Severn Barrage#Environmental impact

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

File:ThomasFulljamesSevernBarrage01.jpg

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 {{convert|1|mi|km|1}}. Since this was before commercial electricity production, the first proposals were based on the desire for a large shipping harbour in the Severn Estuary, road and railway transport, and flood protection.{{cite journal|last=Carne|first=Brian|year=1995|title=Thomas Fulljames 1808–74|journal=Transactions of the Bristol & Gloucestershire Archeological Society|volume=CXIII|pages=16–17|url=http://www2.glos.ac.uk/bgas/tbgas/v113/bg113007.pdf|access-date=10 August 2008|archive-date=4 October 2011|archive-url=https://web.archive.org/web/20111004201836/http://www2.glos.ac.uk/bgas/tbgas/v113/bg113007.pdf|url-status=dead}}

File:Severn River Tidal Power Project 1921.JPG Magazine 1921]]

No action was taken on Fulljames's proposals and three quarters of a century later, in 1925, an official study group was commissioned. An awareness of the large tidal range of 14 metres (46 ft),{{cite web|url=http://www.environment-agency.gov.uk/commondata/acrobat/severnpositionmay2006_1508223.pd|format=PDF|work=UK Environment Agency|title=Severn Estuary Barrage|date=31 May 2006|access-date=3 September 2007 |archive-url = https://web.archive.org/web/20070930155720/http://www.environment-agency.gov.uk/commondata/acrobat/severnpositionmay2006_1508223.pd |archive-date = 30 September 2007}} second only to Bay of Fundy in Eastern Canada,{{cite book|title=Extreme Depositional Environments: Mega End Members in Geologic Time|first1=Marjorie A.|last1=Chan|last2=Archer|first2= Allen William|location= Boulder, Colorado|isbn=0-8137-2370-1|publisher=Geological Society of America|year=2003|url=https://books.google.com/books?id=b3_1Ry0gDqEC&q=bristol+channel&pg=PA152|page= 151}}{{cite web|url=https://www.bbc.co.uk/bristol/content/articles/2005/07/04/bristolchannel_feature.shtml|title=Coast: Bristol Channel|work=BBC|access-date=27 August 2007}} 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).{{cite web|url=http://www.burnham-on-sea.com/news/2006/brean-down-barrage-04-03-06.shtml|title=£650 Million barrage plan unveiled|date=4 March 2006|publisher=Burnham on Sea.com|access-date=10 August 2008}} The viability was tested a few years later in 1931 when Paul Shishkoff,Pavel Aleksandrovich Shishkov (1887–1958) ([http://wap.kortic.borda.ru/?1-10-30-00000386-000-10001-0 Biographical information in Russian.]) a Russian immigrant, demonstrated a {{convert|300|hp}} prototype tidal generator at Avonmouth.{{cite web|url=http://www.raeng.org.uk/events/pdf/Severn%20Barrage%20transcript.pdf|title=The Severn Barrage|publisher=Royal Academy of Engineering|access-date=10 August 2008|url-status=dead|archive-url=https://web.archive.org/web/20110612045919/http://www.raeng.org.uk/events/pdf/Severn%20Barrage%20transcript.pdf|archive-date=12 June 2011|df=dmy-all}} It included a novel mechanism for spreading the power output over 24 hours. The full barrage was estimated at £5 million at the time.[https://books.google.com/books?id=t-QDAAAAMBAJ&dq=Popular+Mechanics+1931+curtiss&pg=PA719 "How Continuous Power Is Produced By Tide", November 1931, Popular Mechanics] article detailed drawing of how unique 24-hour tidal system worked

In 1933 the Severn Barrage Committee Report (HMSO) from a committee chaired by Lord Brabazon recommended that an 800 MW barrage across the English Stones area would be the best option.{{cite web|url=http://www.sd-commission.org.uk/publications/downloads/TidalPowerUK3-Severn_barrage_proposals.pdf|title=Research Report 3—Severn Barrage Proposals|publisher=Sustainable Development Commission|page=17|access-date=10 August 2008|archive-date=10 September 2008|archive-url=https://web.archive.org/web/20080910123911/http://www.sd-commission.org.uk/publications/downloads/TidalPowerUK3-Severn_barrage_proposals.pdf|url-status=dead}} The work was interrupted by World War II and then revived in 1945 when engineers predicted an output of 2.2 terawatt hours (TWh) per year.{{cite web|url=http://www.foe.co.uk/resource/briefings/the_severn_barrage.pdf|title=The Severn Barrage|date=September 2007|publisher=Friends of the Earth|page=27|access-date=10 August 2008}} A further government study looked at barrage options in 1948 and estimated the construction costs at £60 million. 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.{{cite web|url=http://www.thisisbristol.co.uk/wdp/news/drawing-board/article-249673-detail/article.html|title=Back to the drawing board|last=Brooke|first=Gerry|date=4 August 2008|work=Western Daily Press|publisher=This is Bristol|access-date=12 December 2009|url-status=dead|archive-url=https://archive.today/20120919172510/http://www.thisisbristol.co.uk/wdp/news/drawing-board/article-249673-detail/article.html|archive-date=19 September 2012|df=dmy-all}} 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.{{cite web|url=http://r-energy.co.uk/history/|title=History of Severn Barrage proposals|last=Bryant|first=Paul|publisher=r-energy|access-date=8 December 2010|url-status=dead|archive-url=https://web.archive.org/web/20110825120359/http://r-energy.co.uk/history/|archive-date=25 August 2011|df=dmy-all}} Despite the ongoing oil crisis, the council established that a barrage could not be economically viable unless the energy situation deteriorated significantly.

