Probabilistic Flood Hazard Mapping Considering Multiple Levee Breaches

• Published in: Water resources research 2022-04, Vol.58 (4), p.n/a
• Main Authors: Maranzoni, A., D’Oria, M., Mazzoleni, M.
• Format: Article
• Language: English
• Subjects: breach scenarios; Entropy; Entropy (Information theory); Environmental risk; Estimates; Flood control; flood hazard; Flood hazards; Flood management; Flood mapping; Flood risk; Flooding; Floods; Fragility; Hazard assessment; Hydrodynamic models; levee breaches; Levees; Levees & battures; Methods; multiple breaches; probabilistic method; Probabilistic methods; Probability theory; Risk management; Statistical analysis; Two dimensional models; Uncertainty
• ISSN: 0043-1397; 1944-7973
• DOI: 10.1029/2021WR030874

Probabilistic methods are widely adopted for residual flood hazard assessment in flood‐prone areas protected by levees. Such methods can consider various sources of uncertainty, including breach location and flood event characteristics, and allow for the quantification of the result confidence. However, the possible occurrence of multiple levee breaches during the same flood event is usually disregarded. This paper presents a probabilistic method based on levee fragility functions and basic probability rules to estimate the probability of selected breach scenarios, including multiple breaching events. The flood hazard classification is based on inundation variables calculated for flood events of different return periods. A combined 1D‐2D hydrodynamic model is used for flood simulations. Probabilistic inundation extent maps and probabilistic flood hazard level maps are then created. Finally, probabilistic flood hazard estimates are summarized in a map of a suitable central tendency of the hazard level, coupled with a map of the Shannon entropy as an uncertainty indicator. This pair of statistical maps provides concise and effective information on a reference flood hazard along with the associated uncertainty. The method was applied to a region located along the middle reach of the Po River (northern Italy). Comparable central flood hazard estimates are obtained for the two sets of breaching events including or not including multiple breaches, with higher uncertainty if multiple breaches are considered. This result highlights the importance of considering multiple breaching events in flood risk management. Key Points A probabilistic method is presented for flood hazard mapping in flood‐prone areas protected by levees, considering multiple breaches Breach scenario probabilities for selected return periods are estimated using levee fragility functions and basic probability rules A “central” hazard level map and an entropy index map are introduced to summarize probabilistic information on flood hazard