The Severn Estuary

The Severn Estuary is one of the largest in Europe and is one of its most important wildlife habitats.

The estuary and the rivers which feed into it contain and support a wealth of wildlife so rich it is considered to be of international importance and is protected by international law. Its saltmarshes and mudflats are used by an average 74,000 birds each winter, its waters support more than 100 fish species and vast numbers of invertebrates. The estuary is a vital migration route for migratory fish, including Atlantic salmon, sea trout and eels.

But the future of the estuary and its wildlife is at risk because of a proposal to build an enormous barrage to generate electricity from the Severn's huge tides. Proposals for a barrage across the Severn have been around for more than 100 years but the urgency of climate change has now brought them back to the fore.

The huge tidal range and high level of surrounding industry and population have long made the Severn Estuary and Bristol Channel a focus for tidal energy schemes. Plans for a Severn Barrage – running 16 km from Lavernock Point near Cardiff to Brean Down near Weston-super-Mare have been discussed for several decades. The UK Government shelved plans for a Severn Barrage in the late 1980s due to cost and environmental concerns. Again, in 2003, a Severn barrage was rejected by the 2003 Energy Review due to 'strong environmental concerns'.

In April 2006, the Welsh Assembly approved the idea of utilising the tidal power of the Severn.

In 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 SDC gave its cautious support to the concept of a Severn barrage, providing a number of strict conditions were met. These included:

• It should be a publicly-led project, and a publicly-owned asset, to avoid short-term decisions and ensure 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 barrage must not divert government attention away from much wider action on climate change.

In late 2007, the UK Government announced a two-year 'Feasibility Study' into the possibility of using a variety of tidal range technologies to generate clean, renewable electricity from the Severn's tides. An initial 'long list' of 10 possible options was assessed and reduced to a shortlist of five announced by Ed Milliband, Secretary of State for Energy and Climate Change, in early 2009.

The five shortlisted options included two tidal lagoon schemes (Fleming Lagoon and Bridgwater Bay Lagoon) and three barrage schemes (Cardiff-Weston Barrage, Beechley Barrage and Shoots Barrage). By far the largest of the five schemes was the original 'Severn Barrage' - the Cardiff to Weston Barrage - which it is claimed would generate 8.6 gigawatts of zero-carbon electricity from the Severn – the equivalent of several large coal-fired power stations. It is claimed that it could supply 5 per cent of the UK's current electricity needs.

DECC published a summary report of the Feasibility Study and its conclusions in October 2010. The key conclusions included:

• A tidal power scheme in the Severn Estuary could cost as much as £34billion and is high-cost and high-risk in comparison to other ways of generating low-carbon electricity.
• A scheme is unlikely to attract the necessary private investment in current circumstances, and would require the public sector to own much of the cost and risk.
• The scale and impact of a scheme would be unprecedented in an environmentally designated area - there is significant uncertainty on how the regulatory framework would apply to it.
• Some habitats including saltmarsh and mudflat would be reduced in area, potentially reducing bird populations of up to 30 species.
• Fish are likely to be severely affected with local extinctions and population collapses predicted for designated fish, including Atlantic salmon and twaite shad.
• Water levels would also be affected and in order to maintain current flood protection levels in the Severn Estuary additional flood defences would be required.

As part of the Feasibility Study, DECC also ran a programme called the 'Severn Embryonic Technologies Scheme'. This funded the investigation of three further proposals for the Severn, using innovative and immature technologies, including a low-head barrage and two tidal fences.

These proposals showed promise for future deployment within the Severn Estuary - with potentially lower costs and environmental impacts than either lagoons or barrages. However the technologies were a long way from technical maturity and therefore more work would be required to develop them to the point where their yields, costs and environmental impacts could be properly assessed.

In 2012, a consortium called Corlan Hafren resurrected the idea of a barrage on the Cardiff-Weston alignment but claimed their proposal had two significant differences:

• Construction could be paid for through private investment, as long as the right level of subsidy from Government could be agreed for the energy produced.
• Low-head rather than a high-head design and would operate on both the flood and ebb tides (rather than just the ebb tide). They claim that as a result of these differences the environmental impacts of their proposal would be much less than those of the Cardiff to Weston barrage examined by the STPFS.
• However, to date, there is no detail on the proposed design or its impacts, and no evidence has been made available to support Hafren Power's claims.

