Barrage Against the Barrage?

Considerable enthusiasm has been expressed in government (e.g. the Sustainable Development Commission chaired by Jonathon Porritt and Rhodri Morgan for the National Assembly in Cardiff) and engineering circles for the creation of a row of turbines in a barrage (Britain's largest power project) across the Severn estuary downstream of Cardiff and Weston-super-Mare (http://www.guardian.co.uk/environment/2007/oct/02/renewableenergy). It is claimed that harnessing the tidal power in this region could provide 5-6% of the UK's electricity for 120 years without at face value adding to the levels of carbon dioxide released into the atmosphere. In terms of the last point, some people have pointed out that construction of the barrage would certainly generate CO2. Although it is also claimed that the barrage would provide a valuable additional river crossing with tourism and commercial benefits to SW England and South Wales, its creation of creation would also have a very powerful effect on a very important area for wildfowl, fish and other animals (most notably, the loss of some 11,000 hectares of inter-tidal mudflats and other habitat). The suggestion that the loss of this RAMSAR site could be 'off-set' by allowing the sea to encroach on to low grade farm land in East Anglia, Wales and elsewhere is a bit disingenuous. The newly created habitat would be welcome but would certainly be in smaller parcels (fragmentation of habitat can be a problem for many species) and is not in the same geographical location (migratory water birds often follow routes with chains of 'refueling' stops). Disturbance by humans in these locations could make them non-viable for the species that are displaced. A relative minor additional sadness is that we would lose the phenomenon of the Severn bore. Difficult choices are clearly evident in this complex equation. The parallels with a barrage in Brittany (France) are not really convincing. This much smaller estuary has very clearly had its entire nature altered by the engineering project. Some writers have suggested that one could get reliable (but not so much) conversion of tidal power to electricity by mounting vertical turbines to the bases of bridging structures in the estuary. It might well be possible to create a barrage that still allowed the relatively full expression of the tides to be expressed (this would involve getting most of the water trapped behind the barrage to leave to allow the mudflats to be exposed for sufficient time for birds to feed etc). To prevent major impact of species, one would also have to ensure that construction of the barrage didn't block the ebb and flow for any substantial period. Similar considerations were applied when constructing a new road bridge at the mouth of the Fleet lagoon to the Island of Portland. That was, in comparison to the Severn barrage, a tiny project and added dramatically to the costs of construction. It seems likely that there will be long and bitter argument about this proposed development.