Regional Debris Flow Risk Assessment Based On GIS And Logistic Regression Model

Kangding and Luding are located in the eastern edge of Qinghai-Tibet Plateau. They belong to the most deep canyon area of plateau and mountains in western Sichuan with high mountain and steep slope. This area belongs to the intersection among Xianshuihe, Longmenshan and Anninghe fault zones which are best known in Sichuan province. In the region, seismic intensity is with high frequency and strength, new tectonic movement is strong, rock is cracked, there are much loose solid materials. Debris flow disaster is well developed under the multiple effects of the earthquake, strong rainfall and human activity which poses a great threat to the local people's life and property security. So this paper chooses Kangding and LuDing as the study area to do the debris flow hazard assessment through the in-depth analysis of development characteristics and formation mechanism of debris flow. Which can provide important evidence for local disaster assessment and early warning forecast. It also has the important scientific significance and practical value to safeguard the people's life and property safety and the security implementation of the national major project.In this article, occurrence mechanism of debris flow disasters in the study area is explored, factor of evaluation with high impact to debris flow hazards is identified, the database of initial evaluation factors is made by the evaluation unit of basin. The factors with high impact to hazards occurrence are selected by using the stepwise regression method of logistic regression model, at the same time the factors with low impact are eliminated, then the hazard evaluation factor system of debris flow is determined in the study area. Then every factors of evaluation factor system are quantified, and the weights of all evaluation factors are determined by using the analysis of stepwise regression. The debris flows hazard assessment and regionalization of all the whole study area are achieved eventually after establishing the hazard assessment model. In this paper, a regional debris flows hazard assessment method with strong universality and reliable evaluation result is presented. The main contents and conclusions are as follows.(1) The natural geography and regional geological environment features in the study area are analyzed based on literature research and field survey. The features of space-time distribution and formation mechanism of debris flows are illustrates in detail.(2) Based on DEM, sub basin units under the condition of many thresholds are extracted through the steps of depression calculation and filling, flow direction extraction, flow accumulation calculation, river network extraction and sub-basins division using the hydrological analysis module of ArcGIS 10.2. Then they are loaded into Google Earth to overlay with it's three-dimensional phase real terrain. As a result, the whole study area is divided into 1674 units by automatically extracting and artificial identification.(3) The system of debris flow influence factors in the study area is built based on the four conditions of debris flow formation. The geological conditions include formation lithology, fault density, seismic intensity and morphological information entropy. The geomorphic conditions include drainage area, surface rolling degree, slope and valley cutting density. The rainfall include mean annual precipitation and annual precipitation variation coefficient. In addition, vegetation cover condition use normalized difference vegetation index (NDVI). The 11 factors are selected as the initial assessment factors of debris flow hazard assessment in the study area.(4) The factors with high impact to hazards occurrence are selected by using the stepwise regression method of logistic regression model, at the same time the factors with low impact are eliminated, then the hazard evaluation factor system of debris flow is determined through the collinearity diagnostics of factors in the study area. The factors are seismic intensity, surface rolling, slope and mean annual precipitation.(5) The factors of the evaluation index system are quantified using the method of standardized watershed unit amount ratio. The relationship between debris flow occurrence and each evaluation factor is simulated using logistic regression model. The weights of evaluation factors are determined, and the model of debris flows hazard assessment is established in the study area.(6) Debris flow hazard evaluation is done in the evaluation unit of drainage basin in the study area, and debris flow hazard degree is zoned according to the standard of debris flow hazard zoning. The result shows that 25 basins are determined as highest danger zone,96 basins are determined as high danger zone,147 basins are determined as middle danger zone, 158 basins are determined as low danger zone,1248 basins are determined as very low danger zone. It can be seen that the zoning result of debris flow hazard evaluation mainly consists with the actual situation by the analysis of classification results. Which can better reflect the present situation and activities trend of the debris flow.