Author(s): V. Bacchi; L. Pheulpin; N. Bertrand

Linked Author(s):

Keywords: River breach; Uncertainty analysis; Flood hazard; HEC-RAS; Garonne River

Abstract: In this study we present a methodology based on uncertainty analysis for the studying of the flow hazard generated by river breaches. This methodology is applied to the 1D storage area model of the Garonne River built with the HEC-RAS code. Assessments of flood hazard and risk, which systematically consider various uncertainty sources, have become the state-of-the-art approaches since 2002. Uncertainties are both associated to the numerical structure of the model, to the knowledge of the physical parameters which force the system and to the randomness inherent to natural phenomena. Even if difficult, these uncertainties should be taken into account from both modelers and decision-makers in order to propose an adapted strategy for risk mitigation. The quantification of the uncertainty related to levee behavior during an inundation event can be a very difficult task but it remains essential to enhance the strategies risk mitigation. Levees play a major role to constraint river flow and their behavior can significantly affect the water levels in the inundated areas in the vicinity of rivers. During an inundation event, levees can be partially damaged and a breach can be formed. The breach initiation and its progression into the levee result from a sequence of physical mechanisms (i.e. piping, landside erosion due to overflowing, slope instability) leading to complex phenomena to be understood. As a result, the uncertainties related to the exact locations of levee breaches, their geometry and the triggering factors of the breach’s initiations are numerous. In order to study and prevent the consequences of a breach on a given area to protect, numerical models including breach processes are generally employed. Levee breaches can be modeled in different ways, depending on the chosen numerical model. As a consequence, the study of the uncertainty related to levee breach corresponds mainly to the study of the uncertainties related to the breach characteristics (i.e. breach geometry) and the failure mechanisms implemented in model. In this context, the aim of our study is to evaluate the sensitivity of flooding associated to levees breaches modeled with a 1D hydraulic model. To do so, a 1D storage area model of the Garonne River was built and validated with HEC-RAS. The study case is based on the 1981 historical flood event of the Garonne River between Tonneins and La Reole.

DOI: https://doi.org/10.3850/978-981-11-2731-1_199-cd

Year: 2018