汶川震区典型泥石流动态演变特征研究——以绵竹市走马岭泥石流为例

TEMPORAL EVOLUTION OF TYPICAL DEBRIS FLOWS IN WENCHUAN EARTHQUAKE AREAS:CASE STUDY OF ZOUMALING-GULLY DEBRIS FLOWS IN MIANZHU COUNTY

汶川地震后,流域内产生大量松散物源,使走马岭沟由一季节性冲沟演变为一条潜在泥石流沟,在地震后的3个汛期内发生多次泥石流,并造成灾害,其中以2008-9-24泥石流和2010-8-13泥石流最为严重。本文利用3期遥感影像并结合野外调查,对走马岭沟泥石流的形成条件进行了论述,对比分析了走马岭泥石流沟2008年、2009年、2010年3个汛期后流域的动态变化特征,主要表现为:(1)在不同降雨强度下,走马岭泥石流具有复合型物源区启动方式,并先从局部性支沟发生泥石流,进而演变为整个流域全面暴发泥石流。(2)经历了2008年、2009年、2010年3个雨季后,走马岭流域物源储量及物源供给形式发生变化,其中崩塌规模增加了1.87%;滑坡增加了25.35%;沟道及坡面松散堆积减少了67.47%,减少部分大部分转化为泥石流沟道堆积物。(3)不同降雨强度下,走马岭泥石流堆积区范围边界变化明显,且不同堆积扇间存在叠加关系;结合走马岭"9.24"堆积扇范围和"8.13"堆积扇前缘堆积痕迹及影像特征,推测出走马岭"8.13"堆积扇堆积面积约8.76×104m2。最后对泥石流成因机理及发展趋势进行了初步分析。结果显示,走马岭为一高频泥石流沟,仍具备形成大规模泥石流的条件。

The Zoumaling stream is a typical debris flow gully because of the large numbers of loose geomaterials induced by the Wenchuan Earthquake. Three debris flow events have occurred after the Earthquake, and caused serious property loss. Two typical debris flow events occurred respectively on September 24, 2008 and on August 13, 2010. This paper combines the RS image and field investigation data. It analyzes the formation conditions of the Zoumaling debris flows, and compares the evolution characters of the gully after three rainy seasons after Wenchuan earthquake using RS image data of 2008, 2009 and 2010. The results show that the source initiation of the Zoumal- ing debris flows with a complex supply process in different rainfall intensity. The debris flow initiation began from the branch gullies, and then evolved into a whole basin debris flow. Secondly, after the three rainy seasons of2008,2009 and 2010, the source volume and its initiation process is changed. The volume of collapses has in- creased 1.87%. l,andslide has increased 25.35%. Sediment of channels and slopes has reduced 67.47%. Most of these have transformed into debris flow sediments. Thirdly, at different rainfall intensity conditions, the boundary of the Zoumaling deposition area has changed obviously. There is an overlay relation among the deposition fans formed in different rainy seasons. Comparing the deposit extent of the Zoumaling -9.24 and the front edge of the Zoumal- ing -8. 13 deposition fan and using the RS images interpretation, the deposition area of the Zoumaling -8.13 is 8.76×10^4m^2. Finally, this paper analyzes the formation and evolution trend of this debris flow gully. The results show that the Zoumaling is a high frequency debris flow gully. The large amount of loose geomaterials are still dis- tributed in the gully, which is the advantageous factor for large debris flow to occur.