Landforms and floods in the Ganges delta and coastal lowland of Bangladesh

Abstract

Regional characteristics of the landform changes in the Bengal lowland are closely related to the characteristics of the floods and tidal surges of each region. Due to the remarkable increase of the discharge in the rainy season, most parts of Bangladesh, except Hill Tract, are covered by floods. Flooding conditions and changes of the river course are closely related to the characteristics of the alluvial landforms in the Bengal lowland. Landforms of the southern Ganges delta are characterized as the deltaic and tidal lowlands with low and flat surfaces. Ground height of the region is 2–3 m, but the flooding inundation depth in the deltaic region is not so deep. In the active delta around the mouth of the Meghna (mouth of the Ganges), landforms are extremely unstable due to the strong river flow in the rainy season and the large quantity of sediments. Height of the islands near the mouth of the Meghna is lower than 3 m and, mostly, 1–2 m above mean sea level. Furthermore, sediments of the islands are very soft unconsolidated silt and clay. The landforms of the active delta are extremely temporal and are easily changed in their forms owing to the flood flow and the aftermath of cyclones. Landforms of the central and western coastal regions of the Ganges delta are characterized as the tidal and deltaic lowlands with low and flat surfaces. Abundant growth of mangrove vegetation in the region west of the active delta is effective for the deposition of sediments. The mangrove forests in the region are also effective against any wave action such as the storm surge erosion by cyclones.