File:SevernBarrageMap.jpg

After just such a deterioration (due to the Iranian Revolution and 1979 energy crisis) 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,{{cite book|title=Tidal power from the Severn Estuary—Volume 1|publisher=HMSO|year=1981|series=Energy Paper 46}} which recommended a {{convert|10|mi|km|0}} 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 7,200 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.{{cite book|last=Institution of Civil Engineers (Great Britain)|title=Developments in Tidal Energy|publisher=Thomas Telford|isbn=978-0-7277-1571-5|url=https://books.google.com/books?id=YhuVRwhvKLcC&q=Severn+Barrage+Wimpey+Atkins&pg=PA3|page=3|year=1990}}

File:ShootsBarrage.jpg

This Wimpey Atkins 1984 study was criticised because it did not tackle the issue of silting{{ukhansard | house=HL | date=7 March 1984 | vol=449 | cc=263-5 }} 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.{{cite web|url=http://www.nce.co.uk/will-the-new-fesibilty-study-into-the-severn-barrage-be-the-first-steps-towards-construction-or-another-false-dawn/110984.article|title=Will the new fesibilty study into the Severn Barrage be the first steps towards construction or another false dawn?|last=McKenna|first=John|date=3 October 2007|publisher=New Civil Engineer|access-date=12 December 2009}} At the highest tidal range, it would develop a peak output of 1,050 MW, and 313 MW output on average throughout the year.

File:ShootsBarrage02.jpg

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.

In April 2009 the Liberal Democrats produced a report called "A Tidal Solution—The Way Forward" that backed the Shoots Barrage along with a number of additional measures for power generation in the Severn Estuary. In September 2009 the report was adopted by the Lib Dem party conference as official party policy.{{Cite news|title=Lib Dems back small-scale Severn Shoots barrage proposal}}

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.{{cite book|title=The Severn Barrage Project: General Report|publisher=HMSO|year=1989|series=Energy Paper 57}} Its members comprised Sir Robert McAlpine, Balfour Beatty, Taylor Woodrow and Alstom.{{cite news|last=Excell|first=Jon|title=Severn barrage could meet five per cent of UK energy needs|url=http://www.theengineer.co.uk/in-depth/turning-the-tides/294921.article|access-date=18 September 2012|newspaper=The Engineer|date=19 June 2006|archive-date=22 April 2014|archive-url=https://web.archive.org/web/20140422233104/http://www.theengineer.co.uk/in-depth/turning-the-tides/294921.article|url-status=dead}} They concluded that the 1981 plans were the best location for a barrage, but calculated that the power output could be larger, at 8,640 MW during flow, or 2,000 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 six nuclear reactors, but different lifespan), and running costs would be £70 million per year (about the same as 1.5 nuclear reactors).{{cite web | url=http://www.berr.gov.uk/files/file31329.pdf | archive-url=http://webarchive.nationalarchives.gov.uk/20071104182842/http://www.berr.gov.uk/files/file31329.pdf | url-status=dead | archive-date=4 November 2007 | title=Energy Review Consultation Response by Severn Tidal Power Group | publisher=Severn Tidal Power Group | access-date=8 December 2010}}

File:SevernBarrageProfile.jpg

The barrage would use existing technology as used in the Rance tidal barrage in France, the Annapolis Royal Generating Station in Canada and the Netherlands 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 midpoint, but high tides would be unaffected (unless the barrage was deliberately closed to prevent flooding).

File:SevernBarrageCaissons.jpg

The barrage would contain 216 turbines each generating 40 MW for the 8,640 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 set of shipping locks, designed to handle the largest container vessels. Construction would take about eight years and would require 35,000 employees at peak build time. The minimum lifespan of the barrage would be 120 years (about three times that of a nuclear reactor), 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. 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.

Evans Engineering have released plans for what they call a Severn Tidal "Reef".{{cite web|url=http://www.severntidal.com/|title=Joseph Evans & Sons Ltd}} 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). The designer, 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 {{convert|2|m|ft}}—thereby reducing the impact of the structure on the estuary water and flow. The smaller head means that the water velocity is much lower and more lower power turbines are required. The load factor will be higher, partly because of the generation being both ebb and flow and the total energy output should (according to a recent report by W.S. Atkins commissioned by the RSPB) be significantly greater than for the Cardiff-Weston Barrage, and is in part a result of siting the structure at the "outer" Minehead to Aberthaw line, which roughly doubles the volume of tidal water available.{{cite news |url=http://news.bbc.co.uk/1/hi/wales/south_east/7748431.stm |title=Severn reef plan is 'more green' |work=BBC News |publisher=BBC |date=26 November 2008 |access-date=8 March 2010}}

On 1 October 2007, the UK's Sustainable Development Commission (SDC) published a report looking at the potential of tidal power in the UK,{{cite web|url=http://www.sd-commission.org.uk/pages/tidal.html|title=Tidal Power|publisher=Sustainable Development Commission|access-date=11 August 2008|url-status=dead|archive-url=https://web.archive.org/web/20080512220123/http://www.sd-commission.org.uk/pages/tidal.html|archive-date=12 May 2008|df=dmy-all}}{{cite news|url=http://news.bbc.co.uk/2/hi/science/nature/7021835.stm|title=Advisers endorse tidal power plan|date=1 October 2007|work=BBC News|publisher=BBC|access-date=11 August 2008|first=Mark|last=Kinver}} 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.{{cite web|url=http://www.sd-commission.org.uk/publications/downloads/Tidal-Public_Stakeholder_Engagement.pdf|title=Engagement report—Public and stakeholder engagement programme|date=October 2007|publisher=Sustainable Development Commission|access-date=11 August 2008|archive-date=10 September 2008|archive-url=https://web.archive.org/web/20080910122455/http://www.sd-commission.org.uk/publications/downloads/Tidal-Public_Stakeholder_Engagement.pdf|url-status=dead}}

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.

