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The tidal range in the Severn Estuary is one of the highest in the world, reaching over 13 metres. Ideas for taking advantage of the Severn's high tidal range for energy generation have been talked about for over half a century.

So what is a tidal barrage and how does it produce electricity?

As water flows into and out of the estuary it carries and enormous amount of kinetic energy. The job of the barrage is to extract as much of that energy as possible. A tidal barrage is really just a long, fairly low dam wall. It has tunnels cut into it to let water flow through it in a controllable way. In the tunnels are huge turbine-generators that spin as the water rushes through them to make electricity.

Dam
Barrage Turbine

The Severn Barrage would be between seven and ten miles long, an absolutely vast structure. It would weigh more than the Great Pyramid in Egypt, which took 30 years to complete and 2,300,000 stone blocks. The barrage would take about 14 years to complete.

The Great Pyramid of Egypt

If the barrage is built it would produce as much power as over 800 wind farms and produce zero greenhouse gases. That’s nearly five per cent of the UK’s energy needs! The big advantage is that a tidal barrage can provide power 24-hours a day all year around. This is something no other renewable source of energy can claim.

Severn Barrage

So what’s the down side?

No gain without pain!

Bird

The first draw back is the sheer cost, about £15 billion. The payback period would be long so any government that decided to build one would have to be pretty brave to invest that much cash. Wind farms and nuclear power may simply be cheaper in the short term, and nearly all governments think in the short term!

There’s no point paying out that kind of money and putting up with all the moaning from the public when it is being built only for another lot to get the credit when it’s finished. And there would be a lot of moans and groans. No one can be sure what effect it would have on the environment of the estuary because nothing on this scale has ever been built before.

It would be sure to have some detrimental effects on the habitats of wading birds in particular. The mudflats and salt marshes provide food for around 60,000 birds. Much of this area would be altered or lost completely.

Spin-offs

La Rance Tidal Power Plant

Building a barrage would have some benefits that are not immediately obvious. It would be possible to build a road across the top of the barrage. It fact, it would be essential to maintain the barrage. This could also be used to take off some of the pressure on the other Severn crossings.

Also, this would be by far the most ambitious barrage ever built anywhere. If British engineers would have to face and solve problems never encountered before, these skills would be highly desirable for foreign countries. Many barrages will surely be built all over the world.

The advantages are too great to ignore. British engineering would lead the world in this field and would bring in millions of pounds exporting the knowledge and expertise worldwide.

A small tidal barrage has been operating at La Rance in France since 1960. The power generating section is only 330 metres long, tiny compared to the Severn barrage. It has produced nearly 240MWs of electricity day in, day out for nearly 50 years. This is enough electricity to supply over 190,000 homes. Over this period it has not suffered a single major mechanical breakdown. Not a bad record for any power station.

The big questions:

Is the barrage a visionary idea that will provide clean green energy for the foreseeable future or would the environmental costs be too high?

How can we balance the threat to habitats from global warming with the threat from alternative energy schemes?

Would it be more cost effective, or simply more sensible, to invest more in energy saving schemes than to just keep on building more power stations of any kind?

Could you supply some of your own energy needs with solar panels or small wind turbines on your house?