汶川地震区震后泥石流活动特征与防治对策
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摘要
2008年5月12日的汶川Ms8.0地震对地表产生强烈扰动,使得泥石流形成条件发生剧烈变化,影响到震后泥石流的活动特征和减灾对策。作者在调查数据的基础上,从固体松散物质条件、微地貌条件和水文条件的变化3个方面,分析了汶川地震区震后泥石流形成条件的变化,认为:汶川地震灾区崩塌、滑坡等产生的松散固体物质达28×108m3,为该区泥石流长期活动提供了丰富的物质基础;流域微地貌突变特别是严重的沟道堵塞,有利于泥石流规模的增大;强烈地表扰动和毁灭性、大面积毁坏植被,改变了地表水入渗、产流和汇流条件,利于侵蚀和洪峰形成。这些流域状态的巨变,构成了有利于泥石流形成的条件组合。从而,导致震后泥石流活动强度急剧增大,使得泥石流成为对地震区影响最为严重的灾害。震后泥石流活动的主要特点有:泥石流沟谷数量增加,大量震前被判定为非泥石流沟的流域暴发了泥石流;激发泥石流的临界雨量明显降低泥石流暴发表现出明显的高频性与群发性;泥石流的容重约提高10%～30%,原来定性为稀性或过渡性的泥石流沟转化为过渡性或粘性泥石流沟;泥石流流量普遍增大,大致可增加约50%～100%,现有规范中泥石流流量计算方法的结果偏小,需要修正。震后泥石流演变趋势为:活动强度由急剧增强的突变转为逐步减弱,期间活跃期与平静期交替出现,第1个泥石流活跃期可能会持续约15年左右;泥石流形成将由降雨控制型逐步转为松散土体控制型;一些松散土体丰富且尚未发生泥石流的面积大于5km2流域,将是未来暴发大规模泥石流的风险源。针对震后泥石流的活动特征、演化趋势和震区泥石流防治中存在的问题,提出:判识潜在泥石流灾害,增强减灾措施的针对性;进行泥石流灾害风险分析,加强风险管理;改进泥石流规模计算方法,适应震区超常规模泥石流防治需求;重新确定泥石流预警报的临界雨量指标,加强监测预警系统建设等灾害防治对策。
The changes of the formation of debris flows after Wenchuan Earthquake were analyzed,including loose materials,micro-topography and hydrological condition.Analysis suggested that the total of the loose mass generated by the collapse and landslides reaches about 28 × 108 m3,which provides abundant materials for debris flows for a long term.The change of landform and especially the blockage of channel will increase the scale of debris flow.The conditions of the surface water infiltration,runoff and flow concentration are changed by the strong surface disturbance and large-scale destructive vegetation damage,which is beneficial to the formation of the erosion and flood peak easier.The great changes of the river basin constitute the conditional combination of the debris flow formation.Therefore,the intensity of postearthquake debris flow increases rapidly and debris flow becomes one of the most serious risk source.The main characteristics of debris flows after Wenchuan Earthquake were as follows.The number of debris flow gully increased,a large number of debris flows occurred in gullies which had no debris flows before the earthquake.The critical rainfall decreased significantly.The events occurred at high frequency and in group.The the density increased by about 10% to 30% and transitional or viscous flows occurred in many gullies of turbulent flows.The discharge increased by about 50% ~100%,beyond the results calculated by the current methods.The tendency of debris flow is that the intensity will grow and then devay,alternative with active and quiet periods.The first active period will last for 15 years.The trigger and control factor depends mainly on the supplies of loose material.The valleys that have rich materials and more than 5 km2 of area will be the most dangerous in the following years.Accordingly,we proposed the strategies for mitigation of debris flow,including discrimination of potential debris flow and specification of countermeasures;risk analysis and management;calculation of magnitude and regular monitoring and warning system.
The changes of the formation of debris flows after Wenchuan Earthquake were analyzed,including loose materials,micro-topography and hydrological condition.Analysis suggested that the total of the loose mass generated by the collapse and landslides reaches about 28 × 108 m3,which provides abundant materials for debris flows for a long term.The change of landform and especially the blockage of channel will increase the scale of debris flow.The conditions of the surface water infiltration,runoff and flow concentration are changed by the strong surface disturbance and large-scale destructive vegetation damage,which is beneficial to the formation of the erosion and flood peak easier.The great changes of the river basin constitute the conditional combination of the debris flow formation.Therefore,the intensity of postearthquake debris flow increases rapidly and debris flow becomes one of the most serious risk source.The main characteristics of debris flows after Wenchuan Earthquake were as follows.The number of debris flow gully increased,a large number of debris flows occurred in gullies which had no debris flows before the earthquake.The critical rainfall decreased significantly.The events occurred at high frequency and in group.The the density increased by about 10% to 30% and transitional or viscous flows occurred in many gullies of turbulent flows.The discharge increased by about 50% ~100%,beyond the results calculated by the current methods.The tendency of debris flow is that the intensity will grow and then devay,alternative with active and quiet periods.The first active period will last for 15 years.The trigger and control factor depends mainly on the supplies of loose material.The valleys that have rich materials and more than 5 km2 of area will be the most dangerous in the following years.Accordingly,we proposed the strategies for mitigation of debris flow,including discrimination of potential debris flow and specification of countermeasures;risk analysis and management;calculation of magnitude and regular monitoring and warning system.
引文
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[11]Shieh C L,Chen Y S,Tsai Y J,et al Variability in rainfall threshold for debris flow after the Chi-Chi earthquake in central Taiwan,China[J].International Journal of Sediment Research,2009,24(2):177-188.
