In recent years, the increasing frequency of debris flow demands enhanced effectiveness and efficiency of warning systems. Effective warning systems are essential not only from an economic point of view but are also considered as a frontline approach to alleviate hazards. Currently, the key issues are the imbalance between the limited lifespan of equipment, the relatively long period between the recurrences of such hazards, and the wide range of critical rainfall that trigger these disasters. This paper attempts to provide a stepwise multi-parameter debris flow warning system after taking into account the shortcomings observed in other warning systems. The whole system is divided into five stages. Different warning levels can be issued based on the critical rainfall thresholds. Monitoring starts when early warning is issued and it continues with debris flow near warning, triggering warning, movement warning and hazard warning stages. For early warning, historical archives of earthquake and drought are used to choose a debris flow-susceptible site for further monitoring. Secondly, weather forecasts provide an alert of possible near warning. Hazardous precipitation, model calculation and debris flow initiation tests, pore pressure sensors and water content sensors are combined to check the critical rainfall and to publically announce a triggering warning. In the final two stages, equipment such as rainfall gauges, flow stage sensors, vibration sensors, low sound sensors and infrasound meters are used to assess movement processes and issue hazard warnings. In addition to these warnings, community-based knowledge and information is also obtained and discussed in detail. The proposed stepwise, multi-parameter debris flow monitoring and warning system has been applied in Aizi valley China which continuously monitors the debris flow activities.

On the basis of 182 gravelly soil samples taken from debris flow source area, the particle size distribution are obtained through laboratory test, fractal dimensions of samples are calculated by fractal theory. Analysis of calculated results show that the gravelly soil samples are mainly one dimension fractal; and it account for 88.46% of the total samples, the value of one dimension fractal is between 2.250-2.798. Based on the calculated fractal dimension, soil samples are configured; and self-made constant head device with controllable waterhead are used to conduct penetration experiment. The experimental results indicate that the correlation between permeability coefficient and fractal dimension is significant. When dry density equals 1.8 g/cm3, the correlation of permeability coefficient and fractal dimension is best; and the relationship between permeability coefficient and fractal dimension shows obvious power function using multiple regression analysis under different density conditions. Moreover, under same fractal dimension (condition), the permeability coefficient decreases with the increase of density; the power function relation between fractal dimension and permeability coefficient is obvious when fractal dimension ranges from 2.450 to 2.600. This study results can provide theory basis for future critical rainfall research; meanwhile, these can improve the universality and accuracy of the existing forecasting models.

“5· 12”汶川地震灾区的泥石流灾害具有规模超大、群发性等特点.针对这些特点,监测预警将是及时有效而经济合理的防灾手段之一.在分析国内外泥石流预警研究进展的基础上,针对目前地震次生泥石流监测预警实践中的一系列问题,提出了一种基于泥石流形成运动过程的泥石流监测预警体系.该体系从泥石流形成机理研究出发,监测泥石流形成运动各阶段的特征参数,并根据各参数预警阈值建立相应的临灾预警等级,形成了全流域的泥石流综合监测预警体系,适用于汶川地震灾区这种高频率、大规模泥石流的防灾减灾工作.

沟道侵蚀型泥石流是泥石流的主要类型之一,研究其起动机理和起动临界条件有助于泥石流治理和预警预报.虽然多年来对沟道侵蚀型泥石流的起动研究有了一些成果,但目前对其起动机理的认识还存在局限,现有起动临界条件计算方法也不成熟,在很大程度上制约了防灾减灾的进展.为深入研究沟道侵蚀型泥石流的形成机理和起动临界条件计算方法,回顾了国内外学者在相关领域的研究成果,系统总结了沟道侵蚀型泥石流起动研究现状,并对沟道侵蚀型泥石流未来研究方向做出展望.

After the ＂5·12＂ Wenchuan Earthquake,plenty of loose soil materials accumulated in Jianping Basin of Longxi River,which is the main source material for debris flows initiation.Three large-scale debris flows occurred in Jianping Gully in 2009 and 2010.In contrast with the pro-earthquake conditions,the terrain and rainfall have not changed a lot and are appropriate for the initiation of debris flow,so loose materials can be regarded as the most significant impact factor for the debris flow characteristics and its development trend.The results based on the analysis of loose materials and its consolidation impact shows that debris flows in Jianping Gully will occur frequently in 5 years.The possibility of catastrophic debris flow will be high.In the next 5~10 years,the frequency and scale of debris flows in Jianping Gully will decline if there is no significant change for the rainfall and no strong earthquake,while large-scale debris flows can also occur under extremely rainfall with low frequency.

