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

ABSTRACT Dense urban development on a hilly terrain coupled with intense seasonal rainfall and heterogeneous weathering profiles give rise to acute debris-flow problems in Hong Kong. The Geotechnical Engineering Office (GEO) of the Hong Kong SAR Government has launched a holistic research and development (R&D) programme and collaborated with various tertiary institutes and professional bodies to support the development of a comprehensive technical framework for managing landslide risk and designing debris-flow mitigation measures. The scope of the technical development work includes compilation of landslide inventories, field studies of debris flows, development and calibration of tools for landslide run-out modelling, back analysis of notable debris flows, physical and numerical modelling of the interaction between debris flows and mitigation measures, formulation of a technical framework for evaluating debris-flow hazards, and development of pragmatic mitigation strategies and design methodologies for debris-flow countermeasures. The work has advanced the technical understanding of debris-flow hazards and transformed the natural terrain landslide risk management practice in Hong Kong. New analytical tools and improved design methodologies are being applied in routine geotechnical engineering practice.

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Predicting Extreme-Precipitation Effects on the Geomorphology of Small Mountain Catchments: Towards an Improved Understanding of the Consequences for Freshwater Biodiversity and Ecosystems

Water ◽

10.3390/w12010079 ◽

2019 ◽

Vol 12 (1) ◽

pp. 79 ◽

Cited By ~ 4

Author(s):

Stefano Segadelli ◽

Federico Grazzini ◽

Michele Adorni ◽

Maria Teresa De Nardo ◽

Anna Fornasiero ◽

...

Keyword(s):

Extreme Precipitation ◽

Debris Flows ◽

Mitigation Measures ◽

Convective System ◽

Stream Channels ◽

Freshwater Biodiversity ◽

Rainfall Analysis ◽

Extreme Precipitation Events ◽

Hourly Rainfall ◽

Precipitation Events

In 2015 an intense rainfall event hit the Valleys of the Trebbia, Nure, and Aveto watercourses in the Northern Apennines. In about 6 h a mesoscale convective system deployed a stunning amount of precipitation of 340 mm, with an extreme hourly rainfall intensity of >100 mm/h. It triggered debris flows along slopes and stream channels, landslides and floods, which caused serious damages. Through the optimal combination of rainfall data and radar volumes, in this work we present a detailed rainfall analysis, which will serve as a basis to create a quantitative correlation with debris flows over elementary hydrological units. We aim at providing an objective basis for future predictions, starting from the recognition of the forcing meteorological events, and then arriving at the prediction of triggering phenomena and to the debris-flow type. We further provide seven observations/case studies on the effects of extreme-precipitation events on freshwater environments in small mountain catchments. Extreme-precipitation events are becoming more frequent and widespread globally but their ecological effects are still insufficiently understood. In general, the effects of extreme events on inland-waters’ ecosystems are highly context-dependent, ranging from deleterious to beneficial. We therefore highlight the necessity of further studies to characterize these effects in more depth to be able to include appropriate mitigation measures in environmental planning and stewardship.

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Characteristics of the Disastrous Debris Flow of Chediguan Gully in Yinxing Town, Sichuan Province, on August 20, 2019

10.21203/rs.3.rs-798905/v1 ◽

2021 ◽

Author(s):

Li Ning ◽

Tang Chuan ◽

Zhang Xianzheng ◽

Chang Ming ◽

Shu Zhile ◽

...

Keyword(s):

