Developing GIS-Based Unit Hydrographs for Flood Management in Makkah Metropolitan Area, Saudi Arabia

Unit hydrographs (UH) are either determined from gauged data or derived using empirically-based synthetic unit hydrograph procedures. In Saudi Arabia, the discharge records may not be available either for several locations or for long time scales, and therefore synthetic unit hydrographs are crucial in flood and water resources management. Available metrological, geological, and land use datasets have been utilized in order to apply the US National Resources Conservative Services (NRCS) methodology in a Geographic Information Systems (GIS) environment. Furthermore, NRCS unit hydrographs have been developed for six watersheds within Makkah metropolitan area, southwest Saudi Arabia. The accomplished results show that the UH time to peak discharge vary from 1.15 hours to 4.47 hours, and the UH peak discharge quantities range from 10.14 m 3 /s to 16.74 m 3 /s. It is concluded that the third basin in Makkah city may be considered as the most hazardous catchment. Hence, it is recommended that careful flood protection procedures should be taken in this area within Makkah city.