Two-dimensional numerical model for debris flows in the Jiangjia Gully, Yunnan Province

Debris flows are recurrent natural hazards in many mountainous regions.This paper presents a numerical study on the propagation of debris flows in natural erodible open channels,in which the bed erosion and sedimentation processes are important.Based on the Bingham fluid theory,a mathematical model of the two-dimensional non-constant debris flow is developed.The governing equations include the continuity and momentum conservation equations of debris flow,the sediment convection-diffusion equation,the bed erosion-deposition equation and the bed-sediment size gradation adjustment equation.The yield stress and shear stress components are included to describe the dynamic rheological properties.The upwind control-volume Finite Volume Method (FVM) is applied to discretize the convection terms.The improved SIMPLE algorithm with velocity-free-surface coupled correction is developed to solve the equations on non-orthogonal,quadrilateral grids.The model is applied to simulate a debris flow event in Jiangjia Gully,Yunnan Province and to predict the flow pattern and bed erosion-deposition processes.The results show the effectiveness of the proposed numercial model in debris flow simulation and potential hazard analysis.     

Fine root distribution pattern of different aged Leucaena leucocephala trees in debris flow source area in Jiangjia Gully,China

Fine root is critical to restrain soil erosion and its distribution pattern is of great influence on the restraining effects. This study studied the fine root biomass(Br) distribution of different aged Leucaena leucocephala(5, 10, 15 years) in debris flow source area in Jiangjia Gully by digging downward to the bottom at different distances to stem in three directions on slope. The results showed the Br increased dramatically by 143% from 5 years to 10 years and then rose slowly by 38% from 10 years to 15 years. The Br of 5 years was significantly asymmetric between uphill and alonghill directions, but there was little difference among directions for other ages, and a concentration trend appeared to exist in downhill and alonghill directions. Moreover, fine root(D≤1 mm) was significantly heavier than that of fine root(1mmD≤2 mm), playing a leading role in the vertical distribution of the whole fine root, with a logarithmic or an exponential function. The results presented may shed light on fine root distribution pattern and evaluation of its effect on slope stability in debris flow source area.     

Disasters and regional risks of debris flow in Zhaotong Prefecture,Yunnan Province,China

Zhaotong Prefecture has the area of 22,434km², where there are more than 330 debris flow ravines, with the average spatial density of 14.7 spots per 1,000km². According to the method of evaluation on the regional risk of debris flow, this study has come to the following conclusions: Qiaojia County-risk grade V; Yongshan, Yanjin, Ludian, Daguan, Weixin and Zhenxiong counties-risk grade III; Yiliang, Suijiang-Shuifu and Zhaotong City-risk grade II. Compared with the field investigation, the result is satisfied.     

Uncertainty analysis on zonation maps of debris flow hazard in Yunnan Province, China

lINTRODUCTIONDebrisflowisoneofthesixprimarynaturalhaz-ards,whichinfluencesthedevelopmentofnationalso-cietyandeconomyinChina.Itsseverityissecondarytoflood,draught,earthquake,typhoon,butstrongerthanbiologicalhazards.Morethan3ooOodebrisflowcreeksarescatteredihthewholemountainousarea,andes-PeciallyconcentratedinsouthwestofChina.DebrisFlowInformationSystem(DFIS)operatedbytheInsti-tuteofMountainHazardsandEnvironmentoftheChi-neseAcademyofScienceshasalreadyestablishedadatabaseandcataloguec…     

Magnitude-frequency relationship of debris flows in the Jiangjia Gully,China

The magnitude-frequency(MF) relationship of debris flows is the basis for engineering designs and risk quantification. However, because of the lack of debris flow monitoring data, research progress in this area has been relatively slow. The MF relationship of debris flows in Jiangjia Gully, Yunnan Province was evaluated based on a regression analysis of 178 debris flow events that occurred from 1987-2004. The magnitude-cumulative frequency(MCF) relationship of the debris flows in the Jiangjia Gully is consistent with the linear logarithmic transformation function. Moreover, observed data for debris flows in Hunshui Gully of Yunnan Province and Huoshao Gully, Liuwan Gully, and Niwan Gully of Gansu Province were used to verify the function. The results showed that the MCF relationship of highfrequency debris flows is consistent with the power law equation, although the regression coefficients in the equation are considerably different. Further analysis showed a strong correlation between the differences in the constants and the drainage area and daily maximum precipitation.     

