To be fair, I think that many people from all apparent sides of the debate have the same motivations, but maybe take a different view on how exactly to protect the environment.

If you have been following the consultation process closely…and reading the small print of the govt’s statements.. you might have noticed that there were, prior to the public consultation stage, 79 principles to be met by any succesful scheme. The govt, as a result of that last stage of consultation, added an 80th condition. That states that the Severn Bore must not be significantly affected.

Whilst that might seem only to be good news for bore surfers and sightseers, it’s actually a lot more than that. The research of Dr Hubert Chanson makes it pretty clear that highly silt-loaded estuaries with tidal bores have a natural system of silt management, and that is the tidal bore itself. This research was put before the inquiry by a friend of mine, Dave Butterton, who secured extensive help from Dr Chanson with his submission.

It seems to me that academics from around the world are queueing up to make their opposition clear to the current proposals. Somehow it seems that British engineers and academics are of the opinion that they know more than the rest of the world, including those who have actually attempted tidal power generation.

Hypertidal estuaries such as the Severn, and tidal bores in particular, are potentially very dangerous things.My opinion is that we’re playing with fire, and the people holding the matches are children.

Neil

I believe we are close to finding a way to capture the energy of river tides without mass destruction of its function and ecology, through the use of modular tidal stream turbines which I fully support.

I agree that there is no tidal bore in the Bristol Channel. From what I can glean, it seems to show it’s first signs around Beachley.

However, you are factually incorrect about the siting of the shortlisted proposals. The Shoots Barrage is also pretty much adjacent to the second crossing, just downstream of Beachley. In my view it is the proposal likely to be the most short-lived, as the silt load is just about at it’s highest at the same point.

I note that there is a proposal for a feasibility study into another barrage on the Loughor estuary, just north of the Gower peninsula.

But (to my mind) more positive news comes from Morecambe bay, where there is now a plan to trial one of the newer designs of tidal stream turbine, which seems to be under consideration instead of the (previously considered) barrage.

Neil

BUT as a ‘green leader’ it would be great to have you supporting the tidal stream option, rather than what is in effect a dam on one of Britain’s finest ecosystems – something the UK has condemed in its World Commission on Dams. Damaging dams are now being built across Europe in the name of climate change.

Why rob Peter to pay Paul when there’s a less harmful alternative.

Alexander

The current proposals for a barrage for a location across the Bristol Channel, and not the River Severn. The dividing line between the River and the Channel is at Avonmouth. All the current proposals are planned to be well downstream of Avonmouth.

There is no tidal bore in the Bristol Channel, but simply a very strong incoming and outgoing tide. The tidal range in the area proposed for the barrage, (either off Weston-s-Mare, or linking the islands of Steep Holm and Flat Holm), is about 10 metres, which is the second highest in the world. The tidal curve published in the Nautical Almanac, and based on the UKHO survey, is almost a perfectly symmetrical sine wave. It can also be see from the tidal diamonds on the marine chart, that the tidal flows are fairly equal in intensity on the flood and ebb. There is only a very small period of slack water (about 20 minutes) between strong tidal flows of over 5kn.

Many of the strong opponents to a barrage in this debate would seem to be using incorrect figures, perhaps based on previous proposals for a barrage across the River Severn, rather than the Bristol Channel. That they are presenting manifestly information about the tides in the Bristol Channel, and have not even bothered to check readily available tidal information on the local Charts and Almanacs, makes me very dubious of their authority.

Even the Sustainable development committee’s Turning the Tide report accepts that barrages start , on completion of construction, at their best level of efficiency , and this reduces from that point onwards to the point where they are no longer viable. We might argue over how long the lifespan is, but the principle essentially remains. They are therefore inherently NOT a renewable source of energy.

Secondly, if you place a barrage across an estuary, that’s it. You can’t feasibly backtrack and decide to do something else instead, because the presence of the structure prevents you from doing so. With tidal stream technology on the other hand, you can.