Debris Flow ◽

Wenchuan Earthquake ◽

Debris Flows ◽

Warning System ◽

Mitigation Measures ◽

High Definition ◽

Flood Peak ◽

The Wenchuan Earthquake ◽

Minjiang River ◽

Monitoring And Early Warning

Abstract On August 20, 2019, at 2 a.m., a disastrous debris flow occurred in Chediguan gully in Yinxing town, China. The debris flow destroyed the drainage groove and the bridge at the exit of the gully. In addition, the debris flow temporarily blocked the Minjiang River during the flood peak, flooding the Taipingyi hydropower station 200 m upstream and leaving two plant workers missing. To further understand the activity of the debris flow after the Wenchuan earthquake, the characteristics of this debris flow event were studied. Eleven years after the Wenchuan earthquake, a disastrous debris flow still occurred in the Chediguan catchment, causing more severe losses than those of earlier debris flows. In this paper, the formation mechanism and dynamic characteristics of this debris flow event are analysed based on a drone survey, high-definition remote sensing interpretations and other means. The catastrophic debris flow event indicates that debris flows in the Wenchuan earthquake area are still active. A large amount of dredging work in the main gully could effectively reduce the debris flow risk in the gully. In addition, it is also important to repair or rebuild damaged mitigation measures and to establish a real-time monitoring and early warning system for the high-risk gully.

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Contribution of Excessive Supply of Solid Material to a Runoff-Generated Debris Flow during Its Routing Along a Gully and Its Impact on the Downstream Village with Blockage Effects

Water ◽

10.3390/w11010169 ◽

2019 ◽

Vol 11 (1) ◽

pp. 169 ◽

Cited By ~ 10

Author(s):

Ming-liang Chen ◽

Xing-nian Liu ◽

Xie-kang Wang ◽

Tao Zhao ◽

Jia-wen Zhou

Keyword(s):

Debris Flow ◽

Debris Flows ◽

Large Scale ◽

Residential Buildings ◽

Solid Material ◽

Sediment Supply ◽

Mitigation Measures ◽

Dry Land ◽

Field Investigations ◽

Abundant Supply

On 8 August 2017, a runoff-generated debris flow occurred in the Puge County, Sichuan Province of southwestern China and caused huge property damage and casualties (25 people died and 5 people were injured). Emergency field investigations found that paddy fields, dry land, residential buildings and roads suffered different degrees of impact from the debris flow. This paper reveals the formation process of the debris flow by analyzing the characteristics of rainfall precipitation and sediment supply conditions in the study area and it approaches the practical application of hazard prevention and mitigation constructions. Doppler weather radar analysis indicates that a very high intensity rainfall occurred in the middle and upper zones of the basin, illustrating the importance of enhancing rainfall monitoring in high-altitude areas. The abundant supply of deposits in gully channels is among the significant causes of a transformation from mountain floods to large-scale debris flows. It was also found that the two culverts played an important role in the movement affecting the processes of debris flows which has substantially aggravated the destructive outcome. The excessive supply of solid material and local blockage with outburst along a gully must receive significant attention for the prediction of future debris flows, hazard prevention and mitigation measures.

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Debris-flow velocity and volume estimations based on seismic data

10.5194/nhess-2020-411 ◽

2021 ◽

Author(s):

Andreas Schimmel ◽

Velio Coviello ◽

Francesco Comiti

Keyword(s):

Debris Flow ◽

Flow Velocity ◽

Seismic Data ◽

Debris Flows ◽

Cross Correlation ◽

Sampling Rate ◽

Early Warning Systems ◽

Velocity Estimation ◽

Mitigation Measures ◽

Strong Control

Abstract. The estimation of debris-flow velocity and volume is a fundamental task for the development of early warning systems, the design of control structures and other mitigation measures. Previous analysis of the seismic energy produced by debris flows showed that the peak amplitudes are representative of the kinetic energy of each surge and debris-flow discharge can be therefore estimated based on seismic signals. Also, the debris-flow velocity can be calculated using seismic data recorded at two spatial separated stations located along the channel by the use of cross-correlation. This work provide a first approach for estimating the total volume of debris flows based on the seismic signal detected with simple, low-cost geophones installed along the debris-flow channel. The developed methods was applied to seismic data collected on three different test sites in the Alps: Gadria (IT), Lattenbach (AT), and Cancia (IT). An adaptable cross-correlation time window was used, which can offer a better estimation of the velocity compared to a constant window length. The analyses of the seismic data of 14 debris flows that occurred from 2014 to 2018 shows the strong control of the sampling rate and the sensor-distance on the velocity estimation. A simple approach based on a linear relation between square of the seismic amplitude and the event magnitude is proposed for a first order estimation of the debris-flow magnitude.

