Rainfall thresholds for the occurrence of debris flows in the Jiangjia Gully, Yunnan Province, China

2015 ◽  
Vol 195 ◽  
pp. 335-346 ◽  
Author(s):  
Jianqi Zhuang ◽  
Peng Cui ◽  
Gonghui Wang ◽  
Xiaoqing Chen ◽  
Javed Iqbal ◽  
...  
Keyword(s):  
Debris Flows ◽  
Yunnan Province ◽  
Rainfall Thresholds ◽  
Jiangjia Gully

scholarly journals A New Method to Evaluate the Combined Performance of Check Dams and Afforestation on Debris Flows Mitigation in a Dry-hot Valley

2021 ◽  
Author(s):  
Liqun Lyu ◽  
Mengzhen Xu ◽  
Guanyu Zhou ◽  
Zhaoyin Wang
Keyword(s):  
Debris Flow ◽  
Debris Flows ◽  
Yunnan Province ◽  
New Method ◽  
Energy Conditions ◽  
Vegetation Coverage ◽  
Economic Losses ◽  
Flow Volume ◽  
Jiangjia Gully ◽  
Check Dams

Abstract Debris flows in waterways can transport large amounts of sediment downstream, which can cause serious damage and economic losses. The vegetation cover in the valley of the Xiaojiang River in Yunnan Province, China—classified as a dry-hot valley—was significantly reduced by logging in the 1950s. Soil erosion intensified and 107 gullies developed, which led to debris flows along the 86 km length of the river. Jiangjia Gully is a tributary of the Xiaojiang River. Historically, debris flows have occurred frequently, blocking the Xiaojiang River seven times between 1957 and 2000. Since 2000, the construction of check dams and afforestation have decreased the volume of debris flows in the three tributaries of Jiangjia Gully. However, different combinations of check dams and afforestation were adopted in the three tributaries of Jiangjia Gully, which has led to the different trends in debris flows behaviour. A new method was established to evaluate the mitigative effect of check dams and afforestation on debris flows. We found that the debris flow volume was proportional to the gravity energy of soil and rock on the gully bank and inversely proportional to the vegetation coverage in a dry-hot valley setting. The method revealed that under different gravity energy conditions, the implementation order of check dam construction and afforestation is important for debris flow mitigation.

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

2011 ◽  
Vol 8 (6) ◽  
pp. 757-766 ◽  
Author(s):  
Hong Peng ◽  
Yanxin Zhao ◽  
Peng Cui ◽  
Wanshun Zhang ◽  
Xuejiao Chen ◽  
...  
Keyword(s):  
Numerical Model ◽  
Debris Flows ◽  
Yunnan Province ◽  
Two Dimensional ◽  
Jiangjia Gully

Granular effect on debris flow rheology

2021 ◽  
Author(s):  
Taiqiang Yang
Keyword(s):  
Shear Rate ◽  
Debris Flow ◽  
Debris Flows ◽  
Shear Thinning ◽  
Dynamical Equations ◽  
Real Rate ◽  
The Real ◽  
Jiangjia Gully ◽  
Material Sources ◽  
Surge Phenomena

<p>Debris flow is characterized by the multi-disperse grain composition and intergranular collision and friction, but the granular effects on rheology are often reduced to the volumetric concentration of solid (C<sub>v</sub>), almost ignoring the specific grain size distribution (GSD). In this study, small debris flows occurring in a tributary of Jiangjia Gully were taken as the material sources for rheology experiments. From the real flows we selected slurries with different C<sub>v</sub> and maximum grain sizes (D<sub>m</sub>) for rheological tests under shearing rate up to 40 (s<sup>-</sup><sup>1</sup>), which is usually the real rate for debris flows in natural conditions. The results indicate that the flows follow the Herschel-Bulkley (HB) rheology, with randomly changing consistency coefficient and relatively constant exponent of 0.45 on average. Only at high shear rate will the flow exhibit Bingham behavior. The HB rheology also reveals shear thinning behavior in surge phenomena observed in the field. Shear-thinning behavior is revealed by the viscosity-shear rate relationship: η<sub>a</sub>=pγ<sup>q</sup>, with the exponent (thinning index) dependent on shear rate. This greatly concerns the surge phenomena observed in field. Moreover, both the yield stress and the effective viscosity are found to be perfectly related to the scaling GSD parameters in power-law and exponential form, with nearly constant exponents independent of the shear rate(Figure 1). The rheology properties can be calculated from their relationships to GSD parameters (μ, D<sub>c</sub>), which in turn can be used to infer the HB rheology for the concerned flows and then build the dynamical equations(Figure 2). This implies the presence of some interlock between the fine and coarse grains. Finally the rheology model (general in HB form) can be completely determined by the GSD parameters. This study has for the first time proposed quantitative formulas for rheology incorporating GSD parameters, which is helpful for more accurate dynamic analysis of debris flow.</p>