The UK Department for Energy and Climate Change (DECC) said it had received the first draft of a business case for the scheme, and that it was an "interesting proposition".

A high profile media-driven campaign, led by former Labour Welsh Secretary Peter Hain MP, followed during 2012-13, as did a change of company name, to Hafren Power. However, the Hafren Power plan collapsed after it was rejected by three independent committees of MPs and by the UK Government.

The House of Commons' Energy and Climate Change Committee concluded that the case for a barrage was "unproven" and stated that Hafren Power "has yet to provide robust and independently verified evidence of the economic, environmental and technological viability of the project". In September 2013 Hain said that the plan was "dead in the water" in the current parliament.

By January 2014, four key figures had resigned from the Hafren Power, including chief executive, non-executive director and economic coordinator and very little has been heard of the company since.

In 2007, the Severn Tidal Power Feasibility Study several tidal lagoon proposals were assessed alongside of the barrage proposals. Over subsequent years, Tidal Lagoon Power have championed plans for a Tidal Lagoon in Swansea Bay (within the Greater Severn Estuary). This proposal has now gone through the planning process and a consenting decision is awaited from Energy secretary, Ed Davey.

TLP have also made clear their intention to explore the possibility of further, much larger, tidal lagoons at much more sensitive sites within the Severn Estuary including at Cardiff, Newport and Bridgwater Bay. Each of these locations would be within the area designated as a Special Area of Conservation (SAC), a Special Protection Area (SAC) and a Ramsar site.

Because of its sheer scale, it's difficult to get an impression of the Severn Estuary. Sometimes it just seems to be a vast expanse of brown mud! But this is deceptive. The estuary contains a huge variety of habitats – sandbanks and mudflats, rocky reefs and islands, saltmarsh, rockpools and shingle. It supports internationally important numbers of birds and large numbers of fish, including species that are rare or endangered elsewhere. This is a truly amazing place. 

What makes the Severn Estuary so special, in fact, almost unique in the world, is the size of its tides. Its immense tidal range (the difference between high and low tides) is the second largest in the world, a staggering 14 metres! 

These huge tides affect everything in the estuary ecosystem. Up to 10 million tonnes of silt are churned up and carried along in suspension by tidal currents running at seven metres per second. The Severn is one of the most dynamic estuarine systems in the world. We believe this extraordinary ecosystem should be cherished. 

The Severn's intertidal habitat – the area of mud, marsh and sand exposed at low tide – is one of the largest and most important for wildlife in Britain. With their high densities of invertebrates these areas are vital for a wide range of fish and bird species – for feeding, breeding, resting and migration. 

They support thousands of wading birds and wildfowl, among them shelduck, redshank and curlews, plus several rare or scarce fish species. The Severn's mudflats and saltmarshes provide both an overwintering ground and an essential stop-over for passing migratory species. 

The Severn Estuary is a key refuelling stop for migrating birds on long-haul international flights between their breeding and wintering grounds. It sits on the 'North Atlantic Flyway', a bird migration route that stretches from Siberia across Europe and down to Africa. The estuary provides a vital service station where birds can rest and refuel.

The Severn is one of the most important estuaries in the UK for wintering waterbirds, especially swans, ducks and waders, which stay on the estuary for the entire winter. Its marshes and mudflats are used by an average 74,000 wintering birds each year. 

During particularly cold winters, when severe weather is affecting Britain's North and East coasts, the estuary assumes even greater national and international importance as wildfowl and waders from many other areas arrive, attracted by the relatively mild climate and abundant food resources. Species such as the European white-fronted goose, dunlin, wigeon and teal use the estuary as a haven in cold conditions. 

In particularly cold winters, bird numbers recorded in the estuary have peaked at more than 100,000. The Severn Estuary is ranked in the top 15 sites for absolute numbers of wildfowl, and is the top UK site for European white-fronted geese.

The Severn Estuary is recognised as internationally important for birds and for wildlife habitats and has been given a number of international conservation designations. 

