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(＜ 30000m3/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 mVs, the preservation ratio is linearly proportional to Sp. For rivers with peak flood discharge higher than 30 mVs (30 - 30 000 mVs) , 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.
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