Study On The Activity And Susceptibility Of Debris Flow In The Upper Reaches Of Minjiang River Considering Slopes With Different Vegetation Coverag

The upper reaches of the Minjiang River are a serious area for mudslide hazards in China.An assessment of mudslide susceptibility in the upper reaches of the Minjiang River can indicate the location of valleys prone to mudslides and better reduce the hazards caused by mudslides.At present,the assessment of mudslide susceptibility in the upper reaches of the Minjiang River mainly considers environmental factors to establish the index system,but lacks the choice of indicators for the physical sources of mudslides.In this paper,based on the previous work,we add a study on the destabilisation conditions of vegetation cover slopes in the upper reaches of the Minjiang River,and quantify it as an indicator factor in the vulnerability evaluation.(1)533 debris flow gullies in the upper reaches of Minjiang River were identified,and their frequencies and properties were divided.Mainly distributed in the watershed area of 1-10km~2,gully density of 2-2.5km/km~2,slope of 30-40,NDVI of 0.5-0.7 and PGA of 0.15-0.2.Using the elevation-area integral to analyze the activity characteristics of debris flow in the upper reaches of Minjiang River,it is found that 91.3%of debris flow in the upper reaches of Minjiang River is in its prime,and the debris flow in the upper reaches of Minjiang River will continue to be active for a long time to come.(2)The root-soil partition of the upper reaches of the Minjiang River was carried out.The root type of plants in the upper reaches of the Minjiang River contains four types:shallow-rooted fibrous type,medium-deep-rooted horizontal type,deep-rooted horizontal type and deep-rooted vertical type;according to the sieve test results of the bulk soil samples on the slope of each lithological zone,the soil types in the upper reaches of the Minjiang River can be divided into sandy soil and gravel soil;by superimposing the root type partition and soil type partition data,seven types of root-soil zones in the upper reaches of the Minjiang River can be obtained.Shallow root fibrous type-sand soil zone,shallow root fibrous type-gravel soil zone,medium-deep root horizontal type-sand soil zone,medium-deep root horizontal type-gravel soil zone,deep root vertical type-gravel soil zone,deep root horizontal type-sand soil zone,and deep root horizontal type-gravel soil zone.(3)The strength parameters of different root soils at four water contents were obtained by the test,and the potential destabilization zone in the upper reaches of Minjiang River was calculated.The cohesive force of the soil in the sandy soil partition is generally greater than that in the gravel soil partition;the internal friction angle of the soil in the sandy soil partition is usually smaller than that of the gravel soil partition.The cohesion of the soil in the sandy soil partition has been decreasing with the increase of water content,while the cohesion of the soil in the gravelly soil partition generally increases and then decreases,but the change of the internal friction angle is not regular.In the upper reaches of Minjiang River in the natural state,the slope stability is good,but with the rise of water content of the soil,the stability gradually decreases.And the destabilization area of the upper Minjiang River is calculated,and the destabilization area of the upper Minjiang River is mainly distributed in the scrub area.(4)Considering the unstable conditions of slopes covered by different vegetation,the provenance index is condensed,and then the factors such as surface undulation and vegetation coverage are selected as other evaluation indexes,and the evaluation index system of debris flow susceptibility considering the unstable and destructive conditions of slopes in the upper reaches of Minjiang River is established.The weighted information model is used to divide the debris flow susceptibility in the upper reaches of Minjiang River,and the AUC value is 0.795.