In 1995, it was classified as a European Union Special Protection Area (SPA). It is also a Ramsar site, a Special Area of Conservation (SAC) and contains seven Sites of Special Scientific Interest (SSSIs) protected by UK law. 

Its tributaries - the rivers Wye and Usk - are also protected under separate SAC designations because of their important habitats for fish. The estuary is a key part of the Europe-wide network of protected sites known as Natura 2000. 

The assessment of proposals to harness the tidal energy of the Severn will be the hardest political test for the Birds and Habitats Directives in the UK. We believe that the tried and tested framework of the Nature Directives provides a vital tool to help make the right choices for the Severn, difficult as they will be. They should not be considered a hindrance to the right kind of development. 

We refute the view that climate change is so serious that the checks and balances put in place by the Nature Directives are inappropriate.  

It is because the situation is so serious that we need a robust and tested system to help ensure that the natural world is not sacrificed unnecessarily. We are arguing that wave and tidal energy solutions which cause less damage to the environment than a barrage should be investigated with the goal of finding the most benign option. The overall aim has to be to deliver the maximum amount of energy for the minimum environmental impact.

The main aims of being an RSPB campaigner are to remind your MP or decision maker that environmental issues are important, and to urge them to take positive action. 

As a constituent and a consumer, you can influence people who make some pretty big decisions. By saying the right thing the right way, you can make others take action for nature. 

You'll also be inspiring your local community to take action as you'll be building support and raising awareness of our campaigns and appeals.   

To find out more visit our campaigning page.

We are committed to tackling climate change - the threat it poses to people and wildlife is so great it demands a revolution in the way we generate and use energy. 

We support the concept of renewable and clean energy production and recognise that tidal power has the potential to generate significant quantities of renewable and clean energy. That said, we also recognise that, like all forms of development, inappropriately designed and/or sited renewable energy developments can cause serious, irreparable and unnecessary harm to biodiversity.   

Old-fashioned methods of generating tidal power - in particular tidal barrages - carry huge risks to sensitive environments. We oppose tidal barrages where they are likely to destroy habitats of international importance for birds and other wildlife. The Severn Estuary is too precious to destroy. 

In 2008, we welcomed the UK Government's Severn Tidal Power Feasibility Study (STPFS). However, the shortlist of five options selected for further investigation was a cause for huge concern. Disappointingly, it rejected more environmentally benign alternatives, preferring instead three traditional barrage schemes and two 'lagoon' schemes.  

As was confirmed by the findings of the STPFS, the largest option of all, a high-head  Cardiff-Weston Barrage – a 16km long concrete dam - would be an ecological disaster, permanently destroying huge areas of vital feeding habitat for birds and blocking the passage of migrating fish with concrete and turbines. 

By holding back a 10-metre head of water above the turbines the barrage would permanently submerge large areas of inter-tidal habitat currently exposed at low tide. These are vital feeding areas for the estuary's birdlife. There would not be enough room left for all the birds, or enough food in those feeding areas that remained. The barrage would halve the Severn's tidal range, reducing the power of its currents to such an extent that millions of tonnes of silt would drop out of suspension. 

We believe there has to be a better way to use the power of the Severn's tides, by working with nature rather than against it. Tidal power can be harnessed by different generating mechanisms with smaller environmental impacts. 

We are open to innovative means of sustainably exploiting the energy resource in the Severn and have consistently called for greater resources and effort to be put behind developing these options. Whilst we welcomed the Severn Embryonic Technologies Scheme, it was under-resourced and formed only a small part of the overall study (£0.5mn out of £20mn).   

As a result, the £20mn STPFS ultimately identified that the short-listed options it considered, including the high-head Cardiff to Weston barrage, were unworkable. It concluded that the high-head Cardiff-Weston barrage was high cost and high risk in comparison to other ways of generating low-carbon electricity and that the scale and impact of the scheme would be unprecedented in an environmentally designated area. 

While we were relieved that the Government dropped plans for a Severn barrage in 2010, we were concerned that the reason cited for this was expressed purely in economic and financial terms: "there is no strategic case at this time for public funding of a scheme to generate energy in the Severn estuary".  We believe that the severity of the ecological impacts should have been sufficient to drop proposals for a barrage once and for all and shift the focus to exploring less damaging ways of harnessing the energy resource of the Severn.  

