Flash floods are among the most common natural hazards in Egypt. Wadi El-Darb, one of the vastest drainage catchment in the
Eastern Desert of Egypt, is considerably subjected to severe flash flood events. The coastal city of Ras Gharib is located at the
outlet of this Wadi, which consequently makes it susceptible to the flash flood hazard. Ras Gharib has a strategic importance to
Egypt that it produces 65% of the petroleum requirement; therefore, the government seeks hard to protect the city. Using
hydrological modeling approach was necessary, especially in case of the lack of hydrological and meteorological data in the
region, to simulate the spatial extent, depth, and speed of the floodwater and then identify the sites at risk of flooding. The
elevation data were extracted from digital elevation models (SRTM and ALOS PALSAR). The soil texture properties can be
derived from Sentinel-1 radar images fused with geological data to produce the hybrid land cover map containing the rock types
and their texture information. Sentinel-2 imagery was used to map the land use/land cover (LULC) in the downstream area of the
basin. The results showed that the rainstorm with 51 mm of precipitation intensity would cause, at the outlet of the Wadi El-Darb
basin, peak discharge rate of 852.73 m3
/s, and the flash flood water can reach Ras Gharib city within 4 h, with an average flood
depth of 1.69 m. Also, the flash flood impacts concentrated in the midtown covering about 2.93 km2
, about 342 houses, 33.35 km
of Ras Ghareb-Minya highway, and 55.9-km long of the internal road network were inundated. The hydrologic modeling results
were validated using Jaccard coefficient (= 0.72), based on the integration of Sentinel-2 images along with aerial photos (captured
post the flood), Google Earth images, and Open Street Map (OSM). Accordingly, this work provides the developing countries
with a practical and quick technique to predict flash flood hazards in arid regions where data are scarce. |
