Post-earthquake changes and prediction of debris flow scales in Subao River Valley,Beichuan County,Sichuan Province,China

Subao River lies along the Beichuan–Yingxiu fault in Beichuan County, which has been heavily impacted by the Wenchuan earthquake on 12 May 2008 and has become sources of many geo-hazards. On 24 September 2008, a rainstorm triggered a large debris flow in the catchment, causing several deaths and significant damages. A case study on changes of the debris flow was conducted in the river. The peak discharges were calculated in the Guanmenzi, Huangnidi, and Daanshan gullies. Results indicated that the peak discharges corresponded to various return periods in different gullies: 200 years in Daanshan, 100 years in Huangnidi, and 50 years in Guanmenzi. However, the triggering precipitation in these three gullies was only of a 20-year return period. The debris flows had undergone significant changes. Analysis indicated that the changes should be ascribed to the flow characteristics, initiation conditions, and the channel blockage impacted by the rapid accumulation of loose material. Channel blockage was the principal factor increasing the scale of the debris flow. The values on the blocking coefficient were presented based on density, height, and other characteristics of dams. Finally, all of the peak debris flow discharges of the Subao River Valley for a 20-year return period were calculated using the recommended blocking coefficient values.     

北京市密云区典型泥石流侵蚀过程分析

泥石流运动过程伴随着剧烈的侵蚀,导致其洪峰流量增加、规模增大、破坏性增强。本文通过对2016年8月12日北京市密云区龙潭沟景区曹庄子沟泥石流为例,通过野外调查和地形扫描分析了该场泥石流的动力侵蚀过程。结果表明:激发该场泥石流的降雨重现期达到20年一遇,为典型短历时、高强度降雨;泥石流体中缺乏粘性颗粒,主要以砂粒为主,但容重达到粘性泥石流标准,为典型高容重、低粘度泥石流体。泥石流侵蚀作用一开始并不剧烈,但随着泥石流运动,这种侵蚀作用增强,导致沟道侵蚀深度增加;沟道中弯道处和地形急变段受到泥石流侵蚀作用最为剧烈,尤其是地形急变段对泥石流的侵蚀作用具有加强效应;侵蚀率与流速同步变化,并且与泥石流体所产生的剪切力呈正相关关系。林木能够降低泥石流流速,消耗泥石流动能,进而减小泥石流破坏性。由于天然条件下的泥石流侵蚀过程研究较少,本文中侵蚀率与地形变化的关系以及泥石流体剪切力的正相关关系为泥石流防治规划设计和该类泥石流的预测预报提供了案例和思路。     

泥石流启动过程PFC数值模拟

泥石流松散碎屑物质具有散粒体的基本特征,在暴雨激发下容易形成泥石流,整个过程具有散粒体大变形的特征。颗粒流理论是基于离散单元法模拟圆形颗粒介质的运动及其相互作用,在模拟颗粒相互作用和大变形问题研究方面具有显著的优越性。为分析泥石流松散碎屑物质启动形成泥石流的过程及其与土体含水率的关系,采用二维颗粒流程序（PFC2D）分析降雨作用下松散碎屑物质启动形成泥石流的过程,揭示崩滑堆积体在降雨作用下含水率超过临界值后质点运动速度和位移增加,松散碎屑物质启动并加速而导致滑坡泥石流连锁式破坏的过程和机制。     

四川省北川县赵家沟地震次生泥石流形成条件分析

赵家沟位于北川县擂鼓镇坪上村西北侧,属汶川地震极重灾区,在地震发生前为一般性清水沟或洪水沟。由于地震的影响,流域内发育了多处滑坡和崩塌,斜坡上和沟道中堆积了大量松散固体物质。在2008年9月24日暴雨的作用下,赵家沟流域发生了百年不遇的泥石流灾害,成为地震次生泥石流沟。通过现场实地调查和室内分析,对地震次生泥石流灾害形成的地质地貌条件、物源条件和水源条件进行了分析。表明地震次生泥石流灾害的发生频率和规模有可能加大,其危险性由于松散固体物质的增大而上升,这是地震次生泥石流灾害显著的特征。     

