An integrated two-layer model for simulating shallow flow, sediment transport and overtopping-induced breach processes

Extreme rainfall may generate flash floods, which may overtop the flood defences (e.g., dam, dike, and levees) and subsequently lead to structure failure, threatening the safety of the downstream population and properties. This work presents a new two-layer modelling approach to simulate surface water flooding and the subsequent dam/dike breach process caused by overtopping. The new modelling framework simulates the surface water flooding process in the upper layer using a high-resolution hydrodynamic model that also considers sediment transport and morphodynamic change. A cell-based infinite slope model is implemented to identify unstable slope/soil and estimate the sliding depth for the lower layer. And a cellular automaton method based on diffusion-wave assumption is further developed to simulate the dynamics of the resulting bed granular movement. The momentum and bed elevation source terms of the hydrodynamic governing equations (the flood layer) and the soil depth of debris flow (the granular layer) are simultaneously calculated in a fully coupled way. This results in a fully coupled flooding induced breach chain model. The proposed model is validated against experimental and real-world tests with different breach types. And the sensitivities of calibrated parameters and mesh sizes are discussed in detail. The results indicate that the proposed model can simultaneously simulate overtopping flooding and the associated slope failure and breach processes.