Waterways and Water Transport in Different Countries by J. Stephen Jeans

print at p. 344) pass over the Mersey and Irwell Navigation at such a height as to allow the passage through the archways of small vessels. To accommodate the larger vessels that will pass up the Ship Canal, the archways of the aqueduct and viaduct would have to be more than double the height. This was the engineering difficulty which the Ship Canal promoters had first of all to encounter and by many it was regarded as insuperable. The suggestion was made that the Ship Canal should end at a point below the aqueduct. Mr. E. Leader Williams, the engineer of the company has, however, proposed to construct a short diversion of the Bridgwater Canal immediately over the line at which it would cross the Ship Canal. The length of the Bridgwater over the Ship Canal will then be formed in the manner of a long movable iron caisson or trough, somewhat deeper in the centre than at the two ends, supported by and turning (when required) upon a circle of live rollers. This caisson is to be filled with water to a depth equal to that of the canal itself, and is to be fitted at either end with watertight gates, which are also to be fixed at either end of the approaches from the canal. [Illustration: THE BRIDGWATER CANAL.—(_a_) Across the Irwell (_b_) Barton Bridge.] Upon the completion of this work, the central portion of Brindley’s aqueduct will be removed, the ends being allowed to remain. The manner of working the new aqueduct will be as follows:—The operator in charge of the machinery will, on descrying an approaching steamship, cause the four watertight gates at the ends of the caisson and of the approaches to be closed, and will then, by means of hydraulic machinery, cause the caisson to revolve for a quarter of a circle upon the live roller which will support it, thus leaving a perfectly clear passage for the vessel. Through this passage, up- or down-going vessels will be able readily to steam, and when clear of the aqueduct the process will be reversed—that is to say, the attendant will cause the caisson to turn back into its original position, and will have his watertight gates opened once more, when the line of the Bridgwater traffic will be clear again, after a very brief interval, and without any loss of the water in the canal. At the ends of the existing line of the canal (after the removal of Brindley’s old aqueduct) it is proposed to construct hydraulic lifts as already stated, by means of which it will be competent to lower barges with full cargoes (the barges remaining afloat throughout the whole operation) from the Bridgwater to the Ship Canal, or, _vice versâ_, to raise them from the Ship Canal to the Bridgwater, thus making Barton a point of interchange of traffic between the high and the low level navigation. The works on the Manchester Ship Canal were commenced in 1886, and are to be completed, under contract, in 1892. The estimate of the promoters is that the canal will have a traffic of 3,000,000 tons per annum, from which a net annual income of 709,000_l._ may be expected. This estimate, however, did not include any coastwise traffic, nor such goods as coal, salt, and iron, and took no account of the future expansion of trade. Another estimate, submitted to Parliament, which included these items, calculated on a revenue of over 9½ millions of tons, and a net revenue of over a million and a half sterling. Whatever the financial results of this great undertaking may be, its future can hardly fail to be well assured, and Lancashire has reason to be satisfied with the energy, capacity, and public spirit that have placed such a valuable means of communication at the disposal of its principal industrial centres.