Post-earthquake changes in debris flow susceptibility in the Upper Minjiang catchment (Sichuan, China), as revealed by meteorological and hydro-meteorological thresholds

2020 ◽  
Author(s):  
Roberto Greco ◽  
Pasquale Marino ◽  
Siva Srikrishnan ◽  
Xuanmei Fan
Keyword(s):  
Water Balance ◽  
Debris Flow ◽  
Wenchuan Earthquake ◽  
Debris Flows ◽  
Strong Increase ◽  
Mountain Range ◽  
The Tibetan Plateau ◽  
2008 Wenchuan Earthquake ◽  
Soil Storage ◽  
Triggering Rainfall

<p>On May 12, 2008, a Mw 7.9 earthquake struck Wenchuan, Longmen Shan Area, in western Sichuan, China, at the eastern margin of the Tibetan Plateau. This earthquake was the largest and most destructive event in the last 60 years, causing more than 87000 casualties. The economic loss was estimated at some 1100 billion RMB. The major fault rupture produced surface displacements up to 3-4 meters, spreading from the epicenter (near the town of Yingxiu) for 240 km along the mountain range.</p><p>The Wenchuan Earthquake triggered almost 200000 co-seismic landslides over a region larger than 110000 km<sup>2</sup>, leading to the accumulation of large volumes of loose material either along slopes or in gullies. After the earthquake, this material caused a strong increase of debris flow occurrence in the subsequent years, mainly in the worst-hit areas, such as Wenchuan, Beichuan and Mao counties. During the years immediately after the earthquake, the rainfall required for debris flow triggering resulted clearly smaller than before (Guo et al., 2016). Afterwards, the response of the debris deposits to rainfall changed, leading to a general recovery of stability and a reduction of debris flow frequency and magnitude (Domènech et al., 2019).</p><p>In this study, the assessment of debris flows occurrence throughout upper Minjiang catchment, to which Wenchuan county belongs, is modeled with two empirical approaches, both based on the available record of precipitations and debris flows in the years 2008-2015. In the first approach, a threshold to predict debris flow occurrence is defined based on intensity and duration of potentially triggering rainfall events (meteorological threshold). With the second approach, also the hydrological conditions predisposing the slopes to debris flows are considered, by assessing the water balance in the catchment with a simplified lumped hydrological model, based on the Budyko framework (Zhang et al., 2008), and defining a threshold to predict debris flows based on rainfall depth and estimated soil storage prior the onset of rainfall (hydro-meteorological threshold).</p><p>The obtained results indicate that the hydro-meteorological threshold allows catching the progressive recovery of stability of the debris deposits much better than the meteorological threshold, leading to identification of increasing thresholds, both in terms of pre-event soil storage and triggering rainfall amount, in the years from 2008 onward. Such a result shows that the adoption of process-based approaches , even empirical and strongly simplified as in the presented case, leads to predictions of debris flow occurrence more robust than those based solely on rainfall information.</p><p> </p><p>References</p><p>Domènech, G., Fan, X., Scaringi, G., van Asch, T.W.J., Xu, Q., Huang, R., Hales, T.C., 2019. Modelling the role of material depletion, grain coarsening and revegetation in debris flow occurrences after the 2008 Wenchuan earthquake. Eng. Geol. 250, 34-44.</p><p>Guo, X., Cui, P., Li, Y., Fan, J., Yan, Y., Ge, Y., 2016. Temporal differentiation of rainfall thresholds for debris flows in Wenchuan earthquake-affected areas. Environ. Earth Sci. 75, 1–12.</p><p>Zhang, L., Potter, N., Hickel, K., Zhang, Y., Shao, Q., 2008. Water balance modeling over variable time scales based on the Budyko framework – Model development and testing. J. Hydrol. 360, 117-131.</p>

scholarly journals Two multi-temporal datasets that track the enhanced landsliding after the 2008 Wenchuan earthquake

