SIR — Re LongBay SeaPower's tidal energy scheme (Free Press April 18): the Admiralty Chart shows that it would involve building a wall up to 50 metres high in places. The water depth approaches 40 metres below high spring tide off Dunster, where the tides rip around Warren Point and the unstable seabed is made of huge mobile sand waves. I'll bet they have never been out there. The proposed scheme for Swansea Bay is actually in a bay, and a wall could follow the contour at, say, ten metres below high tide, and tides are much weaker. Capturing the potential energy of the trapped water in both cases would require emptying the "lagoon" (settling pond would be more accurate) twice a day through massive hidden turbines; not much fun for a boater in trouble even if he can afford the hugely expensive marina fees. The wall would prevent wave action all along the coast, rendering the beaches lifeless for both animals, birds and people. Instead, the lagoon would rapidly fill with gloopy mud, on a timescale of 125 years according to the plans. They should find a physicist to explain why efficient power supplies necessarily exploit large energy gradients. The latest generation of solar cells, for example, take the sun's energy and create temperatures approaching 1000°C before generating electricity. Low energy gradient tidal power, wind turbines, solar cells etc will always be wasteful of taxpayers' money. The lagoon would wreck North West Somerset and its main tourist attractions, including our wonderful old harbours. Richard Clarke, Minehead.