四川省小流域泥石流危险性评价

Hazard Assessment of Debris Flow in Sichuan Province

泥石流危险性评价是泥石流防灾减灾的重要内容。本文以四川省为研究区,以DEM为数据源,通过提取水流方向,计算汇流累积量,实现四川省小流域划分。基于收集的已查明泥石流流域资料,分析了泥石流孕灾环境与成灾特点,选择流域高差、流域面积为指标,建立基于能量条件的潜势泥石流流域判识模型,对划分的小流域进行判识,识别出7798个小流域具备泥石流发生所需能量条件,面积为31.1×104km2,占四川省总面积的64.18%。进而建立了泥石流危险性评价指标体系和可拓物元模型,开展了小流域泥石流危险性评价,划分了危险度等级,得到中度、高度、极高危险区的小流域个数分别为1946、1725和1002个,面积分别为9.1×104、7.7×104和3.4×104km2,中度以上危险区面积共20.2×104km2,占四川省总面积的41.67%。最后对评价结果可靠性和各等级泥石流危险区在各地市级行政区、各大流域的分布进行了分析。其结果对促进泥石流判识与危险性评价理论,区域泥石流防灾减灾与山区可持续发展等具有重要的理论和现实意义。

Hazard assessment is important for the prevention and mitigation of debris flow disaster. This study takes Sichuan Province as the research area. Based on the DEM data, we realize the demarcation of the small watershed in Sichuan Province by extracting the direction of water flow and calculating the accumulation of the flow confluence. Based on the collected information of debris flow watershed, we selected the watershed elevation difference and watershed area as the indicators. The identification model of potential debris flow watershed based on the energy condition was built by analyzing the hazard-formative environment and characteristics of debris flow hazards. A total of 7798 small watersheds with the required energy conditions for debris flow occurring were identified by utilizing the established model among all the demarcated small watersheds, which is 31.1 ×10^4 km^2 accounting for 64.18% of the total area of Sichuan Province. The indicator system of debris flow hazard risk assessment and the extension matter-element model were established from the energy condition of the debris flow occurring, the condition of the loose solid materials, the precipitation condition and the condition of human activity. These determine the weights of the assessment factors, of dividing the grade of the hazard risk, by which it classifies the hazard risk degree of small watershed debris flow. The number of the moderate, high and very high hazard degree is 1946, 1725 and 1002, with an area of 9.1×10^4 km^2, 7.7×10^4 km^2 and 3.4×10^4 km^2, respectively. The total area of moderate hazard areas is 20.2×10^4 km^2, accounting for 41.67% of the total area of Sichuan Province. Finally, the analyses were made for the reliability of assessment results and the distribution of the different hazard degree of debris flow areas in different municipal administrative districts and the major river valleys. All the known small watershed of very high hazard degree are identified as debris flow watersheds. The 896 watersheds of moderate hazard degree do not belong to the identified debris flow and 1233 watersheds of high hazard degree do not belong to the identified debris flow, either. They are the key area for disaster prevention and reduction in Sichuan province in the next few years. The results of the analyses have the great theoretical and practical significance for enhancing the debris flow identification, the prevention and mitigation of regional debris flow disaster. The sustainable development of mountainous areas and also the theory of the risk assessment of debris flow hazard.