裂点发育及其对堰塞坝的稳定性影响
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摘要
通过野外调查及试验对堰塞坝的稳定和裂点的发育进行研究,发现堰塞坝的稳定性主要取决于泄洪道内阶梯-深潭系统的发育程度Sp和坝体上游洪峰的水流能量p。堰塞坝的保存与溃决情况采用保留的坝高比进行定量描述,对于洪峰流量小于30 m3/s山区河流,保留坝高比与Sp呈线性相关;洪峰流量大于30 m3/s(<30 000m3/s)时,河道稳定所需的最小河床结构强度Sp随着单宽水流能量p的增加而增大。堰塞坝泄洪道内不发育阶梯-深潭系统或发育程度较低的坝体,Sp值小于稳定河床最小的阻力强度,将会发生下切、溯源冲刷并引起溃坝。保留的堰塞坝在泥沙淤积和水流的长期作用下会形成裂点,对河床下切起到控制作用,降低再次发生滑坡的风险。大型裂点能改变河床演变和河流地貌,连续堰塞坝形成的裂点能长期保存并形成优美的自然景观,创造良好的河流生态环境。
This paper studies the stability of landslide dams and development of knickpoints by field investigations and experiments,and analyzing satellite images.The stability of landslide dams depends mainly on the development of step-pool system and stream power of the flood flow.The development degree of step-pool system is represented by a parameter Sp,which was measured with a specially designed instrument.A preservation ratio of landslide dams is defined as the ratio of preserved height after flood scouring to the original height of the dam.For streams with peak flood discharge lower than 30 m3/s,the preservation ratio is linearly proportional to Sp.For rivers with peak flood discharge higher than 30 m3/s(30-30 000 m3/s),the minimum Sp value for stable channel increases with the unit stream power p.For a landslide dam with poorly developed step-pool system,Sp is smaller than the minimum value and the outburst flood incises the spillway channel and causes failure of the dam.For preserved landslide dams with sediment deposits in the quake lakes,a knickpoint may be developed if it is stabilized by long-term action of the flow.Large knickpoints can totally change the fluvial processes and river morphology.If hundreds of landslide dams occurred simultaneously on a reach of a mountain river,the potential energy of bank failure and the slope erosion are greatly reduced and sediment yield from the watershed may be reduced nearly to zero.The quake lakes may be preserved for long term and become beautiful landscapes.Streams with long term unfilled quake lakes have good aquatic ecology.
This paper studies the stability of landslide dams and development of knickpoints by field investigations and experiments,and analyzing satellite images.The stability of landslide dams depends mainly on the development of step-pool system and stream power of the flood flow.The development degree of step-pool system is represented by a parameter Sp,which was measured with a specially designed instrument.A preservation ratio of landslide dams is defined as the ratio of preserved height after flood scouring to the original height of the dam.For streams with peak flood discharge lower than 30 m3/s,the preservation ratio is linearly proportional to Sp.For rivers with peak flood discharge higher than 30 m3/s(30-30 000 m3/s),the minimum Sp value for stable channel increases with the unit stream power p.For a landslide dam with poorly developed step-pool system,Sp is smaller than the minimum value and the outburst flood incises the spillway channel and causes failure of the dam.For preserved landslide dams with sediment deposits in the quake lakes,a knickpoint may be developed if it is stabilized by long-term action of the flow.Large knickpoints can totally change the fluvial processes and river morphology.If hundreds of landslide dams occurred simultaneously on a reach of a mountain river,the potential energy of bank failure and the slope erosion are greatly reduced and sediment yield from the watershed may be reduced nearly to zero.The quake lakes may be preserved for long term and become beautiful landscapes.Streams with long term unfilled quake lakes have good aquatic ecology.
