Open Access

Die frühislamische Stadt Qurḥ / al‑Mabiyat in Saudi-arabien ist aufgrund ihrer Lehmziegelarchitektur stark gegenüber Starkregen und Sturzfluten gefährdet, wie das Ereignis von 2019 zeigte. Auf Basis von Fernerkundungsdaten und Feldversuchen wurden mit einem instationären hydrologisch‑hydraulischen Modell (Mike SHE) die Abflüsse für das heutige und historische Einzugsgebiet rekonstruiert. Die Analyse zeigt, dass moderne Verkehrs- und Bahndämme das Einzugsgebiet auf das Fünffache vergrößern und Abflüsse heute direkt auf die Stätte lenken. Historisch verliefen die Abflüsse aufgrund einer oberhalb der Stadt gelegenen Mauer sowie eines deutlich kleineren Einzugsgebiets überwiegend seitlich an der Siedlung vorbei. Die Ergebnisse belegen, dass die historische Bevölkerung durch gezielte bauliche Maßnahmen das Sturzflutrisiko wirksam reduzierte und dass heutige Schutzkonzepte an diese naturnahen Abflussverhältnisse anknüpfen sollten.

Effective response to flood events requires high-resolution, frequently updated data on flooded areas for comprehensive flood risk assessments. Unmanned aerial vehicles (UAVs) equipped with conventional camera systems and classification based on orthophotos from photogrammetric postprocessing and artificial intelligence are widely used to detect flooded areas. However, these methods often involve time-intensive pre- and postprocessing steps and fail to incorporate geometric factors such as elevation data and water depths. This study introduces SSegRef2Surf, a novel tool that integrates classified flood raster data with terrain information. SSegRef2Surf refines and optimizes coarse raster classifications by filling shadowed areas and correcting misclassified regions. This tool reduces data requirements for AI training and minimizes postprocessing time, enabling near real-time flood monitoring. All processes necessary for SSegRef2Surf were optimized through sensitivity and accuracy analyses to reduce postprocessing duration to a minimum. A comparison of the SSegRef2Surf results with two-dimensional (2D) numerical model results for a flood event revealed discrepancies in the 2D model, caused by inaccuracies in the underlying terrain data. This comparison showed that 30% of the flooded areas identified in the 2D numerical results were incorrect, while missing areas (11%) were added. This highlights the significant potential of SSegRef2Surf for near real-time flood monitoring and traceability of flood events, as combining UAVs’ high-frequency surveying capabilities with SSegRef2Surf allows for more effective validation and optimization of 2D models.

Through the mobilization of movable objects due to the extreme hydraulic conditions during a flood event, blockages, damage to infrastructure, and endangerment of human lives can occur. To identify potential hazards from aerial imagery and take appropriate precautions, a change detection tool (CDT) was developed and tested using a study area along the Aisch River in Germany. The focus of the CDT development was on near real-time analysis of point cloud data generated by structure from motion from aerial images of temporally separated surveys, enabling rapid and targeted implementation of measures. The differences identified in the study area using distance comparison (M3C2) were segmented into individual components and categorized. Subsequently, the data was compared to existing two-dimensional hydrodynamic numerical calculation results (HQ100). The implementation of the CDT is feasible for a variety of RGB camera-equipped aerial vehicles due to the point cloud-based analysis and postprocessing. By overlaying and visualizing the detected changes with numerical simulation results, a quick assessment of the hazard potential in the event of a possible flood can be made. In the case of the study area along the Aisch River, the localization of construction materials, a steel container with debris pile, and a motor vehicle in the flood hazard zone of a potential HQ100 event could be confirmed, although no mobilization of the materials was to be expected due to the expected hydraulic conditions of a flood event.

Im Rahmen der Freibordbemessung an Staudämmen stellt der Wasserübertritt grundsätzlich ein Tabu dar. Mit der Durchführung unabhängiger Untersuchungen erfolgte die Prüfung der Prognosefähigkeit numerischer Verfahren bzgl. des Wellenauflauf- und Wellenumlenkprozesses an Dammböschungen mit und ohne Wellenumlenker. Des Weiteren wurde im Hinblick auf die erforderliche Größe von Wellenumlenkern ein Dimensionierungskonzept entwickelt, welches auf Datensätzen basiert, die mittels kalibrierter hydrodynamisch-numerischer Modelle gewonnen wurden.