Assessing flash flood hazard in an arid mountainous region

Although flash floods are one of the major natural disasters that may hamper human development in arid areas, aspects of the process leading to their initiation remain uncertain and poorly understood. In the present study, wadi El-Alam Basin, one of the major basins in the Eastern Desert of Egypt that is frequently subjected to severe flash flood damage, is selected for investigation. Here, a hydrological modeling approach was used to predict flash flood hazard within the basin. Earlier work conducted for the same basin showed that such approach is successful and was able to accurately highlight the locations of historical flood damage. However, such work was based on one set of arbitrary model parameters. The present study has taking into account the rainfall as the excitation factor in the adopted hydrological modeling. The study aims to build on the earlier study by investigating impacts of variation of rainfall depth, areal coverage, and location on flash flood generation. Results demonstrate that the basin under study requires a rainstorm intensity of at least 40 mm in order to initiate surface runoff with a noticeable flood peak at its main outlet. The location of rainstorm has a major effect on the shape of the basin final hydrograph. Furthermore, in the study basin, the upstream flood appears to be of a magnitude and a peak flow that is much higher than those for downstream ones, which believes to be strongly attributed to the surface steepness and impermeability of the former. The used approach shows to be useful in the rapid assessing of flash flood hazard in mountainous desert and could be adopted, with appropriate modifications, elsewhere in arid regions.