scholarly journals Quantitative Analysis of the Debris Flow Societal Risk to People Inside Buildings at Different Times: A Case Study of Luomo Village, Sichuan, Southwest China

2021 ◽  
Vol 8 ◽  
Author(s):  
Li Wei ◽  
Kaiheng Hu ◽  
Jin Liu
Keyword(s):  
Quantitative Analysis ◽  
Debris Flow ◽  
Debris Flows ◽  
Evaluation Model ◽  
Alluvial Fan ◽  
Economic Losses ◽  
Rural Settlements ◽  
Societal Risk ◽  
Flow Intensity ◽  
The Village

Debris flows, which cause massive economic losses and tragic losses of life every year, represent serious threats to settlements in mountainous areas. Most deaths caused by debris flows in China occur in buildings, and the death toll is strongly dependent on the time people spend indoors. However, the role of time spent indoors in the quantitative analysis of debris flow risk has been studied only scarcely. We chose Luomo village in Sichuan atop a debris flow alluvial fan to study the influence of the temporal variation in the presence of people inside buildings on the societal risk. Two types of days (holidays vs. workdays) and two diurnal periods (daytime vs. nighttime) were considered in our risk evaluation model. A questionnaire survey was conducted for each family in the village, and the probability of the temporal impact of a debris flow on every household was calculated based on the average amount of time each member spent in the house. The debris flow hazard was simulated with FLO-2D to obtain the debris flow intensity and run-out map with return periods of 2, 10, 50, and 100 years. The risk to buildings and societal risk to residents were calculated quantitatively based on the probabilities of debris flow occurrence, the probability of the spatial impact, and the vulnerabilities of buildings and people. The results indicated that societal risk on holidays is always higher than that on weekdays, and societal risk at night is also much higher than that in the daytime, suggesting that the risk to life on holidays and at night is an important consideration. The proposed method permits us to obtain estimates of the probable economic losses and societal risk to people by debris flows in rural settlements and provides a basis for decision-making in the planning of mitigation countermeasures.

Quantitative analysis of the debris flow risk to concentrated rural settlement in southwest Sichuan, China

2021 ◽  
Author(s):  
Li Wei ◽  
Kaiheng Hu
Keyword(s):  
High Risk ◽  
Debris Flow ◽  
Debris Flows ◽  
Large Scale ◽  
Sichuan Province ◽  
Horizontal Distance ◽  
Rural Settlements ◽  
Residential Areas ◽  
Planning Stage ◽  
Societal Risk

<p><strong>Sichuan Province in southwest China is highly susceptible to debris flow disasters and suffers much damage to buildings and loss of human lives in concentrated rural settlements each year</strong><strong>.</strong><strong> By combining geographic information system (GIS) and Deep Encoding Network (DE-Net) methods, we proposed an automatic identification method for buildings highly susceptible to debris flows with large-scale digital elevation data and high-resolution remote sensing imagery based on a vulnerability matrix containing different threshold values of the horizontal distance (HD) and vertical distance (VD) between buildings and channels. A case study in Puge County, Sichuan Province, demonstrated the high identification potential of the method for buildings susceptible to debris flows in large areas with only scarce information available. Meanwhile, We chose </strong><strong>a high-risk village</strong><strong> in Puge County to study </strong><strong>debris flow risk to buildings and residents. Different</strong><strong> types of days and diurnal periods were considered in </strong><strong>the analysis of societal risk to residents</strong><strong>. The </strong><strong>results</strong><strong> indicated that societal risk to residents on holidays is always higher than that on weekdays, and societal risk at night is also much higher than that in the daytime. </strong><strong>The identification results of buildings vulnerability provide valuable information regarding high-risk residential areas to governments and facilitate targeted measure design at the initial planning stage, and the proposed method of societal risk provides a basis for decision-making in the planning of mitigation countermeasures in a specific settlement.</strong></p>

scholarly journals The Model for Dilution Process of Landslide Triggered Debris Flow —A Case of Guanba River in Tibet Southeastern Plateau

