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Some proposals also include a double track [[railway]] line across the barrage. A railway would have a longer approach up to a fixed bridge over the locks. The approach would be greatest for non-[[electrified]] heavy railway capable of taking freight, slightly less for non-electrified passenger line, and less still for electrified passenger line. However, there is no electrification in the Bristol or Cardiff areas. An alternative to a fixed bridge would be a [[swing bridge]], though there is concern expressed at this reducing capacity through the locks and on the railway. However, two swing bridges, one at either end of the lock would mean that one bridge could be kept open to railway traffic at all times. The double track could be reduced to single track at this point without creating too much of a bottleneck, or if double track is required this could be worked around by grade separating the two lines and having double-decked bridges. The line could then be used to partially relieve the [[Severn Tunnel]].
Some proposals also include a double track [[railway]] line across the barrage. A railway would have a longer approach up to a fixed bridge over the locks. The approach would be greatest for non-[[electrified]] heavy railway capable of taking freight, slightly less for non-electrified passenger line, and less still for electrified passenger line. However, there is no electrification in the Bristol or Cardiff areas. An alternative to a fixed bridge would be a [[swing bridge]], though there is concern expressed at this reducing capacity through the locks and on the railway. However, two swing bridges, one at either end of the lock would mean that one bridge could be kept open to railway traffic at all times. The double track could be reduced to single track at this point without creating too much of a bottleneck, or if double track is required this could be worked around by grade separating the two lines and having double-decked bridges. The line could then be used to partially relieve the [[Severn Tunnel]].

The option for a new fixed rail link has implications for several wider transport proposals. One of the proposed routes for an Irish Sea Tunnel is from Fishguard, which would generate large amounts of extra freight traffic which the current Severn tunnel - already operating at capacity - could not handle. Additionally, a new [[high speed rail]] route has been suggested between London, Bristol, and Cardiff, which faces similar capacity constraints.


==Opinions==
==Opinions==

Revision as of 18:38, 15 December 2008

Template:Future infrastructure

File:Severn estuary barrages.png
Barrage locations considered over the years. Black indicates lines of most interest, with associated peak power generation at that location.

The Severn Barrage is the name of a number of ideas 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 UK Government is currently undertaking a Severn Tidal Power Feasibility Study which will consider all tidal range technologies (including barrages, lagoons and others) in the Severn estuary.

The building of such a barrage 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.

History

There have been numerous proposed projects over the years, initially to provide a safe harbour and more recently to generate electricity.

Early Projects

File:Fulljames.jpg
Thomas Fulljames's own impression of his proposed Barrage

In 1849 Thomas Fulljames, a civil engineer and the county surveyor for Gloucestershire proposed a barrage from Beachley to Aust (now the site of the first Severn Bridge), a span of just over 1 mile (1.6 km). Since this was before serious electricity demand, the first proposals were based on the desire for a large shipping harbour in the Severn Estuary, and also road and railway transport and flood protection.[1]

No action was on Fulljames proposals and three quarters of a century later, in 1925, an official study group was commissioned. An awareness of the large tidal range of 15 metres (49 ft),[2] second only to Bay of Fundy in Eastern Canada,[3][4] led to a proposal to generate 800 Megawatt (MW) of electricity at English Stones and although considered technically possible, it was prevented on economic grounds (then costing £25 million).[5] The viability was tested a few years later in 1931 when Paul Shishkoff, a Russian immigrant, demonstrated a 300 horsepower prototype tidal generator at Avonmouth.[6] It included a novel mechanism for spreading the power output over 24 hours. The full barrage was estimated at £5 million at the time.

In 1933 the Severn Barrage Committee Report (HMSO) from a committee chaired by Lord Brabazon recommended that a 800MW barrage across the English Stones area would be the best option.[7] The work was interupted by World War II and then revived in 1945 when engineers predicted an output of 2.2 terawatt hours (TWh) per year.[8] A further government study looked at barrage options in 1948 and estimated the construction costs at £60 million.[6] By the time of the next study in 1953 the estimated cost had risen to £200 million.

In 1971 a report by Dr Tom Shaw, a tidal Power expert and advocate proposed a barrage from Brean Down to Lavernock Point. The scheme was estimated to cost £500 million.[citation needed] In 1975 the Central Electricity Generating Board (CEGB), published a study with evidence from Bristol and Salford universities for the Secretary of State’s Advisory Council on Research and Development for Fuel and Power.[9] As this was the era of cheap oil, the council established that a barrage could not be economically viable unless the energy situation deteriorated significantly.

