HISTORICAL CHANGES IN THE GANGES-BRAHMAPUTRA DELTA FRONT

Detailed early chartmaking by the British East India Company and the R oyal Navy in India and present-day Bangladesh provide one of the most accurate databases available to track the evolution of a major delta f ront over the last 200 years. Digital databases of shoreline position and shallow bathymetry of the Ganges-Brahmaputra delta front were cons tructed using gee-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 activ ely prograding subaerial delta: an average of approximately 7.0 km(2)/ yr of new land have accreted in the river mouth region since 1792. Dig itate shoals, forming in association with accretion of elongate island s in the river mouth region, are coalescing in 8-15 m water depth to f orm a relatively coarse-grained lobate feature that is prograding over the muddy, subaqueous delta on the inner shelf. The morphology of sho al growth suggests the Ganges-Brahmaputra mouth has evolved eastward o ver the late Holocene as a series of digitate shoal-channel complexes. West of the active river mouth in historical times, the delta front i s sediment starved and is undergoing retreat at rates of about 1.9 km( 2)/yr.