud-free, adequately registered, and at comparable tidal stages. Rates of shoreline change were calculated for >16,000 transects generated at 50 m intervals along the entire mainland coastline (>1,100 km) and major islands, using the End Point Rate (EPR) method in the Digital Shoreline Analysis System (DSAS) extension in ArcGIS®. Erosion characterises most of the seaward margin of the Sundarbans in western Bangladesh. Retreat rates of up to 20 m/yr are typical, with little evidence that local devastation of the mangrove fringe by Cyclone Sidr in November 2007 had resulted in uncharacteristic long-term rates of retreat where it made landfall. Erosion exceeded accretion in the Barguna Patuakhali coastal zone, most of which eroded at up to 20 m/yr, but with truncation of the southern tip of the Patharghata Upazila at up to 100 m/yr. In Bhola, erosion at rates of up to 120 m/yr were observed along much of the coast, but in the Noakhali Feni coastal zone, similar rates of erosion were balanced by rapid accretion of the main promontory by more than 600 m/yr. Rates of change were more subdued in the Chittagong and Cox’s Bazar coastal zones of southeast Bangladesh. Islands in the Meghna estuary were especially dynamic; Hatiya Island accreted along some of its shoreline by 50 km2 between 1989 and 2009, but lost 65 km2 through erosion elsewhere, resulting in the island moving south. Similar trends were observed on adjacent islands. The overall area changed relatively little across the entire coastline over the 20-year period with accretion of up to 315 km2, countered by erosion of about 307 km2.Bangladesh, at the confluence of the sediment-laden Ganges and Brahmaputra Rivers, supports an enormous and rapidly growing population (>140 million in 2011), across low-lying alluvial and delta plains that have accumulated over the past few thousand years. It has been identified as one of the most vulnerable places in the world to the impacts of climate change and sea-level rise. Although abundant sediment supply has resulted in accretion on some parts of the coast of Bangladesh, others are experiencing rapid erosion. We report a systematic assessment of rates of shoreline change over a 20-year period from 1989 to 2009, using Landsat satellite images with pixel resolution of 30 m on the ground. A Band ratio approach, using Band-5 divided by Band-2, discriminated the water line on images that were largely cloud-free, adequately registered, and at comparable tidal stages. Rates of shoreline change were calculated for >16,000 transects generated at 50 m intervals along the entire mainland coastline (>1,100 km) and major islands, using the End Point Rate (EPR) method in the Digital Shoreline Analysis System (DSAS) extension in ArcGIS®. Erosion characterises most of the seaward margin of the Sundarbans in western Bangladesh. Retreat rates of up to 20 m/yr are typical, with little evidence that local devastation of the mangrove fringe by Cyclone Sidr in November 2007 had resulted in uncharacteristic long-term rates of retreat where it made landfall. Erosion exceeded accretion in the Barguna Patuakhali coastal zone, most of which eroded at up to 20 m/yr, but with truncation of the southern tip of the Patharghata Upazila at up to 100 m/yr. In Bhola, erosion at rates of up to 120 m/yr were observed along much of the coast, but in the Noakhali Feni coastal zone, similar rates of erosion were balanced by rapid accretion of the main promontory by more than 600 m/yr. Rates of change were more subdued in the Chittagong and Cox’s Bazar coastal zones of southeast Bangladesh. Islands in the Meghna estuary were especially dynamic; Hatiya Island accreted along some of its shoreline by 50 km2 between 1989 and 2009, but lost 65 km2 through erosion elsewhere, resulting in the island moving south. Similar trends were observed on adjacent islands. The overall area changed relatively little across the entire coastline over the 20-year period with accretion of up to 315 km2, countered by erosion of about 307 km2.
