Integrating Remote Sensing and geomorphological analysis to assess the impacts of the Derna dams collapse

Between September 10th and 11th, 2023, the catastrophic failure of two dams released approximately 30 million m³ of water and debris, devastating large portions of the city of Derna along the northeastern coastline of Libya. This disaster resulted in over 10,000 fatalities and displaced thousands, underscoring the increasing socio-economic impacts of flood-related hazards. This study examines the geomorphological and urban context of the event, with a particular focus on the role of urban sprawl and its interaction with the geomorphic characteristics of the Wadi Derna. Its watershed covers 575 km² and is crossed by a drainage with short runoff times, making the region particularly susceptible to flash floods. Over the past century, the city’s expansion has predominantly occurred in lower, flood-prone areas of the alluvial fan, significantly increasing the exposure and vulnerability of the population to extreme events. High-resolution satellite imagery from ESA’s Pleiades and SPOT 6 and 7 missions was pivotal in reconstructing the settlement dynamics of Derna and assessing the geomorphic impacts of the 2023 flood event. Digital Elevation Models (DEMs) derived from these data supported a DEM of Difference (DoD) analysis, allowing precise quantification of topographic changes and sediment displacement. Moreover, the integration of remote sensing data enabled the detailed mapping of flood extent and the assessment of damages, particularly in areas where field surveys were not feasible. Funded by the Italian Ministry of University and Research under the PRIN project "GEOTRes – Geoheritage Threatening and Resilience", this work underscores how remote sensing can support flood hazard mapping and the analysis of the impacts of extreme flood events in vulnerable settings.