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Yu G.,Key Laboratory for Geo hazards in Loess Area | Zhang M.,Key Laboratory for Geo hazards in Loess Area | Cong K.,Gansu Institute of Geo Environment Monitoring | Pei L.,CAS Beijing Institute of Geographic Sciences and Nature Resources Research
Quarterly Journal of Engineering Geology and Hydrogeology | Year: 2015

Critical rainfall thresholds can be the key to ensuring effective debris-flow forecasting. They are significant for the study of the trigger mechanisms of debris flows, for the forecast of the characteristics of future events, and for the development of engineering guidance for mitigation. Using a hydrological approach, we first calculated the flood peak discharge at different frequencies and then the corresponding rainfall thresholds for the initiation of different scales of debris flows in Zhouqu County, China. This was followed by the establishment of a functional relation between the intensity and duration of rainfall events that trigger debris flows of different warning levels in two initial soil conditions (dry and moist). This, in turn, yielded four warning levels and two preliminary warning levels. For the two early soil conditions (dry and moist) in the Sanyanyu Gully of Zhouqu County, the Level I (red) warning values for rainfall triggering debris flow are 56 and 51 mm h-1, respectively; the Level II (orange) warning values are 41 and 38 mm h-1, respectively; the Level III (yellow) warning values are 32 and 30 mm h-1, respectively; and the Level IV (blue) warning values are 24 and 22 mm h-1, respectively. The Level V preliminary warning values are 17 and 16 mm h-1, respectively; and the Level VI preliminary warning values are 10 and 9.5 mm h-1, respectively. The rainfall intensity and duration were found to exhibit a power function relation, I = aDß, where the values of a and ß vary with the warning levels. Rainfall events capable of triggering debris flows in the new thresholds and intensity-duration relations presented here can be used for forecasting purposes and in operational geohazard warning systems. These research results also provide a scientific basis for regional hazard mitigation and reduction in Zhouqu County. © 2015 The Author(s). Source

Peng J.,Changan University | Fan Z.,Changan University | Wu D.,Changan University | Zhuang J.,Changan University | And 3 more authors.
Engineering Geology | Year: 2014

Continuous and heavy precipitation triggered a large loess landslide at the southern Dagou Village of Mapaoquan Town, Tianshui City, Gansu Province of China on July 21, 2013. The landslide debris rapidly turned into a debris flow that was deposited in the ravine mouth with the volume of 1.9×105 m3. Detailed field mapping, three-dimensional laser scanning, aerial photograph interpretation, and laboratory tests were carried out to study the formation and moving characteristics of the landslide and subsequent debris flow. The results showed that: 1) The peak flow velocity and peak discharge of the debris flow were estimated to be approximately 7.2m/s and 730m3/s, respectively. The velocity had a tendency to first increase and then decrease from the head to entrance in the Dagou gully. 2) The analysis of rainfall conditions showed that the effective antecedent rainfall within 7days and hourly rainfall intensity which triggered the slide-debris flows was 239mm and 20mm/h, respectively. Compared with the critical rainfall in this area, the effective antecedent rainfall was found to be more significant in triggering this event. 3) The mean and effective particle sizes were approximately 0.73-1.3mm and 0.036-0.087mm, respectively, and had the same distribution along the gully as the velocity, which confirmed the process of the variation in the flow velocity. 4) The scale amplification was very obvious in the formation and moving process of the slide-debris flows. © 2014. Source

Jiang S.,Water Resources University | Wen B.-P.,Water Resources University | Zhao C.,Gansu Institute of Geo Environment Monitoring | Li R.-D.,Gansu Institute of Geo Environment Monitoring | Li Z.-H.,Gansu Institute of Geo Environment Monitoring
Journal of Asian Earth Sciences | Year: 2016

Slow-moving landslides generally are long-lived and characterized by continuous movement with some fluctuation in sliding rate following changes of environmental factors, such as rainfall and earthquake. Analysis on kinematics of this type of landslide is essential for understanding its mechanism and identifying causal factors controlling its movement behavior. This paper presents a study on kinematics of a giant slow-moving landslide in northwest China, called the Xieliupo landslide, which is about 72 × 106 m3 in volume and has been slowly moving for more than 100 years. This study is conducted using archival high resolution remote sensing images from multi-sources over a period about 43 years and the data from 15-month GPS monitoring. Six sets of multi-source remote sensing images in 1969, 1971, 2004, 2008, 2010 and 2012 with spatial resolution higher than 2.5 m were used, and GPS monitoring data were recorded from September 2012 to December 2013. Obvious geomorphologic changes identified from the images in 1971 and 2004 confirm that this landslide did move slowly in the past. Quantitative analysis reveals that movement of the landslide was persistent and behaved in a block by block mode with the greatest and the least velocities in its middle and lower parts, respectively. Distance measurement between the homologous point pairs on the orthorectified images in 2005, 2010 and 2012 indicates that annual ground displacement of the landslide ranged from 0.52 m to 6.54 m in the seven years. GPS monitoring data shows that the landslide ground displacement in the 15 months varied from 0.49 m to 2.91 m, and annually between 0.39 m and 2.33 m, with a rather uniform movement pattern as identified using the remote sensing images. GPS monitoring results also reveal that the landslide movement is intermittent inter-annually. It is further discussed that movement behavior of the landslide is largely controlled by its topography with great influence of the active fault along its left hand flank and river erosion at its toe. Rainfall may affect inter-annual movement behavior of the landslide. © 2016. Source

Jiang X.,Water Resources University | Wen B.,Water Resources University | Jiang S.,Water Resources University | Feng C.,Water Resources University | And 2 more authors.
Jilin Daxue Xuebao (Diqiu Kexue Ban)/Journal of Jilin University (Earth Science Edition) | Year: 2015

Suoertou landslide, an old giant landslide in Zhouqu County in Gansu Province, has been moving slowly since 1970's. The geological environment indicates that the slow-movement was controlled by behavior of slide's materials under four factors, including weight of the slope, activity of its boundary faults, incision of Bailongjiang river at its toe, and the groundwater within the slope; although only the slope weight has been confirmed for its importance. Based on the field investigation and monitoring data analysis, numerical simulation was adopted to analyze the contribution of the other three factors to the activity rate of the slide. It was found that the creep behavior of Suoertou landslide was mainly controlled by the groundwater and active fault in addition to its rheological nature, in which the effect of rise of water table was great than active fault on the dynamics of the slide. The numerical simulation results showed that Suoertou landslide's dynamic modes were similar with different velocity under different controlling factors. It was also found that when boundary faults were activated, the velocity of Suoertou landslide increased by 20%-47% compared to the condition of only gravity was considered; the landslide's velocity increased with the increasing of water table, the velocity increased by 20%-97% with 1 m rise of the water table. However, the incision of Bailongjiang river had only an influence on the velocity of the front part of the slide, and the amplitude of its velocity had no obvious positive relationship with the flow rate of Bailongjiang river. © 2015, Jilin University Press. All right reserved. Source

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