基于树木地貌法重建山洪泥石流历史事件--以北京密云区龙潭沟流域为例

认识区域山洪泥石流活动史是预测未来气候变化背景下灾害发展趋势的基础。利用树轮中的生长干扰信息,可以对未知山洪泥石流历史事件准确定年。本文以北京市密云区龙潭沟流域的曹庄子沟和合峪沟两条泥石流沟为研究对象,利用树木地貌学方法,在已知灾害年基础上获取阔叶树杨树的树轮生长扰动百分比,再重建未知灾害年并进行验证。结果表明:树轮对灾害的响应要滞后一年;2011年曹庄子沟的山洪导致该沟流通区、左岸、右岸和堆积区的树轮生长扰动百分比分别为-30.59%、43.78%、43.47%、-30.44%;2016年曹庄子沟的泥石流导致该沟四个分区的树轮生长扰动百分比分别为-46.08%、-45.15%、-46.64%、-37.32%。根据上述结果,推求并验证了曹庄子沟其他灾害年为2002、2013年,合峪沟灾害年为1997、2002、2011、2013、2016年。研究区1997、2002、2011、2013、2016年的响应树比例分别为35.42%、66.07%、46.43%、32.14%、58.93%,利用响应树比例能够区分灾害严重年份和次严重年份。2010年至今,该流域山洪及泥石流灾害活动频数有所增大,未来该流域再发生山洪泥石流灾害可能性仍较大。

Reconstruction of torrent and debris flow events based on dendrogeomorphology--A case study of Longtangou basin in Miyun District,Beijing

Knowledge of historical debris flows are fundamental for prediction and warning in the background of climate change.Some unknown events can be determined by the abnormal tree ring records.This research uses dendrogemorohology to reconstruct debris flows on basis of the tree ring growth disturbance of broad-leaved tree.The tree ring samples were analyzed in the Caozhuangzi(CZZ)and Heyu(HY)watershed of Longtangou basin,Miyun county,Beijing.The result shows that the tree-ring abnormality delays one year to torrent and debris flow event.In CCZ watershed,the disturbance ratios at the site of transportation area,left bank,right bank and depositional area were-30.59%,43.78%,43.47%,-30.44%after the torrent in 2011 and-46.08%,-45.15%,-46.64%,-37.32%after the debris flow in 2016.Therefore,the year of 2002 and 2013 in CCZ and the 1997,2002,2011,2013 and 2016 in HY could be deemed as reconstructed events.The disturbance ratio in the study area in 1997,2002,2011,2013,and 2016 were 35.42%,66.07%,46.43%,32.14%,and 58.93%,respectively;and can distinguish between severe and sub-severe disaster years.Additionally,the debris flow activity in the two watersheds seems to increase since 2010 and increasing debris flow potential exists in future.