2018 ◽  
Vol 22 (2) ◽  
pp. 103-111 ◽  
Author(s):  
Jun Li ◽  
Ningsheng Chen
Keyword(s):  
Debris Flow ◽  
Water Flow ◽  
Debris Flows ◽  
Evaluation Model ◽  
Flow Density ◽  
Flow Section ◽  
Average Depth ◽  
Flow Discharge ◽  
Study Results ◽  
Density Evaluation

Understanding and modeling the downstream dilution process of a landslide triggered debris flow is the foundation for recognizing the boundary condition and dilution mechanism of this type of debris flow, and this serves as the theoretical basis for the categorized control of viscous debris flows, diluted debris flows, hyperconcentration flows and flash floods in a drainage basin. In this study, taking as an example a typical debris flow that occurred in the Guanba River on Tibet’s southeastern plateau on July 6th, 1998, empirical models are used to calculate the density, water flow discharge, debris flow discharge, average depth of loose materials and channel gradient at 11 cross-sections upstream to downstream in the debris flow. On this basis, the dilution characteristics and debris flow dilution process are analyzed in this study. According to the correlation between the debris flow density and the water-soil ratio and channel gradient, we have established the density evaluation model for the debris flow dilution process, which can predict the dilution process of a landslide triggered debris flow. The study results include the following four aspects: (1) The key factors in the dilution process of landslide triggered debris flows are the water flow discharge, average depth of loose materials and channel gradient. (2) The debris flow dilution characteristics in the Guanba River in 1998 include the occurrence of the debris flow dilution process after a significant increase in the water-soil ratio; an increase in the proportion of fine particles after dilution of the debris flow; and the size distribution of grain is “narrowed.” (3) In accordance with the density and dilution characteristics, the debris flow dilution process in the Guanba River can be divided into the upstream viscous debris flow section, midstream and downstream transitional debris flow section and downstream diluted debris flow section. (4) The density evaluation model for the debris flow dilution process is expressed by the Lorentz equation, and this model can reflect the debris flow dilution process such that the debris flow density will decrease gradually with an increase in the water-soil ratio and decrease in channel gradient. The density evaluation model for the debris flow dilution process has been verified by three debris flow cases, which include Gaoqiao Gully, Haizi Valley, and Aizi Valley

scholarly journals Debris-flow activity in abandoned channels of the Manival torrent reconstructed with LiDAR and tree-ring data

2011 ◽  
Vol 11 (5) ◽  
pp. 1247-1257 ◽  
Author(s):  
J. Lopez Saez ◽  
C. Corona ◽  
M. Stoffel ◽  
A. Gotteland ◽  
F. Berger ◽  
...  
Keyword(s):  
Debris Flow ◽  
Tree Ring ◽  
Debris Flows ◽  
Temporal Distribution ◽  
Alluvial Fan ◽  
Tree Ring Data ◽  
Pine Trees ◽  
Spatio Temporal ◽  
Flow Activity ◽  
Abandoned Channels

Abstract. Hydrogeomorphic processes are a major threat in many parts of the Alps, where they periodically damage infrastructure, disrupt transportation corridors or even cause loss of life. Nonetheless, past torrential activity and the analysis of areas affected during particular events remain often imprecise. It was therefore the purpose of this study to reconstruct spatio-temporal patterns of past debris-flow activity in abandoned channels on the forested cone of the Manival torrent (Massif de la Chartreuse, French Prealps). A Light Detecting and Ranging (LiDAR) generated Digital Elevation Model (DEM) was used to identify five abandoned channels and related depositional forms (lobes, lateral levees) in the proximal alluvial fan of the torrent. A total of 156 Scots pine trees (Pinus sylvestris L.) with clear signs of debris flow events was analyzed and growth disturbances (GD) assessed, such as callus tissue, the onset of compression wood or abrupt growth suppression. In total, 375 GD were identified in the tree-ring samples, pointing to 13 debris-flow events for the period 1931–2008. While debris flows appear to be very common at Manival, they have only rarely propagated outside the main channel over the past 80 years. Furthermore, analysis of the spatial distribution of disturbed trees contributed to the identification of four patterns of debris-flow routing and led to the determination of three preferential breakout locations. Finally, the results of this study demonstrate that the temporal distribution of debris flows did not exhibit significant variations since the beginning of the 20th century.