Individual turbines can be placed, added to with more arrays of turbines, taken out of service for maintenance or when a better version becomes available to increase efficiency etc.

I hear what your saying, but don’t believe the barrage could offset the mountain that would have to be torn down & transported to the estuary, not to mention that Cement is one of the largest CO2 producers in the world & there would be many tons of this. The last info I read on cement CO2 output, indicated that an average 3 bed house build puts out 25-30years worth of car use CO2 just from the cement curing, so I’ve no idea what a commercial concrete structure produces, but it will be of many times greater magnitude.

If you have ever been to sea, or used the coastal waters, you will know that the Tide waits for no man. As far as wave energy is concerned, its a bit hopeless like wind (but good in that it offsets fossil fuel when its working), very variable in output & requires a large over scaling & dispersed installation to avoid the short comings of periods of light to no wind conditions. I’m sure you are aware, no wind = no waves, so two NON producing renewable’s at the same time! OK wave has a lag behind wind, but its NOT consistent, nor predictable, as in guaranteed!

Tidal turbines for high flow areas were mentioned & linked by another poster, but like offshore wind that kind of structure is both offensive visually (not to me, I like electricity) & obstructive to navigation & thus likely to be involved in accidents. I have a couple of design ideas for high torque systems, designed for low tidal flow areas, thus maximising the tidal potential. These are self contained completely submerged, self cleaning systems that could be tuned to work almost anywhere there is a tidal flow, which is practically everywhere around the UK coast. A 3knot+ current would be sufficient to generate consistent predictable guaranteed power !

The Severn estuary alone could produce more energy than any barrage system using this technology & it would produce a base load 24×7 obviously with peak periods during maximum tidal flow, regardless of direction & NO siltation problems. In fact areas of obstruction produce localised increases in tidal streams, so rather than a hindrance, they are a potential benefit !

If you have ever done any navigation, you will appreciate the fact that the tide NEVER stops (slack) everywhere at the same time & can often be running in opposite directions within very short distances. These turbine systems would be more expensive than wind, but with 100% guaranteed power delivery 24×7, its a no brainer.
I’m fairly certain the cost would be less than the expected outlay on both Nuclear & the Barrage & would produce 100% of the UK’s electricity requirements & as the power would be generated all around the UK, long haul transmission losses would be avoided to boot, saving approx 15% of the energy currently generated, but lost in transmission.

Just go visit Skomer Island & witness the tide running through the sound between it and the mainland, tidal speed of up to 8 knots, and a visible head of water of 6-8ft difference between the up & downstream sides. Similar streams can be witnessed under the new Severn crossing, where the stream reaches 5-7knots. You could place one of these turbines between each of the bridge legs, where the bridge acts as an obstruction increasing the flow !

Submerged turbines designed to last, tick all the boxes, no visual drawbacks, can be placed almost everywhere around the coast with no danger to general shipping, other than that trawlers can’t operate in the immediate vicinity, but that just makes the turbine areas marine reserves in effect, which is great for sea life. And they give guaranteed power delivery, which no other distributed renewable source can claim, conventional hydro does not count, as its concentrated & pretty much maxed out in the UK.

Just a couple of thoughts. Unfortunately I don’t have the means to build, test or assess these systems, but hope to find a company that can.

Regards

Chris W.

The next 10 years is critical to curbing climate change which could make <60% of species extinct! So even if it were a bridging step (excuse the pun) it would be worth building the barriage for 100 years providing the carbon impact of building it was significantly less than the CO2 saved.( Ia ctually believe that with correct flow control, the siltation issues is managable and the life of athe barriage would be much longer).

Any substantiation of coastal potential tidal power and devices to harness it which you mention would be appreciated

If you are goinf to sea, then I thought that wave power with floating devices was better 12.5% of our current UK electricity demand could be provided that way.. probably easier than coastal tidal but I await to hear from you about that.

regards
Adrian

Go tidal & forget barrages, they consume vaste amounts of energy to build & the Severn will silt it up very quickly once the flow is killed off, not to mention that barrages only produce power for limited periods during the day & those periods vary with the tides ! So nothing about a barrage is sustainable or predictable.

