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Analysis of Erosion and Accretion pattern of Selected Coastal Island of Bangladesh.

Abstract:  The coast line of Bangladesh has always been undergoing through several changing phases caused by radical accretion and erosion of lands along the coastal zone. Huge sediment supply by the Ganges-Brahmaputra-Meghna river system contributes significantly for land accretion whereas combined effect of natural calamities and anthropogenic activities causes considerable erosion, especially along the central coast, the western deltaic coast and eastern cliff coast of Bangladesh. The present approach is taken to give an overview of land changes in Bangladesh coast through GIS analysis using multi temporal satellite imageries since 1973 to 2010 with a view to quantify and qualify the changes of coastal area caused by land accretion and erosion.

From short and long time interval analysis reveals that the entire coast of Bangladesh exhibits a mixing trend of land accretion and erosion. The overall scenario affirm by the composite image analysis over thirty seven years shows that the central part of Bangladesh coast is in slightly erosional phase, the Meghna Estuary is in gaining phase. Study reveals that about 87254 ha area of land has been reclaimed during the last 37 years (1973-2010) in central coast. There are many islands in the central part of Bangladesh coast. These islands are more or less in steady condition. During the time span 1973-2010 Sandwip island are prone to erosion. Sandwip Island is discovered to experience loosing phase, losing 7167.7 hector during the time period 1973-2010. Urir char exhibits accretionary phase during 1973-2010 contributing only 18472.6 hector. Bhola and Hatia islands are also prone to erosion. Bhola Island is observed to loosing phase, losing 10285 hector during the time period 1973-2010.Whereas Hatia Island exhibits accretionary phase during 1973-2010 and accretion in this particular area is about 2081.6 hector. Present study reveals that about 1270.6 hector area of Monpura Island being accreted since 1973 to 2010.

Devastating action of major cyclones, storm surges, longshore current, strong tidal action, local wave action and of course anthropogenic activities are the most probable causes of land erosion. Mangrove plantation, Heavy sediment load coming from GMB are the major cause of land accretion. The temporal erotic changes with overall tendency might be related with short-term episodic phenomena.

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