Tuesday, 21 October 2014
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The Engineer Q&A: The Severn Barrage

The Severn Barrage is an idea that refuses to die. People have been proposing and dismissing building a barrage across the Severn Estuary since 1849 – meaning the concept is seven years older than The Engineer. The estuary holds an estimated 8 to 12GW worth of theoretically harnessable power, and now with climate change targets making the need for renewable energy more urgent than ever, the Severn Barrage is once again up for debate.

Over the last few weeks, MPs on the Energy and Climate Change Committee have been hearing evidence for and against building a barrage, so we’re likely to hear some kind of official pronouncement later this year. The government’s official position (based on a 2010 feasibility study) is that there is no strategic case for public investment in a Severn tidal scheme in the intermediate term, so if a barrage were to be built it would likely be a privately funded development.

The debate around such a scheme is a complex one due to the busy shipping lanes that run through the Severn and the potential environmental issues it could create. But given that very few tidal barrages of this size have ever been built anywhere in the world, there are also big questions around what building a Severn barrage would actually involve. Indeed, there’s also the question of whether a barrage is the best way to harness the immense tidal power of the estuary.

As the Commons hearings continue, we’ve assembled our own panel of experts to answer your questions on what are the engineering challenges in building a barrage in the Severn, whether and how we can physically and economically overcome them, and what other options might we pursue for generating electricity from the tides.

Answering your questions will be:

  • Hafren Power - a private consortium proposing the construction of a Severn barrage
  • Tidal Electric - a US firm that specialises in tidal pool technology
  • Prof Roger Falconer - president of the International Association for Hydro-Environment Engineering and Research, and director of the Hydro-environmental Research Centre at Cardiff University, an expert who has spent years studying the issue
  • Norman Haste - former project director for the Second Severn Crossing
  • Dr Peter Tavner - emeritus professor at Durham University’s School of Engineering and Computing Sciences, an expert in large renewable energy projects and the technology of turbines, generators and grid connectors.

If you wish to put a question to one or all of our experts, please post a comment below before midday on Thursday. We’ll then collate and forward the questions to our panel and publish the responses online next week and in the next digital issue of The Engineer.

While they may be able to address some environmental points, our experts are best positioned to answer questions related to the engineering challenges of generating electricity from a barrage or other tidal technology and the practical difficulties of building and operating a large structure in the constantly changing environment of the Severn estuary.

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Readers' comments (18)

  • I'm idly wondering to what extent the suppression of the natural water flow would slow down the rotation of the Earth; presumably the effect is negligible but is the calculation of the effect part of any feasibility study carried out by any of the proponents?

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  • I was just thinking of exactly the same thing as Roger Taylor's comment. Planetary scientists and climatologists consider this when trying to work out the long term patterns of global wind currents. It is posited that exchanges of angular momentum between solid Earth, its oceans and its atmosphere affect length of day. Much of the momentum is considered to be a true exchange thus exchanging back again, keeping length of day near constant in the long run. However, frictional losses do mean a small net loss in energy and therefore angular momentum and length of day. As for the barrage it is all energy loss and so must have an effect on length of day.

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  • The barrage is all a plot buy industry. Slow down the days Mon to Fri, get cheap electricity and longer working hours. Then speed it all up at the weekend to get everyone back to work. How devious is that?

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  • With the advent of in water turbines is it really necessary to build a barrage at all, surely it would be much simpler to build an underwater farm of pods that could be removed as and when needed for service. That way the majority of flow wont be disrupted and you’d be taking advantage of tide all but at slack water.

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  • In the spirit of joined up thinking that seemed to be popular a while ago.
    We have the idea of the barrage, offshore wind farms, wave power, and spend a fortune on bridges. These discussions never seem to add all of them together.
    Add in a few fish farms, marina, and flood a valley in the Welsh hills for storage. Then what are the numbers?

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  • If we built a deep water harbour on the seaward side of the barrage, and gave financial support to all affected upstream industries so that they could have first allocation of space, then run a rail service out to the dock, would this change the cost benefit ratio in favour of building. Turbine servicing could be super efficient and not be weather dependent.

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  • Perhaps if the difference between the promised output of wind farms and the actual output was widely publicised, the opposition to the Severn Barrage would lessen. Whilst appreciating the thinking behind Tony Howells comment maybe simplicity, the idea of the barrage would be to create a large holding area to eliminate the slack water problem. A barrage needn't be complicated, just substantial enough, and it could still be easily arranged so that the turbines would be lifted for maintenance. Perhaps the country should stop financing wind farms, and provide more resources for the research to tidal power generation (to BRITISH companies of course).

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  • Given that shipping, wildlife etc. would be affected by a barrage my suggestion would be to build a floating pontoon. Like the Mulberry Harbours during WW2 a number of floating concrete pontoons could be built which generate electricity by the action of the tides rising and lowering. It could even be constructed in the form of an island which could house hotels etc. Pontoons could be constructed at several places at once around the coast and floated into place. This would speed up the time of implementation. No wildlife would be affected, there would be no silt build-up and shipping would not be affected. It would be nice to hear any comments that the committee may have on the above proposal.
    David Searle

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  • The Panel will recognise the significant negative impacts of the barrage on shipping and the environment. Whilst HP suggest some of the impacts might be mitigated there are alternative technologies to produce power from the Estuary that do not have the same impacts. Which particular technologies do the Panel consider present the best alternative options to generate electricity from the Severn Estuary and Bristol Channel?

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  • Hafren Power have described their own proposals as inchoate. Does the Panel consider that they are able to comment with any authority on the basis of such limited information?

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