经济学人下载:堤坝除险 以水御水

Science and technology
科学技术

Flood defences
防洪减灾

Dambusterbusters
堤坝除险，以水御水

Some clever, new ways of stopping rivers flooding
防止河水泛滥的绝妙新方法

THE destruction of New Orleans by Hurricane Katrina in 2005.
2005年的卡特利娜飓风摧毁了新奥尔良。

showed the importance of keeping levees—the artificial banks that contain the flow of partly canalised rivers—in tip-top condition.
这场惨剧提示我们部分渠化的河流其人造大坝即使在洪峰到来，河水漫坝的情况下也要挺住而不出现垮塌是多么重要。

In practice, though, that is hard.
然而，实际上这很难做到。

Levees fail for many reasons, not all of them associated with violent storms,
导致堤坝垮塌的原因很多，并非全都是狂风暴雨所致。

and there are so many of them that keeping an eye on all of them is an almost impossible task.
而且堤坝数量众多，难以对所有的堤坝状况都进行密切监视。

It is good, therefore, to have a backup plan to block up unexpected holes before they can cause too much damage.
因此，事先储备预案极为重要，一旦堤坝出现未曾预料的缺口时能够及时予以封堵，以防造成更大灾难。

The traditional approach is to throw bags filled with sand or rocks into a breach.
一旦堤坝出现裂口，传统的做法是向缺口抛掷沙袋和石块。

Such bags, though, are heavy and unwieldy—particularly if they have to be filled far from the breach and then carried there.
然而这些沙袋死沉，难以搬运。如果不得不在离裂口较远的地方灌装沙袋再运过去的话，这项工作就难上加难。

William Laska of the Science and Technology Directorate at America's Department of Homeland Security has therefore sought out alternatives.
威廉·拉斯卡在美国国土安全部所属的工程科技处工作，

He has found several technologies that have a common theme:
他找到了解决这一难题的办法。

they all use water itself to help stem the flood.
这些方案有一个共同点：以水御水。

The largest of the new devices is designed to block deep breaches.
这些新发明的装置中体积最大是设计用来堵塞宽深堤坝裂口的。

The Portable Lightweight Ubiquitous Gasket is a sausage-shaped balloon made of polyester and PVC, and fitted with motorised pumps.
这种装置叫做便携式通用轻型堵漏包。它是由聚酯纤维和聚氯乙烯制作的圆柱形气球，并安装了发动机带动的水泵。

When dropped into a river, PLUG's pumps switch on automatically and begin forcing water into the balloon through a valve.
把这个装置投入河中，水泵就自动开始工作，通过一个阀门把河水注入气球。

The air thus displaced is expelled through a second valve until the device is 80% full, at which point the pumps shut themselves down.
河水不断注入，球内的空气通过另一组阀门被挤出。就这样直到水充满了80%的球体后水泵就自动停了下来。

Filled thus far, PLUG is still buoyant and will float wherever the current carries it.
灌了这么些水PLUG仍然可以浮于水面，随河水任意漂流。

If it has been dropped in the right place, that will be towards the breach it is designed to fill.
如果投放的位置恰当，它就会漂到堤坝的裂口处。

And there, if all goes well, it will stick—blocking the hole in a manner suitable to its rather contrived acronym.
在这里如果一切顺利的话，就像这个装置有点蹩脚的的英文首字母缩略语道出的，它就会像一个塞子一样堵住裂口。

Prevention, however, is always better than cure, and the second of Mr Laska's devices is designed to stop levees being breached in the first place.
常言说治病不如防病，对待堤坝亦然。拉斯卡先生发明的第二种装置就是用于事先防止堤坝出现垮塌。这

In this case the acronym of choice is REPEL.
种装置的全称是泥土坝便置保护装置，其英文首字母的缩略语REPEL也正好有防御的意思。

REPEL is made of the same material as PLUG, but instead of being thrown into the water and carried to its destination by the current,
它与第一种装置使用同样材料制作，但不是要把它投入河中由水流带到裂口处。

it is laid out flat on a levee that is in danger of being overtopped and thus eroded by the river it is supposed to contain.
一旦河水猛涨漫过堤坝就会对泥土坝造成冲蚀，危及堤坝的安全。此时可以把REPEL铺在堤坝顶上保护堤坝。

In normal circumstances merely placing a layer of protective material on top of a levee in this way would not do much good.
一般来说如果只是这样在堤坝顶部铺一层类似的保护材料在漫坝时不会起到什么作用。

The force of the water would quickly wash it away.
水流的力量会很快将它们冲掉。

However, REPEL has a series of tubes that sit on top of it and can be pumped full of water in a manner similar to that employed by PLUG.
而ERPEL在其上部装上了一系列的粗管，可以如第一种装置一样往这些粗管里灌水。

The weight of these tubes holds the protective layer in place, while the gaps between the tubes permit the overspill to escape.
这些装满水的管子的重量足以固定住这些保护层，漫出堤坝的河水可以在粗管间溢过。

Some flooding from that overspill results—but not as much as if the spill were allowed to erode and destroy the levee itself.
这样虽然有一些河水漫出堤坝，但造成的损失会远远小于由于土坝在水流侵蚀下而垮塌产生的后果。

Yet simply halting floodwaters and preventing short-term damage is not enough.
然而只是堵住了洪水防止了眼前的灾难并不完美。

Neither PLUG nor REPEL can be used permanently.
PLUG与REPEL都是应急设施。

It is the third of Mr Laska's acronyms, REHAB,
拉斯卡先生还有第三套装置，其首字母缩略语是REHAB，又正好有重建之意。

that allows engineers to make permanent repairs.
工程师们可以用它对堤坝进行永久性的修复。

The Rapidly Emplaced Hydraulic Arch Barrier,
该装置的全称叫做便置式拱形折流坝。

made of the same material as the other two devices, can be put in place around a plugged breach to keep it sealed and dry once the PLUG has been removed.
它与前两种装置采用相同材料制作，可以围住一个被暂时封堵住的堤坝裂口，使之与河水隔开。此时就可以将PLUG这个塞子撤掉，晾干堤坝裂口处的泥土。

First, the arch is filled with air and floated to the desired location.
首先将这个拱坝注入空气使它能够漂到指定的位置。

Then, once it is in place, it is partly flooded and allowed to sink to the riverbed around the breach, making a tight seal.
一旦到位，就向拱坝内灌水使它沉到裂口周围的河床上，形成了一道严密的围堰。

That done, a second set of pumps evacuates the gap between the arch and the PLUG, allowing workers access to the site.
这些工作完成后，再调用一组水泵将拱坝与堵塞间的水全部抽干，堤坝抢修工人们就可以进入现场进行堤坝的修复作业了。

Not only is installing REHAB easier and faster than building a conventional temporary dam, it is also less wasteful.
设置一道重建拱坝与常规的方法建临时围堰相比不仅省时、省工，而且还省钱。

A conventional temporary structure is demolished after use.
常规的临时围堰在完工后还需要拆除。

REHAB can simply be floated away and reused—it will have rehabilitated itself, in other words.
这种重建拱坝用完后只需充气排水就可浮起拖走重新使用，这也就是说，这种拱坝是可重复使用的。