Uncertainty in debris flow rainfall thresholds

2021 ◽  
Author(s):  
Matteo Berti ◽  
Alessandro Simoni
Keyword(s):  
Debris Flow ◽  
Debris Flows ◽  
Measurement Errors ◽  
Critical Conditions ◽  
Model Parameters ◽  
Average Intensity ◽  
Rainfall Thresholds ◽  
Sources Of Uncertainty ◽  
Time Space ◽  
Physically Based

<p>Rainfall is the most significant factor for debris flows triggering. Water is needed to saturate the soil, initiate the sediment motion (regardless of the mobilization mechanism) and transform the solid debris into a fluid mass that can move rapidly downslope. This water is commonly provided by rainfall or rainfall and snowmelt. Consequently, most warning systems rely on the use of rainfall thresholds to predict debris flow occurrence. Debris flows thresholds are usually empirically-derived from the rainfall records that caused past debris flows in a certain area, using a combination of selected precipitation measurements (such as event rainfall P, duration D, or average intensity I) that describe critical rainfall conditions. Recent years have also seen a growing interest in the use of coupled hydrological and slope stability models to derive physically-based thresholds for shallow landslide initiation.</p><p>In both cases, rainfall thresholds are affected by significant uncertainty. Sources of uncertainty include: measurement errors; spatial variability of the rainfall field; incomplete or uncertain debris flow inventory; subjective definition of the “rainfall event”; use of subjective criteria to define the critical conditions; uncertainty in model parameters (for physically-based approaches). Rainfall measurement is widely recognized as a main source of uncertainty due to the extreme time-space variability that characterize intense rainfall events in mountain areas. However, significant errors can also arise by inaccurate information reported in landslide inventories on the timing of debris flows, or by the criterion used to define triggering intensities.</p><p>This study analyzes the common sources of uncertainty associated to rainfall thresholds for debris flow occurrence and discusses different methods to quantify them. First, we give an overview of the various approaches used in the literature to measure the uncertainty caused by random errors or procedural defects. These approaches are then applied to debris flows using real data collected in the Dolomites (Northen Alps, Itay), in order to estimate the variabilty of each single factor (precipitation, triggering timing, triggering intensity..). Individual uncertainties are then combined to obtain the overall uncertain of the rainfall threshold, which can be calculated using the classical method of “summation in quadrature” or a more effective approach based on Monte Carlo simulations. The uncertainty budget allows to identify the biggest contributors to the final variability and it is also useful to understand if this variability can be reduced to make our thresholds more precise.</p><p> </p>

scholarly journals Landslides distribution at tributaries with different evolution stages in Jiangjia Gully, southwestern China

2019 ◽  
Author(s):  
Xia Fei Tian ◽  
Yong Li ◽  
Quan Yan Tian ◽  
Feng Huan Su
Keyword(s):  
High Frequency ◽  
Debris Flows ◽  
Satellite Image ◽  
Flow Regimes ◽  
Southwestern China ◽  
Grid Cells ◽  
Jiangjia Gully ◽  
Material Sources ◽  
Main Material

Abstract. Jiangjia Gully (JJG) is known for its high frequency and variety of debris flows, especially the intermittent surges of various flow regimes and materials. Observation indicates that the surges come from various tributaries with different landslides activities. In this study, 81 tributaries of JJG are taken from DEM with 10 m grid cells, and the hypsometric curves are used to characterize their evolution stages; five stages are identified by the evolution index (EI, the integral of the hypsometric curves) and most tributaries are in relative youth stage with EI between 0.5 and 0.6. Then 908 landslides are interpreted from Quickbird satellite image of 0.61 m resolution, and it is found that LD (LD = landslides number in a tributary/the tributary area) increases exponentially with EI, while LAp (LAp = landslides area in a tributary/the tributary area) fluctuates with EI, meaning that landslides are inclined to occur in tributaries with EI between 0.5 and 0.6, and thus these tributaries are the main material sources supplying for debris flows.

