Narrator: Listen to part of a lecture in an environmental science class.

旁白：请听一段环境科学的讲座。

Professor: Now, there is growing interest these days in generating electricity from renewable energy sources, right?

教授：现在，人们对利用可再生能源发电越来越有兴趣，对吧？

From developing wind farms to tapping into an underground source of geothermal energy.

从开发风电场到开采地热能，可见一斑。

And when you're considering a new project, it's important to look at the costs as well as benefits of developing that energy source.

考虑一个新项目时，既要考虑开发该能源的好处，又要考虑成本，这两者都很重要。

Let me give you an example of the kind of thing I am talking about.

我给大家举个例子。

There is currently a lot of interest in harnessing the power of the oceans, of the ocean tides, that is, the movement of huge amounts of water which causes the water level of oceans to rise and fall.

目前人们对利用海洋的力量有浓厚的兴趣，也就是能引发海洋的水位上升和下降的海洋潮汐。

The idea is that if we can harness that tidal energy, it'd be a great clean renewable energy source.

其理念是，如果我们可以利用这种潮汐能，那将是一种很好的清洁可再生能源。

One place where this tidal energy can be harnessed is at a shallow body of water, such as an estuary.

而可以利用潮汐能的一个地方是浅水区，比如入海口。

Now, can anyone tell us what an estuary is?

谁能告诉我们入海口是什么？

Yes, Ted.

Ted。

Student: An estuary is where a river enters the ocean.

学生：入海口是河流流入海洋的地方。

The fresh water meets the ocean water.

淡水与海水相遇。

Sometimes it is covered in water.

有时，入海口会被水淹没。

Sometimes it is not.

有时不会。

Professor: Some parts of the estuary, as the tides go in and out, but other parts are always submerged.

教授：由于潮汐的涨落，入海口的某些部分确实会这样，但还有一部分一直是淹没在水中的。

Now, estuaries are an ideal place to try to capture energy from changes in tides because, well, there is an exceptionally large difference between the water level at high tide and at low tide.

入海口是试图从潮汐变化中获取能量的理想场所，因为在高潮和低潮时水位有非常大的差异。

All that movement of water generates a lot of energy.

这些大量的水的运动会产生巨大能量。

And one way to harness that energy is by building a structure called a barrage there.

而利用这种能量的一种方法是建拦河坝。

A barrage is basically a large low dam that's built across an estuary.

拦河坝就是一个建在入河口的大型低坝。

When the tides go in and out, the moving water flows through tunnels in the barrage.

当潮汐涨涨落落时，水会流过拦河坝中的隧道。

So you have huge amounts of water trying to flow through these relatively small tunnels and that turns turbines that generate electricity.

因此，当大量的水要流经这些较窄小的隧道时，就能带动涡轮机发电。

Now, these estuaries are important because of their high level of biological productivity.

这些入海口很重要，因为它们有很高的生物生产力。

They are home to lots of birds, fish and other marine life.

它们是很多鸟类、鱼类和其他海洋生物的家。

So when you propose to construct a barrage, you have lots of issues to consider.

因此要建拦河坝时，需要考虑的很多问题。

For example, it would change the existing water levels in the estuary.

例如，拦河坝的建设会改变入海口现有的水位。

Since a lot of water is getting held up by the barrage, the incoming tides won't go as high, but they wouldn't be as low during low tide, either.

由于拦河坝拦截了大量的水，即将来临的潮汐不会涨很高，但落潮时，也不会很低。

This might help prevent flooding.

这可能会有助于防洪。

But it would also affect the mudflats, those areas of mud that normally are exposed when the tide recedes.

但也会影响到泥滩，泥滩是潮水退去后露出的淤泥地带。

Student: But don't lots of birds rely on exposed mudflats for food?

学生：但是，不是大量的鸟要依赖露出的泥滩提供食物吗？

I mean, don't they eat tiny animals that live in the mud?

我是说，它们不吃泥田中的小动物吗？

And what about those tiny animals?

那些小动物又怎么样了呢？

What would happen to them if the mudflats were endangered?

如果泥滩受到威胁，会有什么事发生到它们身上？

Professor: So you are seeing some of the potential problems with the barrage.

教授：所以你看到了拦河坝的一些潜在问题。

But consider this, right now, the water in an estuary is very cloudy.

但是想想另一面吧，现在入海口的水是浑浊的。

The tidal currents are constantly churning up the sediments that rivers deposit in the estuary.

潮汐流不断搅动着河流入海口沉积的沉淀物。

But a barrage would reduce the tidal currents.

而拦河坝会减少潮汐流。

So a lot of that sediment would settle to the floor of the estuary.

所以很多沉淀物会沉积到入海口的海底。

It wouldn't get stirred up so much.

不会被搅拌起。

The water would be clearer, allowing more sunlight to reach deeper into the water, which might lead to more food for birds and other animals, attracting new wildlife to the area.

水会更清澈，能更多的阳光能到达更深的水中，这可能会为鸟类和其他动物带来更多的食物，也会吸引新的野生动物到该地区来。

So it's a complicated environmental picture.

因此，这是一个复杂的环境问题。

Student: Have they tried this anywhere?

学生：他们尝试过这样做吗？

Built a barrage?

建过拦河坝吗？

Professor: Yes, there are several in operation.

教授：建过，有几个拦河坝正在使用中。

There is one in France.

其中一个在法国。

Now, they have to be careful there about how they turn on the turbines because they create currents and waves that can affect boats.

拦河坝工作人员需要小心翼翼地使用涡轮机，因为涡轮机推动的水流和波浪会影响船只。

But I haven't read about any major ecological problems.

但目前我还没有看到任何重大的生态问题。

In fact, the fishing is supposed to have improved.

事实上，捕鱼业应该有所改善。

Plus there is even more bird life.

而且现在有更多的鸟生活在泥滩。

But some of the barrages we're considering now would be much larger than that one.

但是有些将要建设的拦河坝比我们现在讨论的要大很多。

There has been one proposed for the estuary of Great Britain's Severn River, one of the largest estuaries in the world.

有人提议在世界上最大的入海口之一——英国塞文河入海口（建一个）。

It would be 16 kilometers long.

会有16千米长。

Just to give you an idea, the barrage in France is less than a kilometer.

就想一下吧，法国的拦河坝还不到1千米。

Outside of environmental concerns, such a project would be hugely expensive and that's another argument against barrages, well, such large ones anyway.

除了环境方面的考虑，这样一个工程，额，也就是这么大的，一定耗资巨大，这也是反对拦河坝的又一理由。

Critics say that it would better to use that money for something else, such as improving the energy efficiency of buildings.

反对者认为，这笔钱最好用于其他方面，例如用来提高建筑物的能效。

You could make a lot of buildings more efficient with all that money and that would reduce the need for electricity.

用这些钱，你可以让很多建筑更加高效，从而减少对电力的需求。