Research On Characteristics And Comprehensive Control Measures Of Dianchichang Gully Post-fire Debris Flow In Xichang

Post-fire debris flow is a special torrent containing a large amount of loose material,which is closely related to forest fire.Its disaster characteristics are significantly different from those of conventional debris flow.So the prevention and control experience of conventional debris flow is not fully applicable to it.After the fire that broke out on March 30,2020 in Xichang,debris flow occurred frequently in burned area,seriously threatening the safety of local people’s lives and property.It is necessary and urgent to study the characteristics of debris flow after fire and put forward comprehensive prevention and control measures.This study takes Dianchichang gully in Xichang,Liangshan Yi Autonomous Prefecture,Sichuan Province as a typical case.Analyzed the characteristics of burned area and watershed.Studied the characteristics of post-fire debris flow disaster.And proposed the corresponding prevention and control measures.The main conclusions are as follows:（1）The burned area covered 83.37%,seriously burned areas accounted for 33.47%.Layer of ash accumulate extensively on the surface in burned area.The mean value of soil in burned area permeability coefficient is 1.33×10^-5m/s.The mean value of soil permeability coefficient in unburned area is 4.42×10^-5m/s.The decrease of soil permeability coefficient is one of the factors inducing debris flow.（2）The basin area of Dianchichang gully is 1.83km².In the basin,the loose material resources are mainly slope material source,channel material source and landslide material source.The total static reserves are about 684,000 m³.The total dynamic reserves are about160,400 m³.The dynamic reserves of slope provenance are 112,000 m³,which is more than69.83%.It is the main source of post-fire debris flow.（3）The first debris flow occurred about a month after the fire.In the first rainy season,a total of 5 debris flow broke out.Moderate to heavy rainfall is common in the area during several debris flow outbreaks.It reflects that the rainfall threshold of post-fire debris flow is low.And post-fire has the characteristics of abruptness and frequency.（4）Accordingly,the corresponding prevention and control measures were propound as follows.The rapid emergency treatment measures include clarifying dead wood on slope surface,vegetation restoration,and building of simple barrier dams in gully.Medium-term governance measures are debris dams in gully and grit basins.And long-term prevention measures are a combination of forest fire prevention and vegetation protection.This scheme has been implemented in Dianchichang gully.Since the completion of these projects,the effects of comprehensive treatments have been preliminarily proved effective for the mitigation of this type of special debris flow.Effectively intercepted multiple debris flow washouts.It can provide reference for post-fire debris flow prevention in the future.