Abstract: Once a barrier lake is breached, it will pose severe threats to the people and infrastructure downstream. Constructing a spillway is the most common measure for risk mitigation, but an urgent, significant issue is how to design its cross section and reduce the excavation volume while ensuring an effective reduction of the breaching flood risk. Based on the soil-water coupling mechanism, this paper develops a new DB-IWHR 2.0 model for automatic spillway optimization design that integrates a hyperbolic erosion model and relevant hydraulic parameters to simulate the vertical and horizontal rapid enlargement of the breach and realize a rapid analysis (in 1 hour) of the whole breaching process. Then, an optimal spillway design is obtained according to the analysis of breaching features. Application to a case study of the "11?03" Baige barrier lake reveals that when the spillway is constructed by the optimal design, the peak flow through the breach is 31041.18 m3/s, nearly the same as its site observed value of 31000 m3/s, while the excavation could be reduced from 135000 m3 to 71029.16 m3, and its deepest section reduced from 15 m to 4.04 m, or a 53% and 27% reduction of the emergency rescue response, respectively. Thus, the stability loss of the barrier dam can be avoided, while the construction time and emergency rescue response time be reduced, implying the emergency rescue work can be faster, more detailed and more effective.

Key words: barrier lake, spillway construction, DB-IWHR 2.0 model, efficient optimization, breach discharge and flood volume