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

Frontiers in Earth Science ◽

10.3389/feart.2021.616113 ◽

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.

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Characteristics of the disastrous debris flow of Chediguan gully in Yinxing town, Sichuan Province, on August 20, 2019

Scientific Reports ◽

10.1038/s41598-021-03125-x ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Ning Li ◽

Chuan Tang ◽

Xianzheng Zhang ◽

Ming Chang ◽

Zhile Shu ◽

...

Keyword(s):

Debris Flow ◽

Wenchuan Earthquake ◽

Debris Flows ◽

Warning System ◽

Mitigation Measures ◽

High Definition ◽

Flood Peak ◽

The Wenchuan Earthquake ◽

Minjiang River ◽

Monitoring And Early Warning

AbstractOn August 20, 2019, at 2 a.m., a disastrous debris flow occurred in Chediguan gully in Yinxing town, China. The debris flow destroyed the drainage groove and the bridge at the exit of the gully. In addition, the debris flow temporarily blocked the Minjiang River during the flood peak, flooding the Taipingyi hydropower station 200 m upstream and leaving two plant workers missing. To further understand the activity of the debris flow after the Wenchuan earthquake, the characteristics of this debris flow event were studied. Eleven years after the Wenchuan earthquake, a disastrous debris flow still occurred in the Chediguan catchment, causing more severe losses than those of earlier debris flows. In this paper, the formation mechanism and dynamic characteristics of this debris flow event are analysed based on a drone survey, high-definition remote sensing interpretations and other means. The catastrophic debris flow event indicates that debris flows in the Wenchuan earthquake area are still active. A large amount of dredging work in the main gully could effectively reduce the debris flow risk in the gully. In addition, it is also important to repair or rebuild damaged mitigation measures and to establish a real-time monitoring and early warning system for the high-risk gully.

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Before the fire: Assessing post-wildfire flooding and debris-flow hazards for pre-disaster mitigation

10.5194/nhess-2019-74 ◽

2019 ◽

Author(s):

Ann M. Youberg ◽

Joseph B. Loverich ◽

Michael J. Kellogg ◽

Jonathan E. Fuller

Keyword(s):

Debris Flow ◽

Local Governments ◽

Debris Flows ◽

Action Plan ◽

Disaster Mitigation ◽

Mitigation Measures ◽

Planning Stage ◽

Increased Risk ◽

Critical Facilities ◽

The City

Abstract. Increasing size and severity of wildfires, and the expanding built environment into the wildland-urban interface makes it imperative that local governments identify, prepare for and reduce risks to people and infrastructure from wildfires and the aftermaths of fires. Here we report on a pre-wildfire assessment of post-fire hazards in Coconino County, Arizona, the mitigation measures identified and implemented as a result of the study, and proposed changes to the assessment methodology for upcoming studies. Results from the Coconino County study indicate that up to 34 % of the buildings, and up to 26 % of the critical facilities countywide are at some level of increased risk of post-fire flooding if no actions are taken to reduce the risk of severe wildfires. As many as 593 homes (2,191 parcels) in Coconino County, as well as 13 dams and other critical facilities, may be impacted by post-fire debris flows. In two smaller areas of detailed study, flood peaks could increase as much as 4–5 times the existing 100-year flood levels, with up to a 350 % increase in the number of buildings in flood-prone areas. Debris flows will likely be limited in aerial extent but could impact a much larger area from following floods and sediment-laden flows. Mitigation measures identified and implemented as a result of this study include County Coconino County coordination with the Kaibab National Forest in regard to forest health projects, development of a post-wildfire emergency action plan for the City of Williams, development of a Post-Fire, Pre-Disaster plan for the City of Williams and educating the City of Williams and County officials and business stakeholders of the post-fire flood risk. Other mitigation measures that are still in the planning stage include installation of additional early flood warning system gages, and increasing building and infrastructure resiliency through channel conveyance improvement and utility protection projects. For two upcoming assessments, we plan to use a new statistical methodology to develop burn severity maps using historical burns, and we plan to employ a new process-based debris-flow model developed for use in Arizona to assess debris-flow inundation limits.

