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The Severn tidal barrage – better alternatives

By Dave Elliott

The report on the Severn tidal barrage from the Select Committee on Energy and Climate Change concluded that the proposal for a £25bn privately funded barrage from Hafren Power was not convincing and lacked detail. Hafren Power had “failed to overcome the serious environmental concerns that have been raised” and had “failed to reassure the ports industry that its business would continue to be viable with a barrage in place”. It went on, “while a tidal barrage could offer decarbonisation and energy security benefits, the Hafren Power project in its current form has not demonstrated sufficient value as a low-carbon energy source to override regional and environmental concerns. Alternative pathways exist to meeting our 2050 carbon targets.” It added that “alternative options for exploiting Severn tidal resources also exist” and it looked at some of them briefly, including the 250–350 MW Swansea Lagoon proposal, the 600 MW “Stepping Stones” Lagoon put forward by Parsons Brinckerhoff/Black & Veatch, and also Rupert Armstrong’s 6 GW Tidal Reef concept.

The committee felt that “a more incremental approach using alternative technologies (such as tidal lagoons) may have the potential to provide a lower-risk, lower-impact option than the Hafren Power barrage scheme”, although they added “whether these alternatives offer better value for money is far from clear at this stage”. An incremental “step by step” approach would reduce the risks associated with going for a large barrage and allow for gradual learning. So, they recommend that “consideration is given to first developing a smaller scale tidal project, in order to build a stronger evidence base for assessing impacts, risks and costs before proceeding with any larger scale scheme”.

That is pretty much what consultants Black & Veatch and Parsons Brinckerhoff had told them in their evidence. Similarly, the Renewable Energy Association had expressed concerns about the “financial and environmental risks” of a large-scale barrage and advocated building a small barrage to begin with, “to assess the costs and monitor the environmental impact”.

The committee noted that the Regen SW and South West Marine Energy Park discussion paper, “Bristol Channel Energy – A Balanced Technology Approach”, had claimed that a combination of tidal, wave and wind technologies could provide up to 14 GW of low-carbon electricity, obviating the need for a “single mega-project which has major economic and environmental and impacts”. The paper also suggested that the focus on a single, “potentially divisive” barrage project is damaging for the marine industry and instead recommends “a more inclusive discussion”.

The alternative options certainly did look worth exploring. Tidal-resource modelling by the Energy Technologies Institute suggested that “the energy yield from a single large-scale Severn barrage could be achieved with a lower level of interaction and impacts through a combination of tidal energy extraction at a number of smaller, different sites”. By contrast, Engineering the Future told them that, with a single barrage, “the timing of energy production would vary with the tides and the amount of power generated would vary significantly between spring and neap tides. Even though there are engineering possibilities to hold back and control water flow through impoundments, there would be some days every month when electricity was produced at times when ordinarily demand would be very low.”

On the economic case for the large barrage, the committee felt that “attracting very large sums of money from long-term investors may prove challenging” and that, with DECC estimating levelised costs at £214–£353/MWh, the CfD strike price for the barrage “would have to be considerably higher than the £100 MWh which Hafren Power have ‘in mind’. Furthermore, the company says it would require this price to be guaranteed for 30 years, twice as long as an offshore wind project. […] As a minimum, the strike price for barrage-generated electricity should not be higher than that for offshore wind, which is expected to be around £100 MWh by 2020 […] If a higher strike price was offered, it would risk swamping the Levy Control Framework to the detriment of other low-carbon technologies.”

The committee also noted that the environmental impacts of the current Hafren barrage plan were “very considerable and that there is a high risk of unintended and possibly damaging consequences”. For example, Hafren Power proposed to use a Very-Low-Head (VLH) turbine design deploying two sets of contra-rotating blades. Generation would be bi-directional on both the ebb and flood tides. The committee noted that the Environment Agency had claims that it was “not aware of any turbine designs which would allow the safe, repeated passage of fish through a barrage at the scale proposed”.

It noted Proferssor Falconer’s estimates were that the scheme “would reduce tidal range in the Severn from its current range of 0 m to 14 m to one of 3 m to 12 m. Low tide would therefore be raised by 3 m, and high tide would be reduced by 2 m. The overall reduction in tidal range would lead to a reduction in intertidal habitats of salt marsh and mudflats, with a resultant impact on bird populations dependent on these areas for feeding grounds.”

The RSPB had suggested a barrage would have “significant adverse effects on the populations of 30 species” with potential “serious effects on a total of 96 European protected sites for birds”. The Countryside Council for Wales said that “Decreased flows and flow speeds incurred by a barrage would reduce the suspended sediment concentration within the impounded area and downstream leading to further changes in the estuary extent and composition of intertidal and subtidal habitat features of the Severn Estuary.”

While Hafren Power cited the La Rance scheme as evidence of the potential for improved biodiversity with a barrage in place, the committee was also told that La Rance was not an appropriate comparator for the Severn “since it is ‘a rocky river valley’ unlike the sediment-rich Severn estuary”. Problems experienced at the Annapolis Royal site in the Bay of Fundy had include “fish mortality, erosion problems downstream and the health of the river upstream”. It was reported that tidal causeways across tributaries there had led to “rapid, unpredictable consequences and no foreseeable return to a state of dynamic equilibrium”. The RSPB pointed to experience in the Eastern Scheldt, where a storm surge barrier was built in the 1980s; the estuary still shows “absolutely no sign of reaching a new equilibrium”.

By contrast the committee noted that with lagoons the environmental impact was thought to be less since they would not affect tides and water flow to the same extent and would not obstruct downstream and upstream migration of fish. In addition, “Land-connected lagoons are located away from navigation channels, and therefore are unlikely to impact on the operations of Severnside ports. A lagoon design would be unlikely to impede the development of other marine technologies in the region.” They noted that the Regen SW and SW Marine Energy Park discussion paper suggested that a fixed barrage would “impact on downstream flow and hence tidal stream generation potential”.

Hafren were clearly not happy and the door is still open for it to come back with an improved proposal, but overall it doesn’t sound very promising or likely. Energy Secretary Ed Davey told the Lib Dem conference in Cardiff earlier this year that the government was “looking for private-sector consortium to come with different projects in the Severn”, but on the Hafren project he commented “I think it’s fair to say their numbers aren’t in the place that they would need to be and there are some questions I know people have of that proposals yet to be fully answered.” By contrast, he said that there had been a “huge amount of work” done independently on “alternatives to a straight barrage, with lagoons and a more displaced, dispersed approach to getting that powerful tide and I think there are some real attractions to that. I am hoping that maybe if people can work through those economics, work through the ecological aspects which are critical, they can present government with proposals that are affordable and attractive.” See,

Select Committee report:

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