Analysis of Barrier Lake Breach Flood Mitigation Under Cascade Reservoirs Operation: A Case Study of the Mogangling Event, Dadu River

The southeastern margin of the Qinghai–Tibet Plateau is characterized by complex geological conditions and frequent disasters such as landslide-induced river blockage and subsequent barrier lake breaching. With the construction of cascade reservoirs in the basin, the potential impacts of historical barrier lakes under the current flood control system remain unclear. Reconstructing the breaching process of barrier lakes is of great guiding significance for regional flood control and disaster mitigation, risk management, and the safe operation of cascade reservoirs in the basin. In this study, the Mogangling landslide barrier lake in the Dadu River basin was selected as the research object. We constructed breach flood hydrographs for the 300 m and 600 m breach scenarios and established a one-dimensional and two-dimensional coupled hydrodynamic model of the barrier lake breach flood based on the integrated flood modeling system (IFMS). The model was used to simulate the propagation and inundation processes of the breach flood under natural propagation without reservoirs and under the joint operation of the cascade reservoirs. Spatially distributed socioeconomic data were then combined with the model to assess flood impacts and the potential disaster mitigation effect of the joint operation of the cascade reservoirs. The results show that the joint operation of the cascade reservoirs can reduce the peak discharge of the barrier lake breach flood by 30.7–97.9%, decrease the total inundated area of downstream riverside towns by 70%, and reduce the GDP losses and the affected population by 89% and 87%, respectively. In addition, artificial excavation of a spillway channel can reduce the peak discharge of the natural barrier lake breach by approximately 30%.