Résumé
Floods in densely urbanized areas have a strong social and economic impact because of the high vulnerability of buildings and transportation networks. This vulnerability is heterogeneous as well as hazard so that a detailed estimate of flood risk requires a relevant description of the structure of the buildings and their environment. The DEUFI (DEtailing Urban Flood Impact) project (2019-2023) focuses on the representation of the detailed hydrodynamic processes and their effect on the modelling of flood risk. While one part of the project is dedicated to several laboratory experiments and their use to improve methods for simulating flow in the streets and in the buildings, a second part is based on two cases of cities (Nîmes and Oullins in France) that suffered flooding in recent years and for which measures are on going to reduce flood risk. Field investigations concern the hydrological features of the flood events, the social environment and the economic damages. Results of the project are shared into the development of new methodologies and their application to these two cities. Advances in hydrodynamic modelling come from systematic identification of the openings of buildings and an adaptation of hydraulic structures equations for simulating flow through these openings considering the various types of openings and the various hydraulic conditions met during an urban flood. The accuracy of 2-D and 3-D hydraulic software is estimated comparing the calculation results to the laboratory measurements obtained on three facilities respectively aiming the opening, building and district scales. Economic damages are estimated by a detailed method that takes into account the actual flow conditions at building scale during an urban flood. Danger for people is assessed for every building following a typology of the buildings, of their use and the sociological features of inhabitants. The advantages of the new methods based on detailed assessment are discussed considering their use for communication to stakeholders and for evaluating flood management plans.