Bondi Committee - 1981

File:Barrage map.jpg
Proposed location of Bondi Committee Barrage

After just such a deterioration (due to the Iranian Revolution and oil shock) the plans were reinvestigated by the Severn Barrage Committee in 1981. This committee was known as the "Bondi Committee" (after Professor Sir Hermann Bondi). The committee investigated 6 possible barrage locations, from English Stones at the top of the estuary, down to a location largely at sea in the Bristol Channel between Lynmouth in North Devon and Porthcawl in South Wales. It produced a major energy paper, [10] which recommended a 10 miles (16 km) long barrage of concrete powerhouse between Brean Down and Lavernock Point, sluice and plain caissons together with sand and rock-fill embankments. It would have generated 7200 MW on the flow of the tides (the largest barrage considered could have produced double that power output). This set of plans was strongly built on a few years later by the Severn Tidal Power Group.

In 1984 Wimpey Atkins proposed a smaller barrage at English Stones, in the hope of creating a smaller more economically viable project that would avoid the environmental impact of a large barrage.[11]

Hooker or Shoots Barrage - 1987

File:Shoots turbine.jpg
Cross section of Shoots Barrage turbine housing

This Wimpey Atkins 1984 study was criticised because it did not tackle the issue of silting and in 1987 Arthur Hooker OBE (a former partner of WS Atkins) in conjunction with Parsons Brinckerhoff prepared a revised barrage proposed at English Stones to better tackle this issue.

Parsons Brinckerhoff further updated their earlier proposal in 2006 and current estimates for this barrage (now known as the "Shoots Barrage") would cost £1.4 to £1.8 billion to build, and generate 2.75 TWh of power per year. At the highest tidal range, it would develop a peak output of 1050 MW, and 313 MW output on average throughout the year. Thus the Shoots Barrage is about 1/7th of the size and cost of the STPG proposals.[citation needed]

File:Shoots cross section.jpg
Cross section of embankment

The barrage would be located just below the Second Severn Crossing – i.e. above Cardiff and Bristol on the estuary – and so much smaller locks would be needed for upstream access to Sharpness and Gloucester docks as the large ports of Portbury and Avonmouth would be unaffected.

Like the STPG proposal, Hooker generates only on the ebb tide. Construction time would be four years. It would be built of rock fill embankment at the coastal sides (more like the proposals for "Tidal Lagoons"), but like the STPG would be sluice caissons and turbines with powerhouse in the middle section.

Severn Tidal Power Group - 1989

The £4.2 million study by Severn Tidal Power Group (STPG) built on the work of the Severn Barrage Committee, but also examined other possible barrages, and produced another major energy paper.[12] 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 – about the same as 6 nuclear reactors, but different lifespan), and running costs would be £70 million per year (about the same as 1.5 nuclear reactors).[citation needed]

File:Barrage profile.jpg
Diagram of the STPG Barrage

The barrage would use existing technology as used in the Rance tidal barrage in France, the Annapolis Royal Generating Station in Canada 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 flooding).

File:Barrage prefab caissons s.jpg
Construction in prefab caissons

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.[citation needed]

The barrage would contain a 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 (about 3 times that of a nuclear reactor), but could easily be 200 years if decent maintenance was performed.[citation needed]

File:Barrage view.jpg
Artist's impression of aerial view of STPG Barrage

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.[citation needed] Margaret Thatcher's government 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. However, there is the question of the applicability of the term "renewable energy" to tidal power, as the root energy source is the rotational kinetic energy of the earth, which is not renewed.

Severn Lake - 2006

In 2006 Gareth Woodham, a businessman from Neath in Wales, submitted plans called "The Severn Lake" to Sedgemoor District Council in the name of Combined Innovations Ltd for a barrage from Brean Down near Weston-super-Mare, to Lavernock Point near Cardiff.[13] According to Woodham, the barrage would feature 14 electricity generating turbines, a dual carriageway, a light railway, four marinas, and two lock gates to give ships passage. It would supply electricity for the whole of the South West, and according to Woodham it would cost about £650 million and take up to 20 years to complete.

However, it is not clear how Woodham's plans, which are more ambitious than those of the STPG, could be delivered for 1/20th of the cost.

