Flood Inundation Mapping Using HEC-RAS 2D Modeling and Examining the Impact of Changes in the Model-Meshing Pixel Scale on the Final Output

Floods as a Natural disaster are incredibly destructive and have detrimental effects on people lives and properties. Engineering and no engineering techniques have been developed for flood mitigation. This work aims to evaluate the impact of floods in the Wadi Al-Arj area, northeast of Taif City, Saudi Arabia. An integrated approach utilizing GIS, remote sensing, HEC-HMS, and HEC-RAS was used for the hydraulic modeling. This technique involved the construction of several maps and subsequent assessments. Within the Wadi Al-Arj basin, satellite images from the Landsat-8 “OLI” 2023, DEM-30 m, geology map, and meteorological data were collected and utilized in the GIS environment to extract various thematic layers, including land use, soil, and rainfall distribution, for hydrologic modeling by HEC-HMS. The flood hydrograph curve for the Wadi Al-Arj Basin was calculated after applying the Muskingum routing method, and floodwater quantities of 18.2 million m3 and a discharge rate of 1,144 m3/s were estimated for a 100-years return period. The flood severity matrix approach was applied to simulate and map flood inundation over the 10-kilometer Wadi Al-Arj stretch using the HEC-RAS-2D model with high-resolution DEM-4 m. Based on the severity index matrix, the flood water depth (m), velocity (m/s), and severity rate (m2/s) were classified into five zones: low (0-0.2), medium (0.2–0.5), high (0.5–1.5), very high (1.5–2.5), and severe (above 2.5). This study also examines the impact of changes in the model-meshing pixel scale on the final result of the simulation. According to previous reports, the 10 m × 10 m pixel simulation results that matched the validation data matched the flooded areas. This study illustrates the two-dimensional capabilities of HEC-RAS and assists specialists in enhancing the management processes.