汶川震区北川县泥石流流域崩滑体时空演变特征

2008年5月12日的汶川大地震引发了大规模同震山体滑坡,随后的强降雨又引发新的山体滑坡,滑坡形成的松散固体物质成为后续泥石流灾害的主要物质来源。为探究强震区泥石流流域崩滑体时空演变特征,文章以北川县魏家沟等8条泥石流流域为例,选取8期遥感影像（2008年震后、“9.24”泥石流发生后、2010年、2011年、2013年、2014年、2015年、2016年）,分别解译崩滑体,统计其空间分布特征。此外,利用归一化植被指数（NDVI）计算研究区内植被覆盖度（VFC）及植被覆盖度恢复率（VCRR）。结果表明：研究区内崩滑体发育面积在强降雨作用后达到峰值,随后呈稳定恢复状态,面积逐年减小。崩滑体在高程900~1 100 m范围、坡度30°~45°范围、坡向90°~135°范围、距沟道150 m范围内发育面积最大。流域内植被覆盖度在2008年“9.24”泥石流灾害后最低,随后呈稳定恢复。自震后到2010年的时期内,植被覆盖度恢复率中等以下区域较多,植被恢复程度较低。2011年之后,流域内大多区域处于植被覆盖度恢复率中等以上等级,植被恢复程度较高。到2016年,研究区植被覆盖度已恢复至较高水平。研究表明：除地层岩性、微地貌等因素影响外,植被对泥石流活动性具有一定的抑制作用。     

Formation and characteristics of post-earthquake debris flow: a case study from Wenjia gully in Mianzhu, Sichuan, SW China

During the three flood seasons following the Wenchuan earthquake in 2008, two catastrophic groups of debris flow events occurred in the earthquake-affected area: the 2008-9-24 debris flow events, which had a serious impact on rebuilding; and the 2010-8-13/14 debris flow events, which destroyed much of the progress made in rebuilding. The Wenjia gully is a typical post-earthquake debris flow gully and at least five debris flows have occurred there. As far as the 2010-8-13 debris flow is concerned, the deposits of the Wenjia gully debris flow reached a volume of 3.1 × 10⁶ m³ in volume and hundreds of newly built houses were buried. This study took the Wenjia gully debris flow as an example and discussed the formation and characteristics of post-earthquake debris flow on the basis of field investigations and a remote sensing interpretation. The conclusions drawn from the investigation and analysis were as follows: (1) Post-earthquake debris flows were a joint result of both the earthquake and heavy rainfall. (2) Gully incision and loose material provision are key processes in the initiation and occurrence of debris flows and a cycle can be presented as the following process: runoff—erosion—collapse—engulfment—debris flow—further erosion—further collapse—further engulfment—debris flow enlargement. (3) The amount of rainfall that triggered debris flows from the Wenjia gully was significantly less than the average daily rainfall, while the intraday rainfall threshold decreased by at least 23.3%. (4) The occurrence mechanism of Wenjia gully debris flow was an erosion type and there was a positive relationship between debris flow magnitude and rainfall, which fitted an exponential model. (5) There were five representative characteristics of Wenjia gully debris flow: the long duration of the occurring process; the long distance of deposition chain conversion during the process of damage; magnification in the scale of debris flow; and the high frequency of debris flow events.     

Study of kinematic characteristics of a rock avalanche and subsequent erosion process due to a debris flow in Wenjia gully,Sichuan, China

Natural Hazards - This paper aims to systematically study kinematic characteristics of Wenjiagou rock avalanche triggered by the M8.0 2008 Wenchuan earthquake and one of subsequent debris flows...     

西藏贡觉县泥石流灾害研究

西藏自治区贡觉县境内对居民存在影响的泥石流沟有3条，即者龙洼Ⅰ沟，者龙洼Ⅱ沟，克西林沟，均位于该县东南部的高山峡谷区。泥石流沟长度均超过2km，沟床平均纵坡降130‰，地表松散物质的厚度都在6．5m以上，其来源有所不同，克西林沟泥石流的固体物质来源于沟谷两侧的也古、拉巴滑坡堆积物；者龙洼Ⅰ、Ⅱ泥石流的固体物质来源主要为岩石风化物质及崩、坡积物。固体物质颗粒粒径分布范围很广，分布曲线均呈三峰型。说明该区泥石流中固体物质含量较高。贡觉县境内泥石流的诱发因素是降雨，为降雨型泥石流。文章根据非饱和土强度理论对贡觉县降雨型泥石流的成因机理进行了研究，提出降雨型泥石流的形成过程可以划分为2个阶段，第1个阶段为基质吸力引起的抗剪强度丧失阶段，与前期实效降雨量有关；第2个阶段为泥石流发生阶段，与短历时强降雨有关。运用上述理论方法，对降雨型泥石流的预测模型进行了探讨。建议用临界雨量线模型框架来建立贡觉县泥石流的预测模型，并依据者龙洼Ⅱ沟泥石流爆发前20d的降雨量数据进行拟合分析，结果表明：文中建议的2个临界雨量线模型框架均适于用建立贡觉县降雨型泥石流暴发的预报模型。     

The ability of debris, heavily freighted with coarse clastic materials, to flow on gentle slopes

