Study On GIS-based Risk Assessment On Debris Flows Of Bailong Basin

Bailongjiang Basin in Longnan regions of Gansu Province is a major disaster area. The terrain in region is very complex, hilly ditch insurance and debris flow is well developed. Debris flow causes significant losses to the local areas, severely affected the local economic development and mountain area construction. The earthquake in Wenchuan has seriously undermined the stability of the mountain, therefore, it is necessary to establish debris flow risk assessment system after the earthquake, and make more effective measures to reduce the harm caused by debris flow.From the two sides that the inner geological environment and external dynamic environment impact debris flow activity, in-depth analysis of the various factors impacting debris flow activity, and fully taking into account potential material source-lithology, the existing source material-landslide of the debris flow activities, debris flow risk assessment system including 11 factors is established. The division is carried out respectively on the debris flow risk degree in the grid and the watershed as a unit, and the following understanding has been made:1. The impact of debris flow on the local areas:First, endangering towns and villages; Second, endangering agricultural production, such as buring land, hazarding farmland, destroying agriculture and water conservancy facilities; Third, damaging transportion, causing hinder and damage of the roads; Fourth, river hazards, such as blocking rivers, silting up the rivers and reservoirs and so on.2. Based on previous research and field studies,161 debris flow ditches in the study area a total drainage area of more than 1 Km2 are determined.49.69 percent of the debris flow ditch drainage areas are below 3 Km2, mainly in the Bailongjiang sides of Wudu, and the outbreak frequency of debris flow is high.3. The rainfall of different durations has different effects on debris flow activity. The sensitivity analysis on debris flow activity with the rainfall of different durations showes that the spatial distribution law between 6h rainfall and debris flow activities is consistent.4. The debris flow evaluation system hierarchy structure model in the study area using AHP method is constructed, and the two-two comparison for the various factors of each hierarchy made respectively, effectively avoiding human individual subjectivity in the assignment of the individual factors, the integrated weights of the various factors that better objectively reflect characteristics of debris flow activities. In this paper, several typical debris flow ditches are used for the verification of the evaluation results, the results show that:there is a high curvature tolerance degree between the debris flow risk assessment results based on AHP method and matter of fact. It is able to reflect the objective laws objectively, and has strong practical applications.