Chris W.

There are many points that I could bring up but perhaps one from the building of Avonmouth Docks will make a good point. The piers at Avonmouth docks were designed by computer, redesigned by computer as they were being constructed so to prevent the silting up of the docks. Within months of the docks opening a contractor was employed to remove silt.

There are so many other things that can be done apart from building a wall across the estuary to produce power that are a great deal more benign that the barrage is crazy.

Dale you do some great work and have some very good ideas but this one is crazy!

Simon, Tidal barrages which have gone wrong, and almost all of them do, are a CAUSE of flooding. The evidence is there if you want to look for it. Start in the Minas basin and Bay of Fundy, and you will find it for yourself.

To link generation of less than 5% of UK electricity consumption with elimination of Fuel Poverty is disingenuous. Fuel Poverty is a major issue, but is almost entirely due to the abysmal quality of our national housing stock and the appalling quality of the heating systems fitted to many of them. To fix this would be neither cheap nor easy, but it would be a very effective way to invest government money, because the energy savings would last for years, and free up sustainable energy production for other essential uses (for those who doubt the effect of energy efficiency work – we replaced a 20 year old boiler and controller with a new one, and saved 60% on our gas bill straight off, despite heating the house all day).

Siltation is only one of the issues that a barrage has to address. Equally important is the vast energy cost of the concrete and other materials needed to construct such a barrage. Studies have suggested that the carbon cost of making the cement needed may well exceed the emissions from generating the whole of the barrage’s electricity (over it’s predicted life) from fossil fuels directly (no-one has yet managed to make cement economically without carbon fuels of some sort). As the recent Mersey Estuary study (http://www.merseytidalpower.co.uk/) showed, there are many possible technologies for extracting energy from the tides, and barrages are really outdated technology with big problems.

Finally, plans already exist (and have funding) for marine current turbines in the Skerries tide-race near Anglesey (http://www.marineturbines.com/18/projects/20/the_skerries/). This is currently a small scheme, but there is massive further potential to generate power from tidal flows around the UK.

Your proposal intrigues me,I have to say. I managed to get an understanding of silt transportation issues only with the help of Dr Daborn,but that was in reference to barrages. I must admit I haven’t the faintest idea how the reef would work in this respect. Have you taken any account of the Moncton scenario? Or do you have any reason for believing that sedimentation will not be a problem?

I get the general idea that the reef extracts less energy from more water,but will this mean that there will be specific areas which are more likely to show a significant amount of deposition?

Regards,and happy new year

Neil

Direct the Professor to the link I provided above on Dr Daborn’s conclusions. He suggests that the critical error is that in these situations, engineers tend to disregard the impact of particle size and biological factors.

When someone can show me why we won’t have another Moncton here, I’ll be a lot closer..not quite all the way, but a lot closer to believing that a barrage is a good option.

Seagen is looking good,and could be used right now from the available evidence.

Have a great christmas.

Neil

I take your point that it could put people off if it failed (note thought that R & D usually follows a path of a few failures before success).

What is odd though is that you continue to only represent the side which objects to the Severn barriage. If you are right and there is no technical solution I’ll be right behind you but you have not demonstrated to me that you have looked around for solutions to the siltation.
That could also potentially be irresponsible – what if there were really a solution you were unaware of and yet you played a part in preventing it by putting people off?

Let just a agree that we both want that tidal power to be harnessed in an effective way and if I get time to research what solutions to siltation there are which go beyond previous experiences/models then I’ll post these up later.

Adrian

When I gained the opinions that I went looking for, I put them into a submission to the Severn SEA. Unfortunately, not being an academic myself, and having only a couple of weeks to do what should have taken 6 months, my submission was full of typos, and didn’t cover half the topics I wanted to include.