2019 ◽  
Vol 11 (1) ◽  
pp. 35-55 ◽  
Author(s):  
Xuanmei Fan ◽  
Gianvito Scaringi ◽  
Guillem Domènech ◽  
Fan Yang ◽  
Xiaojun Guo ◽  
...  
Keyword(s):  
Wenchuan Earthquake ◽  
Debris Flows ◽  
Temporal Evolution ◽  
The Tibetan Plateau ◽  
Mass Wasting ◽  
Epicentral Area ◽  
2008 Wenchuan Earthquake ◽  
Rain Gauges ◽  
Multi Temporal ◽  
Coseismic Landslide

Abstract. We release two datasets that track the enhanced landsliding induced by the 2008 Mw 7.9 Wenchuan earthquake over a portion of the Longmen Mountains, at the eastern margin of the Tibetan Plateau (Sichuan, China). The first dataset is a geo-referenced multi-temporal polygon-based inventory of pre- and coseismic landslides, post-seismic remobilisations of coseismic landslide debris and post-seismic landslides (new failures). It covers 471 km2 in the earthquake's epicentral area, from 2005 to 2018. The second dataset records the debris flows that occurred from 2008 to 2017 in a larger area (∼17 000 km2), together with information on their triggering rainfall as recorded by a network of rain gauges. For some well-monitored events, we provide more detailed data on rainfall, discharge, flow depth and density. The datasets can be used to analyse, on various scales, the patterns of landsliding caused by the earthquake. They can be compared to inventories of landslides triggered by past or new earthquakes or by other triggers to reveal common or distinctive controlling factors. To our knowledge, no other inventories that track the temporal evolution of earthquake-induced mass wasting have been made freely available thus far. Our datasets can be accessed from https://doi.org/10.5281/zenodo.1405489. We also encourage other researchers to share their datasets to facilitate research on post-seismic geological hazards.

The remobilisation of seismically-sourced sediment by debris flows in Wenchuan: A grain size perspective

2020 ◽  
Author(s):  
Erin Harvey ◽  
Xuanmei Fan ◽  
Tristram Hales ◽  
Daniel Hobley ◽  
Jie Liu ◽  
...  
Keyword(s):  
Grain Size ◽  
Debris Flow ◽  
Wenchuan Earthquake ◽  
Debris Flows ◽  
Real Field ◽  
Saturation State ◽  
2008 Wenchuan Earthquake ◽  
Seismic Landslides ◽  
The 2008 Wenchuan Earthquake

<p>Co-seismic landslides can mobilise up to 3 km<sup>3</sup> of loose sediment within minutes. However, the export rate of this sediment is largely unconstrained. For example, it is estimated that a decade after the 2008 Wenchuan earthquake at least 90% of the co-seismic sediment remains stored on the hillslope. Post-earthquake debris flows are the main conduit by which such hillslope debris reaches the fluvial network but the mechanics that govern the triggering and runout of such flows remain unclear and as such they appear to behave largely unpredictably.  Material grain size is a key control on both triggering and runout, since it affects both hydrological (e.g. water loss during flow; saturation state before triggering) and frictional properties of the system. However, our understanding of the role of grain size in the genesis and evolution of debris flows remains poorly explored, largely due to limitations in real field data. Existing estimates for landslide and debris flow deposit grain size distributions (GSDs) are currently limited by 1. inconsistency of applied methods; 2. the very poor sorting of these sediments; 3. inaccessibility, and 4. inherent intra-deposit variability in GSD. </p><p>Our research aims to better understand the role of grain size using an unprecedentedly detailed set of field-constrained GSDs across the post-seismic landslides and debris flows of the 2008 Wenchuan earthquake. Here we present data quantifying the grain size distribution across two debris flows using two different techniques. The two debris flows occurred in response to prolonged rainfall in August 2019 and mobilised co-seismic debris from the 2008 earthquake. In the field, we selected four to eight 1 m x 1 m x 0.5 m pits along the centre line of each debris flow at regular intervals and sieved the pit material into 8 cm, 4 cm, 2 cm and 1 cm fractions at 10 cm depth increments. Boulders >8 cm were measured and weighed individually. Smaller samples were then collected from the finer fraction (<1 cm) and sieved further in the laboratory. The coarse fraction was independently constrained from calibrated photogrammetry, and this was coupled to drone surveying to ensure the coarsest fraction (≥1 m) was correctly represented. This study presents a detailed estimate of post-earthquake debris flow GSDs with the overarching aim to better understand sediment transport and deposition from debris flows in the years following an earthquake.</p>

