溪流杀人机器：低位差堰/低头坝 Low-Head Dams 转录自古早：http://www.doyouhike.net/forum/202669,0,0,1.html Low-head dams: A not-so clear and present danger by Virgil Chambers, Executive Director, National Safe Boating Council 低位差堰/低头坝Low-Head Dams：未明情况及存在的危险 by Virgil Chambers，国家安全划艇协会理事会 执行董事 Rivers can be treacherous, not only because of the tremendous power they possess, through the movement of flowing water, but because of structures they flow over, around and through. 河流可能会很危险，不仅是因为通过水流的力量，所产生的巨大的力量，而且是因为水下 ，或周边及流经的结构。 Hazards like "strainers," fallen trees and debris collecting between rocks and bridge piers that can trap floating objects, are generally conspicuous. And those familiar with the dynamics of moving water know how the force of the water, as it comes in contact with different obstructions, can actually hold objects. 如“筛检程式”似的危险，折断倒下的树木，及岩石及桥洞、码头之间所堆有的杂物，他 们可能会是漂浮物的陷井，通常是很显着的。那些对流水运动动力熟悉的人知道当它接触 到其他不同的阻碍物时，水可能会有困住物体的力量。 Bridge piers and rocks are potentially dangerous basically because they don't move and the water does. If the water is moving fast enough, anything or anyone coming in contact with these structures can be held tight against their upstream side. Once pinned in this way, escape is difficult. We can easily understand the danger and what is happening when water holds an object against an obstacle. 桥洞、码头及岩石基本上说应是潜在的危险，因为他们静止而水流动。如果水流速度足够 快，任何接触到这些结构的物体或任何人都可能会被紧紧地陷入在上游中。一旦被陷在里 面，要逃脱是很困难的。可以容易理解危险的存在，及当水流把物体困在阻挡物中间。 However, the distinction is not so clear with the dangers associated with the river's most perilous obstruction, the low-head dam. It is a man-made structure, typically built to back up water in a reservoir for a variety of reasons. This wall-like structure pools the water as it flows over the crest and drops to the lower level. 然而，区别不是很明显，当与河流最危险的阻挡物关联时，如低水头坝。这是人工结构， 主要是建设以储水在水库中，以做各种用途。这种象挡水墙似的结构当流过顶部时积成水 塘，并在低水位时跌落。 This drop creates a hydraulic, which is a backwash that traps and recirculates anything that floats. Boats and people have been caught in this backwash. A person caught in the backwash of a low-head dam will be carried to the face of the dam, where the water pouring over it will wash him down under to a point downstream called the boil. The boil is that position where the water from below surfaces and moves either downstream or back toward the dam. A person who is caught in a low head dam struggles to the surface, where the backwash once again carries him to the face of the dam, thus continuing the cycle. 这种水位跌落产生了水力，产生回流从而陷进并回圈任何漂在上面的东西。船或者人可能 会被水吸入这种回流中。当人被吸入低水头坝时，会被带到面向水坝的上游，在那里水从 头上流下，将人向下冲刷，至下面某处後向下游走，这被称做“Boil”。“Boil”是一个 位置，在水面下的某处此位置上，水或者被向下游冲或者又被带到坝上。人被困入低水头 坝时，总想浮在水面上，然而被回流所困，被水冲回坝的位置，无法顺水流向下游，这样 持续回圈。 To complicate matters, these dams are usually loaded with debris, such as tires and logs on the surface and rocks and steel bars just below, posing additional problems should a person get trapped in this dangerous structure. 这些堤坝通常会聚积很多杂物，如水面上有轮胎，枯木，水底有石头和钢筋，事情会更复 杂，而且会造成其他附加的问题。 Dams do not need to have a deep drop to create a dangerous backwash. During periods of high water and heavy rains, the backwash current problems get worse, and the reach of the backwash current is extended downstream. 无需多深堤坝就能形成危险的回流。在高水位季及多雨季节里，回流的水流问题就更严重 ，回流的区域可能会扩展到下游。 Small low-head dams that may have provided a refreshing wading spot at low water can become a brutal death trap when river levels are up. Simply put, it is not the drop of the dam which is the lethal danger, but the backwash current. This backwash current is governed by volume of water and flow. 能够提供低水位涉水点的小型低水头坝当水位上升时可能会产生致命死亡的陷井。从坝上 落下不是致命的，但回流是致命的。回流的水流是由水量及流动决定的。 From downstream, you may not realize the danger until it’s too late. From upstream, low-head dams are difficult to detect. In most instances, a low-head dam does not look dangerous, yet can create a life-threatening situation. You should always pay attention to warning signs, markers or buoys and keep well clear of low-head dams. 向下游走时，你可能没有意识到危险，当你意识到时，已经太迟了。向上游走时，低水头 坝不易发觉。在更多的事例中，低水头坝看起来不怎麽危险，但是可能会产生危及生命的 情况。您必须小心注意警告牌，标记及浮标，主动意识它的存在。 Thanks to Virgil Chambers for this article. 谢谢 Virgil Chambers。 --

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