Risk analysis of flood protected zone with complex boundary conditions and multi-flood sources

In order to estimate the risk of dike-break flood in the flood protected zone under multi-flood sources and complex boundary conditions, a one-dimensional multi-breach model and a two-dimensional flood routing model were established based on unsteady flow control equation. A dam-break model was used to couple rivers and flood protected zones, and local mesh refinement method and approximate structure generalization method were used to deal with water division and blocking resulting from the complex boundaries such as roads in the flood protected zones. Four flood scenarios of the flood protected zone from Hannan to Baimiao from three flood sources including the Yangtze River, Hanjiang River, and Dongjinghe River were simulated. The flooding area, economic loss and flood-affected population were compared and analyzed by the loss rate method based on inundation depths. The results showed that the model established in this study was reasonable and stable. The complex boundary had a significant impact on the flood routing, and the risk differed significantly depending on the flood sources. The worst situation was observed in a 300-year flood occurred in 1954 in the Yangtze River at the dike-break position of Xiangxin, resulting the submergence of 3 790 km² area, a flood-affected population of 1.968 million, and an economic loss of 80.2 billion yuan. This study can provide strong technical supports for flood risk management and decision-making of refuge and migration.