Severn Barrage
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The Severn Barrage is any 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.
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[edit] History
There have been numerous proposed projects over the years, initially to provide a safe harbour and more recently to generate electricity.[edit] Early projects
In 1933 the Severn Barrage Committee Report (HMSO) from a committee chaired by Lord Brabazon recommended that a 800 MW barrage across the English Stones area would be the best option.[7] 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.[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.[9] 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.[10] 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.
[edit] Bondi Committee – 1981
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.[12]
[edit] Hooker or Shoots Barrage – 1987
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.[13] At the highest tidal range, it would develop a peak output of 1,050 MW, and 313 MW output on average throughout the year.
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" [14] 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.[15]
[edit] 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.[16] 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).[citation needed]
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.[citation needed]
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[edit] Severn Tidal Reef – 2007
Evans Engineering (Joseph Evans & Sons Limited) have released plans for what they call a Severn Tidal "Reef".[17] 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 2 metres (6.6 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.[18][edit] 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,[19][20] 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.[21]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
[edit] UK Government study announced – 2007
Main article: Severn Tidal Power Feasibility Study
A two year feasibility study was announced in late 2007,[22] a the terms of reference were announced on 22 January 2008,[23]
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, previously lead by John Hutton, Secretary of State for Business, Enterprise and Regulatory Reform, is now being lead by Ed Miliband, 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.
In July 2009 the Government response to consultation confirmed detailed study would be carried out in the second phase on the 5 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.[26]
[edit] Economic impact
[edit] Power generation potential
The Severn Barrage plans would provide a predictable source of green energy during lifetime of the scheme, 5% of the UK's output from the 10-mile version.[27] 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.[19] 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.[28]It could continue to operate for around 120 years,[19] compared with 30–40 years for nuclear power plants.[29] An additional benefit would be to improve energy security.[19]
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.[30]
This cyclic power generation pattern could negatively affect economics and efficiency of other power generators and additional power transmission lines that will only be cyclically utilized.[citation needed]
[edit] Construction costs
The estimated costs of the most recent plans are huge. Figures are as high as £23 billion.[31] Recent studies [32] 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.[edit] Local impact
Any large-scale barrage would create leisure-friendly water conditions behind it. Flood protection would be provided by the barrage, covering the vulnerable Severn estuary from storm surges from the sea. 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.[33]However, shipping would have to navigate locks, and existing estuary industries, including fisheries, would be damaged and jobs lost. All industrial discharges into the River Severn (e.g. from Avonmouth) would have to be reassessed.[citation needed]
[edit] 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.[34] There are nature reserves and Site of Special Scientific Interest (SSSI) on the islands of Flat Holm[35] and Steep Holm.[36]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").[37]
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."[38]
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.[38] There are claims that the migration of fish would be hampered, but these are contested. The Severn bore would also be weakened or 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.[citation needed]
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.[40]
[edit] 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,[41] 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.[42][43]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.
[edit] 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.
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