Observations of many debris-flow deposits on gently-sloping alluvial fans have disclosed that debris commonly is heavily loaded with coarse clastic material and contains large isolated blocks. The paper describes how debris charged with coarse granular material can transport large blocks, yet flow on gentle slopes. Experimental results of mixing sand-sized particles with a slurry of clay plus water indicate that 45–55 vol. % of a single size, and up to 64% of two selected sizes, can be added before interlocking occurs. Theoretical analysis of multi-size classes suggest that 89 to more than 95 vol. % debris can be clastic materials without significant particle interlocking. The clay fraction, even if minor, plays a critical role in determining strength properties of debris. The mixture of clay plus water provides a cohesive slurry that supports fine-grained particles within the debris, as well as reduces the effective normal stresses between the particles. The increased unit weight of the clay plus water plus fine-grained particles allows the support of coarser grained particles. The pyramiding upon the clay-water slurry continues until the entire debris mass is supported in a virtually frictionless position because of the reduced effective normal stress and the lack of particle interlocking. Thus, the ability of debris flows to support large blocks can be understood in terms of the high unit weight of the displaced debris plus the strength of the fluid phase; that is, the blocks float in the debris as a result of a small density difference between the blocks and the debris, plus the cohesive strength of the clay-water slurry. Also, the ability of coarse clastic debris to flow on gentle slopes probably is a result of poor sorting of debris-flow materials which contain minor amounts of clay. The poor sorting allows the debris to have a high density yet have essentially no interlocking of clasts. The high density of the debris reduces effective normal stresses between clasts, thereby reducing apparent friction of the mixture.     

西藏洛隆县巴曲冰湖溃决型泥石流演进过程模拟研究

巴曲冰湖溃决型泥石流紧邻川藏铁路某车站,可能对其建设及运营产生威胁。首先基于现场调查和遥感解译查明了巴曲泥石流的基本特征,采用规范公式计算了巴曲暴雨泥石流的动力学参数。然后采用无量纲堵塞指数（DBI）评价了巴曲沟内7个主要冰湖堰塞坝的稳定性。评价结果表明:巴曲1#冰湖堰塞坝的DBI值处于非稳定区,3#、4#和6#堰塞坝的DBI值处于非稳定区与稳定区之间,存在发生冰湖溃决的风险。最后,采用快速物质运动模拟软件（RAMMS）单相流数值方法,模拟分析了巴曲沟在4个极端场景下的冰湖溃决演进过程。模拟结果显示:巴曲冰湖溃决后的演进过程分为开始-汇流-冲出-停积四个阶段,共历时约4.5 h。在1#—4#及6#冰湖堰塞体全部溃决工况下,冰湖溃决泥石流在沟口的最大流速为5.92 m/s,最大深度为4.35 m,最大流量为1 954.42 m3/s,为暴雨型泥石流的5.1倍。除此之外,4个场景下冰湖溃决洪水的影响范围都经过拟建车站,泥石流最大深度分别为1.91,3.36,1.53,4.35 m。因此在车站设计时需采取排导槽或导流堤等工程措施进行防护治理。上述研究结果可为川藏铁路选线及青藏高原东部地区的冰湖溃决型泥石流防治提供参考。     

Evaluating effectiveness of mitigation measures for large debris flows in Wenchuan,China

Landslides - To cope with frequent debris flow hazards, many cascade check dams and diversion channels have been adopted in Wenchuan, Sichuan, China, on the eastern margin of the Tibetan plateau....     

四川省盐源县小河沟泥石流灾害调查研究

2015年6月21日,四川省盐源县盐塘乡境内突降暴雨,诱发泥石流灾害。在查明泥石流地形地貌、物源条件、水源条件的基础上,分析了小河沟泥石流的静力学和运动特征,探讨了泥石流的启动、堆积过程以及成灾特征。结果表明:强降雨是诱发泥石流的动力因素;本次灾害规模为小型,成灾原因是由于沟道内未修建专门的泥石流防护工程,同时防洪设施修建标准较低,导致防洪坝淤满,泥石流流量大于排导槽设计流量,流体溢出排导槽冲向村民房屋,造成灾害。因此,应该开展地质灾害高发区地质灾害隐患排查、地质灾害早期识别方法探索,建立泥石流实时监测系统,开展早期预警,及时撤离群众。     

Analysis of the triggering conditions and erosion of a runoff-triggered debris flow in Miyun County,Beijing, China

