  Fig. 7 is a general plan showing the barrage in relation to Tilbury and Gravesend shores. Fig. 5 is a cross section of the river showing the vertical dimensions and contours. Fig. 6 shows a section and details of construction. Generally it is proposed to form the barrage of mass concrete, faced with granite on all exposed faces. The tunnel will be formed in the solid monolith as the work proceeds, and afterwards connected north and south with the existing railways. The foundation is in the chalk. The method of construction will be by cofferdam, to enclose an area sufficient for the walls and locks, which, when completed, can be opened for the up and down traffic of the river while the construction of the weirs and sluices is proceeded with. The sluices will be left open for the free passage of the tides until the closing of the barrage, which will take place at high water of a Spring tide. The locks will be worked electrically from a power-house built upon the central pier of the locks; the power to be obtained from dynamos operated by the fall of part of the water flowing over the dam. A pilot tower will be fixed from which the river traffic will be signalled and regulated, and the locks, movable bridges, etc., controlled. The locks as shown are four in number, each provided with internal gates in addition to the outer ones, in order that these locks may be worked in long or short lengths to suit the traffic. The lengths provided in this way will be 300 ft. 500 ft., 700 ft. and 1000 ft., and the widths 80 ft. and 100 ft. It is not likely that these dimensions will ever be exceeded by steamships. The number of vessels passing up and down the river per day averages 220, but few of these exceed 300 ft. in length. It will be easy to lock this number up and down, or three times the number with this series of locks, one important advantage to the shipping being that, instead of waiting tides at Gravesend, each vessel as she arrives, at any hour, can be locked in a few minutes, up or down, without waiting. Special provision will be made for rapidly and safely passing into and out of the locks with the use of power capstans and gear. The sluices will be of steel, sliding in roller guides, balanced and operated each by its own motor. At or near low water a large volume of water will be sluiced into the lower river to scour the approach to the locks as often as found necessary. A system of signalling from the Upper Thames to the barrage will be employed to notify any heavy rainfall or freshet coming down the river, so that by lowering the sluices water may be |
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