针对洞庭湖团洲垸2024年7·5溃堤洪水,采用湖泊与民垸整体二维水动力数值模拟方法,从宏观过程、细部水流结构等方面全方位复盘团洲垸的溃堤洪水,并开展钱团间堤溃决洪水危险性计算。模型准确计算了溃口内外水位的平衡时间;准确给出了团洲垸溃口流量、溃口内外水位、蓄洪量、淹没面积等随时间的变化过程;准确再现了溃口处的水面跌坎,据此揭示了溃口附近水位低于下游湖区同期水位的原因;绘出了溃口附近水位及流速的平面分布,定量分析了溃口附近水面的“外凹内凸”特征及纵横比降。与实测数据相比,模型的水位计算相对误差在溃堤洪水过程中(除溃决初期)一般在10 cm以内,在溃口内外水位达平衡后降至5 cm以下;流量计算相对误差一般在5%以内,峰值流量相对误差2.5%。模型水量守恒统计误差为0.6%;团洲垸最大进洪量的模型计算值与水文部门基于蓄洪量-水位曲线分析结果的差别为6.8%。在洪水复演的基础上,沿钱团间堤自北向南假定了3个溃口,分别在封堵/不封堵已有团洲垸溃口的条件下,开展钱团间堤的溃堤洪水过程计算。从流场、溃口流量过程、民垸蓄洪量和淹没面积等方面,定量评估了钱团间堤溃堤洪水的危险性。研究结果为洪水情势与风险评估、堤防守护等提供了技术支撑。针对真实溃堤洪水计算所提出的河湖与蓄滞洪区一体化二维模拟、民垸精细建模、试算获得溃口断面地形时间序列的研究方法,取得了良好的模拟效果和精度,该方法可供同类研究借鉴。

A two-dimensional (2D) hydrodynamic model is developed to investigate the dike-break flood at Tuanzhou township alongside the Dongting Lake on July 5, 2024. Integrating both lake and township into a single model, we comprehensively reconstruct the dike-break flood, capturing macroscopic flood processes and detailed flow structures. The model also assesses the flood risk associated with a potential failure of the Qianlianghu-Tuanzhou dike. The model accurately determines when the water levels inside and outside the breach reach equilibrium. It provides precise historical data on breach discharge, water levels inside and outside the breach, flood storage volume, and inundated areas in Tuanzhou township over time. Additionally, the model replicates the water surface scarp around the breach, explaining why water levels near the breach are lower than those in the downstream lake area. The water level and flow velocity distributions around the breach are plotted and analyzed. Moreover, the characteristics of concave water surface outside the breach and the convex water surface inside the breach, together with the water-level gradients are also quantitatively examined. Comparison with field data reveals that the model’s water level error is generally below 10 cm during the dike-break flood (except for the initial breach stage), and drops to less than 5 cm once equilibrium is reached. The discharge error is typically under 5%, with peak discharge error at only 2.5%. The model’s water conservation error is 0.6%, and the discrepancy in maximum flood volume between the model and hydrological department’s results obtained from flood volume versus water level curve is 6.8%. Based on the dike-break flood reconstruction, we design three breaches along the Qianlianghu-Tuanzhou dike and simulate dike-break floods with the existing breach at Tuanzhou township under both blocked and unblocked scenarios. We further quantitatively assess flood risks related to potential dike failures by analyzing the flow field, discharge processes, flood storage, and inundated areas. The findings offer technical support for flood risk assessment and levee protection. The systematic method for simulating real dike-break floods in this study includes integrated modeling of rivers/lakes and townships, detailed township modeling, and iterative calculations to determine breach topography over time. These methods enable accurate simulations of dike-break floods and can serve as a reference for similar studies on dike-break floods.