The occurrence of debris flow from channel-bed failure is occasionally noted in small and steeply sloping watersheds where channelized water flow dominates debris flow initiation. On August 12, 2016, a debris flow from channel-bed failures occurred in the Caozhuangzi Watershed of the Longtan Basin, Miyun, Beijing. Rainfall records over 10-min intervals and field investigations including channel morphology measurements were used to study the triggering conditions and erosion process. The results indicated that the occurrence of this event lagged the peak 10-min rainfall interval and that the cumulative rainfall prior to the occurrence time played an important role in its formation. A mean 10-min rainfall intensity–duration expression in the form of I₁₀?=?5.0?×?D^?0.21, where I₁₀ denotes the mean 10-min rainfall intensity and D is the rainfall duration ranging from 10 to 60 h, was proposed. The debris flows have low proportions of grain size fractions <?0.1 mm and higher fractions of grains 0.1–2 mm in size, indicating that the flow had low viscosity and was coarse-grain dominated. Channel morphology analysis revealed that abrupt changes in topography in the study area, including a steep section, a concave stream bank area, and a partial concave stream section were eroded more extensively than other sites. The maximum sediment erosion volume and erosion depth were not proportional to the variation in stream gradient. Consideration of the degree of erosion in the channel at sites with abrupt morphology changes, the maximum sediment erosion volume, and the erosion depth and volume at the initial channel site and downstream region of forest area together showed that the prime factor controlling erosion was entrained sediment volume. This work, thus, provides a case study regarding the triggering conditions of runoff-triggered debris flows and the topographical changes by debris flow erosion.     

Vulnerability assessment of population in mountain settlements exposed to debris flow: a case study on Qipan gully,Wenchuan County,China

Natural Hazards - This research selected the Qipan gully as a study area for field investigation. The vulnerability of the population to debris flows in Qipan gully was assessed. Several valuation...     

绵竹清平8·13群发泥石流成因、特征与发展趋势

2010年8月13日凌晨,5·12汶川地震极重灾区绵竹市清平乡发生群发泥石流灾害,27条沟谷发生泥石流,占泥石流沟总数的69.4%,其中以文家沟泥石流最为严重。在调查基础上,分析了8·13特大群发泥石流的成因、特征和发展趋势,并提出了灾后规划重建中的地质安全问题。从成因上看,8·13特大群发泥石流是5·12汶川地震和强降雨共同作用的结果;从特征上来看,泥石流呈现出暴发空间的群发性、启动过程的复杂性、发生过程的持续性,成灾过程的链式性、危害形式的多样性、泥石流规模的放大性和泥石流隐患的隐蔽性等7个方面的特征;清平乡各沟8·13泥石流冲出方量约占物源总量的10%～50%,泥石流存在进一步频发、群发的态势,建议在灾后规划重建的过程中,应全面科学评估清平乡泥石流灾害的链式效应和地质环境容量问题,将地质灾害的防治同规划重建密切结合。     

通化县泥石流地质灾害的分布及其形成条件分析

本文阐述了通化县泥石流地质灾害给人民带来的危害、泥石流地质灾害分布特征、形成条件,影响因素。明确指出了泥石流地质灾害的防治措施。     

Dominant particle support mechanisms in debris flows at Mt Thomas, New Zealand, and implications for flow mobility

Within zones of little or no deformation by internal shearing in debris flows at Mt Thomas, about two-thirds of the weight of large particles is supported by buoyancy and about one-third by static grain to-grain contact. In boundary shear zones of low velocity flows and in high velocity, turbulent debris flow, grain-to grain contact is replaced by turbulence and dispersive pressure. Cohesive strength of the clay + silt + water interstitial fluid provides less than 2 % of the force keeping particles larger than 1 cm gravel in suspension. Excess pore pressure is generated in the interstitial fluid by the weight of coarse particles suspended in the slurry. According to Coulomb strength theory, pore pressures measured in these debris-flow slurries reduce the shear strength of the material to less than 10 % of what it is in the unsaturated state. The excess pore pressures are slow to dissipate because of the small connections between pore spaces that result from the extremely poor sorting of the debris and the presence of silt and clay in the pore fluid. Maintenance of sufficient pore space to trap fluid and facilitate flow on low-gradient slopes may be accomplished by dilatancy and subsequent partial liquefaction of the debris during shear.     

GIS-based hazard mapping and zonation of debris flows in Xiaojiang Basin,southwestern China

Debris flow sites were identified at 140 locations in the Xiaojiang Basin in Yunnan province, southwestern China. Their spatial distribution and catchment characteristics are described in detail on the basis of previous research, air photo interpretation, field investigation and mapping using Geographical Information Systems (GIS). Using a statistical approach, a quantitative model of hazards assessment and zonation was developed through synthesis analysis of basin areas, gradients, and the relative reliefs of these debris flow sites. In terms of debris flow hazard assessment, areas within the Xiaojiang Basin can be classified as severe, heavy and light hazard regions.     

Group-occurring landslides and debris flows caused by the continuous heavy rainfall in June 2019 in Mibei Village,Longchuan County,Guangdong Province,China

Natural Hazards - From June 10th to 13th, 2019, a continuous heavy rainfall occurred in Longchuan County, Guangdong Province, causing many landslide hazards. Among Longchuan County districts, Mibei...