Compared to the whitewater streams that tumble down mountainsides,the meandering rivers of the plains may seem tame and lazy.But mountain streams are corralled by the steep-walled valleys they carve.their course are literally set in stone.Out on the open plains,those stony walls give way to soft soil,allowing rivers to shift their banks and set their own ever-changing courses to the sea:courses that almost never run straight.
同山顶飞流直下溅出银白水花的湍流相比，平原上蜿蜒的河流就太无趣了点。不过 山间的湍流被困于它们蚀刻出的深谷。水流游走于巨石之间。到了开阔的平原 石壁被柔软的土壤取代，河岸地势逐渐提高 并由此奔向大海：但奔流时从不走直路。
At least not for long.because all it takes to turn a straight stretch of river into a bendy one is a little disturbance and a lot of time.And in nature,there's plenty of both.Say,for example,that a muskrat burrows herself a den in one bank of a stream.Her tunnels make for a cozy home,but they also weaken the bank,which eventually begins to crumble and slump into the stream.
即使有时间也不长，因为 如果想把直流扳弯只需细微的干扰和极长的时间。自然中 这二者可不缺。比如 一只麝鼠在河岸某侧打出一个洞。这地道是为温暖小窝造的 但削弱了河岸，使其破裂并落入水流中。
Water rushes into the newly-formed hollow,sweeping away loose dirt and making the hollow even hollower,which lets the water rush a little faster and sweep away a little more dirt...and so on,and so on.As more of the stream's flow is diverted into the deepening hole on one bank and away from the other side of the channel,the flow there weakens and slows.
水流冲入刚形成的洞中，带走松散的泥土 让洞更深，这也使水流流速加快 带走更多的泥土 周而复始 由于有深坑一侧的河水流量更多 在河的另一侧 水流流速有所降低。
And since slow-moving water can't carry the sand-sized particles that fast-moving water can,The dirt drops to the bottom and builds up to make the water there shallower and slower,and then keeps accumulating until it becomes new land on the inside bank.Meanwhile,the fast-moving water near the outside bank sweeps out of the curve with enough momentum to carry it across the channel and slam it into the other side,where it starts to carve another curve.
由于缓流携带砂砾的能力不及湍流，泥土便落在水底 逐渐堆积 使该处河水更浅 流速更慢，泥土继续积聚 直到内岸变成新的土地。与此同时 外岸处的湍流 冲出弯曲处 带着足够的冲力横穿河道 撞在河岸另一侧 并开始割出另一道弧。
And then another,and then another,and then another.The wider the stream,the longer it takes the slingshotting current to reach the other side,and the greater the downstream distance to the next curve.In fact,measurements of meandering streams all over the world reveal a strikingly regular pattern:the length of one S-shaped meander tends to be about 6 times the width of the channel.
一道又一道 一处接一处。河流越宽 弹弓般的水流到达岸的时间就越长，弧间沿流距离也越长。实际上 对全世界蜿蜒河流的测量结果 展现了一个惊人的规律：S形曲流的长度大约为河道宽度的6倍。
So little tiny meandering streams tend to look just like miniature versions of their bigger relatives.As long as nothing gets in the way of a river's meandering,its curves will continue to grow curvier and curvier until they loop around and bumble into themselves.When that happens,the river's channel follows the straighter path downhill,leaving behind a crescent-shaped remnant called an oxbow lake.
所以 小弯流看上去正像是大弯的“迷你版”。若河流弯曲时不受外界阻碍，其弯曲处的弧度会越来越大直到形成环绕回自己身上，此时 河道会沿一条直路流下山，留下新月状的“牛轭湖”。
Or a billabong.Or a lago en herradura.Or a bras mort...We have lots of names for these lakes,Since they can occur pretty much anywhere liquid flows,or used to.which brings up an interesting question:what do the Martians call them?