基于流域演化的泥石流敏感性分析

基于泥石流来源于某些处于特殊演化阶段的分支小流域的理论,分析了面积高程曲线及其参数与泥石流活动的关系。面积高程曲线积分值S表征流域内松散固体物质量,S/2对应的相对高差比值K表征流域源地面积在不同高程的分布,以S和K为参数提出泥石流敏感性分析思路。针对汶川县主要公路(都汶公路和省道303)沿线泥石流敏感性分析,在Arcgis、Matlab等软件的支持下,基于震前1:50 000地形数据,计算了研究区泥石流流域的S和K。根据计算结果,初步判定了各流域的地貌发育阶段,以及流域源地汇水区的高程位置。并根据震后泥石流实际活动情况,对于S小于0.5但又属于震后频发型,或者S值大于0.5但其面积较大且分支较多泥石流沟,进行了次一级子流域的面积高程值计算,判定其易发生泥石流具体源地。最后,根据流域面积高程值S得出了研究区泥石流敏感性分级图,分析结果基本反应了地貌演化对泥石流发生能力的潜在影响。

SENSITIVITY ANALYSIS OF DEBRIS FLOW ALONG HIGHWAY BASED ON GEOMORPHIC EVOLUTION THEORY

Debris flow is one of common disasters in the mountain aera, especially after the richer scale 8.0 earthquake in Wenchuan on 12 May 2008, in Sichuan Provence. A large quantityof loose materials which are caused by earthquake in vally are provided for debris flow. Expiated by heavy rainfall, regional group debirs flow hazards occurs, and causes serious property loses and threatens people's life. So the prediction of debris flow is urgent task now. But the formation of debris flow is so complicated that can't be predicted accurately. Some researchers consider small valley is the most active agent in landscape evolution, and debris flow in it takes the most energetic role in mass transportation. According to A.N.Stranler'S geomorphologic erosion circulation theory, the parameter of a drainage basin's hypsometric integral(S) is used for describing basin geomorphology. Lately the hypsometric integral has become an index to infer activities of disaster in some ravine, and is used to find the source region of debris flow. The paper, based on the theory of debris flow was derived from certain branch watershed which in special evolution stage, the relationship of hypsometric curve and the debris flow activities was anglicized. For the curve, integral value(S) of hypsometric integral curve was characterization of the solid material reserves for debris flow in the ravin. The larger parameter S is the indication of younger geomorphology stage of the ravine, and more rock,soil or other materials can be provided for debris flow. And parameter K which is the elevation ratio corresponding S/2 was characterization of elevation position of the debris flow source area initially. The larger parameter K is the indication of the higher elevation of the cathment area, and also better condition for the water gather for debris flow. As to sensitivity analysis for debris flow along highway in wenchuan county which has been seriously damaged in the earthquake, With the support of spatial analysis function of Arcgis and the matlab software, 1:50 000 terrain data before the earthquake in 2008 is used to calculate the parameter S and K for each debris flow ravine. The results showed landscape development stage of the basin and the elevation of catchment area. According to the actual disaster activity after earthquake, the hypsometric integral value of sub level basin debris flow gully with the features of S below 0.5 but frequent outbreaking, or large area and more branches was calculated. The results were used to discriminate the specific source for the debris flow. And according to S, the debris flow sensitivity were graded determined in the end. Then the potential influence of geomorphic evolution to debris flow activity was explained the results.