Like Mark I have long been an advocate of clean power generation (and got terrific flak from Clarksonite petrolheads on one site and accusations of being a tofu-wearing, sandal-toking hippy on a couple of others - I didn't want to do it, but I torched them for their trouble), for I was seen as one of those much-hated Jeremiahs crying "Doom!" from the wilderness, or as some sort of lost-the-plot elitist posho whom everyday considerations didn't touch when everyone else knew that flying and driving everywhere for fivepence was still the only real world, commonsense solution. Well, times and opinions change.
Hydel, IF it doesn't BLOCK rivers or SHRED travelling / migrating FISH, must be considered an option now (so, too, wave and tidal power). But as for a re-born Severn Barrage now being championed by a private consortium in these days of less strict planning regulations all in the cause of kickstarting ever-continuing economic growth (which, to my mind, got us into mess in which we now find ourselves in the first place - I remember the cleaner, road- and car-free "dirty" Britain of my childhood and youth, and I am not ninety), well...
Some well-designed, non-fish impacting turbines on some weirs - okay, fine; but a monster like the Severn Barrage - let's just say that I have seen what such affairs did to dozens of once-great mahseer rivers in India (killed them as fisheries and sources of fish for local people), seen, too, just what they are doing in the States at the moment - ripping out dozens of great dams...