Relationships among three repeated large-scale debris flows at Pubugou Ravine in the Wenchuan earthquake zone

2014 ◽  
Vol 51 (9) ◽  
pp. 951-965 ◽  
Author(s):  
S. Zhang ◽  
L.M. Zhang ◽  
H.X. Chen
Keyword(s):  
Debris Flow ◽  
Wenchuan Earthquake ◽  
Debris Flows ◽  
Large Scale ◽  
Solid Materials ◽  
2008 Wenchuan Earthquake ◽  
Hill Slope ◽  
Earthquake Zone ◽  
The Hill ◽  
Channel Deposits

The 12 May 2008 Wenchuan earthquake in China triggered numerous landslides. Loose landslide materials can easily evolve into deadly debris flows during wet seasons. During the period from 2008 to 2011, three separate large-scale debris flows occurred in the Pubugou Ravine near the epicentre of the earthquake that were among the largest repeated debris flows ever reported. Approximately 1.76 × 106 m3 of sediment was deposited during these three events. This paper aims to (i) analyze the movements of solid materials during the repeated debris flows, (ii) discuss the evolution of the initiation mechanisms of these debris flows, and (iii) evaluate the changing depositional morphology of the debris flow fans and examine the particle sizes of the debris flow materials. To achieve the above research objectives, timely field investigations were undertaken in the past 5 years after each of these debris flow events. Satellite images were used to delineate the boundaries of the initiation areas, the transportation channels, and the deposition zones of these debris flows. With the occurrence of the repeated debris flows, the hill slope deposits gradually evolved into channel deposits and the solid materials in the channels moved toward the gully mouth. Hence, channelized flows gradually became dominant. The debris fan materials of the repeated debris flows became coarser and coarser over time. The three debris flows were all characterized by coarse boulder fronts.

scholarly journals Two multi-temporal datasets to track the enhanced landsliding after the 2008 Wenchuan earthquake

2018 ◽  
Author(s):  
Xuanmei Fan ◽  
Gianvito Scaringi ◽  
Fan Yang ◽  
Guillem Domènech ◽  
Xiaojun Guo ◽  
...  
Keyword(s):  
Wenchuan Earthquake ◽  
Debris Flows ◽  
Temporal Evolution ◽  
The Tibetan Plateau ◽  
Mass Wasting ◽  
Epicentral Area ◽  
2008 Wenchuan Earthquake ◽  
Rain Gauges ◽  
Multi Temporal ◽  
Coseismic Landslide

Abstract. We release two datasets that track the enhanced landsliding induced by the Mw 7.9 2008 Wenchuan earthquake over a portion of the Longmen mountains, at the eastern margin of the Tibetan plateau (Sichuan, China). The first dataset is a geo-referenced multi-temporal polygon-based inventory of pre- and coseismic landslides, post-seismic remobilisations of coseismic landslide debris, and post-seismic landslides (new failures). The inventory covers 462.5 km2 in the earthquake's epicentral area, from 2005 to 2015. The second dataset records the debris flows that occurred from 2008 to 2017 in a larger area (~ 17,000 km2), together with information on their triggering rainfalls recorded by a network of rain gauges. For some well-monitored event, we provide detailed information on rainfall, discharge, flow depth and density. The datasets can be used to analyse, at various scales, the patterns of enhanced landsliding caused by the earthquake. They can be compared to inventories relative to past or new earthquakes or other triggers to reveal common or distinctive controlling factors. To our knowledge, no other inventories that track the temporal evolution of earthquake-induced mass wasting have been made freely available thus far. Our datasets are available at https://doi.org/10.5281/zenodo.1405490. We also encourage other researchers to share their datasets to facilitate research on post-seismic geological hazards.

scholarly journals A multivariate statistical method for susceptibility analysis of debris flow in southwestern China

2020 ◽  
Vol 20 (5) ◽  
pp. 1321-1334
Author(s):  
Feng Ji ◽  
Zili Dai ◽  
Renjie Li
Keyword(s):  
Debris Flow ◽  
Debris Flows ◽  
Loose Material ◽  
Southwestern China ◽  
The Tibetan Plateau ◽  
Type I ◽  
Quantification Theory ◽  
2008 Wenchuan Earthquake ◽  
Antecedent Precipitation ◽  
Dadu River

