Debris Flow Susceptibility Assessment and Runout Prediction: A Case Study in Shiyang Gully, Beijing, China

At 14:00 on 18 June 2017, floods occurred in Shiyang gully at the junction of Beijing and Hebei Province, China. The floods put 12 people at risk, 6 of whom died. After the occurrence of the floods, the environment in Shiyang gully has undergone tremendous changes. There are many loose residual materials in the watershed. Therefore, it was necessary to evaluate the debris flow susceptibility of Shiyang gully after the disaster. The factor analysis method, entropy weighting method and geomorphic information entropy method were used to evaluate the debris flow susceptibility of each sub-watershed in Shiyang gully. By comparison with the technical standard published by the China Ministry of Lands and Resources, it was found that the susceptibility assessment results are not ideal. To improve the accuracy of the assessment results, we used a comprehensive method. The accuracy of the susceptibility assessment obtained by the comprehensive method is 87.5%. This accuracy shows that the comprehensive method is applicable to the susceptibility assessment of debris flows in this region. To predict the runout path of potential debris flows in four sub-watersheds with very high susceptibility, the authors used the SFLOW software developed by Jilin University to simulate the debris flow hazards. Combined with the on-site investigation data, debris flows in the four sub-watersheds were simulated at 10-, 20-, 50-, and 100-year recurrence intervals. The obtained runout path could provide some guidance and reference for the avoidance of disasters and treatment of debris flows.