However, the info from Prof Haslett and Dr Daborn was good quality, so I passed it on to Stuart Ballard of Saveoursevern.org, as he seemed better at getting information out there than I am.

He was already posting information about Moncton on his website, but this quotes Dr Daborn’s report to a proposed project in Australia, which he believes is similar to the Severn, with the exception that what is said about mangrove is pretty much transferrable to areas of saltmarsh.
http://saveoursevern.org/dr-graham-daborns-report-on-silting/
With respect Adi, as you say, you haven’t had time to follow all the developments. That is an approach which I characterise as irresponsible,as you are a strong advocate for a barrage without having (apparently) scratched below the surface.
I don’t know Dale’s approach, but if it is similar to your own, then I say again, it was highly irresponsible to go into print without doing the background work. You seem to be trying to make a round peg fit a square hole..the evidence is right there…barrages don’t as a rule, work.

My biggest fear is that we take this huge risk and build something enormous which goes belly up, then Joe public says “stuff renewables..huge cost…didn’t work…lets go nuclear” etc.

But on the other hand, I welcome the chance to exchange views with anyone who is as passionate about renewables as you seem to be. I’m right with you on that.

Cheers

Neil

Merry Christmas anyhow

Adi

I’m by no means suggesting we do nothing, or build nothing. Tidal stream turbines can now be used in the Severn estuary, so why did the govt rule that option out?

Maybe because the engineering interests on the SDC have no investment in it..call me cynical, but how closely have you been monitoring their activities? There are some things I have been made aware of which I wouldn’t post anywhere, because I can’t afford lawyers. But here’s something to ponder: The Shoots barrage was originally backed by Parsons-Brinckerhoff. The technical specs for report no 3 within ” Turning the Tide” was carried out by Black and Veatch, a member of the Parsons-Brinckerhoff group. Parsons-Brinckerhoff were then awarded the contract to run the feasibility study for the govt..

Come on guys. You don’t have to be a crazy conspiracy theorist to think it’s worthwhile asking a few difficult questions here. The process is meant to be transparent, right? All of the “technical experts” on barrages who contributed to the SDC document that I’m aware of.. and I’m not claiming to have checked them ALL out, are people who seem to have a (possible..alleged) vested interest in building a barrage.

So start building your knowledge again, if that’s where it comes from. Why are the canadians, the most experienced people in the world with tidal range…why are they no longer considering most of these sorts of scheme? Look for a few people with no axe to grind. If we screw this up, we could be killing the estuary, and that is only the beginning of it. We are messing with tidal flows. Where are the modelswhich show how they will be altered? Where, given that a large proportion of the tide will “bounce ” off the structure, where will that water go? Where will have an enhanced tide? Are those areas prepared for seaborne flood events? Are they prepared for heavy duty coastal erosion?

Adi, did you mean the Thames barrier? I’m not sure that’s relevant. The problem with the Severn does not exist on all rivers. It has an extreme silt load, and sources of new silt material available in abundance on both sides of any potential structure. It is dissimilar to the Thames in that respect, and that is critical.

Power generation on an inflowing tide is possible, but not efficient. It reduces the amount of water that will enter the embayment, and it acts under lower pressure, or at least, the operators would have to wait until nearer high tide so that there is a decent head of water outside the barrage to load the pressure on, but there is a strong element of “diminishing returns” here. On the other hand, it would extend the effective generating period.This is covered in research report 3 of the SDC report, and I don’t have any evidence to contradict their findings.

You cannot ignore those fluctuations in the tidal patterns, they too form part of the equation. For example, I believe the biggest tide of the last year about a metre at Sharpness smaller than that of the previous year (not sure about that, but I think it’s in the ball-park). Now going back to my previous post about water levels, that actually represents a massive reduction in power generation potential.And those spring tides only occur for a couple of days every two weeks. Today, the tidal range was only 6 metres at Sharpness, and about 7 metres at Bristol. As a silt alleviation method, I believe it is proposed that the turbines be set a little higher up the barrage wall. I don’t know how high, but let’s say a modest 2 metres. Then factor in that Prof Roger Falconer, who seems very much pro-barrage, says that a barrage will reduce the tidal range to some extent.. I don’t know his figures, but I think you can see where I’m going with it…how much tide will actually be generating power, even on a big spring tide?

