Morphological change assessment of a coastal island in SE Bangladesh reveal high accumulation rates

Abstract

It is essential to comprehend various morphological aspects, change dynamics, and stressors on the coastal environment in both contemporary and historical contexts. This study examines the potential for morphological changes in land use, erosion-sedimentation patterns, shoreline changes, and sediment accumulation on Sonadia Island in Southeast Bangladesh. To evaluate the extraordinarily high sediment accumulation phenomenon, the researchers used toposheets, historical maps, numerous satellite images, and field work observations. The investigation revealed that the shoreline of the island is subject to regular and rapid modifications. The island’s area coverage was 1.65 km2 in 1779, but it has grown 21 times to 36 km2 in 2021. From 1972 to 2021, the current study looks at land-use/land-cover changes on Sonadia Island, including mangrove (12.15 to 20.22 km2), tidal mudflats (6.69 to 4.63 km2), salt/shrimp fields (0 to 3.33 km2), dune (1.30 to 3.33 km2), beach sands (5.07 to 4.57 km2), and man-made forest (0 to 1.06 km2), as well as spatial changes in land. Between 1972 and 2021, erosion and sedimentation reached 1.35 km2 and 14.09 km2, respectively, resulting in a depositional rate of 0.29 km2 per year and an erosional rate of 0.03 km2 per year. The high accumulation rates are linked to shoreline activities such as mixing and reworking fluvial systems, longshore currents, tidal activity, strong waves, and seasonal current circulation patterns.