Britain to Harness Tides.

Progress, Volume XVI, Issue 7, 1 March 1921, Page 157

Britain to Harness Tides.

A Million Horse-Power Possible. he striking photograph shown on the next page taken from otficial material and issued with the •authority of the transport Ministry, gives a pictorial presentation of the great Severn Barrage Scheme, the first big effort in England to utilise tides for generating electricity. Ihe scheme has been developed by three distinguished engineers in the service of the Government, Sir Alexander Gibb, Mr. J. Ferguson, and Mr. T. R. Menzies.

Owing to its formation, the Severn Estuary affords many favourable features for such a development. ihe principal points of the scheme are shown in the photograph, and include a threemile long barrage with automatic sluices, a road and railway viaduct, a ship lock, a reservoir in the Welsh hills, and an enormous power station, the capacity of which, it is estimated, will be a million horse-power.

“Harnessing Niagara” has ceased to be a proposition approaching the miraculous, for the feat was achieved long since, and there are several other engineering accomplishments of the same kind, one or two of them in Scotland. But it has been left to the British Ministry of Transport to announce a scheme of magnitude transcending everything yet devised, and worked out in detail “to a logical conclusion to employ the rotating forces of the earth, in conjunction with the attractive powers of the sun and moon, for the use and benefit of mankind.”

The words quoted are from a memorandum of the Ministry of Transport issued recently, and the document, in its closing paragraph, commends the venture as “opening up a vista which is little short of a revolution in the industrial life of the West and Midlands of England, effectually solving the problem of congestion for all traffic between South Wales and the West of England, both by road and rail, and bringing within the reach of all classes of the community the blessings of light, purity, and power.”

The following are the principal details of the scheme:—

Resources Available.

A Committee of the Board of Trade, under the presidency of Sir John Snell, has been looking into the water-power resources of the United Kingdom which could be made available for industrial purposes, and the memorandum of the Ministry of Transport sets out the conclusion that “the power available' in the Severn dwarfs into insignificance all the other potential sources of inland water power within the United Kingdom put together.” The river is unique in combining in itself all the conditions essential to the economic development of tidal water power on a large scale. Those conditions are:—

An exceptionally high range of tide. An estuary of large capacity.

An ideal geographical situation, in relation to the industrial centres of the country. Suitable land along the banks of the estuary for the development of industrialism.

The Need of the Moment. With the memorandum is issued a map showing the site of the proposed tidal water power in relation to the chief industrial areas. The Birmingham and South Wales districts, of course, are most immediately affected, but just north of the Birmingham and Coventry areas are those from Nottingham to Leeds, and from Stafford to Liverpool and Manchester and beyond. The study of the whole project was undertaken by the Ministry “in view of the necessity for immediate increased railway communication between South Wales and other parts of the Kingdom; the long-felt need of access over the Severn Estuary for vehicular traffic; and the possibility of combining these with a large scheme for cheaper power for industrial purposes.” These studies, which have been worked out by the Civil Engineering Department of the Ministry, have resulted in the formulation of a comprehensive scheme, on a site further down the River Severn than the Beachley scheme, and of a very much greater potentiality, which provides; Over half a million horse-power during a tenhour day, with A peak-load capacity of over a million horsepower at an estimated cost for generation at present-day prices of A little over a halfpenny per Board of Trade unit. The largest horse-power of any scheme now in existence is the 385,500 of the Amalgamated Niagara Falls Company.

An incidental advantage of the scheme would, it is urged, be the annual saving of three to four million tons of coal, and “its execution would mean the employment for a period running into years of an army of men of all grades, both technical and labouring, whose numbers could not fail to run into many thousands.”

