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A barrage too far?

By Dave Elliott

The proposal for a privately funded tidal barrage across the Severn Estuary continues to attract media attention. Last year Peter Hain, former shadow Welsh Secretary, who is backing the idea, had a meeting with David Cameron which he says was a ‘more productive than might have been expected’. Lord Heseltine also included the Barrage as one of the large infrastructure projects he proposed in his recent report to government. The Energy and Climate Change Select Committee has also been looking at it again.

The new barrage proposal is being led by engineering consortium Corlan Hafren, backed by Halcrow, Arup, and Mott MacDonald, and it is claimed that a number of sovereign wealth funds (e.g. Qatar) might provide finance- all in, around £30bn could be needed.

Previous plans for a Barrage by the Severn Tidal Power Group (STPG) were seen as much too expensive and too environmentally damaging: most environmental and wildlife groups like RSPB were strongly opposed and in 2010 the government decided against supporting it as a public project. But it left the door open to private developers. Hafren’s plans involve installing a larger number of larger diameter slower rotation speed low-head turbines, each with a 9-meter (30 foot) diameter, 1,064 in all, mounted in a barrage 11 miles between Lavernock Point on the South Wales coast and Brean in Somerset.

The power station element of the project would, it’s claimed, cost about £25 billion. New road or rail crossings might also be added, raising the costs, and there would be a need for extra flood control and waste-water/sewage clean up, although the barrage might help reduce the impact of surge tides and also reduce silt being carried in suspension. In which case, the water would be clearer, increasing the potential biological productivity, since light would penetrate more deeply.

The barrage would generate electricity on both ebb and flood tides, unlike in earlier plans. Although the total output would be less (you can’t then take either cycle to completion), output would be spread over a longer period in each tidal cycle and extend the time when the mud flats were exposed by about 60%. This, and the changed water turbidity, should lessen the environmental impact to some extent, mitigating the loss of inter-tidal habitat for the bird population. In addition, given the slower rotation speeds, large fish could get through more easily.

The barrage would generate about 16.4 TWh of electricity a year, about 4% of UK needs, but of course, given the changing tidal cycle, even with ebb and flow generation, its output would not match demand patterns well, so its actually useable contribution would be much less.

In 2007 the Sustainable Development Commission suggested that overall the STPGs version would only cut UK emissions by 0.92%:

Not much for £25-30bn! You’d get better C/£ cuts from almost any other renewable option. But Cameron has evidently asked ministers to look at the proposal which, given its size, would require new hybrid bill legislation.

It seem unlikely to go ahead: if at some point there were major energy storage facilities on the grid, then the barrage might make some sense, but as I have argued before, for now it seems a poor strategic option:

In addition, many of the environmental issues still remain. RSPB have yet to decide their position, but the Green Party recently produced a report opposing the new proposal, and backing lagoons and tidal reefs/fences instead:

Friend of the Earth (FoE) have always backed lagoons as a better bet, e.g. Tidal Electrics proposals for Swansea Bay:

A report from two MPs also backed lagoons and identified a whole series of potential sites in the Severn estuary:

These were free-standing fully offshore lagoons, which it is claimed would, unlike a barrage, have minimal impact – they would not slow the flow , or interfere with shipping. For some reason however, DECC has always been hostile to lagoons
But It has only looked seriously at inshore projects , which partly enclose some coast line (thus saving some construction costs) FoE say these would have more environmental impact on inshore ecosystems . The DECC study of the Severn options (barrages, fences and lagoons) is at

In addition to the Severn, there have been detailed studies and comparisons made of fully offshore lagoons and of barrages elsewhere e.g for the Mersey and Solway Firth : basically the conclusion was that offshore lagoons win in terms of eco-impact, but may be more expensive/kWh, partly since they are smaller. See and

There has also been a proposal for a 1GW rated £2m barrage 11 miles across the Wash: see

That is sometimes called lagoon, but it impounds the whole Wash, so it’s not really a lagoon in the sense used above of something in an estuary. The RSPB have opposed it.

Personally I see free-standing tidal turbines (or flow turbines in permeable fences) as much better (you can scale up the numbers) , lagoons as intermediate and barrages as hopeless, especially large ones ; as the study of the STPG proposal produced for WWF and other NGO concluded, a Cardiff-Weston barrage would be about the most expensive energy option there is. See:

A critical vjew was also taken in a recent report on the new Severn Barrage proposal by renewable Regen SW and consultancy firm Marine Energy Matters, which says that tidal lagoons and tidal fences, tidal stream technology, wave and wind power could far less harmful to the environment, and provide up to 14 GW of low carbon energy capacity, more than double that of the proposed large Hafren Barrage.

Even with ebb and flow generation, it seem likely that the big barrage would still also be inflexible, still delivering large busts of power, albeit over longer periods, but still often unrelated to demand. And it would take a long time to build- maybe up to a decade, including planning. By contrast, large numbers of free standing tidal turbines can be installed quickly and incrementally at different sites around the UK coast, so as to produce a more nearly continuous net output: given the delayed tidal maxima at successive points, their peak outputs would occur at different times. At present there are proposals for up to 2GW of tidal current turbine projects at sites in and around the UK, including off Wales and Scotland. We can see how that turns out – and learn as we go. There may be a case for smaller barrages, or more likely, lagoons, but a big problem with large barrages is that it’s all or nothing- you cant build half of one, and if it turns out to have problems (e.g. silting up) you maybe stuck with expensive remedial measures, or even complete failure.

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