北京怀柔7·16暴雨泥石流发育特征与形成机理

CHARACTERISTICS AND MECHANISM OF THE RAINSTORM-INDUCED DEBRIS FLOW ON JULY 16 IN HUAIROU,BEIJING

2018年7月16日北京怀柔云蒙山地区突发山洪泥石流灾害,国道G111和省道S310多处毁损,周边4个乡镇506人被迫紧急转移。本文通过灾害发生前后高清卫星影像解译和现场详细调查,研究了区域内典型泥石流沟的地形地貌特征和松散固体物质来源,分析了泥石流形成的降雨激发条件,估算了容重、流速、流量等重要参数,并基于沟床块石稳定性分析改进了泥石流启动与降雨强度之间的关系式。研究表明,怀柔7·16泥石流属极端气象条件下短历时强降雨所激发的稀性泥石流,在连续2h降雨条件下,其临界激发雨强不低于8~15mm·h^(-1),物源主要来自于沟床堆积物的揭底输移,沟床岸坡松散堆积体侧蚀增加了物源补给,强降雨条件下很可能再次发生类似规模的泥石流。该研究可对今后区域内泥石流的防灾减灾工作提供参考。

On July 16,2018,a large debris flow occurred in the Yunmeng Mountain region of Huairou district,Beijing.The event seriously destroyed two downstream highways of G111 and S310,forced an emergent transfer of 506 people in adjacent 4 towns.This paper interprets the high-resolution satellite images of pre-and post-event and in-situ investigation,and studies the geomorphologic and geologic characteristics of two typical debris flow gullies and the sources of solid materials,analyzes the rainfall condition of debris flow initiation,calculates the major parameters such as bulk density,flow velocity and total amount of the primary process,and deduces a quantitative relationship between the initiation of debris flow and the rainfall intensity on the basis of stability analysis of gully blocks.The results reveal that“7·16”event belongs to dilute debris flow triggered by the short-time heavy rainfall.Under continuous rainfall for 2 hours,the critical rainfall intensity that could trigger debris flow is no less than 8~15mm·h^(-1).The solid materials of debris flow are mainly sourced from the gully-bed erosion and the lateral erosion.It suggests that debris flow of same type and scale can be very likely to take place under similar rainfall conditions.The study can provide a useful reference for future hazard prevention and mitigation.