A disparity between erosional hazard and accretion of the sundarbans with its adjacent east coast, Bangladesh: a remote sensing and GIS approach

Abstract

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.