Tidal lagoons – a practical solution for the Somerset Levels?

Peter Kydd, Parsons Brinckerhoff

The recent flooding on the Somerset Levels highlighted challenges for everyone involved, and in many respects, showed the brilliance of the British in a crisis. But that is of little consolation to those who have been adversely impacted by the floods.

So how did we get into a situation that scientists and engineers could predict, but for which our infrastructure was unprepared. Are we perhaps too focused on short term agendas, rather than using our knowledge and experience to help inform a longer term infrastructure strategy?

Most stakeholders involved in the Somerset Levels flooding and its response do have their own long term plans. The Government understands the need for a long term climate change adaptation strategy and the need to influence the private sector to deliver long term stability. In parallel, the Environment Agency knows it must secure the optimal flood defence solutions with a limited budget, while sea levels rise and rainfall becomes more frequent and intense.

Unfortunately, none of these plans helped the situation on the Somerset Levels or on the Thames, where a combination of rainfall and rising groundwater is presenting an equally challenging situation.

So what should we do differently in the future? Our plans must consider the challenges we will face as a nation and how we can address them effectively. We also need to demonstrate best value, using one infrastructure asset for multiple purposes and thus developing greater benefits. This kind of thinking is currently the exception rather than the rule and must become more prevalent.

"The Bridgwater Bay lagoon could produce a substantial energy yield and has lower environmental impacts than barrage options.  It also offers the larger net gains in terms of employment” 

Delivering tidal power from the Severn Estuary has been one such challenge, with proposal after proposal for a barrage being rejected by the Government. However, have we been setting ourselves the correct objectives? Instead of “how do we generate power from the Severn with acceptable environmental and economic impacts?” should we instead be asking “how can we make best use of our expertise to deliver stakeholder’s needs, alongside generating power from the Severn?”

While these may sound similar, they offer different solutions. The rephrased question opens us up to exploring wider benefits, potentially at the expense of energy generation, but taking account of different, and no less important, stakeholder needs.

The Bridgwater Bay Tidal Lagoon option, conceived by Parsons Brinckerhoff as part of the Government’s Severn Tidal Power Feasibility study, is a case in point. This was conceived as a renewable energy generation project with a capital cost of £12bn to generate 6.2TWh/yr of electricity (around 2% of UK annual demand)  from 3.6GW of installed capacity.   It would involve the construction of approximately 16km of embankment from Brean Down, across Bridgwater Bay to landfall just east of Hinkley Point, creating a lagoon area of over 80 sq km.

 The Bridgwater Bay Lagoon offered a number of advantages over the barrage, as summed up in the executive summary of the Government’s report, which stated: “ a lagoon across Bridgwater Bay .....is also considered potentially feasible.....  The Bridgwater Bay lagoon could produce a substantial energy yield and has lower environmental impacts than barrage options.  It also offers the larger net gains in terms of employment;” 

 Assuming it were to be developed as a renewable energy project, the presence of the lagoon would provide a very effective long-term solution for the Somerset Levels by preventing tidal surge flooding and acting as a storage facility – with the water levels in the basin kept artificially low during major flood incidents to store run-off from the flooded Levels.  The cost of this benefit would be limited to the cost of lost generation for the small period of time the lagoon would not be generating, whilst avoiding cost from flooding further upstream both by preventing tidal ingress over multiple tidal cycles and allowing a greater hydraulic gradient for flood waters to discharge.

The opportunity is there for us as engineers to think more holistically about infrastructure, rather than through the segmental boundaries we sometimes impose on ourselves. Our key priority at the moment must be to ensure the messages we pass on to politicians are fit for both the short and long-term, joined up and compelling. There is no other profession which has our insight into the national infrastructure. We have State of the Nation, so why not also State of the Future?


Peter Kydd is UK strategic development director at Parsons Brinckerhoff