{{Use dmy dates|date=March 2015}}

{{Main|Severn Tidal Power Feasibility Study}}

A two-year feasibility study was announced in late 2007,{{cite web |url=http://www.whitehallpages.net/news/archive/35633 |title=John Hutton calls for open minds on the future of the Severn barrage |access-date=1 December 2010 |work=BERR|archive-url=https://web.archive.org/web/20110724132224/http://www.whitehallpages.net/news/archive/35633|archive-date=24 July 2011}} and the terms of reference were announced on 22 January 2008,{{cite web|url=http://www.gov-news.org/gov/uk/news/severn_tidal_power_study_could_unlock_massive/42538.html|archive-url=https://archive.today/20120910194409/http://www.gov-news.org/gov/uk/news/severn_tidal_power_study_could_unlock_massive/42538.html|url-status=usurped|archive-date=10 September 2012|title=Severn tidal power study could unlock massive renewable potential|access-date=8 December 2010|date= 22 January 2008|work=BERR}} following the publication of the Turning the Tide report from the Sustainable Development Commission. This study builds upon past studies and focuses on a variety of tidal range technologies including barrages and lagoons, and innovative designs such as a tidal fence and a tidal reef in the Severn estuary.

The study, initially led by John Hutton, Secretary of State for Business, Enterprise and Regulatory Reform, was then led until the 2010 General Election by Ed Miliband, who was at that time the Secretary of State for Energy and Climate Change.

The study aims to gather and assess evidence to enable the Government to decide whether it could support a tidal power scheme in the Severn Estuary and if so on what basis.

Key work areas involved are:

• The environmental impacts on biodiversity and wildlife; flood management; geomorphology; water quality; landscape and compensatory habitat;
• Engineering and technical areas such as options appraisal; costs; energy yield, design and construction, links to the National Grid and supply chain;
• 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.

The feasibility study concluded its first phase when a public consultation was launched on 26 January 2009. The consultation covered a proposed short-list of potential tidal power project options from an initial list of 10 schemes, processes that were undertaken during shortlisting and the proposed scope of the Strategic Environmental Assessment (SEA). The SEA is a formal environmental assessment of plans or programmes which are likely to have significant effects on the environment.{{cite web |url=http://www.berr.gov.uk/energy/sources/renewables/explained/severntidalpower/strategicenvironmentalassessment/page47489.html |title=Strategic Environmental Assessment |access-date=27 August 2008 |work=BERR |url-status=dead |archive-url=https://web.archive.org/web/20090327082208/http://www.berr.gov.uk/energy/sources/renewables/explained/severntidalpower/strategicenvironmentalassessment/page47489.html |archive-date=27 March 2009 |df=dmy-all }} A consortium led by Parsons Brinckerhoff (PB) and Black & Veatch (B&V) has been appointed to manage this part of the project. The process is guided by a stakeholder steering group. The study will culminate in a full public consultation in 2010.{{cite web|url=http://www.berr.gov.uk/files/file43809.pdf|title=Severn Tidal Power Q&A|publisher=Department for Business Enterprise and Regulatory Reform|access-date=11 August 2008|url-status=dead|archive-url=http://webarchive.nationalarchives.gov.uk/20081230185343/http://www.berr.gov.uk/files/file43809.pdf|archive-date=30 December 2008|df=dmy-all}}

In July 2009 the Government response to consultation confirmed detailed study would be carried out in the second phase on the five schemes that were proposed for short-listing in January. It also announced work to bring forward 3 further schemes that are in the very early stages of development. In September 2010, The Observer reported that the government intended to rule out the possibility of public funding for a complete barrage, while recommending that further feasibility studies be carried out on smaller projects.{{cite news|url=https://www.theguardian.com/environment/2010/sep/05/severn-green-energy-project-loses-funding|first=Tim|last=Webb|title=Severn green energy project loses government funding|work=The Observer|date=5 September 2010|access-date=10 September 2010|location=London}} On 18 October the government announced that the project was being abandoned.{{cite web|url=https://www.bbc.co.uk/news/uk-england-somerset-11564284|title=Severn barrage tidal energy scheme scrapped by Huhne|work=BBC News|date=18 October 2010|access-date=21 April 2014}}