With a total population of 278000, Sandwip has long been facing severe land erosion and accretion problems because of its geographical setting in the coastal area of Bangladesh. This research aimed to assess the erosion and accretion status along with the shoreline movement of this island based on multi temporal Landsat imagery and hydrological data from 1974 to 2014. The results revealed that water discharge and water level data are positively correlated with erosion and negatively correlated with accretion data. The results also indicate that the island has lost around 90 km 2 of its stable and gained around 17 km 2 of new land. The erosion activity is mostly happening in the northwestern, western, and southern banks whereas accretion has been occurring at a slower rate in the northern and eastern banks of the island. Because of this dynamic erosion-accretion activity the shoreline of the island has been moving towards the northeast side. This 40 years' data analysis solemnly affirms that maximum shoreline movement towards the land was 4004 meter in the southern bank with annual rate of approximately 100 m per year. At the same time interval, maximum seaward movement of the shoreline was observed in the northeastern portion (NSM >2247 m) at a maximum net rate of around 56 m per year (EPR = 55.85 m per year). Because of this idiosyncratic characteristic Sandwip's total land area was reduced to 73 km 2 during 1974 and 2014.
Asian Journal of Geographical Research, 2019
Coastal zones are the most dynamic feature of earth surface in which lithosphere, hydrosphere and atmosphere gets into contact with each other. Such dynamic process should be monitored with great importance as a large portion of the world’s population is living along the coastal zones. This paper focuses on delineation of the changes in the coastal land areas of Chittagong in Bangladesh through the shifting of coastline. Chittagong coastal area is around 245 km with an unbroken 125 km gently slopped sandy sea beach in Cox’s Bazar. However, due to both the natural phenomenon and human interventions, coastline in these areas has been changing gradually. These changes have occurred in relation to land biomass, erosion and accretion rate. Therefore, shoreline geometry analysis can help understand such dynamic coastal process. Several satellite images from Thematic Mapper (TM) and Enhanced Thematic Mapper (ETM) were used for the long term coastline change analysis. The digital shoreline ...
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 engineering advancements, 2022
Bhola, the largest island of Bangladesh located at the estuarine mouth bar of the Bay of Bengal is very dynamic and unique in nature due to its physiographical configurations and is experienced severe morphological i.e. erosion-accretion changes. Of late, monitoring of coastal morphology and changes in shoreline trend analysis has conveniently been done through the integration of remote sensing satellite imageries and GIS techniques. The present study is an endeavor to detect and analyze the morphological changes on Bhola Island. Multi-temporal satellite images are the main data sources to attain the objectives through the integration of RS and GIS. The study concludes from the recent 42 years (1974-2016) satellite data that-the Island is in the losing phase since 1974. The erosion processes are still active along the eastern and northeastern parts of Bhola Island due to the direct influence of the Meghna Estuary on the land by the steep bank slope, high tidal water pressure, and loose bank materials. Erosion is the burning issue on Bhola Island and due to this a large number of people are landless every year. On another side, accretion is being operated in a large part surrounding the Island increasingly in the southern part due to backwash sediment deposition by channel and estuary with the favor of a gentle topographic slope along the bank.
Bangladesh Journal of Scientific Research, 2016
A ~65 km coastal stretch has been analyzed to estimate the change dynamics of Kutubdia Island with the help of digital shoreline analysis system (DSAS). This study investigated the reliability of medium resolution satellite imagery for mapping shoreline positions and for estimating historic rates of changes. Nine shoreline positions were extracted on 1972, 1976, 1980, 1989, 1999, 2004, 2009, 2011 and 2014 covering a long term of 42 years period. Rates of shoreline changes were estimated by four statistical methods namely, end point rate (EPR), linear regression rate (LRR), weighted linear regression (WLR) and least median of squares (LMS) by using DSAS and subsequently all the methods were verified with the correlation coefficient (R).The scrutiny of shoreline changes shows that the erosion during the last 42 years has affected the island, with some exception, at the north and west segment where minor accretion has been documented. The average rates of changes estimated for north, s...