The clay content of the gravel soil from the upstream area of a debris flow has significant influence on the pore pressure and shearing strength. This is a problem that has to be solved in studying the debris flow initiation mechanism. Based on the three-axial experiment, this paper studies the relationship among the shearing strength, pore pressure, collapsibility and clay content of the sample from Jiangjia ravine of Dongchuan in Yunnan of China. The experiment indicates that (1) when the clay content is 3. 75% ∼ 7. 50%, the collapsibility of the sample is greater and when it is 5%, that of the sample is the maximum; (2) in the UU experiment, the pore water pressure of the samples with 3. 75% ∼7. 50% clay content has the greater increase, and in the CD experiment, the pore water pressure of the sample with 12. 5% clay content has the greater increase; (3) the gravel soil with 5% clay content is the easiest to demolish; (4) under the same conditions of rainfall and gradient, the gravel soil with 3. 75% ∼7. 50% clay content is most likely to motivate a large-scale devastative debris flow.

Two giant debris flows occurred in Bayi gully in Dujiangyan County,respectively on August 13 and 18,2010,affecting seriously local people＇s daily production and life.Based on field investigation data obtained from Bayi gully,the causes and the dynamic characteristics of the debris flows was analyzed,and a detailed risk assessment were carried out.The study results show that the loose material source,rainfall amount and topographic conditions of Bayi gully were contributed to the initialization of debris flows.The debris flows in Bayi gully were giant in magnitude and high in risk.The study provides a reliable basis for the debris flow prevention and mitigation in Bayi gully.

This paper is based on combination study of the 5.12 Wenchuan earthquake-induced typical debris flow events.In the paper the debris flow landscape and landform,the precipitation and the earth condition were studied firstly.After that the Wenchuan earthquake debris flow-triggering models were revealed.These models include(1) valley triggering;(2)slope collapse and landslide triggering;(3)loose soil eroded by stream and rains;(4)landslide surface liquefied;(5) gully eroded.And the debris flow-triggering mechanism was explained at last.The debris flows of quake-stricken area distribute in the arid valley which abounds in weathered crust granite,clastic rock and metamorphic rock,and the precipitation nodes

This paper describes a study about the impact of earthquakes on debris flows with a focus on the Great Wenchuan Earthquake 2008 in China. The land form, precipitation, and source material are the three key factors for debris flow initiation in the Wenchuan surrounding area. Classifications and examples of four types of debris flow initiation triggering (gully triggering, slope triggering, liquefaction triggering, and gully erosion triggering) have been presented. The initiation mechanisms are attributed to hydraulic and geomechanical aspects. The actual debris flow cases linked with the Great Wenchuan Earthquake and other earthquakes in China have been used to illustrate the increased magnitudes of debris flows due to a large amount of loose materials created by the seismic actions. The critical precipitation for debris flows is reduced by the earthquake. It is predicted that the impact of the Great Wenchuan Earthquake on the local debris flows would be significant in the next 5–6 years, and much less in the following years (up to 20 years). Finally, the debris flow system will reach a relative stable stage. This prediction is based on the historical observations at other earthquake areas and the qualitative analysis on debris flow initiation mechanisms.

Critical rainfall assessment is a very important tool for hazard management of torrents and debris flows in mountainous areas.The complexity of outbreak of torrents and debris flows is depended on critical rainfall.There is an urgent need to quantify the critical rainfall distribution in the area so that better hazard management could be planned and if real time rainfall forecast is available,and torrent and debris flow early-warning could be issued in advance.This study is based on 49-year observations(1954~2003) of up to 678 torrent and debris flow events.Generally,the contour maps from 1 hour and 24 hours have similar patterns.Three zones with low,medium and high critical rainfalls have been identified.The value of the 1 hour critical rainfall varies from 5~120mm,which is most closely with the outbreak of torrents and debris flows.The value of the 24 hour critical rainfall varies from 35~235mm,which is very important to the outbreak of torrents and debris flows.On this basis,it focuses on the critical rainfall torrents and debris flows in Chengdu.Finally,it classifies regions of torrents and debris flows in Chengdu based on critical rainfall characteristics of Chengdu.