In December 2011 it was reported that the government was talking to Corlan Hafren, a private sector consortium,{{cite news|url=https://www.bbc.co.uk/news/uk-wales-16070872|title=New talks on Severn barrage plan from Cardiff to Weston|work=BBC News|date=7 December 2011|access-date=19 January 2012}} about a proposal to build a privately financed barrage from Lavernock Point to Brean Down.{{cite news|last=Hutchinson|first=Clare|title='Real cost' of Severn Barrage £34bn|url=http://www.walesonline.co.uk/news/wales-news/2010/10/19/real-cost-of-severn-barrage-34bn-91466-27498178/|access-date=18 September 2012|newspaper=WalesOnline|date=19 October 2010}} The Department for Energy and Climate Change said it had received the first draft of a business case for the scheme, and that it was an "interesting proposition". The campaign was led in 2012 by politician Peter Hain.{{cite news|last=Evans|first=Bethan|title=Barrage bid to be looked at – again|url=http://www.thewestonmercury.co.uk/news/barrage_bid_to_be_looked_at_again_1_1507465|access-date=17 September 2012|newspaper=The Weston & Somerset Mercury|date=9 September 2012|archive-date=1 August 2013|archive-url=https://web.archive.org/web/20130801050420/http://www.thewestonmercury.co.uk/news/barrage_bid_to_be_looked_at_again_1_1507465|url-status=dead}} It has been suggested by Atkins that similar schemes could be trialled on smaller estuaries in advance of the Severn, for example the Mersey and Duddon.{{cite news|last=OConnell|first=Dominic|title=Severn barrage awaits the right time and tide|url=http://www.thesundaytimes.co.uk/sto/public/roadtorecovery/article587453.ece|archive-url=https://web.archive.org/web/20131002180507/http://www.thesundaytimes.co.uk/sto/public/roadtorecovery/article587453.ece|url-status=dead|archive-date=2 October 2013|work=The Sunday Times|date=27 March 2011|access-date=18 September 2012}} However the Hafren Power plan collapsed after it was rejected by three independent committees of MPs and by the Government. On 14 January 2014 it was announced that the chairman and Chief Executive of Hafren Power had resigned, putting an end to the Severn Barrage project.{{cite web|last1=Shipton|first1=Martin|title=Four key figures in Hafren Power resign|url=http://www.walesonline.co.uk/business/four-key-figures-hafren-power-6504734|publisher=Wales Online|access-date=8 October 2015|date=14 January 2014}}

The 2022 Russian invasion of Ukraine drew attention to uncertainty about energy supply and uncertainty over external energy costs. A Severn barrage is again being considered and an independent commission was started to research this. If successful, it is claimed that the barrage could supply 7% of total UK energy needs.[https://www.theguardian.com/environment/2022/mar/08/severn-estuary-tidal-energy-plan-back-on-agenda-amid-ukraine-crisis Severn estuary tidal energy plan back on agenda amid Ukraine crisis] The Guardian

The Severn Barrage plans would provide a predictable source of sustainable energy during lifetime of the scheme, with claims of up to 5% of the UK's electricity output from the 10-mile version.{{cite news|url=http://news.bbc.co.uk/1/hi/wales/7850609.stm |title=Shortlist for Severn energy plans |author=BBC |access-date=5 March 2010 | work=BBC News | date=26 January 2009}} This could reduce the cost of meeting UK's renewable energy targets, and help the UK to meet such targets, including those to tackle climate change. This is because of the few carbon emissions associated with the plan, because unlike conventional power generation, the Severn Barrage plans do not involve the combustion of fossil fuels. A consequence of this plan is that the carbon payback time—the time it takes for saved carbon emissions (those produced by generating the same amount of power in other ways) to outstrip those produced during construction— could be as little as four-and-a-half months, although likely to be around six.{{cite web |url=http://www.utilityweek.co.uk/news/uk/electricity/severn-barrage-will-pay-back-c.php |title=Severn Barrage will pay back carbon in less than six months, says study |date=2 March 2009 |access-date=8 March 2010 }}{{Dead link|date=October 2023 |bot=InternetArchiveBot |fix-attempted=yes }}

It could continue to operate for around 120 years, compared with 60 years for nuclear power plants.{{cite web|url=http://www.iaea.org/NewsCenter/News/2007/npp_extension.html |title=Extending the Operational Life Span of Nuclear Plants |publisher=International Atomic Energy Agency |work=IAEA.org |date=8 March 2010 |access-date=8 March 2010}} An additional benefit would be to improve energy security.

However, although power supply is predictable, peaks in generation from the barrage do not necessarily coincide with peaks in demand. There are two major tidal cycles affecting power output:

• semi-diurnal cycle: the familiar daily rise and fall of the sea with a full cycle every 24 hours and 50 minutes, with two high and low tides, giving maximum power generation opportunities a few hours after each of the two high tides;
• spring-neap cycle: a 29.5 day tidal range cycle with the lowest power days producing about 25% of the power of the highest power days.{{cite report|pages=25, 77–79|url=http://www.sd-commission.org.uk/publications.php?id=607|title=Turning the Tide, Tidal Power in the UK|date=30 September 2007|publisher=Sustainable Development Commission|access-date=8 March 2010|archive-date=4 September 2009|archive-url=https://web.archive.org/web/20090904021113/http://www.sd-commission.org.uk/publications.php?id=607|url-status=dead}}

Just under eight hours per day of generation time is expected.

Estimated costs for existing plans could be as low as £10bn and as high as £34bn. Recent studies{{cite report|url=http://severntidalpowerconsultation.decc.gov.uk/supporting_documents|title=DECC Severn Tidal Consultation Supporting Documents|date=23 April 2009|publisher=DECC|access-date=25 May 2009|url-status=dead|archive-url=http://webarchive.nationalarchives.gov.uk/20090420102254/http%3A//severntidalpowerconsultation.decc.gov.uk/supporting_documents|archive-date=20 April 2009|df=dmy-all}} have suggested that the smaller short-listed options could be privately financed, and so in effect the matter of cost and risk becomes a private one between the building consortium and their banks. Schemes of the scale of Cardiff-Weston are likely to require significant Government involvement. If the banks feel that a smaller project is viable and decide to lend the money at an acceptable cost of finance then the projects will go ahead (subject to planning and other approvals). None of this cost would directly fall on the tax-payer but any support mechanism for the tidal power would be likely to fall on consumers. There would, though, be secondary knock-on costs from the tidal power project that might be met by the tax-payer, such as modifying existing ports, provision of compensatory habitat and dealing with environmental change. However, these would be offset by the positive knock-on effects, such as flood protection – which would have otherwise also cost tax-payer money. Whether the parties actually decided to exchange money for these knock-on effects would be a matter for Government negotiation.

