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为什么河流是弯曲的? – 译学馆
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为什么河流是弯曲的?

Why Do Rivers Curve?

与山坡上奔腾流下的溪水相比,平原上
Compared to the whitewater streams that tumble down mountainsides, the meandering rivers
蜿蜒的河流可能看起来无精打采且慵懒。但是,山溪会被它们所雕刻而成的山壁所阻拦
of the plains may seem tame and lazy. But mountain streams are corralled by the steep-walled
-它们的流动方向总是一成不变的。在空旷的平原上,
valleys they carve – their courses are literally set in stone. Out on the open plains, those
那些石头墙给软土让步,给予河流更多的自由空间去改变河岸
stony walls give way to soft soil, allowing rivers much more freedom to shift their banks
并让它们千变万化的流向集中于大海:河的流向几乎从来不是直的。
and set their own ever-changing courses to the sea: courses that almost never run straight.
至少不会很久,因为将一个直的河段变成弯曲的,
At least not for long, because all it takes to turn a straight stretch of river into a
需要很多的阻挠和大量的时间-而且在大自然中
bendy one is a little disturbance and a lot of time  – and in nature, there’s plenty
通常两者都兼有
of both.
比如说,麝鼠会在溪流的一岸给自己挖个洞穴。
Say, for example, that a muskrat  burrows herself a den in one bank of a stream. Her
她的隧道让洞穴变成一个舒适的家,但是这样做的同时,麝鼠也在削弱河岸,
tunnels make for a cozy home,  but they also weaken the bank, which eventually begins to
最终导致河岸崩裂并塌落到河水中。
crumble and slump into the stream.
河水涌进新建成的洞穴中,清走了松软的泥土并使洞穴更空,
Water rushes into the newly-formed hollow, sweeping away loose dirt and making the hollow
这让河水流得更快并带走更多河岸上的泥土…
even hollower, which lets the water rush a little faster and sweep away a little more
反复如此。
dirt from the bank…and so on, and so on .
随着越来越多的流水被转移到河流一岸上的深洞中,
As more of the stream’s flow is diverted into the deepening hole on one bank and away
并远离河道的另外一岸,那里的流水变得孱弱且缓慢。
from the other side of the channel, the flow there weakens and slows. And since slow-moving
并且缓慢的流水不能带走那些只有湍急流水可以带走的沙粒大小的颗粒,
water can’t carry the sand-sized particles that fast-moving water can, that dirt drops
泥土落到河道底部并累计起来,使那里的流水变得更浅更慢,
to the bottom and builds up to make the water there shallower and slower, and then keeps
并不停累积,直到河流边缘在河岸中间形成一个新的陆地。
accumulating until the edge of the stream becomes new land on the inside bank.
与此同时,靠近河岸内部的湍急的流水
Meanwhile, the fast-moving water near the
会扫出一条有足够动力的弯道去跨越河道
outside bank sweeps out of the curve with enough momentum to carry it across the channel
并撞击到河的另一边,在那里开始刻画另一条弯道。
and slam it into the other side, where it starts to carve another curve . And then another,
然后一条又一条。河流越长,反弹到达另一边的时间也越长
and then another, and then another. The wider the stream, the longer it takes the slingshotting
顺流到下一个弯道的距离也越远。
current to reach the other side, and the greater the downstream distance to the next curve.
事实上,关于全球蜿蜒的河流的测量揭露了一个惊人的模式:
In fact, measurements of meandering streams all over the world reveal a strikingly regular
一个S形状曲流的长度趋向大约有河道宽度的六倍长。
pattern : the length of one S-shaped meander tends to be about six times the width of the
所以小型的蜿蜒的河流,
channel . So little tiny meandering streams tend to look just like miniature versions
就像是它们近亲的缩小版。
of their bigger relatives.
只要没有东西阻挡一条河的蜿蜒而流,它的弯道会继续变得更加曲折,
As long as nothing gets in the way of a river’s meandering , its curves will continue to grow
直到它们弯曲成圆并撞击自身。当这发生时,
curvier and curvier until they loop around and bumble into themselves. When that happens,
河流沿着更笔直的道路下坡,留下一条新月形状的痕迹,
the river follows the straighter path downhill, leaving behind a crescent-shaped remnant called
这叫牛轭湖,或者叫马蹄湖、死臂…
an oxbow lake. Or a billabong. Or a lago en herradura. Or a bras mort …
我们给这样子的湖取了很多名字,
We have lots of names for these lakes, since
它们常常就发生在流动的河水上,并引出了一个有趣的问题:
they can occur pretty much anywhere liquid flows – which brings up an interesting question:
火星人怎么称呼它们?
what do the Martians call them?

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