GIS-Based Flash Flood Hazard Evaluation in Helwan-Atfih Area, Egypt

Flash flooding is one of the most noteworthy natural disasters in arid regions, especially in urban areas. The Helwan-Atfih area is a heavily populated region and part of the Eastern Desert drylands of Egypt. It is characterized by ten drainage basins that dissect it and drain toward the Nile River (Wadies of Degla, Hof, Al-Gebbu, Garawy, Hera, Al-Hay, Al-Werg, Al-Nowya, Al-Reshrash, and AL-Atfehe). Landsat-8, STRM-DEM, and CFSR remote sensing satellite data of 15 m, 30 m, and 0.3-degree resolution, respectively, were prepared and utilized to evaluate flooding hazards within the study area using the GIS-weighted overlay technique. Weighted overlay analysis is a GIS-based multi-criteria decision-making technique. This technique was performed to delineate the most vulnerable areas for flooding, depending on 14 thematic layers representing the multi-class factors that influence flood hazard (nine morphometric parameters, slope, relief, lineament density, surface lithology, and surface runoff). According to the morphometric parameters, the basins of the study area are characterized by moderate drainage densities, and moderately permeable subsoil. Limestone occupies 83.41% of the total lithological units within the basins’ area, which indicates a high flooding potential. Steep slopes are primarily observed in the southern basins, especially in the Al-Reshrash basin. Wadi Al-Atfehe and Wadi Al-Reshrash have the lowest lineament density areas, reflecting a higher flooding hazard. The total runoff volume ranges between 2.42 × 10⁶ and 12.08 × 10⁶ m³. Based on the results, Wadi Al-Reshrash receives the highest runoff volume (12.08 × 10⁶ m³) and has the highest slope degree (57^○-71^○). 85.4% of its area is covered with limestone and it has a low to moderate lineament concentration. Accordingly, Wadi Al-Reshrash is the most prone basin to flooding within the study area, followed by Wadi Al-Werg, while the other basins show a moderate flood hazard degree.