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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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  • HP's proposal is based upon the concept of using in excess of 1,000 low head turbines. How long do the panel consider it will take to develop these new turbines from the current concept stage to a fully operational, proven machine, and then manufacture them with the full performance guarantees, maintenance and support services?

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  • Hafren Power's proposal depends on foreign investment. Overseas investors may have their own ideas on where in the world is the best location to build the new turbines. What factors do the panel consider will determine where the turbines will be built and where in the world do they think is best placed to take on this task?

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  • I have said this before; why did they not build something into the severn bridge when they had the chance. Surely someone could have designed a system to do both at the same time! Hopeless!

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  • Ian Morris makes an important point, but to some degree the climate for that kind of radical approach is destroyed by the political dogma of the EC and the UK government. (They both get their knickers in a twist over the infrastructure responsibilities of the state)

    Witness this classic piece of neoliberal idiocy:-

    “The UK could face fines of £250,000 a day over failure to implement EU internal energy market rules in Northern Ireland. The rules separate energy production and supply.” (These rules have their formative roots in the Common Agricultural Policy school of economic intellectual rigour, oddly enough.)

    I have two questions and one answer.

    Hafren Power state in their written evidence - “The barrage will produce . . base-load electricity on average for 15.25 hours a day.”

    I understand ‘baseload’ to mean continual - uninterrupted - 24/7. Am I right?

    How do you propose to match electricity output to demand? (especially in a future ‘zero carbon’ grid, composed of inflexible (baseload) nuclear power and intermittent renewables.)

    My point being - 3GWh dispatched to meet peak demand earns the best price. Potential supply when there is no demand has little value. That inherent inefficiency would be embedded for the lifetime of the proposed design and this barrage could be working for centuries without any need to rebuild its core fabric.

    The turbines should drive water pumps to fill a couple of hundred raised-weight air/water accumulators. All the electric gear would then be mounted above, in a few dry, readily accessible generator houses. One thousand 3MW generators, or 30 @ 100MW - take your pick. Change the shape of the concrete caissons from boxes to cylinders. I think that qualifies as joined-up thinking.

    Instead of (in fact) being yet another source of intermittent generation, the barrage would be transformed into utterly dependable ‘peaking’ plant. The incompetent (and unworkable) plans to allocate this role to gas (the Energy Bill) should be scrapped, then investors would be given all the right messages and the UK would truly lead the world in ‘green’ energy. It’s a political choice that only intelligent politicians can make. Every part of the rebuilding of our electricity infrastructure should be a private/public co-production, with the emphasis on the scientific evidence and the ‘public’ involvement, because private monopolies never work in the consumers’ interest.

    The bespoke manufacturing dock at Port Talbot will need to produce these caissons in thousands, not hundreds, and do so for generations to come, because ALL marine installations should be ‘SIRG’ - storage integrated renewable generation. The Atlantic Array would be the perfect pilot project. Rush into the deployment of intermittent offshore wind (and wave) and repent at your leisure.

    The output of windfarms could be firmed-up at 70% of ‘nameplate’ capacity and gross over-capacity would be a nightmare avoided.

    Neoliberal fundamentalists destroyed the ‘market’ for innovation decades ago, (R&D and IPR are the province of the private sector, they say!!) and then they destroyed the ‘market’ for energy storage technologies when the privatised electricity ‘market’ was designed with cretinous economic theories.

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  • What is the track record of Hafren in this field?

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  • Just get on and build it To me its a no brainer. Decent road link and rail link, once built a relatively low cost and efficient way of producing power from what I believe is the second largest tidal estuary in the world in terms of change in the height of the water. Just make sure that the design allows for the change and maintenance of the immersed equipment from above not from the sea and make it future proof for replacing and upgrading the hardware. all of the technology exists so get on with it we need it now before the country is covered in near useless expensive wind turbines

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  • I tried to interest the Scottish Govt. [ i spoke to John Swinney [Treasurer] at a low Carbon conference, to install a barrage plus 4 lane road at the Forth Estuary crossing on the grounds that although the tide is smaller than the Severn, it would have two major benefits:

    1] achieve a crossing that also could be selectively closed at low tide to aid flood run-off for the upper valley [falkirk / Alloa and mostly Stirling]
    2] to act a a permanent barrier once the sea level rises [most of Scottish industry in the Forth/Cldye basins are no higher than 10metres above sea level.]

    So Scottish independence or bird watching at Slimbridge and evensong in Gloucester or Cardiff Cathedrals could be protected in AD2100+ whilst London goes Glugg-glugg!

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  • I am in total agreement with Charles Beecham, just build it! A sizeable sea lock somewhere in the scheme would ensure navigation continuity, and also provide a safety valve, should rainfall flooding occur further upstream. Lets hope the government moves as quickly on this scheme as they do on the wind turbines, but this time keep the monies within the UK. Perhaps they should kick the HS2 into the weeds, for the time being and get advisors who are real practical thinking engineers. They are scoring a lot of own goals with the present crop of advisors, who do not seem to be on the same planet as the rest of us, certainly from the fees they are paid, they must commute from other worlds!

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