Comparison Between HEC-RAS and TELEMAC-2D Hydrodynamic Models of the Loire River, Integrating Levee Breaches

Throughout history and in the present era, flooding has represented a significant challenge, resulting in substantial property damage and a noteworthy loss of lives, despite extensive risk mitigation measures and billions invested in flood defenses globally. The Loire river, the longest in France, has a rich history of flooding. To mitigate floods, levees have been built since the Middle Ages. For this study, a 2D hydraulic model was built using HEC-RAS, covering a 50-km strech of the river from Gien to Jargeau. Building upon a previously developed numerical model of the study area by IRSN using TELEMAC-2D, the HEC-RAS model was created based on its data and assumptions. The objective was to assess the performance of both software by comparing the obtained results. The HEC-RAS numerical model has been calibrated for the largest recorded flood event, which occurred in 2003, and validated on two other major floods. This allowed us to estimate the impacts of flooding, with a particular focus on the simulation of an estimated 1000-year return period flood and incorporating the analysis of multiple levee breach scenarios. Furthermore, the results obtained with the hydrodynamic models implemented using HEC-RAS and the existing TELEMAC-2D model were summarized, encompassing their performance, capabilities, limitations, and the analysis of levee breaches scenarios testing various breach parameters. This analysis provides a robust set of criteria to guide to selection of the most suitable tool for further studies based on the objectives of each project.