Abstract
Flood damage assessment is becoming now more important because of flooding disasters around the world. Severe rainstorms are common occurrences in some regions of Saudi Arabia that result in hazardous floods damaging the infrastructure and development plans. This study is applied in order to assess the flood hazards in the study area and to propose some countermeasures to reduce the flood damage. In recent years, Riyadh has experienced several flooding events that caused damages in and around the city in different locations due to the change in climate and land use. The paper presents a framework for a study of flood damage assessment of vulnerable area in Riyadh that was exposed to severe damages occurred by flash floods. As well as, conduct-ing analyzes of morphology, metrology, hydrological and hydraulic analysis are included. Then, proposing a plan to mitigate the damages happened to the study area. The prediction of rainfall depths for 50 and 100-y were estimated using the frequency analysis to be 46.5.6 and 52.2 mm, respectively. The peak flow rates at the catchment outlet for 50-and 100-y return periods were estimated to be 256.0 and 291.0 m3/s, respectively. The weighted Curve Number value of Wadi basin was estimated to be 81. In the hydraulic modelling, the Manning roughness coefficient was increased to 0.03 to dissipate the energy at the baffles and drops. The scour depths at the bridge piers were estimated assuming that the valley cross section does not tolerate the high water velocities. The study recommended taking into account the expected scour depth which obtained from the hydraulic modelling and the Wadi bed condition to guide the designer to use deep foundations at the piers of the bridge to overcome and alleviate from the flash flood impact.