Cause and prevention model of typical river-blocking debris flow disaster: A case study of Qingjia gully debris flow in Pingwu County
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摘要:
为探寻典型堵河型泥石流致灾和防治模式，以涪江流域中上游典型堵河型泥石流卿家沟为例，通过调查走访、实地测量、综合论证等方法，总结出了典型堵河型泥石流4种主要致灾模式: 主河上游淹没及次生灾害、主河下游洪水及次生灾害、主河异岸冲蚀和淹没、泥石流沟口渐进式后退淤堵。基于该型泥石流的基本特征和致灾机理，提出了两种防治模式: 一是中上游拦砂固源，沟口原沟排导模式; 二是堆积区沟道改移防治模式。结果表明，两种模式在防灾技术层面上均具有较高的可行性。研究可为堵河型泥石流灾害的防治提供新的视角和方法，对类似特征泥石流灾害防治具有借鉴意义。
Abstract:In order to explore the cause and prevention model of typical river-blocking debris flow disaster, the authors took Qingjia gully debris flow, a typical river-blocking debris flow in the middle and upper reaches of Fu river basin as a study case, and adopted the investigation, field measurement, and comprehensive analysis methods. Four main disaster-causing modes of typical river-blocking debris flow were summarized, including upstream inundation and secondary disaster, downstream flooding and secondary disaster, cross-shore erosion and inundation of the main river, and progressive retreat and siltation in the debris flow channel mouth. Two prevention and control models were proposed based on the fundamental characteristics and disaster-causing mechanisms of this type of debris flow. The first model is sediment interception and source stabilization in the middle and upper reaches, and original channel diversion at the mouth of the gully. The second model is deposition area channel relocation and control. The results show that both models have high feasibility at the technical level of disaster prevention. This study could offer new perspectives and methods for the prevention and control of river-blocking debris flow disasters, and has significant reference value for the prevention and control of debris flow disasters with similar characteristics.
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表 1 研究区不同设防频率下雨强值
Table 1. Rainfall intensity calculation results for different fortification frequencies in the study area
频率P/% 平均值/(mm·h-1) 变差系数Cv1 模比系数Kp 设计雨强/(mm·h-1) 1 2.872 57.44 2 2.522 50.44 5 20 0.53 2.050 41.00 10 1.696 33.92 20 1.336 26.72 
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表 2 卿家沟泥石流流量
Table 2. Debris flow discharge calculation for Qingjia gully
频率P/% 泥沙修正系数φ 暴雨洪水流量QP/(m3·s-1) 堵塞系数Dc 泥石流洪峰流量Qc/(m3·s-1) 1 0.67 55.57 2.5 231.56 2 0.67 47.02 2.5 195.93 5 0.67 35.86 2.5 149.40 10 0.67 27.78 2.5 115.74 20 0.67 19.90 2.5 82.93
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表 3 泥石流过流量和固体物质冲出量
Table 3. Debris flow excess flow and solid matter flushing output
频率P/% 泥石流过流量Q/104 m3 固体物质冲出量QH/104 m3 1 14.67 5.87 2 12.41 4.97 5 9.47 3.79 10 7.33 2.93 20 5.25 2.10
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表 4 根据流量堵塞涪江判别结果
Table 4. Assessment results for Fu river blockage based on discharge
频率/% 主河单宽流量QM/(m3·s-1) 泥石流单宽流量QB/(m3·s-1) 交角θ/(°) 判别系数CF 2 5 16.33 90° -6.36 5 5 12.45 90° -6.09
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表 5 根据规模堵塞涪江判别结果
Table 5. Assessment results for Fu river blockage based on scale
主河水面宽B/m 水下安息角φw/(°) 沟口原堆积扇或岸坡的坡度α/(°) 泥石流堆积体纵坡φc/(°) 主河水深h/m 三角形堵河所需泥石流体积Qs/m3 30 18° 6° 4.5° 2.5 5 952.94
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表 6 拦砂坝设置基本情况
Table 6. Basic information of sediment storage dam design
有效坝高/m 回淤面积/m2 回淤长度/m 库容/104 m3 15 8 929 114~130 5.09
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表 7 设坝后下游排导工程流量设计参数
Table 7. Downstream conveyance project flow parameters after dam design
频率P/% 泥石流重度γc/(t·m-3) 泥沙修正系数 堵塞系数Dc 泥石流洪峰流量Qc/(m3·s-1) 2 1.660(1.50) 0.67(0.43) 2.5(1.8) 195.93(121.44) 5 1.660(1.50) 0.67(0.43) 2.5(1.8) 149.40(92.60) 注: “()”内为设置拦砂坝后下游泥石流流量特征参数。
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表 8 不同泥石流治理模式优缺点对比表
Table 8. Comparison table of advantages and disadvantages of different debris flow prevention and control models
治理方案 治理效果 经济性 优点 缺点 中上游拦砂固源、沟口原沟排导模式 拦砂固源条件较好时，两者相当; 条件较差时，模式二更优 模式一多设拦砂坝，后期仍需定期清淤。模式二改沟长度一般短于原自然沟道，排导工程长度更小。模式一工程建设和维护成本一般较高 ①治理工程几乎不改变原沟道位置和形态;
②治理工程征地协调工作难度小①工程建设规模大，拦砂坝需定期清淤，工程建设和维护成本较高;
②中上游拦砂固源工程布设条件较差时，仍存在堵河风险;
③交汇角改变幅度小，主河水动力条件差，主河宽度窄，除减少固体物质冲数量外，其余堵河基本要素改变有限堆积区沟道改移防治模式 ①改沟后纵坡较陡，堆积区淤积条件改善;
②改沟后交汇角大幅减小，主河变宽，主河水动力条件更强，泥石流堵溃主河情况得到根本改善;
③改沟方案圬工量小，维护成本低①改沟可能占用房屋或耕地，拆迁或征地难度较大;
②改沟后需要对原沟道进行复垦，耕地占补平衡手续复杂
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