| Debris flow gullies of Longtangou Watershed in Miyun is more active in recent years.The debris flow was triggered by heavy rainfall respectively in July 24,2011,July 15,2013 and August 12,2016.Through successively detailed investigations on Longtangou Watershed,it was found that Longtangou Watershed had the characteristics of broken terrain,complex landform conditions,big difference of elevation,long river course and low flood discharge stand,which lead to frequent occurrence of the debris flow.At the same time,human irrational activities led to local ecological deterioration,vegetation degradation and provenance accumulation in the gullies,which made it easily to cause debris flow and brought great threat to the local people's lives and property security.So in this paper,three typical debris flow gullies of Longtangou Watershed in Miyun are selected to analyze their features;risks of the debris flow gullies are calculated by Liuxilin Method and the corresponding prevention and cure suggestion are put forward at the same time,which provide theoretical and technical support for the prevention and control of debris flow in this area.The main conclusions are as follows:1,The average slope of the hillside is 42.1 °;Most of the valleys display as morphology;minor gullies display as "U" morphology in the circulation area.Downward erosion depth of the trench bed is about 1.0m-2.0m.Provenance's type and quantity in three gullies are all extremely rich,containing slope wash,landslide,collapse,trench bed accumulation,old debris flow deposits accumulation,soil layer and broken bedrock.The provenance quantity in Lishuyu Gully,Aiwa Gully and Caozhuangzi Gully are respectively 280,300m3,143,100m3 and 145,700m3;Rainfall is an important condition triggering debris flow.In Longtangou watershed,rainfall conditions triggering debris flow are analyzed by the method of obtaining maximum rainfall at successive n hours,I=40.0D-0.33,C=40.0D0.67.2,Through analyzing the flood marks and samples obtained in field investigation,it is obtained by calculation that the debris flow's bulk density in Longtangou Watershed is between 1.90 and 1.98 g/cm3,and they all belong to viscous debris flow with velocity distributing in 2.56?2.75m/s;every gullies's peak discharge of a storm is between 50.91?98.64m3/s and the corresponding total solid amount dashing out at one time is 26,900?59,400 m3.3,The determining factors and the influencing factors of the debris flow bursting are made the principal component analysis by the SPSS software,ascertaining the weigh of the factors including of 9 influencing factors namely the main ditch length,the development stage,the average slope,the ultimate balance coefficient,the shape coefficient,the maximum rainfall of 3h,the lithology of the formation,unstable ratio of the ditch bed ratio,etc.and 2 determining factors namely frequency of occurrence,gullies solid matter coefficient of the debris flow).The risk degree of the three main debris flow gulliess in the Longtangou watershed is calculated:the 3 debris flows are in the prime stage(0.442,0.532,0.395,respectively)and have high risk(0.6248,0.6293,0.6060,respectively),which seriously threaten the local people's production and life.4,In view of the present situation of Longtangou Watershed,the prevention suggestion is put forward that it should mainly combine geotechnical engineering measures and biological measures,with monitoring system aided.Geotechnical engineering adopts "stability,interception and discharge"as principle;Biological engineering focuses on hillsides closed off for forest conservation,restoring local ecology and making full use of functions,such as precipitation retention,soil and water conservation and runoff regulation;and so as to restrain the occurrence of debris flow or reduce the size of debris flow.In this paper,debris flow disaster monitoring system and watershed monitoring station were put forward to establish,which will provide information technology support for local people. |
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