Some of the Provisions. The scheme provides for a level road for vehicular traffic over the Severn, which would obviate a detour for all traffic between Newport and Bristol of about 50 miles by way of Gloucester. , It also provides for the quadrupling of the Great Western Railway Company’s line, when required, between the West of England and South Wales, at a considerably less cost than could be achieved in any other way. It also creates a locked basin of over 27 square miles for shipping purposes on the Upper Severn above the line of the Severn Tunnel, ; . a very large portion of which would be suitable for the accommodation of vessels of the largest size, and usable at all states of the tide. This portion of the scheme, by bringing the great shipping further up the estuary and nearer to the existing industrial

areas, would materially shorten the distance and lessen the cost of transit to inland places such as Birmingham. The problem of allowing shipping to pass up and down the river without interfering with or interrupting the passage of trains across the bridge over the river would be met by the provision of a locking basin capable of taking the largest ships on the line of the navigable channel and intersecting the barrage. The’ships would be led into and worked

through this locking basin by electric locomotives, somewhat similar to those in use on the Panama Canal. The railway and road traffic would be passed over either end of this basin by means of lifting bridges operating in such a way as to ensure that there is no delay either to railway, road, or river traffic. This is effected by duplicating the railway into the form of a loop where it crosses the locking basin, and so controlling and interlocking the arrangements as to allow continuous free passage for the railway or road traffic on one or other branches of the loop with safety.

Storing Up Energy

There is about five times as much water power available during a big spring tide on the Severn as there is during a small neap tide, and it is quite impossible to generate power at a constant rate during the day, whatever system of turbines and turbine working may be adopted. It therefore becomes absolutely necessary to store part of the energy obtained from turbines working in the dam which is available during the periods of spring tides and during the period of working, in order to make good the deficiency of energy which exists during the neap tides, and during those periods when the turbines are not working. The method of storage which has been adopted is that of pumping sea water from a low level to a high level when surplus energy is available, and of using the same water to drive other turbines in passing from the high level to the low level at periods when the stored-up energy is required for industrial, purposes. An artificial salt-water lake has been provided for at a high elevation in order to achieve the object desired. It is designed to force the water up from the low level of the River Wye in a tunnel driven through more than a mile of solid rock, and made to discharge into the lake. This tunnel would be 40ft. in diameter, or nearly four times the area of an ordinary double-line railway tunnel, and would be the largest tunnel of its kind in the world.

Enormous EnterprisesThere would be two separate installations in connection with the power scheme:(i) A great concrete dam or barrage across the Severn within which sluices and turbines would be installed for utilising the power of the tides, and with which would be combined the road bridge and the railway bridge over the. Severn at this place; and (2) an energy storage plant comprising the great high-level lake and tunnel in combination with an immense pumping and turbine power house on the banks of the tidal portion of the Wye. The site which has been selected for the great dam or barrage lies close to the line of the Severn Tunnel. An almost ideal site is provided. At this place the estuary is about 2\ miles wide, with low-lying country on either side. The greater part of the bed of the river is exposed dry at low water, and there are great sheets of rock known as “English stones,” covered with seaweed, occupying an area of very nearly a square mile.

The “English Stones The upper structure of these rocks is what is known as “Keuper mari,” and between these rocks on the English side and the rocks on the Monmouth shore side there is a wide deep channel worn out of the solid Pennant sandstone, known as “The Shoots.” The rocks on either side shelve steeply into this deep gully, which is rather wider and very much deeper than the Thames at Westminster. It is proposed to construct the hydro-electric barrage

along the edge of these rocks on either side of the river, utilising "The Shoots,” or deep gully, as a tail race for carrying away the water from the turbines, and an ingenious form of dam has been devised of great structural strength in reinforced concrete to suit the circumstances of the case. Within this dam there will be chambers, in which the turbines and generating machinery will be housed.

The method which it is proposed to adopt in order to utilise the power of the tides is to trap the water in the upper part of the estuary above the dam at high water so as to create an artificial difference in the level between the water thus impounded above the dam and the water in the estuary below the dam, for a period of several hours round about the period of low tide. During these hours, when the difference of level exists between the water inside and the water outside, sufficient water inside will be allowed to pass through the turbines in the hydro-electric barrage to generate upwards of a million horse-power.

Such are the main lines of the Ministry of Transport’s stupendous scheme.