Why did this proposal even get this far?

There are other options which are available now, today. Why are we not looking at them the way we’ve been looking/wasting time on tidal range?

Tidal fence? No. Good idea, but almost as bad for siltation as a barrage. Go to Sharpness on one of the days when they have to clear their breakwater (which is effectively a fence) of silt. See it for yourself.

Tidal stream turbines: many won’t work in most of the Severn estuary because it is too shallow for them, but there are designs that will, and that can be placed in numerous locations. Lower maintenance, less environmental damage,no obstruction to shipping (thus removing the fairly powerful anti-barrage lobby of the Bristol Port Company)..what’s wrong with that?

The tidal reef structure is one I find fascinating. In theory, it seems to be sound thinking. It operates on a low head of water, so the natural flows are less obstructed. For the most part it’s under the water, so there’ll be less nimbyism on the score of ruining anyone’s view. I don’t know if it will cause a siltation problem, but as the stated aim is to extract less energy from more water over a longer period, I would imagine that silt WOULD be an issue, but on a much reduced scale.

One last point. If/when the gulf stream stops, and we get a tad chilly over here, silt will be much less of a problem. It will still occur, but the flocculation process which makes it such a problem will be interrupted, as those organisms won’t beable to have the same effect on the mud at greatly reduced temperatures. It isn’t a problem where ice, or glacial melt-waters are prevalent.

Personally, Strangford Lough is where we should be looking for inspiration.

Tidal stream turbines are the way forward, barring any new advances in tidal range technology.

Neil, most of your concerns don’t worry me except the build up of silt OUTSIDE – the inside build up is managable in my opinion. How about asking the engineering company that originally proposed the barrier in the 80’s about the build up of silt fronm the outside? They did numerous studies. (I’ll try and dig out the contact I spoke to who was still there 3 years ago). Also what is the power potential of inflow turbine systems (or other alternative tidal harnessing like lagoons)? If it isn’t a great deal less- fine, but I suspect it is massively less.

As an ecologlost I find that we are our own worst enemy particularly on renewables. In the name of environment people complain about wind turbines.. in Iceland a huge dam project I visited a few years back – which could have saved vast amounts of carbon going into the air was fought by environmentalists. Biofuel, the most flexible and storable of all renewables has been thrown out by many environmentalists because they fail to be able to differentiate between that which is sustainably sourced and that which isn’t.
And so on..

Neil another point: If the gulf stream stops as soon as it is feared it could, you wont have any of the long term tide cycles to worry about! Even if the barriage is built the gulf stream is likely to stop anyhow – potentially rendering those concerns void.

Dale, could someone find out why the interested engineering companies seem to think the silt build up Outside isn’t a problem?

Tidal and Biomass and Wind and Solar and Wave must all play parts in the package of solutions for the future. Tidal has got to be easier than an equivalent amount of capacity from wave power (which could power 12.5% of current UK demand whilst tidal could power 15%).

Adi

The basics about tidal circulation around the Atlantic Basin is well set out , though,and I wish I had learned by reading that section , rather than the soporific stuff i was presented with.

In the case of tidal range, it is very important to recognise the importance of apparently subtle variations in long term tide cycles. There are several of these, each with their own characteristics, such as the Nodal and Saros cycles, both of which are in the region of 18 years long. Overall they give rise to variations in max spring tide height for a given year of only 3 or 4%, but there have been some very relevant findings about relative fish stocks varying in number along with those cycles in the Minas basin, and a relatively small variation in tide height can give a disproportionately large variation in available energy… for an example of this, look up the max tide heights at Avonmouth over a 25 year period on the website of Proudman’s Oceanographic research.. look at the heights for this year, and compare not only with the height for 2015, but also for how many really big tides there will be.

