Professor Roger A. FALCONER
12th January, 2009
The Editor Penarth Times
I read with interest the letter from Paul Kinnersley in this week’s Penarth Times, where he states that the tidal lagoon is cheaper and more efficient than a Severn Barrage and he encourages ‘all your readers (to) make their views known urgently to our elected representatives’. I would be grateful if Mr Kinnersley could first explain how an offshore lagoon could possibly be ‘cheaper and more efficient’ than a barrage, which links to the land.
Basically the barrage and lagoon work on the same principle, in that they create an impoundment, hold back the water and then release the water from within the impoundment when there is a sufficient water level difference either side of the wall (barrage or lagoon). The amount of energy available for supply is proportional to the water level difference either side of the wall and, in particular, the plan surface area of the impoundment.
The Cardiff to Weston barrage will impound approximately 500 square kilometres of water and will have an impoundment perimeter of approximately 160km and of which 144km of which is already in place from the Welsh and English foreshores from Cardiff and Weston to Gloucester respectively, with closure of the impoundment needing just the 16km wall (barrage).
If the dimensions of the proposed Swansea Bay offshore lagoon are considered typical, the 5 square kilometre impounded lagoon will require a 9 km wall to be built all the way around the impounded waters. In equating areas only, which I accept is an approximation, we would need typically about 100 lagoons to give the same potential power as a barrage, with each lagoon being 2.5 times the size of Cardiff Bay (which has a surface area of 2 square kilometres). At low tide the lagoon would expose a 9km wall, of approximate height 12m or more and which would be comparable to the height of a two-storey house.
Whilst I fully accept there are a number of environmental concerns about a barrage, particularly with regard to the loss of intertidal habitats for the bird populations and fish migration, a barrage will also bring a number of benefits which also need to be considered. For example, it will provide protection against sea level rise, generally reduce flood risk (both upstream and downstream), provide clearer water in much of the estuary with the reduced currents, and create more jobs (estimated – 40,000) and tourist opportunities for Cardiff and the region.
I trust that your readers will consider all of the issues regarding the complexity of renewable tidal power generation in the Severn Estuary, before urgently writing to their elected representatives.
Professor Roger Falconer