Process and characteristics of “7·5” Huangniba gully debris flow in Muli County of Sichuan Province and and prevention suggestions
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摘要:
2021年7月5日项脚沟七条支沟在连日降雨的情况下相继暴发泥石流灾害，因群测群防体系的高效运转，避免了20户118人因灾伤亡和1421万元的经济损失，实现了成功避险。黄泥巴沟是暴发泥石流的支沟之一，流域面积14.47 km2，此次灾害中冲出物规模12×104m3，损毁房屋数间。黄泥巴沟在2020年“3·28”森林火灾中地表植被焚毁严重，导致其泥石流孕灾环境发生剧烈变化，在鲜有泥石流活动的背景下，于2020年和2021年数次暴发泥石流灾害。通过实地调查，得出发生剧烈变化的泥石流孕灾环境和沟口外村寨旧有布局格式之间的矛盾是导致下坪子村受灾严重的关键原因，然后推断整个灾害过程：先前暴发的泥石流冲出物堵塞村寨中部沟渠，随后流出的山洪因无法顺畅排泄而发生大面积漫流，导致村寨所受损失倍增。首要的治理措施是修建一条连接沟口与主河的排导槽并重新规划村寨布局，使泥石流可以顺畅的排泄到主河之中并且使村寨建筑远离泥石流的直进范围。最后分析了此次群防群测体系的成功实践，总结经验以供参考。
Abstract:On July 5, 2021, debris flow disasters broke out in the seven branch ditches of Xiangjiao gully under the condition of consecutive days of rain. Due to the efficient operation of the mass prediction and disaster prevention system, 20 households with 118 casualties and 14.21 million yuan of economic losses were avoided. Huangniba gully was one of the tributaries of debris flow outbreaks, with a drainage are of 14.47 km2. The scale of the debris flow flushed out objects was 12×104 m3, and several houses were damaged. During the "3·28" forest fire in 2020, the surface vegetation in Huangniba gully was severely burned, which led to dramatic changes in its debris flow disaster-pregnant environment. In the background of few debris flow activities in Huangniba gully, debris flow disasters broke out several times in 2020 and 2021. Through field investigation, it was concluded that the contradiction between the drastically changed disaster-pregnancy environment of the debris flow and the old layout of the villages was the key reason for the serious disaster in Xiapingzi Village. The entire disaster process is as follows: after the debris flow blocked the internal ditches of the village, the outflowing mountain torrents were not able to be discharged smoothly, causing a large area of flooding, which caused doubled the losses to the village. The primary treatment measures were to build a drainage channel connecting the ditch mouth and the main river and re-plan the layout of the village, so that the debris flow can be smoothly discharged into the main river and the village buildings were kept away from the direct range of the debris flow. Finally, the successful practice of the mass people monitoring and prevention system was analyzed, and the experience was summarized for reference.
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表 1 黄泥巴沟流域山坡坡度分级统计
Table 1. The slope classification statistics of Huangniba gully
项目 山坡坡度/（°） 合计 <15 15～25 25～35 ＞35 地表面积/km2 1.42 4.22 4.98 3.85 14.47 所占比例/% 9.8 29.1 34.4 26.7 100 
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表 2 沟道断面尺寸表
Table 2. Channel section size table
断面名称 宽度/m 深度/m 断面1 4 3.5 断面2 9 4.2 断面3 9.5 4.8 断面4 10.2 3.8
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表 3 形态调查法计算结果
Table 3. Calculation results of the morphological survey method
参数 Q/（m3·s−1） A/m2 V/（m·s−1） nc R/m I 取值 70.988 15.6 4.458 0.1 1.381 0.129
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表 4 黄泥巴沟梯形排导槽设计表
Table 4. The parameters of the trapezoidal drainage canal for Huangniba gully
参数 Q
/（m3·s−1）M I b
/mD10
/mmD50
/mmh
/m取值 70.99 6.95 0.074 3.52 1.175 20.58 3.28
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