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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]

Liangshan Prefecture, located at the northeastern edge of the Hengduan Mountain System and within the southern section of the Sichuan-Yunnan tectonic belt in Sichuan Province, China, a region prone to landslides, collapses and debris flows due to its active tectonics, complex topography and significant river erosion. By analysing a dataset of environment factors and geological hazard catalogue, the research uses the Relief algorithm to identify critical influencing factors for each hazard type, selecting 10, 9 and 9 factors for landslides, collapses and debris flows, respectively. Five models are used to assess the vulnerability of these hazards: the Information Value model, the Evidence Weight model, the Logistic Regression model, and both the Evidence Weight-Logistic Regression and the Information Value-Logistic Regression coupled models. The effectiveness of these models is confirmed by confusion matrix and ROC curve analyses, with the combined models showing particularly high accuracy in assessing susceptibility. High risk zones were identified in specific areas and along major fault zones in Liangshan Prefecture. The research provides significant insights into the susceptibility of geological hazards in mountainous and canyon regions, offering a comprehensive approach that goes beyond the limitations of single model applications. This methodology not only provides more accurate and comprehensive results, but also serves as a fundamental reference for geological hazard mitigation and management in Liangshan Prefecture, potentially benefiting similar regions worldwide. [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]

Multi-period debris flows have been developed in the last glacial period of the late Pleistocene-Holocene near the Grand Bend of the Yarlung Zangbo River in southeast Tibet, which combined to form a modern large-scale fan-shaped accumulation. The debris flows in the Bangga gully, Pai Town, were explored by ground survey, borehole, and 14 C dating methods to investigate the chronological sequence of formation, accumulation depth, and outrush range. The analysis results show that there are still small-scale debris flows in the tributaries of the Bengga gully, and they are widely accumulated in the channel, but no debris flow accumulation has been found in the existing accumulation fan area. The Holocene debris flows in the Bunga gully were active around 8500 years ago, and the cumulative accumulation depth of a single period is about 10.9 m. The two carbon samples in the light gray silt sand formed by the shallow lake facies (fluvial facies) show that the modern riverbed of the Yarlung Zangbo River was deposited at a depth of about 0.4 m in 40 to 100 years, and the annual average deposition rate was about 4~10 mm. The boreholes at 2906.1~2896.7 m and 2849.4~2848.2 m above sea level reveal a thickness of 9.4 m and 1.2 m cake-like bluish-gray clay in turn. It is assumed that two river-blocking events occurred. The above results could provide a reference for the study of the debris flow activity characteristics since the Holocene in this region. [ABSTRACT FROM AUTHOR]

The southwest mountainous region in China is the worst-hit area due to the most developed geohazard chains. In order to better understand the pattern of the geohazard chains in this region, we analyzed the main control factors and characteristics of the geohazard chains based on 19 typical geohazard events in history. Three classification patterns, namely landslide-type, collapse-type, debris flow-type, and five typical hazard-inducing processes, were summarized. A typical hazard-inducing chain process in each model was selected for analysis. On this basis, we discussed the mechanism of the geohazard chain, the construction of a database and technical standard system, and the measures for preventing and controlling transboundary basin chain-type geohazards, aiming to provide a reference for the regional geohazard prevention and mitigation plan, and the major engineering projects' construction and people's safety in town. [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]

Single-layer reticulated shells are widely used in spatial structures. One critical factor that has to be considered in the design of reticulated shells is the significant adverse impact of high temperature caused by fire on the structures. In order to study the variation of elasto-plastic bearing capacity under high temperature by fire, four types of single-layer reticulated shells (i.e. K6, Geodesic, Schwedler and Lamella) are investigated under two typical fire conditions (i.e. global nonuniform temperature distribution and local high temperature) by the geometrically and materially nonlinear analysis and statistical methods. Practical design formulae for calculating the elasto-plastic bearing capacity of reticulated shell structures under different fire conditions and ambient temperatures are proposed based on the numerical simulation results. [ABSTRACT FROM AUTHOR]

Generation of debris flows is related to poorly sorted mixtures of soil, catchment topography, and rainfall characteristics. Runoff in a valley resulting from intensive rainfall can induce sediment movement within stream beds or along adjacent banks. The water flow in channels is affected by rainfall parameters such as duration, intensity, cumulative rainfall, etc., and is the key factor in debris movement. In this paper, the rainfall characteristics and occurrence conditions of debris flow in Xiongmao Gully on 26 July 2016 were explored. Using data from field surveys and indoor simulation experiments, evaluations of critical discharge parameters for debris movement were performed. Furthermore, debris distribution and the critical discharge characteristics were analyzed via investigation of the catchment topography and cause of the debris flow, and analysis was made of the critical discharge parameters initiating channel debris movement. A K-value clustering analysis method was applied to characterize the rainfall pattern of the study area and its effects on calculation of debris flow. The results showed that for the debris flow in Xiongmao Gully, the debris initiation in the middle reaches of the gully provided the majority of solid particles for the disaster on 26 July 2016, and the upstream confluent provided catchment. Based on the relationship determined by laboratory tests, the calculated critical discharge was 43.8 m3/s, less than the peak discharge (Qc = 66.7 m3/s) calculated by morphological method. In addition, it was indicated that the dominant rainfall patterns of the studied area were first-quartile and second-quartile, i.e., the rainfall occurred primarily at the early or middle stage of this rainfall event. The critical discharge for the debris flow on 26 July was achieved at 5% rainfall frequency, and the larger runoff volume was generated from a short heavy rainfall. According to specific catchment characteristics, such as distributed hydrological analysis, critical discharge, and rainfall pattern of debris flow, forewarning of a damaging debris flow could be made more effective. [ABSTRACT FROM AUTHOR]