The river blockage characteristics of “8·20” large-scale debris flow and the hazard prediction in Banzi gully in Miansi Town，Wenchuan County
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摘要:
汶川地震后，板子沟曾发生过多次大规模泥石流，尤其是2019年“8·20”泥石流对沟口的道路桥梁以及村寨造成了严重的破坏，将主河道向对岸严重挤压，今后仍存在较大堵河的风险。文章在野外调查以及对泥石流基本特征和形成条件综合分析的基础上，分析了堵河特征，计算了不同频率下泥石流的堵河参数，并预测了各频率下溃决洪水对绵虒镇可能产生的影响。计算结果表明，频率为2％、5％和10％的泥石流造成岷江堵塞的可能性较小，假设发生堵河事件，绵虒镇也不会受到溃坝洪水的危害。频率为1％的泥石流很可能造成主河堵塞。体积约57.38×104 m3的泥石流物质可以到达岷江，形成高度约为51.61 m的堰塞坝。在主河洪水的作用下，堰塞坝发生溃坝，溃坝洪水的峰值流量为5 935.49 m3/s，到达绵虒镇后降至2 312.25 m3/s。由于相应的洪水深度（4.00 m）大于防护堤的高度（3.50 m），因此溃坝洪水很可能会对绵虒镇防护堤附近民房造成破坏。为今后大型泥石流堵河特征的分析，以及溃决洪水对下游城镇可能造成的影响提供了参考。
Abstract:After Wenchuan earthquake, many large debris flow have occur in Banzi Gully. Especially in 2019, the "8·20" debris flow caused serious damage to the roads, bridges and villages in the gully mouth, mail river was seriously squeeaed to the other side and there is a big risk of blocking the river in the future. Based on the field investigation and comprehensive analysis of the basic characteristics and formation conditions of the debris flow, the characteristics of river blockage are analyzed, the parameters of river blockage under different debris flow frequency are calculated, and the possible impact of dam-breaking flood under each frequency on Miansi Town is predicted. The results show that debris flow with frequencies of 2%, 5% and 10% are less likely to cause river blockage of Min River, and if there was a river blocking event , the town of Miansi would not be exposed to dam-breaking flood. The debris flow with a frequency of 1% are likely to cause river blockage. The debris flow material with a volume of 57.38×104 m3 can reach the Min River to form a dam with a height of about 51.61 m. Under the action of the main river flood (1890.0 m3/s), the dam will be broken, and the peak flow rate of the flood was 5935.49 m3/s, which dropped to 2312.25 m3/s while arrive at Miansi Town. Since the flood depth (4.00 m) is higher than the height of the protective embankment (3.5 m), the flood is likely to damage the houses near the protective embankment of Miansi Town.This paper provided a reference for the analysis of the characteristics of large-scale debris flow blockage in the future, as well as the possible impact of the collapse flood on downstream towns.
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Key words:
- Banzi gully /
- debris flow /
- river blocking /
- dam-breaking flood /
- hazard prediction
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表 1 板子沟泥石流基本运动参数计算结果
Table 1. Calculation results of the basic motion parameters of debris flow in Banzi gully
计算内容 参数 单位 频率 1% 2% 5% 10% 容重计算 
t·m−3 1.70 1.62 1.50 1.42 流速计算 
/ 12.50 12.50 12.50 12.50 
/ 0.74 0.59 0.44 0.34 
t·m−3 2.60 2.60 2.60 2.60 
m 6.10 4.05 2.02 1.32 
/ 0.23 0.23 0.23 0.23 
m·s−1 10.64 8.70 5.95 4.78 洪峰流量计算 
mm·h−1 38.54 35.02 30.10 26.4 
/ 0.93 0.93 0.93 0.93 
/ 0.88 0.87 0.85 0.84 
/ 2.79 2.63 2.39 2.20 
h 2.75 2.84 2.98 3.11 
m3·s−1 197.32 173.81 143.22 119.76 泥石流流量计算 
/ 3.00 2.80 2.60 2.40 
m3·s−1 1028.15 776.17 535.98 385.27 一次冲出总量计算 
s 3600 3600 3600 3600 
104 m3 97.72 73.77 50.94 36.62 
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表 2 形态调查法泥石流流量计算结果
Table 2. Results of flow calculation by morphological investigation method of debris flow in Banzi gully
断面
位置断面高程
/m沟道宽度
/m平均泥深
/m过流面积
/m2平均流速
/(m·s−1)峰值流量
/(m3·s−1)断面1 1255 71 2.1 149.1 4.74 707.39 断面2 1263 70 2 140 4.77 667.49
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表 3 不同频率下泥石流堵河参数计算结果
Table 3. The calculation results of river blockage parameters at different frequencies
P/% 
/(t·m−3)
/(m3·s−1)
/(m·s−1)
/(m3·s−1)
/(m·s−1)
1 1.70 1028.15 11.70 1890 5.40 2.00 2 1.62 776.17 9.57 1890 5.40 1.18 5 1.50 535.98 6.54 1890 5.40 0.52 10 1.42 385.27 5.26 1890 5.40 0.28
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表 4 其他堵河公式计算结果
Table 4. The calculation results of the river blockage parameters at different frequencies
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表 5 不同频率下泥石流堵河高度计算结果
Table 5. The calculation results of the height of river blockage at different frequencies
P/% 
/m3
/m
/m
/m
/m3
/m3
/m1 97.72 18.20 243.47 273.04 40.33 57.38 51.61 2 73.77 16.95 221.76 248.65 31.15 42.61 44.48 5 50.94 15.47 196.10 219.81 22.23 28.71 36.51 10 36.62 14.30 175.74 196.94 16.49 20.12 30.56
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表 6 不同频率下堰塞坝溃坝洪水计算结果
Table 6. The calculation results of dam-breaking flood with different frequencies
P/% 
/m
/(m3·s−1)
/(m3·s−1)
/m3
/104m3
/(m·s−1)
/m1 51.61 5935.49 2312.25 285.26 3.64 7.24 4.00 2 44.48 4760.71 1704.09 199.88 3.06 6.45 3.31 5 36.51 3555.03 1108.91 121.37 2.39 5.47 2.54 10 30.56 2735.38 725.68 74.38 1.86 4.64 1.96
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为表示泥石流堵塞度；
为爆发频率；
在为沟口主河宽度；
为泥石流流量；
为主河流量；
为支沟纵比降；
为主河纵比降。
为表示泥石流堵塞度；
为泥石流入汇角；
在为沟口主河宽度；
为泥石流流量；
为主河流量；
为支沟纵比降；
为主河纵比降；
为泥石流容重。
图(7)
表(6)
计量
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