The formation and failure of natural dams
The formation and failure of natural dams
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DOI：
10.3133/ofr87392
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发表时间：
1988-07
期刊：
影响因子：
3.1
通讯作者：
John E. Costa;Robert L. Schuster
中科院分区：
文献类型：
--
作者：
John E. Costa;Robert L. Schuster
在自然过程形成的众多水坝中，由山体滑坡、冰川冰和新冰期晚期冰碛形成的水坝对人民和财产构成最大的威胁。滑坡坝形成于各种各样的自然地理环境中。形成滑坡坝的最常见的质量运动类型是岩石和碎片雪崩;岩石和土壤滑塌和滑动;以及泥浆，碎片和泥土流。形成堤坝的滑坡最常见的引发机制是过多的降雨、融雪和地震。根据滑坡坝与谷底的关系，可将其分为六类。I型水坝（我们能够分类的世界各地184座滑坡水坝中的11%）不能从一个山谷延伸到另一个山谷。II型水坝（44%）跨越整个谷底，在某些情况下，在相对的山谷两侧堆积材料。III型大坝（41%）从滑坡破坏的上游和下游移动相当长的距离。IV型坝（<1%）是罕见的，涉及来自山谷两侧的材料的同时破坏。V型坝（<1%）也很罕见，当一次滑坡将多个碎片送入山谷并在同一河段形成两个或多个滑坡坝时就会形成。VI型坝（3%）包括一个或多个在河流或山谷下延伸并出现在山谷对面的破坏面。许多滑坡坝在形成后不久就倒塌了。在我们的73个记录滑坡坝失败的样本中，27%的滑坡坝在形成后不到1天就失败了，大约50%在10天内失败。到目前为止，超限是最常见的故障原因。故障的时间和由此产生的洪水的大小由以下因素控制：大坝的尺寸和几何形状;堵塞物的材料特性;蓄水池的流入速率;蓄水池的尺寸和深度;基岩对水流的控制;以及工程控制，如人工溢洪道、改道、隧道和爆破或常规开挖的计划破坏。冰坝可以形成至少九种类型的冰坝湖。最危险的是由支流冰川筑坝的主要山谷中形成的湖泊。破坏可能是由于冰坝下方或穿过冰坝的排水隧道或冰坝上方的通道的侵蚀而发生的。寒冷的极地冰坝通常通过出口通道的下融而在冰上或边缘排水。温度较高的温冰坝往往会因冰内或冰下的突然破裂和排水而失效。新冰期晚期冰碛堰塞湖位于近几个世纪以来受山谷冰川进退影响的陡峭山区。这些新冰期晚期的水坝构成了危险，因为（1）它们足够年轻，植被还没有稳定它们的斜坡，（2）许多坝面比休止角更陡，（3）这些水坝和湖泊直接从陡峭的裂缝冰川和近乎垂直的岩石斜坡向下倾斜，以及（4）这些水坝的下游是陡峭的峡谷，峡谷中有容易被侵蚀的物质，这些物质可以被纳入水流中并增加洪峰。最常见的破坏机制是由冰瀑、落石或雪或岩石雪崩产生的湖中一个或一系列波浪造成的漫顶和破裂。冰芯或冻土的融化以及管涌和渗漏是其他可能的破坏机制。天然大坝可能会导致上游洪水，因为湖泊上升和下游洪水，由于大坝的失败。虽然数据很少，在相同的潜在能量在坝址，自来水洪峰从冰川冰坝的故障小于那些从滑坡，冰碛，结构化的土坝和堆石坝故障。冰碛坝的破坏似乎产生了一些最大的下游洪峰的潜在能量在坝址大于1011-1012焦耳。洪峰自然溃坝的差异似乎受大坝特性和溃坝机理的控制。
Of the numerous kinds of dams that form by natural processes, dams formed from landslides, glacial ice, and late-neoglacial moraines present the greatest threat to people and property. Landslide dams form in a wide range of physiographic settings. The most common types of mass movements that form landslide dams are rock and debris avalanches; rock and soil slumps and slides; and mud, debris, and earth flows. The most common initiation mechanisms for dam-forming landslides are excessive rainfall and snowmelt and earthquakes. Landslide dams can be classified into six categories based on their relation with the valley floor. Type I dams (11% of 184 landslide dams from around the world that we were able to classify) do not reach from one valley side to the other. Type II dams (44%) span the entire valley floor, in some cases depositing material high on opposite valley sides. Type III dams (41%) move considerable distances both upstream and downstream from the landslide failure. Type IV dams (<1%) are rare and involve the contemporaneous failure of material from both sides of a valley. Type V dams (<1%) also are rare and are created when a single landslide sends multiple tongues of debris into a valley and forms two or more landslide dams in the same reach of river. Type VI dams (3%) involve one or more failure surfaces that extend under the stream or valley and emerge on the opposite valley side. Many landslide dams fail shortly after formation. In our sample of 73 documented landslide-dam failures, 27% of the landslide dams failed less than 1 day after formation, and about 50% failed within 10 days. Over-topping is by far the most common cause of failure. The timing of failure and the magnitude of the resulting floods are controlled by dam size and geometry; material characteristics of the blockage; rate of inflow to the impoundment; size and depth of the impoundment; bedrock control of flow; and engineering controls such as artificial spill-ways, diversions, tunnels, and planned breaching by blasting or conventional excavation. Glacial-ice dams can produce at least nine kinds of ice-dammed lakes. The most dangerous are lakes formed in main valleys dammed by tributary glaciers. Failure can occur by erosion of a drainage tunnel under or through the ice dam or by a channel over the ice dam. Cold polar-ice dams generally drain supraglacially or marginally by downmelting of an outlet channel. Warmer, temperate-ice dams tend to fail by sudden englacial or subglacial breaching and drainage. Late-neoglacial moraine-dammed lakes are located in steep mountain areas affected by the advances and retreats of valley glaciers in the last several centuries. These late-neoglacial dams pose hazards because (1) they are sufficiently young that vegetation has not stabilized their slopes, (2) many dam faces are steeper than the angle of repose, (3) these dams and lakes are immediately downslope from steep crevassed glaciers and near-vertical rock slopes, and (4) downstream from these dams are steep canyons with easily erodible materials that can be incorporated in the flow and increase flood peaks. The most common reported failure mechanism is overtopping and breaching by a wave or series of waves in the lake generated by icefalls, rockfalls, or snow or rock avalanches. Melting of ice cores or frozen ground and piping and seepage are other possible failure mechanisms. Natural dams may cause upstream flooding as the lake rises and downstream flooding as a result of failure of the dam. Although data are few, for the same potential energy at the dam site, ownstream flood peaks from the failure of glacier-ice dams are smaller than those from landslide, moraine, and structed earth-fill and rock-fill dam failures. Moraine-dam failures appear to produce some of the largest downstream flood peaks for potential energy at the dam site greater than 1011-1012 joules. Differences in flood peaks natural-dam failures appear to be controlled by dam characteristics and failure mechanisms.