Arab Gulf Journal of Scientific Research
PurposeThis study aims to determine shoreline change statistics and net erosion and accretion, along the Kuakata Coast, a magnificent sea beach on Bangladesh’s southernmost point.Design/methodology/approachThe research follows a three stages way to achieve the target. First, this study has used the geographic information system (GIS) and remote sensing (RS) to detect the temporal observation of shoreline change from the year 1991 to 2021 through satellite data. Then, the digital shoreline analysis system (DSAS) has also been explored. What is more, a prediction has been done for 2041 on shoreline shifting scenario. The shoreline displacement measurement was primarily separated into three analytical zones. Several statistical parameters, including Net Shoreline Movement (NSM), Shoreline Change Envelope (SCE), End Point Rate (EPR) and Linear Regression Rate (LRR) were calculated in the DSAS to quantify the rates of coastline movement with regard to erosion and deposition.FindingsEPR a...
ASSESSMENT OF THE DYNAMICS OF COASTAL ISLAND IN BANGLADESH USING GEOSPATIAL TECHNIQUES: DOMAR CHAR
Erosion and accretion rate are found very high in the estuary of an active delta which can be observed by satellite imageries. According to the multispectral satellite imageries it is found that accretion of Domar Char (a little island belongs to Meghna estuary) was more than 1192 hectares in last 25 years. The study was conducted in five years interval from 1990 to 2015 using spatial analyst extension of ArcGIS. It is revealed that accretion rate is about 208 hectares/year and erosion is about 160 hectares/year, which indicates the dynamic nature of the island. According to Landsat imageries about 2500 hectares of land rose in five years (1990 to 1995) and again lost 2300 hectares of land in next five years (1995 to 2000). Though the total area of intertidal zone has decreased, the area of barren land, vegetation and sand dune has increased over the time.
The Sundarbans, UNESCO affiliated world heritage site and world largest mangrove forest covering with (~10000) km 2 along the coastal areas of Bangladesh and India. Bangladesh is one of the most vulnerable countries due to sea level rise caused by global warming. In the present situation world mangrove forest are declining at alarming rate. The extensions of this mangrove forest continuously changing with the nature of Bay of Bengal coast. This paper presents the contrast result of erosional hazard and accretion of Sundarbans with its adjacent east coast of Bangladesh. This study based on images of Landsat MSS, Thematic Mapper (TM), Enhanced Thematic Mapper (ETM), and Operational Land Imager (OLI) from Landsat 8. Landsat images from 1980 to 2014 were analyzed. The result shows the net erosion rate of Sundarbans is higher than its adjacent east coast. The study area has been divided into two phases-Phase I and Phase II. Phase I represents only Sundarbans and Phase II represents adjacent east coast. These two phases has equal longitudinal distance. Many small channels and river supply water and sediment into the Sundarbans. The adjacent east coast of Sundarbans lies on the Meghana estuary that experienced with huge amount of sediment flow. The Sundarbans has been facing erosional stage with a rate of net erosion about 3 km 2 y-1 whereas the adjacent east coast facing an accretional stage with rate of accretion about 1 km 2 y-1. The highest erosion rate of Phase I (Sundarbans) was 10.61 km 2 y-1 and highest erosion of Phase II adjacent east coast was 18-km 2 y-1 in the period of 1989-1999. The highest accretion rate in the Sundarbans was 6.48 km 2 y-1 in the period of 1999-2006 and in the Phase II, accretion rate was 16.43 km 2 y-1 in the period of 1980-1989. The lowest erosion rate was 3 km 2 y-1 in Phase I and 2.11 km 2 y-1 in Phase II in the period of 1999-2006. The reworking area in phase I is about 37 km 2 and phase II is about 51 Km 2 .So, water is highly active in adjacent east coast than Sundarbans. Though the mean sea level is increasing at a same rate in two different phases but the accretion and erosion rates are not same. From this study, it is established that Sundarbans has lost 113.31 km 2 of its land in the 34 years of study period whereas; adjacent east coast has gain about 35 km 2 lands. The rate of water discharges and sediment supply are not same in two different phases. It plays a vital role in erosion and accretion process. Therefore, Sundarbans are declining at frightening rate than its adjacent east coast.