dspp wrote:The reason EDF said they would never do another La Rance was because of the landwards/upstream ecological impacts.
regards, dspp
The estuary barrage is a strange hybrid: you have two separate movements of water. It's a hydro power station superimposed on a tidal enclosure. The two power sources add to each other as water flows out at low tide, but subtract from each other on the high tide as water flows in from both river and ocean. Overall, not an optimal configuration. And that's before even considering estuary mud and silt, which is of course constantly fed by the river.
The new generation of lagoons, starting with Swansea, are a rather different proposition. They're not estuaries and mudbanks, they're areas of sea on stretches of coast without significant water outlets. So a better proposition for energy generation over both rising and falling tide, and indeed, part of the R&D work for Swansea has been the design of new turbines optimised for generation from flows in both directions.
And of course, less ecological impact than a barrage or a hydro power dam. That is to say, both intuitively and in that the ecological impact studies for Swansea have been extremely comprehensive: more so than for any remotely comparable infrastructure project I'm aware of.
An exception to very-low-ecological-impact is the proposed lagoon for the Bridgewater bay, where it will serve a dual purpose. In normal conditions it will generate power like Swansea and the others. But with a hinterland prone to major flooding, it'll also serve as flood defence when necessary, maintaining a low-tide water level inside the lagoon and thus helping floodwater to drain more easily from the land.
