320 Mr. W. A. Tait [March 4, 



2. The installation of low-pressure turbines, generators, etc., at 

 the dam. 



3. The filling of the reservoir by the flood tide. 



4. The driving of the turbines by the issuing water during the 

 ebb tide. 



5. The construction of high-level reservoirs. 



6. The equalisation of the tidal power over a fortnight by means 

 of water pumped up to the high-level reservoirs and drawn from 

 them at time of slack water to drive high-pressure (or secondary) 

 turbines. 



7. The construction of a lock for navigation purposes. 



8. The provision of improved facilities for navigation above the 

 barrage. 



The main points of difference are in respect to the railways and 

 roads, i.e. whether they are to be constructed — 



1. At the low level with an opening span ; or 



2. At the high level without an opening span. 



As regards the proposed dams, it would appear that a rock foun- 

 dation is available at each of the sites. It is intended that these 

 dams should have suitably controlled openings. 



The Institution of Civil Engineers is in possession of a copy of a 

 survey made by the late Admiral Beechey, which survey has, I under- 

 stand, been of considerable use to the originators of the two schemes 

 now under discussion. 



Besides the tidal water, the barrage at Beachley will have to 

 dispose of flood water from an area of 4,500 square miles. 



The barrage at the tunnel site will have to dispose of a consider- 

 ably greater quantity of tidal water, together with the flood water 

 from an additional 1,600 square miles. 



The tidal current is occasionally 8 feet per second at Beachley, 

 and practically no part of the bed of the river on the proposed line 

 of the barrage is laid bare at low water. 



The estuary at the site near the tunnel is much wider than at 

 Beachley, and the current, in present circumstances, at high water 

 is accordingly less. Practically the whole of the proposed barrage at 

 the lower site can be built in the dry at low water. 



The greatest depth at low water at both sites is about 60 feet, 

 with the difference that this depth extends for a considerably greater 

 width at the Beachley site than at the tunnel site, and with the further 

 result that at certain states of the tide the current will be greater at 

 the tunnel site than at the Beachley site. 



The great quantity of water to be operated upon, and the limited 

 head available, will necessitate room for many large turbines, and in 

 consequence it has been determined that the barrage at either site 

 should not be constructed in the shortest line across the river ; thus : 



The Beachley barrage is proposed to be 9,800 feet in length, 

 instead of about 5,700 feet. 



