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The Severn Barrage is the name of any number of ideas - past and present - for building a barrage from the English coast to the Welsh coast over the Severn tidal estuary. Ideas for damming or barraging the Severn estuary (and Bristol Channel) have existed since the 19th century. The purposes of such a project has typically been one, or several of: transport links, flood protection, harbour creation, or tidal power generation. In recent decades it is the latter that has grown to be the primary focus for barrage ideas, and the others are now seen as useful side-effects.

The building of such a barrage - wherever on the coast it would be sited - would be a huge engineering feat, comparable with some of the world's biggest construction projects. The huge size and cost of most of the ideas over the years are what have kept plans firmly on the drawing board. However, the fact that these ideas refuse to go away even after over a century, and continue to win new converts and supporters among each new generation of people, suggests that there is an aspect both feasible and desirable to the Severn Barrage, that keeps drawing people back to discuss it.

Various projects

There have been numerous proposed projects over the years, some more rational than others.

Severn Barrage Committee - 1981

The most significant of the recent plans is that proposed by the Severn Barrage Committee in 1981. This proposed a 16 km long barrage of concrete powerhouse, sluice and plain caissons together with sand and rock-fill embankments. It would have generated 7200 MW on the flow of the tides. This set of plans was strongly built on a few years later by the Severn Tidal Power Group.

Severn Tidal Power Group - 1989

The Severn Tidal Power Group (STPG) built on the work of the Severn Barrage Committee, but also examined other possible barrages. They concluded that the 1981 plans were the best location for a barrage, but calculated that the power output could be larger, at 8640 MW during flow, or 2000 MW average power. This would provide 17 TWh of power per year (about 6% of UK consumption), equivalent to about 18 million tons of coal or 3 nuclear reactors. The cost in 1989 was calculated to be about £8 billion (£12 billion in 2006 money), and running costs would be £70 million per year.

The barrage would use existing technology as used in the Rance tidal barrage in France and the Dutch sea barrages. Power would be most efficiently generated only in the flow direction, and this effect on tidal range would mean that the tidal extent would be halved by losing the low tide rather than the high tide. That is, that the tide would only go out as far as the current tidal mid-point, but high tides would be unaffected (unless the barrage was deliberately closed to prevent a high-tide).

The barrage would contain 216 x 40 MW turbines for the 8640 MW total. Arrays of sluices would let the tide in and then close to force it out through the turbines after the tide has gone out some distance outside the barrage. This deliberate building of a head on the water builds pressure that makes the turbines more efficient.

The barrage would contain a huge set of shipping locks, designed to handle the largest container vessels. Construction would take about 8 years and would require 35,000 employees at peak build time. The minimum lifespan of the barrage would be 120 years, but could easily be 200 years if decent maintenance was performed.

The STPG appraisal concluded that the electricity generated from the barrage would make the scheme economically viable if given certain "green" advantages, and that the environmental impact was acceptable. The government of the day did not accept this and shelved the plans. However, since then global warming has radically altered the public perception of environmental damage; and soaring oil, gas and energy costs have made the economics of the barrage much more favourable. The advent of renewable energy discounts favours electricity generated from "green" sources; and in addition, much lower interest rates make the cost of loans much lower, and long-term financing of such massive projects is now more viable. Consequently, there have been renewed calls for these plans to be re-appraised.

Benefits and Disadvantages

Benefits

Disadvantages

  • Enormous project of a size that the UK is unused to dealing with
  • Shipping would have to navigate locks
  • Severn bore may be weakened
  • Some of the low-tide mud-flats would be lost, taking with them some of the wading birds that make the estuary a protected area
  • Existing ecosystems would be heavily altered, with new species moving in and perhaps dominating old species

Dangers?

It should be noted that, unlike river dams, there is no danger associated with collapse of a tidal barrage. If a freak earthquake were to break the barrage, the water would flow out (or in) at the speed of the tide, just as it does now, and just as it would during construction. This would only represent a danger to those caught directly in the current, as it does now. Even so, it is inevitable that a 16 km long structure will be hit by shipping in the timescale of 200 years, and this must be accounted for.

Construction Costs

The estimated costs of the most recent plans are huge - perhaps £10-15 billion. However, the recent plans have assumed that the project would be privately financed, and so in effect the matter of cost becomes a private one between the building consortium and their banks. If the banks feel that the project is viable and decide to lend the money then the projects will go ahead; if they don't then it wont. None of this cost would directly fall on the tax-payer. There would though be secondary knock-on costs from the barrage that might be met by the tax-payer, such as modifying existing ports and dealing with environmental change. However, these would be offset by the positive knock-on effects, such as transport links and flood protection - which would have otherwise also cost tax-payer money. Whether the parties actually decided to exchange monies for these knock-on effects would be a matter for Government negotiation.

Environmental Impact

The environmental impact of the barrage would certainly be huge. The present strong tidal currents in the estuary serve to lift up silt sediment and so keep the water very thick with fine particles. This blocks light-penetration and means that the Severn Estuary marine environment is actually a relative desert, in terms of both plant and fish life. The calming effect of the barrage on the tidal currents would lead to much less sediment being lifted and better light penetration, changing significantly the habitat in the water, and probably making it significantly more productive. However, the estuary is a quite unique harsh environment as it is and it is legitimately argued that "making the desert bloom" is a form of environmental destruction.

It should be noted that the barrage will not create a "lagoon" - as both opponents and supporters have sometimes claimed ("stagnant" or "blue" respectively). The tidal power stations by definition require that the tide flows through the barrage, and the tidal range would still be a massive 8m.

The RSPB opposes any Severn Barrage because of the effect it will have on the birds' habitat in the estuary. Friends of the Earth support the idea of tidal power, but oppose barrages because of the environmental impact. They have proposed their own plans based on the concept of tidal lagoons (see references), whereby vast manmade lagoons in the estuary catch water and drain it through turbines. This idea is based on a prototype now being designed at Swansea bay. However, leading figures in the construction industry are sceptical that the lagoons can be economic or practical on the scale that would be necessary to reach the power output of a barrage.

The environmental effects of the barrage still need a great deal more analysis before final conclusions can be drawn.

Vested Interests

It has been suggested that powerful construction industry based vested interests are the main force behind Severn Barrage proposals. Clearly, any project with a budget of several billion pounds will rouse numerous vested interests both for and against it. However, in order to understand where the vested interests might lie, it is necessary to see the wider picture. The alternative to any Severn Barrage would probably be three nuclear power stations; and these are huge facilities that would have to be built by someone - the same construction industry that stands to gain from the barrage. Friends of the Earth admit that their proposals for "lagoons" would require 20 times as much construction material as the Barrage to build, and so should be even more desirable for the construction industry if driven by vested interests. In the end, the vested interests of those wanting the Barrage built will come up against the vested interests of those who do not want it built; and these include not only bird protection and environmental groups, but also the nuclear and oil industries.

See also

External Links

Energy in the United Kingdom | Electric power | Renewable energy | Coastal construction | Tide

 

This article is licensed under the GNU Free Documentation License. It uses material from the "Severn Barrage".

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