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THE GREAT THAMES BARRAGE

"Public Works,"

CONDUCTED BY THE EDITOR OF

"The Surveyor and Municipal and County Engineer."

A high-class magazine dealing with Governmental and Municipal enterprises in all parts of the world. Published on the 15th of each month.

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Subscriptions are payable in advance, and should be made payable to The St. Bride's Press, Ltd., and crossed "National Provincial Bank of England, Ltd." They should be forwarded to the St. Bride's Press, Ltd., 24 Bride Lane, Fleet Street, London, E.C.

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? SEE BACK OF COVER.

It is not necessary to emphasise in any way the fact that something must be done in the tidal Thames to bring the Port of London up to date, and to maintain it as the great inlet of British commerce. What with numerous newspaper articles, magazine reviews, reports of Royal Commissions and others, and a general murmur of complaint from all persons who use the port for their business or the river for traffic purposes, there have recently been abundant evidences that things are not as they should be. Everyone is agreed on this point, but when it comes to the question of a remedy, there agreement ends and confusion begins.

And, first, to briefly catalogue the complaints from all sources. They are as follows:-- Insufficient depth of water in the river for the increasing size and tonnage of steamships. Tide-waiting at Gravesend and at the dock entrances, inward and outward. Excessive dues. Vexatious restrictions owing to conflicting and overlapping authorities in the river. Excessive cost of barging, pilotage, and labour in loading and discharging. Loss of time at the port. Dangerous navigation, due to tides, bends in the river, narrow channel, fogs, and the crowded state of the river. That these complaints are well founded is generally admitted.

The Royal Commission on the Port of London, the Board of Trade, as representing the Government, the Thames Conservancy, the dock companies and others recommend the deepening of the river by dredging as a remedy for , and as a partial remedy for and . As to no remedy seems to be proposed by either, but rather an increase of dues, or in lieu thereof a charge upon the rates of London through the London County Council.

Partly to amend it is proposed by all the above authorities, except the Thames Conservancy, that a Port Trust should be created to control the river, instead of the present conflicting authorities of the Thames Conservancy, Trinity House, the City Corporation and the Watermen's Company.

But as to there is no suggestion of amendment, nor is it expected that the proposed deepening of the river will materially improve the dangerous navigation .

The Government has sought to give effect to the Report of the Royal Commission on the Port of London in this Bill, which reached the stage of Committee of the whole House, and was then suspended till next Session .

But as there were seventy petitions presented against the Bill, and a large number of amendments stand on the notices for Committee of the whole House, it may justly be concluded that the Bill satisfies no one, and that the attempt of the Government to force it through the House by stifling discussion of most of its vital points in Committee was a flagrant violation of public rights, and will have a disastrous effect on the future settlement of the question.

In 1755 Smeaton proposed the dockisation of the River Clyde as a means of providing a sufficient depth of water for the increasing trade of the Port of Glasgow. His plan was rejected, and the Clyde Trustees have since expended ?7,430,000 in dredging and improving the river to a low-water depth of 20 ft., and now spend annually a large sum in maintaining this depth.

Thos. Howard proposed the dockisation of the Avon at Avonmouth in 1877 to provide a sufficient depth of water for vessels passing to the Bristol Docks up and down the Avon, there being a rise and fall of tide in the Severn of nearly 40 ft. His proposal was not adopted because the extraordinary range of tide would have left the entrance unapproachable at low water, causing delay in the Severn Channel.

Messrs. L. Murray and W. C. Mylne recommended the dockisation of the River Wear in 1846, but this was not carried out.

The Czar of Russia has recently approved a great dockisation project, consisting of a dam with locks and sluices across the Straits of Kertch, in the Black Sea, to raise the level of the Sea of Azov for the purpose of facilitating navigation to the port of Taganrog and the River Don. The Sea of Azov will then become a fresh-water lake, with an increased depth of water and an area of 10,000 square miles. The dam will be nine miles long, and is estimated to cost ?5,000,000.

There is, however, no actual instance of the dockisation of a tidal river from which any data can be obtained.

The Thames, moreover, differs entirely from any of the foregoing rivers, and must be considered on its own merits. The map shows that it is already dammed and provided with locks at thirty-four places between London and Oxford, the object of these dams being the maintenance of a uniform level of water for navigation and boating purposes, and to prevent the river running dry in the dry season and exposing the muddy foreshores.

But from Teddington Weir to its estuary the Thames is tidal, and there is no obstruction to the tidal flow except the bridges and the half-tide weir at Richmond, which merely holds up sufficient water to cover the foreshores for the advantage of the riparian owners and of boating.

To understand clearly the conditions to be dealt with, it is necessary to consider the daily movements of tide, the affluents, the dock and wharf business and the traffic of the river.

The maps show the tidal river and estuary from Teddington to the North Foreland.