Abundant debris deriving from the landslides and rock avalanches triggered by large earthquakes could significantly alter the characteristics and occurrence frequency of debris flows in the earthquake stricken areas.There is an urgent need for a quick and easy method to assess debris flow hazard to aid the recovery activities by the local residents.Conventional methods are mainly based on field investigations which are time consuming and resources demanding.In addition,as the loose materials are gradually taken away by debris flows,the debris flow occurrence frequency will change with time and more regular updates are needed with the debris flow hazard maps.Therefore,a GIS based system using satellite remote sensing and digital elevation model is proposed in this study.The debris-flow potential index based on the volume of unstable debris is used as the assessment criterion.The proposed method is applied to a case study in the river area affected by the Wenchuan Earthquake 2008.It has been found that the resulted hazard map corresponded well with the observed debris hazards.The validity of the proposed method is depended on the digital data and need regularly update from the latest satellite images with more up-to-date debris accumulation information.

After the Wenchuan Earthquake,a plenty of loose materials accumulated in the southwest of China,and it can be easily initiated to form debris flow under the action of precipitation.In 2010,a rare drought disaster struck the southwest,which can lead to forest fire,and strong rainfall after this period.At the same time,clay par-ticles in the loose materials shrink under the action of longtime drought.However,clay particles swell after absorb-ing the rain t,hen they block the void,resulting in the increase of pore water pressure and decline of shear strength,under this circumstancesi,t is much more easily for the initiation of debris flow.Based on the risk charac-teristic of debris flow in history,combining with the discipline of earthquake activity and arid area,t this region was divided into three danger zones,and prevention strategies were proposed.

This paper presents a method to calculate debris flow concentration in debris flow channel without observation data.The derived formula can use the debris flow slurry concentration and fine grain content to calculate the debris flow concentration,and the upper-limit size diameter of debris flow slurry determines the concentration and the fine grain content.It also puts forward a new method to use the maximal diameter of the debris flow deposit on the cliff as the upper-limit size diameter,and points out the way to determine the debris flow slurry concentration and the fine grain content.The debris flow slurry concentration is mainly determined by the consistency of slurry's yield stress.And the calculation method has a good inosculation with the popular calculation method in practice.

The debris flow triggered by construction spoils of mines and major projects turns into an important natural disaster.According to the characteristics of debris flow and the requirement of its prevention and control in mines,the paper summarizes three prevention and control modes of construction spoils-induced debris flow based on some representative cases of successful prevention and control of debris flow in the history,they are:(1) the comprehensive control mode of slope stabilizing in upper reaches area,blocking in middle reaches area and draining in lower reaches area,(2) the mode of intercepting in middle reaches area and draining in lower reaches area,(3) and the mode of blocking in middle and lower reaches areas and draining in lower reaches area.

Critical rainfall assessment is a very important tool for hazard management of torrents and debris flows in mountainous areas. The Wenchuan Earthquake 2008 caused huge casualties and property damages in the earthquake-stricken area, which also generated large quantities of loose solid materials and increased occurrence probabilities of debris flows. There is an urgent need to quantify the critical rainfall distribution in the area so that better hazard management could be planned and if real time rainfall forecast is available, torrent and debris flow early-warning could be issued in advance. This study is based on 49-year observations (1954–2003) of up to 678 torrent and debris flow events. Detailed contour maps of 1 hour and 24 hour critical rainfalls have been generated (Due to the data limitation, there was insufficient 10 minute critical rainfall to make its contour map). Generally, the contour maps from 1 hour and 24 hours have similar patterns. Three zones with low, medium and high critical rainfalls have been identified. The characteristics of the critical rainfall zones are linked with the local vegetation cover and land forms. Further studies and observations are needed to validate the finding and improve the contour maps.

汶川5·12地震不仅造成了特大地震灾害,同时还诱发了大量的次生山地灾害,主要包括崩塌(滚石)、滑坡、堰塞湖和泥石流等.崩塌、滑坡不仅阻塞了救援道路,严重延缓了救援进度.还形成了30多个堰塞湖.地震和滑坡活动还将促进泥石流活动,使震区泥石流进入活跃期,在后期降水作用下形成严重的泥石流灾害.通过初步分析,提出了震区次生山地灾害应急减灾措施和恢复重建中的减灾措施.

5·12汶川地震激发了龙门山风景区崩塌、滑坡、泥石流、堰塞湖等链状次生山地灾害.通过应急调查发现,该区已有堰塞湖5处,危害性崩塌、滑坡6处,已成灾泥石流沟1条,潜在泥石流沟11条,根据各处灾害的主要特征,确定堰塞湖的危险程度,提出山地灾害处理建议.