As a cost comparison, Hinkley Point C nuclear power station (also being built on the Severn Estuary) will cost £25bn, and deliver 3.2GW of power sold at £92.50 per megawatt hour (MWh) of electricity generated for the 35 years of the contract.{{cite news|last1=Syal|first1=Rajeev|title=Deal to build UK nuclear plant should be finalised within weeks|url=https://www.theguardian.com/environment/2015/aug/04/deal-to-build-uk-nuclear-plant-should-be-finalised-within-weeks|access-date=8 October 2015|work=Guardian|date=4 August 2015}} The Hafren scheme proposers state they would require £25 billion capital investment, and power costs would be £160 per MWh for the first 30 years, and £20 per MWh thereafter. Other schemes have been costed at between £150 and £350 per MWh.

Some say that a large-scale barrage would create leisure-friendly water conditions behind it but with around 10 m rise and fall this would still be one of the largest tidal ranges in the UK bringing with it significant danger to any leisure users. Flood protection would be provided by the barrage, covering the vulnerable Severn estuary from storm surges from the sea but drainage from land upstream would be impeded causing worse flooding there. Also higher water levels downstream of the barrage could cause flooding on the Somerset Levels. New road and/or rail transport links could be built across a barrage if demand rises in the future, as outlined below. Any barrage could provide a boost to the local economy – construction industry in the short term, tourism and infrastructure in the long term.{{cite web | url= http://www.earthtoys.com/emagazine.php?issue_number=07.08.01&article=barrage | publisher= Earth toys | title= £14 Billion Tidal Barrage Proposed for Severn Estuary | date= 28 October 2008 | access-date= 28 October 2008 | archive-date= 10 July 2011 | archive-url= https://web.archive.org/web/20110710163648/http://www.earthtoys.com/emagazine.php?issue_number=07.08.01&article=barrage | url-status= dead }}

However, shipping would have to navigate locks and the reduced depth of water would prevent much existing shipping from being able to access docks in Wales and Bristol putting thousands of jobs at risk.{{cite web|title=Severn Barrage 'would destroy port jobs'|url=http://www.southwestbusiness.co.uk/news/11012013084710-severn-barrage-would-destroy-port-jobs/|publisher=SouthWest Business|access-date=30 August 2017}} Other existing estuary industries, including fisheries, would be damaged and jobs lost.{{cite book|title=A Severn Barrage: second report of session 2013–14, Vol. 1: Report, together with formal minutes, oral and written evidence|date=2013|publisher=The Stationery Office|isbn=9780215058843|page=35|url=https://books.google.com/books?id=oKpAk1vsbj8C&q=Severn+Barrage+jobs+fisheries&pg=PA35}} All industrial discharges into the River Severn (e.g. from Avonmouth) would have to be reassessed.{{cite web | url=http://www.ukmpas.org/pdf/Sitebasedreports/Severn_Estuary.pdf | title=The Severn Estuary: Occasional Paper No 13 | publisher=Marine Biological Association | access-date=8 December 2010 | archive-date=28 July 2011 | archive-url=https://web.archive.org/web/20110728141620/http://www.ukmpas.org/pdf/Sitebasedreports/Severn_Estuary.pdf | url-status=dead }}

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.{{cite web|url=http://www.foe.co.uk/resource/press_releases/severn_barrage_is_not_the_11042006.html|title=Severn Barrage is not the answer|date=11 April 2006|work=Press Release|publisher=Friends of the Earth|access-date=11 August 2008}} There are nature reserves and Site of Special Scientific Interest (SSSI) on the islands of Flat Holm{{cite web|url= http://www.bbc.co.uk/wales/southeast/sites/flatholm/pages/overview.shtml|publisher= BBC|title= Flat Holm—About the island|date= 3 April 2008|access-date= 12 April 2008}} and Steep Holm.{{cite web|url=http://www.english-nature.org.uk/citation/citation_photo/1002935.pdf|work=English Nature|title= Steep Holm|access-date=6 September 2007}}

The Barrage was not supported in the 2003 Energy Review due to "strong environmental concerns".{{cite web|url=http://www.berr.gov.uk/files/file10719.pdf |title=Energy White PaperOur Energy Future—creating a low carbon economy |date=February 2003 |publisher=Department of Trade and Industry |access-date=11 August 2008 |url-status=dead |archive-url=http://webarchive.nationalarchives.gov.uk/20100817004324/http://www.berr.gov.uk/files/file10719.pdf |archive-date=17 August 2010 }}

The RSPB opposes any Severn Barrage because of the effect it will have on the feeding grounds that 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 would not be enough room left for all the birds and there would not 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."{{cite web|url=http://www.edie.net/news/news_story.asp?id=11703&channel=0|title=Barrage bad for birds|publisher= (Environmental Data Interactive Exchange)|access-date=10 August 2008}}

File:ReducedTurbidity.jpg

The present strong tidal currents in the estuary serve to lift up silt sediment and so keep the water thick with fine particles—around 30 million tonnes of suspended sediment move in the Estuary on a high Spring tide. 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.{{cite journal|last1=Kirby|first1=R.|first2=T|last2=Shaw|date=March 2005|title=Severn Barrage, UK–environmental reappraisal.|journal=Proceedings of the Institution of Civil Engineers – Engineering Sustainability|volume=158|issue=3|pages=31–39|doi=10.1680/ensu.2005.158.1.31}} The zone of maximum turbidity is confined to the inner Severn and does not extend westwards into the Bristol Channel.Collins, M.B., 1987. Sediment transport in the Bristol Channel: a review. Proceedings of the Geological Association 98, 367–383. An estimated 6.4 million tonnes/year of sand moves up and down the Bristol ChannelHarris, P.T., Collins, M.B., 1988. Estimation of annual bedload flux in a macrotidal estuary, Bristol Channel, U. K. Marine Geology 83, 237–252. which would be blocked by a tidal barrage; the potential environmental consequences of interrupting this flux of sand include local coastal erosion and loss of coastal habitats.

