Hydrodynamics of long-duration urban floods: experiments and numerical modelling

Abstract. Flood risk in urbanized areas raises increasing concerns as a result of demographic and climate changes. Hydraulic modelling is a key component of urban flood risk analysis; yet, detailed validation data are still lacking for comprehensively validating hydraulic modelling of inundation flow in urbanized floodplains. In this study, we present an experimental model of inundation flow in a typical European urban district and we compare the experimental observations with predictions by a 2-D shallow-water numerical model. The experimental set-up is 5 m  ×  5 m and involves seven streets in each direction, leading to 49 intersections. For a wide range of inflow discharges, the partition of the measured outflow discharges at the different street outlets was found to remain virtually constant. The observations also suggest that the street widths have a significant influence on the discharge partition between the different streets' outlets. The profiles of water depths along the streets are mainly influenced by the complex flow processes at the intersections, while bottom roughness plays a small part. The numerical model reproduces most of the observed flow features satisfactorily. Using a turbulence model was shown to modify the length of the recirculations in the streets, but not to alter significantly the discharge partition. The main limitation of the numerical model results from the Cartesian grid used, which can be overcome by using a porosity-based formulation of the shallow-water equations. The upscaling of the experimental observations to the field is also discussed.