溪流殺人機器：低位差堰/低頭壩 Low-Head Dams 轉錄自古早：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/低頭壩Low-Head Dams：未明情況及存在的危險 by Virgil Chambers，國家安全划艇協會理事會 執行董事 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. 河流可能會很危險，不僅是因為通過水流的力量，所產生的巨大的力量，而且是因為水下 ，或周邊及流經的結構。 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“篩檢程式”似的危險，折斷倒下的樹木，及岩石及橋洞、碼頭之間所堆有的雜物，他 們可能會是漂浮物的陷井，通常是很顯著的。那些對流水運動動力熟悉的人知道當它接觸 到其他不同的阻礙物時，水可能會有困住物體的力量。 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. 橋洞、碼頭及岩石基本上說應是潛在的危險，因為他們靜止而水流動。如果水流速度足夠 快，任何接觸到這些結構的物體或任何人都可能會被緊緊地陷入在上游中。一旦被陷在裡 面，要逃脫是很困難的。可以容易理解危險的存在，及當水流把物體困在阻擋物中間。 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，區別不是很明顯，當與河流最危險的阻擋物關聯時，如低水頭壩。這是人工結構， 主要是建設以儲水在水庫中，以做各種用途。這種象擋水牆似的結構當流過頂部時積成水 塘，並在低水位時跌落。 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. 這種水位跌落產生了水力，產生回流從而陷進並迴圈任何漂在上面的東西。船或者人可能 會被水吸入這種回流中。當人被吸入低水頭壩時，會被帶到面向水壩的上游，在那裡水從 頭上流下，將人向下沖刷，至下麵某處後向下游走，這被稱做“Boil”。“Boil”是一個 位置，在水面下的某處此位置上，水或者被向下游沖或者又被帶到壩上。人被困入低水頭 壩時，總想浮在水面上，然而被回流所困，被水沖回壩的位置，無法順水流向下游，這樣 持續迴圈。 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. 這些堤壩通常會聚積很多雜物，如水面上有輪胎，枯木，水底有石頭和鋼筋，事情會更複 雜，而且會造成其他附加的問題。 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. 無需多深堤壩就能形成危險的回流。在高水位季及多雨季節裡，回流的水流問題就更嚴重 ，回流的區域可能會擴展到下游。 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. 能夠提供低水位涉水點的小型低水頭壩當水位上升時可能會產生致命死亡的陷井。從壩上 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動決定的。 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. 向下游走時，你可能沒有意識到危險，當你意識到時，已經太遲了。向上游走時，低水頭 壩不易發覺。在更多的事例中，低水頭壩看起來不怎麼危險，但是可能會產生危及生命的 情況。您必須小心注意警告牌，標記及浮標，主動意識它的存在。 Thanks to Virgil Chambers for this article. 謝謝 Virgil Chambers。 --

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