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. There are claims that the migration of fish would be hampered, but these are contested. The Severn bore would also be eliminated. Any barrage would be likely to stimulate coastal erosion in some areas, and create a negative visual impact upon the landscape (subjective, similar to wind turbines). There would also be negative consequences of the huge amount of concrete (and other materials) needed, with the quarrying of stone likely to impact on other areas.

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.{{cite web|url=http://www.defra.gov.uk/corporate/ministers/speeches/ben-bradshaw/bb070316.htm|title=Speech by Ben Bradshaw MP to the Wave and Tidal Conference of the British Wind Energy Association|last=Bradshaw|first=Ben|date=15 March 2007|publisher=Department for Environment, Food and Rural Affairs|access-date=11 August 2008|url-status=dead|archive-url=https://web.archive.org/web/20081113235950/http://www.defra.gov.uk/corporate/ministers/speeches/ben-bradshaw/bb070316.htm|archive-date=13 November 2008|df=dmy-all}}

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,{{cite web | url= http://www.foe.co.uk/resource/briefings/severn_barrage_lagoons.pdf | title= A Severn barrage or tidal lagoons? A comparison | work= Friends of the Earth Cymru |date=January 2004 | access-date=1 October 2007}}

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 proposed at Swansea bay. However leading figures in the construction industry are sceptical that the lagoons can be economic.{{cite web | url= http://www.dti.gov.uk/files/file30617.pdf | title= Tidal Lagoon Power Generation Scheme in Swansea Bay | work= Department of Trade and Industry and the Welsh Development Agency |date=April 2006 | access-date= 1 October 2007 |archive-url = https://web.archive.org/web/20070630221746/http://www.dti.gov.uk/files/file30617.pdf |archive-date = 30 June 2007}}{{cite web|url=http://www.sd-commission.org.uk/publications/downloads/TidalPowerUK2-Tidal_technologies_overview.pdf|title=Research Report 2—Tidal technologies overview|date=October 2007|publisher=Sustainable Development Commission|access-date=11 August 2008 |archive-url=http://webarchive.nationalarchives.gov.uk/20090511193942/http://www.sd-commission.org.uk/publications/downloads/TidalPowerUK2-Tidal_technologies_overview.pdf |archive-date=11 May 2009}}{{cite news |url=https://www.ft.com/content/da4baf02-db14-11e6-86ac-f253db7791c6 |archive-url=https://ghostarchive.org/archive/20221211221217/https://www.ft.com/content/da4baf02-db14-11e6-86ac-f253db7791c6 |archive-date=11 December 2022 |url-access=subscription |url-status=live |title=Tidal power swamped by dubious mathematics |author=Jonathan Ford |newspaper=Financial Times |date=15 January 2017 |access-date=15 January 2017 }}

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.

Another possibility is to construct one or more tidal fences across the Severn estuary which would generate power using tidal stream generators. This has been put forward by the Severn Tidal Fence Consortium, and groups including IT Power and a number of industry and academic groups.

{{cite web|url=http://www.itpower.co.uk/node/141|title=Tidal Fence instead of Severn Barrage}}

This would attempt to maximise the potential power generated whilst allowing for shipping to reach Cardiff and Bristol without hindrance (through gaps at least 650 m wide) and wildlife to maintain their existing habitats. The group has now been contracted by the UK government to investigate the idea under the Severn Embryonic Technology Scheme (SETS).

{{cite web|url=http://www.itpower.co.uk/node/160|title=IT Power to lead Severn Tidal Fence Consortium with potential alternative to the Severn Barrage}}

The group estimates that it would cost £3.5bn to construct an outer fence from Aberthaw to Minehead which would generate 1.3GW or 3.5TWh/year. It is also investigating an inner fence from Lavernock Point to Brean Down including Flat Holm and Steep Holm islands. Both fences could possibly be built.

The fence would permit the migration of salmon and would only slightly affect the mudflats used by migrating birds. In addition it could significantly reduce the flood risk in the Severn estuary.

{{cite news|url=http://news.bbc.co.uk/1/hi/wales/7509904.stm|title=Severn tidal 'fence' idea floated|publisher=BBC | date=16 July 2008}}

A second approach to a tidal fence being explored by VerdErg uses a different way of generating electricity called the Spectral Machine Energy Converter (SMEC).

{{cite web|url=http://www.decc.gov.uk/en/content/cms/what_we_do/uk_supply/energy_mix/renewable/severn_tidal_power/embryonic_tech/embryonic_tech.aspx|title=Severn Embryonic Technologies Scheme|access-date=25 December 2010|url-status=dead|archive-url=https://web.archive.org/web/20101121141622/http://decc.gov.uk/en/content/cms/what_we_do/uk_supply/energy_mix/renewable/severn_tidal_power/embryonic_tech/embryonic_tech.aspx|archive-date=21 November 2010|df=dmy-all}}

This uses the flow past Venturi tube sections as a pump without moving parts to create a large secondary flow which drives turbines on the sea bed.{{cite web|url=http://www.verderg.com/index.php?option=com_content&view=article&id=95&Itemid=66|title=SMEC Technology Basic Principles|access-date=25 December 2010|archive-date=17 July 2011|archive-url=https://web.archive.org/web/20110717193847/http://www.verderg.com/index.php?option=com_content&view=article&id=95&Itemid=66|url-status=dead}}

Verderg estimate that they could produce output of 13.7TWh/yr at a cost of £9.9bn using the Lavernock Point/Brean Down connection.