Severn Tidal Reef - 2007

Evans Engineering (Joseph Evans & Sons Limited) have released plans for what they call a Severn Tidal "Reef" [1]. This is a novel structure which aims to overcome the environmental side-effects of a barrage, and can be conceptualised as being half-way between a barrage and a tidal "fence" (a linked string of tidal-stream turbines). One of the engineers, Rupert Evans, had previously worked on a tidal fence proposal, but since dismissed it as unworkable.

The reef reduces environmental impact by working with a much smaller "head" of water (just 2m) and thereby reducing the impact of the structure on the estuary water and flow. The smaller head means that the water flow speed is much lower, and therefore the energy extracted is much less. However, the structure aims to compensate for this by generating in both ebb and flow directions, and by siting the structure at the "outer" Minehead to Aberthaw line, which roughly doubles the volume of tidal water available.

Sustainable Development Commission - 2007

On 1 October 2007, the UK's Sustainable Development Commission (SDC) published a report looking at the potential of tidal power in the UK,[14][15] including proposals for a Severn barrage. The report draws on a series of five evidence-based reports, one of which summarises all the available evidence from previous studies on a number of Severn barrage options, but focusing on the Cardiff-Weston and the Shoots schemes. The SDC also commissioned a programme of public and stakeholder engagement, which included a national opinion poll and a series of local and regional workshops.[16]

The SDC gave its support to the building of a Severn barrage, providing a number of strict conditions were met. These include:

  • A Severn barrage should be publicly led as a project and publicly owned as an asset to avoid short-term decisions and ensure the long-term public interest
  • Full compliance with the EU Habitats and Birds Directives is vital, as is a long-term commitment to creating compensatory habitats on an unprecedented scale
  • Development of a Severn barrage must not divert Government attention away from much wider action on climate change

The SDC also raised the challenge of viewing the requirement for compensatory habitat as an "environmental opportunity", through the potential to combine a climate change mitigation project with the adaptation that will be required to respond to the effects of climate change. A publicly led project would enable the use of a low discount rate (2%), which would result in a competitive cost of electricity, and would limit the economic impact of even a very large-scale compensatory habitats package. Electricity production costs are not competitive if a commercial discount rate is applied.

UK Government study announced - 2007

A two year feasibility study was launched in 2007[17] and the terms of reference were announced on 22 January 2008[18] following the report from the Sustainable Development Commission. This study focuses on a variety of tidal range technologies including barrages, lagoons, a tidal fence and a tidal reef in the estuary and builds upon past studies. It aims to provide an up-to-date analysis of all the key issues involved. The study led by John Hutton, Secretary of State for Business, Enterprise and Regulatory Reform (BERR) has strong support from Jane Davidson, Minister for Environment, Sustainability and Housing in the Welsh Assembly Government as well as other government departments.[19][20]

The study aims to gather and assess evidence to enable Government to decide whether it could support a tidal power scheme in the Severn Estuary. The study will be taking advice as necessary and will be engaging with stakeholders and the public on a regular basis.

Key work areas involved are:

  • The environmental impacts on biodiversity and wildlife; flood management; geomorphology (the study of the evolution and configuration of rocks and land forms); water quality; landscape and compensatory habitat;
  • Engineering and technical areas such as options appraisal; costs; design and construction and links to the National Grid;
  • Economic considerations - financing; ownership and energy market impacts;
  • The regional social, economic and business impacts;
  • Planning and consents - regulatory compliance; and
  • Stakeholder engagement and communication.[21]

Part of the study includes a Strategic Environmental Assessment (SEA)[22], which is a formal environmental assessment of plans or programmes which are likely to have significant effects on the environment. A consortium led by Parsons Brinckerhoff (PB) has been appointed to manage this part of the project. The process is guided by a stakeholder steering group.

The feasibility study will be a two-phase process with two public consultations. The first phase is likely to run until late 2008 and will reach an initial view on whether there are any fundamental issues that would prevent a tidal scheme in the Severn Estuary. Subject to the decision, the second phase will look at the issues in more detail and culminate in a full public consultation late 2009 to early 2010.[23]

Benefits and Disadvantages

Benefits

  • Predictable source of "green" energy during lifetime of barrage
  • Home-grown facility, independent of foreign uncertainties
  • Flood protection for the vulnerable Severn estuary, including against global warming sea level rises
  • Transport links for road and/or rail
  • Better shipping and boating conditions behind the barrier
  • Boost to local economy - construction industry in the short term, tourism and infrastructure in the long term Cite error: The <ref> tag has too many names (see the help page).
  • Reduced turbidity (cloudiness) of water will improve the density and spread of invertebrate colonies in the estuary. This should lead to better carrying capacity for migratory fish and birds. Cite error: The <ref> tag has too many names (see the help page).

