Professor Roger Falconer FREng will talk about the Severn Barrage, Cardiff 12th Jan.

Professor Roger Falconer FREng, Halcrow Professor of Water Management, Cardiff University, Monday, 12th January 2009, 19:00 (Refreshments at 18:30)

University of Bristol, Merchant Venturers’ Building, Woodland Road, Bristol, BS8 1UB

The presentation will review the current main Severn Barrage proposals, as originally promoted by the Severn Tidal Power Group, together with giving a brief overview of alternative options such as the Shoots Barrage and Offshore Tidal Impoundments.

In particular, emphasis will focus on assessing the potential hydro-environmental impact of a barrage, including the implications for geomorphological and flood risk changes. An outline will also be given of recent research undertaken by the Hydro-environmental Research Centre at Cardiff University on bacterial-sediment interactions and the application of computational hydro-environmental models.

For further information please contact John Eley –

Comment – will be interesting to see if he goes into the reasons why the government has impeded Tidal Electric’s proposals, which could be fully funded by the private sector and ready to go, whereas all the various studies of the barrage (3 so far) has shown it has a hopeless economic case. Also interesting if he will discuss the factor of 8 (800% error) in the claimed recent cost calculations by Parsons Brinkerhoff for BERR- see an earlier news item.


  1. Reply

    Hi Dave,

    Not much to add, Dave. I have never met Professor Falconer, but have seen numerous statements attributed to him. He appears to be a barrage salesman. His comments about tidal lagoons have been a bit dim, to the effect that “they will silt up,” as though he were the only one aware of the sediment transport issues in the Severn Estuary. His “fatal flaw” type statements about the tidal lagoon’s siltation problem presupposes that we would build these enormous projects and then walk away from them, blithely abandoning maintenance responsibilities to nature.

    On the other side of the coin, when confronted with the sewage dispersal problem caused by the Severn Barrage, he glosses it, pretending that it does not exist. All of the upstream gravity-operated sewage outfalls will cease to function and what sewage does come down the Severn will be blocked from its usual out-migration to the ocean, making the Severn headpond the world’s smelliest body of water. Prof. Falconer is exactly the right person to be waving this red flag, but has chosen to deny it.

    Peter Ullman

    From: Dave
    Sent: Tuesday, December 30, 2008 10:35 AM

    To: Peter Ullman
    Subject: Severn Barrage talk

    Peter – a comment on the news item perhaps?



  2. Reply

    Dear Sirs

    Your website has been brought to my attention and I have just read the above. I would like to make three points.

    Firstly, Halcrow are not ‘in on the Barrage scheme’ and sponsorship of my post is based on our research activities in a range of fields, other than the barrage, and particularly river flooding.

    Secondly, and in particular, the statement made by Peter Ullman is grossly incorrect. So far as I can recall I have never – at least intentionally -been ‘confronted with the sewage dispersal problem caused by the Severn Barrage, (and) glossed it, pretending that it does not exist’. Our modelling studies of the Severn Estuary have included all of the riverine and sewage effluent inputs throughout the Severn Basin and as far as we are aware one would find it difficult to cite a more copmprehensive study of any estuary where more detailed simulations of sewage inputs have been included. Hence our assessment of the ‘sewage dispersal problem’ is extensive and we have not glossed over the topic.

    Thirdly, any confined coastal embayment with a narrow entrance and high incoming velocities is potentially prone to sedimentation associated with the well known phenomenon of tidal pumping. If this is a ‘fatal flaw’ then it would be appreciated if Mr Ullman could produce his technical calculations to show that he has fully investigated this potential problem and that the adverse pressure gradients will be too small to create undue sedimentation. If he is not prepared to produce the evidence to confirm that he has fully investigated a potential problem raised by myself – as well as others – the I would be grateful if he could refrain from misquoting me on your website.

    Thank you

  3. Reply

    Dear Dr. Falconer,
    I am not really sure whether you would consider this a suitable forum for discussion on the subject. However if you would be so kind as as to engage with me, and perhaps increase my understanding of the subject it would be appreciated. I wish to take part in the public consultation currently underway on the scope of the STP feasibility study, and would like to do so from as balanced a standpoint as possible.

    My understanding of the currently geomorphology of the estuary in regards to fine cohesive sediments is thus;
    They are presently in a state of dynamic equilibrium within the estuary, falling in and out of suspension in varying amounts depending on the lunar cycle, with up to 30MnT in suspension during springs falling to 4MnT during neaps. The major reservoir or sink for these particles is Brigwater bay which has overall estimated budget of between 300 and 1000MnT. Extra input through fluvial sediment to the system is relatively low at about 1MnT per year.

    The potential problem that you have appeared to have addressed is of course the disturbance to this dynamic equilibrium that a tidal barrage would create. The tidal pumping you refer to is the net upstream movement of particles leading to sedimentation upstream of a proposed barrage.
    Where my understanding fails me and you hint of why with reference to ‘adverse pressure gradients’in your response to Mr Ullman is why this suspended matter will not now accrete in the new, lower energy, deeper water, environment upstream of a barrage? It is generally accepted that increased water clarity will result upstream of a barrage so where will that silt accrete? Surely it will not all end up back in Brigwater Bay?
    Please assist me directly in my understanding of these processes as I cannot find detailed explainations against this hypothesis within the topic papers or elsewhere.