Alternative approach for works controlling stony debris flows

2020 ◽  
Author(s):  
Carlo Gregoretti ◽  
Matteo Barbini ◽  
Martino Bernard ◽  
Mauro Boreggio
Keyword(s):  
Debris Flow ◽  
Debris Flows ◽  
High Elevation ◽  
Valley Bottom ◽  
Check Dams ◽  
Retention Basin ◽  
Retention Basins ◽  
Solid Liquid ◽  
The Impact ◽  
The Village

<p>Many sites of the Dolomites are threatened by channelized debris flows: solid-liquid surges initiated by the entrainment of large quantities of sediments into the abundant runoff at the head of channel incised on fans, can dramatically increase their volume along the downstream routing. This is the case of the Rovina di Cancia site where solid-liquid surges forming in the upper part of the basin can increase their volume up and over 50000 m<sup>3</sup>, seriously impacting the downstream village of Borca di Cadore. The debris-flow channel ends just upstream the village that in the past was hit by four debris flows (three in the recent years) that caused victims and destructions. Control works built until now are not sufficient to protect the village from high magnitude debris flows and a definitive solution calls to be planned. Present works are a flat deposition area, 300 m downstream the initiation area, an open dam under construction downstream it, and  two retention basins at the end of the channel. Between the open dam and the upstream retention basin, there are the rest of eight check-dams made of gabions, built in the 60s and progressively damaged or destroyed by the debris flows occurred after their construction. This series of check-dams limited the entrainment of solid material and the occurrence of localized scours. The initial plan is the substitution of the check-dams with concrete structures and the widening of the dowsntream retention basin through the raising of high elevation embankment downstream it and the following demolition of the actual dyke. Finally, a channel crossing the village and national route on the valley bottom will deliver the fluid phase from the widened basin to the Boite river. All these control works have a very high cost for construction and maintenance and severely impact the village with the presence of a non-negligible residual risk. These drawbacks call for an alternative solution that is searched looking at to the morphology. Downstream of the open dam and on its right side, there is a deep impluvium that ends on a large grass sloping area. The novel solution requires the construction of a channel through the right high bank that deviates the debris flow into the impluvium. The impluvium, widened through the excavation of the surrounding slopes, is closed at the outlet by  an open dam. Downstream the open dam, a channel will lead to a retention basin, where most of storage volume is obtained from the excavation of the grass sloping area, limiting the elevation of the dykes At the end of this basin an open dam will deliver the debris-flow fluid part to a channel passing under the national route and joining the Boite river. Such a solution composed of a deviatory channel, two retention basins (the deep impluvium and that excavated on the sloping grass area) and the channels between and downstream them, has quite a lower costs of construction and maintenance, eliminating the impact on the village because occupying uninhabited areas without interrupting the main roads.</p>

Debris-Flow Risk Assessment

2016 ◽  
Author(s):  
Matthias Jakob ◽  
Kris Holm ◽  
Scott McDougall
Keyword(s):  
Risk Assessment ◽  
Debris Flow ◽  
Debris Flows ◽  
Numerical Models ◽  
Risk Tolerance ◽  
Nuclear Industry ◽  
Decision Makers ◽  
Economic Losses ◽  
Landslide Risk ◽  
Frequency Magnitude

