1921] on Severn Crossings and Tidal Power 323 



Care would of course have to be taken in the arrangements of 

 reservoir works to make certain that the inlet and outlet of the high- 

 level reservoirs were kept far apart in order to facilitate the settle- 

 ment of silt before the water was drawn off to the secondary turbines. 



Time alone will show whether the moving parts of the secondary 

 turbines will wear quickly with Severn Estuary water. It would, 

 however, be of advantage that pumping experiments should be made 

 for a year or two with a view to ascertaining whether there would be 

 a sensible diminution of the available storage caused by the deposit 

 of silt. 



It has been suggested that the secondary or high-pressure turbines 

 should be driven by water free from silt, and such a provision, if it 

 could be effected economically, would no doubt be found of advantage 

 for prolonging the life of the centrifugal pumps also. 



It should be kept in view that the originators of both schemes 

 propose that the Avater level above the barrage shall never in future 

 be drawn down so low as at present. This should improve the 

 quality of the water to be lifted by the centrifugal pumps at the 

 expense possibly of certain other interests. 



(A slide was exhibited to show the equalisation of the tidal power 

 over a fortnight.) 



The holding up of the water level above the barrage will be an 

 important feature in facilitating the use of the estuary above the 

 barrage for navigation purposes, and great developments on either 

 side of the estuary, above the barrage, may be looked for. 



Below the barrage there are enormously valuable dock interests 

 on both sides of the channel, and it is only reasonable that the 

 probable effect of the construction of the proposed barrage should be 

 most carefully considered, and, if necessary, adequate measures 

 adopted so that these interests may not be prejudicially affected. 



Formerly it was the custom to deride tidal power mainly on 

 account of its several inconveniences : — 



1. The amount of power available varied from day to day. 



2. The maximum power was not available at the same time every 

 day. 



Sir George Darwin was somewhat outspoken on the subject in 

 his classic work on " The Tides." 



" It has been supposed by many that when the coal supply of the 

 world has been exhausted, we shall fall back on the tides to do our 

 work, but a little consideration will show that, although this source 

 of energy is boundless, there are other far more accessible funds on 

 which to draw. 



" I saw some years ago a suggestion that the rise and fall of old 

 hulks on the tide would afford serviceable power. If we picture to 

 ourselves the immense weight of a large ship, we may be deluded for 

 a moment into agreement with this project, but numerical calculation 

 soon shows its futilitv. The tide takes about six hours to rise from 