Extra height of tide equals extra water captured in a tidal range facility. Given the likely shape of the bed ..a flattened “V” shape,,the profile of the Severn estuary in all dimensions, a higher tide of ,lets say, only a foot more water means a massive increase in potential energy stored, because the area in which it is stored gets wider, the higher the tide is. But equally, tides such as we have had this year, at the bottom of a cycle, will produce a great deal less energy for the same reason.

So much as it would be good to simplify tidal energy, when you do so, you sacrifice truth to simplicty, and that isn’t helpful.

Then there is the question of siltation… why is it not mentioned? It isn’t a constant, and it has killed several barrage schemes.Again, over simplifying has removed truth.

Tidal stream. I didn’t notice any mention of the turbine off Lynmouth. Did I just miss it?

Overall, I like the style, but the content is poor, and that saddens me. This is the kind of misinformation that has got us to the place where people think it’s a great idea to commit an act of monumental vandalism in the name of protecting the planet in some way.

David J.C. MacKay. “Sustainable Energy – without the hot air”. UIT Cambridge, 2008. ISBN 978-0-9544529-3-3. Available free online from http://www.withouthotair.com.

I have just read Chapter 14, “Tide”, which has a good coverage of tidal power including barrages. This includes two Severn barrage proposals, one at Weston-super-Mare and the other further down the estuary.

All of the reasoning is backed by calculation. Not a particularly easy read but well worth the effort.

Definitely a positive step in “cutting UK emissions of twaddle – twaddle about sustainable energy”.

“Tidal turbine breaks energy record for generating renewable electricity.”

http://environment.uk.msn.com/news/headlines/article.aspx?cp-documentid=12025662

I agree with Neil: you’re making a mistake. Huge engineering projects are tempting because they appear to offer an economy of scale at a time when a very rapid level of change is needed; however, I can’t think of a single example where the costs predicted have been realistic in even the short term… and I have seen and commented on hundreds of schemes, both energy-related and otherwise, as an ecologist, over the last 20 years. Messing around with the most powerful river in the country, with huge tidal ranges, huge and variable silt loading, fishing and navigation issues, and a vast area of internationally-protected ecosystem, is not justifiable. Especially given the uncertainty over the success of such a scheme.

I am also very worried about the lack of concern for the ecology here. To state baldly that “the only losers are the Big Six” is quite extraordinary, because the environmental damage would be colossal, even without considering the enormous amount of aggregates that would be required for the project. Don’t ever forget that the damage caused on the ground is a fraction of the impact of big engineering projects. All that stuff has to come from somewhere: gravel and sand extraction, Portland cement, imported structural materials… lots of carbon involved there, and lots of towns and villages with trucks going through day after day, week after week. Is Dale suggesting that every reputable conservation body is either mistaken or not worth considering? Given the fuss that we would likely be making if a foreign government proposed something so damaging to a large area of protected ecosystem, I find this amazing.

Please don’t fall for the promise of ecological mitigation! Even when it works as predicted (rarely) and when money remains to carry it out (almost never – it’s always the first thing to be squeezed out when costs rise) it can’t replace an established habitat on such a scale.

Saying that the system would be damaged by climate change in any case is an argument for *not* doing anything which would stress the environment to this degree… estuarine systems are very good at adapting to everything except confinement. They need to be left unimpeded. Note also that flooding from strictly tidal sources (like the “tsunami” of 1606) is not normally such a problem for the county as “filling up”, i.e. caused by rainfall. Flash flooding is *not* improved by any form of barrage; it doesn’t come from offshore and might even be made worse by impeding the flow out of the estuary.

The above comments seem fairly obvious to me, and I don’t think I’m alone in that respect. We mustn’t let our strong desire for a solution to the problem of unsustainable electricity production corner us into supporting yet another huge, unpredictable scheme with many hidden costs – and ecological damage which would be prohibitively expensive, or impossible, to remedy.