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Preface Results of the open session on "Documentation and monitoring of landslides and debris flows" for mathematical modelling and design of mitigation measures, held at the EGU General Assembly 2009

Natural Hazards and Earth System Science ◽

10.5194/nhess-11-1583-2011 ◽

2011 ◽

Vol 11 (5) ◽

pp. 1583-1588 ◽

Cited By ~ 2

Author(s):

L. Franzi ◽

D. Giordan ◽

M. Arattano ◽

P. Allasia ◽

M. Arai

Keyword(s):

Debris Flows ◽

Mitigation Measures ◽

Future Research ◽

General Assembly ◽

Special Issue ◽

Laboratory Equipment ◽

Simulation Techniques ◽

Scientific Papers ◽

Open Session ◽

Landslides And Debris Flows

Abstract. The papers that are here presented and summarised represent the recent scientific contributions of some authors coming from different countries and working in the fields of monitoring, modelling, mapping and design of mitigation measures against mass movements. The authors had the opportunity to present their recent advancements, discuss each other needs and set forth future research requirements during the 2009 EGU General Assembly, so that their scientific contributions can be considered the result of the debates and exchanges that were set among scientists and researchers, either personally or during the review phase since that date. In this resume, the scientific papers of the special issue are divided according to different thematic areas and summarised. The most innovative scientific approaches proposed in the special issue, regarding the monitoring methodologies, simulation techniques and laboratory equipment are described and summarised. The obtained results are very promising to keep on future research at a very satisfactory level.

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Assessment of the 2019 Chamoson debris flow event (Swiss Alps)

10.5194/egusphere-egu2020-15074 ◽

2020 ◽

Author(s):

Marc-Henri Derron ◽

Valérie Baumann ◽

Tiggi Choanji ◽

François Noël ◽

Ludovic Baron ◽

...

Keyword(s):

Debris Flow ◽

Debris Flows ◽

Heavy Rain ◽

Peak Discharge ◽

Swiss Alps ◽

Mitigation Measures ◽

Size Classification ◽

Cone Apex ◽

The Right ◽

The Village

Debris flows triggered by heavy rain are common and can cause huge damages in Alpine valleys. In this case we documented the changes occurred in the Losents&#233; valley after the 11 August 2019 event, which caused two death and several damages to the village of Chamoson. The Chamoson basin is located in the Alps on the right side of the Rh&#244;ne valley. Three main rivers drain the Chamoson basin, the Losents&#233;, the Cry and the Tsen&#233;. The main debris flow event occurred in the Losents&#233; sub-basin. The Losents&#233; River is 9 km long from the sources at 3000 m until the alluvial cone apex at 600 m. In the upper part of the Chamoson basin thick loose debris cones and glacial deposits lie on steep slopes, the geology of the middle basin is formed by unstable clayey shales with several active landslides on both lateral valley slopes.The village of Chamoson is located on the huge alluvial cone built with torrential events from the three main rivers. Since the XIX century, several big debris flow events (1898, 1923, 2003, 2018) were recorded in this area and mitigation measures were built in the principal rivers. Unfortunately, the 2019 debris flows overflowed the channels limit when the flows reached the alluvial cone apex, reaching the road and took a car with 2 persons inside. Upstream in the middle basin 2 wood bridges were destroyed and many concrete or stone walls (mitigation measures) along the river were damaged.After the event we acquired pictures with a drone from the sources area and the Losents&#233; river valley in order to have a post event image. With this image we could analyse and map the source areas and the inundated areas in the Losents&#233; channel. We did also field observation along the river.After comparing the pre- and post-event images we mapped the middle and upper basin inundated areas by the 2019 event and the described the deposits and eroded sections along the river. We calculated the peak discharge of 1000 m3/s for this event using the inundated transversal profile area near the cone apex and the flow velocity obtained from a movie. The peak discharge corresponds to 4 in the size classification for debris flows (Jacob et al., 2005).Reference:Jakob, M. (2005). A size classification for debris flows.&#160;Engineering geology,&#160;79(3-4), 151-161.

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