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[14]Xie Hong,Zhong Dunlun,Jiao Zhen,et al.Debris flow in Wenchuan Quake-hit area in 2008[J].Journal of Mountain Research,2009,27(4):501-509.[谢洪,钟敦伦,矫震,等.2008年汶川地震重灾区的泥石流[J].山地学报,2009,27(4):501-509.]
[15]Zhuang J Q,Cui P,Hu K H,et al.Characteristics of earthquake-triggered landslides and post-earthquake debris flows in Beichuan county[J].Journal of Mountain Science,2010,7(3):246-254.
[16]Du Ronghuan,Zhuang Shucheng.Study on glacial debris flow in Guxiang Gully,Xizang[M]//Bulletin4of Institute of Glaciology and Geocryology,CAS,Lanzhou.Beijing:Science Press,1980:79-86.[杜榕桓,章书成.西藏古乡沟冰川泥石流研究[M]//中国科学院冰川冻土研究所集刊(4).北京:科学出版社,1980:79-86.]
[17]崔鹏,柳素清,唐邦兴,等.风景区泥石流研究与防治[M].北京:科学出版社,2005.
[2]Cui Peng,Han Yongshun,Chen Xiaoqing.Distribution an-drisk anaysis of dammed lakes reduced by Wenchuan Earthquake[J].Journal of Sichuan University:Engineering Science Edition,2009,41(3):35-42.[崔鹏,韩用顺,陈晓清.汶川地震堰塞湖分布规律与风险评估[J].四川大学学报:工程科学版,2009,41(3):35-42.]
[3]Cui P,Chen X Q,Zhu Y Y,et al.The Wencuan Earthquake(12 May 2008),Sichuan Province,China,and resulting geohazards[J].Nature Hazards,2009,DOI10.1007/s11069-009-9392-1.
[4]Huang Runqiu.Mechanism and geomechanical modes of landslide hazards triggered by Wenchuan8.0Earthquake[J].Chinese Journal of Rock Mechanics and Engineering,2009,28(6):1239-1249.[黄润秋.汶川8.0级地震触发崩滑灾害机制及其地质力学模式[J].岩石力学与工程学报,2009,28(6):1239-1249.]
[5]Yin Yueping.Researches on the geo-hazards triggered by Wenchuan Earthquake,Sichuan[J].Journal of Engineering Geology,2008,16(4):433-444.[殷跃平.汶川八级地震地质灾害研究[J].工程地质学报,2008,16(4):433-444.]
[6]Tang Chuan,Liang Jingtao.Characteristics of debris flows in Beichuan epicenter of the Wenchuan Earthquake triggered by rainstorm on September 24,2008[J].Journal of Engi-neering Geology,2008,16(6):751-758.[唐川,梁京涛.汶川震区北川9.24暴雨泥石流特征研究[J].工程地质学报,2008,16(6):751-758.]
[7]Yin Yueping.Rapid and long run-out features of landslides triggered by the Wenchuan Earthquake[J].Journal of Engineering Geology,2009,17(2):153-166.[殷跃平.汶川八级地震滑坡高速远程特征分析[J].工程地质学报,2009,17(2):153-166.]
[8]You Yong,Liu Jinfeng.The influence on debris flow prevention in the upriver of Minjiang after Wenchuan Earthquake.Journal of Sichuan University:Engineering Science Edition,2009,41(Sup):16-22.[游勇,柳金峰.汶川8级地震对岷江上游泥石流灾害防治的影响[J].四川大学学报:工程科学版,2009,41(增刊):16-22.]
[9]Liu C W,Huang H F,Dong J J.Impacts of September 21,1999 Chi-Chi earthquake on the characteristics of gully-type debris flows in central Taiwan[J].Natural Hazards,2008,47(3):349-368.
[10]Chen Y S.An influence of earthquake on the occurrence of landslide and debris flow[D].Taipei:National Cheng Kung University,2008.
[11]Shieh C L,Chen Y S,Tsai Y J,et al Variability in rainfall threshold for debris flow after the Chi-Chi earthquake in central Taiwan,China[J].International Journal of Sediment Research,2009,24(2):177-188.
[12]Cui Peng,Wei Fangqiang,Xie Hong,et al.Debrisflow and disaster reduction strategies in western China[J].Quaternary Sciences,2003,23(2):142-151.[崔鹏,韦方强,谢洪,等.中国西部泥石流及其减灾对策[J].第四纪研究,2003,23(2):142-151.]
[13]康志成,李焯芬,马蔼乃,等.中国泥石流研究[M].北京:科学出版社,2004.
[14]Xie Hong,Zhong Dunlun,Jiao Zhen,et al.Debris flow in Wenchuan Quake-hit area in 2008[J].Journal of Mountain Research,2009,27(4):501-509.[谢洪,钟敦伦,矫震,等.2008年汶川地震重灾区的泥石流[J].山地学报,2009,27(4):501-509.]
[15]Zhuang J Q,Cui P,Hu K H,et al.Characteristics of earthquake-triggered landslides and post-earthquake debris flows in Beichuan county[J].Journal of Mountain Science,2010,7(3):246-254.
[16]Du Ronghuan,Zhuang Shucheng.Study on glacial debris flow in Guxiang Gully,Xizang[M]//Bulletin4of Institute of Glaciology and Geocryology,CAS,Lanzhou.Beijing:Science Press,1980:79-86.[杜榕桓,章书成.西藏古乡沟冰川泥石流研究[M]//中国科学院冰川冻土研究所集刊(4).北京:科学出版社,1980:79-86.]
[17]崔鹏,柳素清,唐邦兴,等.风景区泥石流研究与防治[M].北京:科学出版社,2005.
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