Turbine blades could be reversed

MIKE ROGERS on February 26 was absolutely correct that the barrage proposal of which he is aware is grossly inefficient.

It will produce power for only about four hours on each tide and often at times of minimum demand. However this is not necessarily so. It all depends on the design of the barrage and method of operation. There is no reason why power should not be generated on the flood tide. Turbine blades could be reversed similarly to aircraft propellers, reversing gear could be fitted to the generator drives or possibly the problem could be overcome by using vertical axis turbines and suitable sluices.

The turbines will be so large and slow moving that fish will be able to pass through them at very little risk. I have heard that a man has passed the turbines on The Rance.

The only proposal which would overcome the times of generation problem was made some 50 years ago. The three basin scheme would have kept continuous flow through turbines but it was a very much larger project and would probably have produced less power.

The question of silting is a pertinent one. I have had considerable experience of silting when sailing from Oldbury. It is heavy in the pill and close in shore but at low water the full length and width of Oldbury Lake bed between the narrow channel on the Oldbury side and slimeroad on the other side is golden sand which used to be harvested by a boat the wreck of which still lay in Littleton Pill when I was last there.

I believe that the same applies to the Langford grounds but it is a long time since I was on Middle Hope at time of low water. Much of the foreshore of the estuary is rocky and I do not recall any significant deposit of silt on these areas.

Has the reservoir on Shepperdine Rocks silted up? I do not know but if silting there were a problem would we be having another nuclear power station built there?

Having given further thought to the subject I think that locks may not be necessary for shipping. If a gap could be left in the barrage it would be possible to prevent flooding upstream and to have some control over generating time by a structure similar to the Thames Barrier.

In the same issue Derek Kraft says that the Dutch built the Zeider Zee after the 1953 floods. This they did not do for the Zuider Zee was a topographical feature of the coast long before then, possibly millennia before. What they did was build a barrage almost 20 miles long between Den Oever in Noord Holland and a point near Zurich in Friesland and built a road on top of it. This turned Zuider Zee into Ijsselmeer.

When I was there around 1958 the fishing fleet was still sailing from Volendam on the western shore of the Ijsselmeer. Unfortunately during the visit, although I reached north of Alkmaar, time prevented a visit to Friesland.

Much of the Ijsselmeer has since been drained for land reclamation but I have heard that they have given up on trying to protect some of their reclaimed land.

KENNETH F TUCKER

Milton Road, Weston