Historical Changes in the Ganges-Brahmaputra Delta Front

Abstract

Detailed early chartmaking by the British East India Company and the Royal Navy in India and present-day Bangladesh provide one of the most accurate databases available to track the evolution of a major delta front over the last 200 years. Digital databases of shoreline position and shallow bathymetry of the Ganges-Brahmaputra delta front were constructed using geo-referenced and projection-corrected early and modern charts, and using LANDSAT imagery. In contrast with earlier published studies, these databases indicate the Ganges-Brahmaputra has an actively prograding subaerial delta: an average of approximately 7.0 km 2 / yr of new land have accreted in the river mouth region since 1792. Digitate shoals, forming in association with accretion of elongate islands in the river mouth region, are coalescing in 8-15 m water depth to form a relatively coarse-grained lobate feature that is prograding over the muddy, subaqueous delta on the inner shelf. The morphology of shoal growth suggests the Ganges-Brahmaputra mouth has evolved eastward over the late Holocene as a series of digitate shoal-channel complexes. West of the active river mouth in historical times, the delta front is sediment starved and is undergoing retreat at rates of about 1.9 km 2 / yr.