Development of a Complete Dynamic 2D Modeling Approach for Flood Management in a Dense City Area in France

A large part of the City of Riom, located in the center of France, is frequently flooded, with a frequency which obviously increases due to the climate change. tone part of this urban area includes a large hospital, which should be at all times secure. A river is passes through the area, partly uncovered and partly covered, which reduces its hydraulic capacity and induces flooding nearby. Once the water is out of the river bed, the water is flowing on the streets and some strategic points are then not accessible. The main objective of the project was to better understand the behavior of the flooding waters and then provide the best solution to reduce the flood damages. Up to now, the common approach was to develop a 1D model to try to represent the reality (use of extended transects at more or less regular distance). However, once in the streets areas, the flow is not going in only one direction but can take many directions (depending on the site topography).

In this project, a new dynamic approach has been developed in order to take into account the entire local conditions. More precisely, to gain an understanding of existing conditions and to analyze potential solutions, PCSWMM, that is a dynamic user-friendly hydraulic model, was used to simulate the various conditions under exceptional events. In addition, the complete precise local conditions, such as the part of the river that is covered, was represented in the model with an adapted mesh grid. It has to be noted that PCSWMM 2D contains various modules that greatly help the user to construct this more detailed model.

Using this approach, the behavior of the flow and the critical constraints clearly appeared and a combination of solutions were proposed to improve the access and development, such as river design additional wall, infiltration improvement, retention basin. The costs of these interventions were compared to the costs due to the flood damages in order for the municipality and hospital to take appropriate decisions in order to implement a common strategy.