Potential sediment sources identification of debris flows in the Jiangjia Gully,China

It is of great significance for gully prevention and management to identify the potential sediment source of debris flow. Debris flow in a gully always originates from tributaries that have different gravity potential energies and sediment condition. In this study, tributaries of the Jiangjia Gully(JJG) in Yunnan province, China, are taken as the study area to determine the possible sediment sources of debris flow. It was found that tributaries with a high evolution index(EI, the integral of the hypsometric curve) always had high gravity potential energy, which favors the occurrence of landslide activity. Furthermore, the relationship between sediment distribution, gravity potential energy, and EI is compared, respectively. The results showed that the EI had a greater influence on the occurrence of landslides, and sediments were concentrated in tributaries with EI between 0.5 and 0.6. Accordingly, tributaries with EI 0.5 were identified as the sediment sources of debris flow. In addition, the shape of a tributary was related to EI and can reflect the condition of water and sediment storage.     

Annual precipitation gray forecast in disaster year of Chedaren debris flow

The Chedaren ravine belongs to high-prone areas of debris flow in Jilin Province,which threaten the local people's life and security seriously. The authors used the residual correction theory to amend the GM (1, 1) model and forecast annual precipitation in disaster year of the Chedaren ravine; it provides scientific foundation for early warning of debris flow disaster in the rainy season based on weather forecast. The prediction results show that annual precipitation is 724.7 mm in 2009; the region will probably occur large-scale debris flow during the rainy season.     

Field observation of debris-flow activities in the initiation area of the Jiangjia Gully,Yunnan Province,China

The Jiangjia Gully, which is located in Dongchuan District, Yunnan Province, China, is a watershed prone to debris flows and has long-term recorded data of debris-flow occurrence. However, the initiation mechanism has mainly been studied by experiments in this watershed. To further reveal debris-flow formation mechanism in the Jiangjia Gully, debris-flow activities in the initiation zone were observed with hand-held video cameras in the summer of 2016 and 2017. In these two years, six debris-flo...     

Experimental analysis of shear strength of undisturbed soil in leucaena forest in Jiangjia Ravine,Yunnan, China

Five leucaena trees of similar age were chosen in Jiangjia Ravine of Dongchuan, Yunnan Province, China, near which the soil samples were collected by digging profiles 2m in depth and 1m in width. In each section, soil samples at different depths were taken for direct shear experiments to determine the root amount and mechanical composition. It is found that the cohesion and internal friction angle of the undisturbed soil are related to the root amount, depth, clay content and breccias content. Cohesion correlates negatively with root content, a finding that differs from that of other researchers. In addition, internal friction angle correlates positively with all these factors.     

Annual precipitation gray forecast in disaster year of Chedaren debris flow

The Chedaren ravine belongs to high-prone areas of debris flow in Jilin Province, which threaten the local people＇ s life and security seriously. The authors used the residual correction theory to amend the GM （ 1, 1 ） model and forecast annual precipitation in disaster year of the Chedaren ravine ; it provides scientific foundation for early warning of debris flow disaster in the rainy season based on weather forecast. The prediction resuits show that annual precipitation is 724.7 mm in 2009 ; the region will probably occur large-scale debris flow during the rainy season.     

THE ORIGIN AND CHARACTERISTICS OF THE GLACIAL DEBRIS FLOW IN THE DUKU HIGHWAY OF TIANSHAN MOUNTAINS，

ＴＨＥＯＲＩＧＩＮＡＮＤＣＨＡＲＡＣＴＥＲＩＳＴＩＣＳＯＦＴＨＥＧＬＡＣＩＡＬＤＥＢＲＩＳＦＬＯＷＩＮＴＨＥＤＵＫＵＨＩＧＨＷＡＹＯＦＴＩＡＮＳＨＡＮＭＯＵＮＴＡＩＮＳ，ＣＨＩＮＡ￥ＸｉｏｎｇＨｅｉｇａｎｇ（ＤｅｐａｒｔｍｅｎｔｏｆＧｅｏｇｒａｐｈｙ...     

The disastrous 23 July 2009 debris flow in Xiangshui Gully, Kangding County, Southwestern China

On 23 July 2009, a catastrophic debris flows were triggered by heavy rainfall in Xiangshui gully, Kangding county, southwestern China. This debris flow originating shortly after a rainstorm with an intensity of 28 mm per hour transported a total volume of more than 480×103 m3 debris, depositing the poorly sorted sediment including boulders up to 2-3 m in diameter both onto an existing debris fans and into the river. Our primary objective for this study was to analyze the characteristics of the triggering ra...     

Nonlinear morphological characteristics of debris flow in Dongcheng area of Helong,Jilin

Helong City is located in the northeastern Changbai Mountain with a poor geological environment, there often occur debris flows, collapses and landslides; especially debris flows restrict the local economic development. Based on fractal theory and the surveying data of 34 debris flows, the authors studied fractal feature of debris flow gully and its various situations of fractal dimensions in different observation scales. The nonlinear relation reveals the development of non-uniformity and self similarity of debris flow gully     

Nonlinear morphologica l characteristics of debris flow in Dongcheng area of Helong, Jilin

Helong City is located in the northeastern Changbai Mountain with a poor geological environment, there often occur debris flows, collapses and landslides; especially debris flows restrict the local economic development. Based on fractal theory and the surveying data of 34 debris flows, the authors studied fractal feature of debris flow gully and its various situations of fractal dimensions in different observation scales. The nonlinear relation reveals the development of non-uniformity and self similarity of debris flow gully.     

