Drainage System and Detailed Urban Topography: Towards Operational 1D-2D Modelling for Stormwater Management

Abstract

Flash floods are increasingly occurring due to climate change and the dramatic increase of population over areas characterized by aging and undersized drainage systems. Many studies are dealing with the topic of urban pluvial flooding, but few of them thoroughly consider interactions between surface runoff and pipe flow. In addition, to get a better knowledge of the processes leading to flash floods in urban areas, the specificities of urban topography features have to be taken into account while modelling dual drainage, such as streets, sidewalks, road curbs, bridges, etc. This paper aims to present a detailed modelling approach at a district scale as a first step, in order to determine impacts of detailed and simplified topography implementation on intense runoff modelling. The second step aims to set up an optimized city scale runoff modelling and management. The coastal Mediterranean city (Nice, France) characterized by steep and low slopes areas suffered from an intense rainfall event in October 2015. This study-case enables to investigate on such problematic as a high-resolution (0.2m) photo-interpreted topographic dataset is available. Investigation based on Geographic Information System (GIS) is followed by 1D and 2D modelling. Results are presented by confronting outcomes given by GIS analysis and hydrodynamic modelling. It is shown that high-resolution data should be used carefully while dealing with urban hydrology and hydraulics. The reflection is driven towards a set of guidelines for modellers interested in helping stormwater operational management.