Integrated hydrological study for flash flood assessment using morphometric analysis and MCDA based on hydrological indices—Al-Sail Al-Kabir, KSA

Flood susceptibility is associated with a variety of factors. A hydrologic study of Wadi Al-Sail Al-Kabir was conducted based on morphometric analysis and hydrological indices. The current study aimed to apply morphometric analysis and multi-criteria decision analysis based on hydrological indices for flash flood risk assessment. RS and GIS were used to obtain morphological parameters. Thirty-six parameters were evaluated and categorized to basin geometry, drainage texture, drainage network, and relief characteristics. Spatial analysis was applied in a GIS environment for flash flood assessment, where 11 related hydrological indices were selected: the sediment transport index, stream power index, terrain ruggedness index, topographic wetness index, topographic position index, normalized difference vegetation index, distance to road, precipitation, elevation, slope, and drainage density. Each index was weighted based on its relative significance using an analytical hierarchy process. It was found that the area is 255.13 km2 (large area) and the wadi is related to the 5th order, consisting of 818 streams with a total length of 564.8 km. Finally, the generated map shows that approximately 40.8% of the wadi classified as high- and very high-risk areas, and 39% as moderate-risk areas. Using the generated map as evidence, planners can prepare an appropriate land-use policy to reduce the threat of flooding.