Sitting on the Tidal fence – Severn Estuary


With targets to reach 15% of the UKs energy supplied by renewable energy by 2020 and legislation committing to reducing greenhouse gases by 80% by 2050 the UK government is under increasing pressure to promote renewable energy[1].  The initial plans for a tidal barrage stretching the whole length of the Servern estuary were dropped due to the damaging effects to both the economy and the environment1.  Following this, three projects deemed to be less environmentally damaging were given funding of £500,000 by DECC  (the UK goverment’s, Department of Energy and Climate Change) through the Severn embryonic technologies scheme (SETS) in order to investigate them as potential alternatives to a tidal barrage1. One of these was the tidal fence consortium involving a two part fence allowing shipping and fish migration to continue, whilst proving to cause little environmental damage to the surrounding ecosystem. The DECC suggests private sector funding to the project as they decided to withdraw further funding of the tidal fence due to the feasibility study conducted in October 2010 concluding the tidal fence to be unable to produce sufficient electricity to make the project cost effective1. This report aims to investigate the tidal fence alternative in more detail in order to provide the DECC with a fuller picture of the options available to effectively manage and harness tidal power as a natural resource in the Severn estuary.

Tidal fence background

The tidal fence could provide a predictable, long term, renewable energy source that could produce up to 5% of the UKs output1.  It would help towards meeting the UKs renewable energy and greenhouse gas targets, whilst showing a proactive approach to climate change and energy security[2]. The innovative technology proposed within the tidal fence could be a blueprint for tidal power, providing incentives for tidal fence schemes all over the UK and the world.  The Severn estuary has the third largest tidal ranges in the world and so would be an ideal location for a tidal fence1. A tidal fence on the Severn Estuary, if constructed would be able to provide energy for around 8 hours per tidal cycle, this would be a predictable and reliable energy output4.

The tidal fence will allow shipping to Cardiff and Bristol via a 650km gap in the fence[3], this will be continuously accessible at all stages of the tide4. The construction, operation and maintenance of the tidal fence will provide 8,000 direct jobs to the South West and Wales and 1300 indirect jobs, boosting the local economy3.

Gaps above and below the tidal fence and the slow rotation of the turbines will reduce disruption to fish migration and stress[4]. Due to the porous nature of the fence the tidal characteristics of the Severn estuary will not be affected and so the mudflats will remain intact maintaining the habitat for intertidal migratory birds4. The tidal fence is seen as a less environmentally damaging alternative to the tidal barrage; however it will have some effect on the environment. The noise in particular could cause problems for wading birds during the construction period4.  The Severn Estuary has a large number of designations to protect its wildlife and their habitats (SSSI, Ramsar, SPA and SCI)4 these will need to be taken into consideration and carefully worked around.

Since the renewable obligation review in 20th October 2011, tidal power will now receive five ROCs (renewable obligation certificate) per megawatt hour of eligible renewable energy output, rather than the previous two. This provides a greater incentive for further investment and is currently the main support mechanism available for renewable energy projects such as the Severn estuary tidal fence[5]

A tidal fence on the Severn estuary would show a compromise between a full tidal barrage and the current situation of no tidal power at all. It would balance environmental, economic and social factors in order to effectively manage tidal power as a natural resource.


The DECC stopped funding to the Severn tidal fence consortium after the initial £500,000, the reasons for this were based on the conservative figure of annual electricity output of 0.88Twh which was deemed to be insufficient in providing enough electricity for the project to be cost effective. In conversation with Ian Godfrey  the Senior Engineer at ITPower  (ITpower leads the Severn tidal fence consortium) it was stated that the tidal fence could in fact reach an annual energy output of 3.4twh, this would significantly increase the energy cost annually that the tidal fence could provide and so changing the cost efficiency of the project7. A simple cost benefit analysis undertaken shows that with the revised output the discounted payback time could be cut from the orginal 16-17 years to only 3-4 years. This result indicates that the DECCs basis for halting public sector funding to the project may have been hasty and a review of the tidal fence’s economic benefits should be undertaken.

The tidal fence is thought to be a good investment for private funding4, but the DECC has concluded it is not a good investment for public sector money, despite having designated £200million to the development of low carbon technologies in the 2010 spending review[6]. The tidal fence could be a good opportunity for the DECC to tackle the energy targets, not only would it effectively manage the Severn tidal power rather than currently leaving it untapped it could also provide a blueprint scheme that could be applied to other areas of the UK and the world. At the moment the DECC has no plans to further investigate tidal power in the Severn estuary, the natural resource is being unmanaged and the potential power output unharnessed.

There will be a number of barriers to overcome in order for the Tidal fence to have a smooth integration; the number of environmental designations may prove problematic. The DECC would also need to work closely with the RSPB in order to determine the best way to leave the local bird populations undisturbed. The increased local traffic in the area during construction times would need to be closely monitored as would the noise created by construction. The increased number of people to the area during the construction phase and operation could be both a benefit and a weakness. Providing jobs will boost the local economy but Is the local area set up for an influx of people? e.g accommodation, services, spaces in schools, this would need to be investigated.

The simple cost benefit analysis of the revised energy output shows that the tidal fence has the potential to be economically worthwhile; it is also thought to be one of the least environmentally damaging options and could provide a reliable renewable energy source for the UK. The recommendation to the DECC is to review the tidal power potential of the Severn estuary and in particular investigate the tidal fence as an alternative to the tidal barrage. Funding should be awarded to the tidal fence consortium to allow them to further experiment with the technology to discard any uncertainties attached to it and to prove the revised energy output. It is also suggested that a survey of social opinions is taken in South West and Wales to determine the public’s view of the tidal fence.


To conclude the Severn Estuary’s tidal power is currently unharnessed and has  the potential to provide the UK with a sustainable, renewable, reliable and long-term energy supply that will help the DECC reach its renewable energy targets and aid the UKs energy security. The UK has enormous tidal power potential not only in the Severn Estuary and could be the leaders in tidal power, providing an example for other countries around the world.  In order to effectively manage the tidal power of the Severn estuary as a natural resource the DECC needs to review the situation, not enough time or funding was given to the Severn tidal fence consortium to fully investigate the tidal fence as a serious contender to the tidal barrage[7]. The social implications of a tidal fence should be further investigated along with a review of the economic and environmental effects.

[1] DECC, Severn tidal power feasibility study conclusions and summary report, (2010).

[2] Sustainable development commission. Retrieved 08.10.2008.

[3] BBC. Daniel Boettcher. Severn tidal fence idea floated. 2008.07.16

[4] ITPower, Ian Godfrey. Severn Tidal Fence Consortium: final report. (2010)

[6] HM- treasury. Spending Review. (2010).

[7] Ian Godfrey. In conversation with. (2011)

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