Flooding to stay afloat - Tidal River Management in Southwestern Bangladesh as sedimentation enhancing strategy to combat sea level rise

Abstract

The Ganges-Brahmaputra-Meghna (GBM) delta in Bangladesh is one of the world’s most vulnerable deltas to climate change and relative sea level rise (RSLR). Tidal River Management (TRM), an indigenous practice from southwestern Bangladesh, can potentially be utilized to counteract RSLR. TRM involves breaching dikes to allow sediment-rich water to flow into low-lying areas inside the polders known as beels, raising land levels through sedimentation. Using 2D morphodynamic models we demonstrated that TRM could elevate land at rates sufficiently to keep pace with projected RSLR even when operated seasonally. With multiple inlets in TRM, the rate of land level increment and spatial uniformity of sediment deposition can be enhanced. Seasonal operation of TRM, especially during monsoons when river salinity is low, would maximize agricultural use of the land throughout the year. The results of 2D morphodynamic models indicate tide dominated flow region and mixed flow regions are most suitable for TRM operation. Moreover, beels located closer to the sea has the highest potential for TRM. Operation of TRM in multiple-beel along the same river reach can be a promising and efficient option to speed up raising land elevation over the entire lower GBM delta. Depending on local conditions repeated application of TRM even during monsoon will be required in the same beel every 3-35 years to keep pace with RSLR. Sedimentation enhancing strategy (SES) like TRM can potentially be used to counterbalances RSLR in deltas around the world facing similar challenges, however, effective governance and stakeholders’ inclusion will be required.