Severn Barrage Tidal Power Scheme

The Severn Estuary can be found between England and Wales where the Severn River meets the Atlantic Ocean near Bristol.

The Severn estuary is notable for having one of the largest intertidal habitats in the UK, which means that it is also one of the rarest ecosystems on the planet. In fact, the estuary has been recognized by the international community and the European Commission as a wetland of international importance, particularly for bird conservation and fish migration, particularly Atlantic Salmon. Estuaries in general are considered unique and critical habitat as they often serve as spawning grounds for numbers of different species.

Severn Estuary Tidal Power Schemes

The other unique aspect of the Severn Estuary is its high tidal range. The tide varies by nearly fourteen meters (fifty feet) from low to high, making it an ideal location for a tidal barrage system. In fact, a system generating over 8.6 gigawatts has been proposed for a site near Cardiff. Such an installation would meet about five percent of Britain’s current energy requirements. This would not be the first time the Severn Estuary has been looked at for its potential to generate power.

The Severn has been looked upon as a potential source of energy for centuries, but the technology to harness its full potential has really only been available since the later part of the nineteenth century. The first proposals dealt mainly with transportation links and flood protection, but more recent proposals have focused on the generation of electricity. The first of these were made in the 1970s.

The first studies were designed to determine feasibility and most indicated that a barrage system that generated power with the outgoing tide would be possible. However, the size of the Severn and the low cost of other forms of electricity generation made the project too expensive. Since that proposal, at least ten others have been put forth for building a barrage in various locations. Some of the locations have been estimated to have the potential to generate as much as 14 gigawatts of power.

The most recent proposal for using the Severn to generate power came in 2011 when the government entered into talks with Corlan Hafren to build a privately financed barrage from Lavernock Point to Brean Down. The research for feasibility of this system comes from a 2007 government study that found the potential not only for massive power generation from the Severn Barrage, but also for massive environmental damage. The UK government abandoned plans at that time, but has since revisited them as the cost of electricity rises and the need to mitigate carbon generation becomes more imperative. In fact, the carbon “payback” time on the Severn Barrage has been estimated to be around six months, which means any carbon debt incurred from building the damn would be fully repaid within six months of completion. It has also been estimated that the system could operate for well over 100 years with minimal maintenance, making it cost effective in the long term even if it is exceptionally expensive in the short term (est. £10 - £34 billion).

Environmental Impact

The intertidal area of the Severn Estuary provides food and shelter to somewhere between 5% and 7% of the migratory birds in the United Kingdom. As a result, the estuary is listed as a Special Area of Conservation as well as a Site of Special Scientific Interest. There is a great deal of concern over the impact that a barrage would have given that a similar installation in France has shown changes to fish populations as well as sediment deposition patterns. Some have proposed that smaller, trial barrages should be built in less critical areas to determine the full extent of the impact before anything is done on the Severn.

Most environmental groups seem willing to compromise and allow for the construction of tidal lagoon systems. These are thought to have far less impact on the overall state of the estuary even though they cover as much as 60% of the area that a barrage would have. Unfortunately, the lower power output of such systems makes them less economically attractive and so the cost-benefit ratio tips away from building them.

Tidal stream generators have also been proposed as potential solutions to the quandary of environment versus economics. Though they would only generate about 1.3 gigawatts as opposed to the 8.6 gigawatts of the tidal barrage, stream generators would interfere less with wildlife habitats and would be much less expensive to install. Stream generators could also be installed in phases to ensure that no unintended adverse impact occurs as the system is brought to full capacity and would cost a maximum of about £10 billion.

Feasibility Studies on the Severn Barrage

A number of different studies on the feasibility and impact of the Severn Barrage have been carried out over the years. This section reviews several of those studies and their key findings.

Wimpey Atkins Study, 1984

• Carried out by the multinational engineering company know as WS Atkins
• Included some environmental analysis, but neglected the problem of silt
• Revised study looked at silt deposits for a smaller barrage at Second Severn Crossing
• Smaller peak output of just over 1 gigawatt at a cost of ~£2 billion

The Severn Barrage Project: General Report": Energy Paper 57; HMSO 1989

• Commissioned by the UK Government
• Found that ebb generation by a barrage from Lavernock Point to Brean Down would be possible from a technical standpoint
• No extensive environmental analysis
• Cost was deemed prohibitive

Sustainable Development Commission and Severn Tidal Power Feasibility Studies, 2007

• Two different UK Government Studies undertaken in 2007
• Explores a variety of technological approaches
• Strong emphasis on biodiversity, wildlife, flood management, water quality, and other environmental factors.
• Encorages the Barrage to be publicly led
• The project was again abandoned in 2010 as a result of the combination of environmental impact and the cost that mitigating such impact would have on the project.