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37 RISE OF SEA LEVEL AND THE SINKING ISLANDS OF SUNDARBAN REGION: A STUDY OF MOUSUNI ISLAND IN INDIA
Journal of Global Resources
Mousuni, a human habitat island in the Indian Sundarban and located on the southernmost tip of Bengal, is under constant threat of inundation caused by sea level rise. It has been hugely affecting the lives and livelihood of the communities living around the coastal region of the Island. The main objective of the present study is to explore the erosional level and sinking of Mousuni Island and to find out the impact of it on the livelihood of the people. Based on the primary and secondary data the findings of the present study show that if the erosional activity of engulfing water of Bay of Bengal continues the Mousuni Island will sink within 80 to 100 years. Submergence of the island increases the vulnerability of the poor people of the island and reducing capacity to cope with the existing problem.
Natural Hazards, 2020
A study was undertaken to assess the morphological variations during the period 1969-2018 in the twenty-one islands in Gulf of Mannar, southeast India, using Survey of India Toposheet, Google Earth images and field survey techniques. The results show that two of the islands have eroded and submerged, fifteen islands area cover has reduced and four have their area expanded during the last 49 years. Overall, the Tuticorin group of islands has experienced the highest percentage of land cover reduction (78.55%), followed by Keelakarai (43.49%), Vembar (36.21%) and Mandapam (21.84%) groups. The exceptions are the four islands of the Mandapam group viz. Hare, Manoli, Krusadai and Shingle, whose area covers have increased (16.44%). A small change in the area of an island induces a greater change in its morphology. From the Island Change Ratio plot, it is observed that islands with an area cover of 10-30 ha have suffered loss of more area cover and undergone mobility from the core area. The constant changes undergone and the mobility exhibited by these islands clearly indicate that they are dynamic. The main factors that are responsible for the current changes in their extent and position are coral mining and sea level rise. Thus, it is clear that the low-lying reef islands of Gulf of Mannar are very dynamic, and that their expansion, loss in area cover and mobility are mainly controlled by coral mining and climate change. Immediate conservation action is necessary to prevent the islands from submergence.
Shrinking of Vann Island, Gulf of Mannar, SE coast of India: assessing the impacts
Vaan Island, which is one of 21 islands in Gulf of Mannar Marine National Park, is chosen as study area which is formed above the coral reef by sedimentation and deposition of tidal and current activities. By using Landsat images, the area (Vann Island) was calculated from the year 1973–2015 with analyzing tools of Qgis and Saga Gis. Multispectral Landsat images were processed to extract and delineate the interface line of island surface and seawater. The area of each year polygon vector is calculated using the Qgis field calculator tool. During the 1973, the area of Vaan Island is about 265,479 m 2 and at present the area is calculated as 40,733 m 2. About 84 % of the island area is reduced and inundated by the seawater due to sea level rise and anthropogenic activities such as coral sand mining, local tourism and fishing activities. At this rate of submergence, it can be predicted that by 2022 Vaan Island will completely submerge into the sea. From this study, it is concluded that geospatial techniques are one of the successful and reliable techniques to map this type of low-lying island to conserve and manage the resources that affected by the geogenic and anthropogenic processes.
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.
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.
Rapid erosion of the coast of Sagar island, West Bengal-India
Environmental Geology, 2005
Coastal environment issues are highly complex and due to settlement, waste disposal, aquaculture, fishing and recreation. As land becomes more and more crowded and terrestrial resources are used up, greater attention must be paid to the development of a coastal zone. Continuous physical interaction amongst the land, sea and atmosphere makes the coast a dynamic zone. The Sagar island coast is tide-dominated and is characterized by tidal creeks, mud flats/salt marshes, mangroves and sandy beaches/dunes. These landforms are subjected to natural processes (cyclones, waves and tides) and anthropogenic activities. Tidal amplitudes up to 6 m during extreme high tide are very common. Sometimes these effects will be much greater during cyclones, which frequently occur in this part of the coast.
Marine Geodesy, 2014
The tsunami waves generated during the Sumatra-Andaman earthquake of 26 December 2004 devastated the coastal area along Trinkat Island, causing sudden changes to the morphology of the landforms. This study uses a series of satellite images to record the short-term morphological response and shoreline changes as well as the recovery of coastal land after its destruction. Results indicate that the island experienced substantial erosion and a significant reduction in land area. Shoreline erosion is more prevalent than accretion at an average linear regression rate of ∼−9 m per year between 2004 and 2013. The major morphological changes at Trinkat Island were observed in coastal inlets, beaches, and bay head-lands. Straight beaches had almost recovered eight years after the tsunami; however, erosion is continually observed in other areas. Our study will help understanding the response and recovery of shorelines in Indian Ocean regions after the 2004 tsunami.
Decadal Shoreline Changes Around Rameswaram Island (1968-2018) Using Remote Sensing and GIS
ECO CHRONICLE, 2018
Shoreline changes associated with Rameswaram Island (latitude 9° 10' to 9° 20' N and longitude 79° 12' to 79° 30' E) has been carried out for the period 1968 -2018, using Geographic information system (GIS). To delineate the shoreline, Landsat imageries from 1978 to 2018 were used and the baseline was taken from SOI toposheet of 1:50,000 Scale for the year 1968. The results showed that shoreline around the island has extended from 72.2 km to 73.5 km, 74.7 km, 76.8km, 76 km and 78.4 km in 1968, 1978, 1988, 1999 and 2018, respectively. Over the past 51 years, the area has enlarged. The changes in area for the year 1978, 1988, 1999 and 2018 were 5.85 km2, 4.80 Km2, 2.23 Km2, 2.40 Km2 and 1.77 Km2 respectively. The results showed that the total conservation area has experienced an accretion of 3.45 Km2 and an erosion of 2.13 Km2. Analyzing the bathymetry, the depth of the buffer zone, 5 km from the island, varied from 0 to 2m, 2 to 5m and 5 to 10 m. The Geological setting of island is distributed between paleo-tidal flat deposits at the center and silt and sand around.