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Spatial and seasonal variability of sediment accumulation potential through controlled flooding of polders in the Ganges-Brahmaputra-Meghna delta of southwest Bangladesh
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  • Md Feroz Islam,
  • Hans Middelkoop,
  • Paul Schot,
  • Stefan Dekker,
  • Jasper Griffioen
Md Feroz Islam
Utrecht University
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Hans Middelkoop
Utrecht University
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Paul Schot
Utrecht University
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Stefan Dekker
Utrecht University
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Jasper Griffioen
Utrecht University
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Abstract

The densely populated coastal areas of the Ganges-Brahmaputra-Meghna (GBM) delta within Bangladesh are in danger of losing up to one fourth of their habitable land by 2100 due to relative sea level rise (RSLR). Tidal River Management (TRM) presents an opportunity to combat RSLR by raising the land level through controlled sedimentation in re-opened polder sections. To date, TRM has been applied to tide-dominated coastal regions, but the potential applicability of TRM for river-dominated flow and mixed flow regimes is yet to be assessed. We apply a calibrated 2D numerical hydromorphodynamic model to quantify sediment deposition in a re-opened polder section (‘beel’) under conditions of river-dominated, tide-dominated and mixed flow regimes for different seasons and flow regulations. Simulation results show seasonality in sediment deposition with monsoon season having the highest. The potential for TRM is largest along the reaches of the tide-dominated region where sediment deposition is highest in all three seasons (Pre-monsoon, Monsoon and Dry season), and almost 28 times higher than river-dominated region during monsoon. Regulating flow into a polder increases trapping efficiency, but slightly lower total deposition than without regulation. Our results show that re-establishing polder flooding without regulating the flow into the polder is a promising strategy for the mixed and tide-dominated flow regions in the delta as the sediment deposition can elevate the land more than the yearly rate of RSLR. Application of controlled flooding like TRM therefore provides opportunity to match the rate of RSLR throughout the GBM delta. TRM can potentially be applied to the sinking deltas around the world to counter RSLR.