Next Coffee House Discussion

Friday 26th May - Is the Severn Barrage a good idea? A speaker will introduce the topic which will be followed by questions and discussion. Open from 7.30 to 9.30pm at Star Anise Arts Cafe at the Painswick Inn, Gloucester Street, Stroud. Click here for more details about the evening.


For more information about the topic see article below

Harnessing the Severn tides - By Jon Lucas, Bristol East Green Party

With climate change developing fast, we are already being overwhelmed by different proposals for tackling it, and the south-west will be in the front line for many of these. Here we have much of the best potential for green energy schemes, with plenty of wind from the Atlantic, reasonably high sunshine levels for solar heating, much rainfall concentrated on the higher parts of the region for water-driven energy, and a vast coastline accompanied by very high tidal ranges. Of all these, perhaps the last has the greatest potential, with tides being the one energy source that can be entirely relied on, being not dependent on the vagaries of the weather but on the lunar cycles that can be predicted for millenia in advance.

With Britain’s long and indented coastline, there is much opportunity to develop tidal generated power schemes. The greatest tidal range around our coastline is found in the Severn estuary and Bristol Channel, with a difference between high and low tides of as much as 40 feet at certain times of the year. Thus we have here perhaps the greatest scope for dependable renewable energy, and it has led to many proposals for developing it, with 2006 looking as if it will be the year when some decisions may be made.

At its simplest, there are two methodologies for creating tidal power: the use of tidal dams or ocean currents. Dams use a barrage or lagoon at a bay or estuary with a large tidal range. Power is generated primarily at ebb tides as the barrage creates a significant head of water, much like a hydroelectric dam. Ocean currents do not need such large constructions, but are harnessed by tapping into the currents where the flow is strongest, this being determined by the lunar cycles along with constrictions and narrow channels in the sea bed. Turbines are used on a similar principle to wind turbines, except that water rather than wind causes the blades to rotate.

Given the realisation of the immensity of the problem we face in dealing with climate change, the temptation for many people, especially the government and other authorities, is to opt for the big scheme that offers seemingly the largest payback in terms of renewable energy. Thus this year we are faced with two schemes promoting a Severn barrage, and as with nuclear power, many people are suddenly giving them their support on the basis that something big needs to be done. Already, at the time of writing, the Welsh Assembly and Bristol City Council are backing the schemes in principle.

For many Greens, including myself, our reaction tends to be the following:
a) We recognise that major changes are needed to tackle climate change and have been saying this for many years.
b) We also recognise that change is best handled by a bottom up approach, with the local communities involved in them from the beginning.
c) To tackle climate change will require much more diverse and decentralised energy production, with energy produced as locally as possible to where it will be used.
d) We have an instinctive awareness that smaller schemes are usually much more adaptable to fast changing situations, are more easily managed and are usually much less environmentally damaging.

Thus, while all the current headlines are given over to discussions about a possible Severn barrage, for many of us the greatest potential for harnessing the Severn tides probably lies in the smaller schemes that are being researched at the moment. The world’s first experimental offshore tidal turbine, the ‘Sea’flow’, was installed in the Bristol Channel off Lynmouth in north Devon in early 2003. Much more powerful types of turbine are now being produced, such as the ‘Sea-Gen’, which is being installed in Strangford Lough in Northern Ireland and connected into the national grid. The company behind this, who are based near Bristol, have an 18 month investigation studying the marine environment and the tidal flows around the Welsh coast. This will examine local navigation and connections to the electricity network, and consider the engineering and financial issues associated with commercial development of tidal stream energy. (f.f.i. www.marineturbines.com).

Another pioneering invention which uses the ocean’s currents to generate power is being developed by Wave Dragon Limited. The Wave Dragon is a floating device that works by channelling water in a reservoir above sea level and using turbines to generate hydroelectric power. These floating units have undergone eight years of testing in Denmark and Ireland, and it is now hoped that up to 11 dragons will be placed in the Irish Sea to generate enough electricity to power over 60,000 homes. (f.f.i. www.wavedragon.net).

It is inevitable, though, that we will be faced with decisions about much larger schemes such as the Severn barrage. A barrage could potentially supply much of the surrounding coastal areas of south Wales and the West Country with its energy needs, but would dramatically alter the local environment. The estuary is a unique habitat for much wildlife due to the tidal range and the large amount of mud that is exposed at each low tide, and the barrage would alter this severely. The Severn bore would also disappear. The barrage would protect inland areas from coastal flooding that is likely to take place more often due to global warming, but it may also cause excessive flooding downstream of the barrage, with the Somerset levels certainly threatened.

Smaller versions of barrages that use similar ideas but without damming the whole estuary are tidal lagoons. These are constructed within the estuary to collect water as the tide rises, and use turbines in the lagoon walls to generate electricity during the ebb tide. While they would probably not cause as much disruption to the local environment or wildlife, their construction costs, in terms of resources used as well as financial, would be immense. They would also be highly visible at low tides, appearing like a series of breakwaters.

Friends of the Earth have concluded that tidal lagoons could potentially generate 6% of the UK’s current electricity demand, as much as 3 or 4 nuclear power stations, at much lower cost than a barrage. They would impound an area 40% smaller than the barrage and not impede shipping, and could be sited a mile off the coast, avoiding the most sensitive sites of inter tidal mud used by wildlife.

There is great suspicion that the current barrage schemes are being put forward under the aegis of tackling climate change, but with profit being the main motive. The schemes also involve the construction of a road across the top of the barrages, which would greatly increase the amount of road-borne transport in the south-west, and include the idea of developing islands constructed along the barrage for executive homes to be built on.

Some big decisions will certainly be made soon, with pressure mounting to give the Severn barrage serious consideration. Climate change will throw up many contradictions in the way that environmentalists consider issues, and this could well be one of our biggest tests.



ALSO OF INTEREST:
The Green Party's Alternative Energy Report, published by Dr David Toke and Dr Simon Taylor in February.

http://www.greenparty.org.uk/news/2439
http://www.greenparty.org.uk/reports/296