We were extremely disappointed that this left the door open for Hafren Power to come back with a revised Cardiff-Weston Barrage scheme just two years later because of their claims that the cost of building the barrage would be met entirely from private investment.  

We remain deeply sceptical that a shore-to-shore barrage on the scale of that envisaged by Hafren Power could be delivered without unacceptable damage to the Severn Estuary, its wildlife, and its communities. 

Along with other concerned organisations, the RSPB believes that a step-by-step approach should be taken to the deployment of renewable energy in the Severn, given the potential for severe adverse environmental impacts to the estuary and our lack of detailed understanding of the nature and scale of actual impacts.  

This would begin with a smaller project or projects which could be monitored carefully and used as test cases for evaluating the impacts of potential larger scale projects further down the line (which might be located within the Severn or elsewhere). By this point there may also be a wider range of wave and tidal stream technologies available to deploy, with lower environmental impacts than the tidal range technologies currently available.    

In November 2012, a new discussion document was published by SWRegen and others "Bristol Channel Energy: A Balanced Technology Approach".  This advocates an approach based on the incremental roll-out of a series of large scale energy schemes as technologies are proven and their environmental impacts can be properly managed. The RSPB welcomed this discussion document and believes its publication marks a good starting point for a more sensible strategy for building up renewable energy.

Tidal Lagoons are a new approach to tidal power on the Severn that is currently making the news, one which holds out the prospect of tapping the renewal energy of the tides whilst keeping the impact to our natural environment within potentially acceptable bounds.  

Tidal lagoons are an interesting new idea which deserves serious consideration. We welcome innovation – indeed the RSPB was at the forefront of stimulating new thinking while we were challenging the folly of building a barrage across the Severn estuary. We’ve been working with Tidal Lagoon Power to explore the opportunities and risks constructively, focussing on their proposals for Swansea Bay. 

But let's be under no illusion, each tidal lagoon installed will change the shape of the coastline, affecting the flow of water through the Bristol Channel, with knock on effects for sediment transport, habitats and flood risk. There is an urgent need for research to understand what the effects of different combinations of lagoons might be, in order to highlight, and potentially mitigate, negative environmental and social impacts. The cumulative effects of large infrastructure projects of this type can be significant and far reaching: research by the University of Liverpool demonstrated that multiple tidal barrages on the UK's west coast had the potential to raise sea level on the east coast of Ireland by several centimetres. 

Rushing to roll out a new technology at multiple sites around the coast risks failing to learn vital lessons – the crucial first step is to agree a sound monitoring programme that validates the modelling and predictions that are, currently,  all we have to go by. 

The biggest risk to the future of tidal lagoons is to fall victim to short term thinking driven purely by financial considerations. The impact of a new technology must be properly understood in the context of the importance of the coast environment in which they are proposed. 

Some aspects of the Severn estuary environment are well known – the distribution of the birds which winter there in internationally important numbers is one example. The Severn is even more important for fish including the globally threatened Atlantic eel and Twaite shad. Disruption of coastal environments can have profound implications for flood management, the complex issues around the potential release of carbon currently locked up in the sediments of the estuary, the survival of archaeological resources and fisheries. Understanding the implications of development on fundamental ecosystem services – those benefits our environment bestow on our lives – is crucial and should not be overlooked in the short term haste to roll out a new technology.

• December 2014 
  Following conversations between Tidal Lagoon Power and the Planning Inspectorate, outline details of a Cardiff Tidal Lagoon scheme appear on the National Infrastructure Planning website. The lagoon would be attached to the shore, with one end around 2km from the entrance to Cardiff Bay and the other 2km from the mouth of the River Usk at Newport. This lagoon would be much larger than the proposed Swansea Bay lagoon and at the widest point it could extend as much as 8km out into the Severn. An application could be submitted to the Planning Inspectorate in the spring of 2017.

