I share concerns over barrageI
10:13am Thursday 24th January 2013 in Letters
I SHARE MP Stephen Doughty timely concern about the environmental and other general issues regarding the proposed Severn Barrage (Penarth Times, January 17).
Certainly the debate up to now is curiously lacking in technical data. There are several major problems as I see it, about which, so far, I have seen no discussion.
Some are as follows:
1: The extraordinary range of the tide in the estuary is solely due to its shape. It is recognised that its unique height is due to an effect known as “tidal resonance”. Once this shape is altered by, say, a full width barrage, the tidal range may revert to that of the open sea. At best it will probably be halved, so reducing the “head” available for generation.
2: The head available will depend upon the height of the impounded water behind the dam. If it is kept at maximum tide height then generation could be possible at most of Ebb and Rise. To achieve this, however, might result in the water above the barrage slowly becoming fresh or brackish due to the many now impounded rivers feeding it. But we all know what happened to Cardiff Bay in the years of transition with its plague of flies and need for oxygenation.
3: The water impounded could be kept at lower or variable height but this would mean generation for a limited period each day and might call for reversible turbines.
4: It is likely that full power would not be available for 24 hours in any barrage scheme. Accordingly conventional power stations of the same capacity or the grid generally would have to be available (on a tidal schedule) to ensure continuity of supply.
5: It is thought that reducing the tidal flow would increase silting and that continuous dredging would be needed above the barrage after some years.
These are just a few of the questions that occur to a layman and that our politicians do not seem to have addressed.
We really need a new and comprehensive study by experts before rushing into a scheme that may not have as much promise as forecast.
Certainly Tidal Flow schemes not needing a barrage would seem to pose less problems.