I WAS interested to read the article regarding the the proposal by Rupert Armstrong Evans, 'a green energy specialist', for a tidal reef across the Severn estuary. Whereas this would eliminate the need for a tidal barrage, with all its detrimental environ

I WAS interested to read the article regarding the the proposal by Rupert Armstrong Evans, 'a green energy specialist', for a tidal reef across the Severn estuary.Whereas this would eliminate the need for a tidal barrage, with all its detrimental environmental effects, such a proposal, comprising 20 floating turbines, would still present a serious navigational hazard.Surely a much better idea for all concerned, including shipping, would be to develop the system currently being trialled off Lynmouth - that of reversible tidal turbines located at depth. A string of these spread over a substantial length of river, parallel to the flow, would generate large amounts of power at all stages of the tide.As a more general response to your 'green energy specialist' yes, tidal power is a far better source than wind, which is both unreliable and unsightly, wave which is equally unreliable and yet another shipping hazard, and nuclear with all its long-term disposal problems. However, has he ever considered the most obvious source of renewable energy - geothermal? We are all sitting on an enormous furnace which has been burning for millions of years, and no doubt will continue to do so. You only have to visit the 'Fire Mountains' on Lanzarote to appreciate the potential. Watch the guide pour a bucket of water down a borehole and, in a matter of seconds, this comes back as a jet or superheated steam. If this process could be made continuous this would power the world's turbines for the next several thousand years. I accept that on Lanzarote, and other parts of the world such as Iceland, the hot magma is much closer to the surface than here in the UK, but modern oil technology has given us the ability to drill to depths in excess of five kilometres. Such deep drilling, if carefully located, could surely provide most the the world's power needs for the foreseeable future.I would be very interested to hear Mr Armstrong Evans' response to my proposals. Peter M Scott - Fosse Barton, Nailsea