• 2 March 2014 
  Tidal Lagoon Power submit an outline Environmental Impact Assessment for a 1.8GW to 2.8GW lagoon between Cardiff and Newport and request a scoping opinion for the project from the planning inspectorate. At the same time, amid great media interest, TLP also confirm that feasibility and engagement work is underway relating to proposed tidal lagoons at Newport, West Cumbria, Colwyn Bay and Bridgwater Bay. 

• February 2014 
  Plans are submitted for a £850m tidal lagoon in Swansea Bay in the Bristol Channel which the developer, Tidal Lagoon Swansea Bay Ltd (Tidal Lagoon Power), claim could provide power for 120,000 homes for 120 years. This is an application for a Development Consent Order to the planning inspectorate, for determination by the Secretary of State for Energy and Climate Change, Ed Davey. His decision is expected in March 2015.

• September 2013 
  Hafren Power’s plans for a tidal barrage generating power on the Severn Estuary is dealt a final blow when the UK Government ruled out proceeding with its plans: "In its current form, the Hafren Power proposals for a Severn barrage does not demonstrate that it could deliver the benefits it claims it would achieve." Ministers reiterated their view that there should be no firm commitments of public financial support – in the form of the "strike price" of a premium for low-carbon power that has been confirmed for wind power and is expected soon for nuclear energy – for tidal barrage schemes until 2019 at the earliest. 

• June 2013 
  The cross-party House of Commons Energy and Climate Change Select Committee hold an inquiry entitled 'A Severn Barrage?' and conclude that Hafren Power had failed to make the case that the barrage would be good for the economy or the environment. The company failed to convince MPs of the viability of the project in three key areas - financial, environmental and acceptability to the public. Its timetable for a new law to pave the way for a barrage was deemed "completely unrealistic". 

• 2012 
  Hafren Power claim to have a new proposal for a Cardiff-Weston barrage that would have a low-head design, operate on both the ebb and flow of tide and have lower ecological impacts both in terms of loss of intertidal habitat and affects on bird and fish species. Despite a lack of any detailed project information to support these claims, Prime Minister David Cameron instructs ministers to look in detail at the new proposal. 

• October 2010 
  In October the conclusions of the Feasibility Study are published. They state that the scale and impact of a scheme would be unprecedented in an environmentally designated area Energy Secretary Chris Huhne says the costs are "excessive" and that the Severn Tidal Power Feasibility Study clearly shows that "that there is no strategic case at this time for public funding of a scheme to generate energy in the Severn estuary". Plans for the barrage are dropped by the UK government. 

• March - April 2010 
  The five shortlisted options are subject to a Strategic Environmental Assessment (SEA) to ensure a detailed understanding of the Estuary's environmental resource, in recognition of its national, European and international nature conservation significance. A number of working groups gather evidence on the possible impacts on biodiversity and wildlife; land and seascapes; flood management; geomorphology; and water quality. The SEA also considers compensatory habitat issues. 

• Early 2010 
  Work continues on the 'embryonic technology' schemes with the goal of developing them to a stage where they can join the main shortlist and be assessed with the other five scheme on 'a level playing-field'. However, the tight timescales and limited funding given to development of these by Government means that this goal is not achieved. 

• 2009 
  Energy and Climate Change Minister Mike O'Brien and Welsh Assembly Government Environment Minister Jane Davidson announce the £500,000 Severn Embryonic Technologies Scheme to bring forward the development of schemes using innovative but 'embryonic' technologies, which offer the potential of a less environmentally-damaging tidal power solution but which are not sufficiently developed for more detailed analysis at this point. In July the Government confirm that Phase 2 of the Feasibility Study will go ahead to carry out detailed assessment on the five schemes that have been short-listed, and the successful schemes are announced for the Severn Embryonic Technologies Scheme funding.

• 2008 
  As part of the Severn Tidal Power Feasibility Study, the Government announce a proposed shortlist of five schemes to harness renewable energy from the tides of the Severn estuary, selected from 10 examined over the previous six months. 

• September 2007 
  The Department of Energy and Climate Change announce a 2-year Severn Tidal Power Feasibility Study to investigate the possibility of using the huge tidal range in the Severn Estuary to generate electricity, building upon previous studies and focussing on a variety of tidal range technologies including barrages, lagoons and newer innovative designs. 

