scholarly journals Modelling of the hydrological connectivity changes in the Minjiang Upstream after the Wenchuan earthquake using satellite remote sensing and DEM data

2015 ◽  
Vol 3 (2) ◽  
pp. 1113-1136
Author(s):  
H. Z. Zhang ◽  
T. H. Chi ◽  
J. R. Fan
Keyword(s):  
Debris Flow ◽  
Wenchuan Earthquake ◽  
Vegetation Recovery ◽  
Hydrological Connectivity ◽  
Horizontal Distance ◽  
Transport Pathway ◽  
Topographic Analysis ◽  
2008 Wenchuan Earthquake ◽  
Recovery Processes ◽  
Flow Formation

Abstract. The 2008 Wenchuan earthquake-induced landslides destroyed larger areas of mountain vegetation and produced large volume of landslide-debris, which made the vegetation's hydrological adjusting function diminished and made the hydrological progresses in slopes changed, resulting in severe erosion and catastrophic debris flows for a rather long time. Since 2008, the landslide-damaged vegetation and its hydrological function have been recovering. In this paper, the Minjiang Upstream watersheds around Yingxiu Town were selected. First, the landslide-damaged vegetation was identified and monitored via multi-temporal (2001–2014) satellite images. Then, the slope materials stability was assessed through topographic analysis of the vegetation survival environments. Then, the hydrological connectivity index (HCI) was defined to describe the upstream sediment production and downstream transport pathway. Finally, results indicated that HCI decreased annually with the vegetation recovery after the obvious increases during the earthquakes. While, analysis of 2008–2013 debris flow events indicated that the areas, the vertical drop to river <1000 m and the horizontal distance to river <2500 m, have high HCI increases and are more susceptible for debris flow formation. Monitoring the landslide-damaged vegetation recovery processes can contribute to assess the hydrological connectivity changes and understand the debris flow formation.

scholarly journals Modelling the role of material depletion, grain coarsening and revegetation in debris flow occurrences after the 2008 Wenchuan earthquake

2019 ◽  
Vol 250 ◽  
pp. 34-44 ◽  
Author(s):  
Guillem Domènech ◽  
Xuanmei Fan ◽  
Gianvito Scaringi ◽  
Theo W.J. van Asch ◽  
Qiang Xu ◽  
...  
Keyword(s):  
Debris Flow ◽  
Wenchuan Earthquake ◽  
Grain Coarsening ◽  
2008 Wenchuan Earthquake ◽  
The 2008 Wenchuan Earthquake

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

&lt;p&gt;Co-seismic landslides can mobilise up to 3 km&lt;sup&gt;3&lt;/sup&gt; 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. &amp;#160;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.&amp;#160;&lt;/p&gt;&lt;p&gt;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 &gt;8 cm were measured and weighed individually. Smaller samples were then collected from the finer fraction (&lt;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 (&amp;#8805;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.&lt;/p&gt;

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

&lt;p&gt;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.&lt;/p&gt;&lt;p&gt;The Wenchuan Earthquake triggered almost 200000 co-seismic landslides over a region larger than 110000 km&lt;sup&gt;2&lt;/sup&gt;, 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 &amp;#64258;ow 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 (Dom&amp;#232;nech et al., 2019).&lt;/p&gt;&lt;p&gt;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).&lt;/p&gt;&lt;p&gt;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.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;References&lt;/p&gt;&lt;p&gt;Dom&amp;#232;nech, 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.&lt;/p&gt;&lt;p&gt;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&amp;#8211;12.&lt;/p&gt;&lt;p&gt;Zhang, L., Potter, N., Hickel, K., Zhang, Y., Shao, Q., 2008. Water balance modeling over variable time scales based on the Budyko framework &amp;#8211; Model development and testing. J. Hydrol. 360, 117-131.&lt;/p&gt;

scholarly journals Evaluation of MODIS-based Vegetation Restoration After the 2008 Wenchuan Earthquake

2021 ◽  
Vol 308 ◽  
pp. 02005
Author(s):  
Cheng Jin ◽  
Kai Yu ◽  
Ke Zhang
Keyword(s):  
Remote Sensing ◽  
Wenchuan Earthquake ◽  
Recovery Rate ◽  
Vegetation Index ◽  
Vegetation Restoration ◽  
Vegetation Recovery ◽  
Entire Study ◽  
2008 Wenchuan Earthquake ◽  
The 2008 Wenchuan Earthquake ◽  
Vegetation Damage

Mountainous vegetation recovery after major earthquakes has been significant for preventing post-seismic soil erosion and geo-hazards. Magnitude 7.9 Wenchuan earthquake struck western Sichuan, China in 2008, caused salient number of geological hazards and caused major vegetation damage. This recovery process could be a very long and fluctuating. And Remote sensing has been an important method of vegetation restoration monitoring. This study aims to use remote sensing technology data to analyze the post-seismic vegetation damage and recovery situation of the 2008 Wenchuan earthquake over years to 2020, and find the relevant factors affecting the restoration of ecological vegetation. This paper examined the vegetation recovery processes following the 2008 Wenchuan earthquake using 16-day interval MODIS normalized difference vegetation index time series from 2000 to 2020. It has been found that the vegetation recovery rate generally increased by years, the entire study area has recovered 49.89% by 2020. In addition, by combining remote sensing imagery and geographic information data, we also found that the heavily affected vegetation areas are mainly located along the southern part of the earthquake surface rupture, where have a very high slope which mainly over 60 degrees. It makes this part having higher probabilities to experiences secondary natural hazards and a fluctuating vegetation recovery rate. Through this research, it can be concluded that remote sensing is an effective method for monitoring vegetation dynamics in a long series. For soil and soil retention and ecological vegetation protection of landslides after the earthquake, it should be more concerned about the areas where have steep slope that over 60 degrees.

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.

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