贵州望谟打蒿沟“6·06”泥石流特征

The "6·06 "Disaster Characteristics and Forming Mechanism of Debris Flow in Wangmo,Guizhou

2011-06-06贵州省望谟县北部普降百年一遇暴雨,引发大规模群发性泥石流灾害,给当地居民生活及交通造成严重损害。其中以打蒿沟泥石流灾害尤为突出,该流域内支沟发育,沟床比降相对较缓,但陡峻的岸坡和较大的汇水面积为泥石流的发生提供了良好的水动力条件。打蒿沟地处碎屑岩发育地区,松散堆积体较厚,并受岸坡坡度影响浅层滑坡发育,现场调查共19处。另外流域内人为破坏严重,村民沿沟垒筑大量梯田也为泥石流活动提供了特殊的人工物源。通过对其4条支沟的研究发现,泥石流形成特征并不一致,其中坡度较缓的2#支沟浅层滑坡发育,为浅层滑坡型泥石流;而坡度较陡的其他3条支沟浅层滑坡发育较少,以沟床物源为主,为沟床启动型泥石流。通过对沟道两侧斜坡坡度的调查统计和分级得出流域内25°～40°的岸坡最易形成浅层滑坡,且当山坡呈上缓下陡时,更利于滑坡的形成。打蒿沟在强降雨条件下依然可暴发泥石流,规模会有所减小,但在类似2011-06-06这类稀遇暴雨作用下仍可造成较大危害。

On June 6,2011 ,most of the northern areas of Wangmo county in Guizhou province had the biggest rain- fall in a century and led to breaking out a large scale group debris flo^s. The disaster caused serious harm to local residents and traffic. The flow disaster characteristics of Dahao gully are particularly outstanding. Some tributaries were developed in Dahao gully. Its gully bed slope is relatively moderate, but steep slope and larger catchment area for the formation of the debris flow select hydrodynamic conditions. The Dahao gully is located in classic rock de- velopment area and has thicker loose deposits. Because the bank slope of Dahao gully is more steep, there are 19 shallow landslides in it according to field investigation. In addition, The landscape is be strongly destroyed by vil- lagers. Terraces were fortified along the ditch for special source of material to the out breaking of debris flow. We can found that the formation mechanism is not consistent by the study of its four tributaries. 2# tributary has more gentle slope and more shallow landslides, so its forming type is the shallow landslide-debris flow. But the rest of three tributaries have more steep slope and they are the gully-shape debris flow . Because less shallow landslides was formed in them, their most of material from the ditch bed. Surveying the slope gradient on both sides of the gul- ly,we can conclude that 25 ~40~ is more easily to form the landslide and more shallow slides were generated when the upper part of the slope is obviously more flat than the bottom of it. According to investigation, the Dahao gully can still outbreaks debris flow in the condition of strong rainfall after this disaste , but the scale will be reduced and it can still causes greater harm under the action of rare and heavy rain similar to ＂6 · 06＂.