EGU21-475
https://doi.org/10.5194/egusphere-egu21-475
EGU General Assembly 2021
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

The physical sustainability of the coastal zone of the Ganges-Brahmaputra-Meghna delta under climatic and anthropogenic stresses

Stephen Darby1, Md. Munsur Rahman2, Anisul Haque2, Robert Nicholls3, and Frances Dunn4
Stephen Darby et al.
  • 1University of Southampton, School of Geography, Southampton, United Kingdom of Great Britain – England, Scotland, Wales (s.e.darby@soton.ac.uk)
  • 2Institute of Water and Flood Management, Bangladesh University of Engineering and Technology, Bangladesh (mmrahman@iwfm.buet.ac.bd)
  • 3School of Environmental Sciences, University of East Anglia, United Kingdom of Great Britain (Robert.Nicholls@uea.ac.uk)
  • 4Water, Climate & Future Deltas Hub, Faculty of Geosciences, University of Utrecht, Netherlands (f.e.dunn@uu.nl)

The Ganges-Brahmaputra-Meghna (GBM) delta is one of the world’s largest deltas, and consists of large areas of low flat lands formed by the deposition of sediment from the GBM rivers. However, recent estimates have projected between 200~1000 mm of climate-driven sea-level rise by the end of the 21st century, at an average rate of ~6 mm/yr. Eustatic sea-level rise is further compounded by  subsidence of the delta, which in the coastal fringes varies from 0.2 to 7.5 mm/yr, at an average value of ~2.0 mm/yr. Therefore, the combined effect of sea-level rise and subsidence (termed relative sea-level rise, RSLR) is around 8.0 mm/yr. Such high values of RSLR raise the question of whether sediment deposition on the surface of the delta is sufficient to maintain the delta surface above sea level. Moreover, as the total fluvial sediment influx to the GBM delta system is known to be decreasing, the retained portion of fluvial sediment on the delta surface is also likely decreasing, reducing the potential to offset RSLR. Within this context, the potential of various interventions geared at promoting greater retention of sediment on the delta surface is explored using numerical experiments under different flow-sediment regime and anthropogenic interventions.  We find that for the existing, highly managed, conditions, the retained portion of fluvial sediment on the delta surface varies between 22% and 50% during average (when about 20% of the total floodplain in the country is inundated) and extreme (> 60% of the total floodplain in the country is inundated) flood years, respectively. However, the degree to which sediment has the potential to be deposited on the delta surface increases by up to 10% when existing anthropogenic interventions such as polders that act as barriers to delta-plain sedimentation are removed. While dismantling existing interventions is not a politically realistic proposition, more quasi-natural conditions can be reestablished through local- sediment management using tidal river management, cross dams, dredging, bandal-like structures and/or combinations of the above measures.

How to cite: Darby, S., Rahman, Md. M., Haque, A., Nicholls, R., and Dunn, F.: The physical sustainability of the coastal zone of the Ganges-Brahmaputra-Meghna delta under climatic and anthropogenic stresses, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-475, https://doi.org/10.5194/egusphere-egu21-475, 2021.

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