Design hydrological event and routing scheme for flood mapping in urban area    

Definition of flood risk maps is a task to which modern surface hydrology addresses a substantial research effort. Their impact on the government of the flood prone areas have increased the need for better investigation of the inundation dynamics [Fema 2002]. This identifies open research problems such as: the definition of the design hydrograph, the identification of the surface boundary conditions for the flood routing over the inundation plan, the choice of the hydraulic model that is the most close to the physical behavior of the flood routing in the specific environment, such as urban areas or river valley. Most of academic and commercial mathematical models resolving the De Saint Venant equations in mono or bidimensional approach, fail on complex topography. Steep slopes, geometric discontinuities, mixed flow regimes, initially dry areas are just the main problems a hydraulic model should solve. In this study, we address two points: the definition of the critical event for an inundation area and a flood routing modelling technique for a highly urbanized flat area. For this latter we show that, in urban areas, a modelling scheme of a network of connected channels and storages, gives a better representation of surface boundary conditions such as aggregation of buildings and road network and sufficient accuracy for flood risk mapping purpose respect to a real 2-D hydraulic routing model. Definition of flood risk maps is a task to which modern surface hydrology addresses a substantial research effort. Their impact on the government of the flood prone areas have increased the need for better investigation of the inundation dynamics [Fema 2002]. This identifies open research problems such as: the definition of the design hydrograph, the identification of the surface boundary conditions for the flood routing over the inundation plan, the choice of the hydraulic model that is the most close to the physical behavior of the flood routing in the specific environment, such as urban areas or river valley. Most of academic and commercial mathematical models resolving the De Saint Venant equations in mono or bidimensional approach, fail on complex topography. Steep slopes, geometric discontinuities, mixed flow regimes, initially dry areas are just the main problems a hydraulic model should solve. In this study, we address two points: the definition of the critical event for an inundation area and a flood routing modelling technique for a highly urbanized flat area. For this latter we show that, in urban areas, a modelling scheme of a network of connected channels and storages, gives a better representation of surface boundary conditions such as aggregation of buildings and road network and sufficient accuracy for flood risk mapping purpose respect to a real 2-D hydraulic routing model.