Abstract. Southwestern China is characterized by many steep mountains and deep valleys due to the uplift activity of the Tibetan Plateau. The 2008 Wenchuan earthquake left large amounts of loose materials in this area, making it a severe disaster zone in terms of debris flow. Susceptibility is a significant factor of debris flows for evaluating their formation and impact. Therefore, there is an urgent need to analyze the susceptibility to debris flows of this area. To quantitatively predict the susceptibility of the area to debris flows, this study evaluates 70 typical debris flow gullies, which are distributed along the Brahmaputra River, Nujiang River, Yalong River, Dadu River, and Ming River, as statistical samples. Nine indexes are chosen to construct a factor index system and then to evaluate the susceptibility to debris flow. They are the catchment area, longitudinal gradient, average gradient of the slope on both sides of the gully, catchment morphology, valley orientation, loose material reserves, location of the main loose material, antecedent precipitation, and rainfall intensity. Following this, an empirical model based on the Type I quantification theory is established for susceptibility prediction for debris flows in southwestern China. Finally, 10 debris flow gullies upstream of the Dadu River are analyzed to verify the reliability of the proposed model. The results show that the accuracy of the statistical model is 90 %.

Research on Risk Level of Debris Flow in an Area

2014 ◽  
Vol 638-640 ◽  
pp. 2015-2018
Author(s):  
Qing Nian Yang ◽  
Shuai Tao Wu ◽  
Zhi Li
Keyword(s):  
Debris Flow ◽  
Debris Flows ◽  
Evaluation Method ◽  
Risk Level ◽  
The Tibetan Plateau ◽  
Adverse Conditions ◽  
Southeastern Margin ◽  
The Sichuan Basin ◽  
Original Vegetation ◽  
Steep Terrain

The research targets at the transition zone from the southeastern margin of the Tibetan Plateau to the Sichuan Basin; it is shown according to field survey: from 2008 to 2010, debris flow occurred twice, resulting in missing of two people, destruction on a lot of farmland and other serious disasters. Such the debris flows were because that the original vegetation was severely damaged after “5.12” earthquake, a lot of loose blocks were scattered in slopes and valleys, and also stimulated by abundant rainfall during rainy season, local steep terrain, as well as narrow valleys. The paper makes qualitative and quantitative evaluation on risk of debris flow within the region by single-valley debris flow risk evaluation method as proposed by Liu Xilin and Tang Chuan et al. it is shown from the results that the risk level H is 0.55, within scope of moderate risk. In case of any adverse conditions, debris flows may occur again.

scholarly journals Characteristics and Prevention of the Debris Flows following Wenchuan Earthquake in Jushui River Basin, An County, China

2014 ◽  
Vol 2014 ◽  
pp. 1-10 ◽  
Author(s):  
Yonggang Ge ◽  
Jianqiang Zhang ◽  
Xiaojun Guo
Keyword(s):  
Debris Flow ◽  
Wenchuan Earthquake ◽  
River Basin ◽  
Debris Flows ◽  
Flash Flood ◽  
River Channel ◽  
Hazard Identification ◽  
Control Mode ◽  
Potential Hazard ◽  
Prevention Measures

After analysing the catastrophic debris flows on August 18, 2012, and on July 9, 2013, in Jushui River basin, An County, the Wenchuan Earthquake seriously striken areas, it was found that they were characterized by the clay soil content of 0.1~1.2%, the density of 1.68~2.03 t/m3, the discharges of 62.2 m3/s to 552.5 m3/s, and the sediment delivery modulus of 1.0~9.4 × 104 m3/km2. Due to intense rainstorm, many large debris flows produced hazard chain, involved in flash flood, debris flow, dammed lake, and outburst flood, and rose Jushui River channel about 1~4 m as well as amplified flood. The hazards and losses mainly originated from the burying and scouring of debris flows, flood inundating, and river channel rise. The prevention of debris flows is facing the intractable problems including potential hazard identification, overstandard debris flow control, control constructions destructing, and river channel rapid rise. Therefore, the prevention measures for the basin, including hazard identification and risk assessment, inhabitants relocating, monitoring and alarming network establishing, emergency plans founding, and river channel renovating, and the integrated control mode for watershed based on regulating the process of debris flow discharge, were recommended for mitigation.