Debris flow monitoring in China

2020 ◽  
Author(s):  
Xiaojun Guo
Keyword(s):  
Debris Flow ◽  
Debris Flows ◽  
Flow Characteristics ◽  
Western China ◽  
Flow Density ◽  
Flow Depth ◽  
Jinsha River ◽  
Flow Monitoring ◽  
Jiangjia Gully ◽  
Set Up

<p><strong>Abstract: </strong>Debris flow monitoring provides valuable data for scitienfic research and early warning, however, it is of difficulty to sucessfully achive because of the great damage of debris flows and the high cost. This report introduces monitoring systems in two debris flow watersheds in western China, the Jiangjia gully (JJG) in Yunnan Province and the Ergou valley in Sichuan Province. JJG is loacted in the dry-hot valley of Jinsha River, and the derbis flows are frequent due to the semi-arid climate, deep-cut topography and highly weathered slope surface. A long-term mornitoring work has been conducted in JJG and more than 500 debris flows events has been recorded since 1965. The monitoring system consists of 10 rainfall gauges and a measuring section, with instruments to measure the flow depth and velocity; and flow density is measured through sampling the fresh debris flow body. Ergou lies in the Wenchuan earthquake affected area and the monitoring began in 2013 to investigate the characteristics and development tendency of post-earthquake debris flows. Three stations were set up in the mainstream and tributaries, with instruments to measure the flow depth, velocity, and density. Over 10 debris flow events were recorded up to date.</p><p>Based on the monitoring output, the rainfall spatial distribution and thresholds for debris flows are proposed. The debris flow dynamics characteristics are analyzed, and the relations between the parameters, e.g. density, velocity, discharge and grain compositions are presented. The debris flow formation modes and the mechanisms in different regions are discriminated and simulation methods are suggested. It is anticipated that the monitoring results will promote understanding of debris flow characteristics in the western China.</p><p><strong>Keywords:</strong> Debris flow, monitoring, rainfall, discharge, formation. </p>

Debris flows rainfall thresholds in the Apennines of Emilia-Romagna (Italy) derived by the analysis of recent severe rainstorms events and regional meteorological data

Geomorphology ◽  
2020 ◽  
Vol 358 ◽  
pp. 107097 ◽  
Author(s):  
Giuseppe Ciccarese ◽  
Marco Mulas ◽  
Pier Paolo Alberoni ◽  
Giovanni Truffelli ◽  
Alessandro Corsini
Keyword(s):  
Debris Flows ◽  
Meteorological Data ◽  
Rainfall Thresholds

Risk Evaluation of Debris Flow in the Cheng-Hai Valley of Yunnan Province

2011 ◽  
Vol 71-78 ◽  
pp. 1560-1564
Author(s):  
Ting Ting Guo ◽  
Shi Guang Xu ◽  
Zhi Quan Yang
Keyword(s):  
Debris Flow ◽  
Debris Flows ◽  
Yunnan Province ◽  
Evaluation Method ◽  
Comprehensive Evaluation ◽  
Solid Materials ◽  
Comprehensive Evaluation Method ◽  
Catchment Areas ◽  
Longitudinal Slope ◽  
Risk Degree

The area of the Cheng-hai valley, located in the centre of Yongsheng county Lijiang city Yunnan province, is an area with dense and frequent debris flow disasters due to unique geology, geomorphology and landform conditions. After in situinvestigation and analyze the present data of these debris flows, we selected six factors, such as catchment areas, the length of main gully, average longitudinal slope of main gull, estimated outflow of every time, potential reserves of solid materials, percentage of grain diameter of solid materials above and beyond 200mm, as main factors for evaluating the risk degree of 6 chosen representative debris flows in the Cheng-hai valley. The multiple-factor comprehensive evaluation method is applied to evaluate the risk degree of debris flow and then the evaluation result shows a good correspond with the practical situation, i.e. this method has a valuable application foreground.

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