基于树木年代学的迫龙沟泥石流灾害历史重建

Reconstruction of Debris Flow Disasters in Polong Gully Based on Dendrochronology

迫龙沟是帕隆藏布下游右岸一级支流,1983、1984、1985和2015年爆发过4次泥石流,重复堵江并形成长约1 km的堰塞湖.个别主沟泥石流事件和沟道内部滑坡、支沟泥石流没有冲出沟口,无文献记录,但是造成沟道中上游河床演变和树木扰动.基于树木年代学,通过分析树木年轮损伤组织、生长抑制和释放动态,重建了迫龙沟40年来的主沟泥石流和沟道内部滑坡、支沟泥石流灾害历史;从树木生长扰动强度等方面探讨了泥石流的流动范围;并通过Wit指数进一步分析了没有历史记录的主沟泥石流、沟道内部滑坡、支沟泥石流发生时间和流动范围.树木年代学所反映的泥石流爆发时间的准确性与泥石流规模有关,泥石流规模太大会导致受扰动树木的灾害历史记忆消灭,不利于大规模灾害发生之前的泥石流事件的定年.沟道内的众多支沟泥石流和主沟内的滑坡会对主沟泥石流事件的定年产生干扰,但是与主沟泥石流同一时间发生的支沟泥石流和主沟滑坡事件会增大Wit指数,利于主沟泥石流灾害事件的定年.

Polong gully is a primary tributary on the right bank of Palong Zangbu River.Four recorded debris flows in 1983,1984,1985 and 2015 repeatedly blocked the river and formed a 1 km-long barrier lake.But some individual debris flow was too small to flush out the gully and be recorded.Based on the method of dendrochronology and the analysis of damaged tissue,growth inhibition and release of tree rings,the temporal-spatial distribution of the main debris flow events,debris flows in the tributaries and landslides in the main gully in the past 40 years were reconstructed.From the intensity of tree growth disturbance,the inundate area of debris flow was discussed.The relationship between the occurrence time of debris flow and inundate area was further analyzed by the index of Wit.The results show that the accuracy of debris flow event dating reflected by dendrochronology was related to the debris flow scale.Extra-large-scale of debris flow would lead to the elimination of disaster historical memory of disturbed trees,which was not conducive to the debris flow dating.The debris flows in the tributaries and landslides in the main gully would disturb the debris flow dating in the main gully.Debris flows in the gully tributaries and landslides in the main gully occurring at the same time would increase the value of Wit,which was conducive to debris flows dating in the main gully.