Reservoir Dam Failure-Oriented Flood Simulation Based on a Zero-Dimensional and Two-Dimensional Coupled Breach Flow Calculation Model

Conventional empirical formulas for calculating the breach discharge of concrete dams often fail to account for the influences of upstream inflow, downstream backwater effects, and irregular breach shapes on dam-break flow, particularly for lake-type reservoirs characterized by high dam height, large storage capacity, and significant inflow. Consequently, there exists a certain deviation between calculated results and actual conditions. To address these limitations, a breach discharge calculation method based on a zero-dimensional (0D) and two-dimensional (2D) coupled model was proposed. The 0D reservoir was conceptualized using water level-storage capacity curves and discharge-storage relationships, while the downstream river channel was modeled using a 2D hydrodynamic framework. The coupling between the 0D and 2D models was achieved through the formulation and solution of a Riemann problem. To represent arbitrary breach geometries, the model modified the elevations of 2D grid nodes at the dam site, enabling accurate simulation of complex flow regimes at the breach boundary and effectively overcoming the shortcomings of traditional empirical formula methods. Taking the Fengshuba Reservoir in Guangdong Province as a case study, the adaptability and rationality of the proposed model were verified by comparing its calculated breach discharge results against those obtained from typical empirical formulas, including the Saint-Venant formula, Schoklitsch formula, U.S. Waterways Experiment Station (WES) formula, and broad-crested weir formula. Based on the analysis of breach discharge reasonableness, the breach discharge calculated by the proposed model was larger than the results of the Saint-Venant, Schoklitsch, and WES formulas. However, since the model fully considered the irregular breach cross-section formed during an actual failure process, the result was slightly smaller than that of the broad-crested weir formula. Furthermore, water balance analysis confirmed minimal model error, indicating that the model accurately reflected the actual breach discharge hydrograph. Additionally, the calculated breach discharge was coupled with a dam-break flood routing model for downstream flood evolution analysis. The simulation results show that a complete dam failure during the flood season would significantly impact Heyuan City and Huizhou City along the main and tributary channels of the East River, while having a lesser effect on Dongguan City and Guangzhou City in the estuary area. The inundation area with water depth exceeding 3 meters reached 561.87 km². The model effectively simulated the propagation of dam-break floods, with results consistent with flood evolution patterns, clearly delineating the inundation impact. This provides critical technical support for simulating dam-break floods from concrete dams and formulating safety emergency plans for reservoir failure incidents.