Dynamic characteristics and risk assessment of debris flow under extreme rainfall in Yizhong River Basin of Deqin, Yunnan Province, from numerical simulation to PINN model

In recent years, the Yizhong River basin in Deqin County, Yunnan Province, has experienced frequent debris flow events, posing a significant threat to surrounding residential areas and infrastructure. This study aims to investigate the hydrodynamic characteristics and hazard risk of debris flows in this basin under extreme rainfall conditions, providing a scientific basis for disaster risk reduction and prevention. The research employed UAV aerial photogrammetry, field investigations, and numerical simulation techniques to construct a high-resolution 3D terrain model of the Yizhong River basin. Using the continuum mechanics method based on deep integration and embedded by Physics-Informed Neural Networks (PINNs), the movement processes of flood-type and landslide-type debris flows were simulated under two extreme rainfall frequencies: 1% and 0.5%. Simulation results reveal that the frequent initiation of debris flows in the Yizhong River basin is influenced by multiple factors, including topography, material source conditions, and rainfall intensity. Under the 1% rainfall frequency, both types of debris flows trigger slope instability along the channel, leading to the entrainment of additional source material and enlarging the affected area. At the 0.5% rainfall frequency, the drainage channels within Deqin County were completely overwhelmed, with major transport arteries largely blocked. Substantial volumes of debris flow material entered the Zhiqu River, with overflow even burying Deqin No. 1 Middle School. Risk assessments for single-channel debris flow in the Yizhong River basin revealed that at the 0.5% rainfall frequency, debris flows within the Yizhong River channel reached an extremely high risk level, highlighting the inadequate capacity of the existing protection measures. Consequently, urgent attention must be given to stabilising unstable slopes along both banks of the Yizhong River basin and constructing drainage and diversion facilities within Deqin County. Future regional disaster prevention and mitigation efforts should prioritise curbing the frequent occurrence of debris flow disasters in the Yizhong River basin at their source.