引文
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[16]Ouimet W B,Whipple K X,Royden L H,et al.The influence oflarge landslides on river incision in a transient landscape:Easternmargin of the Tibetan Plateau(Sichuan,China)[J].GSA Bulle-tin,2007,119(11-12):1462～1476
[17]Korup O.Geomorphometric characteristics of New Zealand land-slide dams[J].Engineering Geology,2004,73:13-35
[18]Duan Xuehua.Ecological impacts of water and sediment transporta-tion o macroinvertebrate community in rivers[D].Beijing:Depart-ment of Hydraulic Engineering in Tsinghua University,2009[段学花.河流水沙对底栖动物的生态影响研究[D].北京:清华大学水利水电工程系,2009]
[2]Cui Peng,Wei Fangqiang,He Siming,et al.Mountain disasters in-duced by the earthquake of May 12 in Wenchuan and disasters miti-gation[J].Journal of Mountain Science,2008,26(3):280-282[崔鹏,韦方强,何思明,等.5.12汶川地震诱发的山地灾害及减灾措施[J].山地学报,2008,26(3):280-282]
[3]Zhou Kuiyi,Su Kezhong,Jia Zhenwen et al.Study on the secondaryflood disasters caused by strong earthquakes since the 14th centuryin China[J].Journal of Natural Disasters,1992,1(3):83-91[周魅一,苏克忠,贾振文,等.十四世纪以来我国地震次生水灾的研究[J].自然灾害学报,1992,1(3):83-91]
[4]Cheng Zunlan,Cui Peng,Li yong,et al.Major disasters and con-trol measures of dammed lakes from landslide and debris flows[J].Journal of Mountain Sciecce,2008,26(6):733-738[程尊兰,崔鹏,李泳,等.滑坡、泥石流堰塞湖灾害主要的成灾特点与减灾对策[J].山地学报,2008,26(6):733-738]
[5]Nicoletti P.G.and Parise M.Seven landslide dams of old seismicorigin in southeastern Sicily(Italy)[J].Geomorphology,2002,46:203-222
[6]Geertsema M.and Pojar J.J.Influence of landslides on biophysicaldiversity——A perspective from British Columbia[J].Geomor-phology,2007,89:55-69
[7]Wang Zhaoyin,Cui Peng,Wang Ruiyi.Mass movements triggeredby the Wenchuan Earthquake and management strategies of quakelakes[J].International Journal of River Basin Management,2009,7(1):1-12
[8]Wenchuan Earthquake Area Atlas of Earthquake-Geological Hazards[M].Beijing:China Map Publishing House,2008:70-71[国家汶川地震专家委员会.汶川地震灾区地震-地质灾害图集[M].北京:中国地图出版社,2008:70-71]
[9]Rosport M.Hydraulics of steep mountain streams[J].InternationalJournal of Sediment Research,1997,12(3):99-108
[9]Lee A J,Ferguson R I.Velocity and flow resistance in step-poolstreams[J].Geomorphology,2002,46:49-71
[10]Wilcox A,Nelson,J M,Wohl,E E.Flow resistance dynamics instep-pool channels 2:Partitioning between grain,spill,and woodydebris resistance[J].Water Resources Research,2006,42,W05419,doi:10.1029/2005WR004278.
[11]Wang Zhaoyin,Melching C S,Duan Xuehua,et al.Ecologicaland hydraulic studies of Step-pool systems[J].Journal of Hydrau-lic Engineering,ASCE,2009,135(9):705-717
[12]Wang Zhaoyin,Xu Jiang,Li Changzhi.Development of step-poolsequence and its effects in resistance and stream bed stability[J].International Journal of Sediment Research,2004,19(3):161-171
[13]Maxwell A.R.and Papanicolaou A.N.Step-pool morphology inhigh-grandient streams[J].International Journal of Sediment Re-search,2001,16(3):380-390
[14]Costa J.E.and Schuster R L.The formation and failure of naturaldams[J].Geol Soc Amer Bull,1988,100:1054-1068
[15]Chen Xiaoqing,Cui Peng,Zhao Wanyu,et al.A discussion of e-mergency treatment of dammed lake caused by“5.12”WenchuanEarthquake[J].Journal of Mountain Science,2010,28(3):350-357[陈晓清,崔鹏,赵万玉,等.“5.12”汶川地震堰塞湖应急处置措施的讨论——以唐家山堰塞湖为例[J].山地学报,2010,28(3):350-357]
[16]Ouimet W B,Whipple K X,Royden L H,et al.The influence oflarge landslides on river incision in a transient landscape:Easternmargin of the Tibetan Plateau(Sichuan,China)[J].GSA Bulle-tin,2007,119(11-12):1462～1476
[17]Korup O.Geomorphometric characteristics of New Zealand land-slide dams[J].Engineering Geology,2004,73:13-35
[18]Duan Xuehua.Ecological impacts of water and sediment transporta-tion o macroinvertebrate community in rivers[D].Beijing:Depart-ment of Hydraulic Engineering in Tsinghua University,2009[段学花.河流水沙对底栖动物的生态影响研究[D].北京:清华大学水利水电工程系,2009]
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