Abstract: Fluvial floods in the Ganges-Brahmaputra-Meghna (GBM) delta are mainly caused by large upstream flows generated by the combined discharges of the Ganges, Brahmaputra, and Upper Meghna rivers. It is widely believed that the nature of flooding in the region will change in the future, mainly because of the effects of climate change. Climate change will impact both the upstream flows and downstream sea levels, and thus will change the hydrodynamics that drive the floods in the region. In addition to climate change, subsidence and sedimentation will also affect the nature of future floods in the region. In this paper, present-day and future fluvial flooding scenarios in the GBM delta are created. This uses two components of the Delft 3D modeling suite: (1) the flow model, and (2) the morphology model. Three present-day flood years are considered, i.e., an average year, a wet year, and a dry year. The nature of future floods is studied in two time horizons – mid-century (2040-2060) and end-century (2079-2099). Different snapshots of future scenarios are considered to represent future wet years with different climatic and sea-level rise scenarios. The analysis shows that the severity of floods will increase in the future, all other factors being equal, with floods starting earlier in the season, inundating a larger area, and having a longer duration. In some locations, the current polder (embankment encircled to protect a particular area from inundation) design heights were not sufficient to withstand the present and future fluvial flooding in the modeled scenarios.

Keywords: Fluvial flood, GBM delta, present-day flooding, climate change, future flooding, numerical model, initiation of flooding, flood duration, coastal embankment

Pages: 977-990