The Severn Barrage is any of a range 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 building of such a barrage would constitute an engineering project comparable with some of the world's biggest. The purposes of such a project have 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. Following the Severn Tidal Power Feasibility Study (2008–10), the British government concluded that there was no strategic case for building a barrage but to continue to investigate emerging technologies. In June 2013 the Energy and Climate Change Select Committee published its findings after an eight-month study of the arguments for and against the Barrage. MPs said the case for the barrage was unproven. They were not convinced the economic case was strong enough and said the developer, Hafren Power, had failed to answer serious environmental and economic concerns.
History There have been numerous proposed projects over the years, initially to provide a safe harbour and more recently to generate electricity.
Early projects
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 . 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.
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), second only to Bay of Fundy in Eastern Canada, 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). The viability was tested a few years later in 1931 when Paul Shishkoff,Pavel Aleksandrovich Shishkov (1887–1958) (Biographical information in Russian.) a Russian immigrant, demonstrated a prototype tidal generator at Avonmouth. It included a novel mechanism for spreading the power output over 24 hours. The full barrage was estimated at £5 million at the time."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. 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. 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. 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. Despite the ongoing oil crisis, the council established that a barrage could not be economically viable unless the energy situation deteriorated significantly.
Bondi Committee, 1981
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, which recommended a 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 George 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.
Hooker or Shoots Barrage, 1987
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 1,050 MW, and 313 MW output on average throughout the year.
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.
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. Its members comprised Sir Robert McAlpine, Balfour Beatty, Taylor Woodrow and Alstom. 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).
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).
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.
Severn Tidal Reef, 2007 Evans Engineering have released plans for what they call a Severn Tidal "Reef". 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 —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.
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, 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.
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