Читать книгу The Great Thames Barrage - Thomas Walter Barber - Страница 6

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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 (14½ ft.) 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.

Fig. 1. The Upper Thames.

Shewing Existing Dams and Locks Between London and Oxford

The Thames, moreover, differs entirely from any of the foregoing rivers, and must be considered on its own merits. The map (Fig. 1) 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.