北京市密云区典型泥石流侵蚀过程分析

Erosion processon of a typical debris flow in Miyun County,Beijing

泥石流运动过程伴随着剧烈的侵蚀,导致其洪峰流量增加、规模增大、破坏性增强。本文以2016年8月12日北京市密云区龙潭沟景区曹庄子沟泥石流为例,通过野外调查和地形扫描分析了该场泥石流的动力侵蚀过程。结果表明:激发该场泥石流的降雨重现期达到20年一遇,为典型短历时、高强度降雨;泥石流体中缺乏黏性颗粒,主要以砂粒为主,但容重达到黏性泥石流标准,为典型高容重、低黏度泥石流体。泥石流侵蚀作用一开始并不剧烈,但随着泥石流运动,这种侵蚀作用增强,导致沟道侵蚀深度增加;沟道中弯道处和地形急变段受到泥石流侵蚀作用最为剧烈,尤其是地形急变段对泥石流的侵蚀作用具有加强效应;侵蚀率与流速同步变化,并且与泥石流体所产生的剪切力呈正相关关系。林木能够降低泥石流流速,消耗泥石流动能,进而减小泥石流破坏性。由于天然条件下的泥石流侵蚀过程研究较少,本文中侵蚀率与地形变化的关系以及泥石流体剪切力的正相关关系为泥石流防治规划设计和该类泥石流的预测预报提供了案例和思路。

The strong erosion during debris flow passage can result in the amplification of peak discharge and flow magnitude,and can consequently increase the damage of debris flow. In this paper,the erosion process of a debris flow was analyzed through field investigations and topography digitization. The debris flow,occurred on 12 August 2016,was located in Caozhuangzi watershed,Miyun County,Beijing. The results found that the triggering rainstorm was 20 years＇ recurrence,and characterized by short duration and high rainfall intensity. The debris flow has high density,low viscosity and few clay components. The erosion process of the debris flow is characterized by progressive pattern,but its extent increases afterwards as the debris flow travels downstream,leading the increase of erosion depth. The most severely eroded sections are located in the wandering areas and the areas where the changes of topography are abrupt. In particular,the abrupt change of channel topography can greatly enlarge the erosion capability of debris flows. The yield rate changes simultaneously with the flowing velocity and the shear stress. The forest at the outlet greatly minimizes the debris flow velocity and reduces the kinematic energy and damage. As studies on the erosion process of natural debris flows are still limited,the relationship among topography change,shear stress and yield rate can provide support for debris flow mitigation and predication.