The river proper--that is, from Teddington to Gravesend--is forty-six miles long, and averages one-third of a mile wide. Its depth at low water varies from 6 ft. at Teddington to 10 ft. at London Bridge and 40 ft. at Gravesend, and the rise of tide at London varies from 17 ft. to 21 ft. and at Gravesend from 15 ft. to 19 ft., the current usually averaging four knots per hour. At London Bridge the Spring tides flow 5 hours and ebb 7 1/2 hours; while at Gravesend they flow 6 hours and ebb 6 1/2 hours.

The river winds about considerably. The straight line distance from Teddington to Gravesend being thirty-three miles, shows that thirteen miles are added to the river in its bends, some of which--as those at Grays, Erith, Blackwall and Limehouse--are short and tortuous.

The longitudinal section of the river from Teddington to Gravesend gives graphically all the data necessary for our purpose. Ordnance Datum is the common datum line of the Government maps. Trinity High Water is the water datum usually adopted in the river. High and low water, ordinary and Spring tides are the levels of the respective states of tide in the river at various points. The highest and lowest known tides are also given, as well as the level of the river bottom and the levels of the principal dock entrance sills and of the crowns of the Thames tunnels, showing their depths below the river bottom.

The curved lines represent the levels of the surface of water at various states of Spring tides and clearly show the tidal wave which ascends the river and by its momentum and volume raises the high-water level at the upper end several feet above that at Gravesend.

From Gravesend to the Nore is an immense triangular area with sandy bottom, muddy foreshores and several deep channels running in the general direction of the Essex coast line, that is, N.E. to the North Sea. The area may be roughly estimated at 120 square miles, and the navigable depth of the principal channels at from 60 ft. to 26 ft. at low water Spring tides.

The volume of the estuary at high water Spring tides may be taken at 2600 million cubic yards, and at low water Spring tides at 1500 million cubic yards, the volumes of the river from Gravesend to Teddington being respectively 180 million and 80 million cubic yards, so that the volume of tidal water entering the river each tide is about 100 million cubic yards.

But there is a daily flow over Teddington weir--excluding the water abstracted by the London water companies--varying during the year on the average as follows:--

Cubic yards. Jan. 11,800,000 Feb. 5,300,000 March 4,100,000 April 3,250,000 May 4,720,000 June 2,900,000 July 1,760,000 Aug. 1,590,000 Sept. 1,160,000 Oct. 1,900,000 Nov. 3,530,000 Dec. 8,230,000

Average daily flow, 4,186,000 cubic yards.

Below Teddington, numerous small affluents add to this volume of upland water as follows:--

Cubic yards per day.

This gives an average volume of 7 1/2 million cubic yards of fresh water descending and mingling with the oscillating tidal water of the river and estuary, which slowly pushes the latter down into the North Sea. Taking the high-water volume in the river as above at 180 million cubic yards, the proportion of fresh water from the upland daily flow is 1/24th, and therefore it will take 24 days to change entirely the water in the tidal river.

Mr. W. P. Birch has shown that the combination of fresh water and sewage which enters the river below Teddington remains in the river, oscillating up and down with the tides for 45 days before it finally gets pushed out into the North Sea.

In this way the discharge of effluents at Crossness and Barking passes up and down in front of London for more than a month, and it becomes apparent that the tidal action keeps the river continually saturated with about 45 days' soilage. It is no wonder, therefore, that the conditions of colour, smell and turbidity of the river below Teddington are so vile as compared with the Upper Thames, especially as to the above sources of filth must be added the tidal current, which is so rapid that it keeps the mud continually in suspension, washing it up at one time, depositing it at another, but never permanently leaving it except in the places unscoured by the upland water, such as docks, backwaters and places out of the main current. It has been acknowledged by all writers that if the upland water should be stopped the Thames would become a stagnant oscillating ditch, because all filth discharged into it would remain in it permanently.

The docks trap a very large proportion of this mud, and it costs at least ?60,000 per annum to clean it out. The mud enters with the locking water and with that pumped to make up the basins.

It is proposed to construct across the river at Gravesend a dam or barrage similar to that across the Nile, containing numerous adjustable sluices, and in addition a series of very large locks, the dam to hold up the river to about Trinity high-water level .

The immediate effects will be these:--

The tides, Neaps and Springs, will be stopped at the dam.

The river will be converted into a long lake having numerous affluents, the principal of which will be its natural flow over Teddington Weir.

It will have a slow downward current, never reversed, so that all that enters it will pass downwards to the dam.

Its level can be regulated to any level above low water by the sluices.

Within from 25 to 45 days of the closing of the dam the upland water will have pushed over the dam all the oscillating foul water of the tidal river, and thenceforward the water of the lake will be the same as that of the upper river, and any soilage in it must enter it by sewage or land drainage.

There will thus be obtained by one work a navigable depth of water varying from 65 ft. at Gravesend to 32 ft. at London Bridge, without dredging or any interference with the river bottom or banks.

But the consequent effects upon the business and usage of the river will be tremendous:--

Ships drawing 30 ft. can then proceed to London Bridge at any hour of the day or night, without waiting for tides.

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