    Many thanks and kind regards,
    David Butterton.

  4. Reply

    First, let me apologize to Dr. Falconer for the tone of my email above. I had not quite expected it to appear as a posted message and I do value decorum in these settings. That said, let us continue to engage on the issues.

    As I mentioned, I have never met nor heard Dr. Falconer speak, but I get many reports from the legions of (offshore) tidal lagoon supporters and have received perhaps 10-20 messages from those who have listened to Dr. Falconer speak about the barrage. Their reports have consistently said that Dr. Falconer is selling the barrage and says tidal laoons will silt up. Hence my statement was second-hand and should be qualified as such.

    Dr. Falconer claims to have carefully studied the sewage dispersal problem for the barrage. Mea culpa. I am wrong to repeat the second-hand reports that he dismisses it. But then the learned water quality expert ends his comments. Perhaps he might comment on sewage dispersal and how sewage would make its way to the sea post-barrage, the fate of water quality with millions of tons of sewage blocked from out-migration, how gravity-operated sewage outfalls would be re-built to operate in a post-barrage environment, and the cost to new solutions to sewage dispersal. This is exactly the kind of issue one woud expect him to explicate. Please do.

    Lastly on siltation. We all know the Severn is quite silty. One glance on Google Earth tells the story. The tidal lagoon operates in both directions. In and out. The openings through which water flows are exactly the same, in and out, out and in. The pressures vary from tide to tide, from moment to moment, but they are equivalent over time, in and out. Yes, Dr. Falconer, silt will enter the lagoon, but silt will also exit the lagoon in roughly equal amounts over time. In and out. The question is whether significant amounts of silt will drop out of suspension while inside the lagoon causing extreme sedmentation. It is the preliminary opinion of our consultants (ABPmer and Yale School of Geology and Geophysics) that the short period of time (6 hours 12.5 minutes) between peaks and the turbidity of the water will allow for virtually no sediment to drop out of suspension. Given that sediment drops out of suspension in inverse proportion to depth, the interior walls are designed with maximum slope to minimise sedimentation. But supposing that all these opinions are incorrect and countermeasures are ineffective and extreme sedimentation does occur, it will simply be dredged, like every port on the Severn is dredged on a monthly basis. The bi-directional nature of the tidal lagoon is quite different from the uni-directional nature of the barrage which the gentlemanly David Butterton points out. Clearly the barrage will have a siltation problem which requires Dr. Falconer’s attention.

    BTW Halcrow produced a report in about 2004 on the coastal erosion problem in Bridgewater Bay with the concluding recommendation being to place an offshore tidal lagoon in front of the vulnerable coastline. Funded by Regen SW and DTI,with the participation of ABPmer, AEA Technology and others, this was quickly buried. Care to comment, Dr. Faconer? Why did Halcrow perform a study which made a tidal lagoon recommendation, not release the publicly-funded report to the public, and then switch to selling the Severn Barrage? Curious. I have a copy of the report if you (or anyone else) would care to see it to refresh your memory.

    Peter Ullman

  5. Reply

    With regard to the post by Peter Ullman on Feb 1. He states that the pressures are….” but they are equivalent over time, in and out.” I am a bit of a novice here so please excuse my ignorance. However, as the tide comes in it is flowing into a constriction (the estuary) so that should increase flow velocity. As it ebbs it is flowing out of a constriction and that should decrease the velocity. I would have expected there to be a flood dominated current regime as a result. I do not know this mind you. I am just politely asking so that someone could correct me.

  6. Reply

    Quite right Peter, that constriction in the estuary leads to tidal asymetry so that the flood tide further up the estuary (at Sharpness for example) only lasts for three hours in a single cycle. As you expected this does lead to higher current velocities on the flood tide.
    Further down the estuary at the site of the proposed Brean Down/Lavernock Point barrage this effect is not as pronounced.
    However, as Dr. Falconer has failed to respond to my concerns I remain unconvinced that shifting a load of sediment from a high tidal-range/current velocity environment into an artificially low tidal-range/current velocity and significantly deeper inpoundment area, such as that that a barrage would create, will not lead to huge amounts of deposition in that impoundment area.
    With regards to lagoons I would imagine that similar problems could exist if the tidal regimes within are significantly different to those outside of the impounded area. If the water levels within the impoundments are similar to those naturally occuring but simply shifted in time then siltation may not be an issue.

  7. Reply

    One of my main considerations in putting forward the Severn Tidal ‘Reef’ is firstly to reduce the ‘stagnation period’ from around five hours to less than two hours (reducing the sedimentation) and secondly the ‘Reef’ is downstream and outside the the ‘envelope’ within which most of the sediment migrates back and forth with each tide, rather than it passing through the turbines and causing wear. It is my feeling that the less one has to modify the natural cycle, the fewer problems one is likley to encounter.

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