Application of extension theory in risk zoning of debris flow in Beijing

The occurrence of debris flow is affected by many factors. Risk zoning of debris flow plays a vital role in the early-warning and prediction of abrupt geological hazards, and exploration of new method is needed in the early-warning and prediction of geological hazards. The extension theory is a new method to solve contradiction matters. Based on extension theory, AHP and GIS, the risk zoning model of debris flow was established in this paper. The result of this research provides a new way in the risk zoning, early-warning and prediction of debris flow     

Dynamic characteristics and hazard assessment of debris flow in Shangyao valley

Shangyao valley is located in Jin’an village of Songpan in Sichuan. Many material sources are accumulated in valleys. The debris flow will be triggered by a rain storm with short-duration and strong intensity, which may threaten people’s lives and property in downstream. Based on the investigation,the formation conditions of debris flow and its dynamic characteristics are analyzed and its hazard assessment is investigated. Research shows that there is the potential cause of debris flow in Shangyao valley,which is of the middle risk class.     

Application of shallow high-resolution transient electromagnetic method( TEM) in geological investigation of debris flow

In the investigation of debris flow, the detection of the source area of the post-disaster debris flow is an important basis for evaluating the distribution of the debris flow accumulation layer and the subsequent control. In this paper, a shallow high-resolution TEM is used to detect the debris flow source area in Dashigou village, Yongji County, Jilin Province. The purpose of this investigation is to determine the depth range of debris flow damage. The detection results show that there is an obvious low resistance zone at about 10 m depth along the survey line, which is in good agreement with the drilling data and the high density electrical detection. It is proved that the depth is the maximum impact depth of the debris flow. The practical engineering proves that the method has high resolution in shallow layer detection, high efficiency and convenience in field acquisition. The maximum detection depth range of this method is 30--40 m, which meets the requirements of high efficiency and accurate detection for regional debris flow source area, and has high practical application value.     

InSAR在云南德钦县一中河泥石流物源汇集及失稳模式中的探究

针对传统方法难以定量描述大尺度泥石流形成机理的问题,提出一种联合SAR卫星影像相位信息和后向散射信息全面识别泥石流发育机制的方法,并使用该方法探究云南省德钦县一中河泥石流物源汇集及失稳模式.通过后向散射系数反演研究区土壤含水量的时空变化趋势,利用升降轨Sentinel-1 A数据获取坡表二维形变.结果表明,研究区土壤含...     

Geomorphic characteristics of hillslope and channelized debris flows: A case study in the Shitou area of central Taiwan

The data on the hillslope and channelized debris flows in the Shitou area of central Taiwan occurred during Typhoons Toraji and Nali in 2001 were applied in this paper. The geomorphic parameters, including the flow length, gully gradient, drainage area and form factor of the debris flows were determined by spatial analysis using a Geographic Information System （GIS） based on the data derived from field investigation, aerial photographs, and topographical maps. According to such determined geomorphic parameters, the threshold conditions and empirical equations, such as the relationship between the gully gradient and drainage area and that between gully length and drainage area and topographic parameter, are presented and used to distinguish the geomorphic characteristics between the channelized and hillslope debris flows.     

CHARACTERISTICS OF ZONAL ANOMALY OF ANNUAL PRECIPITATION IN THE NORTHEASTERN CHINA

The characteristics of zonal anomaly and change rule of temporal distribution of annual precipitation in the northeastern China are revealed in this paper with EOF (Empirical Orthogonal Function) and REOF (Rotated Empirical Orthogonal Function) methods and results are drawn in the standard relief maps with GIS technology for practical application. Data used in the study were obtained from 208 meteorological stations over the northeastern China from 1961 to 2001. EOF results show that the first 3 loading vectors could give entire spatial anomaly structure of annual precipitation. In the Northeast Plain including the Songneng Plain and the Liaohe Plain, there is a regional compatibility (whether wet or dry) of annual precipitation change and this precipitation pattern has occurred since the late 1980s to the present. There also exist annual precipitation patterns of wet (or dry) in south and dry (or wet) in north and wet (or dry) in east and dry (or wet) in west. REOF results display 8 principal precipitation anomaly areas by the first 8 rotated loading vectors: the west plain, the Liaodong hills, the Sanjiang Plain, the Liaoxi hills,the Changbai Mountains, the Hulun Buir Plateau, the southwest plateau and the Liaodong Peninsula.