Sustainability of Coastal Embankments in Bangladesh: Integrated Evidence from Typical Polders

Abstract

Bangladesh, a low-lying country in the Bengal delta, is highly vulnerable to tropical cyclones and associated storm surges, which pose severe threats to coastal communities and agriculture. This study evaluated the structural integrity and functional resilience of two coastal embankments (Polders 47/1 and 48) in Kalapara Upazila, Patuakhali District, in the coastal region. Employing high-precision RTK GNSS elevation profiling, storm surge modeling, post-cyclone inundation mapping, salinity assessment, and InSAR land subsidence analysis, this research provided a comprehensive understanding of embankment sustainability. First, a Trimble RTX-enabled RTK GNSS survey was conducted based on existing embankment geometry and elevation. Second, the storm surge from Cyclone Sidr was simulated using the Delft3D-FLOW model to estimate worst-case inundation extents relative to measured embankment heights. Third, Sentinel-1 SAR imagery and ground-truth data quantified actual flood inundation during Cyclone Remal in 2024, while Sentinel-2 optical indices validated against field electrical conductivity measurements assessed post-cyclone soil salinity changes. Finally, time-series InSAR with determined spatial subsidence rates estimated future changes in embankment elevations to evaluate future sustainability against cyclonic and storm surge events. The results indicate that large embankment segments, particularly in Polder 47/1, lie below simulated surge levels, leading to extensive overtopping and prolonged waterlogging. Salinity indices increased significantly post-Remal, and subsidence hotspots exceeded 14 mm/yr, undermining the long-term efficacy of the embankment. This study concluded that existing embankment infrastructure is insufficient under current and future climatic pressures. These findings emphasise the urgent need to integrate engineering advancements with nature-based solutions and community-involved monitoring to enhance coastal resilience and protect livelihoods.

Keywords

Bangladesh / Coastal embankment / Polder / Storm surge / Subsidence / Sustainability

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