Some simulations have also been done on the partial barriers envisaged by Dynamic tidal power which have similar advantages.

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 greater the amount of energy it could transfer—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.

A 2009 Paper by Atkins{{cite web|url=http://www.rspb.org.uk/Images/Atkins_technical_note_tcm9-216761.pdf|title= Technical Note: The optimum position for a tidal power barrage in the Severn estuary, Reference CJ0040.6680/TN-001r3|author = Atkins, R Rainey|publisher = Atkins|access-date=20 May 2012}} re-evaluated the potential energy which could be generated from the various locations, and concluded that, contrary to earlier studies and computations, the maximum power potential would come from an Ilfracombe-Gower barrage, much further west even than the earlier Minehead-Aberthaw proposals. This was attributed by the study to several calculation elements which were neglected in previous numerical models.

It is possible that some types of barrage could be used for transport links between southern England and southern Wales, and more specifically the areas around Weston super Mare and Cardiff but no demand surveys have been carried out to show whether such a link would be useful to commuters or businesses. The east–west position of any future barrage will affect the utility of any transport links across it. 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 61.3 m) 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. There is no electrification presently in the Bristol or Cardiff areas, but this would change with the electrification of the Great Western Main Line. 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.

If the barrage is built further west, any transport connection would instead link more isolated areas of the Devon-Cornwall peninsula with the cities of South Wales and the ports of Pembrokeshire.

• The former Prime Minister of the United Kingdom Tony Blair{{cite web|url=http://thisisbristol.co.uk/displayNode.jsp?nodeId=144936&command=displayContent&sourceNode=144919&contentPK=17565890&moduleName=InternalSearch&formname=sidebarsearch|title=BLAIR BACKS SEVERN BARRAGE}}{{Dead link|date=October 2023 |bot=InternetArchiveBot |fix-attempted=yes }} (who backed it in the last weeks of his tenure)
• The Chairman of the Climate Change Committee, Lord Deben, formerly John Selwyn Gummer (who has shares in a company bidding for the project){{cite news|last1=Brooker|first1=Christopher|title=The tangled tale of Lord Deben and a dodgy Severn barrage|url=https://www.telegraph.co.uk/comment/9498568/The-tangled-tale-of-Lord-Deben-and-a-dodgy-Severn-barrage.html|access-date=5 September 2016|work=Telegraph|date=25 August 2012}}
• The Welsh Parliament
• Former Welsh First Minister Rhodri Morgan{{cite news| url=http://news.bbc.co.uk/1/hi/wales/5039918.stm | work=BBC News | title=Experts disagree on river barrage | date=2 June 2006 | access-date=6 April 2010 | first=Gareth | last=Jones}}
• The South West Regional Assembly
• Weston Super Mare MP John Penrose{{cite web|url=http://www.epolitix.com/EN/MPWebsites/John+Penrose/46df5559-c191-4af4-bf06-4a53a0192893.htm#7|title=ePolitix.com – John Penrose|access-date=5 September 2006|archive-date=30 September 2007|archive-url=https://web.archive.org/web/20070930201812/http://www.epolitix.com/EN/MPWebsites/John+Penrose/46df5559-c191-4af4-bf06-4a53a0192893.htm#7|url-status=usurped}}
• Former Cardiff Central MP Jenny Willott{{cite web|url=http://edmi.parliament.uk/EDMi/EDMDetails.aspx?EDMID=30613%09%09%09%09%09%09%09&SESSION=875|title=UK Parliament – Early Day Motions By Details}}
• Northavon MP Steve Webb{{cite web|url=http://thisisbristol.co.uk/displayNode.jsp?nodeId=144936&command=displayContent&sourceNode=144919&contentPK=16976765&moduleName=InternalSearch&formname=sidebarsearch|title=thisisbristol.co.uk}}{{Dead link|date=October 2023 |bot=InternetArchiveBot |fix-attempted=yes }}{{cite web|url=http://webbsteve.blogspot.com/2007/03/time-to-put-some-energy-into-power-from.html|title=The Webb log: Time to put some energy into power from the Severn}}
• Ogmore MP and Parliamentary Under Secretary of State for Wales Huw Irranca-Davies{{cite web|url=https://publications.parliament.uk/pa/cm200203/cmhansrd/vo030204/halltext/30204h05.htm|title=House of Commons Hansard Debates for 4 Feb 2003 (pt 5)}}
• Kingswood MP Roger Berry{{cite web|url=http://thisisbristol.co.uk/displayNode.jsp?nodeId=144936&command=displayContent&sourceNode=144919&contentPK=17372301&moduleName=InternalSearch&formname=sidebarsearch|title=BACKING FOR £14BN TIDAL BARRAGE BID}}{{Dead link|date=October 2023 |bot=InternetArchiveBot |fix-attempted=yes }}
• Gower MP Byron Davies {{cite web|title=Byron Meets with Chancellor over Tidal Lagoon|url=https://www.byrondavies.org.uk/news/byron-meets-chancellor-over-tidal-lagoon|website=byrondavies.org.uk|access-date=21 November 2016}}
• Scientist and "Gaia" theorist Dr. James Lovelock CBE
• Former Welsh Secretary The Lord Hain

