Research on flood risk zoning of the Jintan urban area in the western region of the Taihu Lake Basin

Flood risk zoning, as a foundation for scientific decision-making, planning, and management in flood prevention and disaster mitigation, can intuitively reflect the overall regional flood risk situation, determine flood prevention functions and their corresponding control characteristics, and clarify the spatial distribution of flood risk levels and control standards. It is an important non-engineering measure for flood prevention. At present, although normative documents such as the Technical Requirements for Compiling Flood Risk Zoning and Prevention and Control Zoning exist as technical references, due to China's vast territory and complex climatic conditions, the analysis methods for flood risk zoning still require further exploration. Especially in areas where complex conditions such as mountains, plains, and polder zones intersect, research on flood risk zoning remains a relevant and necessary topic.

　　To study analysis methods for flood risk zoning in transitional urban areas between mountains and plains, this paper selects Jintan Urban Area, located in the central part of the Western Region of the Taihu Lake Basin, as the research object. It defines zoning units, analyzes sources of regional floods and floodwater magnitudes, and uses a constructed flood risk analysis model for Jintan Urban Area to conduct flood simulation calculations, determine flood risk levels, and generate a flood risk zoning map for the district.

　　(1) Taking into account the topography and geomorphology of Jintan District, the catchment area, and the relationship between rivers and embankments, the area is divided into two zones: a mountain flood threat zone and a flood control zone for major rivers. According to the distribution of polder areas and main rivers in the district, 26 zoning units are identified in the flood control zone and one in the mountain flood threat zone.

　　(2) Based on the calculation results of flood scenarios with different return periods in Jintan District, the analysis and classification of risk elements and levels are conducted. The results show that when Jintan Urban Area experiences a flood with a 50-year return period, the inundated area reaches 298.03 km², and the inundation depth in most areas exceeds 1 m. For a 100-year return period, the inundated area expands to 325.58 km², with the majority of inundation depths falling within 1.0–2.0 m. Flood risks in Jintan District are categorized into three levels: high, medium, and low. The high-risk zone covers 96.43 km², the medium-risk zone 165.81 km², and the low-risk zone 556.31 km². No extremely high-risk areas are identified.

　　(3) According to the results of flood risk zoning and prevention/control zoning, future flood management in Jintan District should focus on areas along the Tongji River, Tongji South River, and Danjin Licao River. The embankment standards for these rivers and polder areas—such as Dongda, Changxing, and Shaqiao—should be upgraded, and overall flood risk management should be strengthened to ensure the district’s flood safety.

　　The results of this paper can serve as a fundamental reference for flood risk management, flood prevention planning, disaster mitigation policy development, and territorial spatial planning in Changzhou City.