Flood Hazards Mapping in Arid Region by Integrating Hydrologic and Hydraulic Modeling: Case Study of Wadi Qows, Jeddah, Saudi Arabia

This research presents an integrated approach of hydrologic and hydraulic modeling in estimating flood discharges and mapping flood inundation during flood hazards in an urban arid region (Jeddah city, Saudi Arabia). A low resolution DEM 90m, as a basis of the model, was used to identify the watershed characteristics. The SCS method was applied to estimate the peak discharges at different return periods by using the coupled WMS and HEC-HMS software. Geometric data and cross sections for flow area and flood plain were based on DEM 90m as a basis of the hydraulic model by using the coupled WMS and HEC-RAS software. The hydrological model showed that the peak discharge could range between 34.8 (dry condition at 10 years return period) and 462.4 m³/s (wet condition at 200 years return period) of the 25th of November 2009 event. While, the expected value is 116.2 m³/s at 10 years return period under normal condition. The modeled flood inundation area has a high similarity with the flood map based on the field measurements at 10 years return period with normal condition. The model showed a 78% similarity of the inundation area, however, the estimated depth has relatively high uncertainty. The results provide an overview of the November 25th, 2009 event from a hydraulic point of view. The results are relatively good, despite the high uncertainty due to a lack of accurate data.