Disadvantages

  • Existing ecosystems would be heavily altered, with new species moving in and perhaps dominating old species
  • Some of the low-tide mud-flats would be lost, displacing some of the wading birds that make the estuary a protected area
  • Lack of industry skill in the UK of a project of this size.
  • Likely to stimulate silting in some areas and coastal erosion in others
  • Enhance flood risk on the seaward side because only a proportion of the water that presently flows up stream will pass through the barrage leaving the remainder to rise up outside possibly raising levels by as much as a metre.
  • Shipping would have to navigate locks
  • Costs associated with navigating the locks would impact trade and commerce
  • Severn bore weakened
  • All industrial discharges into the River Severn (e.g. from Avonmouth) will have to be reassessed.
  • Negative visual impact upon the landscape (subjective, c.f. Wind turbines)
  • Huge amount of concrete (etc.) needed - quarrying of stone likely to impact on other areas.
  • Cost of build would mean the buy back time would be considerable and the barrage may only have a finite life span due to silting up behind barrage negating the "green" element.[citation needed]

Dangers

Unlike river dams, there is no danger associated with collapse of a tidal barrage. If a freak earthquake (or a ship collision) 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.[citation needed]

Environmental impact

The Severn Estuary is a Special Area of Conservation due to the European importance of its ecology. The inter-tidal area provides food for over 85,000 migratory and wintering water birds, and represents 7% of the UK's total estuaries.[24] There are nature reserves and Site of Special Scientific Interest (SSSI) on the islands of Flat Holm[25] and Steep Holm.[26]

The Barrage was not supported in the 2003 Energy Review due to "strong environmental concerns" (The same paper also described nuclear power as "an unattractive option").[27]

The RSPB opposes any Severn Barrage because of the effect it will have the feeding grounds 85,000 birds depend on, stating "The impact a barrage would have is huge. This is one of the most important sites in the UK for wild birds and the chances of them surviving if it went ahead are fairly slim. There wouldn't be enough room left for all the birds and there wouldn't be enough food for those that remained. The estuary is one of the UK's most important sites for water birds and its wildlife value must be taken fully into account."[28]

File:TURBIDITY REDUCED.jpg
Possible effect of turbidity reductions in Severn Estuary

The present strong tidal currents in the estuary serve to lift up silt sediment and so keep the water 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.[29]

The barrage will not create a "lagoon" - as both opponents and supporters have sometimes claimed. Tidal power stations by definition require that the tide flows through the barrage, but the tidal range in the Severn would be halved.[28]

DEFRA claims that the environmental effects of the barrage still need more analysis before final conclusions can be drawn. The Sustainable Development Commission is investigating UK tidal resources, including tidal power in the Severn Estuary and its environmental impact, and should report mid-2007.[30]

Tidal lagoon alternative

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,[31] whereby man-made lagoons in the estuary would fill and drain through turbines. Their proposals would include lagoons covering up to 60% of the area covered by the barrage, which in some smaller configurations would not impound water in the ecologically sensitive inter-tidal areas of the estuary. The lagoons could be sub-divided so power would be generated at more states of the tide than a barrage, with lower peak output, giving economic advantages to set against the higher construction cost of longer barriers. 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.[32][33]

A set of Tidal lagoons known as the "Russell Lagoon concept" were studied and dismissed by the 1981 Bondi Committee report, rejected on the grounds of both economics and environmental damage. Studies suggested that tidal currents around and between the lagoons would become extremely fierce and damaging.

Effects of different site locations

One of the complicating factors in assessing the impacts of a barrage is the large number of possible locations and sizes for the barrage. Generally, the larger the barrage the bigger its environmental impact, and the bigger the amount of energy it could create - and therefore the bigger carbon offset it could have by way of its renewable power generation.