• The Commons Welsh Affairs Select Committee
• The Commons Energy and Climate Change Select Committee
• Former UK Science Minister Lord Sainsbury
• North Somerset MP and International Trade Secretary Liam Fox
• The Bristol Port Company
• RSPB Wales[http://politics.guardian.co.uk/green/story/0,,1761552,00.html Estuary energy plan makes waves], The Guardian, 26 April 2006
• Friends of the Earth Wales
• World Wildlife Fund Wales{{cite news| url=http://news.bbc.co.uk/1/hi/wales/4898514.stm | work=BBC News | title=Concern over Severn barrage plan | date=11 April 2006 | access-date=6 April 2010}}
• Gwent Wildlife Trust{{cite web|url=http://www.gwentwildlife.org/what-we-do/campaigns/severn-barrage|title=Severn Barrage—Gwent Wildlife Trust}}
• Avon Wildlife Trust{{cite web|url=http://www.wildlifetrust.org.uk/avon/wildlife/78-severn_estuary.htm|title=The Severn Estuary a very special place}}
• Political commentator George Monbiot{{cite news| url=http://news.bbc.co.uk/1/hi/wales/6696915.stm | work=BBC News | title=Monbiot attacks Welsh energy plan | date=27 May 2007 | access-date=6 April 2010 | first=Gareth | last=Jones}}

{{Portal|England|Energy}}

• Cardiff Bay Barrage
• Centre Port
• Mersey Barrage
• Energy policy of the United Kingdom
• Energy use and conservation in the United Kingdom
• Tidal power
• Tidal resonance
• List of tidal power stations
• Saint Petersburg Dam
• Tidal Lagoon Swansea Bay

{{reflist|2}}

{{Commons category|Severn Barrage}}

• [https://www.youtube.com/watch?v=ZMPP1ZNyfjk FILM End To Higher Flooding – New Technology Revealed protecting upstream Severn, self financing and protects ecology.]
• [http://www.decc.gov.uk/severntidalpower Department of Energy and Climate Change]
• [http://www.wales.gov.uk/severtidal Welsh Assembly Government]
• [https://web.archive.org/web/20110723014221/http://www.severnestuary.net/sep/resource.html Severn Estuary Partnership: Tidal Power Resource Page"]
• [http://www.sd-commission.org.uk/publications/downloads/TidalPowerUK3-Severn_barrage_proposals.pdf SDC paper "Tidal Power in the UK: Research Report 3 – Severn barrage proposals"] {{Webarchive|url=https://web.archive.org/web/20071012213725/http://www.sd-commission.org.uk/publications/downloads/TidalPowerUK3-Severn_barrage_proposals.pdf |date=12 October 2007 }}
• [http://www.foe.co.uk/resource/briefings/severn_barrage_lagoons.pdf Friends of the Earth "Tidal Lagoons" Plans]
• [http://www.dti.gov.uk/files/file30617.pdf Independent report on "Tidal Lagoons" for the DTI and the Welsh Development Agency] {{Webarchive|url=https://web.archive.org/web/20070630221746/http://www.dti.gov.uk/files/file30617.pdf |date=30 June 2007 }}
• [https://www.bbc.co.uk/gloucestershire/content/articles/2006/10/30/barrage_feature.shtml BBC Gloucestershire background videos and information]
• [http://www.wwf.org.uk/filelibrary/pdf/turningthetide_full.pdf World Wildlife Fund "Turning the Tide"] {{Webarchive|url=https://web.archive.org/web/20060925231100/http://www.wwf.org.uk/filelibrary/pdf/turningthetide_full.pdf |date=25 September 2006 }}
• [https://web.archive.org/web/20060419010714/http://www.dti.gov.uk/renewables/publications/pdfs/severnbarragemainreport.pdf Severn Tidal Power Group report for UK Government DTI]
• [https://web.archive.org/web/20060215203215/http://www.dti.gov.uk/renewables/publications/pdfs/t0900212ra.pdf Appendices to – Severn Tidal Power Group report for UK Government DTI]
• [http://www.ice.org.uk/downloads//Severn%20Barrage(1).pdf Institute of Civil Engineers Severn Barrage environmental reappraisal] {{Webarchive|url=https://web.archive.org/web/20070927213801/http://www.ice.org.uk/downloads//Severn%20Barrage(1).pdf |date=27 September 2007 }}
• [https://www.theguardian.com/frontpage/story/0,,1761578,00.html Estuary energy plan makes waves The Guardian 26 April 2006]
• [https://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=43328 Institute of Electronic Engineers Severn Barrage Tidal power appraisal]
• [https://publications.parliament.uk/pa/cm199899/cmselect/cmenvtra/171/171m22.htm Memorandum by the Severn Tidal Power Group to Parliamentary Committee]
• [https://web.archive.org/web/20060928085838/http://www.severnestuary.net/scosla/ Standing Conference on Severnside Local Authorities (SCOSLA)]
• [https://www.theyworkforyou.com/whall/?id=2007-04-24a.262.0 Westminster Hall Debate on the Severn Barrage]
• [https://web.archive.org/web/20080512220123/http://www.sd-commission.org.uk/pages/tidal.html Sustainable Development Commission project looking at 'Tidal Power in the UK']
• [https://www.severncommission.co.uk Severn Estuary Commission]

{{South West powerstations}}

{{Energy in the United Kingdom|sources}}

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