Discrimination of Debris Flow Types and Evaluation of Landslide Sediment Supply Capacity: A Case Study of the Jiuzhai Valley Meizoseismal Area Postearthquake

After the Jiuzhai Valley earthquake, postseismic effects reactivated coseismic deposits, posing a high risk of triggering chain disasters such as debris flows. Based on existing empirical discrimination methods, a discrimination model for debris flow with different channel types (DMDFDC) after the earthquake is developed to thoroughly analyze the long-term evolution characteristics of debris flow disasters with different channel types. Subsequently, the landslide sediment supply capacity of each debris flow subwatershed is assessed by evaluating the landslide activity and the coupling relationship between landslide activity and its interaction with gullies. The results indicate that the DMDFDC can accurately discriminate between narrow-steep and wide-gentle types of debris flows, with a threshold value of T = 1.5. Over 5 years after the earthquake, the landslide supply capacity of 299 subbasins in the region exhibits an overall oscillating decline with extreme rainfall events. In years with heavy rainfall, the supply capacity of the narrow-steep type of debris flow is significantly higher than that of wide-gentle ones. In contrast, the opposite is observed without extreme rainfall events. In addition, high-capacity landslide supply areas gradually shifted toward the middle and lower reaches of the basin from 2017 to 2022, and it is projected to recover to preearthquake levels by around 2032.