The largest barrages (sited beyond Hinkley Point and towards Minehead on the English side and Aberthaw on the Welsh side) would significantly affect the entire Severn Estuary and much of the Bristol Channel, but could generate 15 GW peak power and protect the whole of the Somerset levels against flooding and sea-level rise caused by Global Warming. The smallest barrages (sited at Aust/Chepstow) would affect only the river and estuary in Gloucestershire, but would also only generate perhaps 0.75 GW peak power.

Construction costs

The estimated costs of the most recent plans are huge. Figures are generally in the £10-15 billion range, but have gone as high as £23 billion.[34] 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. 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.

Vested interests

It has been suggested[who?] 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 state 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.

It is possible that a barrage could be used for transport links between England and Wales, and more specifically the areas around Bristol and Cardiff. Various proposals include a dual carriageway road giving a further crossing in addition to the Second Severn Crossing and the Severn Bridge. The road would have to be taken over the sea locks on a bridge at a height of the Bridge of the Americas (i.e. with a clearance of 61.3m) if the locks are Panamax-sized.

Some proposals also include a double track railway line across the barrage. A railway would have a longer approach up to a fixed bridge over the locks. The approach would be greatest for non-electrified heavy railway capable of taking freight, slightly less for non-electrified passenger line, and less still for electrified passenger line. However, there is no electrification in the Bristol or Cardiff areas. An alternative to a fixed bridge would be a swing bridge, though there is concern expressed at this reducing capacity through the locks and on the railway. However, two swing bridges, one at either end of the lock would mean that one bridge could be kept open to railway traffic at all times. The double track could be reduced to single track at this point without creating too much of a bottleneck, or if double track is required this could be worked around by grade separating the two lines and having double-decked bridges. The line could then be used to partially relieve the Severn Tunnel.

The option for a new fixed rail link has implications for several wider transport proposals. One of the proposed routes for an Irish Sea Tunnel is from Fishguard, which would generate large amounts of extra freight traffic which the current Severn tunnel - already operating at capacity - could not handle. Additionally, a new high speed rail route has been suggested between London, Bristol, and Cardiff, which faces similar capacity constraints.

