Development of an integrated flood model for the North Four Rivers system in Tianjin City

Flood control and waterlogging management in plain river network regions face significant challenges due to the weakened runoff generation and confluence processes, which limit the effectiveness of traditional hydrological models. Large-scale two-dimensional hydrodynamic models offer high accuracy but are hindered by high computational costs and low efficiency. To address these issues, this study develops an integrated flood regulation model for the north four rivers system in Tianjin city by coupling hydrological models, one-dimensional riverine hydrodynamic models, flooding and drainage models, and two-dimensional surface hydrodynamic models. The model employs a two-dimensional approach within flood detention areas to simulate water dynamics, while outside these areas, a structured framework of "hydrological model–drainage unit–pumping station–riverine" is used for calculations. This approach ensures accurate simulation of riverine hydraulic factors under small to medium flood scenarios and provides reliable predictions for flood routing in detention areas during extreme flood events. The proposed model offers an efficient and practical methodology for hydrodynamic modeling in complex river network systems.