汶川震区文家沟泥石流成灾机理与特征

文家沟位于绵竹市清平乡,属于 5 ·12 汶川Ms8.0级地震极重灾区。地震发生后的3个汛期内,文家沟曾先后发生5次典型泥石流灾害,其中以2010年8月13日泥石流灾害最为严重,规模与灾情巨大,社会影响深远。在对文家沟泥石流跟踪调查的基础上,探讨了泥石流的成灾机理和特征。研究表明:(1)文家沟泥石流是地震和强降雨共同作用的结果,其成因可归纳为震因与物源以及雨因与水源两个方面,在整个泥石流形成和发生的过程中,呈现出洪流-侵蚀下切-崩滑-席卷-进一步侵蚀下切-进一步崩滑-增大泥石流规模—……的"滚雪球式"循环过程; (2)泥石流发生所需的雨量、雨强条件和水动力条件都显著降低,泥石流规模和雨量之间呈现出明显幂函数关系; (3)发生过程呈现出持续时间长、运动距离远的特征; (4)成灾过程呈现出明显的链式效应,危害形式多样; (5)泥石流频率呈现出高发性,规模呈现出放大性。最后提出了文家沟泥石流研究与防治的建议。

MECHANISM AND CHARACTERISTICS OF WENJIA-GULLY DEBRIS FLOW IN EPICENTER AREA OF WENCHUAN EARTHQUAKE

Wenjia gully is located at the epicenter area of the 2008 Wenchuan Earthquake.A huge landslide was ever triggered by the earthquake.During the passed three flood seasons,at least five typical debris flows occurred at Wenjia gully.In particular,a severest debris flow occurred on Aug.13, 2010. It had a volume up to 3.1×10⁷m³.Five residents lost their lives unfortunately and hundreds of new-built houses were buried during the catastrophic event.However,it was fortunate that almost all the residents evacuated successfully before the debris flow occurred.In this paper,on the basis of tracking investigation,the mechanism and characteristics of the Wenjia-gully debris flows were discussed and some suggestions were put forward.The acknowledges obtained after investigation and analysis are as follows: (1)The debris flows were caused by both Wenchuan earthquake and strong rainfall.As the debris flow formation is concerned,a circle was presented as runoff-erosion-collapse-engulfment-erosion-collapse-enlargement-,and so on; (2)The critical rainfall initiated debris flow was significantly decreased and a power-law relation is existed between debris flow magnitude and daily rainfall,which can be used to predict the volume of debris flow on the basis of weather forecasting; (3)As the occurrence process is concerned,the debris flow lasted for a long duration and moved a far distance; (4)In terms of destroying process,a clear chain characteristic was taken on with several damage ways; (5)Debris flow magnitude was enlarged and the frequency was higher obviously.