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My Lords, I congratulate the noble Lord, Lord Cameron, on securing this debate, because the subject has always been of great interest to me. It must have been nearly 50 years ago, when I was a young engineer, that I worked on the Severn barrage project. It was in the days when big projects were great fun. We built the Thames barrier—I did not build it, but others did—big airports in the middle of the countryside and the Severn barrage. I remember people at the time saying, “We might need 500 million tonnes of rock, but we can knock down a few Welsh hillsides and put them in the sea; that will be all right”. Somehow, we have to build a piece of concrete, presumably, that will take all the turbines that the noble Lord mentioned—he is quite right—get them out there and sink them as a big caissons, a bit like the D-day ones 20 or 30 years on. We will have a nice road and railway across the middle and that will be fine.
As the noble Lord said, the benefit of tidal power is that you can predict when the tides will flow. We looked at Morecambe Bay and the Severn and found that, because there was a difference of three hours between the tides—there is always a difference of three hours, I am told—we could get a consistent output of power, presumably with suitable connections between the two. We are a long way from that but you can predict it, which makes it very different from wind turbines, which have a really good place in our energy mix now but you cannot predict them as well. So I am a great believer in tidal generation. Where I disagree with the noble Lord, Lord Cameron, is that I think the technology, as many noble Lords have said, has moved forward to underwater turbines, either fixed to the seabed or on pontoons. The Devon and Cornwall local enterprise partnership is looking at pontoons for putting a windmill in the air and turbines underneath, moored offshore. That seems the best of both worlds and a technology we should be looking at to harness the tides. We must harness them.
Many noble Lords have talked about good locations and there are many of them. I am sure it can be done. My worry about barrages goes back to my time spent looking at this project. We ended up getting worried about quite a few things. In the Severn, birds are obviously very important—not just at Slimbridge but in quite a few other places. They are in other places, too. Silting would be a serious problem in the Severn, not just if there were a barrage across the middle, but even if it were something like that at Swansea Bay. You can never tell, without doing a great deal of work, how much the silting will change. Will it get better or worse, and how much maintenance dredging would you have to do if you wanted to keep shipping? Of course, the Port of Bristol has always been very much against the Severn barrage, as noble Lords will understand, for very good reasons.
There was also a proposal, I think, as part of Boris Johnson’s idea of building an airport in the Thames estuary, to put a bridge or a dam across the Thames, not only to be able to get across by road or rail but also to generate electricity. The tidal range is much less on the Thames than on the Severn, but the silting problem would have been just as bad, and it is bad enough there anyway. What not everybody seems to appreciate is that you have to find all the rock—it is mostly rock, I think—to build such barrages. To take the example of Swansea Bay that the noble Lord, Lord Cameron, mentioned briefly, one proposal was to get the rock from the east side of the Lizard peninsula in Cornwall, where I live, from an old quarry. All the rock would have gone out by sea, quite a few jobs would have been created locally and there would have been very little extra traffic. The environmental fuss that was made, rightly or wrongly, about taking a comparatively small amount of rock to build this, compared with going all the way across the Severn, was quite surprising to me.
We have to recognise that, in the state we are in now, when we are all very good at protesting at things and opposing things—I am quite good at that myself sometimes—we have to think about the best way of avoiding too much disruption. I suspect that with something like the Severn barrage or Morecambe Bay, you would end up getting the rock from somewhere like Sweden or Norway, or perhaps the Outer Hebrides, with lots of rock to ship. We may have moved on and I hope we can therefore direct more attention to the new technologies, as I call them, of underwater turbines, than we do at the moment. I know that the La Rance barrage in France works well, but that was built a long time ago. It may be therefore that the technology of barrages is being overtaken by the technology of underwater turbines, such as those on board barges or on the seabed.
The noble Lord said that once one is built, there is no maintenance. I slightly disagree with him there. Turbines, whether in barrages or on the seabed, need maintenance. The sea is a pretty hostile environment and there is not much you can do about that. You have to find a way of maintaining them easily, whether off a barge, a roadway or whatever. The way that the offshore industry—not just oil but windmills as well—has taken the technology forward will mean that that will get easier and therefore cheaper in the future. But it still needs doing.
The addition from the barrage point of view was mainly the cost of dredging. If you are trying to keep a shipping lane open or dealing with the changes that happen when the tide comes in and out or goes around, it will need dredging. We have all read about the River Nile and the Aswan Dam, which is completely different because it brings silt down from the middle of Africa. It may have seemed a wonderful scheme 50 years ago, but now it is almost full of silt. The same could happen in the Bristol Channel and in many other rivers. There is a great deal of silt in there and one never knows quite what will happen to the silt and how it will affect it.
I support the need to get much more energy for our country out of tidal movement. There are many places where we could do it; we should be encouraging the research and development of things that sit on the seabed, on barges or wherever they may be. I have a friend who has been dealing with the trials on the Pentland Firth. Amazingly, he has only a 15-minute window during which he can drop things on the seabed before the tide starts rushing in the other direction. They are doing it, so it works—it just needs a bit more development. I would therefore argue against any more lagoons of any size, which will cause more problems in the future. Together, I hope we can get the sum total of a great deal more tidal energy than we have at the moment.