Abstract: Extreme floods often occur in the middle Yangtze River. The Jingjiang flood diversion zone needs to be operated during these events to protect the safety of the levees along the Jingjiang Reach. Therefore, it is important to be able to predict the potential flood risks to people and property in such an area for the purpose of flood management. In this study, an integrated numerical model for estimating the flood risks in a flood diversion zone is proposed, including a module for predicting the 2D hydrodynamic processes of flood inundation in a study area with complex topography, and a special module for estimating the flood risks to people (children and adults) and property (vehicles, buildings, and crops) using newly developed safety criteria. The proposed model was used to predict the flood inundation process and variation in hazard degrees of people and property, based on a hypothetical discharge hydrograph during the operation of the Jingjiang flood diversion zone. The model predictions show high flood loss rates for various flooded objects such as people, vehicles, buildings, and crops, with a mean loss rate for these subjects of 75% after 140 h. This suggests that the operation of a flood diversion zone should be cautiously considered, as it would likely result in a huge loss of people and property. Furthermore, an investigation was conducted into the effects of different roughness coefficients and people stability criteria on the model predictions. The results show that variable Manning’s roughness coefficients need to be used in the hydrodynamic module according to different underlying surface conditions, and a mechanics-based criterion for the stability of people in floodwaters should be adopted to assess the potential hazard degrees.

Key words: People hazard; Property hazard; Flood risk assessment; Numerical modelling; Jingjiang flood diversion zone

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