Title: Fate and stability of the Ganges-Brahmaputra River delta – role of coupled human-natural systems
Speaker: Dr. Steven Goodbred
Professor and Chair, Dept. Of Earth and Environmental Sciences, Vanderbilt University
Abstract: The Bengal basin receives two great rivers of the world, the Ganges and Brahmaputra, that together drain 75% of the monsoon-drenched Himalayan arc. Delivering ~1 billion tons of sediment annually, these braided streams are laterally mobile and today support ~100,000 km2 of active delta plain. At the coast, the delta system interfaces with a dynamic marine environment, where 3-m tides propagate ~100 km inland, along with storm surges from the nearly annual tropical cyclones. Sediment transported by these tides and marine incursions are essential to maintaining vast areas of the delta that receive little direct fluvial input. In addition to being geologically superlative, this massive delta is also home over 150 million people living in Bangladesh and West Bengal, India, giving the system great societal relevance, and strain.
The first major impact of humans on coastal dynamics began in the 1960s when ~5000 km2of intertidal islands were embanked to increase arable land for food production. One response of this coastal engineering has been the subsequent infilling of ~1000 km of large tidal channels. Remaining tidal channels have experience another major change with an >1m amplification of the tidal range, driving ~1.5 cm/yr rate of mean high water rise that is 3X faster than that for mean sea level. Other tidal channels are reorganizing, with an ongoing basin capture that is enabled by the system’s looping (i.e., interconnected) channel network and mass exchange between adjacent tidal basins. One consequence of this flow reorganization has been the widening of several tidal channels, thereby weakening embankments and leading to their failure during a 2009 cyclone. Together, these changes reflect a strongly coupled human-natural coastal system with significant feedbacks and societal consequences.
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