Severe failure of improperly designed and poorly constructed structures may occur due to the amplified and prolonged ground motion during an earthquake, and hence prediction of the ground motion characteristics at the soil surface is crucial. In this study, based on the prepared simplified engineering geomorphic map, we performed a one-dimensional (1D) nonlinear site response analysis for seismic site characterization of the recently proposed Detailed Area Plan (DAP) area of Dhaka City, the Capital of Bangladesh. The engineering geomorphic unit-based map was prepared from image analysis and verified with the collected borehole data and surface geology map. The study area was classified into three major geomorphic units and seven sub-units subject to the subsurface soil profiles. Nine earthquake time histories, seven from the PEER NGA WEST2 data set and two synthetics, and seven identified subsurface soil profiles were used for nonlinear site response analysis, along with the BNBC 2020 uniform hazard spectrum as the target spectrum. For the selected earthquake ground motions, the near-surface soil response of the DAP area showed de-amplification of acceleration in the short period and amplification of acceleration in the long period. The amplified long-period acceleration could cause severe damage in inappropriately designed and poorly constructed long-period structures. The outcome of this study could be used to prepare a seismic risk-sensitive land use plan for the future development of the DAP of Dhaka City.

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.

The Sylhet district in Bangladesh experiences frequent flooding due to its geographic setting and heavy monsoon rainfall, further intensified by human-driven activities, including rapid urban expansion, land-use/land-cover alterations, and river encroachment, which collectively cause significant damage to communities, infrastructure, and agriculture. This study aims to delineate flood risk in the district by integrating flood hazard and vulnerability maps using an enhanced GIS-AHP (Analytical Hierarchy Process) approach that incorporates 14 hazard and 8 vulnerability factors. Employing AHP, influencing weights were assigned to hazard and vulnerability defining factors, thereafter mapped in GIS to assess the spatial characteristics of the flood hazard index (FHI) and flood vulnerability index (FVI), thus collectively producing the flood risk index (FRI). Validation of the FHI map was conducted through Receiver Operating Characteristic curve analysis, yielding an Area Under the Curve of 0.858. The results also indicated a high level of correspondence with the flood inundation maps for 2004 and 2022. The FVI map was validated by qualitative analysis, confirming its contextual reliability. The assessment reveals that moderate flood hazard dominates across the district, with upazilas like Companiganj, Gowainghat, Bishwanath, and Balaganj having moderate hazard levels above 80%. However, vulnerability levels are higher in densely populated settlement areas, particularly in Sylhet Sadar, Golapganj, Dakshin Surma, and Biswanath upazilas. Moreover, 74.26% of Sylhet falls within the moderate-risk category. The high-risk zones are mainly clustered in Sylhet Sadar, Biswanath, Dakshin Surma, and Golapganj, where over 40% of the land area is classified as high-risk. The FRI map’s performance was further evaluated using recent flood event information, revealing that flooded areas mostly correspond to moderate- and high-risk zones.