2016年帕隆藏布流域群发性泥石流的活动特征及成因分析

Characteristics and Geneses of the Group-Occurring Debris Flows Along Parlung Zangbo River Zone in 2016

帕隆藏布流域山高谷深、构造强烈、冰川广布,区域内冰川泥石流数量多、规模大、分布密、暴发频率高。2016年9月5日,流域内几条泥石流集中暴发,造成较为严重的财产损失,并阻碍了G318国道的正常通行。为研究本次群发性泥石流的成因,指导泥石流的监测预警工作,在实地调查的基础上,分析了泥石流的地形地貌条件、物源条件、水热条件。分析结果表明:本次暴发泥石流的沟谷具有良好的地形条件,流域高差大,沟道纵比降大,尤其沟谷上游因冰川作用而形成的冰蚀围谷利于水源、物源的聚集。泥石流以沟源处的松散冰碛物为主要物源。此外,北岸比通沟泥石流因沟岸崩滑物源丰富、沟道狭窄,形成多处堵点,产生堵溃放大效应。南岸赤担隆巴泥石流则沟道宽缓,崩滑物源较少。本次群发性泥石流的诱发因素主要为强降雨。泥石流暴发前两日出现强降雨,使得沟内松散物质含水量增加,趋近饱和,稳定性降低。泥石流暴发当日再次出现强降雨,直接激发了泥石流。经对暴发当日小时雨量分析,认为比通沟泥石流由凌晨2点的集中降雨启动,但由于沟道堵塞严重,龙头数小时后才到达沟口。赤担隆巴由当日11点的集中降雨启动,随后顺沟下泄,堆积于老扇之上,形成灾害。经分析,沟口观测的激发本次泥石流的小时雨量为3.3～3.6mm,推测主要形成区激发泥石流的小时雨量为7.6～8.3mm。

Parlung Zangbo River Basin has the features of high mountains,intensive tectonism and widespread glacier.The glacial debris flows along Parlung Zangbo River Basin was large in number and scale with dense dissemination and high frequency.The group-occurring debris flow caused heavy losses of property and blocked the G318 Road on September 5th,2016.In order to investigate the cause of the debris flow and strengthen disaster monitoring,geography,sources of debris flows and hydrodynamic conditions were analyzed.The results indicated that the debris flows were easily formed because of the favorable landform,giant gaps among different elevation,great longitudinal river slopes and deeply ice eroded valley.The unconsolidated glacial sediments are the main sources of debris flow in this area.In addition,as with a less wide gully and a more abundant provenance of collapse and landslide,the debris flow block-outburst occurred frequently on north bank while the debris flow gully on the south bank occurred less with a contrary condition of the inducement.The predominant triggering factor of this group-occurring glacial debris flow was the heavy rainfall.The antecedent rainfall had saturated the provenance which was then initiated by the following heavy rain.The Bitong Valley debris flow occurred at 2:00 am through research.However,it reached the Parlung Zangbo River Basin a few hours later because of being blocked.The debris flow in Chidanlongba Valley started at 11:00 am and then rushed out the gully and deposited on the old alluvial fans.The hourly rainfall which triggered the debris flow measured in the piedmont was 3.3~3.6 mm,the estimated hourly rainfall was 7.6~8.3 mm in the debris flow initiated area.