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The Wenchuan earthquake strongly disturbed the earth surface and induced sufficient loose debris in the mountain basin, which supplies sufficient solid materials for debris flow initiation. Recently, a catastrophic debris flow was induced by strong rainfall on June 26, 2023 in the Banzi basin. Inconsistent with the first few years of the Wenchuan earthquake, the hillslope landslide sediment supply for debris flow occurrence is limited after 15 years of the Wenchuan earthquake, and the materials supplied for debris flow in the later period are mainly obtained from alluvium deposited along the channel. Simultaneously, this debris flow was triggered by flash flood through strongly erosion channel materials. However, although 15 years have passed since the Wenchuan earthquake, the triggering rainfall conditions have still not returned to pre-earthquake level. This debris flow first initiated in the upper branches of the basin and then gradually transported downstream at an average discharge of 806.99 m3/s, and approximately 82.80 × 104 m3 solid materials were transported out the Banzi basin to form a debris flow fan with length of 120 m and width of 260 m in the Minjiang River, which poses a serious threat to the resettled population and destroy the reconstruction infrastructures. Importantly, there are still sufficient solid materials deposited in the basin, this could result in debris flow activity continuing for an unpredictable time. Therefore, implementation early warning, prevention, and mitigation measures in this basin are still important for debris flow disaster management in the later period of Wenchuan earthquake. [ABSTRACT FROM AUTHOR]

Large amounts of co-seismic landslides provide abundant debris sources following a strong earthquake and are prone to initiate and generate debris flow under heavy rainfall. Assessing the susceptibility they pose and what drives their movement in the years following the mainshock has not yet been attempted, primarily because multitemporal debris flow inventories are lacking. This study conducted statistical analyses using the multitemporal debris flow inventory (2008–2021) following the 2008 Wenchuan earthquake and a set of conditional factors (debris source, terrain, and hydrology). The dynamic susceptibility evaluation model was created using logistic regression. The temporal evolution of these factors affecting debris flow runout was explained. Our findings suggest that topography variables grew rapidly after the earthquake, while debris source factors dominated for seven years after the disaster before declining progressively to zero. These findings may have significant consequences for traditional susceptibility assessment models in regions where co-seismic landslides are the dominant debris flow source. [ABSTRACT FROM AUTHOR]

On August 20, 2019, a catastrophic debris flow occurred in the Cutou catchment, leading to the formation of a dam in the Min River. This debris barrier triggered a chain of multiple hazards, resulting in widespread flooding of houses upstream and downstream. To understand and assess the impact of this hazard chain, we conducted a comprehensive study using numerical modeling, field survey, the solid material reserve, and the probabilistic method. We began by conducting a detailed investigation of the 2019 event and calibrated the model parameters using survey data. Subsequently, we simulated and analyzed the entire process of hazard chain event, which was divided into four stages by the characteristics of water level. Finally, we developed a comprehensive and efficient approach for hazard assessment using the solid material reserve method and the probabilistic method. This approach enabled us to generate a hazard distribution map for the debris flow chain, providing valuable insights for effective hazard prevention in the Wenchuan area. [ABSTRACT FROM AUTHOR]

Rainfall characteristics influence the formation of runoff and peak discharge, but there are few studies on the variability of rainfall time distributions and their influence on peak discharge in Wenchuan County. This study analysed the variability of the rainfall time distributions in Wenchuan County by using the Huff curve and their impact on the peak discharge by coupling the HEC-HMS model. A total of 817 rainfall events were collected from Wenchuan County, and most of them were characterized by short rainfall durations. The rainfall time distribution patterns were classified as Quartile I, Quartile II, Quartile III, and Quartile IV, and the variability of the rainfall time distribution for each pattern was analysed based on the probability curves. The variability of the rainfall time distribution in Wenchuan County is significant, but the variability of the same rainfall time distribution in different regions is small. The Huff curve for Wenchuan County was developed, and it can be applied to storm designs in the future. The peak discharges for Quartiles I–IV increased gradually. The trigger response of debris flows for Quartile I is a rapid rainfall-triggering response pattern, and the trigger response of debris flows for Quartile II is an intermediate rainfall-triggering response pattern, but the trigger response of debris flows for Quartiles III and IV is a slow triggering response pattern. The debris flows in the Wenchuan earthquake area were widely triggered by rainfall time distribution patterns of Quartiles I and II. [ABSTRACT FROM AUTHOR]

Debris flow activity increased after the Wenchuan earthquake, and many debris flows continue to occur. Recently, a catastrophic debris flow event was triggered by strong rainfall on 20 August 2019 in Wenchuan County, China. The main purposes of this article are to analyse the activity characteristics of this disaster and further to analyse the long-term activity of debris flow in Wenchuan County based on the analysis results of this disaster. According to a field survey and remote sensing image interpretation, this strong rainfall triggered 15 debris flows that occurred simultaneously in the large watershed in northern Wenchuan County, and they were characterised by strong channel erosion and a disaster chain effect. The activity and sediment supply capacity of landslides have decreased significantly, and the landslides that provided materials for this debris flow event are mainly distributed on both banks of tributaries. The amounts of triggering rainfall and antecedent accumulated rainfall for this debris flow event were 13.7 mm and 47.1 mm, respectively. In addition, the channel runoff formed by strong short-duration rainfall eroded the channel deposits, and temporary check dams failed due to slope failures; these are the main causes for debris flows in the next period. Analyses of the debris flow volume versus watershed area and the maximum erosion modulus prove that the debris flow activity in Wenchuan County is decreasing with time, but more than 5~10 years will be required to recover to the pre-earthquake level. [ABSTRACT FROM AUTHOR]