Morpho-dynamic Responses of Braided Bars in Climate Extreme

Abstract:

Climate change is supposed to increase river discharge and sea level that will impact river bar/island people. Most of the disaster mitigation plans do not consider the effects of climate change when assessing the flood risks. In this study, we apply a numerical model-based approach to quantify the potential impacts of climate change on flood risk of braided river’s (Brahmaputra-Jamuna) bars and islands. Recent studies showed that with increased global warming, flood inflows may increase by 8% to 63% by the end of 21^st century in the Brahmaputra-Jamuna River. Global warming may also change the temporal distribution patterns of precipitation that will affect flood-wave propagation characteristics of the river. This may cause increased incidents of peak synchronization with other rivers resulting prolonged floods simultaneously triggered by sea level rise. To assess it, we have set up a morphodynamic model for Brahmaputra-Jamuna River where climate projections for RCP 8.5 (Representative Concentration Pathway 8.5) are enforced by a hydrologic model of Brahmaputra basin and coastal model of Bay of Bengal at upstream and downstream boundary, respectively. Our results showed that the floods in Brahmaputra-Jamuna River gets intense, earlier, frequent and prolonged due to climate change and it is likely to continue till the end of November. The study further reveals that the bars/islands can be affected dis-proportionally in climate-induced hazards based on their location/position. The bars at the downstream part of the river would be mostly affected by the floods in changing climate. The bank-attached bars seem lightly affected than mid-channel bars. This study will help the policy makers to make a sustainable flood management plan for the bar/island dwellers.

Keywords: bank-attached bars; DELFT3D; mid-channel bars; peak synchronization; RCP 8.5.