Debris flows are one of the most destructive landslide processes worldwide, given their ubiquity in mountainous areas occupied by human settlement or industrial facilities around the world. Given the episodic nature of debris flows, these hazards are often un- or under-recognized. Three fundamental components of debris-flow risk assessments include frequency-magnitude analysis, numerical scenario modeling, and consequence analysis to estimate the severity of damage and loss. Recent advances in frequency-magnitude analysis take advantage of developments in methods to estimate the age of deposits and size of past and potential future events. Notwithstanding, creating reliable frequency-magnitude relationships is often challenged by practical limitations to investigate and statistically analyze past debris-flow events that are often discontinuous, as well as temporally and spatially censored. To estimate flow runout and destructive potential, several models are used worldwide. Simple empirical models have been developed based on statistical geometric correlations, and two-dimensional and three-dimensional numerical models are commercially available. Quantitative risk assessment (QRA) methods for assessing public safety were developed for the nuclear industry in the 1970s and have been applied to landslide risk in Hong Kong starting in 1998. Debris-flow risk analyses estimate the likelihood of a variety of consequences. Quantitative approaches involve prediction of the annual probability of loss of life to individuals or groups and estimates of annualized economic losses. Recent progress in quantitative debris-flow risk analyses include improved methods to characterize elements at risk within a GIS environment and estimates of their vulnerability to impact. Improvements have also been made in how these risks are communicated to decision makers and stakeholders, including graphic display on conventional and interactive online maps. Substantial limitations remain, including the practical impossibility of estimating every direct and indirect risk associated with debris flows and a shortage of data to estimate vulnerabilities to debris-flow impact. Despite these limitations, quantitative debris-flow risk assessment is becoming a preferred framework for decision makers in some jurisdictions, to compare risks to defined risk tolerance thresholds, support decisions to reduce risk, and quantify the residual risk remaining following implementation of risk reduction measures.

scholarly journals Sedimentology, dynamics and debris flow potential of Champadevi River, southwest Kathmandu, Nepal

1970 ◽  
Vol 10 ◽  
pp. 9-20
Author(s):  
Naresh Kazi Tamrakar ◽  
Achut Prajapati ◽  
Suman Manandhar
Keyword(s):  
Debris Flow ◽  
Debris Flows ◽  
Alluvial Fan ◽  
Shear Stresses ◽  
Stream Power ◽  
Huge Amount ◽  
Sedimentary Characteristics ◽  
Unconsolidated Material ◽  
Flow Potential ◽  
Headward Erosion

Mountainous and hilly regions are potential for debris flows, one of the major forms of natural disasters, which cause serious damage in downstream areas. The southwestern region of the Kathmandu Valley experienced catastrophic flows in the Champadevi River and its two tributaries (the Aitabare and the Raute Rivers) in July 2002. These rivers were investigated for morphologic, hydraulic and sedimentary characteristics to evaluate potential of debris flow in the area. The Raute and the Aitabare Rivers have tendency of headward erosion due to abrupt drop of gradient down the scarp of the alluvial fan deposit composed of unconsolidated matrix-supported gravel and mud. Because of this tendency, the rivers erode their substrate and banks, and contribute slope movements by sheding a huge amount of clasts and matrix. Therefore, instability condition of rivers and unconsolidated material available in the river courses potentially contribute for debris flow. The tractive shear stresses in the Aitabare, the Raute and the Champadevi Rivers (1.27, 1.60 and 0.48 KPa, respectively) exceeds twice the critical shear stresses required to transport 90th-percentile fraction of the riverbed material (0.14, 0.18 and 0.11 KPa). The stream powers (10.8, 17.2 and 5.1 m-kN/s/m2) of these rivers also greatly exceed the critical stream powers (0.21, 0.35 and 0.18 m-kN/s/m2) required to initiate traction transport. Because the tractive shear stresses and the stream powers that are achieved during bankfull flow are several times larger than the corresponding critical values, even the flow having stream power exceeding the critical stream power may potentially generate debris flow.   doi: 10.3126/bdg.v10i0.1416 Bulletin of the Department of Geology, Tribhuvan University, Kathmandu, Nepal, Vol. 10, 2007, pp. 9-20

Debris Flow Hazards and its Mitigation Works in Xianbuleng Gully, Jinchuan County, Sichuan Province, China

2012 ◽  
Vol 166-169 ◽  
pp. 2769-2773
Author(s):  
Jin Feng Liu ◽  
Yong You ◽  
Xing Chang Chen
Keyword(s):  
Debris Flow ◽  
Debris Flows ◽  
Case Analysis ◽  
Sichuan Province ◽  
Alluvial Fan ◽  
Drainage Canal ◽  
Hydraulic Condition ◽  
Township Government

