1921] on Severn Crossings and Tidal Power 32] 



The barrage near the tunnel is proposed to he 25,0<m) feet in 

 length, instead of about 11,500 feet. 



The additional length will add considerably to the cost. On the 

 other hand, the long dam, with proper sluices and weirs, will facili- 

 tate the upward passage of tidal water and the downward passage of 

 tidal and flood waters, subject always to the eddies that may be 

 formed where the currents have to change their direction. 



The configuration of the land adjoining the estuary will necessi- 

 tate adequate provision for disposing of the surplus water when the 

 River Severn, or the Rivers Severn and Wye, as the case may be, 

 happens to be in flood at or near the time of high water. 



One special reason for keeping this point in view is that the pro- 

 posed method of working will, in point of fact, prolong the time of 

 high water very considerably more than at present, and so increase 

 the tendency to flooding. 



(A slide was exhibited showing the proposed method of working.) 



There are records of very large floods having taken place during 

 the last 150 years, but in one of the most recent, i.e. during the con- 

 struction of the Severn Tunnel, the actual height of the tide was 

 found to be 10 feet above the calculated height for that night. 



While all proper care must be taken at either site to prevent 

 flooding of low-lying land, it is particulaly necessary to guard against 

 any flooding of the Severn Tunnel for two reasons : — 



1. The Severn Tunnel is much the more important of the present 

 railway crossings of the estuary, and must not be interrupted. 



2. From 12 to 30 million gallons of water have to be pumped 

 from the tunnel daily according to the weather conditions. 



This water, though fairly hard, was described by Prof. Percy 

 Frankland as of an extraordinarily high degree of bacteriological 

 purity and of great organic purity. It may become very valuable 

 when there is plenty of power available in the neighbourhood. 



With a comparatively small and varying head, only slow speeds 

 will be attained by the turbines, and this will involve considerable 

 expenditure upon machinery. 



Both schemes depend to a great extent on the satisfactory working 

 of large turbines with comparatively low falls. It appears, therefore, 

 to be of first consequence that such turbines should be installed and 

 tried under as nearly as possible similar conditions. 



There appear to be several suitable places in Scotland where such 

 turbines could be effectively tested before the erection of the Severn 

 Barrage has been decided upon. One likely place is Loch Seaforth, 

 which is an arm of the sea near Stornoway, and which has an inner 

 loch running nearly at right angles to the outer loch, with a rather 

 rapid race near the point of junction. 



The construction of a comparatively short barrage near this 

 junction would facilitate the use of the storage in the inner loch, 

 which has a surface area of nearly one square mile. The rise at 