• May 2007 
  Trade Secretary Alistair Darling publishes an energy white paper calling for support for wind, wave, tidal and other 'renewable' energy technologies. He says Government want to encourage the development of tidal power. 24 MPs sign an early day motion calling on the UK Government to urgently reappraise the idea of a Severn Barrage.

• 2007 
  Evans Engineering propose the 'Tidal Reef', sited on an 'outer' alignment between Minehead and Aberthaw, roughly doubling the volume of tidal water available for power generation. The reef would be designed to overcome the environmental side-effects of barrages whilst generating on both the ebb and flow of the tide. The design would minimise environmental impact by working with a much smaller 'head' of water, reducing the impact of the structure on the estuary. In a review, WS Atkins estimates its energy output could be significantly greater than for the Cardiff-Weston Barrage.

• 2006 
  Welsh businessman Gareth Woodham submits a proposal called 'The Severn Lake' for a barrage on the Cardiff-Weston alignment, featuring 14 electricity generating turbines, a dual carriageway, a light railway, four marinas and two lock gates to give ships passage. Woodham claims it will supply electricity for the whole of the South West and will take up to 20 years and about £650 million to complete.

• 2003 
  The Welsh Assembly Government publish a report on renewable energy and press for another study to look at the feasibility of a tidal power barrage across the Severn Estuary.

• 1989 
  The Severn Tidal Power Group pick up on the Bondi recommendations. Their £4.2 million study builds on the work of the earlier Severn Barrage Committee, and concludes that the Cardiff-Weston line is the best location for a barrage, is technically feasible and would have an annual output of approximately 17 terawatt hours, or nearly 5 percent of the UK's current electricity. Construction cost is calculated to be about £8 billion and running costs around £70 million per year. Government again decides that a Severn barrage is not a cost-effective option for generating electricity.

• 1981 
  The Bondi Committee investigate six possible barrage locations, from English Stones at the top of the estuary, down to a location in the Bristol Channel between Lynmouth and Porthcawl. It recommends a 10-mile long concrete barrage on the Cardiff-Weston line.

• 1971 
  Dr Tom Shaw revives interest in a Severn Barrage, proposing a 10-mile long barrage from Brean Down to Lavernock Point - the so-called 'Cardiff-Weston Barrage'. This is again rejected on economic grounds – this time the estimated cost is £500 million.

• 1953 
  Another feasibility study - the estimated cost has risen to £200 million.

• 1948 
  When a further government study looks at barrage options in 1948, construction costs are estimated at £60 million and considered too costly.

• 1933 
  The Severn Barrage Committee Report again recommends an 800 MW barrage across the Shoots channel. This idea is revived again after World War II.

• 1925 
  An official study group is commissioned to consider tidal power generation in the Severn. This leads to a proposal to generate 800 MW of electricity by constructing a 3 mile long tidal barrage across the Shoots channel, now occupied by the Second Severn Bridge. Although considered technically possible, it is rejected on economic grounds – the estimated cost in 1925 was £25 million.

• 1849 
  Thomas Fulljames, county surveyor for Gloucestershire, propose a barrage stretching just over 1 mile from Beachley to Aust on the line now spanned by the First Severn Bridge. This pre-dates serious electricity demand but offers a large shipping harbour in the Severn Estuary, road and railway links, and protection from flooding.

RSPB briefing on the implications of the Eastern Scheldt (Oosterschelde) for the Severn Estuary.

A report by Dutch Ministry of Water Management scientists on the nature, flood safety, shipping and fisheries impacts of the construction of a storm surge barrier on the Eastern Scheldt (Oosterschelde) estuary in The Netherlands.​​​​​​​

• Severn Estuary Partnership

• Bird guide: Bewick's Swan 

• Bird guide: Dunlin 

• Bird guide: Redshank 

• Bird guide: Shelduck

• DECC - Feasibility Study Conclusions

• Energy and Climate Change Select Committee (January 2013) 

• Regen SW & Partners, Bristol Channel Energy: A balanced technology approach (November 2012) 

• RSPB Severn Barrage written evidence to Parliament 

• Severn Tidal Power SEA Environmental Report (May 2010)