Field Investigation and Research on Giant Debris Flow on August 14, 2010 in Yingxiu Town, Epicenter of Wenchuan Earthquake
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摘要: 2010年8月14日强降雨过程导致汶川震区映秀镇红椿沟泥石流暴发, 泥石流堰塞堆积体堵断岷江主河道, 导致河水改道冲入映秀新镇, 引发洪水泛滥; 造成映秀镇13人死亡、59人失踪, 受灾群众8 000余人被迫避险转移.由于这场泥石流灾害发生在汶川地震震中区, 是地震与降雨共同作用下的结果, 研究其形成与成灾过程对于进一步认识强震区泥石流发育特征具有重要的意义.根据现场调查和航空图像解译, 分析了红椿沟泥石流流域特征, 特别是地震条件下的泥石流物源特征, 在此基础上讨论了泥石流起动过程和堆积过程.红椿沟泥石流典型实例表明了汶川震区泥石流已进入一个新的活跃期.因此, 应该开展对汶川地震区的泥石流风险评估和监测、早期预警等研究, 采取有效的工程措施控制泥石流的发生和危害.Abstract: A rainstorm triggered debris flow hazard occurred in Hongchun valley, Yingxiu town, epicenter of the Wenchuan earthquake on August 14, 2010. This event transported huge material sediment to the watercourse of the Minjiang River and produced a natural dam, resulting in flash flood in the new Yingxiu town. The flood claimed 13 lives, with a further 59 listed as missing. About 8 000 local residents were rapidly evacuated from their homes. The debris flow resulted from the coaction of the rainfall and earthquake. Therefore, it is significant for better understanding of development characters of debris flows to conduct the research on the initiation and movement process in high seismic intensity area. This paper studies characteristics of the initiation conditions and depositional fans of the debris flow based on field reconnaissance and interpretations of aerial photographs, focusing on loose sediment supply in source areas of debris flows. On the basis of the above analysis, the initiation and deposition process of debris flows are discussed. The catastrophic event indicates that the areas impacted by the Wenchuan earthquake become more prone to debris flow occurrences in the future. So it is important to assess debris flow risk and take measures to enhance hazard monitoring and offer early warnings for debris flows in the earthquake areas. The control work is also necessary for debris flow hazard mitigation.
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Key words:
- debris flow /
- barrier dam /
- inundation /
- Wenchuan earthquake /
- Yingxiu town
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图 1 摄于2008年5月18日的航空影像反映的红椿沟泥石流流域特征及地震诱发的滑坡特征
Fig. 1. Aerial photograph taken on 18 May, 2008 shows the drainage area of the Hongchun debris flow and characterization of the earthquake induced landslides
图 2 泥石流暴发前后映秀镇降雨累积
Fig. 2. Cumulative curve of rainfall prior to and after debris flow occurrence in the Yingxiu town
图 3 泥石流起动区的滑坡体被表层水流冲蚀成的沟道
Fig. 3. Surface-flow eroded the gully in the landslide deposits of debris flow initiation area
图 4 H1滑坡溃决后的沟道特征
Fig. 4. Channel features after outburst of H1 landslide in debris flow basin
图 5 红椿沟泥石流发生前后堆积扇特征
a.泥石流发生后形成的大型堆积扇，阻断岷江河道，掩埋公路；b.泥石流发生前的老堆积扇
Fig. 5. Depositional characteristics of the Hongchun valley prior to and after "8·14"debris flow occurrence
图 6 摄于2010年8月15日的航空照片反映了红椿沟泥石流扇及其壅塞堆积体，以及映秀新镇洪水泛滥灾情(由四川省地质环境监测总站提供)
Fig. 6. Aerial photo taken on August 15, 2010 shows the Hongchun debris flow fan and natural dam, and inundation in newly reconstructed Yingxiu town
图 7 映秀新镇被洪水泛滥，洪水水深2.0~3.5 m，水淹时间长达7日
Fig. 7. Newly reconstructed Yingxiu town was flooded due to debris flow dam. Flood water-depth was estimated at 2.0-3.5 m and flood duration lasted 7 days
图 8 泥石流搬运的最大巨石，其长、宽、高分别为8.5 m×4.5 m×4.0 m
Fig. 8. Maximum size boulders with length, width and height of 8.5 m×4.5 m×4.0 m, transported by debris flow
表 1 映秀镇红椿沟“8·14”特大泥石流总量计算
Table 1. Calculated results of total volume of debris flows
堆积扇总面积(m2) 壅塞体面积(m2) 壅塞体度(m) 壅塞体泥砂量(104 m3) 扇体上段堆积面积(m2) 扇体上段堆积厚度(m) 扇体上段扇堆积泥砂量(104 m3) 泥石流总量(104 m3) 96 510 49 700 7~9 39.7 78 500 2.0~6.0 31.4 71.1 
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表 2 泥石流容重计算
Table 2. Calculation of densities of debris flows
P2(%) P05(%) γd(g/cm3) C 断面1-1' 67.1 8.6 2.07 0.629 断面2-2' 75.4 5.1 2.03 0.606 平均 71.25 6.85 2.05 0.618
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表 3 泥石流的运动速度、流量和总量计算
Table 3. Calculation of velocity, discharge and volume of debris flows
R(m) S D50(mm) D10(mm) A(m2) V(m/s) Q(m3/s) T(s) Wc(104 m3) Ws(104 m3) 断面1-1' 1.15 0.15 3.7 0.08 86.0 8.67 745.76 5 400 80.5 49.7 断面2-2' 2.61 0.16 4.3 0.25 88.7 7.85 696.45 5 400 75.2 46.5
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