This paper presented a case analysis of debris flow hazards and its mitigation works. The Xianbuleng Gully which is located in Jinchuan County, Sichuan Province was selected as study area. This gully is an old debris flow gully which once burst out many debris flow disasters in history. If debris flows occur again in this gully, the township government, the center school and 13 village houses nearly 300 persons on the alluvial fan will be exposed to great risk.The environment settings and the hazard characteristics of the Xianbuleng debris flow were introduced first in this paper. Then, mitigation works especially the drainage canal under the optimal hydraulic condition were planned and designed in the gully for decreasing the debris flow hazards.

scholarly journals The January 2014 Flashflood in the Ambato River (Catamarca, Argentina)- A Case Study of Megaboulders Fluvial Transport

2021 ◽  
Vol 2 (2) ◽  
pp. 3150-3166
Author(s):  
Moshe Inbar ◽  
Julio A. Costello ◽  
Jorge Eremchuk
Keyword(s):  
Urban Areas ◽  
Field Studies ◽  
Urban Environments ◽  
Bedload Transport ◽  
Alluvial Fan ◽  
Economic Losses ◽  
Arid Environments ◽  
Stream Power ◽  
The Village

Megaboulders mantle the steep channels of mountainous rivers, and moderate incision rates by increasing channel roughness. Direct measurement of the transport of boulders in natural rivers is difficult, therefore there are few field studies on the subject. The transportation of megaboulders downslope in catastrophic floods in urban environments releases a destructive power. This study analyses the Ambato river flood that occurred in Argentina in January 2014 with an assumed recurrence interval of 1:100 years. The flood was caused by concentrated rainfall in the upper basin, at an elevation of 4000 m. The Ambato river forms a boulder alluvial fan drained by episodic floods. The 2014 flood caused casualties and economic losses in the village of El Rodeo in the province of Catamarca. Several houses and a bridge were destroyed and vehicles were swept away. All bedload sizes- including megaboulders with 2000 mm b-axis- were transported during the flood. The empirical equation for stream power value and the unit bedload transport rate of megaboulders were validated. An assessment of boulder mobility is necessary to mitigate flow hazards in mountainous urban areas. The effects of climate change in semi-arid environments would be greater if they involved increased precipitation or more extreme rainstorms due to events such as El Niṅo.

scholarly journals Formation-Evolutionary Mechanism Analysis and Impacts of Human Activities on the 20 August 2019 Clustered Debris Flows Event in Wenchuan County, Southwestern China

2021 ◽  
Vol 9 ◽  
Author(s):  
Yu Li ◽  
Xing-nian Liu ◽  
Bin-rui Gan ◽  
Xie-kang Wang ◽  
Xing-guo Yang ◽  
...  
Keyword(s):  
Debris Flow ◽  
Human Activities ◽  
Debris Flows ◽  
Large Scale ◽  
Field Investigation ◽  
Mitigation Measures ◽  
Southwestern China ◽  
Economic Losses ◽  
Mechanism Analysis ◽  
Prediction And Prevention

Characterized by large scale, high frequency, and strong destructiveness, debris flow has become the most noticeable geohazards throughout the world, especially in the mountainous areas of southwestern China. On August 20, 2019, large-scale heavy rainfall pummeled Wenchuan County, Sichuan Province, Southwestern China, which resulted in a cluster of debris flows (the “8·20” clustered debris flows event), and caused considerable economic losses (approximately 3.4 billion RMB were lost) and heavy casualties (48,862 people were displaced, 16 people died and 22 people went missing). Based on field investigation, image data interpretation, mechanism analysis, and other methods, this study reveals the formation mechanism, dynamic evolutionary process, and impacts of human activities on the “8·20” clustered debris flows event. Results from a comprehensive analysis indicate that the occurrence of short-term, high-intensity rainfall and the excessive supply of solid material were the main factors that triggered this catastrophic event. With the debris flow flowing into the main river, this event presented an extremely apparent disaster chain effect. It is also found that improper site selection and inadequate design of human activities played a crucial role in the movement process of the debris flow that directly aggravated the losses. Finally, to improve debris flow prediction and prevention, some early warning and mitigation measures are discussed.

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.

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