Magnitude estimation of a landslide-triggered debris flow in the Serra do Mar Mountain Range, Brazil

2020 ◽  
Author(s):  
Victor Carvalho Cabral ◽  
Fernando Mazo D'Affonseca ◽  
Marcelo Fischer Gramani ◽  
Agostinho Tadashi Ogura ◽  
Claudia Santos Corrêa ◽  
...  
Keyword(s):  
Debris Flow ◽  
Magnitude Estimation ◽  
Cross Sections ◽  
Debris Flows ◽  
Mountain Range ◽  
Serra Do Mar ◽  
Solids Concentration ◽  
Geomorphic Features ◽  
Total Magnitude ◽  
Future Events

<p><span>Debris flows represent great hazard to communities and infrastructures, since they move quickly and are very destructive. In Brazil, debris flows mainly occur in the Serra do Mar Mountain Range, where thousands of casualties were reported in the last two decades due to these phenomena. This study aims at estimating the magnitude of a debris-flow event that occurred in Serra do Mar on February 2017, at the Pedra Branca watershed in the State of Paraná. Debris-flow magnitude refers to the volume of material discharged during an event and is an important aspect of debris-flow hazard assessment. The Pedra Branca event was initiated by rainfall-triggered shallow landslides, damaging local oil pipelines and farms. The magnitude estimation is based on the combination of empirically based equations and the geomorphic features of the debris flow, acquired from <em>in situ</em> and aerial investigation. 28 cross-sections were made along the river channel, considering post-event channel width, erosion and accumulation depth, as well as depositional features. Sediment sources and accumulation areas were identified and delimitated based on high-resolution (1:500) aerial drone photographs. The results indicate that the landslides that initiated the event released approximately 26,884.5 m<sup>3</sup> of sediments (V<sub>i</sub>) into the main channel of Pedra Branca and that the volume eroded (V<sub>e</sub>) and accumulated (V<sub>d</sub>) along the channel are, respectively, 82,439 m<sup>3</sup> and 22,012 m<sup>3</sup>. The estimated total solids volume (V<sub>s</sub>) is 87,274 m<sup>3</sup>, assuming that V<sub>s</sub> = V<sub>i</sub> + V<sub>e</sub> - V<sub>d</sub>. Moreover, considering a solids concentration of 57% calculated according to empirically-based equations for Serra do Mar, the debris flow had a total magnitude of 153,113 m<sup>3</sup>. These estimations suggest that the February 2017 debris flow mobilised great volume of material and that 15% of the total volume accumulated on the channel bed, which can be remobilised by future events. Further research on debris-flow dynamics and recurrence at the Serra do Mar Mountain Range is recommended to mitigate future hazards.</span></p>

scholarly journals Debris-flow activity in five adjacent gullies in a limestone mountain range

2015 ◽  
Vol 42 (1) ◽  
Author(s):  
Klaus Schraml ◽  
Markus Oismüller ◽  
Markus Stoffel ◽  
Johannes Hübl ◽  
Roland Kaitna
Keyword(s):  
Debris Flow ◽  
Debris Flows ◽  
National Park ◽  
Regional Scale ◽  
Field Investigation ◽  
Mountain Range ◽  
Sediment Sources ◽  
Aerial Vehicle ◽  
Flow Activity ◽  
Local Variability

Abstract Debris-flows are infrequent geomorphic phenomena that shape steep valleys and can repre-sent a severe hazard for human settlements and infrastructure. In this study, a debris-flow event chro-nology has been derived at the regional scale within the Gesäuse National Park (Styria, Austria) using dendrogeomorphic techniques. Sediment sources and deposition areas were mapped by combined field investigation and aerial photography using an Unmanned Aerial Vehicle (UAV). Through the analysis of 384 trees, a total of 47 debris-flows occurring in 19 years between AD 1903 and 2008 were identified in five adjacent gullies. Our results highlight the local variability of debris-flow activi-ty as a result of local thunderstorms and the variable availability of sediment sources.

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