Opinions

Backers

Opponents

See also

References

  1. ^ Carne, Brian (1995). "Thomas Fulljames 1808-74" (PDF). Transactions of the Bristol & Gloucestershire Archeological Society. CXIII: 16–17.
  2. ^ "Severn Estuary Barrage" (PDF). UK Environment Agency. 31 May 2006. Retrieved 2007-09-03. {{cite web}}: Check date values in: |date= (help)
  3. ^ Extreme Depositional Environments: Mega End Members in Geologic Time. Boulder, Colorado: Geological Society of America. 2003. p. 151. ISBN 0813723701. {{cite book}}: |first= missing |last= (help); Missing pipe in: |first= (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)
  4. ^ "Coast: Bristol Channel". BBC. Retrieved 2007-08-27.
  5. ^ "£650 Million barrage plan unvieled". Burnham on Sea.com. 4 March 2006. Retrieved 2008-08-10.
  6. ^ a b "The Severn Barrage" (PDF). Royal Academy of Engineering. Retrieved 2008-08-10.
  7. ^ "Research Report 3 - Severn Barrage Proposals" (PDF). Sustainable Development Commission. p. 17. Retrieved 2008-08-10.
  8. ^ "The Severn Barrage" (PDF). Friends of the Earth. September 2007. p. 27. Retrieved 2008-08-10.
  9. ^ Bryant, Paul. "History of Severn Barrage proposals". r-energy. Retrieved 2008-08-11.
  10. ^ Tidal power from the Severn Estuary"-Volume 1. Energy Paper 46. HMSO. 1981.
  11. ^ Institution of Civil Engineers (Great Britain). Developments in Tidal Energy. Thomas Telford. p. 3. ISBN 9780727715715.
  12. ^ The Severn Barrage Project: General Report. Energy Paper 57. HMSO. 1989.
  13. ^ "The Severn Lake". The Severn Lake. Retrieved 2008-08-11.
  14. ^ "Tidal Power". Sustainable Development Commission. Retrieved 2008-08-11.
  15. ^ "Advisers endorse tidal power plan". BBC News. BBC. 2007-10-01. Retrieved 2008-08-11.
  16. ^ "Engagement report - Public and stakeholder engagement programme" (PDF). Sustainable Development Commission. October 2007. Retrieved 2008-08-11.
  17. ^ "John Hutton calls for open minds on the future of the Severn barrage". BERR. Retrieved 2008-08-27.
  18. ^ "Severn tidal power study could unlock massive renewable potential". BERR. 22 January 2008. Retrieved 2008-08-28. {{cite web}}: Check date values in: |date= (help)
  19. ^ "Severn Tidal Power". Welsh Assembly Government. Retrieved 2008-08-27.
  20. ^ "Severn barrage details unveiled". BBC. 22 January 2008. Retrieved 2008-08-27. {{cite web}}: Check date values in: |date= (help)
  21. ^ "The Feasibility Study". BERR. Retrieved 2008-08-27.
  22. ^ "Strategic Environmental Assessment". BERR. Retrieved 2008-08-27.
  23. ^ "Severn Tidal Power Q&A" (PDF). Department for Business Enterprise and Regulatory Reform. Retrieved 2008-08-11.
  24. ^ "Severn Barrage is not the answer". Press Release. Friends of the Earth. 2006-04-11. Retrieved 2008-08-11.
  25. ^ "Flat Holm - About the island". BBC. 3 April 2008. Retrieved 2008-04-12. {{cite web}}: Check date values in: |date= (help)
  26. ^ "Citation - Steep Holm" (PDF). English Nature. Retrieved 2007-09-06.
  27. ^ "Energy White Paper - Our Energy Future - creating a low carbon economy" (PDF). Department of Trade and Industry. February 2003. Retrieved 2008-08-11.
  28. ^ a b "Barrage bad for birds". Edie (Environmental Data Interactive Exchange). Retrieved 2008-08-10.
  29. ^ Kirby, R. (March 2005). "Severn Barrage, UK–environmental reappraisal". Proceedings of the Institution of Civil Engineers 2005: Engineering Sustainability. 158 (3). Institution of Civil Engineers: 31–39. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  30. ^ Bradshaw, Ben (2007-03-15). "Speech by Ben Bradshaw MP to the Wave and Tidal Conference of the British Wind Energy Association". Department for Environment, Food and Rural Affairs. Retrieved 2008-08-11.
  31. ^ "A Severn barrage or tidal lagoons? A comparison" (PDF). Friends of the Earth Cymru. January 2004. Retrieved 2007-10-01.
  32. ^ "Tidal Lagoon Power Generation Scheme in Swansea Bay" (PDF). Department of Trade and Industry and the Welsh Development Agency. April 2006. Retrieved 2007-10-01.
  33. ^ "Research Report 2 - Tidal technologies overview" (PDF). Sustainable Development Commission. October 2007. Retrieved 2008-08-11.
  34. ^ "Severn barrage cost hits £23bn". QS Week. 2008-05-19. Retrieved 2008-05-23. {{cite news}}: Check date values in: |date= (help)
  35. ^ BLAIR BACKS SEVERN BARRAGE
  36. ^ BBC NEWS | Wales | Experts disagree on river barrage
  37. ^ ePolitix.com - John Penrose
  38. ^ UK Parliament - Early Day Motions By Details
  39. ^ thisisbristol.co.uk
  40. ^ The Webb log: Time to put some energy into power from the Severn
  41. ^ House of Commons Hansard Debates for 4 Feb 2003 (pt 5)
  42. ^ BACKING FOR £14BN TIDAL BARRAGE BID
  43. ^ Estuary energy plan makes waves | Special Reports | Guardian Unlimited Politics
  44. ^ UK Parliament - Early Day Motions By Details
  45. ^ UK Parliament - Early Day Motions By Details
  46. ^ Agendas, Minutes and Reports
  47. ^ BBC NEWS | Wales | Experts disagree on river barrage
  48. ^ Defra, UK - About Defra - Ministers' speeches: Speech by Ben Bradshaw MP
  49. ^ Tide turns in favour of Severn Barrage electricity - Telegraph
  50. ^ Ministers support Severn Barrage
  51. ^ Greens welcome Severn Barrage bid - but not for its merits
  52. ^ Gloucestershire Green Party - towards a just, equitable and sustainable society
  53. ^ Green Party South West - Southwest Greens support Tidal Power in Severn Estuary
  54. ^ a b Estuary energy plan makes waves, The Guardian, April 26 2006
  55. ^ BBC NEWS | Wales | Concern over Severn barrage plan
  56. ^ thisisbristol.co.uk
  57. ^ The Severn Estuary a very special place
  58. ^ BBC NEWS | Wales | Monbiot attacks Welsh energy plan
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